The Adaptive Optics Revolution: A History

The Adaptive Optics Revolution A History

Science  |  History  |  Military

is the historian for the Air Force Research Laboratory’s Directed Energy and Space Vehicles directorates in Albuquerque. He is the author of Airborne Laser: Bullets of Light and Science and Technology: The Making of the Air Force Research Laboratory.

isbn 978-0-8263-4691-9

Author photo: courtesy of Air Force Research Laboratory. Jacket design: Kathleen Sparkes

University of New Mexico Press unmpress.com | 800-249-7737

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Robert W. Duffner

Jacket photo: Courtesy of Robert Q. Fugate. Exploration of the heavens and a fascination with the dynamics of light all started at an early age for Bob Fugate in his backyard in Dayton, Ohio, in 1954. At age 13 he purchased a defective telescope at a local flea market and took it home. There he tore the device apart, made the necessary adjustments, and reassembled it so it worked properly. It was a proud moment for the serious-minded boy scientist sitting in a rickety folding chair guarding his most prized possession. It was also a sign of things to come. Years later, Fugate became a leading scientific expert for the Department of Defense in the up-and-coming fields of laser guide stars and adaptive optics while serving as the Technical Director of Starfire Optical Range in a remote high desert telescope site at Kirtland Air Force Base, New Mexico.

Adaptive optics is the most revolutionary breakthrough in astronomy since Galileo pointed his telescope skyward four hundred years ago. It is critical technology that enables astronomers to answer challenging questions about the universe. Robert Duffner has written a unique history of the invention of laser guide stars and other contributions to adaptive optics made by the Department of Defense. He had access to a large collection of primary source material housed in the offices of government scientists and in the Air Force Research Laboratory’s archives at Kirtland Air Force Base, Albuquerque. Duffner also interviewed seventy-one prominent scientists who played key roles advancing adaptive optics research.

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ver the last four decades, a formidable and persistent team of scientists from the Air Force Research Laboratory, MIT/Lincoln Laboratory, and private contractors led the way in achieving groundbreaking advances in adaptive optics. They demonstrated laser guide star techniques and made adaptive optics practical on large telescopes. The military aggressively pursued the development of adaptive optics for two reasons—imaging of man-made space objects for space situational awareness and laser weapons. A significant part of this research occurred at the Starfire Optical Range in New Mexico and the Maui optical site in Hawaii. The program remained classified during the 1970s and 1980s, but the government declassified it in the early 1990s, enabling significant technology transfer to the astronomy community.

The Adaptive Optics Revolution

Robert W. Duffner

Robert W. Duffner

Foreword by Robert Q. Fugate

4/13/09 9:20:36 PM

The Adaptive Optics Revolution

The Adaptive Optics Revolution

A History

Robert W. Duffner

Foreword by Robert Q. Fugate

University of New Mexico Press  |  Albuquerque

© 2009 by the University of New Mexico Press All rights reserved. Published 2009 Printed in the United States of America 14 13 12 11 10 09    1 2 3 4 5 6 Library of Congress Cataloging-in-Publication Data Duffner, Robert W. The adaptive optics revolution : a history / Robert W. Duffner ; foreword by Robert Q. Fugate. p. cm. Includes bibliographical references and index. ISBN 978-0-8263-4691-9 (cloth : alk. paper) 1. Optics, Adaptive—History. 2. Optics, Adaptive—Research—United States—History. 3. Laser guide star adaptive optics. 4. Lasers—Military applications. 5. Space telescopes. I. Title. TA1522.D84  2009 621.36'9—dc22 2009005843

Book and jacket design and type composition by Kathleen Sparkes. The text in this book was composed with typeface Minion Pro ot 10.5/14, 26p. The display type is Helvetica Neue.

✩ For Rupert and Winifred

Contents Foreword by Robert Q. Fugate  |  ix Preface  |  xiii Introduction  |  xix List of Acronyms  |  xxv

Chapter 1: Sputnik, Reality, and Technology  |  1



Chapter 2: Early Days: The Romans  |  17



Chapter 3: Rome and Itek: First Adaptive Optics Systems  |  41



Chapter 4: Laser Guide Stars  |  65



Chapter 5: Fugate’s Rayleigh Guide Star Experiments  |  89



Chapter 6: Lincoln Laboratory  |  119



Chapter 7: Sharing the Gold: Astronomical Nuggets  |  145



Chapter 8: Strategic Defense Initiative  |  169



Chapter 9: Airborne Laser  |  203



Chapter 10: 3.5-Meter Military Telescope Complex:



Chapter 11: 3.67-Meter Military Telescope Complex:



Chapter 12: Sodium Guide Star Laser: The Future  |  313

Starfire Optical Range, New Mexico  |  237 Maui, Hawaii  |  277

Conclusion  |  339 List of Interviews  |  349 Notes  |  355 Index  |  439

Fore word

Adaptive optics: What is it? Why should I care? For nearly 400 years, astronomers have lived with blurry images of the planets, stars, galaxies, and indeed the universe when looking through their ground-based telescopes. Looking through the atmosphere with a highmagnification telescope is like looking through shower glass with your eye. You can see shapes on the other side of the glass, but you can’t make out any detail—you couldn’t, for example, see people’s faces clearly enough to positively identify them. Earth’s atmosphere acts like a shower glass for astronomers. They can make out shapes, but only with limited clarity. Large telescopes provide two critical ingredients for making new discoveries about the universe: they gather a lot of light, and they have the potential to provide detail and clarity (resolution). Eight-, 10-, and soon-to-be 30-meter class telescopes certainly gather a lot of light, but because of the atmosphere, they only provide the same image detail as an 8-inch telescope in your backyard. The most important science (for example, investigating whether there is carbonbased life on planets outside the solar system) is critically dependent on the fine details. Astronomers are losing out on that science because of the atmosphere. The science lost by observations from the ground was the main justification for building the Hubble Space Telescope—astronomers wanted to get on the other side of the “shower glass,” where a large telescope can

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gather lots of light and provide the resolution they are entitled to based on the laws of optics, not the limits imposed by the atmosphere. In 1953 Horace Babcock, an astronomer at Mount Wilson and Palomar observatories in California, had an idea that would enable astronomers to remove in real time the distortions created by the atmosphere. His idea was revolutionary, since it removed the distortions from the optical waves before they were focused on film in a science camera. Today we call his concept adaptive optics. There are other imaging techniques for getting beyond the limits imposed by the atmosphere. One, still in use today, was to make many very-short-exposure images and process them afterward. This approach is, however, limited to very bright objects. Long-exposure techniques were not effective, because if the telescope’s resolving power was not sufficient, details would not be recorded in the first place. Babcock’s idea was somewhat complicated, and the technology really didn’t exist at the time to support a practical implementation. However, by the mid-1970s, sensors and opto-mechanical devices had matured sufficiently that the first demonstrations of the concept could take place. In 1982, the Defense Advanced Research Projects Agency (DARPA) and the U.S. Air Force put into service the first practical adaptive optical system, called the Compensated Imaging System (CIS), on the 1.6-meter telescope on top of Haleakala on the island of Maui in Hawaii. This system provided the U.S. Defense Department images of bright earth-orbiting satellites at nearly the full resolving power of a 1.6-meter telescope. The goal was to get detailed images of new Soviet satellites on the first or second revolution after their launch. It was a significant step forward to space situational awareness in the Cold War era. Adaptive optics works by analyzing the rapidly changing shape of light waves passing from the subject being imaged through the atmosphere into the telescope. The optical wave distortions are corrected by reflecting the wave off a mirror (called a deformable mirror) whose shape is adjusted to be the opposite of the measured distortion. After reflection off the deformable mirror, the wave shape is restored to what it was before it entered the atmosphere. Adaptive optics thus effectively removes the atmosphere’s distortion. The most obvious source of light waves for analyzing the distortions (most often called the guide star) is sunlight reflected from the subject being

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imaged. However, a serious limitation arises for dim objects: they don’t provide enough light for the adaptive optics sensor (called the wavefront sensor) to make a measurement. It’s all a matter of timing. The wavefront sensor must measure the distortions on the optical wave much faster than the rate at which the distortions are changing. The distorted waves change to a new shape about 100 times per second. However, objects of high scientific interest to astronomers are just too faint to provide enough light to make the required measurements and subsequent corrections to the shape of the deformable mirror in one hundredth of a second. In fact, restricted to using natural stars bright enough for the wavefront sensor to operate adequately, adaptive optics is effective over only 1 percent of the sky—useful but not really adequate. This book tells the story of how a classified U.S. defense research program created a solution called laser guide stars that solves the problem of inadequate numbers of bright natural guide stars. The concept is to create an artificial guide star by pointing a laser beam in the direction of the target to be imaged and using the light backscattered by atoms and molecules in the atmosphere as the source of the light waves for the wavefront sensor. The idea was invented by members of the U.S. defense community during the Cold War era for correcting high-power laser beams directed against an adversary’s satellites. Laser guide star technology is now part of satellite imaging research conducted by the U.S. Air Force. The initial laser guide star experiments were done under a veil of secrecy in special-access programs sponsored by DARPA. The results were kept secret for over 10 years but eventually released to the public and subsequently embraced by the astronomy community. Robert Duffner, an Air Force historian, recognized an important story in the contributions made to adaptive optics by the Air Force and other Department of Defense (DoD) organizations. His detailed research and comprehensive account of the events, people, politics, and security of the DoD’s development of laser guide stars and adaptive optics for large telescopes is recorded in this book. Some astronomers feel that the development of adaptive optics is on a par with the invention of the telescope for producing new science about the universe, and ultimately about where humankind fits in the grand scheme. If you are a technical person interested in the historical events that led to scientific revolution, this book will fascinate you and provide details you Foreword

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can’t find elsewhere. If you are a tax-paying citizen, this book will reveal the positive side of a highly successful military research program and give insight into the dedicated people that made it possible—a view not available in the popular media. Adaptive optics has other civilian, industrial, and scientific applications: human vision research, laser eye surgery, ultra-highbandwidth laser communications between ground and space, and materials processing, to mention a few. These applications have benefited significantly from the accomplishment of the military programs in adaptive optics. This book is “the rest of the story”—a story that Robert Duffner has documented in great and fascinating detail. I highly recommend it to all. Robert Q. Fugate New Mexico Institute of Mining and Technology

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Preface

An important reason for undertaking this project was to assess the contribution of the Department of Defense (DoD) in the relatively new field of adaptive optics. The intent was to capture a history that serves as a bridge between a narrow group of highly specialized scientists and a wider general audience. In the past, the DoD has often been accused of wasteful spending on huge programs extending over decades that ended up going nowhere. That may have been true in many cases, but the question is: Did adaptive optics research represent the other side of the coin? Does it show that DoD did sponsor successful long-term research programs that proved to be revolutionary and produced large military dividends? The government kept this program classified during the 1970s and 1980s, but by the early 1990s much of the secrecy surrounding the new technology had been lifted. This presented an opportunity to write a history as documents became declassified. Moreover, many of these primary source documents were housed in the offices of government scientists and in the Air Force Research Laboratory’s archives in the Historical Information Office at Kirtland Air Force Base. As the historian for the Air Force Research Laboratory’s Directed Energy and Space Vehicles directorates, I had access to this unique collection. One of the essential tasks of a historian is selecting a credible topic to write about. At first glance, that might seem easier said than done. That process does not always lead to a clear-cut decision, taking into consideration

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that at the beginning of a writing project one usually does not have all the facts or knowledge to judge whether a particular topic is worth pursuing. However, after consulting with a number of scientists and others, I became convinced that the story of the development of adaptive optics deserved telling. Not only was there an abundance of primary source documents to examine, but scientists who had participated directly in research programs advancing adaptive optics were available for interviews. As it turned out, I interviewed 73 people (listed at the end of the book), all with different personalities but all sharing the belief that adaptive optics was a revolutionary change. They possessed a wealth of first-hand knowledge and truly were the pioneers of the adaptive optics movement. This account covers one slice of the historical pie, intentionally focusing on the interaction of various military organizations with heavy emphasis on the Air Force laboratory community. Although the relationship between military researchers and private-sector astronomers is addressed, a comprehensive treatment of astronomers’ contributions to adaptive optics—a legitimate subject—is beyond the scope of this book. This book started one hot Albuquerque afternoon with a chance encounter with Bob Fugate, who was about to cross the street in front of the Directed Energy headquarters building on Kirtland Air Force Base. As he stepped off the curb, I yelled, “Bob, do you have a minute?” He turned and squinted to make out who I was, and I could tell he was not anxious to stop and talk, especially about history. I had been leaving messages for him for several weeks to no avail, to try to get an appointment with him to discuss writing this history. Fugate had a strenuous schedule, and he was more interested in making scientific progress in the real world than in reminiscing about the history of his work over the past three decades. Eventually, I got a chance to sit down with Bob Fugate when he called me unexpectedly saying we could get together in his office at the Starfire Optical Range. As it turned out, he had a strong appreciation for the value of history, but his jam-packed schedule gave him little time to reflect on his and his colleagues’ life-long accomplishments relating to the integration of laser guide stars, adaptive optics, and large telescopes. By the time we finished, he supported the idea of a history of adaptive optics. Over the next several years, Fugate was a man of his word. He is recognized throughout the world as one of the leading authorities on adaptive

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optics, and I am grateful for his assistance. I feel fortunate to have worked with him. Once the research and writing got under way, he gave generously of his time and knowledge to make sure I had the right information to capture all parts of the story. I quickly learned he was a stickler for detail. He hunted down too many documents to mention and provided photographs and diagrams to illustrate important concepts and events. From the start he showed extreme patience making complex science and technology understandable. Moreover, he identified individuals I should interview to clarify all types of issues—the roles of different scientists and military and civilian leaders, hardware, budgets, accomplishments and failures, contributions of contractors, government facilities, Air Force missions, relationships with astronomers, and much more. I also thank him for his careful reading of all the chapters and his thoughtful comments. Another pillar of strength was Jim Mayo, an expert on large telescopes, who provided immeasurable insight and technical know-how to keep me focused on getting the facts straight on a complicated subject. He is a unique and very enthusiastic individual with an abiding interest in history. On too many occasions to count, Jim showed up at my office late in the day to check on how things were going and to offer encouragement. He was always willing to make the time to sit down and explain how things worked and to convey to me why and how large telescopes made a substantial difference in adaptive optics. I am grateful to Jim for reading the entire manuscript and offering his many helpful comments. Although Fugate and Mayo head the list of experts to whom I am indebted, many others also provided invaluable information and perspective on adaptive optics, lasers, and large telescopes. At the Directed Energy Directorate, R. Earl Good, L. Bruce Simpson, Gregory J. Vansuch, William E. Thompson, Craig A. Denman, Charles L. Matson, Charles B. Hogge, Edward A. Duff, John R. Kenemuth, Mark A. Kramer, and Lawrence D. Weaver were especially helpful in providing their viewpoints on many technical and people issues. I appreciate their wise counsel, which included pointing out discrepancies and how they could be fixed. A number of military officers and civilian scientists who worked at the Air Force Weapons Laboratory in the 1970s and 1980s, and at Phillips Laboratory in the 1990s, shared their experiences in the development of adaptive optics. Although there are too many to list here, I especially want to thank Preface

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Joseph F. Janni, Leonard John Otten III, John C. Rich, James L. McNally, John J. Russell, Brent L. Ellerbroek, David P. Dimiduk, and Robert F. Walter. To keep me straight on the workings and contributions of Rome Laboratory, I relied on Raymond P. Urtz, Donald W. Hanson, and Thomas W. Thompson. John W. Hardy, who led the early adaptive optics effort at Itek, was incredibly knowledgeable and very gracious, as was Jay Richard Vyce. Especially helpful in explaining the contributions of Lincoln Laboratory were Darryl P. Greenwood, Louis C. Marquet, Charles A. Primmerman, Charles Higgs, Daniel V. Murphy, and Thomas H. Jeys. I am grateful to J. Roger P. Angel, who gave me an eye-opening tour of his large telescope mirror manufacturing facility under the football stands at the University of Arizona, and equally thankful to William “Will” Happer at Princeton University for sharing his experiences as a Jason, as well as how he came up with the sodium laser concept. James C. Wyant, at the University of Arizona, took time to explain the contribution of his white shearing interferometer. At the national level, a number of key leaders who influenced the course of adaptive optics offered their candid comments on the pros and cons of the program. James A. Abrahamson, the former director of the Strategic Defense Initiative Organization (SDIO), made time to meet with me and underscored the importance of adaptive optics and its application to potential future laser weapon systems. Rettig Benedict Jr. and Thomas W. Meyer, two well-informed individuals who worked at SDIO and DARPA in the area of directed energy, clarified where adaptive optics fit into the big scheme of strategic and tactical planning. The following influential leaders also helped: Anthony “Tony” J. Tether, who served as the DARPA director; Paul D. Nielsen, commander of the Air Force Research Laboratory; Donald L. Lamberson and John R. Albertine, members of the Air Force Scientific Advisory Board; Ronald M. Sega, formerly assigned to the Office of the Director, Defense Research and Engineering; Lester L. Lyles, former commander of the Air Force Materiel Command; Ralph E. Eberhart, former commander of Air Force Space Command; and former Secretary of the Air Force James G. Roche. All concurred that adaptive optics was a revolutionary enabling technology destined to have a positive effect on Air Force missions of today and tomorrow. Also, G. Wayne Van Citters from the National Science

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Foundation put into perspective how military work on adaptive optics was relevant to astronomers. I would be remiss not to mention the major contractors that made enduring contributions over the years to the design, construction, and operation of a variety of telescopes and adaptive optics systems. I spent a rewarding afternoon in Massachusetts with Mark A. Ealey, president of Xinetics Inc., listening to his fascinating explanation of how deformable mirrors evolved. I spent an invigorating morning in California with David L. Fried, founder of the Optical Sciences Company, who amazed me with his memory—and his meticulous filing system, filled with records documenting the brightest individuals and most successful experiments advancing adaptive optics. I also spent several hours with Fried’s successor, Glenn A. Tyler, president of the Optical Sciences Company, who described the importance of adaptive optics to the Airborne Laser. Also, I am grateful to Kenneth W. Billman at Lockheed Martin, who shared his experiences and perspective on the Airborne Laser. Rene Abreu, formerly of Hughes Danbury Optical Systems and later with the Goodrich Corporation, provided information on the design, fabrication, and integration of the adaptive optics system with the 3.67-meter telescope on Maui. Rusty Hughes, of Trex Enterprises, the troubleshooter for the Maui adaptive optics system, enlightened me on the day-to-day operation of this sophisticated and sometimes temperamental piece of hardware. Three other participants who had a solid grasp of the twists and turns of the history of adaptive optics were Robert S. Cooper, of Titan Systems Corporation; Richard A. Hutchin, chief executive officer of the Optical Physics Company; and James E. Pearson, formerly of Hughes Research Laboratory and United Technologies Optical Systems. Several historians read the manuscript and offered helpful suggestions. I thank Donald R. Baucom for his knowledgeable and insightful perspectives about science and technology in the Department of Defense and the Air Force. Lawrence R. Benson presented solid commentary, especially on chapter 1. I am indebted to Daniel F. Harrington (Air Combat Command) for sharpening his editorial scalpel and applying it to every chapter in the manuscript. At the Air Force Research Laboratory’s (AFRL) Corporate Information Office at Kirtland, Michael D. Pietryga, Carlos A. Fernandez, and Stephen T. Martinick smoothed the way through the government chain of command to allow me to complete this work. They understood the value of this project Preface

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and offered their steady support. They gave me the time, freedom, and travel budget to interview key individuals throughout the country. I thank everyone in the AFRL Historical Information Office at Kirtland for their professionalism and support. They include Danielle E. Fraley, Kevin R. Ruybal, Stephen F. Watson, Barron K. Oder, Sylvia A. Pierce, and Rhonda O. Toba, who performed a variety of services that contributed to the final product. Also, I appreciated all the prompt responses from the staff of the AFRL Technical Library at Kirtland, especially those provided by Maryhelen Jones, Elizabeth Luebchow, Sandy Pacheco, and Maggie Cinnella. Danielle E. Fraley and Kevin R. Ruybal, two exceptionally hard-working University of New Mexico students, deserve special gratitude. In the early stages of this project, Danielle developed and organized over 220 subject files. And she built and tailored several databases to make it possible to quickly access the documents, articles, notes, photographs, schematics, fact sheets, and more contained in a comprehensive filing system. These files grew exponentially over the years and became the core source material for the book. In the latter stages of formatting the manuscript, Kevin proved to be a reliable and indispensable worker. He scanned all the photographs and schematics to provide high quality illustrations for the book and carefully checked 795 citations. When questions arose on historical details, Kevin conducted thorough searches and always found documents to corroborate or refute facts in question. Finally, I am grateful to the University of New Mexico Press, especially to its editor-in-chief, W. Clark Whitehorn, for his refreshing open-mindedness and steady support of this project. Adaptive optics is different from most topics the Press publishes, and I am thankful to Clark for seeing this as an opportunity to present an unusual subject with a strong connection to the history of science and technology in New Mexico. I appreciate the editorial improvements Maya Allen-Gallegos and her staff made in transforming the manuscript into a final product. Also, I have been extremely fortunate in the assistance I received from Amanda Morgan, the copyeditor, who made valuable suggestions throughout this book. Her superb editorial skills and meticulous attention to detail reduced unruly sentences to their essence and improved the quality of the storyline. A special thanks to Richard W. Schuetz for his constant support and interest.

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Introduction

Adaptive optics is the most revolutionary technological breakthrough in astronomy since Galileo pointed his telescope skyward to explore the heavens 400 years ago. The recent marriage of large ground-based telescopes capturing huge amounts of light with advanced adaptive optics technology has resulted in spectacular high-resolution images of objects in space that most scientists only a few decades ago would not have dreamed possible. Today, telescopes equipped with adaptive optics allow astronomers and other scientists to look deeper into the universe than ever before. The Department of Defense led the way in the development of adaptive optics by funding research programs carried out primarily at Air Force laboratories over the last 40 years. The military needed to collect sharp images of satellites, missiles, reentry vehicles, and space debris to support its space object identification mission. It also wanted to use adaptive optics to compensate laser beams propagating from the ground through the atmosphere to intercept satellites and missiles in space. Research on compensated laser beams was needed before any laser weapon system would be able to effectively engage satellites and missiles in space during a future conflict. Astronomers have relied on telescopes to survey the heavens for hundreds of years. Hans Lippershey (1570–1619) of Holland is credited with inventing the telescope in 1608. Almost immediately, Dutch officials at the highest level of government recognized the potential military application

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of Lippershey’s invention and asked him if he could build a binocular telescope; such a device would be a tremendous advantage on the battlefield. But the Italian Galileo Galilei (1564–1642), a mathematics professor at Padua, constructed his own telescope in 1609, which performed much better than Lippershey’s. One of the reasons for the success of Galileo’s telescopes was that he had learned how to grind and polish his own lenses using higher quality glass. At the time he was the finest lens maker in all of Europe. His first lenses, not quite 2 inches in diameter, worked well enough to allow Galileo to observe planets, craters on the moon, spots on the sun, the moons of Jupiter, stars of the Milky Way, and other celestial bodies. The images collected by Galileo’s first telescope appeared about nine times larger than those observed by the naked eye. Galileo attracted considerable attention because he was the first to describe the images he viewed through his telescope in writing, in a pamphlet called The Starry Messenger, published in 1610. His astronomical observations challenged the long-held belief that the Earth was the center of the universe, as espoused by the Greek philosopher Aristotle (384–322 BC), the Greek astronomer Ptolemy (AD 83–161), and others. Armed with empirical observations of the sun, planets, and stars provided by his new telescope, Galileo became an ardent supporter of the Polish astronomer Nicholas Copernicus’s (1473–1543) heliocentric theory that the sun was the center of the universe and the Earth moved around it. Although his scientific findings were correct, the Roman Catholic Church condemned Galileo and branded him a heretic for challenging the conventional teaching that the Earth was the center of the universe. Galileo fitted two lenses inside the lead tube of his simple refractive telescope. He positioned a small concave lens at the end closest to the observer’s eye and a larger convex lens at the opposite end. These lenses were small and of poor quality by today’s standards; the larger measured only 4.4 centimeters (1.7 inches) in diameter. The magnification power of his telescopes increased to 8, 20, and eventually 30. However, the clarity of fine detail (resolution) of objects viewed through Galileo’s telescope was limited by the inferior optical quality of his lenses. Telescopes slowly evolved from using small refracting lenses to larger reflecting mirrors to collect and focus light. In a refracting telescope like

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Galileo’s, light rays pass through a lens, which bends (refracts) and focuses the light rays to a point to form an image. How much the light is bent depends on the density of the medium (such as air, water, or glass) through which the light passes and on the wavelength of the light (shorter light waves bend more than longer waves). Reflecting telescopes, on the other hand, use curved or parabolic mirrors to focus light to form an image. The largest telescopes today are reflective.1 Galileo’s telescope was not big enough for atmospheric turbulence to be a problem in terms of distorting images. It was not until the Englishman Isaac Newton (1643–1727) built a reflecting telescope in 1668 that telescopes became large enough in diameter and high enough in quality to be vulnerable to turbulence. By 1730 the Scotsman James Short (1710–1768) had invented the parabolic reflecting telescope, and by 1789 Sir William Herschel (1738–1822) had constructed a reflecting telescope with a 4-foot diameter mirror. In spite of these advances, the problem of atmospheric turbulence remained because bigger telescopes encountered a larger viewing area of atmospheric turbulence and, therefore, collected more distorted light than smaller telescopes. In the last four decades, adaptive optics has emerged as the most advanced technology for generating images of space objects. Every major new telescope in the world today is equipped with adaptive optics, and many older reflecting telescopes—and some refracting telescopes—are being retrofitted with adaptive optics. Adaptive optics has revolutionized the telescope, transforming it into an extraordinarily precise optical instrument capable of generating extremely sharp images. That transformation has occurred thanks to the giant strides made by DoD research programs in the development of the basic components of an adaptive optics system—laser guide stars, wavefront sensors, high-speed computer processors, and deformable mirrors— that have made it possible for large ground-based telescopes to remove distortions from light waves and produce images with resolution at or near the limits set by the laws of physics. Today’s computer-controlled telescopes equipped with adaptive optics can view stars and galaxies 500 million times fainter and with 2,000 times more resolution than the unaided eye can see. Large telescopes cannot produce high-resolution images without the help of adaptive optics. A basic physics formula explains why large telescopes Introduction

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need adaptive optics to compensate light to produce high-resolution images and to compensate laser beams to make them of high quality and powerful enough to disable a target.

The Resolution Formula A telescope’s ability to detect fine detail in an object at a distance is defined as resolution or resolving power and is governed by the formula R=λ/D, where R is the angle in radians between two resolved objects, λ (lambda) is the wavelength in meters of the incoming light received by a telescope, and D is the diameter in meters of the telescope’s primary light-collecting mirror. Resolution can be thought of as the ability of an imaging system to make a clear distinction between close but separate objects. The formula shows that resolution is inversely proportional to the size of the telescope’s aperture or primary mirror. The bigger aperture results in a smaller resolution number, which translates to higher resolution or a sharper detailed image. A 13-centimeter (5-inch) telescope resolves detail as small as about 1 arc-second (1/3,600 of a degree) at visible wavelengths, which is very good resolution. One arc-second is approximately the angular size of a quarter viewed from 3 miles away, so at that distance, an observer with such a telescope could just barely distinguish two quarters placed an inch apart. In comparison, a 1.3-meter (4.3-foot) aperture theoretically has a higher resolution—about 0.1 arc-second at visible wavelength, which would allow one, for example, to easily distinguish heads from tails on the quarters at the same range. A telescope with a 10-meter (10.9-yard) aperture can resolve detail as fine as 0.013 arc-second, enough to read the letters on the quarter spelling out “IN GOD WE TRUST.”2 Bigger telescopes can also see fainter objects. The light-gathering ability of a telescope is determined by the area of its primary mirror, enabling bigger mirrors to see fainter objects. The starlight collected by a telescope decreases as the square of its distance from the star, but increases as the collecting area of the telescope’s primary mirror increases (proportional to the square of the mirror’s diameter). This means the maximum distance at which a telescope can detect a light source increases linearly with the telescope’s diameter. If a 1-meter telescope can detect a star of a certain

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brightness at distance X, then a 4-meter telescope would be able to detect a star of the same brightness at a distance of 4X. If a 1-meter telescope can detect a galaxy at a distance of one billion light years, a 10-meter telescope could detect a similar galaxy 10 billion light years away. Another way of conceptualizing this is that doubling the diameter of a telescope’s primary mirror results in being able to see an object in space that is only 25 percent as bright as observed by a mirror half as big. For example, at the same distance, a 2-meter telescope can see a star of a given brightness but a 4-meter telescope can see a star that is only one-fourth as bright. Doubling the diameter of a telescope’s primary mirror quadruples its area, which in turn quadruples the amount of light the telescope can receive from a celestial object. This is where atmospheric turbulence becomes a problem. Although bigger telescopes can collect more light and thus detect fainter objects, their ability to resolve fine detail is reduced dramatically by turbulence-induced distortion, which causes a 10- or 30-meter telescope to produce the same fuzzy image as a smaller backyard telescope. Turbulence affects larger telescopes more seriously than smaller ones. And this is where adaptive optics becomes important. The new technology makes it possible to compensate for those distortions and allow large telescopes to achieve the resolving power the formula says they can based on their diameter, namely λ/D. Adaptive optics allows the best of both worlds—maximum resolving power and maximum ability to detect faint objects. It helps cancel out the damaging effects of atmospheric turbulence by unscrambling distorted light received at a telescope to produce the best possible images allowed by the laws of physics. A bigger telescope’s adaptive optics system will produce higher-resolution images of objects viewed at the same range as a smaller telescope with a comparable adaptive optics system. NASA built the Hubble Space Telescope to operate in the vacuum of space to avoid the effects of the Earth’s atmosphere. Launched in 1990, Hubble eventually achieved the resolving power of its 2.4-meter aperture, approximately 12 times that of the same size telescope on the ground. NASA plans to deploy a follow-on to Hubble, the 8-meter James Webb Space Telescope, in 2013. The largest modern ground-based telescopes, equipped with adaptive Introduction

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optics, under the right conditions, are producing higher-resolution images than the Hubble Space Telescope. Space telescopes will continue to take advantage of other unique features offered only by space platforms, such as low background infrared, wider corrected fields of view, and ability to observe at wavelengths that are severely absorbed or not transmitted at all by the atmosphere. Future space-based and next-generation ground-based telescopes with adaptive optics are likely to complement each other in producing scientific discoveries in the years ahead. Although adaptive optics is a major breakthrough, it represents only the beginning of a scientific revolution. All signs indicate that over the next 20 years adaptive optics will surpass its current level of performance to generate the best images scientists have ever been able to capture.

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List of acronyms

AAS American Astronomical Society ABL Airborne Laser ABLE ACE Airborne Laser Extended Atmospheric Characterization Experiment ABLEX Airborne Laser Experiment ACE Atmospheric Compensation Experiment ACT Advanced Concepts Testbed ADONIS AMOS Daytime Optical Near-Infrared Imaging System AEOS Advanced Electro-Optical System AFRL Air Force Research Laboratory AFSC Air Force Systems Command AFSPC Air Force Space Command AFWL Air Force Weapons Laboratory ALL Airborne Laser Laboratory AMOS ARPA Maui Optical Site APRA Midcourse Optical Observatory Station ARPA Midcourse Observation Station Air Force Maui Optical Station Air Force Maui Optical Site Air Force Maui Optical and Supercomputing Site APAC astral point ahead compensation ARPA Advanced Research Projects Agency (see also DARPA)

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ARS active ranging system ARTO Advanced Radiation Technology Office BILL beacon illumination laser BMDO Ballistic Missile Defense Organization BUPRL Boston University Physical Research Laboratory CCD charge-coupled device CIA Central Intelligence Agency CIS Compensated Imaging System CLASP Closed-Loop Adaptive Single Parameter COIL chemical oxygen iodine laser DARPA Defense Advanced Research Projects Agency (see also ARPA) DDR&E Director, Defense Research & Engineering DE Directed Energy (AFRL Directorate) DEER Directed Energy Experimental Range DELTA Drone Experiment Laser Test and Assessment DoD Department of Defense FAA Federal Aviation Administration fasor frequency addition source of optical radiation FFRDC Federally Funded Research and Development Center FSSS Future Security Strategy Study FTT Field Test Telescope GBFELTIE Ground-Based Free Electron Laser Technology Integration Experiment GEN I Generation I Closed-Loop Experiment GEN II Generation II Closed-Loop Experiment GEODSS Ground-Based Electro-Optical Deep Space Surveillance HARP High Altitude Reconnaissance Platform HoPE Horizontal Path Experiment ICBM intercontinental ballistic missile IDA Institute for Defense Analyses IRST infrared search and track LAAT Large Aperture Acquisition Telescope LACE Low-Power Atmospheric Compensation Experiment laser light amplification by stimulated emission of radiation

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LDEF LFAT LITE maser

MDA MHPCC MIT MOMS MPM MSSC MSSS NASA Nd:YAG Nd:YLF NOAO NoDyCE NOP NRO NSF OCULAR PA&E PL PSSC PZT RADC RAND RME RPAC RTAC SAB SAGE SAM SDI SDIO

Long Duration Exposure Facility Large Field Acquisition Telescope Laser Integration Technology Program microwave amplification by stimulated emission of radiation Missile Defense Agency Maui High Performance Computing Center Massachusetts Institute of Technology mobile optical measurement system monolithic piezoelectric mirror Maui Space Surveillance Complex Maui Space Surveillance System National Aeronautics and Space Administration neodymium: yttrium aluminum garnet neodymium: yttrium lithium fluoride National Optical Astronomical Observatory Non-cooperative Dynamic Compensation Experiment North Oscura Peak National Reconnaissance Office National Science Foundation Optical Compensation of Uniphase Laser Radiation program analysis and evaluation Phillips Laboratory Physical Science Study Committee lead zirconate titanate Rome Air Development Center Research and Development Relay Mirror Experiment ray point-ahead compensation Real-Time Atmospheric Compensation Air Force Scientific Advisory Board Semiautomatic Ground Environment surface-to-air missile Strategic Defense Initiative Strategic Defense Initiative Organization

List of Acronyms

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SFG sum frequency generation SOML Steward Observatory Mirror Laboratory SOR Sandia Optical Range Starfire Optical Range SWAT Short-Wavelength Adaptive Techniques THAAD Theater High Altitude Area Defense TILL track illumination laser TRAPAF Target Return Adaptive Pointing and Focus USSPACECOM U.S. Space Command USSTRATCOM U.S. Strategic Command WDD Western Development Division WIYN Wisconsin, Indiana, Yale National Optical Astronomy Observatory XLD Experimental Laser Device Yb:YAG ytterbium: yttrium aluminum garnet

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Sputnik, Reality, and Technology

Military research on adaptive optics originated in a small Department of Defense research and development organization known as the Advanced Research Projects Agency or ARPA. That organization pursued cutting-edge research beginning in the 1970s that led to the development of sophisticated adaptive optics technology that supports a variety of military and astronomical systems today. Without ARPA’s financial backing and encouragement, it is unlikely that rapid progress in adaptive optics would have been possible. To understand why ARPA was set up in the first place to support defense research programs, one must return to the 1950s. At that time, volatile political circumstances threatened to disrupt the military balance of power between the United States and the Soviet Union. President Dwight D. Eisenhower’s decision to establish ARPA on 7 February 1958 (by way of DoD Directive 5105.15 and Public Law 85–325, dated 12 February 1958) was a direct response to the Soviet Union’s dramatic launch of the world’s first man-made satellite, Sputnik I, on 4 October 1957. A metallic ball weighing only 184 pounds and measuring about 23 inches in diameter, which circled the earth every 96 minutes at a speed of 18,000 miles per hour in an orbit 550 miles out in space, Sputnik marked the start of the modern space age. It shocked the world and, rightly or wrongly, convinced the U.S. government and the public that the Soviets were far ahead

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Photo 1. From the roof of Boston University’s Physical Research Laboratory

building, scientists tracked the first Sputnik across the night sky. In back, left to right: Bill Britton, Jim Chadderdon, Grant Ross, Joe Vravel, Bill Attaya, and Ray Babcock; Harold Alpaugh in the foreground.

of the Americans in the space race. America’s prestige reached a low point in 1957. Using Sputnik I as their Cold War ace card in the hole, the Soviets took full advantage of every opportunity to remind the world of the superior expertise of the gifted scientists who were responsible for this amazing technical feat.1 The Soviets were not simply engaged in idle talk. Barely 29 days had elapsed since Sputnik I began bleeping across the heavens when the Soviets staked another claim to technological supremacy in space. To add political insult to technological injury, the launch of Sputnik II on 3 November 1957 was even more spectacular, as its payload (1,121 pounds) weighed more than six times that of Sputnik I. Americans winced when they learned that the second Sputnik also carried a live dog, named Laika, suggesting the Soviets already had a program under way to put a man in space.2

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Photo 2. The first U.S. photograph of Sputnik I—the world’s first artificial

satellite, which ushered in the Space Age. The dotted line of light represents the satellite’s path. Photo taken by a team of Boston University scientists.

This was a brutal blow to the Americans in the opening round of an international prizefight that would ultimately decide who would reign in space. The triumphant launch of two consecutive Soviet satellites into orbit—followed by Sputnik III, a 2,914-pound geophysical satellite launched on 15 May 1958—sent a message that the Russians had outpaced the United States in developing the capability to build boosters with enough thrust and lift capacity to place heavy objects into orbit.3 Even prior to the launch of Sputnik I, on 26 August 1957, the Soviet Union had announced it had successfully test-fired the world’s first intercontinental ballistic missile (ICBM), dubbed the R-7. The Soviet Union was ahead of the United States in the missile race. What worried top Pentagon officials was the possibility that the Soviets might launch ICBMs into space loaded with nuclear weapons that could reach targets in the United States. Sputnik had ushered in the space race, but at the same time, in the eyes of American military leaders, it had accelerated a dangerous arms race.4 Sputnik, Reality, and Technology

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In reality, the U.S. space program did not lag appreciably far behind the Soviet Union’s. In fact, the American program was ahead of the Soviets in many core areas such as microelectronics, computers, guidance systems, sensors, solid fuels, nuclear warhead design, and survivability of systems. But Soviet development of reliable and powerful launch vehicles—specifically ICBMs—caused the United States to stumble momentarily, which gave the impression to the public that the country was in deep trouble. Top DoD officials were aware ahead of time that the Soviets were about to launch their first satellite. But that knowledge, shared by a relatively small group, did little to calm the fears and emotions of the majority of the people who believed that communism was on the verge of trumping the democratic way of life. As Walter A. McDougall wrote in his Pulitzer Prize-winning history of the space age, “As it happened, the public outcry after Sputnik was ear-splitting.” The press fueled these worries by reporting Sputnik as the Pearl Harbor of American science. The psychological effect of Sputnik on the American public was huge.5 Faced with this crisis, the United States realized it had to reform its educational system, perceived to be weak and complacent, by placing more emphasis on science and technology so that the universities could turn out a larger pool of disciplined scientists, mathematicians, and engineers. These talented individuals would manage multidimensional research and development activities in America’s modern aerospace companies and government laboratories. Everyone agreed that the United States had to reestablish the importance of math and science in the minds of all Americans if the nation was going to be able to deal with the rising Soviet threat.6 A renewed interest in building stronger math and science curricula reached down into high schools across the country. A year before the launch of Sputnik, a group of concerned university professors and high school teachers formed the Physical Science Study Committee (PSSC) at the Massachusetts Institute of Technology. The goal of PSSC was to develop a new high school physics course and textbook to get more young Americans interested in physics. Over time more money, provided primarily through the National Science Foundation, found its way to support PSSC’s mission. One student who participated in the newly designed PSSC high school physics course was Jim Mayo, a Memphis teenager who went on to spend over four decades of his career in the field of optics working for the Air

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Force and private industry. He later vividly remembered signing up as a youngster for one of only two PSSC high school physics courses offered in Tennessee. This positive educational experience persuaded Mayo to pursue a career in science. He recalled the new PSSC physics course “was driven almost entirely by Sputnik.”7 Once the cosmic dust of Sputnik had settled, cooler heads prevailed after taking time to analyze the long-term significance of this Soviet first. Many pointed out that the United States and the Soviet Union had planned to launch civilian satellites for scientific purposes as part of International Geophysical Year activities in 1957–1958. Looking back with the benefit of over 50 years of hindsight, the argument could now be made that the United States should have been more aggressive in placing its first satellite in orbit. But at the time, it seemed the government’s plan was on schedule to launch a research satellite as part of its Vanguard program for the International Geophysical Year.8 Dr. James R. Killian, president of the Massachusetts Institute of Technology, appointed a month after Sputnik I as special assistant to the president for science and technology, concluded America had not failed and was not as vulnerable as many people suspected. He was confident the United States would be able to put its first satellite up soon. As he was quick to remind people, “The Army Ballistic Missile Agency had demonstrated in a test firing of its Jupiter C [rocket] on 20 September 1956, that it could probably have put a satellite into orbit ‘on that day.’” The Jupiter-C had climbed to 682 miles, easily a high enough altitude to place a satellite into orbit.9 Killian’s words may have been correct, but they provided little comfort to the millions of Americans worried about the fact that the Soviets had beaten the United States into space. Many believed there was a huge “missile gap.” To counter the impression that America was falling behind, Eisenhower’s secretary of defense, Neil H. McElroy, directed the military services on 8 November 1957 to launch an American satellite as soon as possible. Scrambling to restore its preeminence in science, the United States attempted on 6 December 1957 to launch a Navy Vanguard rocket and place its first satellite into space. That effort ended in disaster as the Vanguard blew up on its launch pad while millions of anxious Americans watched on television. The scattered remains of the charred rocket showed that the United States had a long way to go to perfect the reliability of its launch vehicles.10 Sputnik, Reality, and Technology

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Failure to launch Vanguard prompted Secretary McElroy to resurrect Project Orbiter, an Army program headed by Major General John Bruce Medaris to develop intermediate-range ballistic missiles, which focused on advancing the Jupiter missile. Wernher von Braun headed a scientific team that worked on this project at the Army Ballistic Missile Agency, located at Redstone Arsenal in Huntsville, Alabama. In late 1956, Secretary of Defense Charles E. Wilson had made the decision to give the Air Force control over development of intermediate-range missiles, specifically the Thor missile. As part of this move, the Army was limited to working on missiles with a range of 200 miles or less. However, after the Vanguard catastrophe, McElroy was anxious to reconsider the Army’s missile program in the hope that von Braun’s team would quickly get a reliable missile ready to boost America’s first satellite into space.11 America’s space picture was not as bleak as many had envisioned. Four months after the launch of Sputnik I, on 31 January 1958, the Army’s fourstage Jupiter-C rocket—which used a modified Redstone missile as its first stage—lifted off an hour and twelve minutes before midnight from launch pad 5 at Complex 56 at Cape Canaveral and boosted the nation’s first satellite, Explorer I, into orbit. America’s first satellite had been built in just 84 days, in an effort led by William H. Pickering, director of the Jet Propulsion Laboratory at the California Institute of Technology in Pasadena. The weight of the Explorer I satellite instrumentation contained in the tip of the fourth-stage Sergeant empty rocket casing totaled 18 pounds. Explorer I was tiny in comparison with Sputnik I and II.12 The U.S. launch restored pride in America’s fledging space program and reassured critics that the United States was capable of meeting the Soviet challenge. However, the more enduring legacy of Explorer I was its discovery and initial measurement of the Van Allen belts of intense cosmic radiation circling the Earth (named after physicist James A. Van Allen from the University of Iowa). Not until almost a year later, on 18 December 1958, did the Air Force place its first satellite into orbit with an Atlas booster. Known as SCORE, for Signal Communications by Orbital Relay Equipment, it was the nation’s first communication satellite and beamed back to millions of Americans a tape recording of President Dwight D. Eisenhower’s Christmas message of peace and good will throughout the world. That was the first time a human voice had been heard from space.13

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Photo 3. Explorer I, America’s first satellite, launched on 31 January

1958. The photo shows the Sergeant fourth-stage rocket that made up the satellite. The forward half of the 6.6-foot long scaled-down version Sergeant rocket housed the satellite instrumentation (temperature sensors, two transmitters and a Geiger-Mueller counter to detect cosmic rays), which was attached to the lower half of the Sergeant rocket casing. The instrumentation section and lower rocket casing— the inert fourth stage that had expended all its fuel—combined to operate as a single satellite unit. To provide stability, the Sergeant rocket spun around its long axis at 750 revolutions per minute. The wispy tentacles protruding from the center of the rocket were antenna wires that made up part of the satellite’s communication system, which sent data to tracking stations on the ground. Explorer I continued to operate until its batteries died on 23 May 1958; it continued to orbit until 1970.

Sputnik, Reality, and Technology

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The success of Explorer I opened the door for the U.S. government and American scientific community to accelerate a plan to use satellites as reconnaissance vehicles to take pictures from space of Soviet missile sites, airfields, submarine and ship staging areas, rail yards, communication centers, and a variety of other targets. A year before Sputnik, the United States had relied on high-flying aircraft to carry out deep-penetration reconnaissance missions over Soviet territory. In late 1954 Eisenhower had authorized the controversial program using U-2 reconnaissance aircraft (U stood for utility) to gather aerial intelligence under the direction of the Central Intelligence Agency (CIA), a civilian organization. U-2 overflights of Soviet territory started on 4 July 1956. (Prior to the U-2s, American RB-47 aircraft conducted a limited number of reconnaissance overflights of Soviet territory to determine the size of the Soviet strategic bomber force.) Eisenhower chose the CIA over the Air Force because he believed having military pilots fly over the Soviet Union would be an act of war. Consequently, pilots who wanted to fly the U-2 had to resign from the Air Force and revert to civilian status temporarily while working for the CIA.14 The president soon found himself on the horns of a dilemma. On the one hand, the spy flights over Soviet airspace violated international law and ran the risk of starting a war. On the other hand, the U-2 provided valuable intelligence, including detailed photos of Soviet missile launch sites, such as the SS-6 ICBM site at Tyuratam. Flying at an altitude of over 70,000 feet— 20,000 feet out of range of Soviet surface-to-air missiles—with a 36-inch folded camera in its nose, the U-2 demonstrated the value of high-altitude reconnaissance. But the fear remained that the Soviets would eventually be able to advance their radar systems to detect and track it.15 After twenty-seven successful U-2 missions, this fear came true when a Soviet SA-2 surface-to-air missile brought down Gary Francis Powers’s U-2 aircraft on 1 May 1960 near the city of Sverdlovsk in western Russia. The Russian missile did not score a direct hit but exploded near the rear of the aircraft, causing it to spiral out of control and crash. Powers bailed out and was captured by a small group of Russian farmers. Soviet Premier Nikita Khrushchev gave a scorching denunciation of the United States at the summit meeting that began in Paris on 16 May and demanded an immediate apology from Eisenhower. The American president declined to

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issue a formal admission of guilt but announced there would be no more U-2 flights over the Soviet Union.16 The U-2 program had left an enduring legacy. One of its most compelling results was to verify that there was no “bomber gap”—the Russians did not have a lead over the United States in terms of the number of intercontinental bombers capable of delivering nuclear weapons. Eisenhower and his advisors were less certain of the progress the Soviets had made in missile development.17 Several years before Powers’s fateful flight, the Air Staff had decided to pursue development of a secret Air Force satellite reconnaissance program called weapon system WS-117L, officially the Advanced Reconnaissance System. General Operational Requirement No. 802, issued by the Air Force in late 1954, initiated preliminary studies. Originally, the Wright Air Development Center at Wright-Patterson Air Force Base in Dayton, Ohio, managed the program. But on 10 October 1955, Air Research and Development Command reassigned the program to Major General Bernard A. Schriever’s Western Development Division (WDD), which had been activated on 1 July 1954 in Inglewood, California, with responsibility for developing the nation’s first ICBM force. (In 1955, WWD moved to permanent quarters in El Segundo, and on 1 June 1957 it was renamed the Air Force Ballistic Missile Division.) The WS-117L transfer was a better fit with WDD because ICBM boosters eventually would be needed to launch reconnaissance satellites into orbit. With the transfer, WDD became responsible for developing the first military satellite system. From that point on, the development of satellites and missiles were linked together.18 To a large degree, the origins of WS-117L went back to a series of RAND studies starting in 1946 that looked at the feasibility of using satellites as reconnaissance platforms to collect intelligence on the Soviet Union’s military capability. Critics argued that a military satellite program would be far too costly and technically impossible. However, over a decade later, in January 1958, the president approved CORONA—this country’s first operational spy satellite program—to move forward as a joint CIA/Air Force program. To make this happen, the space photographic mission was separated from WS-117L and became the core of the covert CORONA program. Developing a more secure satellite reconnaissance system to replace the more vulnerable U-2 was one of the fundamental goals of CORONA.19 Sputnik, Reality, and Technology

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The CIA, with Eisenhower’s approval, took the lead in acquiring and developing imaging equipment and selecting targets to be photographed. Some friction and resentment existed between the CIA and Air Force as the CIA—responsible for the technical development of the imaging equipment for CORONA—emerged as the dominant player under this dual but unequal and informal management arrangement. However, in spite of their disagreements, the CIA and Air Force tried to work as a coordinated team to make the program a success. In reality, the struggle over control of CORONA continued as the Air Force felt it should play the leading role in directing the program. To end the squabbling, the National Reconnaissance Office (NRO) was established in September 1961 to manage all U.S. reconnaissance projects, including CORONA. Joseph Charyk, a former undersecretary of the Air Force and NRO’s first director, reported directly to the secretary of defense. CORONA lasted for 14 years and launched 145 satellites that produced 800,000 images before the program shut down in May 1972. Although CORONA ended, the U.S. satellite reconnaissance program did not. CORONA’s successors developed and deployed increasingly sophisticated space imaging systems that form an integral part of the U.S. national security structure today.20 Eisenhower chose Richard M. Bissell Jr., who was special assistant to the director for planning and development at the CIA, to manage the CORONA program. Brigadier General Osmond Ritland, who was General Bernard Schriever’s vice commander at the Air Force Ballistic Missile Division in Los Angeles, headed the Air Force portion of CORONA and worked closely with Bissell. Bissell was a logical choice because in 1954–55 he and Kelly Johnson, of the now famous Lockheed “Skunk Works” in California, were the catalysts for the successful development of the U-2, which went from concept to operation in a record 18 months. Lockheed also served as the prime contractor for CORONA.21 Two options seemed plausible for getting satellite reconnaissance images of ground targets back to Earth. One involved taking images using television cameras and then transmitting the video. A disadvantage was that the atmosphere could disrupt transmission of TV signals, resulting in poor images. The second method involved using cameras developed by Itek and Fairchild that recorded images on film designed by Eastman Kodak for use in space. At a predetermined point in orbit, the film would be ejected from the satellite

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in a container attached to a parachute. On its way down over the Pacific Ocean, the capsule carrying the film would be caught by an Air Force cargo aircraft—in the first years of CORONA a C-119 Flying Boxcar, later a C-130 Hercules. The air recovery crew used a trapeze-like frame extending from the rear of the aircraft to snag the capsule and winch it onboard. Then the film would be delivered back to base. CIA analysts would immediately examine the film to gain the most up-to-date intelligence on Soviet military facilities. Because electronic imaging technologies had not yet been fully developed, Eisenhower in January 1958 chose the film option, and it lasted until electronic imaging became more workable in the 1960s.22 The first attempts to snag the film capsules in midair, between February 1959 and July 1960, all ended in failure. Problems with four solid-propellant spin rockets caused the film capsules to veer off course, entering a different orbit and not reentering the atmosphere. Once engineers fixed that problem, Air Force Captain Harold F. Mitchell, piloting a C-119 on 19 August 1960, recovered the first space capsule in midair over the Pacific—the first object ever returned from a space orbit to earth. From then on, the Air Force was successful in retrieving the film capsules.23

Creation of the Advanced Research Projects Agency Despite the success of America’s first satellite in orbit, the nation’s military and political leaders still had to grapple with how to recapture U.S. dominance in science and technology after Sputnik. The immediate question was what could be done to expedite the discovery of new technologies that would enhance the nation’s war-fighting capabilities—specifically, how could the Defense Department develop radical technologies in order “to defeat existing and emerging national security threats.” The creation of the Advanced Research Projects Agency (ARPA) in January 1958 offered one long-range approach. At first, the small DoD agency reported directly to the secretary of defense. Today the agency—now called the Defense Advanced Research Projects Agency or DARPA—reports to the director of defense research and engineering in the Pentagon.24 Over the years ARPA underwent a number of name changes that reflected the shifting political climate. On 23 March 1972, ARPA’s name changed to Sputnik, Reality, and Technology

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DARPA to emphasize the fact that the new technologies the agency developed would eventually be transitioned into products and systems to support military operations. Understandably, Congress wanted a return on the money it spent on research and development; that meant getting new technologies into the field to sustain military missions. Nearly 20 years later, on 22 February 1993, DARPA briefly reverted to its original name, ARPA, as the notion of defense was deemphasized at the end of the Cold War. On 10 February 1996, as the threat of terrorism escalated and the need for defense increased, the agency was renamed DARPA.25 ARPA was initially headed by Roy Johnson, a former vice president of General Electric, and physicist Herbert York, from the University of California at Berkley, who served as ARPA’s first chief scientist. Its goals were not only to regain U.S. dominance in science and technology and to avoid technological surprises like Sputnik, but to be able to inflict technological surprises on an enemy, such as stealth aircraft, precision-guided weapons, and unmanned aerial vehicles.26 Originally, ARPA was responsible for both military and civilian satellite programs, partly to reduce competition and infighting among the three military services to gain control of space programs. However, Air Force leaders vehemently opposed this arrangement and argued the Air Force was the logical service to manage all military space programs. It took some time to sort out the nation’s space organization. In July 1958, Eisenhower signed into law the creation of the National Aeronautics and Space Administration (NASA) to manage the civilian space program free from military interference. In September 1959, Secretary McElroy announced the transfer of military space projects from ARPA to the three military services. Consequently, ARPA focused exclusively on military research and development, which included space and a wide range of other areas of scientific interest to the military.27 As a civilian-operated research and development agency, ARPA’s immediate goal was to recruit the best scientific and engineering minds in the country to conduct high-risk research that would lead quickly to the demonstration of extraordinary technical capabilities. ARPA’s intent was to rattle scientists out of their traditional comfort zone and force them to head off in different directions to come up with radical innovations to strengthen national security. The objective was to concentrate on technological breakthroughs of a “revolutionary nature,” as opposed to incremental

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improvements of existing systems using “old knowledge” that represented an evolutionary step-by-step approach for advancing research and technology. ARPA’s game plan was to fund DoD laboratories—working with private contractors and universities—to pursue nontraditional research projects. The resulting new knowledge would create new capabilities to be used in the development and deployment of radically innovative weapon, surveillance, and other military systems. The scope of these programs was limited only by the imagination of scientists.28 To attract such free thinkers, ARPA offered generous amounts of money and imposed the bare minimum of restrictions, empowering scientists to conduct independent research without interference. The focus was always on getting out of the way and encouraging scientists to do the impossible. ARPA officials knew that failures were likely, but if a 100-to-1 long shot came in, the payoffs would be incredibly high in terms of accomplishing military missions and saving lives.29 ARPA was the catalyst for the first stage or proof of concept, and in some cases, continued to support a project through the development of prototype systems. Then it usually dropped out of the process and it became the responsibility of one of the military services to pursue further development of the new technology. That meant the Air Force, Army, or Navy had to come up with its own money to fund and sustain research of the new technology to move forward with the development and engineering integration phases. ARPA functioned primarily as a funding agency that distributed work to government laboratories and private contractors. It conducted no laboratory research internally.30 ARPA concentrated on the future needs of the military services but did not have the authority to issue formal requirements to the military. The operating commands and Joint Chiefs of Staff made decisions on weapon requirements, with final approval from Congress. ARPA advocated and pursued the advancement of never-before-thought-of technologies and answers to strategic and tactical questions that the operating commands had yet to ask. Rettig Benedict, who worked for ARPA in the late 1970s and early 1980s in the area of directed energy, explained that ARPA’s job boiled down to alerting and pushing the operating commands to be receptive to new tools that could be integrated into their war fighting machine. As a recent DARPA report described it, “DARPA focuses on capabilities Sputnik, Reality, and Technology

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military commanders might want in the future, not what they know they want today.” That was often a difficult sell, because most career-minded commanders were more interested in perfecting current weapon systems to meet their immediate needs than in revolutionary weapons that most likely would not become operational for several decades.31 By investing in this course of action, the United States believed it would be in a stronger position to keep one step ahead of the Soviets. ARPA’s earliest funding went to support research and development in areas including lasers, solid-propellant chemistry, undersea and satellite surveillance, active illumination reconnaissance, and defense against ICBMs. By the mid-1960s and early 1970s, ARPA was taking the lead in the relatively unknown but rapidly growing field of adaptive optics, which many considered to be the most revolutionary advancement in astronomy and optics since Galileo built his first telescope in 1609.32 Military service chiefs, commanders at the operating command level, and scientific advisory boards had very little to do with getting adaptive optics work started in the Air Force. It was fundamentally a grass-roots movement spurred on by the intense interest of working scientists and the financial backing of ARPA. ARPA had the advantage of a mandate to support risky ventures without being penalized if the technology did not lead to a practical military application—a luxury that government laboratories did not enjoy.33 Why in the mid-sixties and early seventies was ARPA particularly interested in adaptive optics? At the height of the Cold War, the threat posed by the increase in the size of Soviet ground forces and Moscow’s ability to attack American cities with nuclear-tipped ICBMs—a danger that had lingered in the minds of many since the Cuban missile crisis of October 1962—was a grave concern to American military strategists. They knew that an effective reconnaissance and surveillance system was essential for keeping an eye on the Soviet Union. But they also realized the inability of conventional optics working with telescopes on the ground to produce quality images of Soviet systems such as satellites. Development of adaptive optics combined with larger telescopes might be the solution.34 Adaptive optics was a logical extension of the nation’s satellite surveillance program, unveiled in the 1950s. While the Eisenhower administration relied on satellite surveillance cameras in space to acquire images of

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objects on the ground, adaptive optics technology in the 1970s took just the opposite path—systems on the ground to acquire high-resolution images of space objects, primarily satellites and missiles. Many defense analysts believed a ground-based system would be less expensive to build, operate, and maintain than a space-based surveillance system. Adaptive optics offered the possibility of measuring and correcting for aberrations caused by atmospheric turbulence in reflected sunlight received from solar-illuminated satellites as a way of obtaining improved images of those satellites. The need was real, as the Soviets had launched 242 military reconnaissance satellites from 1965 through 1973. By collecting more accurate data on Soviet satellites, the United States would be in a much better position to evaluate the enemy threat. Moreover, in time of peace and war, adaptive optics would be an invaluable enabling technology for determining enemy satellite damage from natural causes or military action.35 Clear images produced with the help of adaptive optics would also be extremely useful in determining the health and operational status of friendly satellites. Radar could image satellites, but it lacked the higher resolution, which adaptive optics provides today, needed to capture the finer details of how a satellite was functioning. High-resolution images, for instance, could reveal if a satellite was positioned properly or if it was tumbling. With such data, adjustments could be made to correct satellite operating deficiencies, saving millions of dollars on satellites that might otherwise be damaged or lost. Finally, many argued that an adaptive optics system on the ground could be better protected and maintained, making it less vulnerable than space surveillance systems.36 At the time, two Air Force customers, Aerospace Defense Command (Cheyenne Mountain, Colorado) and the Space and Missile Systems Organi­ zation (Los Angeles), were especially concerned with identifying Soviet satellites and the functions they performed. Imaging enhanced by adaptive optics could potentially produce much better images than the conventional radar on which they then relied, which produced relatively poor images.37 Rettig Benedict recalled, “The radar community [at MIT’s Lincoln Laboratory in Massachusetts] was exploring a concept called range profiling—that is, the radar return was recorded as a function of time and interpreted as an ‘image’ in the range direction.” ARPA also funded projects at Lincoln Laboratory and elsewhere that produced “a two dimensional Sputnik, Reality, and Technology

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‘image’ by using the rotation of the object relative to the radar to measure a Doppler signal. When combined with the range data, a range-cross range image was obtained, quite different from an optical image.” This technology was useful but was not adequately developed until the early 1980s.38 Besides imaging space objects, ARPA was also looking at the possibility of using adaptive optics on space platforms for producing improved images of ground targets. As it turned out, adaptive optics was not needed for that purpose. Looking down from a space platform to obtain an image of an object on the ground is relatively easy to accomplish, because atmospheric turbulence is very close to the ground and thus does not blur the image. This has been proven over the years with the use of very high-resolution space cameras, which do not require adaptive optics. Project CORONA successfully used space cameras specially designed in the early 1960s by Itek Corporation in Lexington, Massachusetts. CORONA’s highly sophisticated cameras gained sufficient intelligence from photos of Soviet missile sites and military installations to make a realistic assessment of Soviet military capabilities. That information helped the United States maintain an advantage over the Soviets during the highly charged brinksmanship of the Cold War era. On the other hand, trying to acquire a clear image of a space object from the ground is very difficult because the most turbulent layer of the atmosphere is near the telescope. Some believed that adaptive optics was the solution to atmospheric turbulence and could enable a telescope to produce a sharp image of a space object.39 Another potential application of adaptive optics was to make laser weapons more accurate by cleaning up the effects of thermal blooming (dispersion of beams caused by atmospheric absorption). This could improve the quality of a high-power laser beam projected from the ground through the atmosphere to intercept and disable Soviet satellites and missiles. All these were legitimate and timely reasons for ARPA to explore adaptive optics. As it turned out, the Air Force laboratory system, funded by ARPA, would take the lead in adaptive optics. The origins of that work can be traced to the Rome Air Development Center, located at a secluded Air Force site in upstate New York.40

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Early Days The Romans

ARPA and the Air Force realized that before any serious work could be performed to design, develop, and build a working adaptive optics system to produce high-resolution images, scientists at several Air Force laboratories would have to better understand the main problem that adaptive optics needed to fix: turbulence caused by temperature fluctuations in the atmosphere. As one expert explained it, “Atmospheric turbulence is generated during the breakup of large-scale convective flows of the air into small spatial scales with the subsequent release of energy. The convective flows are driven by solar heating and radiative cooling of the earth’s surface and the resulting temperature gradients.”1 The atmosphere is constantly moving at different speeds, much like the surface water in the oceans. Some sections of the oceans can be perfectly calm with a mirror-like surface, while at the same time, other regions of the oceans experience violent churning surf and tidal wave conditions. In the atmosphere, similar conditions exist. Temperature changes at various altitudes in the atmosphere (60–90 kilometers or 37–56 miles in depth) equate to changes in the air density refractive index, which acts as a lens to cause one section of a

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light wavefront to bend differently and move faster ahead or lag behind other sections of the same wavefront. This produces the undesirable condition of an uneven wavefront. In other words, these random temperature fluctuations in different regions of the atmosphere conspire to produce a non-uniform and constantly swirling mixture of air, which in turn degrades the quality and intensity of a laser or light beam as it moves unpredictably through each sector of the atmosphere. Instead of all parts of the light wavefront traveling in a straight flat line in the same direction, atmospheric turbulence causes the light to follow an erratic path. The goal of adaptive optics is to get all sections of the wavefront to move in the same direction.2 Light travels as perfect plane waves from a point in space until at the end of its long journey it interacts with the natural thermal turbulence in the atmosphere. As a result, the turbulence impinges all across the light beam and distorts the quality of the beam. Atmospheric turbulence is most intense in the lower region of the atmosphere—from the Earth’s surface to about 4 miles up—where light beams, after having traveled millions of light years through space undisturbed, are very susceptible to distortions during the last fraction of a second of their long journey to Earth. (A light year is the distance light travels in a year, or about 6 trillion miles.) Distortions in the light occur because of the unevenness of the various layers of the atmosphere—each layer exhibits a different refractive index—which distorts or bends the light. Consequently, when this out-of-phase or “wrinkled” light filled with peaks and valleys (no longer a plane or flat wavefront) is collected and focused by a telescope, the resulting image is severely distorted and appears as a blur rather than a razor-sharp image. This optical effect is similar to the way distant objects appear to shimmer and blur when viewed through summer heat waves dancing above a hot asphalt road.3 Adaptive optics offered a way to correct this problem by restoring light to near its original, undisturbed condition before it enters the atmosphere. Putting it in lay terms, Robert K. Tyson, author of Principles of Adaptive Optics, defined it as “a method of automatically keeping the light focused when it gets out of focus.”4 The effects of air turbulence are more severe on shorter-wavelength light than on longer-wavelength light. If short-wavelength lasers used with large telescopes could be corrected for atmospheric distortion by using adaptive optics, then a laser could travel an extended range and still deliver

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Figure 1. The problem of atmospheric turbulence is that it causes a

blurred image. An adaptive optics system compensates or corrects for atmospheric turbulence to produce a sharp image of space objects.

sufficient energy on target. That would be a huge advantage for a groundbased laser weapon. Bigger telescopes collect more light, but are more vulnerable to atmospheric interference and thus need an adaptive optics system to produce high-resolution images or a tightly shaped laser beam. (Adaptive optics is only effective on telescopes with primary mirrors larger than about 20 centimeters or 7.9 inches.)5 Early Days

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But before any adaptive optics system could be designed, the first step was for scientists to better understand air turbulence and how it distorts light traveling through it. Then they would be able to design a ground-based adaptive optics system that would use an assortment of sensors, processors, and deformable mirrors to correct the distortion and produce quality images.6 In contrast, the $1.5 billion Hubble Space Telescope (deployed from the bay of the shuttle Discovery on 25 April 1990), with its 2.4-meter mirror, operates in the vacuum of space and produces high quality images of heavenly objects because it does not have to contend with atmospheric turbulence, which is absent in space; it does not require adaptive optics. However, it was very costly to build, launch, and maintain—and there is only one Hubble, with a long line of scientists waiting to use it. To build a fleet of Hubbles would be prohibitively expensive. But there is a realistic alternative: adaptive optics installed on telescopes on the ground that are available to a large number of users. For example, the 10-meter Keck I telescope in Hawaii cost $94.2 million, a fraction of Hubble’s price tag. Under the right conditions, over a narrow slice of sky (about 20 arc-seconds for visible light), ground-based telescopes can achieve images equivalent to those generated by the Hubble Space Telescope, although the Hubble can achieve those images over a larger field of view (28 arc-minutes in diameter).7 Some of the first military experiments to accurately define the effects of atmospheric turbulence on light and laser beams began in the mid-1960s at the Verona Test Facility at the Air Force’s Rome Air Development Center (RADC). RADC became involved in these experiments after the discovery of the laser. (A laser is a concentrated beam of light. The acronym stands for light amplification by stimulated emission of radiation). The laser breakthrough, on 16 May 1960 by Theodore H. Maiman at Hughes Aircraft Company’s Research Laboratory in Malibu, California, was unexpected. In 1958 two of the country’s most respected scientists, Charles H. Townes and Arthur L. Schawlow, had predicted the operation of an optical maser (microwave amplification by stimulated emission of radiation), considered to be the forerunner of the laser. In spite of the critics who showed little faith in his approach of using ruby as a lasing medium, Maiman stuck by his convictions and steadfastly continued to conduct his experiments. He bypassed everyone and used a flash lamp to excite a single rod made from ruby crystal to produce the first working laser.8

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Almost immediately, the laser caught the attention of the defense community, which was interested in its potential as a precision weapon. Scientists already knew that short-wavelength lasers shine brightly and can deposit maximum energy on target, but atmospheric turbulence interfered with the process. Because of this, RADC became involved in a number of studies and experiments in the mid-1960s directed at learning as much as possible about the degrading effects of air turbulence on laser beams. Another problem encountered was a phenomenon called thermal blooming, which is a nonlinear distortion that defocuses and spreads out a laser beam and can rob it of power.9 Conducting laboratory and field experiments would be a necessary first step to understanding exactly how the atmosphere influenced the behavior of a laser beam. With accurate measurements of atmospheric turbulence, RADC scientists would be better prepared to assess the feasibility of using lasers for surveillance radar, communications, imaging of space objects using ground-based telescopes, and other missions. Adaptive optics, developed with military sponsorship, would become one of the most important supporting technologies for these missions.10 The military was interested in adaptive optics’ potential utility for enhancing not only imaging but also for weapon systems. At the same time that work on adaptive optics moved forward in the late 1960s and early 1970s, the Air Force was investigating the merits of airborne lasers for air-to-air and theater missile defenses. If adaptive optics could solve the problem of air turbulence for laser beams, then the chances in the future for developing a ground-based laser antisatellite weapon would be greatly improved. Hence, adaptive optics was considered an essential enabling technology. Without it, it would take 100 to 1,000 times more laser power to deliver enough energy on target to disable or destroy the target. In sum, from the military’s viewpoint, adaptive optics could be applied to two different missions: compensating light to produce sharp images of space objects and compensating laser beams to propagate through the atmosphere with a minimum of disruption.11 The real-world application of these two missions, imaging and laserbeam propagation, were closely connected. For instance, before a compensated laser beam could engage a satellite, an adaptive optics system would need to locate the target by imaging it so the ground-based telescope could Early Days

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track it. Next, the adaptive optics system would have to sample the pointahead angle in relation to the satellite and the telescope on the ground, to collect sufficient air turbulence data in order to compensate the outgoing high-energy laser beam traveling along the path from the ground to the satellite. In other words, before you can shoot the satellite, you must find it and track it.12 RADC was a tenant organization located on Griffiss Air Force Base, a Strategic Air Command site in upstate New York near Syracuse responsible for operating a B-52 bomber wing. Verona, located about seven miles west of RADC, started out as a radar test facility in the 1950s, but later became an RADC optical test site. Raymond P. Urtz, a physicist who jointed RADC in 1961 after graduating from Manhattan College, became the leader of a series of pivotal atmospheric turbulence and laser beam propagation experiments conducted at Verona that were jointly funded by ARPA, RADC, and the Air Force Cambridge Research Laboratory, located at Hanscom Air Force Base, Massachusetts.13 Urtz was a competent scientist who liked to be in control. Even-tempered, self-assured, action-oriented, and all business, he was respected as someone who could get things done and deliver when the chips were down. He knew how to work the system. His approach resembled the turtle’s more than the hare’s, and he usually crossed the finish line first. Those who worked for him viewed him as a strong leader who led by example—they never had any doubt about who was in charge. He stood tall in his 5-foot-10 frame. His experience and New York street smarts combined to make him the type of manager who under-promised and over-delivered. Strong-minded with a hefty dose of tenacity—some might even describe him as stern—he took great pride in laboring long and hard in attacking difficult technical problems. Although demanding, he listened well and used the ideas of his scientific team to resolve the most perplexing technical issues. In addition, as a program manager, Urtz paid special attention to ensure prudent spending. He took his responsibility to protect the taxpayers’ money seriously.14 Urtz didn’t give up easily, no matter how tough the task. Accuracy in collecting and analyzing data was the cornerstone of his scientific work ethic. Once he had the information, he didn’t hesitate to make decisions. Steady determination and persistent resolve were his two strongest attributes, and they delivered quantitative and qualitative results. If he had weaknesses, he

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was reluctant to show them. It was the combination of all these sturdy character traits nurtured and refined over the years that added up to his consistently high level of performance that eventually elevated him to the top leadership position at Rome. In summer 1997, the new Air Force Research Laboratory (AFRL) commander, Major General Richard R. Paul, chose Urtz to become AFRL’s first Director of the Information Directorate at Rome. Urtz was extremely effective in managing people. He had a knack for matching the right person to a job. He and his team of “Romans” were truly scientific pioneers in the mid- and late 1960s. They were ahead of the pack— including researchers in university astronomy departments—conducting a variety of laboratory and real-time field experiments demonstrating the effects of atmospheric turbulence on laser beams propagated horizontally through the atmosphere a few feet above the ground. One of the prime reasons lasers were used as a light source in those experiments was because a laser displays a uniform or coherent wavefront, sometimes referred to as a flat wavefront or plane wave (like the smooth surface of a table) when undisturbed by atmospheric turbulence. That meant all of the photons (packets of light) along the laser wavefront are precisely “in step” or in perfect alignment—no photon ahead or behind its neighboring photons to its left and right. It is these in-step photons packed tightly in the wavefront that determine the quality and intensity of the beam.15 Unlike laser light, which is directed in one very specific direction, ordinary light waves, such as those given off by a light bulb, have many different frequencies and travel in all directions (360 degrees). Scientists knew exactly what an undisturbed coherent laser beam wavefront (consisting of only a single frequency) should look like—when focused ideally, the laser produced a near-diffraction-limited (almost theoretically perfect) image of a single point. By comparing a known uniform wavefront with a wavefront transmitted through the atmosphere, one could measure the degree of distortion the beam suffered as a result of atmospheric turbulence.16 At the broadest level, the purpose of the experiments at Verona was to better understand how random atmospheric turbulence affected laser propagation. That work involved propagating a laser through the atmosphere and collecting turbulence data to determine what degree the composition of the atmosphere—temperature, wind, and humidity—threw the uniform wavefront of a laser beam out of alignment. This phenomenon was known Early Days

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as phase shift and accounted for distortions (tip and tilt in X and Y directions) as well as higher-order aberrations (such as defocus, coma, and astigmatism errors) in the beam. It is the same phenomenon that causes starlight to twinkle and can produce a degraded or blurred image in a telescope. A variety of low-power lasers (5 microwatts to 25 watts) were used for these experiments, including helium neon, argon ion, and carbon dioxide.17 Urtz, who worked for the Space Surveillance and Instrumentation Branch of RADC’s Surveillance Division, led the Verona work efforts and served as the program manager. He and his colleagues explored numerous experimental approaches to collect and analyze data that would define atmospheric turbulence. A significant portion of the data collection consisted of remote probing of the atmosphere using micro sensors to determine micro fluctuations in temperature. Micro thermal probes mounted at various locations around the Verona test site measured temperature fluctuations in the atmosphere with thin-diameter wires to determine the magnitude of turbulence in different regions of the atmosphere. Balloon-borne radiosondes rising to altitudes of 100,000 feet collected data on temperature, wind speeds and directions, and humidity. A variety of other instruments were utilized, including acoustic sounders, turbulence profile sensors, and turbulence meters. Acoustic sounders were basically acoustic radars that emitted sound pulses that were reflected by temperature gradients in the air. By measuring and analyzing returned signals, Urtz and his team were able to determine the strength and height of turbulence levels. Turbulence meters were capable of measuring optical turbulence at ground levels.18 Urtz recalled using a series of mirrors (mounted on a concrete pier for stability) to direct a laser beam parallel to the ground and send it to a shearing interferometer located several hundred meters away in a laser propagation test facility (located in a tower) that provided a laboratory-quality environment in the field. There a Fourier plane shearing interferometer chopped the light wave on and off, creating bands that were used to determine the degree the light wavefront was out of phase. Phase errors were measured in micrometers. As Ray Urtz explained it, “the incoming wavefront is sheared and made to interfere with itself. Interference fringes [bright and dark bands] occur in the area of overlap. The fringe pattern is sensed by a series of small detectors and the wavefront deformation computed by measuring the fringe distortion.” By comparing the distorted wavefront

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to an ideal wavefront, one could calculate how much the wavefront was distorted from a plane wave. Another technique involved measuring the time-averaged modulation transfer function of an optical imaging system observing targets through the atmosphere. Equipment was devised to scan several points across the wavefront to measure distortion.19 Although most of the work at Verona concentrated on defining atmospheric turbulence and its effects on the quality of laser beams, some experiments looked at ways to improve imaging of space objects by methods other than adaptive optics. One of these techniques was called shadow imaging. “The whole idea,” as Urtz described it, “was to put a series of small telescopes in a line on the ground, and when the satellite passed through the path of a star, you could develop a silhouette for that satellite and it was a high-definition silhouette image.” That technique did not tell the viewer what was inside the satellite, but it did show what the outside of the satellite looked like, which would be useful for identification of foreign satellites as part of the Air Force’s space object identification program.20 Collecting the experimental measurements used to build a more accurate and comprehensive database on atmospheric turbulence took several years and used a number of different scientific approaches. Most experiments took place on the ground at the Verona test site, but on several occasions Rome researchers conducted airborne tests. For example, one series of tests from 1967–1968 consisted of flying a B-57 research aircraft belonging to RADC to measure the effects of upper-atmosphere (troposphere) turbulence on light. Attached to the underbelly of the plane was a 1,200-watt tungsten lamp. The atmospherically induced fluctuations in light amplitude were measured as the B-57 approached and passed over the Verona test site. The lamp could be seen 50 miles away.21 Flights took place at night and usually lasted for three or four hours with on average 35 to 40 flyovers of the test site, ranging from 15,000 to 45,000 feet in altitude, to sample turbulence at various levels of the atmosphere. A Nike radar tracked the B-57, with a telescope attached that collected light from the plane. The light was directed to a scintillometer that measured intensity fluctuations (changes in amplitude of the optical wavefront of the light) to determine how much the light beam had been distorted as it traveled from the aircraft to the telescope on the ground. This data helped to determine the intensity of atmospheric fluctuations and how they Early Days

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changed with the seasons, winds, and altitude. Urtz reported, “We’ve found that wind speed and fluctuations seem closely correlated.”22 Although the B-57 succeeded in collecting substantial scientific data, this particular series of experiments unexpectedly caused quite a stir in Rome and the surrounding area. The flyovers took place at night, and many unsuspecting residents found the eerie, bright-blinking lights, slowly moving across the darkened New York sky, unsettling and flat-out scary. A number of people called the Rome police department to report sightings of unidentified flying objects. One eyewitness, Mrs. Lloyd Bumpus, became frightened when driving and seeing a red light in the sky moving closer to her car. Bumpus’s passenger, Mrs. Henry Hilliker, was sure the object was not an airplane. Hilliker described the object as an oval shape that looked like it was rotating. “As it came through the air,” she said, “it was like a paper plate floating, except with a controlled action as if it actually was being steered.” Since the program was unclassified, RADC officials told the public what the Verona tests were all about, but a smiling Ray Urtz remembered later that many people simply did not believe that explanation. They seemed to long for a more mysterious explanation of the unfamiliar “bright-light” phenomenon.23

Laying the Groundwork—Partnering With Itek The work conducted at Verona gathering and analyzing atmospheric turbulence data from the mid-1960s through the early 1970s was an important first stage of research that had to be completed before anyone could start thinking about designing and building hardware for an adaptive optics system. Precise quantitative measurements of air turbulence formed the foundation. Building an adaptive optics system to make the required corrections to the beam and produce a high-quality image of the object being viewed was the critical next step. Rome played a big part in that step. One of the military’s first major efforts in adaptive optics was a joint research program funded by ARPA (now DARPA) and initiated in March 1973 by RADC and Itek Optical Systems, a private company headquartered in Lexington, Massachusetts, only a few minutes from Hanscom Air Force Base. The program was called

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the Real-Time Atmospheric Compensation system or RTAC, and it was the first Rome research effort dedicated to building a working adaptive optics system. Even before Rome came into the picture, Itek had invested its own money to initiate preliminary concepts on the design of RTAC—conducted by John W. Hardy—under the company’s independent research and development program.24 Formed in September 1957 as a venture capital investment with $600,000 supplied by Laurance Rockefeller, Itek (short for information technology) set out to develop products related to “information acquisition and utilization.” This involved, according to Itek’s first public notice, distributed in October 1957, “handling, storage, retrieval and presentation of information,” a cover phrase that translated to aerial and space reconnaissance in the classified world. Itek’s main business was to develop large surveillance cameras that would fly on reconnaissance satellites and take panoramic pictures of the Soviet Union. Richard Leghorn, who headed Eastman’s Kodak’s European Division, and Theodore “Teddy” Walkowicz, an advisor to Laurance Rockefeller, were the two driving forces responsible for the creation of Itek. Both men carried strong military credentials and had a special interest and ample experience in promoting aerial reconnaissance as a means to monitor the number and status of Soviet nuclear and conventional weapons before a war broke out.25 As an officer in the Army Air Forces in World War II, Leghorn had flown aerial reconnaissance missions taking photos of German defenses in preparation for the Normandy invasion. After the war he collected nuclear effects data by taking aerial photos of atmospheric tests at Bikini Atoll in the Pacific. In the late 1940s he became aware of, but did not yet avidly support, RAND studies advocating satellites as the preferred reconnaissance platforms of the future. He did not believe the technology was mature enough to justify spending large amounts of money for a satellite reconnaissance program. Instead, he thought balloons and high-flying aircraft undetected by Soviet radar were the most realistic and least vulnerable platforms for reconnaissance missions. However, after extended discussions with Merton E. Davies, RAND’s point man and advocate for getting the government to sponsor a satellite development program, Leghorn changed his mind. He became convinced that satellite reconnaissance was the best way to acquire intelligence on the Soviet military capabilities and accurate targeting prior to the start of hostilities. Early Days

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This new approach made sense since the closed society of the Soviet Union made it more difficult to collect human intelligence.26 Air Force Colonel Bernard A. Schriever also influenced Leghorn’s change of heart. Schriever, a staunch supporter of the idea that science and technology would transform military systems, went on to lead the country’s intercontinental ballistic missile program when he took charge of WDD in 1954. WDD’s sole mission was to develop the boosters that would launch American ICBMs (intercontinental ballistic missiles). But the Air Force had a strong secondary interest in WDD. It recognized that if powerful enough boosters could be built to lift ICBMs, then those boosters could also launch satellites into orbit. This dual interest in satellites and boosters was the main reason why the WL-117L satellite program shifted from Wright-Patterson Air Force Base to WWD in fall 1955. The move would take over a year to complete.27 Recalled to active duty in 1951, Leghorn served as an Air Force intelligence officer at the Pentagon. His job as an Air Force Reserve colonel was to assess the various reconnaissance options available to the United States. In 1953 he issued his findings as part of an Intelligence and Reconnaissance Development Planning Objective prepared for Colonel Schriever. Leghorn concluded that a combination of actions—high-altitude balloons, highaltitude reconnaissance aircraft, and eventually low-orbiting earth satellites—would all be needed to meet the nation’s surveillance needs. By the mid-1950s, and especially after the launch of Sputnik in 1957, Leghorn came to believe that less vulnerable satellites should replace the high-altitude (U-2) aerial-reconnaissance aircraft that were keeping an eye on Soviet Union. He believed satellites would provide invaluable intelligence on the extent of Soviet arsenals and serve as detection and monitoring platforms, thereby keeping nuclear arms control agreements honest. (The Soviet Union tested its first atomic bomb in August 1949 and a hydrogen bomb in August 1953.) In addition, in time of war, satellites out of harm’s way in space could provide early warning of an enemy attack, identify missile targets, and furnish timely post-strike bomb damage assessments to help plan future operations. Leghorn became Itek’s first president in 1957, and Walkowicz became one of the company’s first directors. Both men were instrumental in turning the concept of satellite reconnaissance into an operational reality by the end of the 1950s.28

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Two other men played critical supporting roles. Duncan E. MacDonald, who was dean of the Graduate School at Boston University and had overall responsibility for the University’s Physical Research Laboratory (BUPRL— formerly the Boston University Optical Research Laboratory, established in December 1946), helped Leghorn set up Itek, while Dow Smith was in charge of the day-to-day running of BUPRL. MacDonald helped to arrange the sale of BUPRL to Itek, as the Pentagon was having a difficult time justifying financing the laboratory and Boston University’s President Harold C. Casey was not overly enthusiastic about using it to support secret government programs. Consequently, Itek bought BUPRL from the university in January 1958 and hired most of its 100 scientists and engineers. McDonald also moved from Boston University to Itek to become one of its vice presidents.29 This highly qualified pool of workers formed the core of Itek’s expertise in optics and electronics. To supplement this initial workforce, Itek began recruiting individuals from private industry. By the end of 1958 the company employed 500 people. Very quickly it acquired a number of lucrative contracts with the CIA and other government agencies. After only one year in business, Itek sales reached $3.5 million, a large sum of money for those days. Within security circles, Itek would become known as the premier manufacturer of high-resolution reconnaissance cameras and other optical equipment supporting government defense projects. It was the scientific leader for the CIA’s (then highly classified) Project CORONA, America’s first photographic reconnaissance satellite program. The Air Force’s role in CORONA—carried out by the Ballistic Missile Division in Los Angeles (formerly the Western Development Division)—was to develop and use its Thor and Atlas missiles to boost the reconnaissance satellites into orbit. Controlling satellites in orbit, recovering payloads, and conducting their own experiments were other Air Force responsibilities. To deflect unwanted publicity and questions that might compromise the classified nature of CORONA, the Air Force referred to its satellite launches as being part of its Discoverer program to conduct an assortment of biomedical and other scientific experiments in space.30 CORONA got off to a shaky start. It took fourteen launches before the first successful midair recovery of a film capsule from a reconnaissance satellite—made by a JC-119 aircraft at 8,500 feet near Hawaii on 19 August Early Days

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1960. (Discoverer 1, launched in February 1959, was the first WS-117L satellite placed in orbit that was now part of the CORONA program.) But that first satellite spool of film ejected by Discoverer 14 was well worth the wait. The 3,000-foot, 20-pound spool produced more photos of the Soviet Union (covering over 1.5 million square miles of territory) than the twenty-four U-2 flights over the Soviet Union from 1956 to 1960 and provided a wealth of intelligence. One high official reported that the photos collected “literally bowled over the intelligence community.” The CIA reported that this first collection of space photographs identified “64 Soviet airfields and 26 new surface-to-air missile (SAM) sites.” Here was solid proof of the real value of satellites functioning as reconnaissance platforms. In the short run, this film from space filled the big intelligence void that had developed after Eisenhower shut down aerial reconnaissance flights over the Soviet Union in May 1960. But more importantly over the long run, it defined the start of this nation’s era of satellite reconnaissance.31 Part of the reason DARPA selected Rome to manage Itek’s work was the earlier series of successful atmospheric turbulence and low-power laser propagation experiments conducted by Rome scientists at the Verona site over the past several years. They had earned a solid reputation for doing excellent work. DARPA recognized they were the logical choice to develop a workable adaptive optics system.32 DARPA had been concerned all along about coming up with better techniques for obtaining high-resolution images of Soviet satellites and foreign reentry vehicles. Conventional image processing using groundbased telescopes and cameras was ineffective due to atmospheric turbulence. DARPA was looking for innovative technology that would reduce the effects of atmospheric turbulence and produce better images of Soviet satellites. The more detailed the image of a satellite, the better chance intelligence analysts had to deduce what was inside it and what its mission was. For example, a detailed image might reveal optical equipment such as sensors aboard a satellite, which would be a strong indicator that the satellite would be capable of surveillance.33 Richard Vyce, Itek’s director of marketing, was aware of this concern and saw it as an opportunity to attract new business and get a jump on industry competitors. Vyce met with DARPA officials in June 1972. Upon returning to Lexington, he sought out John W. Hardy, an extremely

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intelligent electrical engineer at Itek who over the years had earned a standing as a person who “could make things work.”34 Hardy, born in England, was a distinguished-looking gentleman with a neatly trimmed mustache. He had an aristocratic presence that might give the mistaken impression that he would fit in more comfortably running an English manor house than unraveling the mysteries of science in some outof-the-way laboratory in Massachusetts. But the laboratory was where John Hardy made his mark. Along the way he acquired many accolades and a reputation as a competent and methodical individual who was adept at breaking down complex science and engineering problems. He considered himself a practical person and liked to design instruments. Although there is no single person credited as the inventor of adaptive optics, Hardy made major contributions to its development, especially its imaging applications.35 As a child, Hardy had been fascinated by optical and electrical gadgets. Taking apart cameras to find out how they worked and building radio sets and amplifiers were his favorite youthful pastimes. Trained in electrical engineering and specializing in telecommunications, he graduated from London University in 1946. After a two-year stint with the Royal Corps of Signals, he began his professional career as a telecommunications engineer developing new equipment, first for Automatic Telephone and Electric Company and later for British Telecommunications Research. When American companies began recruiting for engineers in Europe, he told his wife, Ethel, “Let’s go to the States and see what it is like; if we don’t like it, we can always come back.” They never returned. Hardy took Westinghouse Electric Corporation’s job offer to work in Baltimore in 1956. He remained there until 1960, when he accepted an engineering position at Itek. He stayed with the company until he retired in 1990.36 After Vyce met with Hardy and explained what DARPA was looking for, Hardy conducted an extensive literature search on atmospheric turbulence. He also checked the methods used to correct for the effects of thermal blooming on a laser, but found those techniques just would not work. After several weeks of looking at various possibilities, he came up with the idea of using a white-light wavefront sensor to measure wavefront gradient across an incoherent light wave made up of many different frequencies. An analog computer would process the wavefront data nearly instantaneously to make corrections to a number of subapertures or sections using Early Days

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a deformable mirror, which would correct for the distortions in the light wave. As Hardy remembered it, “I finished off with the design of a system, which measured wavefront slope independently over a large number of subapertures, and this was processed analogically coupled into a deformable mirror.” He wrote up the details in a technical report titled “Space Object Imaging From The Earth’s Surface,” released in November 1972. Hardy and Vyce then briefed DARPA’s Strategic Technology Office on 3 November to sell the RTAC adaptive optics system. Hardy wrote an RTAC proposal that was formalized into his technical report, which was submitted by Itek to DARPA on 30 November 1972. This proposal recommended that Itek build and test an adaptive optics feasibility model.37 DARPA was impressed by Hardy and Vyce’s presentation. They were a formidable team—Hardy took care of the scientific and technical issues, while Vyce promoted Itek’s ability to get the DARPA job done expeditiously at a fair price. Hardy was confident he could design, build, and operate a compensated imaging system that would remove atmospheric distortions.38 Prior to Hardy’s proposal, DARPA, as well as universities and private industry, had been pursuing the idea of restoring blurred images by data processing techniques after a camera had already taken the picture and the image was recorded on film. That traditional post-detection method involved trying to restore the image by scanning and digital processing. That did not work very well, because the image was usually so degraded that no amount of scanning or digital processing with the equipment available at the time could significantly sharpen the image. Hardy argued that the way to improve images was to use an adaptive optics system that would be able to restore or sharpen the images of incoherent light before the image was recorded by a camera. This method consisted of sampling the incoming light to detect the distortions over the wavefront, and changing the settings on the deformable mirror, which in turn would make corrections to the follow-on flow of distorted light reflecting off the deformable mirror. This compensated light could then be sent to a camera to produce a sharp image. Again, the key point was that making corrections to the incoming light would take place before the camera took an image of the object.39 One of the long-term objectives of Itek’s initial contract with ARPA and RADC was to prove that an adaptive optics system could compensate incoherent white light made up of multiple frequencies and produce clear,

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sharp images of satellites. The job ahead would be extremely difficult, and Itek trusted Hardy to lead the RTAC technical effort.40 Although DARPA was receptive to Hardy’s proposal, the agency was aware of the enormity of the problem of atmospheric turbulence and its degrading effect on light transmitted through the air. As far back as 1703, Sir Isaac Newton had recognized that telescopes “cannot be so formed as to take away that confusion of the rays which arise from the tremors of the atmosphere. The only remedy is a most serene and quiet air, such as may perhaps be found on the tops of the highest mountains above the grosser clouds.”41 Two and a half centuries later, an astronomer named Horace W. Babcock, working at the Mount Wilson Observatory in the San Gabriel Mountains near Pasadena, California, wrestled with the same problem. Babcock, considered the first serious modern thinker to propose a solution to the problem using adaptive optics, said that only rarely did telescopes produce sharp images of space objects: “one may consider himself fortunate to experience one hour out of 1,000 of the finest seeing, even at the best locations.” However, when good seeing conditions are available—in the absence of atmospheric turbulence where most of the light converges in a diameter smaller than 1 arcsecond—uncompensated telescopes located on high mountains can produce images 10 times better than the same telescopes at sea level. Unfortunately, the very best seeing conditions occur infrequently even on the highest mountaintops, and the images produced still exhibit significant distortion from atmospheric turbulence.42 Besides Babcock, two distinguished Russian physicists, Andrei N. Kolmogorov in 1941 and V. I. Tatarskii in 1961, had made important early contributions, defining the properties and structure of atmospheric turbulence, which served as the mathematical foundation for others to build on. Building on Kolmogorov’s work, Tatarskii was the first to describe through mathematical modeling the wavefront structure function, which appeared in his book Wave Propagation in a Turbulent Medium, published in 1961. This groundbreaking work was considered the bible of theoretical atmospheric turbulence in the 1960s. Urtz recalled that he and his team geared much of the work at Verona to collect empirical data on atmospheric turbulence to test and refine Tatarskii’s theory.43 Most in the scientific community consider that the concept of adaptive Early Days

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optics started in 1953 when Babcock published his seminal paper on realtime sensing and correction. He proposed correcting light distortions by placing a thin layer of oil over a mirror’s reflective surface. By depositing an electric charge on the oil film, “through electrostatic forces the oil film is distorted according to the desired pattern. Through refraction this results in a controlled deviation of the light rays reflected by the mirror.” In other words, Babcock suggested that his procedure would be an effective technique for reducing the amount of distortion in a light wave and improving imaging of objects. Regrettably, the Carnegie Institute, which supported research at Mount Wilson, did not have the financial resources to turn Babcock’s theory into reality. Although Babcock never built a system, many consider him the father of adaptive optics because he came up with the first concept of adaptive optics. It would take another 20 years before Itek would successfully demonstrate the first real-time adaptive optics system.44 In spite of all the unresolved problems with distorted light, Hardy and Vyce’s compelling presentation to DARPA in November 1972 led to a contract award to Itek in spring 1973. Out of that contract emerged an Itek team led by Hardy that collaborated with a Rome team of scientists and engineers that set out to build a working adaptive optics system. Hardy went to Rome to meet with Urtz, who was responsible for administering the DARPA contract, and to coordinate the details of the entire project. This project was a major departure from the earlier Verona work, which had concentrated on defining and measuring atmospheric turbulence to determine its effects on beam quality. Hardy’s proposed adaptive optics system—for which he received a U.S. patent in December 1975—would be radically different because it would seek to compensate for atmospheric aberrations to produce a good quality image. As Hardy explained: Babcock deserves great credit for recognizing a general solution to the problem of turbulence compensation, but it was realized that the system he proposed was far too limited to be useful for military purposes. The new system had to be capable of correcting images of a rapidly moving satellite under all turbulence conditions—satellite passes only last a few minutes, so it is not possible to wait for better conditions. So Itek used a totally new approach to adaptive optics: the wavefront sensor was a shearing

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interferometer, based on work by James Wyant; the corrector was a deformable monolithic piezoelectric mirror (MPM), and the control system was a parallel processor. The MPM was a completely new concept developed by Julius Feinleib, Steven Lipson, and Peter Cone at Itek.45 James Wyant was one of the most impressive members of the Itek team that made these laboratory experiments work. He credited Ralph Berggren, his colleague at Itek, for the theoretical groundwork, but it was Wyant in 1972 who built the first practical white-light shearing interferometer. This device functioned as a sensor that calculated the shape of the wavefront— that is, how much the light was bent by atmospheric turbulence. That was accomplished by interfering two beams of light from which measurements of wavefront gradient or slope (optical aberrations in the beam) could be made. The slope data were then sent to an analog computer to be processed to determine the shape of the wavefront. Once the shape was determined, then the surface of the deformable mirror could be changed to remove the aberrations from the wavefront.46 The wavefront sensor had to detect and feed that new beam data in the form of electronic signals to the computer at a very high speed if it was to accurately reflect the most current conditions of the laboratory atmosphere. That meant the computer had to continually keep up and send in real time new information to the deformable mirror by way of computer-driven electronics to tell each section of the mirror (that matched its corresponding section of the distorted wavefront that needed to be corrected) exactly how much to change its shape to compensate for distortions in the beam. In essence, the computer converted wavefront sensor signals to compensated signals that changed the settings on the deformable mirror. Each cycle of sampling atmospheric turbulence, measuring distortions in the incoming light as it changed several hundred times a second, and adjusting the shape of the deformable mirror, occurred in milliseconds—thousandths of a second; this was known as a closed-loop system.47 Julius Feinleib at Itek was an independent and innovative thinker who headed a small team that devised the concept and design of the deformable monolithic piezoelectric mirror or MPM built by Itek. These were the first deformable mirrors made, a big step forward that made Itek the leader in Early Days

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Figure 2. Schematic of Itek’s first deformable mirror, used in the Real-Time

Atmospheric Compensation experiment.

the field. The small MPM (2 inches in diameter and 0.05 inches thick) was made of glass. Its actuators were made of a ceramic material called lead zirconate titanate, commonly known as PZT. Embedded in the solid block of piezoelectric material and positioned behind the mirror’s surface were 21 actuators (small pistons), each of which moved in a precise direction over a very short distance (a few micrometers) when stimulated by electrical voltage. The glass mirror was bonded to the block of piezoelectric material, as described in Figure 2.48 When the actuators were subjected to small jolts of electricity, the shape of the mirror surface changed to remove the distortions from the light beam. Hardy stated he wanted to use a sufficient number of actuators “to test the concept without the task’s becoming too complex. So we settled, rather arbitrarily, on 21 actuators.” Attached to the top of the piezoelectric block was a thin sheet of glass, which was optically polished and silvered to form a highly reflective surface. Once the wavefront sensor measured the distortions in the beam, that information was processed, converted to the appropriate electrical control signals, and sent to the mirror to place

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Figure 3. Adaptive optics works by measuring the distortion in a wavefront

(left) and placing the conjugate, or opposite, of that distortion on the surface of a deformable mirror (center), which in turn corrects the distortion, straightening out the wavefront on reflection (right).

the mathematical conjugate or opposite wavefront configuration of the distorted beam onto the mirror surface. Some referred to this technique as “distorting the distortion” or putting eyeglasses on a telescope so it could see better. In short, the deformable mirror transformed a distorted wavefront into a nondistorted wavefront (see figure 3).49 Electrical pulses sent from the reconstructor along a series of thin wires to the actuators allowed them to make precise corrections to the mirror’s surface. Each time a predetermined amount of electrical voltage reached one of the actuators and set up an electrical field, that actuator pushed or pulled against its assigned area of the glass (subaperture), causing it to move slightly (on the order of 10 microns or one hundredth of a millimeter, about oneeighth the diameter of a human hair—not visible to the naked eye). Each of the 21 actuators moved at a different rate and distance, so the glass surface was no longer flat or rigid; the shape changed several hundred times a second. Deformable mirrors were sometimes referred to as rubber mirrors. Once the beam reflected off the surface of the deformed mirror, a camera captured the compensated beam, producing a sharp rather than a blurred image.50 Early Days

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Although one major application of adaptive optics was improved imaging of space objects, scientists were also interested in a second important application, sending a compensated laser beam to intercept a target in the atmosphere or in space. In the latter case, the beam had to exit the telescope and travel through many layers of atmospheric turbulence before reaching its target. As Bob Fugate, the Air Force’s leading authority on adaptive optics, explained it, “When the laser beam leaves the telescope it will be distorted and tilted to exactly match the conjugate of the aberrations induced by the propagation medium [the atmosphere and/or space]. As the wavefront propagates through the aberrating medium, the preset distortion is undone and the beam arrives at the object with a near perfect wavefront.” In either scenario—imaging or laser beam projection—adaptive optics is a complex scientific process that demands a high degree of hardware and software precision to correct for atmospheric turbulence.51 During Itek’s glory days, the company’s main interest was developing adaptive optics systems for imaging, not for engaging space targets. Its monolithic piezoelectric mirrors were not built for high-power laser applications. Those uncooled mirrors could not deliver the stroke—the amplitude or the right amount of physical bending of the deformable mirror—to correct the wavefront of an outgoing laser beam. Nor could they absorb the heat deposited on their surfaces by an outgoing high-energy laser beam.52 Interest in adaptive optics extended beyond military applications into the medical community. Some optical scientists compared the imaging principles of an adaptive optics system to how the human visual system works. The biological makeup of a person’s eye gives it the capacity to adapt to various light conditions in order to obtain the best possible image of whatever it is looking at. Working together, the brain and eye focus on the object viewed. The brain—analogous to a wavefront sensor and high-speed processor—interprets light conditions and determines what corrections the eye should make to produce the best image. Those corrections are made “through biomechanical movement of the lens of the eye. This is both a closed-loop and phase-only correction.” The iris of the eye is critical because it “can open or close in response to light levels, which demonstrates adaptive optics in an intensity control mode. And the muscles around the eye can force a ‘squint’ that as an aperture stop is an effective spatial filter and phase-controlling mechanism.” While the human eye performs all these

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processes naturally and spontaneously, manufacturing an adaptive optics system from scratch was a difficult and challenging scientific endeavor.53 A wavefront sensor, a high-speed processor (reconstructor), and a deformable mirror were the three critical components of any adaptive optics system. All these parts had to work in harmony with one another in real time for the system to perform properly. As John Hardy pointed out, “The main problem in building adaptive optics is the design of the overall system, rather than individual components.” One report described the symbiotic relationship among these key components in more technical language: “The wavefront sensor is an optical instrument that measures the gradient of the distorted wavefront over small regions called subapertures, and the reconstructor is a computer that estimates the phase error at certain points in the aperture by mathematically manipulating the wavefront gradients measured by the wavefront sensor. The computed phase errors are the basis for corrective signals applied to the deformable mirror.” The process of integrating advanced optics and electronics to make all the components to work together as one integrated unit is referred to as electro-optics.54 The Department of Defense was more than willing to invest in adaptive optics research because it offered considerable potential strategic payoffs for the nation. The second half of the twentieth century was tumultuous. No one knew what unpredictable event might erupt and transform the Cold War into a “hot” war. Beginning in the late 1960s and into the 1970s, government adaptive optics research programs—conducted in secret—were in an enviable position for attracting money and qualified military and civilian scientists. That effort extended over the next three decades and led to the systematic advancement of the diverse technologies required to make an adaptive optics system work. The work was critical in the eyes of senior strategic decision-makers, who believed adaptive optics was a promising multidimensional technology that could assist laser beams to perform satellite and ballistic missile defense missions, as well as to obtain high-resolution images of space objects, both natural and manufactured. To turn that lofty strategic vision into reality, Rome Air Development Center and Itek Corporation joined forces as the early leaders in the development of the first adaptive optics systems.

Early Days

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Rome and Itek First Adaptive Optics Systems

As RTAC took off, Urtz went to his boss in 1973 and asked for more people to accommodate his increased workload. He understood the long-term significance of the RTAC work. The more competent people he could assign to this project, the more he believed he could build up Rome’s in-house expertise. Given the green light to hire, Urtz recruited electrical engineer Don Hanson. That came about because of one brainy lieutenant, named Darryl Greenwood, who worked for Urtz. Greenwood was the first to investigate the control servo requirements for an adaptive optical system. He analyzed an adaptive optical system in terms of the rate at which corrections needed to be made in order to stay up with changes in the atmosphere. This rate has become known as the Greenwood frequency. Later, he conducted groundbreaking adaptive optics work using sodium wavelength lasers (0.589 microns) at Lincoln Laboratory.1 Greenwood and Hanson met through their wives, who worked together. Hanson, who had been working on radar electronic counter-countermeasures at Rome since he entered the Air Force as a civil servant in 1968, said

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years later that he suspected Greenwood “whispered in Urtz’s ear” to hire him. Urtz took Greenwood’s advice and brought Hanson onboard, which turned out to be a savvy move. Besides Hanson, Urtz also hired Jim Cusack and Tom Pitts, two highly competent physicists who became indispensable members of Rome’s in-house compensated imaging team.2 Hanson eventually became Urtz’s right-hand man and over the next 10 years proved to be a key contributor to Rome’s tightly knit group of researchers. Working for Urtz gave Hanson invaluable on-the-job training. Along the way he earned his PhD in electrical engineering from Syracuse University.3 A committed and enthusiastic scientist, Hanson had a pleasant personality and quiet self-confidence that suited him well for working with others. He got along with people, but he was not averse to defending an unpopular point of view. He had that All-American manner about him that gave one the feeling he wanted the ball with the score tied and three seconds to go in the game. He was organized and methodical in how he approached day-to-day issues. He didn’t need Stephen Covey to remind him of the importance of setting priorities. He took pride in hitting the bull’s-eye and became impatient with those who continually nicked the outer fringes of the target.4 Hanson was thoughtful and precise in the way he presented answers to questions. He was technically smart and always interested in how things worked. He read widely, poring over technical reports to better understand and master complicated adaptive optics technologies. He achieved a large share of his scientific expertise through his firm work ethic and on-the-job experience that led to him making good decisions. From the start, he was a strong proponent of adaptive optics, and was extremely effective in coordinating projects between DARPA and contractors such as Itek. Like Urtz, Hanson over the years combined his scientific and management talents to build a solid reputation as an up-and-coming leader in the Air Force civilian research community. He rose steadily through the ranks and became the director of AFRL’s Sensors Directorate in August 2000, splitting his time between Wright-Patterson and Rome. In May 2005, Hanson replaced Ray Urtz, who after 44 years of civil service retired from his job as director of the Information Directorate at Rome.5 In March 1973 Rome awarded a contract to Itek to build the Real-Time Atmospheric Compensation system (RTAC)—not a fully operational system but a small-scale model with 21 actuators. Rome scientists worked with Itek

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Figure 4. In Real-Time Atmospheric Compensation, a telescope collects

distorted light that reflects off a deformable mirror to a wavefront sensor, which measures distortions in the beam. Corrections are calculated and sent by a data processor to actuators on the back of the deformable mirror, which reshape the mirror surface by placing the conjugate, or opposite, of the wavefront’s distortion. As follow-on incoming (distorted) light from the telescope strikes the reshaped deformable mirror, the distortion in the mirror cancels out the distortion in the light beam, and the corrected or “compensated” beam is reflected off a beam splitter, which sends the light to an image sensor or camera to produce a sharp image.

personnel to set up the RTAC equipment on a tabletop. It was then tested under laboratory conditions at Itek’s facility in Lexington. As part of the experimental procedures, scientists positioned a soldering device underneath the light path to create temperature and turbulence fluctuations similar to, but not exact duplicates of, those the beam might encounter in the operational world outside the laboratory. However, laboratory testing was a critical first step in the process to develop adaptive optics technologies.6 Rome and Itek

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Photo 4. RTAC testing at Itek. The deformable mirror is located in the black box (upper-right center of photo), and the analog computer is the vertical console at right.

After 9 months of intense work, Hardy’s three-person Itek team successfully demonstrated its laboratory RTAC system late at night a few days before Christmas 1973. They had proved that an adaptive optics system could correct for simulated wavefront distortions in a test laser beam. Hardy had worried that too much voltage to the 21 actuators during the experiment might generate large oscillations that could damage or destroy the mirror. This was a major concern, because the monolithic piezoelectric deformable mirror developed by the Itek team was the only one in existence and could not be easily replaced.7 Years later Hardy wrote, “It was with some trepidation that the 21 feedback loops were closed for the first time. We were elated to find that the compensation system was perfectly stable. When optical distortions were introduced into the beam, the RTAC produced well-corrected images.”

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Photo 5.

John Hardy making adjustments to the first RTAC breadboard at Itek in December 1973.

Characterizing the work as a major breakthrough, he added, “This was the first test of an adaptive optical system using a wavefront sensor, reconstructor, and deformable mirror, similar to those in standard use today.” With the success of RTAC, Hardy was optimistic about the future, believing that advanced adaptive optics systems using large telescopes eventually could obtain compensated images of satellites.8 Don Hanson, who served as the Rome project engineer for RTAC, reported that Itek had done an excellent job. He pointed out that the purpose of the RTAC experiments was not to image an object but to focus the corrected low-power test laser beam on a film to show that distortions had been taken out of the beam. To verify this, Hanson and his team observed Rome and Itek

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what was known as the Airy diffraction pattern, discovered by British astronomer George Biddell Airy (1801–1891): when light is sent through a telescope with a circular aperture and focused, a distortion-free beam will produce an Airy diffraction pattern consisting of a central bright spot of peak intensity (containing about 84 percent of the focused light) surrounded by several concentric dark rings. If there were no adaptive optics, the beam would randomly scatter or dance around rather than produce this sharp pattern.9 RTAC did not image an object (it imaged the focused test laser beam), but it did produce a good quality Airy pattern over an extended period of time, which meant the adaptive optics system was working. In other words, RTAC proved its wavefront sensor and deformable mirror were responding together quickly enough in real time to correct for simulated atmospheric turbulence under laboratory conditions. The excellent Airy pattern allowed one to deduce with a high degree of probability that with the RTAC system turned on, a good image of an object could be attained. However, imaging of objects would be reserved for future projects.10 Because the rate of change of atmospheric conditions in the real world was different from those simulated in the laboratory, the next step for the Rome/Itek team was to test the RTAC system outdoors at the Verona test site. Once transported to Verona and reassembled, RTAC had to undergo some minor changes so it could be integrated with the telescope system there. The marshy fields around the telescope tower at Verona made setup and operation of the precision test equipment more difficult, and the experiments did not start until late spring.11 Don Hanson was in charge of running the field tests. A low-power helium-neon laser was set up and fired at various ranges. Scientists collected atmospheric effects data by passing the beam through a 1-meter telescope mounted in a tower, processed and analyzed the data, made corrections to the deformable mirror, and focused the beam to determine if the Airy pattern revealed that the atmospheric distortions had been removed from the beam. These efforts showed steady progress.12 By the first week of June 1974, RTAC had proved it could compensate for the adverse effects of atmospheric turbulence on a helium neon laser beam transmitted along a horizontal path three feet off the ground over a distance of 300 meters. Hanson recorded the importance of this historic

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breakthrough when he wrote in his project notebook on 4 June 1974, “This is the first known successful predetection compensation [correcting the wavefront before it is recorded on film] of real atmospheric turbulence.” The test took place about 9:00 p.m. RTAC usually worked better at night, when atmospheric turbulence dropped off significantly. Between 6:30 and 10:00 p.m. was generally the optimum time, when solar heating is balanced by radiant cooling from the earth, providing a lull in the turbulence, sometimes called the evening neutral event. On 6 June, Hardy visited the Verona site and described his observations on the operation of RTAC with its laser beam traveling over a distance of more than three football fields. Around 3 p.m. the telescope was aligned with the laser, which was at the 1,000-foot range. The RTAC was set up to use an 11.4-inch diameter section of the 40-inch telescope. The RTAC locked on immediately when the loop was closed, and consistent operation was obtained for several hours. The improvement in resolution appeared very similar to that obtained in the laboratory with localized thermal turbulence. By monitoring the shearing interferometer outputs it was possible to determine the phase shift due to the turbulence which at this time was less than 2 waves peak to valley, which is the maximum capability of the phase corrector.13 More tests followed during the summer, confirming the reliability and credibility of the RTAC system. Rome and Itek scientists were elated. In July, Hardy presented the findings from the RTAC experiments to the Optical Society of America meeting in Boulder, Colorado. Twenty years later, writing in the 1994 special issue of the Journal of the Optical Society of America devoted to adaptive optics, Rett Benedict underscored the enduring legacy of RTAC when he pronounced, “The success of the experiments led to the acceptance of this technique of wave-front compensation, designated phase compensation, which is the one in use today.”14 The results of the RTAC laboratory and field tests marked a turning point for adaptive optics research—the first working prototype of a system to compensate for distortions in a laser beam caused by atmospheric turbulence. As Rome described it, RTAC “became the first practical approach Rome and Itek

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to atmospheric compensation that could be used to enhance astronomical seeing.” RTAC grabbed the attention of a small and determined group of pioneering researchers who sensed they were on the verge of unraveling a number of complicated problems and dramatically altering what they could do to improve beam quality and imaging.15 Two basic themes emerged from the RTAC research at Rome. First, the military—specifically, Rome Air Development Center (teamed with Itek) and DARPA—led the way in adaptive optics research. Rome and Itek far outdistanced other contractor and university groups investigating the problem. Without a doubt, as Hanson pointed out, the Itek team led by John Hardy deserved much of the credit for conceptualizing, designing, and building the wavefront sensor and deformable mirror for the RTAC system, as well as for integrating all the other critical components and making RTAC work.16 None of Rome and Itek’s achievements would have been possible without the support of the Department of Defense. The military mission to acquire a reliable ground-based system for imaging satellites drove adaptive optics research. Mathematician David L. Fried, an influential adaptive optics researcher, wrote, “almost all the work done to establish the field of adaptive optics was funded with military objectives in mind.” This longterm effort demanded a steady flow of money from DARPA and highly skilled personnel from RADC and Itek. The Department of Defense had deep financial pockets lined with taxpayer dollars year after year to fund government and contractor personnel—as well as very expensive hardware—through the Air Force laboratory system. Universities across the country were interested in solving the same problems, but they lacked the financial resources to sustain a program of this magnitude. They were unaware that the government was engaged in an aggressive adaptive optics program because, at that time, the program was classified.17 A second theme was that the Rome work reinforced DARPA’s confidence when its investment of less than $100,000 generated large technical dividends. Hardy described it as extraordinary that the Air Force had gotten such a big return on its investment. He was also amazed that such a major technical accomplishment as RTAC took place in only 9 months. “It was astonishing that thing [RTAC] came so quickly,” Hardy said. “It is one of these things where you think, oh yes, it is obvious, but before you’ve got

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it, it isn’t obvious at all. They did a great job in coming up with this device. It really did everything we wanted.”18 Hanson summed it up best when he remarked after the successful demonstration of RTAC, DARPA said, “this stuff might really work—let’s put some real money into this program.” Those at DARPA, including its director, Dr. Stephen J. Lukasik, were extremely pleased by the breakthrough. Rome had done exactly what DARPA’s charter expected in developing revolutionary technology quickly. For the future, it seemed plausible that adaptive optics could be used with larger telescopes. Overall, the RTAC test results convinced DARPA officials that they had a possible solution to their problem of imaging satellites. Consequently, DARPA embarked on an aggressive and high-risk plan to funnel even more dollars into adaptive optics research and development. Based on its enviable track record, it was no surprise that a large share of this money found its way to Rome to support even larger and more challenging programs over the next 15 years.19

Rome’s First Prototype Adaptive Optics: The Compensated Imaging System There was no shortage of contractors interested in competing and bidding for these challenging new DARPA programs, which represented the next phase of adaptive optics research. Rome, with the help of contractors, planned to build on the knowledge gained from RTAC to develop a more ambitious system that could be used with much bigger telescopes—for example, by greatly increasing the number of actuators on a deformable mirror. This project took shape in 1975 and was called the Compensated Imaging System or CIS.20 Captain Jim Justice, working as a program manager at DARPA, was extremely influential in endorsing the CIS program. He worked closely with Urtz at Rome to make sure DARPA dollars found their way to RADC. They intended that CIS would become an integral component of an operational telescope that could obtain near-diffraction-limited images of earth-orbiting satellites on a routine basis. (A diffraction-limited image is the best possible image the laws of physics will allow. It is not theoretically possible to produce a perfect image.) The plan called for the AMOS (ARPA Midcourse Optical Rome and Itek

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Observatory Station) 1.6-meter telescope on Maui to be equipped with CIS to produce improved images of space objects. This meant imaging satellites. But before this scaled-up system could be built, Rome insisted on preliminary engineering feasibility studies to determine the various scientific techniques and hardware that might be used to build it.21 In 1975 Rome issued separate contracts to a number of companies (Lockheed, Itek, the Optical Sciences Company, Hughes, Avco-Everett, Perkin-Elmer, and others) to obtain input on what approaches they would pursue to develop a more advanced adaptive optics system. One contractor, Hughes Research Laboratory in Malibu, California, thought there was no need to have a wavefront sensor if one tweaked the incoming beam and deformable mirror by using a multidither or trial-and-error technique, moving the mirror until a good image was produced. Another contractor proposed shining a laser beam through different types of crystals to remove wavefront distortions. The competition eventually came down to a horse race between Itek and Perkin-Elmer. On 18 June 1975, Rome awarded $1.125 million to each to develop their compensated imaging proposals. That was phase 1 of the CIS program.22 Itek and Perkin-Elmer presented similar systems, but there were fundamental differences in the types of devices to be used. Perkin-Elmer favored a Hartmann sensor to measure the wavefront. The company also pushed for using a thin-membrane mirror, similar to stretching plastic wrap tightly over the top of a bowl. By placing a metallic coating over the thin membrane and then applying electrical current, scientists could alter the surface area of the mirror to reduce distortions in the beam. One criticism of this approach was that the thin membrane might lack durability over time. Itek stuck with making improvements to the solid monolithic piezoelectric mirror (made of lead zirconate titanate, also referred to as PZT) it used in the RTAC experiments. In addition, Itek favored using Wyant’s white light shearing interferometer instead of a Hartmann wavefront sensor, because the latter had potential alignment problems when separating the beam into a large number of sections in order to measure the amount of distortions across the entire wavefront.23 Halfway through phase 1 of CIS, Itek’s Richard A. Hutchin made a significant contribution by introducing a new interferometer that, with one grating, was simpler to use and more efficient than Wyant’s device and less

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susceptible to misalignment. Hutchin’s invention was an improvement of Wyant’s shearing interferometer, which helped propel Itek ahead of PerkinElmer in the CIS competition. Hutchin had joined Itek in 1972 and earned a reputation as a very bright individual and an extremely capable physicist. Later, he rose to the position of chief scientist with Itek (1978–1979) before going out on his own as an independent consultant in 1980.24 Before making a final decision to award phase 2 of the CIS contract, Rome formed a group of compensated-imaging experts to review contractor proposals. One of the most influential members was mathematician David L. Fried, who was considered the leading theoretician on the compensation of atmospheric turbulence. Others who participated included Darryl Greenwood, who by this time had moved on to work at the Massachusetts Institute of Technology’s Lincoln Laboratory (a federally sponsored center for research and development with special emphasis on the application of technology to national defense), Marvin King from Riverside Research Institute (an independent nonprofit organization performing engineering research in the public interest), and a number of other scientists from within and outside the government. Urtz called and chaired many meetings, affording all the members an opportunity to exchange ideas and give their recommendations.25 Using input from the group along with its own assessment of the final two contractor proposals, Rome on 5 January 1976 announced its selection of Itek, based on its technical expertise, its previous experience in the development of RTAC, and its proposed hardware, as the winner of the CIS contract. The contract was funded out of DARPA Order 2646, with the approval of DARPA’s director, Dr. George H. Heilmeier (1975–1977). David Fried believed “the outstanding fundamental characteristics” of Hutchin’s interferometer “played a major part in making possible the successful completion of the [CIS] adaptive optical system.” DARPA was extremely supportive of this technical effort from the start and was committed to seeing the CIS program to a successful conclusion. Once again, RADC served as the technical and management agent to administer the contract on behalf of DARPA. Hanson served as the first CIS program manager until fall 1978, when he left RADC to work full-time on his PhD. John Vasselli, who had been working on the CIS team, served as the new CIS program director until late spring 1979. At that time, Hanson returned to RADC and reassumed Rome and Itek

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Photo 6. CIS team photo taken in July 1981 at Itek Optical Systems in

Lexington, Massachusetts. Back row, left to right: Paul Mailhot, Itek (CIS program manager); Darryl Greenwood, Lincoln Lab (scientist); Don Hanson, RADC (CIS program manager); John Doyle, Itek (department manager); David Fried (DARPA consultant, the Optical Sciences Company); John Vasselli, RADC (scientist); Earl Holbrooke, Itek (field engineer); Marvin King, Riverside Research Institute (DARPA consultant); Ben McGlamery, Scripps Oceanographic Institute (DARPA consultant); Bill Adamo, Itek (technician). Front row, left to right: Randy Moore, Itek (field engineer); Edward Wallner, Itek (systems engineer); Bill D’Agostino, Itek (engineer); John Hardy, Itek (CIS chief engineer); Rich Hutchin (formerly Hudgin), Itek (scientist); Steve Moody, Itek (technician); Sam Ronkin, Itek (technician).

his role as the CIS program manager, replacing Vasselli. The Itek contract underwent twenty amendments over the next several years. By the time the last amendment was put in place on 17 March 1981, the government had invested over $20 million in CIS.26 DARPA believed CIS would greatly enhance ground-based space surveillance. From 1976 through 1981 Rome and Itek labored to design, develop, test, and deploy the CIS hardware. John Hardy served as Itek’s chief engineer for CIS because of his expertise and experience with the RTAC project. He was responsible for the overall design of the CIS and depended on

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the expertise of two other highly regarded Itek scientists, Hutchin and Edward P. Wallner, who were key members of his design team. Hardy also called upon scientists from other organizations. David Fried and Marvin King, consultants to DARPA, as well as Ben McGlamery from the Scripps Oceanographic Institute in California and Darryl Greenwood of Lincoln Laboratory in Massachusetts offered valuable input. All were considered the top leaders in their fields.27 CIS was a much more complex and larger system with many more problems than RTAC. RTAC fit in a suitcase, but CIS was a huge system mounted on the side of a large telescope. The CIS deformable mirror measured 4 inches in diameter, roughly twice the diameter and four times the area of the RTAC deformable mirror. In addition, CIS had eight times as many actuators as RTAC. As Hardy described it: The CIS used the same basic technology as the RTAC, but expanded to a much larger aperture, with 168 actuators compared to 21 on the RTAC. It was also more than twice as efficient optically, using both transmitted and reflected light from the wavefront sensor gratings. The CIS employed four large end-on photomultiplier tubes, 608 detectors in all. These arrays had to be water-cooled to minimize the thermal noise in photocathodes.28 The logistical plan called for CIS—weighing several thousand pounds— to be installed on the 1.6-meter telescope atop the 10,023-foot summit of Haleakala at AMOS on Maui, Hawaii. Haleakala is a dormant volcano that last erupted in the late 1700s. The name means “house of the sun” in Hawaiian. The clean, dry air at the summit made it an ideal location for viewing space objects. This would allow CIS to demonstrate its space surveillance value in the real world by acquiring images of space targets—specifically, satellites in low-earth orbit. To accomplish this, the CIS would be working in tandem with a large astronomical telescope. Large telescopes were impressive in terms of the amount of light they collected, but they were not as effective in terms of producing high-resolution images by simply using a lens to focus light. As Urtz put it, “Optical phase distortion imposed by atmospheric turbulence causes a loss in resolution capability of from 10 to 30 times a system’s theoretical performance.” This meant the light entering a large telescope was Rome and Itek

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severely distorted. The missing link that would clean up this distorted light to produce clearer images was the development of Itek’s high-performance adaptive optical system, in this case, CIS.29 Another problem was that CIS was not a fixed system attached to a stable base. As Hanson explained, “We had to put this adaptive optical system [CIS] on the back of a telescope that swung around through space and so when you designed it, you had to design for changes in gravity—all that kind of stuff, which made it more complicated.” Also, there was limited space between the telescope and the walls and floor of the facility that housed it, so the CIS hardware could not be too large or it would interfere with the operation of the telescope. Plus, some worried that the CIS was too heavy to be mounted on the 1.6-meter telescope and that it would pose safety issues.30 Even after years of operation, experts still worried about the size, weight, and safety issues associated with the CIS. In 1990, an Air Force review team made up of David Fried, Paul Idell, and Jim Mayo inspected the 1.6-meter telescope. Mayo remarked that he “was amazed that the 1.6-meter telescope could even carry the load on the telescope’s inner gimbal, let alone work as well as it had over the years.” When a 3.67-meter telescope was built in the 1990s at the Maui facility (see chapter 11), to avoid the need for massive loads on the gimbal, a coudé facility—a laboratory room with optical equipment for analyzing light—was built underneath the floor of the telescope to house the unwieldy adaptive optics equipment.31 Originally, fabrication of the full-scale CIS at Itek’s Lexington facility was set for 1978, but technical problems turned out to be tougher than anticipated. For example, Itek had to design and build a 168-actuator monolithic piezoelectric mirror (the next generation of the RTAC mirror), which was more difficult and time-consuming than any deformable mirror it had manufactured up to that point. Delays also drove up the price of the final product from an estimated $7 million to $20 million by the time the CIS was originally scheduled for installation in 1980. However, in July 1981 RADC completed its final review of the CIS Acceptance Test and gave Itek approval to ship the CIS to Maui.32 Given authorization to ship the system, Itek and RADC began making preparations and taking extra care in packing up the CIS so that all its components would arrive safely. Once that was completed, the CIS was flown to Maui and trucked up a steep, winding mountain road to the top of Haleakala.33

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After the CIS arrived at Maui in the summer of 1981 and technicians began installing the system on the telescope, it became apparent that there would be more delays because of the many interface control issues that had to be resolved. For example, how would the camera that would be taking images with the corrective adaptive optics—which had been built by another contractor, Avco Everett—be integrated into the CIS built by Itek? Avco Everett Research Laboratory was the site contractor that operated and maintained all the telescopes at the Maui site and had some very definite ideas and opinions on how the new adaptive optics hardware components should be incorporated into the 1.6-meter telescope. Although there were a large number of complex interface control documents, Itek and Avco eventually came to agreement on all the disputed points so work could proceed.34 By December 1981, technicians had made significant progress installing and testing the CIS. In March 1982, the Rome scientists aimed the telescope at a star. The first image danced around and looked washed out and blurry. But when Don Hanson pushed the button to activate the adaptive optics on the telescope, “closing the loop,” a dramatic change occurred: the image became much brighter, clearer, and more detailed. This was the first time a stellar image was obtained using the CIS in conjunction with a telescope. “This major milestone,” RADC reported, “indicated that the basic design concepts of the CI system were correct.” Hardy concurred, stating, “The CIS gave us the real proof of how impressively adaptive optics can enhance the performance of ground-based telescopes.”35 On a scale of one to ten, with ten being the theoretically best possible image, Hanson rated the images eight, and Hutchin called them “massively better than what they had before.” Although not all of the air turbulence effects had been removed from the starlight, all agreed that this was an exciting achievement, proving for the first time that light traveling through the atmosphere could be corrected using adaptive optics technology. The CIS was also able in the summer of 1982 to take a single blurry image that represented two stars and turn it into two distinct images. In other words, CIS as the world’s first operational adaptive optics system mounted on a large telescope succeeded in producing clear binary images that previously had appeared as a single fuzzy image.36 Although the first CIS images represented a major milestone, that Rome and Itek

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Photo 7. Maui’s 1.6-meter telescope (upper right) with Compensated Imaging

System and its electronic wiring bundle attached underneath (center right).

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accomplishment was classified and could not be made public, even though the Rome/Itek team knew that astronomers in the private sector were pursuing similar approaches trying to produce better images of space objects. As Urtz described it, “We were far ahead of them” in advancing compensated imaging technology. Urtz gave ample credit to ARPA for “their willingness to invest in this broad area.”37 In June 1982, the CIS at Maui produced its first good quality satellite image. For imaging a satellite, the 1.6-meter telescope did not look at starlight to make wavefront corrections. Instead, CIS used sunlight reflected off the satellite. Its wavefront sensor (shearing interferometer) consumed most of that light to calculate the amount of distortion in the light wavefront, leaving only a fraction of light to image the satellite. Theoretically, in the absence of air turbulence, a 1.6-meter telescope should be able to resolve features on a 1-foot object at a distance of 500 miles. But if that same telescope had to collect light that had passed through the atmosphere and been degraded by air turbulence, it would have difficulty resolving 12-foot objects at that range. The purpose of the adaptive optics on the 1.6-meter telescope was to remove the distortions in the light to produce a near-diffraction limited image equivalent to one-foot resolution at a distance of 500 miles.38 The best window of opportunity for viewing a low-earth-orbit satellite passing over Maui was a couple of hours after dusk or before dawn, as sunlight reflected off the satellite as it appeared above the horizon. (This is known as the terminator phase, when a satellite is outside Earth’s shadow and the viewing telescope is still in the dark.) A smaller telescope with a wide field of view initially acquired and tracked the target satellite shortly after it appeared above the horizon. An operator positioned the satellite in the center of the console display to improve the accuracy of the satellite track. The satellite was then aligned in the center of the 1.6-meter telescope field of view for optimum viewing. The telescope collected the reflected sunlight from the satellite, and the CIS adaptive optics made the wavefront corrections to produce a high quality image of the satellite. This work represented another significant turning point; the Rome/Itek team had succeeded in gathering the first images of space objects observed by a phase-compensated telescope. The images proved to scientists that the theory of compensated imaging could be packaged into an electro-optical

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hardware system that, when combined with an operational telescope, could take the distortions out of light waves.39 Although imaging of the first satellite was a major step forward, the CIS was not flawless, and over the next 8 years Rome, Itek, and Avco scientists at Maui continually worked together to refine the system. One concern was to make the package lighter and more compact—for example, to develop an actuator that would require less voltage. The original version needed power supplies of up to 2,000 volts to make corrections to the deformable mirror’s surface. One of the daunting challenges was to develop an actuator that would require less than 2,000 volts to distort the surface of the deformable mirror. Another concern was that the CIS had only 168 subapertures and actuators. Although this was a giant leap forward from RTAC’s 21, a still higher number of subapertures and actuators would translate to finer spatial-scale corrections and produce better quality images. In addition, scientists were always looking at new ways to increase computer-processing speeds.40 One of the original CIS cameras, a short-exposure video system, failed to operate properly and had to be replaced with a new RCA camera. The shearing interferometer also needed to attain faster processing times, and there was discussion on whether to improve the original sensor or switch to a ShackHartmann wavefront sensor, a simpler and more light-efficient device. Part of the problem was that a wavefront sensor consumed most of the collected light, leaving only a small portion to create an image of the object. This made the CIS less effective for viewing dim objects. And less than one percent of the stars visible to the naked eye on a clear night were considered bright enough to serve as a natural guide star to furnish sufficient light to support an adaptive optics system. During the 1980s, the Air Force Weapons Laboratory and Lincoln Laboratory made significant headway in demonstrating Rayleigh and sodium guide stars as a way to obtain high quality images from dim objects in space, as described in chapters 5 and 6.41 Despite its early successes, the primary customers—first Aerospace Defense Command and later Space Command (established on 1 September 1982 and redesignated Air Force Space Command (AFSPC) on 15 November 1985)—were not totally sold on CIS. Strategic Air Command, the Foreign Technology Division at Wright-Patterson Air Force Base, and the Central Intelligence Agency, on the other hand, were impressed. There were some drawbacks. CIS viewing time was restricted to a few hours in any 24-hour

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period. Sometimes bad weather and clouds interfered with obtaining good images. Another problem was that images were captured on tapes that had to be shipped to the customer, creating a delay between the real-time capture of images of satellites and the time they were available for interpretation and analysis.42 On the more positive side, Air Force Systems Command committed to using CIS to test the Miniature Homing Vehicle as part of the nation’s space defense program. CIS also served non-DoD customers. For example, CIS provided NASA with satellite images that were useful for determining inorbit problems, such as satellite stability and damage incurred from space debris. Satellite images furnished useful surveillance and intelligence data to help NASA tell whether a satellite was functioning properly by observing such characteristics as the timely and proper deployment of its solar panels. CIS also provided quality images of the Hubble Space Telescope in 1992.43 Although CIS had both strengths and weaknesses, the DoD and the Air Force heaped high praise on it. In the eyes of the highest leaders in government, CIS represented “a significant advance in Department of Defense capabilities and an outstanding addition to the state of knowledge within the scientific community.” Hardy put it another way, stating that “CIS was huge compared with the RTAC. . . . The big proof concept came with CIS because that really was the groundbreaking thing as far as big telescopes are concerned.”44 The Harold Brown Award, given for significant achievement in research and development in support of the Air Force mission, thrust adaptive optics into the spotlight. Raymond Urtz received this prestigious award in 1982 for his technical competence and outstanding leadership “that produced a scientific breakthrough in the use of deformable [adaptive] optics to overcome the effects of atmospheric distortion on images of space objects.” This recognition was not restricted just to CIS, but extended back to cover Urtz’s work with adaptive optics from November 1973 through November 1981. The award was named for Harold Brown, a strong proponent of military research who served as secretary of the Air Force from 1 October 1965 through 14 February 1969 and secretary of defense from 21 January 1977 through 20 January 1981.45 Although the award recognized 8 years of superb work, including the atmospheric turbulence experiments conducted at Rome’s Advanced Rome and Itek

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Photo 8. Harold Brown (left) presents the Harold Brown Award medallion to

Ray Urtz on 27 October 1982 for his adaptive optics work.

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Optical Test Facility at Verona in the early 1970s and the RTAC program, it paid special attention to the contribution made by CIS. The CIS was important to the DoD for two reasons: First, the adaptive optics technologies developed and proven under the CIS program are critical to other high technology programs in existence throughout DoD. Secondly, the CIS itself will make available to the DoD operational community a source of satellite imagery never before available. The CIS sensor itself and future generation compensated imaging systems will be instrumental in fulfilling critical mission requirements in the area of satellite identification and assessment. The message was that adaptive optics technology had been progressing steadily over the previous 8 years, but that the future offered the promise of even more spectacular technology gains in the imaging of space objects.46 The Harold Brown Award was granted to individuals rather than teams, but Urtz was the first to point out that he was accepting it on behalf of all the people who were responsible for the advances in adaptive optics at Rome. That group included Air Force civil servants and military personnel as well as private contractors and the very small group of university scientists who had been cleared to participate in the program. In Urtz’s mind, there was plenty of credit to go around, and no single person anyone could point to as the discoverer of adaptive optics. Advancing the technology had moved forward relatively briskly thanks to the contributions of a number of people with different talents. However, Raymond Urtz was the principal person who brought this diverse team together, fostered a good work environment, and kept the program on track from the conceptual phase to the production of a quality CIS.47 CIS had performed exceptionally well, considering it was the first adaptive optics system mounted on an operational telescope. The original plan was for it to remain on the telescope for only a few years before being dismantled to make way for more advanced systems, but it continued to produce good images of space objects beyond its anticipated lifetime. During the 1980s it was the largest adaptive optics system in existence, and the telescope to which it was attached became one of the workhorses on Maui. Rome and Itek

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After 2 years, Hardy was still enthusiastic about its steady performance, noting that the system “had resulted in the collection of images of unprecedented quality and detail from a ground-based telescope, giving proof of the feasibility of image compensation on large telescopes.” CIS had gained a reputation as the elder statesman of adaptive optics telescopes by the time it was retired in the late 1990s. Moreover, its success led to the development of the 3.67-meter Advanced Electro-Optical System that went into operation with its adaptive optics in autumn 1998 atop Haleakala.48 In many ways, all current adaptive optics systems can be traced back to the work of the RTAC and CIS programs at Rome. The design of those systems provided great efficiency and flexibility, optimizing performance under varying conditions of atmospheric turbulence. Hardy earned acclaim as a scientific revolutionary because he was the first to apply theoretical principles to create a workable adaptive optics system. Hardy considered the basic design concept he came up with to build these two systems to be his “most important contribution to the development of adaptive optics.”49 In 1983 Urtz moved from the CIS program to work on command-andcontrol technology in the Senior Executive Service at RADC. Over the years Hanson deserved much credit for his technical management abilities in keeping the RTAC/CIS program moving forward. He left CIS in 1987 to become the associate director of the Photonics Laboratory at RADC. In spite of these two key personnel losses, the Rome/Itek team continued to move forward, making CIS a better performing system. In 1984 management and operation of the Maui site transitioned from DARPA to RADC.50 In December 1990, Air Force Systems Command—the organization responsible for funding and managing Air Force research and development programs—made an unpopular decision that many workers at Rome regarded as politically based. As a result of an Air Force laboratory reorganization, compensated imaging work and the management of the Maui site were transferred in May 1991 from Rome to the newly formed Phillips Laboratory at Kirtland Air Force Base in Albuquerque, New Mexico. The rationale for this change was that research and development activities at Maui aligned more logically with the directed-energy laser work and space research and development at Phillips (DoD defined directed energy as those technologies that relate to the production of a beam of concentrated electromagnetic energy or atomic or subatomic particles, i.e., lasers, microwaves, and

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particle beams.). Predictably, that decision was an emotional blow to Rome, given the work its scientists and engineers had done on compensated imaging since the 1960s. Many felt this was a morale buster to the electro-optical workforce at Rome, but in the end, the decision remained in force. Rome was no longer in the adaptive optics business, but the enduring legacy Rome left behind had paved the way in making revolutionary technological contributions to the development of adaptive optics.51 Even during the 1970s and 1980s, Rome was not the only Air Force research and development organization working on adaptive optics. Several hundred miles southwest of Rome, the Air Force Avionics Laboratory’s Reconnaissance Division made its home at Wright-Patterson Air Force Base in Ohio. The division conducted theoretical studies and experiments on the effects of the atmosphere on photo-optical and electro-optical reconnaissance systems. One of the goals of that work was to gain a better understanding of atmospheric turbulence and the effect it had on the large loss of resolution for film-based photographic reconnaissance systems, especially at high altitudes. Numerous aircraft and some balloon-borne experiments at Wright-Patterson measured atmospheric turbulence for different air masses, geographic locations, and atmospheric and meteorological conditions. A large part of that effort involved using RB-47s, RB-57s, and U-2s to collect turbulence data at various altitudes. This work proved that, except for the most severe atmospheric turbulence, the turbulence-induced wavefront error for down-looking imaging was not serious.52 To learn more about turbulence and its effects, the Reconnaissance Division operated the Cloudcroft Electro-Optical Observatory high in the mountains of southern New Mexico. The observatory was involved in active and passive imaging, tracking, and space object identification. In summer 1975 it was taken over by the 405B Laser Communication Program, managed by the Space and Missile Systems Organization in California. Air Force decisions to cut back on AFAL ground-based surveillance programs resulted in less and less work devoted to turbulence measurements. That left Rome as the principal agency for conducting the Air Force’s atmospheric compensation research.53 A number of organizations and individuals deserve credit for the success of adaptive optics; from the late 1960s through the 1980s, Rome and Itek were significant players. Itek, for the most part, did not design mirrors for use in directed-energy weapons, which would have to handle an intense Rome and Itek

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thermal flux load. Mark Ealey, the president of Xinetics Inc. (which manufactures mirrors for the commercial and military markets) and a former employee of Itek, observed that for mirrors used for compensated imaging, “Itek technology was the absolute flagship technology—just no doubt about it.” Demonstrating a “hardware capability” with deformable mirrors was a revolutionary contribution by Itek that had a tremendous influence on the future development of adaptive optics technology.54 During this same period and paralleling the Rome/Itek work, MIT’s Lincoln Laboratory assumed an increasing role in adaptive optics, working on improved laser beam propagation for future weapon systems. While Rome and Itek worked on producing high-resolution images of satellites, Lincoln focused on developing corrections for thermal blooming in high-energy laser beams as they moved through the atmosphere. Hughes Research Laboratory, Pratt & Whitney, and United Technologies Optical Systems were the dominant directed-energy leaders developing cooled mirrors that could accept high-power laser beams. During the 1980s and 1990s, Lincoln shifted more of its attention to testing systems to compensate for the effect of atmospheric turbulence on laser beams.55 Scientists and technologists at Rome Air Development Center and then Rome Laboratory laid the foundation in the late 1960s and the 1970s for the development of adaptive optics technologies, especially in the area of imaging. Rome continued to play a prominent role in the 1980s, but during that time the Air Force Weapons Laboratory won high praise for its work on laser guide stars—an important innovation in adaptive optics, which is the subject of the next chapter.

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Laser Guide Stars

At the same time that Rome researchers were making significant headway with programs such as RTAC and CIS, the Air Force Weapons Laboratory at Kirtland Air Force Base began assuming a more active role in the development of adaptive optics. Although Rome and Kirtland pursued similar programs, there was a fundamental difference in how the command leadership and senior scientists at each site looked at the application of adaptive optics to specific Air Force missions. At Rome, the focus was primarily on imaging objects in space, essentially a surveillance mission to identify friendly or enemy satellites, and to learn more about satellite configuration and specific applications. In contrast, Kirtland sought to use adaptive optics for weapons applications as part of the Air Force’s and the Strategic Defense Initiative Organization’s antisatellite and antiballistic-missile defense missions. That was a tall order, as AFWL first had to perfect a number of technologies using low-power lasers and sophisticated optics at AFWL’s Starfire Optical Range (SOR), located in a remote, off-limits section of Kirtland.1 SOR was a critical part of the military’s adaptive optics work. There, AFWL scientists developed building-block technologies that eventually

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would result in high-power ground-based lasers able to engage and disable enemy satellites and missiles. Weapon applications were not restricted to high-power lasers. For instance, part of an antisatellite mission might use low-power lasers to disrupt a satellite’s sensors or electronic components rather than destroy it.2 Although one of the Air Force’s long-range goals was to be prepared to develop laser weapons to intercept satellites, missiles, and other potential targets, the more immediate job of SOR was to explore and better understand the technology issues associated with finding, tracking, and projecting focused lasers on satellites or other targets. Obtaining clearer images of space objects was a big part of this process. SOR was not in the business of trying to build a laser weapon, but instead concentrated on conducting experiments to improve and perfect those adaptive optics technologies essential for the success of future military imaging and laser weapon systems.3 Part of the reason SOR became involved in compensated laser research was that in the mid-1980s the F-15 Miniature Homing Vehicle program was canceled. The goal of that politically sensitive program had been to have an F-15 fly to an altitude of 60,000 feet and then launch a small missile that would intercept and destroy a satellite overhead. The problem was that success—impacting the satellite—would create a large amount of space debris that could interfere with operation of our own space systems. When the program shut down, it left a technological vacuum in terms of what would be available to replace it. One of the most promising options at the time was the use of laser guide stars, telescopes, and adaptive optics working together to deliver a compensated ground-based laser beam to a satellite target. The Department of Defense authorized SOR to pursue research in this area. Hence, 1987 marked the origin of a ground-based laser technology antisatellite program at SOR funded by the Air Force with the aim of demonstrating the performance and feasibility of those technologies that offered the most promise of a future ground-based laser system.4 The man who would lead the adaptive optics technology effort at SOR was an able physicist and experimentalist named Robert Q. Fugate (the Q stands for Quentin, in honor of Quentin Kelly, an Army buddy of his father). Fugate became one of the undisputed leaders in the nation in the field of adaptive optics. He, more than any other individual, transformed SOR into a world-class adaptive optics research site.5

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Fugate—The Man Bob Fugate’s rise to the top of the adaptive optics world came as no surprise in light of his life growing up in the Midwest. Born in Jenkins, Kentucky, in 1943, he moved with his family to Dayton, Ohio, after the Second World War. He admired and was greatly influenced by his father, Arthur, a high school math teacher who served as a pilot in the Army Air Forces during the war. In Dayton, both his parents worked in the business anchor of the town, the National Cash Register Company, his father on the assembly line and his mother in the payroll department. What Fugate remembered most was that his family was middle class and hard working, but there was no record of a scientific pedigree from previous Fugate generations. He proudly described his parents as “commoners” who instilled a strong sense of self-worth and a powerful work ethic in their only child. Above all, he brought away from his childhood experiences the fundamental principles he applied throughout his entire life—commitment, hard work, persistence, focus, and unwillingness to consider the possibility of failure.6 At an early age Fugate began showing signs of unusual talent that would point him down the scientific road he would travel for the rest of his life. When only 8 years old he developed an interest in amateur radio. With the encouragement of his father, the younger Fugate took and passed the Federal Communication Commission’s novice test to obtain his ham radio license, decoding five words of Morse code per minute. At the age of 13 he purchased an old Unitron telescope at a flea market. When he found it didn’t work, he took the defective telescope apart, cleaned and refurbished the parts, put it back together, and pointed it to the heavens, beginning his fascination with light and images in an unheard of neighborhood in Dayton in the 1950s.7 Throughout his high school years, his interest in science continued to grow. He freely admitted that he and his closest friends were the “nerds and geeks” of their class. That didn’t matter, especially when he was engaged in scientific adventures, including concocting rocket fuel in his mother’s electric skillet for the launch of unpredictable model rockets from an abandoned lot near his home. “It was a scene right out of the movie October Sky,” he recalled, laughing. His curiosity and willingness to try new things led to solid scientific accomplishments that set Bob Fugate apart from his peers. For example, while a high school senior he built from scratch some Laser Guide Stars

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rather elaborate electroluminescence panels. That project won him the Westinghouse Science Talent Search prize and earned him a ride in a Navy plane to Florida, where he spent an unforgettable week on a minesweeper.8 By the time he finished at Belmont High in Dayton, there was no doubt in Fugate’s mind that he would pursue a career in science. Although National Cash Register awarded him a 4-year scholarship to the University of Cincinnati in engineering with the promise of a good job awaiting him after graduation, he turned it down. He wanted to be a physicist, and his heart was set on attending Case Institute of Technology in Cleveland. That decision placed an extra financial burden on his parents, but they supported him completely. While at Case he spent a great deal of his time using the student telescope at the Warner and Swasey Observatory 25 miles east of Cleveland. Across the hall in his dormitory lived Jim Wyant, who later developed a white-light shearing interferometer, a critical component of the CIS program at Rome discussed earlier. Fugate graduated from Case in 1965 with high honors and an undergraduate degree in experimental physics.9 Fugate’s senior thesis at Case, under the direction of Professor Don Schele, focused on measuring sodium chloride at 77 degrees Kelvin. The thesis was turned into an article and published in The Journal of Physics and Chemistry of Solids in 1966. Fugate also won the Dayton C. Miller Prize for the best senior thesis. Those accolades, with a strong recommendation from Schele, earned Fugate a NASA fellowship at Iowa State University working under Professor Clayton Swenson. Swenson, it turned out, had a profound effect on how Fugate tackled difficult physics problems, especially his insistence that his students would build—rather than buy—their experimental equipment.10 Fugate has a definitive presence. His most revealing physical feature is a sense of balance and proportion, the very character traits that govern his thinking. If he were a car, Fugate would be a Ford Taurus, even though today he has chosen an Infiniti G-35 sports coupe the manufacturer describes as “laser red” to power him through what he openly describes as his mid-life crisis. He appears to be in better shape than most men his age and takes pride in not looking like the stereotypical disheveled scientist. He is his own man. He would rather wear jeans to work than to suit up in a coat and tie. Clearly, there is an order and well-thought-out structure to his life both in terms of how he presents himself and how he attacks difficult mental

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Photo 9.

Dr. Robert Q. Fugate played the lead role advancing the Air Force’s adaptive optics program.

problems. Getting organized and sticking to the game plan to get something done are important to him. Fugate’s intense focus applies also to his life outside the scientific community. His wife, Marilyn, will readily attest that when her husband goes into a store he heads straight for the item on the shelf he wants and then leaves. He doesn’t roam the aisles. Even if it is just picking up groceries, Fugate is committed to completing the task at hand in the most efficient way. From his photograph, Robert Fugate looks more like the dean of an Ivy League college in New England than like a front-line scientist getting his hands dirty tinkering with temperamental lasers and optics in the high desert of New Mexico. Few would suspect he is one of the world’s leading authorities working on complex telescopes that are literally changing our image of the universe. And that’s the way he likes it. Fugate gives the appearance of a man who is at complete peace with Laser Guide Stars

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himself, one who exudes quiet confidence and intellectual ability. Initially, he seems friendly and somewhat remote at the same time. It’s almost as though he doesn’t want to waste too much time getting to know you unless he sizes you up as an individual who is serious about accomplishing some worthwhile project that will improve the status quo. Nor is he likely to make you feel overly at ease at first. Rather, as is the case with many prominent scientists deeply immersed in their research, he is more analytical than emotional in his dealings with those outside the circle of his closest and most trusted associates. In short, it takes a little time to get to know Bob Fugate. Unassuming, Fugate does not seek the spotlight. Slick Air Force slogans designed to inspire have little or no effect on his overall persona. Primarily self-motivated, he takes a hands-on approach and invests extraordinarily long hours—often 16 or more at a stretch—pursuing a variety of activities to obtain the best scientific results possible. Delegating more work to others goes against his nature. His inclination is to be totally involved in all aspects of a work effort, to approach it as a perfectionist, and to set the bar high for himself and for others. During the early days his work schedule was so hectic that, when he was able to break away and participate in family activities with his wife, his son, Jeff, and his daughter, Elizabeth, he almost seemed like a mystery guest.11 Fugate has managed to effectively organize and direct a diverse team of scientists and technicians, which started out as a team of three and grew to a 100-person operation involving government civilians and military and contractor personnel. One of his professional strengths has been his consistent ability to attract competent scientists and engineers, get them focused on a project, and keep them there. Besides working well with people, he is articulate. “He knows how to take technology,” as one former associate put it, “and turn it into prose that decision makers can understand and put into context of what is important for the Air Force and is one of the reasons he is so successful. He can translate science into language for a non-scientist. This is incredibly important.”12 In a group of highly qualified people engaged in leading-edge research, egos tend to soar. Fugate has succeeded in keeping those egos in check by establishing and nurturing a strong team. The combination of Fugate’s scientific know-how and his serene but strong and capable leadership style has played a large part in accounting for the advancement and success of the

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Air Force’s complicated and technically challenging adaptive optics program over the last two decades.13 Fugate is also the type of person who can do more with less. If he didn’t receive enough money for a project, rather than complaining about the situation, he would get his staff together to build the equipment he needed, an approach he has practiced since his college days. Colonel Tom Meyer, who ran the directed-energy section of the Strategic Defense Initiative in the late 1980s and early 1990s, observed that Fugate “could do with far less [money] and still produce excellent results.” No matter what the financial obstacles, Fugate had a knack for getting things done.14 In all fields of endeavor, people weigh their contributions differently. Some measure their sense of self-worth by the amount of money they have accumulated. Others seek constant praise and recognition for their performance. But another category of individuals values the long journey of plain hard work to reach scientific accomplishments of lasting importance. Fugate belongs to the last group. And at the start of his journey working for the government there was some rough going. One of the major turning points in his life was his decision to move from Dayton, Ohio, to Albuquerque, New Mexico.

DARPA Explores Options Fugate arrived at the Air Force Weapons Laboratory at Kirtland in a rather roundabout way. Early in his career in the 1970s he had worked at the Avionics Laboratory at Wright-Patterson Air Force Base in Dayton, Ohio. There one of his responsibilities was to investigate Rayleigh scattering of high-energy lasers related to intelligence collection missions. In Rayleigh scattering, focused laser light is reflected in all directions by molecules (nitrogen, oxygen, and aerosols) high in the atmosphere. A portion of that light travels back down to a telescope (backscatter) where it can be separated and analyzed. The phenomenon is named after Lord Rayleigh (1842–1919), born John William Strutt, a British physicist and mathematician who won the Nobel Prize for physics in 1904. Rayleigh’s pioneering work in advancing the theory of backscattered light provided the foundation for developing the laser guide star as an effective technique for measuring atmospheric turbulence by Fugate and others in Laser Guide Stars

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the 1980s. At Wright-Patterson, Fugate essentially did laser detection work to improve threat-warning techniques so pilots would know if a laser was aimed at their eyes or their aircraft. That and other work had given Fugate a strong background in experimental research. While at the Avionics Laboratory, he had collaborated with Captain Ron Grotbeck on several beam control experiments making aerosol measurements on high-energy laser beams.15 In summer 1978, Fugate, still assigned to the Avionics Laboratory, spent several months on temporary duty at Kirtland making off-axis backscatter measurements from a 10.6-micron carbon dioxide laser beam used on the Air Force’s first Airborne Laser Laboratory (ALL) aircraft. He conducted this work behind the ALL hangar at the east end of the Albuquerque International Airport runway, where a high-power beam was propagated downrange to a target 1 kilometer (0.6 miles) away. Part of his research looked at using Rayleigh scattering (viewed from the side of the beam) as a way to remotely sense if an adversary was propagating a high-energy laser through the atmosphere to threaten an aircraft.16 By fall 1978 Fugate was back at Wright-Patterson. Grotbeck, by then a major, had been reassigned from the Avionics Laboratory to the Weapons Laboratory, where he headed the laboratory’s Pulsed Laser Systems Branch, responsible for conducting a series of beam control experiments to support the planned second-generation airborne laser program, or ALL-II. Grotbeck lobbied to get Fugate assigned to help him with the pulsed CO and CO2 beam control test efforts. Meanwhile, Fugate’s job at WrightPatterson had become increasingly consumed with contract management work that entailed more travel and temporary duty assignments. That did not appeal to Fugate the physicist, so in November 1978 he agreed to transfer to Kirtland. It took a year to overcome bureaucratic obstacles in the civilian personnel office before he officially reported to Grotbeck and began working at AFWL on 1 October 1979.17 Grotbeck assigned Fugate to SOR to investigate a number of beam control problems. SOR had performed hundreds of ground tests in the 1970s to validate the performance of the carbon dioxide laser and the associated beam control system that would eventually be installed in the ALL. But once those tests were done and attention turned to flight-testing the ALL, SOR had turned into a virtual ghost town. It was from this inauspicious beginning that Bob Fugate took the first step of a 25-year journey that would transform SOR

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into a first-rate adaptive optics research facility equipped with some of the best telescopes and optical diagnostic equipment in the world.18 For the next 3 years, Fugate spent most of his time upgrading the site and working on pulsed beam control research. The work included a series of experiments propagating a very high repetitive rate copper vapor laser (100 watts) to a downrange rotating target (rotoplane) at a 1-mile target site. One of the main goals was to measure the effects of air turbulence on a visible pulsed short-wavelength copper vapor laser (called the Tag laser) as it traveled in a horizontal path from the SOR to the target. This laser had a shorter wavelength than a potential infrared weapon laser. (Shorter wavelengths have more power but are more affected by the atmosphere.) By 1983, Fugate was heavily engaged in running the Advanced Tag Team Phase I Experiment, which focused on improving data processing equipment and software to convert the turbulence measurements so that they could describe the amount of wavefront distortion in the laser beam. The experimental data helped to better define the fundamental physics of local air turbulence caused by temperature and wind gradients. These atmospheric distortion measurements also provided a knowledge baseline needed to design any future ground-based, short-wavelength laser weapon system.19 Precision and care in the collection of atmospheric measurements in near real time was one of the most challenging parts of this Advanced Tag Team Experiment. Once collected, the data were compared to effects of air turbulence on an infrared laser propagated along the same path as the copper vapor laser, to determine how air turbulence affected performance of different wavelength lasers. Results vastly improved understanding the effects of atmospheric turbulence on laser propagation.20 From 1981 on it became evident that the expertise Fugate gained from his experimental work at SOR would play an important role in supporting new adaptive optics concepts emerging from DARPA-sponsored research. The beam control experiments Fugate oversaw at the revitalized SOR facility would eventually lead to the startup of AFWL’s adaptive optics program. DARPA was the agency that first funded research in 1982 at SOR into the feasibility of using what would be known as a laser guide star to correct for the degrading effects of atmospheric turbulence on light.21 A guide star is a man-made reference source of light (as opposed to a natural star or solar-illuminated satellite) that passes through a path in Laser Guide Stars

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the atmosphere and becomes distorted because of atmospheric turbulence. Those distortions can be measured to provide the data needed to define the distorted shape of the light beam. That information is then used to adjust a deformable mirror to compensate for the distortions. (A control algorithm converts wavefront sensor measurements into deformable mirror actuator commands.) The laser guide star is also referred to as a laser beacon, synthetic beacon, artificial star, and artificial beacon.22 Until the early 1980s, adaptive optics used hardware systems, such as CIS, that relied on passive illumination—collecting light emitted exclusively from the object being imaged. This system was adequate as long as the object was bright enough to provide the luminosity needed to acquire and process the wavefront distortion data with enough light left over to produce a high-resolution image of the object. But the vast majority of heavenly objects viewed by ground telescopes appear as very dimly lit objects. With only a small amount of light available to start with, and most of it consumed by a wavefront sensor, there was insufficient light remaining that could be sent to a camera to produce a sharp image of the object.23 Because of this limitation, DARPA and others began searching for ways to maximize the use of available natural light. From 1978 through 1980, DARPA provided seed money so that Richard Hutchin at Itek and Robert Hunter at Western Research Corporation (later ThermoTrex Corporation) in San Diego could search for a controlled light source independent of the light emitted from the object being viewed. Hutchin had pursued one possibility in 1977, called the ray point-ahead compensation (RPAC) method, which studied the possibility of projecting a single pulsed laser beam into the atmosphere to be focused at some high altitude, resulting in the illumination of a fairly large area. This was one of the first guide star concepts. By observing the return backscatter from the side of the beam, Hutchin hoped to build an atmospheric turbulence profile. Hutchin and Don Hanson conducted RPAC experiments in 1980 at Rome to test this theory, but the tests were unsuccessful because the experimental design turned out to be much more complicated than originally envisioned.24 Much of Hutchin’s and Hunter’s work focused on developing a number of backscatter theories built on mathematical analysis and modeling. At the time, neither of them was able to prove any of their concepts experimentally. Yet both were pioneers who contributed to introducing and conducting the

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preliminary theoretical work on backscattering techniques that would be applied to adaptive optics systems. Their preliminary theoretical work and research efforts led to an artificial Rayleigh guide star system, which would be critical to the development of superior adaptive optics systems.25 Julius Feinleib, Itek’s chief scientist, left in 1978 to form his own company, Adaptive Optics Associates, in Cambridge, Massachusetts. He kept abreast of Hutchin’s preliminary theoretical work on the use of independent light sources. One summer night in 1981 Feinleib was observing a laser beam transmitted through the atmosphere as part of a detection and ranging experiment using one of the telescopes at the Air Force’s Maui Optical Station on Haleakala. As he stared at the laser beam penetrating the dark sky, it occurred to him that it might be possible to use the beam to sample air turbulence in the lower section of the atmosphere—the area closest to the telescope, where the air was most dense and turbulence did the greatest damage to the quality of the beam. Using the backscattered light from a man-made reference star, created by a laser focused to a small point in the sky (active illumination), it might be possible to measure air turbulence levels without having to rely exclusively on the limited amount of natural light available from the star being imaged (passive illumination)—because the light from both sources would degrade at the same rate.26 Feinleib’s approach, known as the “A” or astral point ahead compensation (APAC) method, was different from the approach Hutchin conceived in 1980, then known as the “S” or shearing point ahead compensation (SPAC) method. Feinleib chose to view the laser backscatter directly below where the laser was focused in the sky, while Hutchin’s approach was to propagate a single laser that separated into two beams as it moved through the atmosphere and observe the return backscatter from a side-angle view. As Hutchin described it, the SPAC could be thought of as “a shearing interferometer in the sky” because the beam interfered with itself and split up.27 In fall 1981, Feinleib submitted a proposal for a single pulsed-laser guide star to Rett Benedict at DARPA. Feinleib’s concept favored using a Hartmann wave-front sensor to measure the backscatter instead of a shearing interferometer as proposed earlier by Hutchin. Benedict was very receptive to Feinleib’s proposition because most people did not believe it was possible to compensate for the effects of turbulence in order for a ground-based laser to perform an antisatellite or space object identification mission.28 Laser Guide Stars

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Feinleib was a “bulldog,” according to one observer. He pushed hard to sell his idea to DARPA. Benedict and others at DARPA recognized the artificial laser guide star concept as just the type of outside-the-box thinking that DARPA had always promoted. Benedict later recalled that when Feinleib “came up with the idea, we clamped the lid down on everything and went classified.” The research program was named LODESTAR. It was routine practice to keep a promising technology program classified until a better understanding of its potential, limitations, and military application could be determined. Most importantly, the government wanted to keep breakthrough technology out of the hands of any adversary and not to reveal the direction the U.S. research effort was taking.29 Feinleib’s artificial laser guide star relied on Rayleigh scattering: some of the light from a laser beam, scattered in the atmosphere, would return to the Earth’s surface as backscatter and be captured by a telescope. The returning light would serve as an artificial star, hence the name. If the outgoing laser was pointed in the direction of the viewed object in the sky, the theory went, the Rayleigh-reflected laser light would follow the same path in the atmosphere to the ground as the natural light from a faint distant object in space. (The light going up to create the guide star and the return light traveled the same path but did not interfere with one another because all the light was of the same wavelength. This is known as the principle of optical reciprocity.) By using only the backscattered laser light to measure atmospheric turbulence and compensate for its distortions, researchers could use all of the small amount of natural light given off by the object, sent directly to a deformable mirror and then to a camera, to create the image. If the laser guide star concept worked, then the Air Force would be in a position to acquire better images of space objects and possibly to generate a ground-based compensated laser beam for antimissile and antisatellite missions in the future.30 Before Benedict would authorize DARPA funding for Feinleib’s proposal, he called a meeting of adaptive optics experts, including David Fried, considered one of the top adaptive optics mathematical theoreticians in the country, who at the time was president of the Optical Sciences Company in Placentia, California. Fried, Benedict, Feinleib, Hanson, Fugate, and a few others met in Boston in fall 1981 to discuss the validity of Feinleib’s approach. Opinions were far from unanimous. Fugate later recalled that

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Photo 10.

John William Strutt, 3rd Baron Rayleigh, laid the theoretical groundwork later used to advance the laser guide star concept. Photo courtesy of the American Institute of Physics Emilio Segre Visual Archives.

Fried stood up at the start of the meeting and blurted out in a feverish pitch, “this will never work because you are not measuring enough of the turbulence.”31 Fried was pessimistic for two reasons. First, he questioned how effective the Rayleigh scattering technique would be since the laser guide star only sampled a small portion of the atmosphere at altitudes between 10 and 20 kilometers from the Earth’s surface. What about all the air turbulence, Fried asked, that existed above the guide star spot in the sky and extended all the way up to the object being viewed? Although the air was less dense and air turbulence was not as intense at higher altitudes, the distortion to the light in this upper region could not be ignored.32 The second reason Fried was not convinced that a laser guide star Laser Guide Stars

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Photo 11. David L. Fried, a mathematical theoretician, founder of the Optical

Sciences Company, and long-time technical consultant to the Air Force, contributed immensely to the success of the laser guide star concept.

would work was a phenomenon known as focal anisoplanatism, which creates a difference in measurement between light from the star or other object to be imaged and light from the laser guide star. The problem was that light from an astronomical object travels to a telescope in a different way than light from the closer guide star. Light from the astronomical object travels in parallel fashion—as if a transparent pipeline, with the same diameter as the telescope’s primary mirror, hundreds of miles long, connected the space object to the telescope— and the light is exposed to turbulence all along the path.33 The artificial guide star, on the other hand, has to be created at an altitude of between 10 and 20 kilometers. At higher altitudes, the air is not dense enough to create sufficient Rayleigh backscatter without much more powerful lasers. (It would take about 16 times more laser power to create a

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guide star at 20 kilometers than to create one of the same magnitude at 10 kilometers.) The backscattered light reflects off the guide star, not in the shape of a pipeline but in a cone-shaped pattern with the tip at the guide star and the base at the telescope’s primary mirror.34 With the “cone” of light from the laser guide star fitting inside the “pipeline” of light from the real star (they both have the same base: the telescope mirror), it is clear that the guide star’s light would not sample atmospheric turbulence in all the areas a star would (between the cone and walls of the pipeline and in the area above the focused Rayleigh laser guide star). This is the focal anisoplanatism area, inside which distortion of the light could not be measured or corrected (see Figure 5). Neither, of course, can turbulence be measured in the area between the guide star and the more distant object to be imaged. (Light emitted by another form of guide star—the sodium guide star, discussed later in this chapter and in chapter 12—travels a longer path that encounters more atmospheric turbulence and thus reduces the problem of focal anisoplanatism, but this method is still far from perfect.) This was a major concern to scientists who were trying to take the most precise measurements possible.35 Although Fried was pessimistic, he kept an open mind. He stayed up most of the night after the meeting trying to figure out exactly what effect anisoplanatism would have on the laser guide star’s usefulness for measuring atmospheric turbulence—but he knew he needed more time to conduct a more thorough mathematical analysis. He was willing to accept the possibility that the numbers might just prove him wrong as to its feasibility.36 Fried and mathematician John Belsher, who worked for Fried’s company, spent several months building mathematical equations and models to determine the effects of the nonsampled area outside the Rayleigh conical beam in order to predict theoretically how well a laser guide star would work. By spring of 1982, Fried had changed his mind. He “showed that useful performance could be achieved even with the wave-front-distortion error caused by focal anisoplanatism” and predicted the guide star would work well enough to sample a sufficient amount of the atmospheric turbulence to produce a higher-resolution image.37 In summer 1982, an independent Defense Department advisory group called Jason asked that briefings on the laser guide star concept be presented at a meeting in La Jolla, California, part of Jason’s DARPA-funded summer Laser Guide Stars

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Figure 5.

Light from a distant star follows a cylindrical or parallel path to the telescope, while reflected light from a much closer Rayleigh laser beacon follows a conical path. In the space between the cone and the cylinder, the star’s light encounters atmospheric turbulence but the laser beacon’s light does not. Scientists debated how much the effect of this difference in sampled space, referred to as focal anisoplanatism, would affect the accuracy of the laser beacon. Schematic is not to scale.

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study program. The purpose of the meeting was to discuss the merits and liabilities of proposed laser guide star technologies, which by this time had become a hot topic.38 Jason (organized in 1958 in response to Sputnik) was an elite group of scientists, predominantly from the university world, who advised the military on a wide range of national security matters, including evaluating new and promising technologies. DARPA had funded the Jasons to conduct a 6-week summer study in 1982 to assess the future course of adaptive optics and to offer ideas on new technologies to advance its application to military systems. Since the Jasons held their meetings primarily in the summer and autumn, many thought the name was an acronym for “July, August, September, October, November.”39 But in reality, the name emerged from a discussion between Princeton physicist (later Caltech president) Marvin L. Goldberger and his wife, Mildred. Goldberger was one of the founding members of Jason and was instrumental in getting the Institute of Defense Analyses to agree to administer Jason’s activities.40 When Goldberger showed his wife the letter confirming that IDA would manage the group, she noticed the IDA logo, which consisted of three pillars and reminded her of a Greek temple. She proclaimed, “I guess you are going to be the Jasons!” She associated Jason, the mythical Greek explorer and his band of followers who sailed on the ship Argo to the land of Colchis in search of the Golden Fleece, with her husband and his fellow scientists, who were about to set off on their own high adventure in search of new scientific knowledge that would be as valuable to the DoD as the Golden Fleece was to Jason.41 At the La Jolla meeting, the Jasons—who had a hard-nosed reputation for evaluating the validity of new scientific proposals—reviewed and discussed the Rayleigh guide star approach briefed by Fried. In addition, Fried presented his findings on focal anisoplanatism that showed a low-altitude guide star would work better with a small-aperture telescope because the larger the aperture, the larger the problem of anisoplanatism. Hutchin then briefed the group on the shearing interferometer (SPAC) approach. The Jasons favored the Rayleigh method. Fugate then described the first proposed Rayleigh guide star experiment, which would focus a laser beam low in the atmosphere and pointed at a star. The goal was to collect and analyze Laser Guide Stars

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the guide star’s backscattered light and compare that measurement with light from the star, in order to more accurately determine the validity of Fried’s prediction of errors in measurements from a laser guide star versus a natural star. In the end, the Jasons supported the notion of a DARPAsponsored project to experimentally test the validity of the Rayleigh theory—using Feinleib’s approach and Fried’s mathematical calculations confirming that the focal anisoplanatism was not as big a problem as originally thought.42 The second outcome of the La Jolla meeting was a contribution by Princeton physicist Will Happer, who would play a pivotal role in laser guide star research over the next two decades. Upbeat, affable, and well respected in scientific circles, Happer was an extremely bright and levelheaded person who was not reluctant to speak out on controversial issues that crossed the lines of science and politics. President George H. W. Bush appointed Happer in 1991 as the director of energy research at the Department of Energy in Washington, DC.43 In that position, Happer challenged claims by Al Gore and others about the severity of ozone layer depletion, and argued that the more critical problem was determining precisely how damaging the ultraviolet sunlight passing through the ozone layer was for animal and plant life. To Happer, there was no compelling proof that low levels of ultraviolet light were detrimental to plants and animals. Although Happer was willing to take an unpopular political stand in the interest of sound science, he was rewarded for his efforts by being dismissed from his job five months after the Clinton administration came into office.44 At the Jason meeting in summer 1982, Happer proposed creating a laser beacon in the mesosphere at an altitude of 90–100 kilometers (56–62 miles). In that region of the upper atmosphere existed a layer of atomic sodium that could be probed by a sodium wavelength laser. Happer proposed causing sodium atoms to fluoresce or glow by raising their electrons to an excited state with a laser precisely tuned to the required wavelength (0.589 microns). As the excited atoms relaxed back to their ground state, they would emit photons of the same orange-yellow color emitted by a sodium street light. Because the atoms emit photons in all directions—but predominantly in the direction the laser beam is traveling (forward scatter) and the direction it came from (backscatter), many of the re-emitted photons would return through

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Photo 12. Princeton University physicist Will Happer came up with the sodium guide star concept.

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the atmosphere to the ground-based telescope just as though they had come from a star. This would produce an artificial star at a very high altitude, orders of magnitude stronger than a Rayleigh guide star. Fugate and others at the meeting were shocked but elated by Happer’s proposal because they simply hadn’t heard about the layer of sodium atoms in the mesosphere!45 Happer keyed on the sodium concept once he understood the benefit of getting the laser beacon to a higher altitude. He speculated that a sodium beacon would significantly reduce the focal anisoplanatism error because of its greater distance from the telescope. As Benedict explained it, “focal anisoplanatism error decreases as the altitude of the laser star increases.” That meant a sodium guide star could provide more comprehensive atmospheric turbulence measurements than a Rayleigh guide star, which encountered a higher degree of anisoplanatism. Thus, an adaptive optics system could do a better job compensating distorted light from a sodium guide star than compensating distorted light from a Rayleigh guide star. Sodium scattering would also be resonant rather than reflective, and would thus produce much brighter light than Rayleigh scattering. If equally powerful lasers produced a Rayleigh guide star and a sodium guide star at the same distance from the telescope, the sodium guide star would be 10,000 times brighter. Hence, a sodium beacon is the only practical way to create a guide star at altitudes required for large-aperture telescopes (greater than 3 meters in diameter). The drawback was that it was very difficult to generate a surgically precise laser beam at the sodium wavelength. More than 20 years after the concept was proposed, sodium wavelength lasers for guide stars are still a very active area of research (see chapter 12). On the other hand, any laser wavelength worked for Rayleigh scattering experiments.46 Happer had gained much of his knowledge about sodium and the mesosphere through his own research efforts at Columbia University in New York City. When pressed to explain how he came up with the sodium laser guide star recommendation at the Jason meeting, Happer explained, “It was a combination of things. In my professional work, I worked a lot with alkali atoms and optically pumped alkali atoms where you shine lasers on atoms. I had spent nearly 10 years studying alkali atoms with light.” So Happer’s research experience played a big part in developing the sodium guide star concept, but so did his association with several very talented and

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Figure 6. The sodium laser guide star, while still much closer to Earth than

a natural star, samples more atmospheric turbulence than the lower altitude Rayleigh laser guide star. Schematic is not to scale. Laser Guide Stars

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influential colleagues who enthusiastically shared their knowledge about sodium in the mesosphere.47 One important such individual was Gordon McDonald, a capable and energetic geophysicist who had studied the upper atmosphere extensively. Happer described McDonald as “knowing a lot about the atmosphere, the oceans, and the interior of the Earth.” McDonald encouraged Happer to attend the laser guide star session at the 1982 Jason meeting, which fundamentally changed the way military researchers looked at laser guide stars.48 Another key Happer acquaintance was Fred Roessler, a smart and respected astronomer from the University of Wisconsin who also had spent a great deal of time studying the sodium layer. Happer got to know Roessler during a sabbatical to Munich, Germany, in 1977. Over coffee, Happer recalled, Roessler “would tell me about the sodium layer and how useful it was to astronomy, and learning about the upper atmosphere, and learning about stars, and how hard it was to observe because they really didn’t have lasers in those days.”49 Happer also furthered his education on the sodium layer through the works of Alfred Kastler, who in 1966 won the Nobel Prize in physics for advancing optical pumping techniques for studying resonances in atoms. The sodium layer was discovered in 1929, and Kastler conducted extensive studies in the late 1930s observing the “glow” of the sodium layer caused by the sun shining on it just after sundown. Using a spectrometer, Kastler confirmed that light came down from this region of the atmosphere in a bright yellow line, the sodium line. He also verified there were large numbers of sodium atoms, released by micrometeorites burning up at an altitude of about 100 kilometers and releasing sodium atoms. That was how the sodium layer was formed. It grows or shrinks each year depending on how many micrometeorites burn up in the upper atmosphere as they head toward Earth.50 Happer’s own research and the knowledge he acquired from his peers positioned him at the right time and place to recommend the sodium laser guide star concept to the Jasons in June 1982. Over the next five weeks, he prepared a report on the sodium laser guide star technique: how many photons one would expect to get back from the sodium layer, how long it took for the sodium layer to absorb and re-emit light, and how a sodium laser guide star would work. That report, completed in August, convinced

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some people who had been lukewarm to the recommendation to agree that the sodium laser guide star approach could work. Happer put Gordon McDonald’s name on the report as a coauthor because, as Happer put it, “I wouldn’t have written the report without Gordon recruiting me to the meeting because I wouldn’t have even joined that study.”51 The seminal discussion about the theory and merits of Rayleigh and sodium guide stars at the 1982 Jason summer meeting resulted in a much higher level of optimism about the future of adaptive optics. Logically, the next step was to demonstrate experimentally that Rayleigh and sodium guide star techniques could accurately measure atmospheric turbulence in the real world. As it turned out, Rett Benedict and DARPA would again play the leading role to ensure these projects were sufficiently funded and staffed.

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Fugate’s Rayleigh Guide Star Experiments

The Jasons’ 1982 summer meeting represented a major turning point in the development of adaptive optics. Rett Benedict became convinced that DARPA should fund parallel programs to investigate two different techniques for creating laser guide stars to measure wavefront distortion—the Rayleigh backscattering method and the sodium-layer guide star. Each would cost an initial $100,000, with several million dollars to follow over the next few years.1 The Rayleigh effort was led by Bob Fugate at Sandia Optical Range at Kirtland Air Force Base. At the same time, Charles A. Primmermann and Ronald A. Humphreys from Lincoln Laboratory headed the sodium guide star investigation at White Sands Missile Range in southern New Mexico. Lincoln used a dye laser built by Avco for its experiments. Although both programs began by looking at stationary space objects, their efforts to measure atmospheric turbulence would in the long run be applied to the Air Force’s antisatellite mission.2 Once it had received the Jasons’ recommendations, DARPA, through Rett Benedict, approached Petras Avizonis in July 1982 at the Air Force Weapons Laboratory to get the first Rayleigh backscatter experiment under way. Avizonis, a no-nonsense sort of guy, was the technical advisor to the lab’s advanced radiation technology office and turned out to be very

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supportive of the experiment. He believed the ideal place to carry out this experiment was at the Lab’s Sandia Optical Range and selected Bob Fugate to be in charge.3 The objective of Fugate’s first proof-of-concept experiment at SOR was to test whether the Rayleigh artificial guide star would work in the real world. As discussed earlier, only a tiny percentage of stars are bright enough that a telescope can use their light to measure atmospheric distortion and still have enough light left to record an image—thus the need for artificial guide stars. Researchers knew that at lower altitudes—where the air is denser and most atmospheric turbulence occurs—the backscatter return is stronger than at higher altitudes. They also knew that shorter-wavelength lasers produced more backscattered photons than longer-wavelength lasers.4 The question became, could the Rayleigh backscatter from a laser beam focused at an altitude of 5 kilometers (about 3 miles) be used to accurately measure the extent of distortion (phase errors) induced on the laser wavefront? To confirm that the measurements were of the highest quality, Fugate’s team needed to compare the data from the guide star with an independent reference—light from a real star. (The difference between the wavefronts of the star’s light and the laser’s backscatter, as discussed in chapter 4, is the focal anisoplanatism error—and the theory, which needed to be verified, was that this error would be small enough that the measurements would still be valid.) The narrow laser beam was directed within a few microradians of Polaris, the North Star. The starlight and the laser backscatter light would travel through nearly identical paths from the atmosphere to a telescope. Polaris was chosen because it does not move in the sky more than one degree in a 24-hour cycle, which allowed the experiment to be conducted without a gimbaled telescope. For most tests, Fugate explained, “the beam was focused at a range of 5 kilometers and the sensor was range-gated to accept backscattered light from 4.5 to 5.5 kilometers.” The gating mechanism allowed scientists to pick the exact altitude of the Rayleigh backscatter they wanted to view.5 Fugate and his small team of military, civilian, and contractor personnel began designing and building equipment in fall 1982 and started testing in late spring 1983. Members of the team included lieutenants Bruce R. Boeke and Richard A. Cleis, Raymond E. Ruane and Lawrence M. Wopat from the Weapons Laboratory, and contractors David L. Fried, George A. Ameer,

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Figure 7. Sketch of the laser guide star concept from Bob Fugate’s lab notebook.

Steven L. Browne, Phillip H. Roberts, and Glenn A. Tyler from the Optical Sciences Company. David Fried worked closely with Fugate to design the experiment. It did not involve a highly sophisticated telescope and optical system sitting high on a mountaintop. Instead, Fugate configured the hardware components of the experiment in a garage-like facility on the east side of the hill at SOR. This facility was originally known as the FTT building, the old home of the field test telescope used to support the Airborne Laser Laboratory program in the early 1970s.6 On the floor of the SOR facility were a laser device and a large table where the optical equipment was mounted. The walls in the corner section of the high bay of the building were hinged, allowing them to fold back, exposing the laboratory to the open air and providing a limited view of the sky. Positioned just outside the large doors was a 60-centimeter (23.6-inch) tracking mirror that served as a beam director. This flat mirror projected a laser beam (10 centimeters or about 4 inches in diameter) into the sky, Fugate’s Rayleigh Guide Star Experiments

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focused the beam on a small spot at an altitude of about 5 kilometers to create an artificial guide star, and collected the light it returned to Earth. To create the Rayleigh guide star—1,000 times brighter than Polaris— Fugate used a commercially available pulsed frequency-double Nd:YAG (neodymium-yttrium aluminum garnet) short-wavelength (0.532 microns) visible green laser that exhibited the desirable optical and thermal qualities and produced a beam of good quality. Another advantage of using a short-wavelength laser was that it produced more photon backscatter than longer-wavelength lasers. Rett Benedict described Fugate’s experimental configuration as “simple and straightforward” and said it was assembled “on an impressively small budget, cobbled together with very few people.”7 When the pulsed laser was turned on, scientists collected backscattered measurements. When the laser was turned off, they collected natural starlight measurements. The experiment did not use a traditional tracking telescope. Instead, the tracking mirror collected the backscattered light from the laser guide star and the natural starlight. From there, an 18 subaperture Hartmann-type arrangement (Risley prism plate) split the light into 18 separate images, which then reflected off the 40-centimeter (15.7-inch) primary mirror to a secondary mirror installed on the optical table. Fugate explained that, as part of the beam analysis, “two distinct sets of 18 such images were formed, one set being images of the laser guide star and the other being the images of the star [Polaris].” Using a series of prisms, the light was further processed to determine the wavefront tilt in each subaperture. This complicated process involved using one side of a camera to look at the 18 subapertures from the starlight while the other side of the camera simultaneously imaged the 18 subapertures from the laser guide star light. These images appeared as 18 spots on each side of the camera. “So we would grab a frame of images,” as Fugate described it, “and we had 18 spots on each side of the camera and then we measured how those spots moved frame to frame. And that’s what told us what the distortion was.” By comparing all these data, the difference between the distortions in the laser backscattered light and the starlight could be determined.8 Setting up and maintaining the optical components for the experiment was a tedious process. The equipment required constant attention and adjustments in order to obtain the precision measurements desired. Time was a critical issue, because there was a series of experiments that took place

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Photo 13. The first Rayleigh laser guide star experiment, conducted in

summer 1983 at Sandia Optical Range on Kirtland Air Force Base, New Mexico. The laser and optical components were housed inside the facility (lower left), with the exception of the 60-centimeter tracking mirror (lower center), which projected the laser beam in the direction of the star Polaris. Because of the classified nature of laser guide star work in the 1980s, this was the only photo taken during the experiment.

over several months to sample a wide range of atmospheric conditions. The more data were collected over a long period, the more reliable the measurements would be. The goal was to develop a comprehensive database that would demonstrate the similarities in the degree of distortions in starlight and laser light traveling along the same path through the atmosphere.9 Testing at SOR was interrupted many times because rain or clouds interfered with the way the laser propagated through the atmosphere. Even when the skies were clear enough to project a beam, the temperature was sometimes so low that when the doors of the test facility opened, Fugate and his team had to work wearing coats and gloves.10 Fugate’s Rayleigh Guide Star Experiments

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By the end of the summer and into October 1983, Fugate’s team was consistently measuring wavefront phase errors from the Rayleigh scattered light. But the best measurements were obtained in December. Findings showed that distortions of light from the natural star and the guide star closely matched. “These results demonstrate qualitatively,” Fugate proudly pronounced, “that laser guide-star beacons are effective in measuring atmospheric-turbulenceinduced wavefront distortion.” Fugate’s experiment proved for the first time that an artificial laser guide star could work. Moreover, Fried’s prediction about the difference in distortion measurements between starlight and laser backscatter was correct, which contributed to a better understanding of the physics associated with focal anisoplanatism. Fried’s theory on the effects of focal anisoplanatism was expressed in scientific language thus: the “meansquare wavefront error created by using an artificial guide-star at a finite distance rather than a real (infinity distant) star is proportional to the fivethirds power of the telescope aperture.” All of this represented a major turning point, as scientists now could point their telescope in any direction in the sky and establish a laser beacon that would accurately measure atmospheric turbulence. As one scientist described it, the guide star experiment was like taking a picture or X-ray of the atmosphere.11 Although the Rayleigh experiment at SOR was successful in proving the theoretical physics of using a laser guide star to detect and measure atmospheric turbulence—an open-loop experiment—it did not demonstrate the ability to correct for that turbulence. Not until 1989—after acquiring SOR’s 1.5-meter telescope—would Fugate and his Air Force Weapons Laboratory associates successfully demonstrate a closed-loop adaptive optics system that included a wavefront sensor, a high-speed computer processor, and a deformable mirror working together to correct for the wavefront distortions caused by the atmosphere.12 The Rayleigh experiment greatly improved the chances of developing a ground-based laser that could intercept a satellite. During this era, there was keen interest in delivering intense laser beams to targets in space, a concept that followed naturally from laser beam weapons being considered by the Strategic Defense Initiative (SDI) for ballistic missile defense. To make this happen required the development of large-aperture (3- to 4-meter) telescopes working in conjunction with high-performance adaptive optics.13 Precompensating an outgoing laser beam for a weapon is the opposite

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of compensating incoming light for an image. In essence, the adaptive optics system would purposely distort the outgoing laser beam wavefront. As it traveled through the atmosphere, distortions it encountered there would cancel out the distortions induced by the system, thus producing an undistorted beam focused on the satellite. The target satellite itself did not reflect enough light to serve as a beacon to measure distortions induced by atmospheric turbulence. However, a laser guide star could serve as an artificial beacon to make adjustments to the deformable mirror to precompensate a laser beam. A laser guide star would also help solve the point-ahead problem when trying to hit a satellite with a laser beam. Although the speed of light is extraordinarily fast (186,000 miles per second), the operator of a ground-based laser system would still need to lead the satellite slightly, much like a duck hunter must aim in front of a duck so that buckshot arrives at the moving target at precisely the right time. For the laser to be successful, a telescope would first have to acquire and track the satellite.14 The telescope would then point the laser slightly ahead of the satellite (approximately 50 microradians) so the laser could hit the satellite. A satellite orbiting at a range of 1,000 kilometers would travel about 50 meters (just over half a football field) from the time reflected sunlight traveled from the satellite to the telescope and the laser beam made the return trip to the satellite. To hit the target, it was essential to be able to measure the air turbulence along the point-ahead path from the laser device on the ground to the target satellite. The tracking and laser paths were different and encountered different degrees of air turbulence. After using a laser guide star to collect air turbulence data along the point-ahead path, an adaptive optics system on the ground would correct for the turbulence and send a compensated outgoing laser beam to hit the satellite as it moved across the sky.15 After the Fugate team produced accurate Rayleigh measurements at SOR in 1983, the Lincoln Lab experiment run by Ronald A. Humphreys at White Sands Missile Range succeeded, in early 1985, in projecting its large dye laser (tuned to the sodium wavelength) into the mesospheric sodium layer (see chapter 6). This was the first experiment of a sodium beacon that returned light to the ground in which two apertures less than a meter apart measured wavefront slopes from a star and from the sodium layer. As predicted by Fried’s theory, the higher-altitude sodium beacon was affected significantly less by focal anisoplanatism than the lower-altitude Rayleigh beacon.16 Fugate’s Rayleigh Guide Star Experiments

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Although the sodium beacon offered a more complete picture of air turbulence than the Rayleigh beacon, there were definite tradeoffs. One was that it was difficult to create a laser suitable for exciting mesospheric sodium atoms. As Humphreys explained, “The laser requirements for a sodium beacon are . . . more demanding than for a Rayleigh beacon. For efficient utilization of the sodium atoms, the laser must have a narrow linewidth and be accurately tuned to the resonant wavelength.”17 It was much easier to produce a Rayleigh beacon. Although it did not sample as much atmosphere as the sodium beacon, a Rayleigh beacon could collect enough data on air turbulence where its effects on light were the most damaging. Predictions made using Fried’s theory indicated a Rayleigh beacon would perform well on a 1.5-meter telescope, but that a sodium beacon would be needed for a telescope in the 3- to 4-meter class. In any case, there was no disputing that Fugate’s and Humphreys’s experiments at different locations in New Mexico—using two different techniques for collecting atmospheric turbulence data—made a fundamental contribution to the advancement of adaptive optics.18 In recognition of his 1983 work on laser guide stars, the Air Force Weapons Laboratory awarded Fugate its Giller Award, the highest honor a scientist could receive for scientific contributions to the laboratory. His work, the award citation read, “thrust the Air Force Weapons Laboratory into the forefront of atmospheric physics understanding” and “contributed immeasurably to the technological achievements of the High Energy Laser Program.” The Strategic Defense Initiative Organization also recognized this work as a major technical breakthrough that was essential for the development of high-energy short-wavelength lasers capable of performing future ground-based laser missions.19

Acquiring the 1.5-Meter Telescope Developing a real-time adaptive optics system at SOR was the next step after confirming that a Rayleigh guide star could measure atmospheric turbulence. The computers available in 1983 took several days to process atmospheric turbulence data, but to be effective, an adaptive optics system would need to process data in near real-time. A millisecond or so after measuring

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wavefront distortion, the system had to be able to convert the measurement to electrical signals that would change the surface of the deformable mirror and compensate for the distortion.20 To build a real-time closed-loop system, Fugate first had to acquire a telescope for SOR, which had not used one in the 1983 experiments. Ideally the aperture should be 2 meters (6.6 feet) in diameter. At the time, that was considered large, and Fugate and his team needed to understand how a telescope that size would perform in terms of air turbulence and wavefront distortions. A large-aperture telescope theoretically offered the advantage of collecting enough light to be useful for military applications such as antisatellite missions. For that type of mission, most experts believed a 4-meter (13.1-foot) telescope would be required. With plenty of light to provide the measurements to compensate for wavefront distortions, a larger telescope could place more laser power on target than a smaller telescope could, if beam compensation technologies could be sufficiently advanced. The only problem was that there was no telescope at SOR to conduct experiments.21 Fugate knew he needed a large-aperture telescope capable of tracking low-earth-orbit satellites to complete the next stage of his research. But it would take him 3 years of tough campaigning before a 1.5-meter telescope would become operational at SOR. Initially, Fugate took his case to the influential Pete Avizonis, the number-two person in the Advanced Radiation Technology Office of the Weapons Laboratory. Fugate proposed purchasing a 1.5-meter telescope mounted on a gimbal that could slew and observe any portion of sky. This would be a tremendous improvement over the existing equipment: a 24-inch flat mirror combined with a 16-inch offaxis parabolic mirror (used for the first Rayleigh experiments) that could move only one degree to track the star Polaris with a laser. Fugate got nowhere with the intractable Avizonis, who guarded the Lab’s money with an iron fist. Avizonis understood the scientific merit of a new telescope but said that the Weapons Lab simply did not have the money to pay for a piece of hardware that carried an estimated price tag of $800,000.22 But Fugate did not give up; the telescope was essential. He explored every potential backer. His next plan of attack was a visit in 1985 to the newly created Strategic Defense Initiative Organization (SDIO) in Washington, DC. (The organization had been formed after President Ronald Reagan’s Fugate’s Rayleigh Guide Star Experiments

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speech on the Strategic Defense Initiative on 23 March 1983.) There, Fugate impressed upon Colonel Tom Meyer, who headed SDIO’s directed-energy programs, the urgency of funding a 1.5-meter telescope at SOR. He assured Meyer the telescope would not only be critical for current adaptive optics research but, looking farther into the future, would also be essential for enabling laser beams to efficiently intercept and disable Soviet satellites.23 Fugate found SDIO very receptive to his proposal, but he also learned that Lincoln Laboratory, which also had been lobbying SDIO to fund a new telescope, was a strong competitor. Lincoln argued that it had been performing research in adaptive optics longer than SOR and was more entitled to a new telescope.24 In the end, Lou Marquet at SDIO decided to fund part of the cost of the proposed 1.5-meter telescope at SOR. Fugate suspected that what swayed SDIO’s decision was the Air Force’s commitment to pay for half of the $1 million cost. That was not the only reason that Marquet, who had worked at Lincoln Lab himself for 18 years and retained a close connection with his former employer, chose SOR over Lincoln. As a federal employee, Marquet felt honor bound to support the strongest proposal, and in this case he found Fugate’s application more convincing. SDIO agreed to pay for half of the 1.5-meter telescope’s cost—the other half of the bill was to be paid by the Air Force. Acquisition of the 1.5-meter telescope depended to a large degree on timing and President Reagan’s announced shift in national policy. SDIO gave a big boost to space technology research, and adaptive optics benefited enormously from it. Without SDIO, it was unlikely that the financial resources would have been available to support construction of SOR’s 1.5-meter telescope. Funding the telescope was a hefty obligation for SDIO and the Air Force, but it turned out to be a wise decision.25 Even though Lincoln lost out on its bid to SDIO for a new telescope, SOR and Lincoln Lab ended up working in parallel on a number of different projects involving laser beacons over the next few years. As an example, Lincoln conducted a series of experiments at Maui called Short-Wave Adaptive Optics Techniques, or SWAT, from May 1988 to April 1991. The purpose of these experiments, funded by SDIO, was to use adaptive optics to image stars and to propagate a low-power laser beam to a low-orbiting satellite. SWAT was the follow-on program to Lincoln Lab’s Atmospheric Compensation Experiment or ACE, conducted in the mid-1980s and also

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funded by SDIO. Scientists had attached beacons to aircraft and sounding rockets that served as a light source to provide air turbulence measurements in order to transmit a compensated laser beam to the aircraft and sounding rockets. Fugate noted that SOR and Lincoln scientists built a very productive relationship, usually meeting twice a year to share adaptive optics theory and experiments.26 Although SDIO funded half the cost of the 1.5-meter telescope destined for SOR, Fugate was responsible for determining exactly what size the telescope should be. He and a couple of colleagues from SOR traveled to Pittsburgh in 1985 to meet representatives of the Contraves Corp., which had a reputation for manufacturing optically superior telescopes. At the start, Fugate had set his sights on having a telescope built relatively quickly with a primary mirror about 1/2 meter in diameter. Once the discussions started with the Contraves engineers, Fugate asked whether they could scale up the telescope to 1 meter. After huddling to discuss the question, the engineers came back and replied that they could easily build a 1-meter telescope.27 Sensing he was on a roll, Fugate then asked, “What about a meter and a half?” More Contraves engineers joined the conversation, and they deliberated longer, but their answer was the same: they could do it. Pushing his luck, Fugate next inquired somewhat sheepishly, “How about 2 meters?” But the Contraves engineers immediately balked; they could not go that big. And that is how the size of the 1.5-meter telescope came about. Contraves used a MOMS (Mobile Optical Measurement System) telescope built for NASA as a baseline. The diameter of the MOMS aperture was only 0.75 meter. They would have to double that to reach 1.5 meters.28 By today’s standards, the meeting between Fugate’s small contingent and the Contraves representatives was remarkable considering all of the business and decision-making that occurred in the span of one afternoon. Part of the reason for this was that Contraves was a highly customer-oriented company that did not fit the mold created by larger aerospace companies that put high price tags on the products they sold to Department of Defense. As Fugate put it, he was very comfortable with Contraves’s business practices and was confident the Pittsburgh company would give SOR the most bang for the buck. He never regretted that decision. Contraves worked closely with Fugate and his team at every stage of the manufacturing process to ensure that specifications were met and the customer was completely satisfied.29 Fugate’s Rayleigh Guide Star Experiments

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Photo 14. A large crane gently lifts the 1.5-meter telescope off a flatbed truck

and prepares to lower it through the roof of the dome on the side of the hill at Starfire Optical Range at Kirtland Air Force Base, New Mexico.

It took Contraves 2 years to design and build the 1.5-meter telescope. Using a standard Cassegrain design, the new telescope came equipped with a parabolic primary mirror and a hyperbolic secondary mirror. Once it was completed, Contraves crated up the assembled telescope and its base, loaded it on a truck, gingerly transported it cross-country, and delivered it to an eagerly awaiting crew at SOR in May 1987. Driving the telescope from Pittsburgh to New Mexico was an event in itself: if the primary mirror had cracked or broken during shipment, it would have been a major setback. But the telescope arrived in perfect condition. It only took 3 days using a crane and lots of nervous manpower to position the telescope on its reinforced concrete base, which was isolated from the dome enclosure in which it was housed. Any unwanted vibrations on the dome’s floor would be isolated and not affect the telescope. Ash-Dome of Plainfield, Illinois, provided the steel dome that surrounded the telescope.30

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Photo 15. Contraves built the 1.5-meter telescope installed at

Starfire Optical Range.

Fugate and his crew rolled up their sleeves and participated in the construction work, using a large crane and scaffolding to put together the interlocking segments of the telescope dome. The building used for the 1983 Rayleigh experiments was modified by pouring a new concrete pier at one corner of the building to accept the 1.5-meter telescope and dome. A second floor was added to the original high-bay Rayleigh building to house the electronics and adaptive optics system to support the new 1.5-meter telescope. Fugate’s Rayleigh Guide Star Experiments

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When finished, the telescope looked through a narrow slit in the dome (an up-and-over style shutter) that shielded it from the wind. Rotating at an azimuthal (horizontal) rate of 10 degrees per second (fast for an astronomical telescope), the telescope and dome revolved in unison so the telescope could view any section of sky. By November, Fugate’s group had installed, aligned, and integrated all components of the telescope and started to test it.31 Fugate’s persistence showed that individual commitment to a cause could make a huge difference. At the time, Lieutenant Colonel Jim Mayo headed the newly formed Optics and Beam Control Division at the Weapons Lab that oversaw Fugate’s Propagation Phenomenology Branch. Like the SDIO’s Tom Meyer and others, Mayo attested to Fugate’s ability to get things done with a minimum of funding and staff. He had first convinced Mayo of the need to acquire a larger telescope, before presenting his case to a wary Avizonis. Not only did he succeed in winning the Lab’s endorsement, but he was able to acquire outside funding from SDIO to support his new venture. The Lab, perhaps not fully recognizing the potential consequences at the time, was about to embark on a whole new level of atmospheric compensation research, beginning with a series of defining experiments at Starfire Optical Range.32

That Magic Moment: Generation I and II Experiments Fugate and his team were relatively sure that the new 1.5-meter telescope would produce good images of astronomical objects. However, Fugate did not want to leave anything to chance and realized that neither he nor his team had hands-on experience operating such a large telescope. As a precautionary measure and to gain a better understanding of the new telescope, he asked Jim Mayo—who had retired from active duty and was working in the civilian world as head of the Optical Engineering group for Logicon RDA in Albuquerque—to conduct an independent evaluation of the 1.5-meter telescope’s optical performance.33 Mayo conducted his assessment in fall 1987 and reported to Fugate in December that as far as he could determine, the optical performance of the telescope was excellent. For all practical purposes, it seemed to be limited only by normal atmospheric turbulence, the thermal environment around

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Photo 16. The 1.5-meter telescope up and running at Starfire Optical Range

with the Manzano Mountains in the background. Air Force scientists used this telescope, equipped with adaptive optics, to conduct the Gen I and Gen II experiments.

the primary mirror, and to some extent, thermal conditioning in the coudé room beneath the telescope. These limitations were to be expected, and Mayo predicted the telescope would operate as advertised.34 With this reassurance in hand, Fugate and his team charged ahead with their experimental plans. SOR’s first successful series of closed-loop adaptive optics experiments were known as Generation I (Gen I) and Generation II (Gen II). Gen I lasted nearly a year, from June 1989 to May 1990. Gen II took place between February and May 1992. Both demonstrated that the SOR adaptive optics system was able to correct continuously for atmospheric turbulence using the laser guide star technique. During Gen I, the Air Force Weapons Laboratory operated SOR. When the Air Force inactivated the Weapons Lab in 1990, Phillips Laboratory took over operation of SOR. While the name of the organization changed, the mission, the people conducting the work, and the research facilities at SOR remained the same.35 Fugate’s Rayleigh Guide Star Experiments

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Although the official start date of Gen I was June 1989, Fugate’s team had already performed a number of preliminary experiments using the 1.5-meter telescope, to help integrate the telescope and the adaptive optics equipment and to get all the equipment calibrated and performing up to operational standards.36 Part of the reason for carrying out the pre–Gen I experiments was to confirm that Fugate’s team actually could close the loop and correct for atmospheric turbulence in the real-world environment. (Closing the loop for the first time was similar to the approach Alexander Graham Bell used to make his first telephone call to a person in the next room.) In late 1988 the team was able to prove that the adaptive optics system would work without using a laser guide star, a series of more extensive experiments followed to perfect the hardware, prove the theoretical concepts, and establish the reliability of the adaptive optics system using a laser guide star.37 After years of work, the confidence level was high in early 1989 among the SOR scientists, engineers, and technicians who had designed, assembled, and demonstrated the first closed-loop adaptive optics system. Fugate described those days as one of the high points of his career. He recalled, “We were so confident that this was going to work that it was almost a matter of course. It just happened to be that that was the particular time. It was a historical event!”38 Fugate drew a bold rectangular border around the 13 February 1989 entry in his SOR lab notebook to mark an important milestone: at 1 o’clock on that cold, dark morning, he and his team succeeded for the first time in closing the loop using the 1.5-meter SOR telescope in conjunction with an adaptive optics system and continuously correcting for distortions, in real time, using the Rayleigh laser guide star technique. The telescope and its optical hardware were configured just as they would be later for the Gen I experiments.39 One of the main reasons for the Fugate team’s confidence was that they had already proven the concept of the laser guide star technique in 1983 without using a telescope. With the 1.5-meter telescope, Fugate believed, closing the loop would be much easier. Still, a great deal of time and energy went into the preparation for this first round of experiments using the 1.5-meter telescope.40 Fugate’s team used the 1.5-meter telescope situated on a two-story concrete pier at the corner of the same building where the 1983 laser guide star

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experiments had taken place for the Gen I and II experiments. All the beam diagnostic equipment and adaptive optics components were mounted on an optical bench that had been built at SOR and was located in a coudé room on the ground floor directly underneath the telescope. All this equipment was housed in a temperature-controlled environment to avoid heat buildup, which could be damaging to the optics.41 For Gen I, the outgoing laser (built by Oxford Lasers Ltd., an English company) was a 75-watt copper vapor laser operating at 5,000 pulses per second that was passed through the telescope and focused at an altitude of 10 kilometers to form a laser guide star. The higher the pulse rate of the laser, the more samples of atmospheric turbulence could be made per second and the better the equipment could keep up with the changing conditions of the atmosphere. The telescope’s 1.5-meter parabolic primary mirror, covered with aluminum and a protective overcoat of silicon monoxide, collected the backscattered light from the guide star and then used the telescope’s secondary mirror and reimaging optics to focus the light to a beam 10 centimeters in diameter, which could then be diagnosed to measure the amount of wavefront distortion in the beam.42 A Shack-Hartmann wave-front sensor built by Adaptive Optics Asso­ ciates, Cambridge, Massachusetts, measured wave-front distortions in light waves from two bright sources—a natural star named Betelgeuse (Alpha Orionis, a giant red star near the shoulder of Orion) and the laser guide star. The wavefront sensor, using a fast charge-coupled device (similar to what is used in video cameras), measured hundreds of times per second exactly how much distortion or tilt was present in each of the 124 small light samples making up the beam that were distributed over 124 corresponding areas (subapertures) that comprised the surface area of the 1.5-meter telescope’s primary mirror. The wavefront sensor used a series of tiny lenses to focus the light reflected off all the subapertures of the primary mirror. It did that by assigning each sample of light across the wavefront to a single lens (124 lenses to 124 samples of light) whose job it was to focus its portion of light in the center of its assigned section of a “lenslet” detector array consisting of 124 subapertures. If there was no distortion in the light, that is a flat wavefront, each light sample would end up focused directly in the center of its assigned subaperture in the detector array. That was rarely the case as each portion of light was displaced from the center of its target because of distortions caused Fugate’s Rayleigh Guide Star Experiments

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Figure 8. Schematic of Shack-Hartman wavefront sensor concept. The inset

shows one magnified subaperture in the CCD array with the focused spot just left of center. If (as was rarely the case) there was no distortion in the light, the light sample would have been focused exactly in the center.

by atmospheric turbulence. (In the upper left quadrant [b] of the CCD array at the top right in Figure 8, the focused spot—a black dot—is just left of center.) However, the Shack-Hartman wavefront sensor could measure the amount of displacement in each of the 124 light samples plus combine all that information by mathematically calculating (matrix multiplying) how much the total light wavefront was displaced or out-of-phase from its ideal focus.43 To bring the distorted beam wavefront back into phase, a high-speed processor took the distortion measurements, computed the opposite displacement or conjugate for each of the 124 light samples (called subapertures), and sent an electrical signal to each of the corresponding actuators on the back of the deformable mirror, which in turn applied the conjugate on the mirror’s thin glass facesheet. Each of the 124 sections of the wavefront was thus corrected individually. As Fugate put it, “We’re measuring

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Figure 9. An electrical signal applied to each actuator determines the degree

of change to each section of the deformable mirror’s surface.

how much the wavefront is tilted over each little part of the aperture of the telescope. We don’t want these rays to be tilted—we want them all to be perpendicular to the telescope and so we make them perpendicular by moving the actuators on the deformable mirror and that’s what fixes them.” All this took place within milliseconds, and then the process started over.44 Using two separate light sources, a natural star and an artificial guide star, allowed almost simultaneous comparison to see if the distortions in the two light sources closely matched. With data revealing similar distortion measurements from the two, Fugate and his team were confident they could accurately change the surface of the 6-inch (15-centimeter) diameter deformable mirror to compensate.45 Computers had to process the data in near-real time to keep up with the constantly shifting pattern of air turbulence and calculate precisely the right voltage to apply to each of the 149 actuators that changed the shape of the mirror—833 times per second. This was one of the biggest challenges for Gen I. The number 833 was based on 1980s computer processing capabilities. Because of advances in high-speed processors over the years, today’s systems can make changes to a deformable mirror 8,000 times per second.46 “What we wanted to do,” Fugate explained, “was to make measurements at a high enough rate that we could then close a control loop on the deformable mirror and stay up with the changes in the atmosphere so we would have a high enough control bandwidth to correct for turbulence on a continuous basis.” That was accomplished, making Gen I a major milestone in the advancement of laser guide star adaptive optics.47 Fugate’s Rayleigh Guide Star Experiments

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Proof that the SOR adaptive optics system worked as predicted were two sets of clear images Gen I made—one using only the light from Betelgeuse to measure the wavefront distortions and to produce an image, and the other using the laser guide star light to measure distortions and the light from Betelgeuse to produce an image. The scientific yardstick for measuring the performance of the adaptive optics system was known as the Strehl ratio, after Karl Strehl, a professor at the University of Mittweida in Germany, who came up with the idea in 1902. The Strehl ratio measures image resolution by comparing the peak intensity spike of a compensated image to a perfect image. It results in a value between 0 and 1; 1 means there are no distortions in the wavefront. As Fugate explained it, “Strehl ratio is kind of like how bright is the brightest part of the image compared to what it would be if there were no distortions.”48 A Strehl ratio of 0.5 is considered very good when viewing objects through atmospheric turbulence. For the Gen I experiments, on average, the Strehl ratio of the images compensated by the laser guide star was 0.202. For images created using only the natural light from the star Betelgeuse, the number was 0.275. That number was higher because a higher percentage of the atmosphere was sampled along the full path of the natural starlight (from the star to the telescope) than along the shorter guide star corridor in the sky. As more atmospheric turbulence samples were taken, more comprehensive data could be collected to make more precise corrections. The natural starlight and laser guide star light produced satisfactory images and compared well with predictions based on the design of Gen I. Furthermore, the brightest parts of the images were 30 times brighter than images collected when the Gen I adaptive optics was not operating. Those uncompensated images appeared as foggy blurs, with Strehl ratios in the 0.03–0.05 range. But Fugate wanted to achieve higher Strehl ratios.49 The Gen I experiments helped pave the way not only for producing clearer images of distant space bodies, but also for ground-based laser beam propagation. The ability to correct for atmospheric turbulence acquired from the Gen I experiments put weapon designers one step closer to an operational ground-based laser weapon for antisatellite/ballistic missile defense.50 After Gen I reached completion, Fugate and his team turned their attention to Gen II, a second-generation adaptive optics system using more advanced hardware components and a much more proficient optical design.

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Among the critical components that resulted in higher quality images was a more sensitive and accurate Shack-Hartman wavefront sensor that used two separate detector arrays—one for the natural starlight and the other for the guide star light. Another was a new and larger deformable mirror, manufactured by Itek for Rome Air Development Center nearly 7 years earlier, which had 241 actuators compared with Gen I’s 149. The mirror consisted of a thin layer of ultra-low-expansion glass provided by Corning Glass in New York. A new processor and a more powerful copper-vapor laser also boosted performance. The new laser had 5,000 pulses per second and an average power of 180 watts, which generated more backscatter light than the 70-watt laser used in Gen I. With more light provided by the laser guide star, more accurate readings of atmospheric turbulence could be acquired, resulting in a higher level of mathematical precision for changing the surface of the deformable mirror. Gen II also used a high-resolution chargecoupled device (CCD) camera—better than the Gen I CCD—to capture images. CCDs made up of a silicon chip with thousands of light-sensitive pixels have replaced film and offer an instantaneous electronic readout of the image.51 On 18 February 1992, the Gen II adaptive optics system at SOR closed the loop for the first time and acquired a sharp image of Betelgeuse. The Strehl ratio of this first image was 0.55, which surpassed the quality of any image created during Gen I. Gen II provided clear images of a number of other heavenly objects including the star Arcturus and the binary stars Capella and Zeta Orionis. To produce these images, the Gen II system made changes to its deformable mirror 1,664 times per second, twice as fast as Gen I. Improved processing speeds and the use of a more powerful laser made possible extremely fast changes to the deformable mirror, removing distortions in the light wavefront. Brent Ellerbroek, a mathematician on Fugate’s team, played a key role by developing the algorithms needed to make the Gen II system work.52 Image resolution improvement from Gen I to Gen II was enormous. For example, prior to Gen II, images of the two parts of the binary star Zeta Orionis were fuzzy. This changed dramatically with Gen II, which produced images at a reduced size, improving the resolution by a factor of nearly 200. The images captured by Fugate’s team rivaled those of the Hubble Space Telescope, and the adaptive optics system used with the 1.5-meter telescope Fugate’s Rayleigh Guide Star Experiments

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was considered the most advanced system anywhere in the world, surpassing the system Lincoln Lab used in its SWAT experiments on Maui.53 The data produced by Gen II were of much higher quality than those from Gen I. On average, Gen II images revealed a Strehl ratio of 0.513 for a natural star and 0.321 for a laser guide star. The best Strehl reading obtained from a single Gen II experiment was 0.64 using light from a star. For a laser guide star, the top Strehl measurement was 0.48. Gen II, when using a laser guide star, was able to capture images at a resolution nearly a factor of 30 better than those taken by an uncompensated telescope. When the openloop images were compared to the closed-loop images, Fugate wrote, “there is an incredible difference in intensity, the open-loop images being barely visible.” At the time it operated, Gen II was the world’s most technically advanced adaptive optics system. It served to establish a solid technical foundation for the Air Force adaptive optics program and reinforced the notion that adaptive optics was a realistic and reliable technology.54 Gen I and Gen II received generous praise from the upper echelons of the Air Force. On 19 June 1992, Major General Robert R. Rankine Jr., deputy chief of staff for technology at Air Force Systems Command at Andrews Air Force Base in Washington, DC, announced that the Air Force Scientific Advisory Board had selected the Fugate team’s work from over 40 nominations as one of the two top science and technology activities in the Air Force.55 Rankine stated he had been following SOR’s work since the early 1980s and was greatly impressed by the progress made, which he described as world-class research that set the example for the entire Air Force laboratory community. Moreover, Fugate’s advances in adaptive optics had attracted national and international attention, which greatly enhanced the scientific reputation of Phillips Laboratory. “As you know,” the general wrote, “the potential payoff of their work is phenomenal. It is the enabling technology for any ground-based laser application, from high-energy weapons to lowenergy communications and imaging.”56 One of the main benefits derived from Fugate’s program was that it helped promote the scientific reputation of the Air Force. SOR had established an enviable track record as the most advanced military adaptive optics research site in the country. In the process, Fugate emerged as a world leader in adaptive optics.57 Gen I and Gen II work laid the groundwork for compensated imaging

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Photo 17. Starfire Optical Range’s 1.5-meter telescope imaged Saturn and its

moon Titan. Above is an image produced without adaptive optics. Below is a much higher-resolution image, produced with adaptive optics, with Titan clearly visible on the right. Fugate’s Rayleigh Guide Star Experiments

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experiments extending into the 1990s. The 1.5-meter telescope became the workhorse of the SOR site and continued to produce high-resolution images of space objects. As an example, in January 1994 the 1.5-meter telescope delivered excellent images of the Orion nebula, a gaseous region 1,500 light years from Earth in the sword of the constellation Orion. These ionized gases surrounding stars are comet-like in appearance and similar in mass to our sun. The Hubble Space Telescope had captured similar images a year earlier, but the SOR images were taken closer to the star that created the Orion nebula.58 SOR’s 1.5-meter telescope also played a key role in the mid-1990s in experiments that advanced techniques for acquiring, tracking, and imaging low-earth-orbiting satellites. As part of that process, SOR’s 1.0-meter coelostat or beam director projected a low-power laser beam to illuminate a satellite passing overhead. The 1.5-meter telescope received the reflected laser light from the satellite and used it as a reference point to track the spacecraft. Since this was active tracking—as opposed to passive tracking, which relied on sunlight reflected off a satellite and was limited to viewing times just before sunrise and after dusk—a satellite could be tracked 24 hours a day, including when it was in the Earth’s shadow and when daytime background light levels were too high for conventional tracking. The reflected light could also be captured and processed by the 1.5-meter telescope’s adaptive optics system to produce high-resolution images of the satellite that would be useful for surveillance and for determining the satellite’s health. Those images were about 25 times better than uncompensated imagery and near the diffraction limit of the 1.5 meter telescope.59 Over the years the steady performance of the 1.5-meter telescope led to a number of collaborative research opportunities in adaptive optics. One such project, sponsored by the Air Force Office of Scientific Research in spring 1994, involved five astrophysicists—four from the Arcetri Astrophysical Observatory in Florence, Italy, and one from the Max Planck Institute for Astronomy in Heidelberg, Germany—who teamed up with Fugate’s group at SOR to conduct experiments using the 1.5-meter telescope and its adaptive optics system. Dr. Domenico Bonaccini, who headed the Italian contingent, was in charge of designing an adaptive optics system for Italy’s new 3.5-meter Galileo National Telescope, scheduled to be operational in the Canary Islands in 1995, and wanted to learn as much as he could about the system at SOR. Fugate and his associates

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were interested in Italian research that looked at the feasibility of transferring the atmospheric compensation functions normally carried out by the deformable mirror to a telescope’s secondary mirror.60 Although beset with poor weather at SOR during most of their 3-week visit, the Italians managed to take advantage of several good nights of seeing conditions. They were able to use their cryogenically cooled nearinfrared camera, working first without the 1.5-meter telescope’s adaptive optics system and then with it, to produce high-quality images of several star groupings. The compensated images acquired using adaptive optics were a marked improvement over the images obtained without it. In addition, the images of a multiple star system taken with the Italian camera were “the first in these wavelength regions [1.25, 1.62, and 2.2 micron bands] made with the SOR adaptive optics system, and will help us [the Air Force] understand system performance in this part of the spectrum.” Part of that understanding was learning more about how well the adaptive optics system performed when viewing two separated stars over a large field of view as opposed to a single, narrow view. Those experimental data helped to determine how closely theoretical predictions of image quality, based on computer modeling, compared with results obtained experimentally.61 SOR made it a policy to take advantage of every opportunity to participate in cooperative research, including work with the 10-meter Keck telescope at Mauna Kea in Hawaii, the largest telescope in the world, and with the Mount Wilson Observatory in California. Moreover, in a move to promote the sharing of knowledge between the military and civilian astronomers—referred to in Air Force parlance as technology transfer— the National Science Foundation (NSF) established funding for astronomers affiliated with universities to spend several weeks using SOR’s 1.5-meter telescope, supporting civilian astronomical research at military facilities. In 1995, for example, the NSF awarded $400,000 to university astronomers to conduct research at SOR on potential applications of adaptive optics to astronomy. The visiting astronomers came from the University of Texas, the University of Chicago, Columbia University, the University of Arizona, Ohio State University, Georgia State University, and the Rochester Institute of Technology. These cooperative agreements went a long way to establish strong research ties between the Air Force and academic astronomers.62 Fugate’s Rayleigh Guide Star Experiments

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Sandia Optical Range: Anchor of Adaptive Optics Research Sandia Optical Range is a 190-foot topographical bump in the relatively flat landscape adjacent to the foothills of the Manzano Mountains, a few miles south of Albuquerque, New Mexico. Located in an isolated and offlimits area in the southeast corner of Kirtland Air Force Base, SOR consists of a hill formed from a natural outcropping of granite that rises 6,240 feet above sea level. The solid granite provides an ideal foundation for stabilizing the telescopes and other sensitive optical equipment used at the site. The Manzanos to the east serve as a natural backstop to absorb stray laser beams fired from the range. SOR is bordered by the Isleta Indian Reservation to the south; land to its north and west belongs to Kirtland Air Force Base. SOR’s total area, including the hill and surrounding downrange sites, is about 3 square miles.63 SOR has been the Air Force’s premier experimental laser and beam propagation test range since the early 1970s. Construction began in February 1970. It became fully operational in March 1971, making it the first high-power longrange laser propagation and test range in the country. It was originally built to support the Airborne Laser Laboratory (ALL), which sought to develop and install a high-energy laser aboard a modified NKC-135 aircraft in order to determine the feasibility of a laser weapon that could engage tactical air missiles. SOR was the most important facility supporting experiments that proved the physics of high-energy lasers as potential weapons. The result of that work eventually led to the engineering integration of a high-energy laser (Air Force Laser I, which was part of the DoD Tri-Service Laser program) with a first-generation field test telescope (FTT) built by Hughes. The job of the FTT pointing and tracking system was to focus and direct a groundbased laser beam to intercept an aerial target. That work was a critical part of Project DELTA, or Drone Experiment Laser Test and Assessment.64 Project DELTA was one of the first field technology tests conducted at SOR. An Air Force Weapons Laboratory team used a CO2 laser in November 1973 to shoot down a radio-controlled aerial target (drone) as it flew a racetrack pattern between SOR and the nearby Manzano Mountains. This was the first time that a high-energy, ground-based laser had disabled an aerial target; it took place when lasers had only been on the scene for 13 years. It served as a political rallying point to sustain laser research in

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general and helped persuade those unfamiliar with the still-new technology of the urgency to move forward with the airborne laser program.65 DELTA could be seen as the first in a long line of technological advances that led to the ALL shooting down five AIM-9B “Sidewinder” air-to-air missiles over China Lake, California, in May 1983. By 1979, for all practical purposes, the ALL had completed its work at SOR and progressed to flight testing. It was at that point that SOR started to shift from an airborne laser facility to an adaptive optics research site. Fugate was responsible for getting adaptive optics research underway at SOR and shepherding it through its difficult early days. Much like the Airborne Laser Laboratory activities at SOR, adaptive optics advanced in small incremental steps but culminated in major technological breakthroughs, such as the laser guide star proofof-concept in 1983, followed by the closed-loop successes of the Gen I and II experiments from 1988 through 1992.66 SOR had several advantages for adaptive optics work. First was its proximity to the laboratory—first known as the Air Force Weapons Laboratory, then as Phillips Laboratory, and then as the Air Force Research Laboratory—which made working there more cost-effective than moving to an operational site such as Maui. At SOR, scientists had complete control over budget, personnel, administrative issues, hardware, real property, and so on, without having to deal with the distractions of an operational organization. Second, from previous programs, SOR already had in place experienced staff and facilities suited for generating laser beams. Third, and probably most important, SOR did not have the luxury of pristine viewing conditions as did the Maui site, sitting at the top of a high mountain in the middle of the ocean—but that was actually an advantage, because the technologies the team aimed to develop would have to perform effectively in the harsh environments that operating commands would face.67 SOR was one of the main reasons that Fugate and other adaptive optics scientists continued working for the Air Force. Not only was the work extremely challenging, but those employed there believed they were making important contributions to the national defense. “We have a unique set of capabilities and equipment,” Fugate pointed out, “that just doesn’t exist at other places, and opportunities to look into what kind of problems exist and how we can help solve those problems.” In addition, funding for SOR research efforts remained steady. Long-term investment and strong commitment to Fugate’s Rayleigh Guide Star Experiments

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SOR were necessary to support SOR’s one-of-a-kind telescopes, optical diagnostic equipment, laser devices, and highly qualified workforce.68 SOR stood in stark contrast to most university operations, which did not have the budgets to compete with this expensive military operation with its cutting-edge facilities and state-of-the-art equipment. This led to some professional rivalries and jealousies. Universities could not compete at that financial level, but the military scientists could certainly compete with academia in terms of advancing the theory and application of adaptive optics. The intellectual capacity of the Air Force military and civilian workforce took good advantage of the first-rate facilities at its disposal by achieving breakthrough technologies in physics and optics before their counterparts in academia.69 While universities were hampered by budget limitations, private industry, motivated almost exclusively by profit, was also at a disadvantage because it was not always willing to maintain a fixed flow of funding for adaptive optics research. Companies made money on a time cycle dependent on when the Air Force awarded contracts, which could be unpredictable because of political and economic factors as well as changes in the military’s mission. Issuance of government contracts could be a tricky and risky business depending on how much the military needed outside help from year to year. A private company had no guarantee of a new or renewed contract from the government. But scientists working on adaptive optics for the Air Force could be more confident of continued funding. Although the Air Force adaptive optics program itself was on stable footing, the name of SOR went through changes. When SOR first opened in 1971, the acronym stood for Sandia Optical Range. On 1 November 1984, it was renamed the Directed Energy Experimental Range or DEER by the commander of the Air Force Weapons Laboratory, Colonel James M. Walton. His rationale was to make the site available for laser research and other promising directed-energy technologies such as microwaves and particle beams. The newly created Strategic Defense Initiative Organization had charged Air Force laboratories with accelerating their research efforts to explore not just lasers but all technologies with potential for helping to achieve the nation’s ballistic missile defense mission.70 The name DEER never caught on, as employees and visitors continued to refer to the site as SOR. Shortly after Colonel John Otten became the

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commander of the Weapons Laboratory in August 1988, he phoned Fugate and told him that he wanted to reinstate the acronym SOR—but that it could not stand for Sandia Optical Range, because too many people associated that with Sandia National Laboratory (also located on Kirtland Air Force Base, but having nothing to do with SOR). Otten directed Fugate to call him back by the end of the day with a new name that would match the initials SOR.71 Otten was the type of commander who wanted to charge ahead and accomplish the mission at hand without delay. Waiting was not his strong suit. That’s why he turned to Fugate for help. He knew Fugate was the most knowledgeable person about SOR and would come up with the right answer. Fugate didn’t disappoint the Weapons Laboratory commander. He proposed the name Starfire Optical Range, based on a photo taken at SOR showing a green laser beam propagating through the dark sky in the direction of a bright natural star far off in the heavens. The image of the “star” combined with the laser’s heat or “fire” seemed a fitting combination. “So I called Otten back,” Fugate remembered, “and suggested that we call it Starfire Optical Range—he loved it and that’s the way it happened.” On 7 December 1988, Otten signed a letter making the name change official.72 The name change was successful, and the research program flourished, but a new problem arose: the Federal Aviation Administration (FAA) became increasingly concerned about the potential health hazards of SOR lasers penetrating the night sky so close to Albuquerque International Airport. The FAA was particularly concerned about the possibility of commercial pilots being exposed to laser light that exceeded eye safety standards and might affect a pilot’s ability to fly or land an aircraft. In general, the FAA considered laser beams “hazardous to aircraft and all persons on board.” The FAA requested that SOR stop firing any lasers where the beam might stray into commercial airspace and direct laser beams only into restricted airspace. But officials said the agency would withdraw its objection if there were adequate safety measures in place.73 On 1 September 1989, FAA and Air Force Weapons Laboratory representatives met at SOR to settle the issue. Much of the meeting focused on the operation of the laser and the aircraft detection radar at SOR. The laboratory’s Major John Anderson led much of the discussion to dispel the perception that all lasers instantly vaporize anyone in their path. He explained that SOR was not using a high-power laser that could blow an airplane out Fugate’s Rayleigh Guide Star Experiments

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of the sky but rather a low-power copper vapor laser beam with only about 30 watts of output—not enough to cause damage unless it was focused directly onto the eye. On average, SOR fired the laser only about five nights per month. Each firing lasted no more than 15 minutes. In short, the laser was harmless and seldom used.74 SOR set up two safety precautions to prevent any laser beam from inadvertently intercepting an aircraft. First, SOR installed a Bendix aircraft detection radar system on the end of the laser telescope. Wherever the beam went, the radar followed along the same path. If the radar malfunctioned, then the laser shut down automatically. During any laser test, the radar would always be able to detect any aircraft within 3 miles of the beam. If that occurred, the test would immediately terminate.75 A second safety procedure involved a human spotter to back up the electronic radar system. The spotter, positioned on the roof of the telescope facility, was to constantly scan the sky before and during a laser test to make sure no aircraft was nearby. As explained to the FAA, “The roof spotter has an auto shutoff switch in his hands. If an aircraft is observed by the spotter before the aircraft enters the radar coverage, the spotter can also shut down the laser beam in one-tenth of a second.”76 As the FAA representatives became more familiar with SOR, they became convinced that the laser testing there was not a threat to aircraft flying near the airport. They agreed that the radar and human spotter system were adequate precautions. However, if SOR used higher-power lasers in future testing, the FAA wanted to study the matter and approve all safety procedures before those tests took place in unrestricted airspace.77 Safety had been a priority at SOR since the beginning. SOR as a firstclass research facility—often referred to as an Air Force center of excellence—was an invaluable national resource that helped Fugate and his team to achieve significant technical milestones. This work was strictly classified. But that changed in 1991 when the Air Force decided to declassify the program and share its revolutionary technology with the astronomical community. Up to that point, astronomers had been unaware of—literally in the dark about—the tremendous progress made by military scientists in the field of adaptive optics.

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Lincoln Laboratory

At the same time that Bob Fugate’s team of Air Force scientists were conducting the Rayleigh guide star experiments, Charles Primmerman was leading a Lincoln Laboratory team at White Sands Missile Range in southern New Mexico that would be the first to experimentally verify the sodium guide star concept. Located in Lexington, Massachusetts, on Hanscom Air Force Base, Lincoln Laboratory had established a reputation as one of the premier research and development institutions in the country. For over 50 years Lincoln has performed theoretical studies and experiments in areas including air and space defense, earlywarning systems, space and tactical battlefield surveillance, computers and signal processing, and advanced electronics. Lincoln’s origins go back to the early days of the Cold War. Because of the growing threat that the Soviet Union had the capability of using longrange aircraft to drop atomic bombs on American cities, Air Force Chief of Staff General Hoyt S. Vandenberg approached James R. Killian, president of the Massachusetts Institute of Technology (MIT), about creating a special laboratory dedicated to developing the technologies needed to defend

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the United States against a nuclear attack. Formed in 1951, MIT/Lincoln Laboratory’s original mission was to assist the Air Force in developing an air defense system made up of dispersed systems of radars that could find and intercept enemy aircraft carrying nuclear weapons. Lincoln Laboratory came into existence as a self-governing research agency under the operational control of MIT. The government funded MIT, which in turn administered the laboratory and paid the salaries of the approximately 200 technical staff who initially worked there. That number grew to over 600 by the early 1980s.1 Lincoln Laboratory fit into a special category known as Federally Funded Research and Development Centers or FFRDCs. Under that arrangement, the laboratory served as a civilian partner to the military but conducted its day-to-day research outside normal military channels of command. Lincoln Lab scientists had a level of technical expertise that was not readily available within the government’s civil service system. Design of a computer-driven air defense system against enemy bombers, known as the Semiautomatic Ground Environment or SAGE, was the first tangible result of Lincoln’s research efforts.2 The Defense Department sponsors several other FFRDCs including the following: the Aerospace Federally Funded Research and Development Center, operated by The Aerospace Corporation, El Segundo, California; Arroyo Center, National Defense Research Institute, and Project Air Force, all run by the RAND Corporation, Santa Monica, California; C3I Federally Funded Research and Development Center, administered by the MITRE Corporation, Bedford, Massachusetts, and McLean, Virginia; the Software Engineering Institute at Carnegie Mellon University, Pittsburgh; the Institute for Defense Analyses Studies and Analyses, operated by the Institute for Defense Analyses, Alexandria, Virginia; and the Center for Naval Analyses in Alexandria, Virginia.3 Over its first five decades, Lincoln Laboratory expanded beyond its original air defense mission to include satellite communications, ballistic missile defense, and space surveillance. By the 1970s and 1980s, Lincoln had become more active in studying the transmission of high-energy laser beams through the atmosphere and the effects of thermal blooming on beam quality—and in investigating adaptive optics. DARPA, the Strategic Defense Initiative Organization, the Air Force, the Navy, and the Army funded a large share of the laboratory’s work.

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White Sands: The Sodium Guide Star Experiment One of Lincoln’s most important contributions to adaptive optics was the sodium guide star experiment that had evolved from discussions at the Jasons’ 1982 summer study. Like the Rayleigh guide star at Kirtland, Lincoln’s sodium guide star was intended for use as a reference light source to replace light from a natural star, but it was located at a higher altitude and returned light to Earth in a somewhat different way. Both were funded by DARPA.4 The goal of the first sodium experiment was to determine how much distortion was present in the laser light returned from the mesospheric sodium layer. This layer is about 10 to 15 kilometers thick and 90 kilometers in altitude. A laser must be tuned precisely to the wavelength of the selected sodium line, usually the D2 line at 589 nanometers, for resonant backscatter to occur from the sodium layer. At that wavelength, a portion of the laser light shined into the sodium layer is absorbed by the sodium atoms and then reemitted. The reemitted light travels to the ground and serves as the sodium beacon. In comparison, light from a Rayleigh guide star is not absorbed and reemitted but rather reflected off molecules in the lower atmosphere.5 For the sodium beacon experiment, Lincoln scientists simultaneously measured distortion of light from a natural star and light from a sodium beacon aligned in the same direction. Measurements from the natural star and the guide showed a good match. At this stage, Lincoln purposely did not attempt to compensate for the distortions in the light, but simply to detect the degree of atmospheric turbulence and distortion. In September 1984, a Lincoln Laboratory team demonstrated for the first time that “phase distortion could be measured with a synthetic beacon in the mesospheric sodium layer.”6 DARPA’s motivation for funding Lincoln was to find out if a sodium beacon could provide the necessary atmospheric turbulence data to accurately propagate a short-wavelength laser beam to an uncooperative target (one with no beacon or light source on it) such as a satellite or missile. To accomplish this required measuring turbulence along the beam’s path and compensating for it with adaptive optics. Because of the satellite’s distance and speed, the synthetic beacon had to be pointed ahead of it (much, as discussed in the previous chapter, as a hunter leads a duck). In the process Lincoln Laboratory

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of solving this problem, scientists had to sample and measure turbulence along the same atmospheric point-ahead path that a laser beam from the ground would follow in order to intercept the satellite.7 This point-ahead angle was determined by the direction of the satellite and the direction of the laser beam trying to intercept it. The formula used to calculate the angle was 2v/c, where v is the target velocity and c is the speed of light. For low earth-orbiting satellites, the point-ahead angle is about 50 microradians. The sodium wavelength laser was aimed in the point-ahead direction, 50 microradians ahead of the satellite. Turbulence measurements from the sodium beacon, which served as a light source from the projected target intercept point, was then used to purposely distort or conjugate the wavefront of the outgoing laser beam in such a way that atmospheric turbulence would cancel out the distortion and put the beam on target.8 Lincoln Lab’s Darryl Greenwood was responsible for the overall sodium experiment at White Sands. Chuck Primmerman, who worked for Greenwood, served as group leader and provided guidance for the sodium beacon test, which was identified as the first Short-Wavelength Adaptive Techniques or SWAT experiment. Primmerman, who had started working for Lincoln Lab in 1975, revealed a deliberate and calm demeanor in his dealings with science and people. One could almost see the wheels turning in his head as he came up with solutions for tough technical problems. He was smart and well organized and earned a solid reputation as one of Lincoln Lab’s leaders in the field of adaptive optics.9 The sodium guide star’s success was the product of work by a number of Lincoln Lab technical staff under the direction of Ron Humphreys, who worked in Primmerman’s group. Humphreys came from the United Kingdom, worked for Lincoln, and then returned to his native land upon retirement. He relied heavily on the engineering talents of Robert Knowlton. Lincoln scientists had two objectives for the experiment: to demonstrate the feasibility of the sodium beacon and to show that it sampled a larger proportion of the atmosphere than a Rayleigh beacon, which would validate the concept that focal anisoplanatism decreases as the beacon’s altitude increases. On both counts, the experiment proved successful. Data showed that sodium beacons provided more complete information on atmospheric turbulence than Rayleigh beacons, and Lincoln Lab scientists

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concluded that an adaptive optics system using a sodium beacon would perform better.10 Humphreys used a 1-meter aperture auxiliary beam director, built by Contraves, that projected a pulsed dye laser from the ground to the sodium layer. The beam director, consisting of two flat mirrors, had no optical power to focus a beam but simply pointed it into the sky. Dye lasers can be tuned to almost any frequency, including sodium. Most of the laser firings occurred in the late evening, when there was less turbulence. The return wavefront from the sodium layer traveled to two receiver systems, subapertures of a Hartmann wavefront sensor located in the beam director—two telescopes positioned on an optical table 76 centimeters (30 inches) apart. Tilt measurements of the wavefront were then compared between the two subapertures. In comparison, SOR used 18 subapertures for the Rayleigh beacon experiment in 1983. Lincoln chose to limit the experiment to two subapertures for simplicity’s sake. Theory suggested that if these measurements were accurate, then it would not be unreasonable to believe that, in time, measurements could be made over four subapertures, then six, and so forth.11 Lincoln Laboratory had trouble from the start with its flashlamppumped pulsed dye laser, built and operated by Avco Everett Research Laboratory. That was one of the main reasons why the sodium beacon experiment did not produce positive empirical results until late 1984. The Avco laser was not a sodium laser per se, but a laser that worked at the sodium wavelength by using a dye—Rhodamine 590 6G chloride, one of the most highly fluorescing materials known—tuned to the desired wavelength. The medium for a dye laser is liquid dye (similar to organic dyes used to color fabric) flowed in a solvent to create lasing action. Perfecting the laser to operate at the desired wavelength required patience and precision. Results frequently fell short of Lincoln Lab’s operating expectations.12 Even under the most favorable conditions, only about one photon in sixteen interacts with the few sodium atoms that exist in the sodium layer. The energy level of the Avco laser was lower than predicted, and it failed at this task. A more potent laser would have produced more photons and increased the probability of photon interaction with the limited number of sodium atoms, which in turn would result in a greater sampling of the desired portion of the atmosphere for turbulence. The laser was also big, complicated, and unpredictable. The circulation pumps and the large tanks Lincoln Laboratory

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Photo 18. Research facilities at White Sands Missile Range, New

Mexico, used for Lincoln Laboratory’s sodium beacon experiment. At right is the dome housing the 1-meter auxiliary beam director that aimed a low-power laser beam to the sodium layer at an altitude of 90 kilometers. This 1-meter beam director originally was set up at Rome Air Development Center’s Verona Test Facility and was later moved to White Sands and used for Lincoln Lab’s sodium beacon experiment. After completion of the sodium work, this same 1-meter beam director was moved to Kirtland Air Force where today it resides on top of the hill at Starfire Optical Range and is used for a variety of optical experiments.

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that stored the chemicals required frequent monitoring and maintenance for the dye laser to work.13 It took nearly 2 years to work out all these problems and reach the point where the sodium beacon experiment was producing a steady flow of data, which occurred between September 1984 and early 1985. In spite of the difficulties, the experiments proved for the first time that a sodium beacon could measure phase distortions in a beam caused by atmospheric turbulence, information needed to make corrections to an outgoing laser beam.14 Lincoln Laboratory was not the first to create an artificial guide star— that honor went to Starfire Optical Range in 1983. But SOR was able to use almost any kind of laser (it chose a visible green frequency doubled Nd:YAG laser), while Lincoln was restricted to using a dye laser tuned to the sodium line of 589 nm, which was a daunting challenge. The Rayleigh beacon was also focused relatively low in the atmosphere, which meant anisoplanatism was a bigger problem, but the return signal was also stronger. The higheraltitude sodium beacon, on the other hand, sampled a greater portion of the atmosphere and had less of a problem with focal anisoplanatism. The two projects complemented each other and made a major contribution to the advancement of adaptive optics.15 Often it takes time before the significance of an experiment and the contributions of the people who worked on it become recognized. Nine years after the sodium beacon experiment, Primmerman received the Technical Achievement Award from the International Society of Optical Engineering for his contribution to laser guide star technology, which the society described as revolutionizing ground-based astronomy. Primmerman was careful to point out that this was a team contribution and that the other key team members—Humphreys, Knowlton, Lee Bradley, Jan Herrmann, and others—were the scientific wizards who made the sodium beacon work.16 To underscore the success of the collaborative approach, Primmerman shared his 1993 award with three contributors from other organizations: David Fried of the Optical Sciences Company; Robert Fugate of the Air Force Phillips Laboratory, and Richard Hutchin of Optical Physics Consulting.17 Lincoln Laboratory’s work on artificial beacons had solved only half of the problem. The team’s next big challenge was to develop a closed-loop adaptive optics system that could assimilate the data on atmospheric turbulence and use it to compensate for distortions in light beams. Lincoln Laboratory

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Maui: The First Closed-Loop Synthetic Beacon Following the success of the sodium beacon experiments at White Sands, Lincoln Laboratory shifted its attention to a series of adaptive optics experiments at the Air Force Maui Optical Site (AMOS) atop Haleakala mountain on the Hawaiian island of Maui. These August 1988 experiments made up the second part of the SWAT program. In February 1988, Lincoln shipped its adaptive optics system to Maui, where it was installed on the 60-centimeter (23.6-inch) beam director. Primmerman remained overall group leader for the work at Maui, but Lincoln Lab’s Byron Zollars, the lead engineer, designed and ran the experiments.18 The SWAT adaptive optics system used a Hartmann wavefront sensor and wavefront reconstructor built by Lincoln Lab and a deformable mirror with 241 actuators built by Itek. The system’s design allowed it to compensate for atmospheric turbulence both in images of space objects and in outgoing laser beams. The purpose of the Lincoln Lab SWAT experiments was to demonstrate that atmospheric compensation could be accomplished using a synthetic beacon. If the adaptive optics system worked, it would produce high-resolution images of stars viewed coaxially with the beacon lasers. Although Lincoln’s pioneering work had been with the sodium beacon, the team decided to use a Rayleigh beacon at Maui instead because of the difficulty in fabricating a sodium beacon.19 Lincoln used a flashlamp to excite a mixture of Coumarin dye, acetic acid amide, and water to generate a low-repetition-rate dye laser for its Maui experiment. Proving the SWAT adaptive optics system could operate in a closed loop meant first sensing the atmospheric distortions in the return beacon laser beam and then compensating for them. The light backscattered from the Rayleigh beacon was collected by the beam director and directed to a wavefront sensor that measured distortions in the light. Based on those measurements, electrical signals were sent to change the shape of the deformable mirror to correct for the distortions. The dye laser’s repetition rate (about 10 pulses per second), as Primmerman reported, meant that the system could not perform as a conventional closed-loop system—it was too slow. Instead, it employed a go-to technique that closed the loop on a pulse-by-pulse basis. This technique is considered a more difficult type of free-running closed-loop system, so that if it worked, a conventional closedloop system was likely to work as well.20

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Photo 19. This deformable mirror was a critical component of the

SWAT adaptive optics system.

In any opto-mechanical control system, there is a lag time between measurement and correction of turbulence that affects how well the system corrects the distortion. The operating sequence in the go-to system entailed firing at five pulses per second and then applying a correction measurement to the deformable mirror in the open-loop position. That setting would be held on the mirror, and a very short exposure of the star (much shorter than the time between laser pulses) would be taken. The mirror’s shape would remain fixed Lincoln Laboratory

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until the next laser pulse, after which the mirror would be reset and another picture of the star would be taken. This process would be repeated over and over again, but each time a mirror correction was made there was no continuous feedback verifying that the mirror was at the right setting. There were intermittent corrections, but not continuous correction.21 The problem with this approach was that the interval between laser pulses (each laser firing) was sufficiently long that the adaptive optics system was always trying to “catch up” to make the next correct setting to the deformable mirror in order to keep up with changing atmospheric conditions. The intervals between laser pulses were measured in milliseconds, but that was long enough for turbulence conditions to change and the mirror settings’ accuracy to deteriorate. The key point was that the time delay between the firing of successive laser pulses made the initial measurement setting on the deformable mirror outdated because during that interval turbulence in the atmosphere changed, which required a new setting on the mirror. The system was always slightly behind real-world conditions. But as one observer put it, that did not detract from the accomplishment of Lincoln’s SWAT experiment at Maui, because any closed-loop system has a time lag.22 Lincoln Lab’s laser fired five pulses per second. In comparison, the laser at Starfire Optical Range ran at 5,000 pulses a second, which made it possible to change the surface of the mirror an incredible 2,500 times per second, responding almost immediately to changes in the atmosphere. The Maui system resembled individual snapshots, while the SOR system resembled a continuous movie. The SOR images were also of higher resolution.23 Lincoln Lab, however, completed its closed-loop synthetic beacon adaptive optics system first—in summer 1988, 5 months before SOR. On 25 August 1988, Zollars and his team recorded “the first stellar image ever compensated for atmospheric turbulence with a synthetic beacon.” This was a major breakthrough, even though the “degree of compensation was relatively poor.” As Zollars explained, “Subsequent to the first experiments, improved equipment and accumulated experience allowed substantial improvements in the quality of the compensated images.” Eventually, the Lincoln team generated images with a Strehl ratio of 0.46, which was considered very good.24 Part of the reason Lincoln could obtain better images in later experiments was that the second phase of the original plan called for switching from a single Rayleigh laser beacon to using four beacons focused very

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Photo 20. This photo shows the complexities of the electro-optical hardware in Lincoln Laboratory’s SWAT adaptive optics system.

close to one another in the same area of sky. This method, called beacon stitching, produced more backscatter, which sampled a wider path of atmosphere. This was a distinct advantage over a single beacon. “Measuring the atmospheric distortion with an array of synthetic beacons,” Zollars wrote, “reduces the wavefront error due to focal anisoplanatism because of the more accurate sampling of turbulence close to the edges of the aperture.”25 Primmerman’s team at White Sands and Maui and Fugate’s team at Kirtland shared a feeling of friendly competition and camaraderie. The goal of both groups was to advance the science of laser guide stars and help the Air Force perform its mission through the use of adaptive optics. So it was not surprising that by the mid-1980s, as Fugate later recalled, scientists from both labs met annually to exchange information on the progress of their research. As Lincoln’s Darryl Greenwood put it, Rayleigh and sodium guide star experiments were complementary and “we all learned from each other in those days.” There was no doubt that Air Force officials appreciated the value of the Rayleigh and sodium beacon accomplishments. However, Lincoln Laboratory

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Photo 21. Air Force Maui Optical Site (AMOS) atop Haleakala on

the island of Maui, Hawaii, where Lincoln Lab conducted the second phase of its SWAT experiments.

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Photo 22. Pioneering adaptive optics scientists in a photo taken circa 1982.

Left to right, Rett Benedict, DARPA; Bob Fugate, Air Force Weapons Laboratory; Dino Lorenzini, DARPA; Darryl Greenwood, Lincoln Laboratory; Don Hanson, Rome Air Development Center; Chuck Primmerman, Lincoln Laboratory; David Fried, the Optical Sciences Company; and Barry Hogge, Air Force Weapons Laboratory.

they also knew that these were expensive and complex experiments riddled with hardware problems and finicky instrumentation.26 Chances were slim that any of these breakthroughs would have taken place without the government’s commitment and willingness to invest heavily over many years. The need for government support for military research and development had been debated at least since 1945, when General Hap Arnold and the distinguished aerodynamicist Dr. Theodore von Kármán led a movement to promote the importance of research and development in the military services. In 1945 they published Toward New Horizons, a military blueprint for the future, arguing that science and technology were crucial to the nation’s defense.27 Lincoln Laboratory

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Adaptive optics research exemplified the spirit of the Arnold/von Kármán legacy. The stakes were high, but so were the potential payoffs. University researchers were at a distinct disadvantage. They lacked the resources to build the large telescopes and conduct the elaborate experiments adaptive optics required. For the most part, universities also lacked the infrastructure to orchestrate large research programs spanning a wide range of organizations—like the government laboratories, the military services, DARPA, private contractors, and federally funded research agencies such as Lincoln Laboratory were able to do. The Air Force laboratory system and Lincoln Lab were in the best position in the 1980s to make advances in adaptive optics research.28 Although early guide star research was classified, that would change dramatically in the early 1990s, when the Air Force decided to share its adaptive optics findings with the rest of the astronomy community. This is discussed in detail in chapter 7.

High-Energy Lasers and Thermal Blooming Lincoln Laboratory—through Greenwood, Primmerman, and others— had established itself as a leader in laser guide star research in the 1980s using low-power lasers. The focus of that work was on improved imaging of objects in space, but that was only one side of the lab’s adaptive optics research. Lincoln had also been involved since the 1960s in experiments using low-power and high-energy lasers to intercept space targets. In the late 1960s and early 1970s Lincoln Laboratory started a major research effort involving high-energy lasers that lasted into the 1990s and continues today at a reduced scale. Initial work focused on theoretical studies and laboratory experiments to better understand laser characteristics and beam quality issues. At that time, DoD was interested in improving beam quality in high-power lasers—first with CO2 gas dynamic lasers and later with chemical lasers—and adaptive optics was one possible solution. The long-term objective was to develop adaptive optics techniques that would reduce the effects of thermal blooming—a high-energy laser beam’s tendency to lose power as it heats up the air through which it passes. This work was primarily funded by DARPA and the Navy with an eye toward

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using high-energy laser weapons for tactical ballistic missile defense, antiship missile defense, air defense, and antisatellite missions.29 The Navy was looking at lasers in the 3.5 micron wavelength range. At that wavelength, a laser operating at ground level was more susceptible to the effects of thermal blooming than to atmospheric turbulence. The Air Force, on the other hand, was interested in placing lasers in planes flying at high enough altitudes that thermal blooming was less of a problem, and thus was more concerned about atmosphere turbulence than thermal blooming.30 Thermal blooming was one of the most daunting obstacles to developing a ground-based, high-energy laser weapon. The problem was that as a laser beam travels through the atmosphere it heats up the air along the way; that spreads out the beam and reduces its intensity at the target. The atmosphere absorbs a small portion of the beam’s energy, and the heated air expands and becomes less dense than the surrounding cooler air. This changes the index of refraction; the burned-through air functions as a lens that bends the laser light outward, defocusing the beam and causing it to “bloom.” Both thermal blooming and atmospheric turbulence distort the laser beam. One of the worst conditions for thermal blooming is when there is no wind, because motionless air absorbs more heat, hence more blooming.31 A low-power laser beam does not heat up the atmosphere as much as a high-power laser does. Consequently, the higher the power of the laser, the greater the thermal blooming and the greater the distortions in the beam wavefront. It can also be more difficult for an adaptive optics system to compensate for thermal blooming than for atmospheric turbulence, depending on the wavelength of the laser and the geometry of the engagement scenario.32 Thermal blooming was thus a serious problem that had to be solved if the military expected to field an effective ground-based laser weapon. Not only does thermal blooming reduce beam quality, but it also limits a weapon’s operating range. Lou Marquet, who had earned a PhD in physics from the University of California, Berkeley, eventually worked his way into jobs aimed at finding solutions to thermal blooming. Marquet was confident but not cocky, willing to take calculated risks and go where the work was most demanding and satisfying. Career management experts did not easily sway him. Rather he opted to follow his own instincts, choosing to move into more risky territory to take the most challenging and scientifically rewarding jobs. He started his career conventionally enough. After 2 years of active Lincoln Laboratory

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duty in the Army Signal Corps, he became an assistant professor of physics and astronomy at the University of Arizona in the early 1960s.33 Though he spent several years teaching, Marquet did not find university life all that appealing. Years later, looking back, he confessed he was just plain bored and unmotivated by university research. He was yearning for something else but didn’t know quite what it was until he met an old friend from Berkeley at a physics conference in New York City in 1966. His friend urged him to interview at Lincoln Laboratory, because there were all kinds of innovative and futuristic research programs going on there. Although knowing little about the Massachusetts laboratory, Marquet followed his friend’s advice and landed a job in 1967 in the lab’s optics group working on ballistic missile defense. The main thrust of this work was to find ways to discriminate, based on infrared measurements, between a real reentry vehicle and a decoy. Marquet recognized that the issue was one of the military’s toughest challenges. He quickly found his niche and ended up staying at Lincoln for the next 18 years. Darryl Greenwood and Chuck Primmerman, two of the recognized leaders in adaptive optics at Lincoln Lab since the mid-1970s, later praised Marquet for initiating and directing the adaptive optics program at Lincoln with enthusiasm and strong leadership.34 Lincoln Laboratory worked for the military, and Marquet was part of a growing corps of military scientists working on specialized and often classified research projects for the government. He found military research more exciting than academic research. Universities often make discoveries, Marquet noted, but in many cases what they discover is not applied to the real world. Does it really matter from a practical standpoint, he pondered, what kind of soil there is on Mars? Academics are content with finding the truth for the sake of truth. On the other hand, military scientists can find the truth, which an adversary can then negate by coming up with a new truth or countermeasure. This “fighting back” aspect, as Marquet put it, forced the military scientist to constantly keep his eye on the practical application of his research and to always be ready to anticipate the research step that will counter an opponent’s latest countermeasure. It was this aspect that made the work more interesting and intellectually satisfying to Marquet.35 In addition, Marquet believed the stakes were higher in military

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research because the outcome often had life-or-death consequences for individuals as well as for the security of the entire country. This was another factor that attracted Marquet to government service.36 Early in his career with the optics group at Lincoln Lab, Marquet found himself heavily involved with high-energy laser beam diagnostic work at Pratt & Whitney’s jet engine test facility in West Palm Beach, Florida. Since the discovery of the laser in 1960, DARPA had been interested in determining the feasibility of laser weapons—specifically, a high-power ground-based laser system for antisatellite and ballistic defense missions. That was DARPA’s motivation for funding Pratt & Whitney’s work on one of the earliest high-power laser devices, called the XLD or Experimental Laser Device. The XLD was a megawatt-class CO2 gas dynamic laser, with a wavelength of 10.6 microns, that worked similar to a rocket engine. Pratt & Whitney had a strong national reputation for design and fabrication of jet engines, which partially explained why the XLD ended up at the company’s Florida test site.37 The XLD operated by combusting a mixture of gases and then flowing the mixture at supersonic speeds through an array of nozzles. This caused a population inversion of excited molecules in the high-speed flow, generating a CO2 laser beam. Although the beam was robust and potentially powerful, it lacked focus and stability. Instead of a pencil-thin beam packing all of the laser’s energy, the XLD beam resembled a big flashlight that shone in all directions (Marquet described the beam as “ugly”) and could not disable or destroy a target at long range. DARPA sought a practical way to harness the energy of the XLD laser into a more coherent beam. Atmospheric turbulence and thermal blooming were the two main hurdles to overcome, and there were no clear solutions at this early stage in laser research.38 As a first step, DARPA asked Lincoln Laboratory to go to West Palm Beach in 1968 and determine exactly what was happening to the quality of the XLD high-energy laser beam. Pratt & Whitney employees knew how to operate and maintain the XLD, but they were not experts in the physics of beam characteristics. DARPA turned to Lincoln Lab for help developing techniques for measuring the behavior of the beam from the time it exited the laser device until it reached the target. Lincoln sent a team of scientists led by Lou Marquet to attack the problem. Gaining a better understanding of beam quality was the first goal. The second step would be to figure out a Lincoln Laboratory

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way to use adaptive optics to compensate for the poor quality of the beam and the additional degradation of thermal blooming.39 From the late 1960s through the mid-1970s, Marquet and his team engaged in theoretical studies and experiments at West Palm Beach to acquire a better understanding of how thermal blooming and atmospheric turbulence affected the behavior of a high-power laser beam. The ultimate objective was to improve propagation of a high-energy laser from the ground to a target in the atmosphere or space. But before that could happen, one of the first problems Lincoln Lab scientists had to solve was how to define the characteristics of a high-energy laser beam. That was not easy. Trying to diagnose the beam profile for a focused high-energy laser beam was impractical, because the beam’s spot would be so small, and the power so high, that the beam would melt any kind of diagnostic device. To solve this problem, Marquet came up with a creative diagnostic method called the transmissive hole diffraction grating technique, which used a copper plate mirror with holes drilled in it. The tiny holes were arranged in a regular pattern that covered an area approximating the diameter of the beam. As the XLD high-power beam struck the copper plate, more than 99 percent of the beam reflected off the plate and was harmlessly dumped into a calorimeter. The remainder—less than 1 percent of the beam—passed through the holes in the copper plate. This attenuated beam was much easier and safer to deal with, as it had only about 100 watts of power as opposed to tens of kilowatts.40 After passing through the holes in the copper plate, the weakened beam reflected off a concave mirror and was focused to a far-field diffraction pattern. The focused beam reflected off another mirror, and a special infrared scanning camera (made by AGA, a Swedish company that built cameras for medical purposes) took an image of diffuse scatter from the beam. This provided vital information on the beam’s characteristics, including shape, size, intensity, jitter, wavelength, phasefront, near- and far-field irradiance, and power fluctuations. Based on these data, overall beam quality could be calculated. Marquet’s technique facilitated the direct measurement of a highpower beam by diagnosing a small but representative portion of it, which served as a true sample of what the high-power beam would look like focused in the near field and the far field on the target. It furnished, for the first time, direct diagnostic measurements of beam quality on a high-power laser.41

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While Marquet and his group were conducting experiments to better define beam quality, two other scientists at Lincoln Lab, Lee Bradley and Jan Herrmann, were developing the first wave optics propagation code that incorporated the effects of thermal blooming. Running the code predicted mathematically how a beam would perform as it propagated through the atmosphere and encountered thermal blooming. It also predicted what would happen to the beam when it was focused on target. The idea was to compare the code predictions—a computer simulation of a laser beam propagating through an absorbing medium—with experimental results to see how closely they matched.42 In 1975 Chuck Primmerman and Dan Fouche conducted the first laboratory experiment to compensate for thermal blooming in a laser beam. This work, conducted at Lincoln Laboratory, validated the accuracy of the Bradley and Herrmann codes. Primmerman and Fouche, under tightly controlled laboratory conditions, transmitted a low-power argon laser beam through an absorption cell that simulated a real world thermal-blooming environment. Using the computer code predictions, they then applied phase corrections to a 57-actuator deformable mirror built by Itek. This was an open-loop adaptive optics system that relied on the experimenters to manually adjust the setting on the deformable mirror at the appropriate time.43 Each time a new setting was placed on the deformable mirror, Primmerman and Fouche measured the intensity of the beam at its focal point to see if the change on the deformable mirror increased or decreased the intensity of the beam at the target. An increase in intensity meant that compensation of the beam was occurring. Experimental results were encouraging: “We see that the peak intensity has increased by almost a factor of 3,” Primmerman and Fouche wrote, “and that the shape of the beam has been greatly improved.” The experiment did not demonstrate perfect compensation in the beam. But even partial correction under controlled laboratory conditions constituted an important first step.44 In the next phase of research, Marquet and his group used a mirror that could accept a high-power laser beam. Pratt & Whitney Aircraft, a subsidiary of United Technologies Research Center, constructed and tested the first high-power, water-cooled mirror at United Technologies Research Center’s facility in East Hartford, Connecticut.45 Everything did not go exactly as planned during the early stages of Lincoln Laboratory

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the mirror’s development. At one point, a technician torqued the mirror too much, producing a big dimple in the middle. One person on the scene reported, “We were all hysterical for awhile. We felt we were in a disaster, but it turned out in those days companies were very responsive. Pratt & Whitney had in parallel built another mirror. They had another mirror actually built and substituted it for the dimpled mirror. They just showed us, they knew it was risky, so they built two mirrors simultaneously and used the second one for the experiments at West Palm Beach.”46 Pratt & Whitney’s water-cooled mirror was a critical component used in conjunction with the XLD laser during the West Palm Beach experiments. Measuring 21 centimeters (8.3 inches) in diameter, the surface of the mirror was made of a thin sheet of molybdenum. Attached to the backside of the mirror were 52 actuators that moved to reshape the front to compensate for distortions in the high-power beam. The contractor shipped the completed mirror in fall 1975 to Pratt & Whitney’s high-energy laser beam test range at West Palm Beach, located on a remote section of Florida wetlands. An unusual feature of this site was the occasional intrusion by the area’s resident alligators.47 Facilities at one end of the range housed the laser device, optics room, offices, and a fuel storage site that provided the fuels to be combusted to produce the laser. Two kilometers (1.2 miles) downrange was a target board mounted on a railroad flatcar, designed and built by Lincoln Laboratory along with 670 meters (0.4 miles) of track perpendicular to the path of the laser beam. The car was remotely controlled and powered by an auxiliary power unit of the type used to start jet aircraft engines. The unit supplied power to a hydraulic pump that powered hydraulic motors on each of the four wheels. When the system started up, the noise was extremely loud and sounded like a jet aircraft engine. While some on-site wanted to name the railroad car The Diffraction Limited—a reference to a perfect beam—Lincoln Lab settled on the name Everglaser. Since the work involved lasers in the Everglades, the nickname seemed to make the most sense.48 The XLD experiments were conducted from 1975 through 1977. Some of the work measured beam characteristics with the beam focused in the near field before being sent downrange. The first compensation tests on the XLD using the 52-actuator deformable mirror looked at techniques for correcting for phase aberrations in the beam as it exited the laser device and moved downstream through the optical train in the optics room. For this particular

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scenario, the beam was not sent downrange. Later tests expanded the beam to 1.2 meters (3.9 feet) and transmitted it downrange to instrumented targets.49 Exiting the laser device, the 7.5 centimeter (3 inch) diameter beam traveled through a pipe into the optics room, where beam diagnostics took place. There the beam was reflected off a series of mirrors in the optical train, and at various stations measurements of beam characteristics—such as phase distortions—were made. Eventually the beam reached a telescope that expanded it to 1.2 meters (3.9 feet). It then left the optics room through a large window and traveled downrange 400 meters (a quarter mile) to a stationary target consisting of a concrete pad. Farther downrange, at 2 kilometers (1.2 miles)— the longest distance the beam traveled—was the mobile railroad car.50 As the beam moved from the laser device through the pipe and into the optics room, the humidity it encountered resulted in thermal blooming. To minimize this, Marquet and his colleagues devised a system that injected fresh air into the laser pipeline. They also set up a series of large floor fans, purchased from the local Sears store, to circulate cool air across and around the beam’s path through the optics room. The makeshift system worked. Fresh air blown across the beam’s path removed much of the stagnant air heated by the laser beam and reduced thermal blooming.51 Marquet’s improvised beam path conditioning system was a simple solution and very successful. He reported that the XLD beam in the pipe went from 16 times diffraction limited to 4 times diffraction limited, meaning the beam suffered less degradation from thermal blooming. Marquet believed this was an important step forward, thanks in large part to Lincoln Lab, in understanding the effects of thermal blooming on a laser moving through the atmosphere—and in scientists’ ability to compensate for it.52 After the high-power deformable mirror was installed, Lincoln ran a series of low-power tests before moving on to using the high-power XLD. One part of those experiments involved reflecting a 30-watt CO2 laser off the deformable mirror. Because of its low power, the laser did not experience thermal blooming. The mirror was adjusted to provide the best focus of the beam in the near and far field. Low-power testing showed what a beam looked like without the effects of thermal blooming. Later, testing of the high-power beam would reveal how badly it was affected by thermal blooming. Also important, the preliminary low-power tests showed that Lincoln Laboratory

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Photo 23. In the XLD’s optics room, floor fans (lower right) purchased

from the local Sears store cooled the high-energy laser beam path to reduce the effects of thermal blooming.

the laser and mirror operated successfully together without causing any damage to the mirror’s surface.53 Firing the high-power XLD laser and assessing how it reacted with the water-cooled deformable mirror was the next phase, which took place from November 1975 to April 1976. A total of 181 tests were conducted, including thirty-one XLD beam diagnosis tests and 140 firings to downrange targets. Fifty-eight experiments propagated the beam to the stationary target at 400 meters. Eighty-two other experiments tested thermal-blooming compensation, sending the beam 2 km downrange to the mobile railroad car. The main goal of these tests was to evaluate the performance of the deformable mirror and determine if it could compensate a high-power laser exposed to thermal blooming and atmospheric turbulence in a real-world environment.54 Efforts to propagate a high-energy beam (of several hundred kilowatts) to the outermost target at the 2-kilometer site were the most realistic experiments to date in terms of simulating what an actual laser weapon system might encounter in the atmosphere. As the 16,000-pound railroad car traveled down the track at under 20 mph, Marquet and his team slewed the

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laser to follow it. (Slewing simulated how an operator on a ship or plane would direct the beam to its target.) Because of the slewing, the beam was constantly moving into a new and fresh path of air, thereby reducing the degree of thermal blooming. The exception to this, and the most problematic for thermal blooming, was the area nearest to where the beam exited the aperture. Test results showed that slewing did not significantly reduce the effects of thermal blooming in that narrow region.55 An unpolished aluminum plate mounted on the railroad car served as the farthest downrange target on which the XLD beam was focused. Prior to sending the laser beam to the target, settings on the deformable mirror were made based on computer code predictions of the intensity of the beam on target. Two infrared cameras took a picture of the beam reflecting off the target, and five detector arrays measured the irradiance on target. That information was transmitted back up range to the optics room and used to adjust the settings on the deformable mirror to compensate for the distortions that had been measured in the beam. Those distortions were constantly changing, resulting in new diagnostic data being transmitted to the optics room and new signals to the mirror. This cycle allowed, “for the first time, continuous monitoring of the far-field beam during thermal-blooming tests with slewing.”56 Marquet reported that the West Palm Beach experiments were the first successful adaptive optics tests using a high-energy laser beam and a deformable mirror to compensate for thermal blooming in the real atmosphere. In summing up the accomplishments of the XLD experiments, Marquet wrote: “In shot after shot during the thermal-blooming compensation tests, the farfield irradiance distribution was significantly improved (factors of up to 2.5 reduction in bloomed area) by using the deformable mirror to add predictive phase compensation to the beam.” However, the system was not yet refined enough to generate the near-diffraction-limited beam needed for a ballistic missile defense or antisatellite weapon system.57 More work did occur in 1977 with a Closed-Loop Adaptive Single Parameter (CLASP) low-power experiment conducted at Lincoln Laboratory by Primmerman, F. Bruce Johnson, and Irving Wigdor. Previous to this, all the XLD experiments were open-loop. Primmerman described CLASP as a proof-of-concept laboratory experiment for a closed-loop system that “compensates for thermal blooming by optimizing only one parameter—the amplitude of the phase correction.”58 Lincoln Laboratory

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Photo 24. Lincoln Laboratory’s mobile railroad car target, dubbed the Everglaser, was positioned 2 kilometers downrange. A high-energy laser beam reflected off the shining rectangular surface near the center of the car.

This first CLASP experiment used a low-power argon-ion laser that reflected off a 57-actuator deformable mirror, which focused the laser beam in the far field. A cell filled with ethyl alcohol and iodine absorbed about half of the low-power beam’s radiated energy, thereby simulating thermal-blooming conditions for a beam slewing through the atmosphere. “The shape of the deformable-mirror correction was fixed,” Primmerman reported, “but the amplitude [of the signal going to each actuator] was adjusted automatically to maximize the far-field intensity.” This approach worked well; the far-field intensity of the beam on target did increase, demonstrating that this closedloop adaptive optics system performed as expected. Primmerman and his colleagues concluded the CLASP system “has shown itself to be a viable concept for thermal-blooming correction.” The next step after this laboratory experiment was to conduct a field test to show that the CLASP system would work with the high-energy XLD laser.59 The CLASP test in the field at West Palm Beach was also a stunning success. As in the laboratory experiment, it collected beam intensity data at the target spot and relayed it to the optics room so changes could be made

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to the 52-actuator, water-cooled deformable mirror. There was no wavefront sensor to measure beam phase aberrations. Instead, CLASP relied on a single-dither approach that made changes to the mirror according to the continuous feedback of data on far-field beam intensity. Lincoln Lab and DARPA, which funded the work, were pleased by the results, which confirmed “the first closed-loop thermal-blooming compensation of a highenergy laser.” Once again, the adaptive optics system did not compensate completely for the high-energy laser beam, but it did prove it could provide limited compensation for thermal blooming in the atmosphere. Time was required to move the scientific process forward.60 Two other important experiments took place at West Palm Beach. One was called OCULAR, which stood for Optical Compensation of Uniphase Laser Radiation. The other was called Target Return Adaptive Pointing and Focus or TRAPAF, the last phase of Lincoln’s experimental program in Florida. Both experiments were designed by Lincoln Lab to look at ways to improve the quality of a high-energy laser beam propagating through the atmosphere.61 Under the direction of Lincoln’s Dave Kocher, planning and design of the OCULAR experiments began in 1975, followed by field testing in June and July 1977. While Pratt & Whitney provided the laser and the 52-actuator deformable mirror, Itek supplied the sensor optics, dither mirror assembly, and driver electronics. The XLD did not exit the laser device as a perfect beam. Rather, a number of forces impinged upon the beam to degrade its quality. Noise signals and vibrations generated by the hardware and gas flow to produce and direct the beam corrupted it as it traveled from the resonator, through the optical train to the deformable mirror, and finally to a telescope that focused it downrange. Moreover, when the beam reflected off a mirror in the optical train, the surface of the mirror absorbed a portion of its heat, which created additional distortions. OCULAR was an adaptive optics system mainly concerned with cleaning up the beam as it exited the laser device and moved through the optical train to the telescope. Corrections made to the beam in this region were referred to as local loop corrections.62 Lincoln Lab scientists used an alignment laser beam in conjunction with a multidither technique (rapidly changing the position of the deformable mirror by trial and error with a “hill climbing” servo loop) to correct for the distorted wavefront of the XLD beam. This concept had originally Lincoln Laboratory

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been developed by Tom O’Meara at Hughes Research Laboratories. The OCULAR experiments were complex because each of the 52 actuators on the deformable mirror had to be individually controlled. Overall, OCULAR “worked as planned with the alignment laser source, even in the XLD acoustic and vibration environment.” As Primmerman pointed out, the OCULAR experiments “demonstrated the first ever compensation for device aberrations in a high-power laser.”63 The TRAPAF experiments, led by Darryl Greenwood, differed from the OCULAR experiments in that they did not use the 52-actuator deformable mirror. TRAPAF’s mirror was of a simpler design, with only four actuators, and could compensate only for tilt and focus. In addition, TRAPAF experiments corrected the beam beyond the local-loop region—that is, compensation took place as the beam made its way downrange to the target on the railroad car. However, results showed that only a small degree of correction occurred because of the higher level of noise associated with the XLD laser.64 Much of Lincoln Laboratory’s experimental work in Florida confirmed theoretical concepts involving the complicated interaction of high-energy lasers with thermal blooming. Not every test worked precisely as planned, and the Lincoln scientists never completely solved the problem of thermal blooming. But they made significant headway toward improving the quality of a high-power beam affected by thermal blooming. At the time, they were the only U.S. experiments applying adaptive optics to the problem of thermal blooming.65 The late 1960s through the mid-1970s were the early days of lasers, and scientists were just beginning to understand thermal blooming. They were familiar with how atmospheric turbulence degraded beam quality, but turbulence was not much of a problem for the XLD 10.6-micron CO2 laser because of its long wavelength. On the other hand, the longer-wavelength beam was more vulnerable to thermal blooming, which was the more difficult scientific nut to crack. If they could have turned back the clock, most Lincoln Lab scientists would have opted to attack the problem of atmospheric turbulence first, rather than the more complex issue of thermal blooming.66

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seven

Sharing the Gold Astronomical Nuggets

Bob Fugate’s team at Kirtland and Chuck Primmerman’s team at Lincoln made pioneering contributions to laser guide star technology in the 1980s that had a lasting effect not only on the United States Air Force, but also on academic astronomy. The military, through DARPA, RADC (later Rome Laboratory), the Air Force Weapons Laboratory (later Phillips and now the Air Force Research Laboratory), and the Strategic Defense Initiative Organization, played a lead role in sponsoring and funding laser guide star research from the 1970s through the early 1990s. Moreover, the Air Force was extremely careful to ensure that all work on laser guide star experiments were kept under tight wraps. With few exceptions, civilian astronomers were unaware that the Air Force had been conducting research involving laser guide stars.1 Since DARPA funded the laser guide star program, it logically became responsible for the program’s security. Laser guide star research remained classified because the Department of Defense considered it breakthrough technology with potential weapons applications. The Air Force did not want to reveal the interest, thrust, and status of its research, because that might convince an adversary to turn its attention to adaptive optics. As a

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first step, DARPA designated the laser guide star research a special-access program, identified as LODESTAR, allowing only a very limited group of people with a “need to know” to obtain or use information about the program. LODESTAR had much tighter restrictions on access than the normal classified government programs.2 DARPA, besides determining who would have access to LODESTAR, also established the security classification guides that spelled out in detail exactly what information could and could not be released about the program. Laser guide star technology was placed on the Military Critical Technologies List, making it subject to rigorous export controls. These restrictions were intended mainly to keep the guide star technology from the Soviets. They remained in place until 1984, when sponsorship of the laser guide star work, along with responsibility for security, shifted from DARPA to the Strategic Defense Initiative Organization. SDIO substantially expanded its investment in LODESTAR technology to support its ground-based antiballistic missile program. In 1991, SDIO scaled back directed-energy research in favor of space-based kinetic interceptors. The space-based chemical laser effort continued, but at substantially reduced funding. LODESTAR research funded by SDIO, and later the Ballistic Missile Defense Organization, was eventually phased out as funding, along with the Soviet threat, decreased.3 At the same time, the Air Force continued down a slightly different road, focusing on the potential of laser guide star research to improve space control applications such as ground-based laser antisatellite weapons. For those types of operations, technology would be needed to sense atmospheric turbulence in the point-ahead direction (the path the laser beam would travel to intercept a satellite), where no natural beacon existed. There were no plans to build an antisatellite system in the short run. Rather, the Air Force engaged in research to demonstrate the feasibility of adaptive optics technology in order to be in the position to build such a system if it was needed in the future. Astronomers, on the other hand, were not interested in perfecting antisatellite weapons. Their main goal was to acquire sharper images of celestial objects—a goal the military shared, but not exclusively.4 Many government leaders strongly believed that SDIO had played a major role in ending the Cold War. By the late 1980s and early 1990s, many also believed that, with the threat of a massive Soviet attack virtually

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eliminated, SDIO had served its original purpose and was no longer needed in its current configuration. The new perception of threat that emerged emphasized third-world nations that might acquire enough technical expertise to launch a missile attack on the United States. Consequently, theater ballistic missile defense became a national defense priority in the post–Cold War period. To prepare for this challenge, Secretary of Defense Les Aspin announced in May 1993 that SDIO had been reconfigured and renamed the Ballistic Missile Defense Organization (BMDO). In January 2002, BMDO’s name changed to the Missile Defense Agency or MDA.5 Two years before SDIO became BMDO, the leadership at SDIO and the Weapons Lab at Kirtland (which had merged with several other organizations to become the Phillips Laboratory in December 1990) jointly made the decision to declassify a large portion of the military’s work on laser guide stars. Several other defense advisory groups—including the airborne laser Independent Review Team, headed by Dr. Bob Cooper—also recommended the move. Parts of the program remained classified, so a new classification guide was needed. That job fell to a small group of people at Phillips Lab headed by Bill Thompson. Thompson, who had a keen eye for detail and who had started working for the Air Force Weapons Laboratory in the 1960s, had the right temperament and a reputation for thoroughness in successfully guiding the most difficult projects through the laboratory’s bureaucratic maze. Because a substantial part of the government laser guide star work had taken place at the Air Force Weapons Lab and Lincoln Laboratory, and because the former was a government entity while the latter functioned as a private contractor, it made sense that the Weapons Lab would be responsible for security.6 To put the new security program on solid footing, SDIO terminated LODESTAR in 1988 and replaced it with a program called HAVE REACH. Now the Air Force was in complete control of security for the laser guide star program. Government code names usually have two words. HAVE was the arbitrary term to denote work performed by Air Force Systems Command, the research and development arm of the Air Force at the time. Thompson came up with the second word, REACH, which conveyed a mental picture of a laser propagating through the atmosphere and reaching for the stars. Later, HAVE REACH came under Air Force Materiel Command (established on 1 July 1992, the result of the merger of Air Force Systems Command Sharing the Gold

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with Air Force Logistics Command). Phillips Lab, which had absorbed the Air Force Weapons Laboratory (AFWL) in 1990, was in turn consolidated with other research and development organizations in 1997 and became the Phillips Research Site of the Air Force Research Laboratory. Today, HAVE REACH is still the responsibility of the scientific security team of AFRL’s Directed Energy Directorate at SOR.7

The Decision SDIO and AFWL worked together to declassify a good portion of the laser guide star work. Initially, Tom Meyer, who was responsible for managing the laser guide star program at SDIO, approached Bill Thompson at AFWL about taking the step to declassify the laser guide star work. Thompson contacted Bob Fugate, who became a strong advocate for this idea. He and others firmly believed that astronomers in the academic community were on the verge of duplicating guide star experiments that military scientists and contractors had already demonstrated in the 1980s. While many others would eventually endorse the move to declassify, Meyer, Thompson, and Fugate led the charge.8 In 1990, while commander of the Weapons Laboratory, Colonel John Otten convened a number of preliminary discussions with Thompson, Fugate, Colonel John J. Russell (director of the lab’s Advanced Radiation Technology Office), and a few others to address the pros and cons of declassifying at least portions of the program. A number of events over the previous 7 years prompted these discussions. For a long time astronomers outside the defense community had been searching for ways to use adaptive optics to produce clearer images of objects in space and documenting their progress.9 Two French scientists, Renaud Foy and Antoine Labeyrie, in 1985 published an influential article contending that it was feasible to use Rayleigh scattering from molecules in the atmosphere and resonance scattering from sodium atoms as laser guide star techniques for adaptive optics systems. Edward Kibblewhite from the University of Chicago and Laird Thompson from the University of Illinois were among a growing number of American astronomers also conducting and publishing research on laser guide stars. Foy and Labeyrie, as well as their American counterparts, were following

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avenues of research that the Air Force and Lincoln Laboratory had already successfully completed.10 Publication of the Foy and Labeyrie paper stirred speculation that someone may have leaked information about the principles of Rayleigh and sodium guide stars. It seemed an odd coincidence that the French paper covered so much of the same information discussed at the 1982 and 1983 Jason summer sessions. Timing seemed also to have played a role. The findings of the Jason summer sessions appeared in two classified reports issued by the MITRE Corporation in McLean, Virginia—the first in 1982 and the second in 1984. Only a year after the second MITRE report, the Foy and Labeyrie article appeared in the open literature. Although no concrete evidence ever surfaced that a Jason member had leaked information, circumstantial evidence caused suspicions to linger in the minds of some through the end of the 1980s. Others such as Chuck Primmerman and Darryl Greenwood put no credence in the leak theory. Greenwood said he asked Foy directly how he came up with the Rayleigh guide star principles he discussed in his 1985 article. Foy’s answer was, “without any help from the United States.”11 Because astronomers (with the possible exception of Foy and Labeyrie) knew nothing about the classified government programs on adaptive optics, they unknowingly expended an enormous amount of time, money, and resources investigating concepts already tried and proven. The duplicated research included detailed measurements of atmospheric turbulence, simulation of laser guide star techniques based on complicated modeling methodologies and computer codes, and experiments that supported or rejected specific compensation techniques. As one government official described it, civilian astronomers were “adopting approaches to solve the atmospheric compensation problem which were in many ways identical to DoD-sponsored work, although the DoD programs were significantly more mature in terms of sophistication of technology and results achieved.”12 This posed a dilemma for the Air Force. If the Air Force kept its own research under wraps, astronomers would waste their time and taxpayers’ money conducting duplicate research. Yet to release the information might benefit the nation’s enemies. The basic question for the Air Force in 1990 became, was it still necessary to keep the laser guide star work classified?13 The answer to that question was no, and the Air Force and SDIO leadership worked closely first with the Weapons Laboratory and then with Phillips Sharing the Gold

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Laboratory to declassify much of its laser guide star findings. Colonel Otten helped ensure that bureaucratic obstacles were overcome to allow the declassification process to proceed. (On 13 December 1990, with the inactivation of AFWL and the formation of Phillips Laboratory at Kirtland AFB, Otten relinquished his duties as AFWL commander and was reassigned to head up the Lasers and Imaging Directorate at Phillips Laboratory.)14 Thompson played a big role in the decision to release the information to the public. He strongly believed that declassification of most of the laser guide star material would benefit both the Air Force and the astronomy community, give Air Force scientists (military and civilian) the credit and recognition they deserved for their contributions to adaptive optics, and enhance the Air Force’s reputation to the worldwide scientific community, to university astronomy departments, and to the public. As long as their work was classified, Air Force scientists were prohibited from publishing their findings in scientific journals.15 Extensive study and analysis took place before the final decision was made to declassify. (The discussion focused on laser guide star work by SOR and Lincoln Laboratory, not the more general topic of adaptive optics. Techniques to correct for distortions in light waves by using wavefront sensors, high-speed processors, and deformable mirrors went back to the 1970s and were not classified.) Because the commanders of the Weapons Laboratory and Phillips Laboratory had authority to declassify material, Thompson and his group did not need outside permission. But they prudently consulted with higher authorities and a number of government agencies before making a decision.16 As a first step, Thompson drafted a letter that was signed by Russell and sent to sixteen organizations that had access to the Air Force adaptive optics program—including the National Science Foundation, Air Force Systems Command, Air Force Space Command, the Secretary of the Air Force Office for Acquisition, DARPA, the Air Force’s Foreign Technology Division, the Jasons, the Defense Intelligence Agency, and SDIO—asking for their comments on declassification. Thompson had previously been in contact with and had briefed some of these organizations beforehand.17 With the letter, Russell attached a paper summarizing the benefits and costs of declassification. The attachment pointed out that astronomers had been duplicating work done by the HAVE REACH program and were

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Photo 25. Colonel John Russell spearheaded the effort to

get input from other government agencies on the decision to declassify adaptive optics research.

publishing their findings in scientific journals for all, including our adversaries, to see, and pointed out the potential benefits to both civilian and military scientists as well as the risks of releasing information from which the country’s adversaries might benefit.18 Most of the concern about declassification focused on the drawbacks of giving an adversary information that could support development of ground-based laser systems for either ballistic missile defense or antisatellite weapons. However, some did not believe the threat was that great, arguing that the knowledge would be useless without complex and Sharing the Gold

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expensive equipment—such as high-speed processors, integrated circuits, and deformable mirrors—which was not readily available in the Soviet Union and elsewhere. The Foreign Technology Division—which kept a close eye on the level of military technology in countries around the world— wrote to Colonel Russell that AFWL’s planned declassification would not likely result “in a significant Soviet gain of military capability.” Moreover, the demise of the Soviet Union and Russia’s subsequent economic struggles left the country with fewer financial resources to devote to the military. In the eyes of many American officials, the threat from that quarter had greatly diminished.19 Other potential consumers of the declassified information were easier to assess. Astronomers were interested in laser guide star technology only for the purpose of obtaining better images of dim space objects, and their work did not threaten the American military establishment. Guide star technology for astronomy did not cross over into the more sensitive areas of satellites, point-ahead problems, and high-power lasers associated with ground-based laser antisatellite research.20 Although there was some risk involved in releasing laser guide star information, Russell, Thompson, Otten, Fugate and others believed sharing information with civilian astronomers would benefit the Air Force in the long run. It would make more brainpower and private research dollars available to pursue a wide range of alternative solutions that would improve laser guide star techniques and adaptive optics in general. As Russell put it, “Because of funding limitations, the astronomy community is likely to be innovative in developing approaches to atmospheric compensation which are less expensive and time-consuming to implement; these approaches may have a direct pay-off to DoD programs.”21 The response Russell received to his letters was positive. Input from Dr. Wayne Van Citters of the National Science Foundation (NSF)—the lead agency for the support of ground-based astronomical research in the United States—represented the general feeling among the organizations polled: declassification would be an exceptional opportunity that would benefit the astronomical community and the government. Van Citters was one of the few astronomers outside the military with a security clearance. He had acquired it in 1979 while a consultant to a number of defense contractors and later while working for SDIO developing detector concepts for

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large telescopes. It was through SDIO that he was given access to the Air Force adaptive optics program.22 Van Citters explained that the NSF was convinced that the next generation of ground-based telescopes would deploy mirrors 2.5 meters in diameter and larger. Adaptive optics would be an absolute necessity for these larger telescopes to produce near-diffraction-limited images. Van Citters’s enthusiasm ran high over the possibility that the Air Force might be willing to share its technical accomplishments with the civilian world. He felt the military’s support was essential for improving the performance of groundbased telescopes. Van Citters made an exceptionally strong appeal in favor of declassification when he wrote back to Colonel Russell: Without assistance [declassification] the astronomical community would have to rediscover much of the basic knowledge that has already been obtained with the Department of Defense support. The availability of the technology and knowledge base from HAVE REACH research would be a tremendous boost to this effort [adaptive optics] in the United States. The value of such a contribution is difficult to quantify, but a conservative estimate would be a savings of at least five years of research and development effort and many millions of dollars. That savings translated to “valuable and scarce astronomy dollars” that would not have to be expended for “a re-invention of the wheel.”23 Van Citters mentioned other tangible benefits that he was confident would be derived from declassification. First, the exchange of information among civilian and military scientists would almost certainly help astronomers as well as benefit “the future defense related programs as the astronomical community pursues developments stressing a different set of performance parameters and applications.” In other words, astronomers might come up with their own breakthroughs in adaptive optics that could be applied to Air Force operational systems. The Jasons sent a similar response, predicting that once astronomers were given access to the military’s guide star program, chances were good that their research would help the DoD programs. The Jasons also pointed out that, if the Air Force did not declassify its guide star work, it was only a matter of time before civilian Sharing the Gold

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astronomers would develop the technology on their own. Claire Max, a respected astronomer (currently director of the Center for Adaptive Optics at the University of California at Santa Cruz) and the first woman to serve on the Jasons, was a strong advocate for the Jasons’ position that the time was right to declassify the government’s adaptive optics research.24 Second, Van Citters pointed out that European astronomers’ publications had captured a large share of the spotlight shining on adaptive optics and argued that it was time that American scientists be given full credit for their research achievements. “They deserve the recognition of their colleagues in the astronomical community,” wrote Van Citters, “and the satisfaction of seeing their efforts under Department of Defense sponsorship help to establish a solid leadership role for the U.S. in this highly visible and popular scientific field.” Van Citters’s assessment of this issue closely matched the position of Phillips Lab and the Air Force.25 The NSF was eager to obtain the most up-to-date information on the military’s progress with adaptive optics, but also viewed declassification as an opportunity for civilian astronomers to acquire expensive stateof-the-art hardware from the government. Following up on that idea, Frederick M. Bernthal, the acting director of the NSF, wrote to the director of the Strategic Defense Initiative Organization, Henry F. Cooper, asking if SDIO might be willing to transfer to the NSF some of the adaptive optics equipment left over from a Lincoln Laboratory experiment conducted at the Air Force’s Maui Optical Site in Hawaii. “Such transfer,” Bernthal argued, “would provide an enormous boost in this effort [research by astronomers] and would be an extremely valuable and visible spin-off from the Strategic Defense research program.” Although the Air Force did not transfer the hardware to the NSF, the government did make arrangements later in the 1990s for civilian astronomers to have access to a variety of governmentowned adaptive optics equipment and to conduct experiments at Starfire Optical Range and Maui. On the other hand, Lincoln Lab did transfer its Atmospheric Compensation Experiment adaptive optics system, used in Strategic Defense Initiative research in the 1980s, to the 60-inch telescope at Mount Wilson in southern California, where it became the first adaptive optics system used in civilian astronomy to image a star after correcting for the effects of atmospheric turbulence.26 There was another important reason Van Citters believed the time was

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right to release the Air Force guide star information. Publication of Foy and Labeyrie’s article in 1985 had stimulated civilian astronomers’ interest in the potential of laser guide stars. As a result, scientists at American universities began submitting grant proposals to the NSF for guide star research, which put Van Citters in an awkward position. Based strictly on scientific merit, he should logically disapprove a proposal on laser guide stars, because he knew that a classified program had already accomplished the research. It did not seem reasonable that tax money should pay for the same research twice. But he could not give this classified explanation to a prospective researcher who did not hold a clearance.27 Van Citters asked for advice from Bob Fugate and Darryl Greenwood. Since there were only a few such proposals, they suggested that it might be wise to grant them NSF funding. One reason was that the number of astronomers interested in adaptive optics was much larger in the civilian world than in DoD. So it would not be a bad idea to approve a few NSF research grants to university researchers who could form a small cadre of civilian experts in laser guide star technology. Another reason was to prevent American researchers falling too far behind the French. With NSF support, American researchers would be in a better position to come up with ideas that could advance adaptive optics beyond what the military had already accomplished. For example, their work might result in improved wavefront sensors and deformable mirrors that could lead to development of an industrial base capable of manufacturing adaptive optics equipment from which the military could benefit. That was a compelling argument.28 Although the NSF did award academic scientists a limited number of grants in the late 1980s, they were only a small minority of American astronomers, and they were conducting research without the benefit of guide star knowledge that the Air Force possessed but could not disclose. To devise a way to share more information with civilian astronomers, Thompson moved forward from informal discussions on declassification to a formal review. The goal was “to provide the information needed to make a rational choice among various options for classification and public release policies for adaptive optics and artificial beam technologies in the compensation for atmospheric turbulence.”29 Thompson realized from the start that he and others would have to do their homework if they expected to convince the Phillips Lab commander, Sharing the Gold

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Colonel Peter J. Marchiando, that it would be in the best interest of the Air Force to declassify the laser guide star information. Marchiando, as commander, had the power of original classification authority, which meant he could declassify any research program work that took place under the organization he commanded. Realistically, however, the commander would be acting on behalf of the entire Air Force on a very sensitive issue if he decided to declassify the laser guide star work. Therefore, it came as no surprise to anyone that he expected Thompson and his group to conduct a thorough and objective assessment before deciding for or against declassification.30 Based partially on responses to the letters Colonel Russell had sent out earlier, Thompson began his formal assessment by developing a benefits and cost analysis for each possible option. Those options ranged from keeping the program classified to five varying degrees of declassification.31 Thompson’s team recommended first to Colonel Otten that the DoD declassify information related to artificial beacons—concepts, theories, and experimental results that pertained to laser guide stars. Fugate was the strongest supporter for declassification, believing that the benefits of sharing information with astronomers outweighed the cost of disclosing technology to our adversaries.32 The main benefit of sharing information, Thompson argued, was that it would create stronger ties between astronomers and the Air Force. That new relationship would bring academic astronomers up to the same level of technical maturity as the Air Force scientists who had participated in classified programs. They would then be able to function as a “second team” and come up with new adaptive optics techniques that could benefit the Air Force.33 Otten agreed with Thompson’s endorsement for declassifying the laser guide star work, but he wanted to make sure not to act prematurely. He sent a letter in March 1991 to the same organizations that Colonel Russell had contacted in June 1990. Otten attached Thompson’s report, plus a description of how the declassified information would be released.34 Otten asked each recipient to review and comment on the Phillips Lab’s assessment process. The response was uniformly supportive. Darryl Greenwood from Lincoln Laboratory’s Optics Division wrote: “I want to applaud your efforts in revising classification policy regarding adaptive

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optics using artificial beacon technologies.” He was encouraged that the Air Force was on the verge of making “a wealth of technology and knowhow” available to astronomers. Knowing that the key to make the declassification decision stick was the issuance of a new classification guide, his final comment to Otten was, “I urge you therefore to move expeditiously on the revisions to the classification guide.”35 As expected, Wayne Van Citters strongly endorsed the proposal. “This action,” he wrote, “would provide information and technology of enormous value to the astronomical community.” He offered his support for a joint DoD/NSF conference as outlined in Otten’s implementation plan. This event would bring together Air Force and academic scientists to share information for the advancement of adaptive optics. In particular, it would give Air Force scientists an opportunity to make presentations covering the technical details of their newly declassified work to all interested astronomers. The conference was tentatively planned to take place in Albuquerque in December 1991.36 A second part of the implementation strategy involved arranging for a special issue of the Journal of the Optical Society of America devoted exclusively to adaptive optics and artificial beacon technology, with a separate editor and a good cross-section of papers representing scientists from government, academia, and private industry. Publication was planned for 1992.37 Once Otten received feedback, he acted quickly. He met Thompson and his group in mid-April; the group was unanimous in favor of declassification. Otten and Thompson next brought their case for declassification to Marchiando. The Phillips Lab commander was impressed by the thoroughness of the assessment process. He also took into account the rationales offered by outside organizations in support of declassification. Marchiando made the final decision in late April 1991 to approve the declassification of laser guide star technologies. Declassification would not become official, however, until the revised classification guide was complete. Thompson had already been working on that for months and was able to distribute it on 15 May 1991. The new guide, signed by Colonel Marchiando, became effective immediately. Even though HAVE REACH information was declassified, each request for information still had to be reviewed by the appropriate government public affairs office before the information could be released to the public.38 Sharing the Gold

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The Announcement Publication of the revised HAVE REACH classification guide, arrangements for the special edition of the Journal of the Optical Society of America, and the planned laser guide star adaptive optics workshop were all critical elements of Phillips Laboratory’s plan to release material on laser guide stars. But of more immediate concern was the need for a dramatic announcement of the Air Force’s successful laser guide star experiments. Bob Fugate would make the announcement. The 178th meeting of the American Astronomical Society (AAS) in Seattle in May 1991 provided the ideal setting for Fugate to announce that his laser guide star work was an unqualified success and that information about it could now be released to the public. A large crowd was expected to attend. Fugate’s proclamation at such a prestigious gathering would represent a huge step by the Air Force in terms of technology transfer by the military to astronomers. But it almost did not happen, because Fugate’s paper was not cleared for public release until the last moment.39 Three months before the AAS conference, Charles H. Townes, who shared the 1964 Nobel Prize for physics, had placed Fugate and Primmerman on the AAS program with identical titles for their presentations. Townes had a security clearance and a strong interest in adaptive optics. He had followed the research at Starfire Optical Range and made two site visits. With Townes’s influence, Fugate and Primmerman would participate in the AAS session listed on the agenda under “Atmospheric Fluctuations: Their Nature and Techniques for Compensation.” Both talks were entitled simply “Adaptive Optics Experiments” and had to be sent up the chain of command for review, first at various Air Force levels and then at the DoD, which would make a final ruling as to whether or not the papers would be cleared for public release. This took time.40 On 1 March, DoD notified Fugate that the title and a one-paragraph abstract of his paper had been cleared, with a reminder that “Clearance of abstract does not satisfy requirement for clearance of entire paper.” DoD wanted time to scrutinize the entire paper before clearing it. However, Fugate was able to submit the cleared title of his paper, which now read “Experimental Discussion of Real Time Atmospheric Compensation with Adaptive Optics Employing Laser Guide Stars,” for inclusion on the AAS Bulletin’s list of papers that would be presented at the Seattle meeting. Fugate, very much

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aware of others’ contributions to the first laser guide star work, listed 16 coauthors: C. H. Higgins, J. L. Wynia, W. J. Lange, A. C. Slavin, W. J. Wild, M. P. Jelonek, M. T. Donovan, S. J. Cusumano, and J. M. Anderson, all from Phillips Laboratory’s Starfire Optical Range; J. M. Spinhirne, B. R. Boeke, and R. E. Ruane, from Rockwell Power Systems in Albuquerque; J. A. Moroney, K. S. Nickerson, and D. W. Swindle, from Adaptive Optics Associates, United Technologies Optical Systems, in Cambridge, Massachusetts; and R. A. Cleis from the Optical Sciences Company in Placentia, California.41 Once the AAS Bulletin was sent out, some people became curious about, and even suspicious of, what Fugate and Primmerman were going to talk about. A number of people called Fugate to ask for details about his presentation. Fugate explained that he could not pass on any information because his paper had not yet been cleared by DoD.42 Two months passed and then another two weeks, but the DoD still had not cleared Fugate’s and Primmerman’s papers. With the AAS meeting date fast approaching, Fugate suspected that Townes used his influence to get the DoD to expedite clearance for the two papers. Although he had nothing in writing, Fugate deduced from the rumor mill that in all probability either Secretary of Defense Dick Cheney or President George Bush made the final declassification decision. On 21 May, only a week before the Seattle meeting, Fugate and Primmerman received notification that their papers had been cleared.43 When Fugate walked up to the podium at one o’clock on 27 May to deliver his paper, he was a little nervous as he gazed out across the audience in the jam-packed room. Nearly 400 people had showed up, some standing two to three deep in the back and along the side walls. Fugate was overwhelmed with the scene; he had never talked to more than thirty people at a time on the topic because of its classified nature. He sensed anticipation in the air; rumors had circulated at the conference that his and Primmerman’s papers would reveal some technological breakthrough in adaptive optics and the use of laser guide stars.44 Fugate did not disappoint the audience; he got to the heart of the matter right away. The first words out of his mouth were delivered in a confident and deliberate manner: “Ladies and gentlemen, I am here to tell you that laser guide star adaptive optics works!” To provide historical substance and scientific credibility to his opening statement, Fugate had projected two Sharing the Gold

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Photo 26. Bob Fugate showed this image during his presentation at the American Astronomical Society Meeting in Seattle on 27 May 1991 to demonstrate the success of Rayleigh laser guide star adaptive optics.

images of the binary star 53 Ursa Major on a large screen behind him. The uncompensated image shown on the left appeared as essentially a blank in the heavens. But the image on the right, compensated with laser guide star adaptive optics, was dramatically clear, an improvement greater than a factor of 25 over conventional astronomical imaging. Fugate explained that the photo “was taken while the deformable mirror was continuously correcting atmospheric wavefront distortions.” For a brief moment there was silence as the audience tried to grasp the significance of Fugate’s startling announcement. Within seconds, the silence was replaced by noisy chatter as the astronomers turned to one another and began muttering about the amazing image that they had just seen.45 Fugate explained that the 53 Ursa Major image was made on 16 March 1990, more than a year after the SOR team had closed a laser guide star loop

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for the first time as part of the Gen I experiment. He told the AAS audience that the Air Force had sponsored laser guide star adaptive optics research since 1982—a shocking revelation to the academic astronomers in the audience—and described his first laser guide star experiment, conducted in fall 1983. Because of the time restraints on his presentation, it was impossible to cover the full history of nearly a decade of Air Force laser guide star work. Instead, he showed the hardware used at SOR, along with a series of other compensated images—as he told the gathering, “just to convince you that we didn’t get one lucky picture.” Although he skipped over most of the technical details—theory, design, and performance of the hardware—Fugate promised that information would be shared at future joint workshops between military and academic astronomers and through publication of scholarly and technical articles.46 Primmerman followed Fugate’s talk with a short presentation on Lincoln Laboratory’s successful sodium laser guide star experiments at White Sands and Maui. Fugate described the scene when the floor was opened for questions as “a forest of hands that went up!” Thompson, sitting in the audience that day, recalled it was “quite a day” as the astronomers were simply flabbergasted by the release of previously classified information. “A lot of people in the audience,” Thompson observed, “were stunned by the amount of work that had already been done by DoD when that was presented at the meeting.” Wayne Van Citters remembered that the people witnessing Fugate’s and Primmerman’s presentations slowly leaned back in their chairs, mentally regrouped, and reacted with one telling word—“Wow!”47 One of the more humorous aspects of the meeting took place when the Fugate/Primmerman portion of the session ended. Laird Thompson, an astronomy professor from the University of Illinois at Urbana-Champaign, was scheduled to speak next on his research on adaptive optics. He was in the unenviable position of following the Fugate/Primmerman talks. As a sheepish Thompson approached the podium and turned to face his audience, he hesitated for a moment and then good-naturally blurted out, “I’ve never felt so scooped in my entire life!” Those in the still buzzing crowd grinned and grimaced at the same time in empathy. Thompson took only a few minutes to summarize his paper and then conceded the remainder of his time to allow the highly charged audience to ask more questions of Fugate and Primmerman.48 Sharing the Gold

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Photo 27. The day after his formal presentation to the American Astronomical Society, Bob Fugate briefed the press on his revolutionary laser guide star findings, while Charles H. Townes (center) and Chuck Primmerman (next to Townes) looked on.

After Thompson sat down, Fugate was bombarded with more questions from the energized astronomers in the audience. How do you do this? What kind of hardware and instrumentation is required? Does it really work outside the laboratory? Where can I get one of these? What are the downsides of the technology? How much does it cost? Can it go on any telescope? How can we get more information? Fugate fielded the questions as best he could, but only covered the tip of the iceberg in his responses because of time restrictions. However, the next day at a news conference at the AAS meeting, Fugate reached out to a larger audience by explaining to reporters the significance of the guide star research and the effect it would have on the military and on astronomers.49 There would be more time available later to share the nearly 10 years of DoD-sponsored research with astronomers. In addition to one-to-one talks at the meeting and Fugate’s news conference, there were two more

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formal public forums for the newly released information. One was a workshop arranged by Fugate and Primmerman and held in March 1992 in Albuquerque. The second was the publication in January 1994 of a special edition of the Journal of the Optical Society of America devoted to adaptive optics. The workshop and the journal were the key parts of Phillips Lab’s plan to release as much of the newly declassified information as possible.50 Fugate and Primmerman took the lead in arranging the Albuquerque workshop, as they were the ones who had made the revolutionary announcements at the Seattle meeting. But neither had a good feel for how many people would show up. Primmerman did not think many people would attend, so Fugate reserved a Phillips Lab conference room that could accommodate 50 or 60 attendees. Within three or four days after the workshop was announced, Fugate was inundated with calls. Over 200 people said they planned to attend. After some last-minute maneuvering, Fugate was able to secure Kirtland’s West Officers Club as the new site of the workshop. The extra space was needed: 205 people showed up to fill the room, including astronomers from Germany, Canada, France, Japan, and Great Britain.51 To add a sense of historical perspective to the workshop, Horace W. Babcock, who had first proposed the concept of adaptive optics back in the 1950s, was invited to make the keynote address. When he got up to speak, the audience waited with great anticipation as to what the venerable dean of adaptive optics would say. Babcock, who now worked at the Carnegie Institution in Washington, looked the audience squarely in the eye, made sure he had their attention, and said in a clear voice, “What took you guys so long?” When the laughter subsided, he went on to deliver his talk on the tremendous strides that had been made in astronomy from the 1890s to the present.52 Fifty-eight presentations followed Babcock’s talk. The papers were divided among four topics: basic principles and experiments, theory, astronomy programs, and applications and components. Fugate presented his experimental findings on Gen I and Gen II, the latter having taken place after the Seattle meeting. Primmerman explained results from Lincoln Laboratory’s SWAT experiment. With Fugate as editor, the papers were published in two volumes, creating a valuable reference source for both the DoD and civilian astronomers.53 A long list of top achievers—a virtual Who’s Who in adaptive optics— made presentations. Francois Roddier, from the Institute of Astronomy at Sharing the Gold

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the University of Hawaii, and Edward Kibblewhite, from the University of Chicago, talked about laser beacons. Government and contractor personnel who had participated in the classified adaptive optics programs in the 1980s presented many of the papers. For example, David Fried, the respected mathematician from the Optical Sciences Company, discussed the complexities of focal anisoplanatism and its effect on laser guide stars. Mark Ealey from Litton/Itek Optical Systems spoke on low-voltage requirements of deformable mirrors. Brent Ellerbroek spent his allotted time on adaptive optics performance predictions under good seeing conditions at Starfire Optical Range.54 The impressive speakers accounted in large measure for the success of the workshop. The astronomers in the audience having access for the first time to the technical details of the previously classified information were simply blown away. Perhaps even more beneficial and rewarding than the formal presentations were the private conversations that took place in the hallways during the breaks. At the end of the workshop, Otten commented, “I don’t think there is anybody in the professional community who should doubt that atmospheric compensation has been demonstrated.”55 One of the highlights of the workshop was a tour, three nights in a row, of Starfire Optical Range, where Fugate showed off the 1.5-meter-telescope and demonstrated the laser beacon. He also showed workshop attendees the site under construction at SOR that would eventually house the 3.5-meter telescope. Needless to say, the academic astronomers were especially taken with the scope and up-to-date hardware of the SOR operation. It was obvious to them that the military had invested heavily in adaptive optics, creating a firstrate research enterprise that had to be the envy of any university astronomy department. There was no denying that adaptive optics was an expensive long-term venture that had been bankrolled to a large degree by the massive financial resources of the DoD. This reinforced the notion that most university astronomy departments could not afford the expensive telescopes and adaptive optics systems needed to compete in this field of research.56 Clearly, workshop participants gained a great deal of knowledge and the tours of SOR were a great success. The downside was that arranging tours created an extra workload for Phillips Laboratory and SOR staff. Fugate and his team were inundated with requests to tour the site over the next couple of years. As he described it: “We had forty tours a month. It was just everyone you could imagine. I mean huge amounts of people.” It took

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an incredible amount of work to conduct tours during the day and night at SOR. Not only did the tours themselves take time, but so did the logistical arrangements beforehand. Since SOR was in a remote and off-limits location, a myriad of security requirements had to be met for each visitor, and transportation had to be arranged from Kirtland to SOR and back in the evening and early morning hours. Although all this was labor intensive, the payoff was substantial, as the tours promoted the Air Force’s scientific reputation as the leader in adaptive optics research.57 The workshop presentations and the tours certainly put Phillips Lab’s adaptive optics contributions on the scientific map. The word spread quickly, but apparently did not reach everyone. A few months after the Kirtland workshop, Otten attended the Optical Society of America’s meeting in Maui, designed to establish long-term communication and collaboration among researchers in adaptive optics, and found some astronomers still expressing surprise over the clarity of images produced using adaptive optics. When one of the speakers showed an image of a star taken in the early 1980s using an Air Force closed-loop adaptive optics system at Maui, two academic astronomers sitting in the row in front of Otten were amazed. One astronomer leaned over to the other and in a troubled voice said, “He [the speaker] certainly must have meant this year, not ten years ago!” Otten recalled, “They just couldn’t believe it. They felt, how could this go on and they not knowing it? This was a group who thought they were well ahead and thought they were going to invent all of this and make their mark on science. It was very gratifying to hear all these professors and astronomer instrument developers who thought this was going to be theirs and in fact the Air Force had accomplished this some years before.” This was only one incident, but it revealed that a few astronomers had a hard time accepting that Air Force scientists had been far out in front of the university community for over a decade in the advancement of adaptive optics.58 Undoubtedly, face-to-face interactions at workshops and meetings served to strengthen cooperation among the various groups involved in adaptive optics—military, contractors, academia, and private institutions. Another means for disseminating information on adaptive optics was the written word: publication of a special edition of the Journal of the Optical Society of America in 1994. Rettig Benedict (W. J. Schafer Associates, Albuquerque), James B. Breckinridge (Jet Propulsion Laboratory, Pasadena, California), and Sharing the Gold

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David L. Fried (the Optical Sciences Company, Anaheim, California) served as editors; 29 articles on atmospheric compensation appeared in two consecutive issues—January and February 1994—of the journal.59 The purpose of the double special issue, as explained by Benedict, was “to present the results of the most recent experimental and theoretical advances in the compensation for atmospheric turbulence.” He pointed out that since the release of formerly classified material in May 1991, “a significant expansion in turbulence-compensation program activities has occurred.” Some of those advances were included in the journal articles, along with research that had taken place in the 1980s.60 The first four papers in the two-volume special edition provided a historical overview of adaptive optics research starting in the early 1980s. Will Happer’s paper appeared first. Originally a classified account written for the Jasons, Happer’s revised article discussed the early concept of creating artificial beacons for atmospheric-turbulence compensation using resonant backscattering from the sodium layer in the upper atmosphere. David Fried’s article followed and addressed the limitations of artificial guide stars caused by the effects of focal anisoplanatism. Ronald Parenti’s paper looked at how Lincoln Laboratory approached the use of laser guide stars for astronomical applications, while the fourth paper, authored by Fugate, covered laser guide star experimental work at SOR in the late 1980s and early 1990s.61 The remaining twenty-five journal articles covered a variety of topics on adaptive optics. Most focused on different aspects of laser guide star theory and field results obtained from Rayleigh and sodium backscattering experiments. Several considered the effects of thermal blooming on laser guide stars. Two articles discussed atmospheric compensation system designs for large-aperture telescopes. Collection and publication of these articles provided a comprehensive foundation and valuable reference guide—based on previously classified research—for astronomers from a diversity of institutions to use to further advance adaptive optics.62 The overwhelming response to the journal’s two-issue special edition was favorable. Not only did the articles open up a valuable source of information, but their publication recognized the military’s civilian scientists for their groundbreaking work over the last 10 years. Rett Benedict, who served as one of the editors, pointed out that the vast majority of astronomers were delighted with the progress that had been accomplished on

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adaptive optics by the military, because they knew these advances could be applied to future telescopes and help astronomers produce high-resolution images of heavenly bodies.63 Benedict recalled only one negative incident related to the special issue. He received a letter from a professor who had been conducting research in adaptive optics. Although his reasons were not completely clear, the professor wrote that he did not believe that people involved in classified work should get any credit for advances in research conducted “behind closed doors.” Benedict’s response to the professor was that military and civilian scientists had to be just as creative as their counterparts in making new scientific discoveries. Just because other people, including university professors, did not know about the classified research, did not change the fact that military and government scientists deserved credit for their findings.64 Fugate attested to the massive outpouring of respect and credit from astronomers in recognizing the military’s leading role in adaptive optics laser guide star work. For the most part, there exists a high level of mutual admiration between DoD scientists and university astronomers. Fugate put it best when he said, “I have never seen such support for government workers as I get from astronomers. Their respect and appreciation is truly amazing—even today.”65 Phillips Laboratory’s decision to declassify more than a decade of research proved beneficial for everyone. Astronomers now had access to a gold mine of information. As Fugate remarked, “One of the things declassifying this technology has done is give people the insight to know they are going in the right directions.” At the same time, the declassification allowed Air Force and contractor scientists to receive the recognition they deserved for their scientific and technical achievements in adaptive optics.66 The scientific reputation of the Air Force and Lincoln Laboratory soared with Fugate’s and Primmerman’s presentations in Seattle in May 1991. In addition, publication of the special edition of the Journal of the Optical Society of America offered strong testimony to the importance of the military’s groundbreaking contributions to adaptive optics. The Air Force’s next challenge would be to apply the technological advances it had discovered to the building of adaptive optics systems that could be mated with new large-aperture telescopes and operational systems under development such as the airborne laser. Sharing the Gold

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Strategic Defense Initiative

By early 1978, the Lincoln Laboratory work at West Palm Beach had wound down and come to a halt because Lincoln scientists believed they had accomplished what they had set out to do. Interest within the Air Force had also moved to shorter-wavelength lasers—such as the chemical oxygen-iodine laser or COIL, first developed at AFWL in 1977, and the Navy’s deuterium fluoride mid-infrared advanced chemical laser or MIRACL. Lincoln had shown at West Palm Beach that adaptive optics could improve but not completely correct for thermal blooming in high-energy lasers. Another reason for not proceeding with more work on thermal blooming was that at the highest levels in the Department of Defense there was a shift of emphasis away from tactical to strategic applications of lasers. First Air Force and DARPA leaders, and later officials at the Strategic Defense Initiative Organization (SDIO), wanted to investigate the potential use of short-wavelength lasers fired from the ground into space, which in general were less susceptible to thermal blooming than longer wavelength lasers. In the 1980s, Lincoln Lab scientists first conducted work on guide stars and then an assortment of other laser/adaptive optics experiments through the early 1990s.1 In January 1983, Marquet left Lincoln Laboratory to join DARPA. His new workplace was on Wilson Boulevard in Arlington, Virginia, just across the Potomac River from the nation’s capital. Bob Cooper, DARPA’s director, asked Marquet to head the organization’s Directed Energy Office. His

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previous experience made Marquet a good fit at DARPA. As one coworker described it, Marquet brought with him “lots of ideas, lots of balls in the air” and was “very energetic and enthusiastic” when he arrived. Many of the projects he was responsible for explored the feasibility of projecting lasers into space to kill targets, specifically missiles and satellites. However, DARPA also looked at other possible applications of lasers. That included using lasers to power future space stations, to communicate with submarines, and for other communication functions, such as bouncing them off space mirrors to ground receivers in place of transmission wires.2 DARPA was not the only organization interested in potential future technologies. In spring 1982, George Keyworth, science advisor to President Reagan, brought together a group of prominent scientists to study new technology options and make recommendations to the president as part of his modernization program for the military. The group was made up of Saul Buchsbaum, David Packard, Edward Teller, and Edward Frieman, who chaired the panel. This was part of a huge military buildup that represented a fundamental shift from the Carter administration’s policy, which had reduced the amount of money spent on national defense. The panel’s job was to take a broad look at the military, across all services, and to identify innovative technologies that could make a difference to military capabilities. Ballistic missile defense was only one part of the program. The panel delivered its final report to the White House Science Council in January 1983, two months before the president gave his landmark Strategic Defense Initiative (SDI) speech.3 The highly classified report was pessimistic about the feasibility of using directed-energy technologies—lasers, microwaves, and particle beams— for developing weapon systems, because they simply had not shown sufficient scientific progress and maturity. Teller, a passionate proponent of lasers in space, vigorously disagreed with the report’s conclusions, saying, as Edward Frieman later remembered, that “the report should be trashed and never see the light of day.”4 There was one notable exception to the panel’s overall negative conclusions. The report singled out adaptive optics as the most promising technology for compensating for atmospheric turbulence in light beams. Panel members arrived at that conclusion based on the successful research at Rome, Kirtland, and Maui. Frieman noted that adaptive optics was a “clever” technology that was appealing because it was understood in terms

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of its theoretical concept and basic science. Moreover, the Air Force had demonstrated that an adaptive optics system could work effectively on its 1.6-meter telescope at Maui (the CIS or compensated imaging system described in chapter 3).5 Keyworth believed that adaptive optics would strengthen the nation’s strategic defense system for several reasons. At the time the report came out, one of the leading proposals advocated by Edward Teller was a space-based X-ray laser system called Excalibur. It would rely on a nuclear explosion in space to generate laser beams that would destroy intercontinental ballistic missiles launched at the United States. Many scientists were skeptical of this plan, because even if the system worked, it would be extremely vulnerable to enemy countermeasures and far too expensive to maintain. Keyworth and others believed that adaptive optics offered a more realistic alternative. If adaptive optics could remove distortions in a laser beam caused by atmospheric turbulence, then a beam transmitted from the ground would have a good chance to intercept an enemy missile. And a laser system installed on the ground could be maintained and defended more easily and at less cost than a space-based system.6 Keyworth believed that adaptive optics was not the end-all solution but a key element to modernizing the existing strategic force structure, the triad of strategic bombers, ICBMs, and submarine-launched missiles. As an enabling technology for an antimissile defense system, adaptive optics could complement and enhance the land-based ICBM leg of the triad by making it more survivable. Also, under this scenario, because success would be less certain, the Soviets would be less tempted to launch a first strike against American land-based ICBMs. Advice to combine adaptive optics with lasers was the type of input that influenced President Reagan’s decision to pursue a revolutionary strategic defense system under his SDIO program.7 Recognition of adaptive optics at the highest level of government encouraged military scientists to invest more money and resources in it. With the establishment of SDI, the Air Force laboratory system, DARPA, and Lincoln Laboratory renewed their commitment to adaptive optics; the consensus was that this technology would work. Over the next two decades, adaptive optics made astonishing progress. Today, nearly every new largeaperture telescope in the world is equipped with adaptive optics. In addition, adaptive optics is an enabling technology for the airborne laser (see Strategic Defense Initiative

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chapter 9), currently under development and designated to serve as the nation’s first high-energy laser weapon system. Marquet’s stay at DARPA was relatively short; President Reagan’s 10-minute “Star Wars” speech to the nation on 23 March 1983 changed everything about strategic thinking. Reagan’s unexpected pronouncement made clear that the nation would focus its resources on the development of strategic space-based weapons to defeat the Soviet ballistic missile threat. The president wanted to make nuclear weapons “impotent and obsolete”; the way to do that was for the United States to move forward with a “comprehensive and intensive effort to define a long-term research and development program, to achieve our ultimate goal of eliminating the threat posed by strategic nuclear missiles.” The press dubbed the president’s presentation his “Star Wars” speech. Reagan objected to this name because it gave a science-fiction aura to a serious goal: moving away from a strategic balance of terror, known as mutual assured destruction, which counted on the fear of annihilation to prevent either side from launching a first strike and had resulted in 30 years of dangerous brinksmanship between the two superpowers.8 The president argued strongly for replacing that approach with a ballistic missile defense. Such a system would intercept missiles during various phases of flight—boost, mid-course, and terminal—toward their targets. This intercept capability would in theory deter the Soviets from launching a nuclear attack, knowing that all their missiles would not get through the U.S. defensive shield. But to some, including the Soviets, the name Star Wars gave an offensively aggressive tone to the new proposal. It seemed plausible to antinuclear and peace groups that SDI weapons could be used not only for defense but also to attack enemy satellites. In addition, a country immune from retaliation might feel free to launch its own nuclear attack. The Kremlin certainly viewed SDI in this way. However, the president responded to his critics by repeating the question he used in his 23 March speech: “Wouldn’t it be better to protect the American people rather than avenge them?” That simple message was intended to convince the public that a shift to a strategy based on defense was the most effective and realistic way to respond to the enormous buildup of Soviet conventional and nuclear forces over the last 20 years.9 Why did Reagan, who was not by any stretch a deep scientific thinker, decide to make his SDI speech, especially in light of the scientific evidence

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he had at his disposal from the Frieman panel and other sources? Frieman speculated, “I think he honestly believed that if a bunch of smart people worked on this problem [ballistic missile defense] they could solve it and then he could protect the country. Simple as that.”10 Although Reagan’s decision may not have been difficult to make, implementation of the new policy was complex and challenging. Two days after his speech, Reagan issued a broad policy statement in National Security Decision Directive Number 85 to begin implementing an SDI program. He tasked his national security advisor, William P. Clark, to formulate detailed instructions for a study “to assess the roles that ballistic missile defense could play in future security of United States and our allies.” Reagan also directed a second study be conducted “to define a long-term research and development program” that would lead to the defeat of any enemy-launched missile attack against the United States.11 Reagan appointed James C. Fletcher from the University of Pittsburgh (a former chief administrator of NASA from 1971 to 1977) to lead a study to assess technologies for defeating a ballistic missile attack. Richard D. DeLaurer, undersecretary of defense for research and engineering, oversaw the work of Fletcher’s Defensive Technologies Study Team, also called the Fletcher Commission. The group worked from 1 June to 1 October 1983, an extremely short time to evaluate such a large and complex topic. Directedenergy weapons emerged from the study as one of five technical areas that SDIO should vigorously pursue. The other four areas involved technologies for (1) surveillance, acquisition, and tracking, (2) kinetic-energy weapons, (3) systems analyses and battle management, and (4) survivability, lethality, and key technologies.12 The main goal of directed-energy research was to develop weapons that could intercept ballistic missiles when they were most vulnerable: in their boost phase (immediately after launch, when the missile is slowly gaining altitude) or post-boost (when the missile has reached full velocity, but before decoys can be deployed). The Fletcher team envisioned using powerful ground- and space-based lasers with sophisticated adaptive optics systems to clean up the beam and accurately direct it to its target, whether the target was in space, in the air, or on the ground.13 The Fletcher study, along with a separate study—the Future Security Strategy Study (FSSS), directed by Fred C. Ikle, undersecretary of defense Strategic Defense Initiative

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for policy, which assessed the political and military implications of the new ballistic missile defense system—convinced Reagan in September 1983 that he was right to go ahead with SDI. Two teams, an interagency team headed by Franklin C. Miller, director of the Pentagon’s Office of Strategic Forces Policy, and a team of consultants led by Fred S. Hoffman, contributed to the final FSSS. The Hoffman report endorsed the president’s strategy to place increased reliance on defensive systems. The defense consultants arrived at a similar conclusion: “U.S. national security requires vigorous development of technical opportunities for advanced ballistic missile defense systems.” It seemed clear that the “vigorous development” would be carried out in large part by SDIO. Findings of the Fletcher study (seven volumes of closely guarded technology assessments along with a 5-year research and development plan) and the two FSSS panels were basically identical in urging the president to pursue the missile defense program.14 Nearly a year after his speech advocating a defensive shield against ballistic missiles, Reagan issued National Security Decision Directive 119 on 6 January 1984 to formally establish the Strategic Defense Initiative Organization. Secretary of Defense Caspar W. Weinberger formally set up SDIO on 27 March 1984 with the mission to establish a ballistic missile defense system. In a memo to all secretaries of military departments and directors of defense agencies, Weinberger attached “the highest priority to the Strategic Defense Initiative” and said that it required support from all DoD employees, both military and civilian. Weinberger also announced the president’s choice of Air Force Lieutenant General James A. Abrahamson as SDIO’s first director.15 Abrahamson was not the first choice for the SDI job, as the secretary of defense had been looking for a civilian with experience in running large military research and development programs. Weinberger’s initial preference was the highly respected John S. “Johnny” Foster, who had served from October 1965 to June 1973 as director of the defense research and engineering office in the Pentagon. However, Foster had been retired for years and was not interested in coming back to take on such a heavy responsibility.16 At a White House meeting attended by Weinberger and General Lawrence A. Skantze, commander of the Air Force Systems Command, the president asked his secretary of defense, “Where is my program director, and why aren’t we getting going on this?” Weinberger replied that there

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was an intensive search under way, but so far they hadn’t been able to find a civilian with the right mix of qualifications.17 At that point General Skantze said, “I know exactly the right person for the job, General Abrahamson. By the way, Mr. President, you know him. You pinned on his third star when you went out for the shuttle landing on the 4th of July at Edwards [Air Force Base]. He may be a general, but he thinks he is a civilian!” A few days later a surprised Abrahamson was standing in front of the secretary interviewing for the job of director of SDIO. Weinberger was impressed with the general’s résumé and his views on strategic defense, which coincided with the president’s. Abrahamson’s experience in successfully leading large defense programs as the director of the F-16 Multinational Air Combat Fighter Program (1976 to 1980) and as the associate administrator for the Space Transportation System at NASA headquarters in Washington, DC, helped to convince Weinberger that he had found the right man for the job. Abrahamson had the right personality and was highly credible in representing the merits of SDI to Congress. He remained as SDIO director for nearly 5 years, leaving in January 1989.18 Reagan was able to persuade Congress to inject billions of dollars— not millions—into SDIO’s elaborate research program. SDIO’s directedenergy work built on foundations created by technology programs from the 1970s and early 1980s sponsored by DARPA and the Air Force, Army, and Navy. DARPA had funded about 75 percent of these efforts, while the Air Force had established its position as the leader in the field of lasers. For example, by the time SDIO had gotten under way, the Air Force had already developed and tested a much-publicized high-power CO2 gas dynamic laser aboard a specially modified NKC-135 aircraft known as the Airborne Laser Laboratory (ALL) under the leadership of Colonel Don Lamberson. (Lamberson went on to become a major general and a leading spokesman for the development of directed energy.) In May 1983, the ALL shot down five AIM-9B Sidewinder missiles over the China Lake Test Range in California—proving for the first time that an airborne laser could intercept and destroy air-to-air missiles.19 The arrival of SDIO had a significant influence on Marquet’s directedenergy group at DARPA. Joseph A. Mangano and Robert Sepucha from Marquet’s team worked on the directed-energy portion of the Fletcher study, which was chaired by Gerold Yonas of Sandia National Laboratory. Strategic Defense Initiative

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Photo 28. A year after his appointment as director of the Strategic Defense

Initiative Organization, Lieutenant General James A. Abrahamson appeared on the cover of Newsweek. Photo courtesy of Newsweek.

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Between 1983 and 1984, when SDIO was officially established, an informal relationship had evolved between DARPA and SDIO. “I was working both for DARPA and SDIO in my DARPA job,” Marquet recalled, “which involved all the different programs in directed energy.” As he explained it, “I was still head of the Directed Energy Office at DARPA, and at the same time I was head of the now forming Directed Energy Office of SDIO.” Eventually, Marquet’s office moved completely out of DARPA and reemerged as a permanent office in SDIO.20 Tom Meyer, an extremely knowledgeable Air Force officer (and a firstrate tennis player) who worked for Marquet, claimed that DARPA’s director, Bob Cooper, was not a huge fan of developing directed-energy technologies for ballistic missile defense. At the same time, General Abrahamson, the director of SDIO, was trying to lure Marquet and his staff to SDIO, which was in the process of shaping its initial management structure. Subsequently, General “Abe” called a meeting with everyone in Marquet’s group to explain the benefits of working for SDIO. Meyer attended the session and remembered: “He [Abrahamson] said, ‘What’s your budget now?’ At the time there was about $300 million a year and there were six or seven of us. . . . He said, ‘What do you think if each of you had $300 million apiece?’ The office [SDIO] was a billion-dollar office, so it was a great sales pitch!” By the time the general finished his presentation, everyone in Marquet’s group was eager to move over to SDIO. “We figured we were getting that big budget,” Meyer recalled, “and we did. The budget went up substantially [from DARPA]!”21 Although Meyer’s account of General Abrahamson’s meeting was accurate, the decision to move Marquet’s directed-energy group to SDIO had already been made. Part of the reason was that Cooper’s boss at the Pentagon, Richard “Dick” D. DeLaurer, undersecretary of defense for research and engineering (DDR&E), knew that President Reagan wanted the SDI program to start big. Cooper was holding two jobs at the time, assistant secretary of defense for research and technology at DDR&E and director of DARPA. Secretary Weinberger appointed Cooper, along with Major General Donald L. Lamberson and Brigadier General Robert R. Rankine (both of whom served as assistants for directed-energy weapons under Deputy Secretary of Defense Paul Thayer) to build the Strategic Defense Initiative Organization “from scratch.” Cooper suggested that it would Strategic Defense Initiative

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make sense to move the entire DARPA laser group into SDIO. That would accomplish two things. First, moving the DARPA group—and other relevant technology programs from the three military services—would help to create a large centralized SDIO organization consistent with the president’s guidance to consolidate all the key technologies under one roof. Second, since Marquet’s laser group was eating up so much of Cooper’s DARPA’s budget—roughly 300 to 400 million dollars annually—Cooper suggested that, to gain some financial relief, “we take the whole laser group and put them into SDIO.”22 The secretary of defense aimed from the beginning to move the missile defense technology programs out of DARPA and into SDIO. The president wanted a centrally controlled SDI program that would administer research in many different technologies. Most of the directed-energy, surveillance technology, and ballistic missile defense programs that transferred to SDIO had already been under way at DARPA for years, primarily in DARPA’s Directed Energy and Strategic Technology offices. Moving the programs entailed a major shift of resources. Of DARPA’s nearly $800 million annual budget, between $300 and $400 million transferred to SDIO. As Cooper pointed out, “When SDIO was formed, we just took those offices and literally formed SDIO out of DARPA.” The move meant that, for all practical purposes, DARPA was now out of the adaptive optics business.23 By spring 1984, everyone in Marquet’s group had moved into the Matomic building in downtown Washington to work full-time for SDIO. Abrahamson and his staff had reservations about the building, because they were convinced there was a group of Russian spies in an apartment directly across the street. That wasn’t the only concern. Marquet recalled that one day he came to work to find the building swarming with pickets demonstrating outside. His initial dismay in believing that Star Wars detractors had discovered the nerve center of SDIO soon vanished when he realized the crowd was protesting the Nuclear Regulatory Commission, which shared the building with SDIO. Nevertheless, everyone felt SDIO offices should be in a more protected area.24 Two years later, SDIO relocated to a secure vault in the basement of the Pentagon, occupying what had formerly been bus tunnels, now closed for security reasons. After a major scrub-down, the area was remodeled into office space. It was not prime real estate in the Pentagon, and it certainly

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was off the beaten path. Abrahamson liked to direct visitors to SDIO by telling them his office was directly under the bakery on the main corridor of the Pentagon. Shortly after the move to the Pentagon, Marquet was promoted and became Abrahamson’s deputy for technology. From the start, Abrahamson realized he needed a technical expert who could advise him on tough scientific questions. As he put it, “Lou was the right guy. . . . he was broadly based and had such an incredible scientific education along with the right instincts.” Marquet remained as SDIO’s deputy for technology until he retired in 1988. For his services, he was awarded the Strategic Defense Achievement Medal by the National Defense Industrial Association.25 To address the missile defense and antisatellite missions, SDIO and DARPA funded numerous scientific projects. One of those projects was an outgrowth of a DARPA program in the late 1970s that put Lincoln Laboratory to work on submarine laser communications. Darryl Greenwood had headed this project, which took place at Lincoln Laboratory and on Maui. The goal was to bounce a blue-green laser off a space mirror and then direct the beam to a submarine under water. Getting a good quality beam from the ground to the mirror—the uplink portion of the experiment—required a reliable adaptive optics system. If the research proved successful, then the Navy could use lasers to communicate with its submarines anywhere in the world.26 The motivation for working on blue-green lasers was partly political. In the late 1970s and early 1980s, many in the military advocated developing laser systems capable of shooting down missiles and satellites. But at the time, research in this area was extremely sensitive. Deploying such a system would violate the 1972 Anti-Ballistic Missile Treaty, signed by the Soviet Union and the United States. Moreover, some felt developing new technologies to intercept and disable missiles and satellites would destabilize the delicate balance of power between the two countries, adding more risks rather than making the United States safer. One way to get around this was to pursue development of lasers for non-hostile purposes such as communication. The resulting technologies could then be applied—at some time in the future if the military situation demanded it—to direct a high-power compensated laser beam against a missile or satellite.27 Until the early 1980s, the Navy showed little interest in using lasers and space mirrors to enhance submarine communications. There were several reasons for this. First, the Navy did not want anyone to know the location Strategic Defense Initiative

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Figure 10. Concept for submarine laser communications.

of its submarines, and feared that a laser beam illuminating the surface of the ocean might give it away. Second, the Navy did not believe the technology was mature enough to improve communications in the immediate future. Third, Navy officials were concerned about the reliability of a system that had to bounce a laser beam off mirrors in space. Some argued that the scheme was unrealistic because it would take an extensive and costly constellation of relay mirrors to cover the globe 24 hours a day.28 Others were more enthusiastic about the technology, including Duncan Hunter, a long-time conservative Republican who represented California’s 52nd Congressional District and served on the House Armed Services Committee. Hunter believed there was merit in the potential application of lasers to submarine communications, and he worked to secure a congressional mandate for the Navy laser research to move forward using DARPA funds until the program ended in the mid-1980s.29 The DARPA project did move forward under the able leadership of a former Navy officer named Bill Wright, who now worked in DARPA’s Directed Energy Office. Based on Wright’s urging, DARPA funded a

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Lincoln Lab team that conducted some very successful experiments. The Navy Ocean Systems Center in San Diego made progress in propagating a laser beam from an aircraft down through the water to a submarine. These initial tests suggested it would be feasible to use lasers to communicate with submarines, but DARPA did not fund the next stage of experiments, which called for reflecting a beam off a space mirror. The Navy remained lukewarm about the project, convinced that the best and most reliable solution was to continue to use its extremely low-frequency 50 Hertz low-bandwidth system, which had operated out of transmission sites in northern Wisconsin and the upper peninsula of Michigan for many years. Although the Navy’s interest in the DARPA-sponsored project faded, DARPA remained committed to the concept of using lasers and mirrors in space—and turned its attention in the opposite direction: away from the oceans and into space.30 The man who would lead the DARPA-sponsored effort to propagate lasers into space and figure out a way to compensate for atmospheric turbulence was Darryl Greenwood at Lincoln Lab. Greenwood had a knack for putting together the right people and managing complicated experimental programs. A tall and imposing figure, Greenwood revealed a down-home and friendly demeanor. Listening carefully, one could detect a slight Texas drawl as he explained esoteric scientific principles. One of the things he was best known for in the scientific community was his discovery of the “Greenwood frequency,” a key principle of adaptive optics. Greenwood left Rome Air Development Center in 1975 after completing his military obligation in the Air Force, hoping for a career with the federal government. As a distinguished graduate of Air Force ROTC at the University of Texas and a PhD in electrical engineering, he had all the right credentials. His thesis focused on laser scattering in atmospheric turbulence, which turned out to be a good match for his work first with the Air Force and later with Lincoln Laboratory. In the early 1970s he gained valuable work experience while at Rome honing his theoretical and experimental know-how in the areas of atmospheric turbulence, laser propagation, and compensated imaging. When rumors circulated that Rome might close, Greenwood decided to apply for a job at AFWL in Albuquerque. The Oklahoma civil service personnel office responsible for processing his application lost his paperwork for several months. While Greenwood waited to hear from AFWL, Lou Marquet recognized his outstanding scientific Strategic Defense Initiative

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Photo 29. Darryl P. Greenwood was a prominent member of the Lincoln

Laboratory team that led a number of adaptive optics programs, including the Atmospheric Compensation Experiment or ACE. A model of the ACE sounding rocket is on top of cabinet.

talents and hired him on the spot in 1975 to work at Lincoln Laboratory. The federal government’s loss was Lincoln Laboratory’s gain.31 Greenwood fit in well at Lincoln Lab, and he distinguished himself early on in his career. By 1981 he had become the leader of the High-Energy Laser Propagation and Beam Control Group, which performed work that led to the SWAT experiments described earlier. The group was responsible for the success of the Atmospheric Compensation Experiment or ACE, a series of laser experiments that ran from 1981 through 1985. ACE involved engaging cooperative targets outfitted with beacons that provided samples of distorted light so researchers could generate compensated laser beams propagating from the ground into space. Greenwood’s expertise with ACE, and his authorship of several influential papers in the late 1970s and early 1980s, elevated him into exclusive scientific company when he became an

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elected fellow of the Optical Society of America in May 1991 for his “contributions to the fundamental understanding and early development of adaptive optics.”32 The purpose of ACE was to demonstrate that a laser beam propagated from the ground through atmospheric turbulence and into space could be compensated using an adaptive optics system, and thus could deposit sufficient energy on a target to disable it. Greenwood and his team divided the ACE research into phases. First a laser would be fired horizontally to a ground target, next to an airplane in flight, and finally to high-altitude sounding rockets. DARPA, and later SDIO, invested heavily in this research. Their long-range goal was to advance new technologies that could be applied to both ballistic missile defense (hard targets) and ground-based antisatellite (soft targets) missions. However, by the late 1980s, SDIO’s interest in ground-based antisatellite research had diminished. The agency turned to space-based lasers as an option for its primary mission of ballistic missile defense. A few years later, in the early 1990s, SDIO decided to reduce its attention on lasers and concentrate on kinetic-kill systems as its main missile defense weapon.33 The ACE adaptive optics systems evolved from the Real-Time Atmospheric Compensation (RTAC) and Compensated Imaging System (CIS) programs of the 1970s, discussed in chapter 3. Itek was the contractor responsible for building components for a new adaptive optics system— based on CIS adaptive optics technology—to be used in ACE. This nextgeneration experimental system consisted of a 69-actuator deformable mirror and a shearing interferometer that defined the distorted wavefront of a laser beam. CIS, as an operational system mounted on the side of a telescope, needed 168 actuators in order to obtain high-resolution images of space objects. ACE, on the other hand, consisted of a smaller, 60-centimeter (23.6-inch) telescope and a breadboard configuration mounted on an optical bench that required fewer actuators because of the smaller aperture—69 actuators were sufficient.34 One of the defining characteristics of the ACE adaptive optics system was that Lincoln scientists used it exclusively to correct an outgoing lowpower laser, not to improve images. ACE was designed to demonstrate theoretical compensation concepts, the first step of which could be accomplished using low-power lasers. Therefore, there was no need for Lincoln Strategic Defense Initiative

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Lab to use high-power lasers for any of the ACE experiments. In addition, all ACE testing used targets that were “cooperative”—they carried a reflector that made it easy for a beam to travel from the ground station to the target and back, carrying the information about atmospheric distortion that the system needed to adjust the outgoing laser beam for maximum impact on the target.35 In 1981 Itek completed fabrication of the ACE wavefront sensor. Lincoln scientists designed and integrated the system on an optical bench and tested it in a laboratory in Lexington. Experimenters introduced simulated atmospheric turbulence conditions into the laboratory environment and fired a laser through that artificial medium. Once laboratory testing demonstrated that the system operated up to specifications, Lincoln shipped the system to the Air Force Maui Optical Site in Hawaii in 1982 and installed it on the 60-centimeter beam director. Lincoln Lab scientists then began their threephase ACE field test program.36 The first phase of ACE involved propagating a laser beam along a horizontal path from a beam director, which remained in a fixed position and did not move, for 150 meters (164 yards) to an instrument trailer on top of Haleakala. A laser at the trailer served as a beacon and traveled from the trailer to the beam director, where the adaptive optics system was located. The adaptive optics system’s shearing interferometer detected and calculated the amount of atmospheric distortion in the beacon’s laser light. Those data drove the changes that had to be made to the surface of the deformable mirror to compensate for the effects of atmospheric turbulence on the outgoing beam traveling from the beam director to the trailer. Because the beam was low power, and absorption of the green light was very low, experimenters did not have to contend with the difficult issue of thermal blooming. The big question for this first phase was to determine if the beam passing through atmospheric turbulence could be tightly focused on the trailer target.37 The ACE phase one experiments conclusively showed that this was possible; the adaptive optics performed well. The relatively short range the laser beam had to travel simplified the compensation process somewhat. But even though the range was short, the turbulence the beam encountered was similar to what it would encounter on a path from the Maui mountaintop to space. Only a small portion of the atmosphere, 150 meters, had to be

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diagnosed, which was easier to do than measuring turbulence and correcting for a beam extending from the ground to space, where the beam would have to traverse long distances through multiple atmospheric turbulence layers that were constantly changing.38 The ACE adaptive optics operated as a closed-loop system that could continuously change the settings on the deformable mirror on a real-time basis. Measurements of beam intensity at the trailer target served as the yardstick to tell if the adaptive optics system was working properly. A solidstate camera at the target spot inside the trailer imaged the beam transmitted from the beam director. Low beam-intensity measurements at the target spot meant turbulence had weakened and degraded the quality of the beam. High beam-intensity measurements on target meant the adaptive optics had canceled out a good portion of atmospheric turbulence. After adjustments were made to the ACE adaptive optics system early in the testing, the phase one ACE field experiments concluded in 1982 and confirmed that a tightly focused ground-to-ground compensated beam propagating from the beam director could be placed on the trailer target.39 While ACE phase one succeeded in sending a compensated laser beam to a stationary target, phase two attempted to transmit a low-power laser over vertical paths from the beam director on the ground to a small Cessna 441 Conquest aircraft flying 10,000 feet above the Maui site. The phase two experiments, led by Jacob “Jack” Lifsitz, took place during 1983 and 1984. Installed on the left side of the Cessna’s fuselage, aft of the wing, was a customized door with a window. As the plane flew in a slow racetrack pattern, it emitted light from an onboard beacon back to the ground.40 Wavefront measurements of the beacon’s distorted light allowed Lifsitz’s team to adjust the deformable mirror settings so that atmospheric turbulence would not degrade the outgoing laser beam. The outgoing lowpower beam from the ground was aimed through the window on the left side of the aircraft. Once the laser beam entered the aircraft, scientists used diagnostic cameras to measure its intensity and determine how well the adaptive optics system on the ground had compensated the beam.41 Results from the ACE phase two experiments were encouraging. This was the first time that an adaptive optics system was able to compensate a laser beam transmitted from the ground to a moving airborne target. Greenwood reported that the beam quality during most of the tests was Strategic Defense Initiative

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Photo 30. Diagnostic aircraft used by Lincoln Laboratory for ACE experiments at Maui.

very good. Beam quality also matched closely to theoretical predictions. Completion of ACE phase two set the stage for an even more demanding sequence of experiments that involved sending a laser beam into space. But before phase three began, attention was temporarily diverted to a more pressing SDI experiment.42 The SDIO High Precision Tracking Test involved firing a laser into space. The first test firing, from the Maui ground station to the space shuttle Discovery on 21 June 1985, was well publicized. General Abrahamson needed to show some dramatic progress with lasers in space, and the shuttle experiment seemed to be the best and quickest way to give SDIO credibility in the eyes of the public. From the start, Abrahamson had viewed the shuttle as an ideal platform for conducting space experiments.43 Some suggested that the president had been pressuring the general to act quickly. But Abrahamson refuted that claim, stating, “Reagan was aggressive. He wanted to see progress, but he didn’t try to direct or try to say do this or do that.” Setting up the SDIO test aboard the shuttle was a slow and arduous process at first. It usually took years of planning before any experiment got a place on the shuttle, and NASA engineers and program managers were reluctant to give preferential treatment to SDIO.44 Abrahamson personally intervened. Before taking over SDIO, he had

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served as the associate administrator for the Space Transportation System at NASA, where he had been responsible for the space shuttle program. After moving to SDIO, he maintained powerful connections at NASA. Chuck Primmerman, on loan from Lincoln Lab to SDIO to work on the High Precision Tracking Test, recalled that the shuttle experiment would never have happened if it were not for General Abe. “He twisted arms at NASA and was able in the shortest time—a record few months—to get the experiment onboard Discovery,” Primmerman said. Others close to the program agreed.45 The only adaptive optics component required aboard the shuttle was an 8-inch (20.3-centimeter) retroreflector—a precision mirror that reflected a laser to the ground. The mirror cost $30,000 and weighed 20 pounds (9.1 kilograms). Even this relatively small item took up precious space. But as Greenwood related, “The astronauts were happy to do the experiment, and we were told one of them gave up space in his personal locker to store the retro.”46 Once in orbit, Discovery astronauts attached the retroreflector to the inside of the forward left side hatch window. The plan called for the shuttle to maneuver on its left side to position the retroreflector directly over the Maui ground site. At that point, the Maui beam director would fire a low-power (4-watt) blue-green argon-ion laser, which would strike the retroreflector and reflect back to the ground, where the adaptive optics system would measure the amount of distortion in the beam caused by atmospheric turbulence. Once scientists had this information in hand, they imaged the beam spot and knew they could compensate a laser beam using the adaptive optics system. However, for this experiment, there was no requirement to send a compensated beam back up to the shuttle. This was a closed-loop experiment but did not involve correction of an outgoing beam. It was an experiment to acquire accurate data on the amount of distortion in the return beam traveling from the shuttle to the ground and to compensate the resultant beam image, but not to compensate an outgoing beam.47 The plan was sound, but the execution was not—at least not on the first try. On 20 June, when the shuttle was orbiting 200 miles above Maui, an operator error caused the Discovery to roll onto its right side instead of its left. The post-mission operations report stated that this error was caused by “an incorrect data format programmed into the universal pointing display. Strategic Defense Initiative

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Figure 11. Schematic of ACE shuttle Discovery experiment conducted

on 21 June 1985.

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The target altitude was entered in feet, not in the required units of nautical miles.” This resulted in the retroreflector facing out into deep space instead of down to the Maui site. Even though the shuttle was pointed in the wrong direction, the Maui team fired its laser on schedule. The low-power beam hit the right side of the shuttle, but caused no damage to the spacecraft; the astronauts reported seeing the beam outside the cockpit window.48 Failure of the first shuttle test strained the patience of some officials in the Pentagon. Tom Meyer received a call from Weinberger’s executive officer demanding to know, “Why didn’t it work?” Meyer reassured him that the software problem was being fixed and the entire Lincoln Lab/Air Force team was confident that the next test would produce the desired results.49 Meyer’s credibility would soon be put to the test. The next day, the shuttle’s navigation software performed on cue and banked the Discovery spacecraft onto its left side so the retroreflector faced Maui. But now there was a problem on the ground: winds gusting from 55–80 mph increased atmospheric turbulence, making it more difficult to track the shuttle and raising concerns about the ground optical system, which would be vulnerable to wind damage while the dome protecting it was open for the experiment. Fortunately, conditions improved just enough to meet minimum safety standards, and the test went forward. The beam left Earth as a narrow ray of light a mere quarter of an inch (a little over half a centimeter) wide. Passing through the atmosphere, it expanded to nearly 30 feet (9.1 meters) by the time it hit the shuttle’s retroreflector, covering the device’s entire surface and more. The portion that was reflected back to earth was measured for wavefront distortion, and that information was used to correct the image of the retroreflector (bright spot on shuttle). The return beam also provided input to an optical device that tracked the shuttle.50 Department of Defense and Air Force officials were excited about the success of the test. General Abrahamson told the news media, “This is an important step in a series of steps that will prove we can effectively shoot lasers from the ground into space without suffering unacceptable atmospheric losses.” One of the more promising signs was the fact that the shuttle had been traveling at 17,000 miles (27,000 kilometers) an hour when engaged by the laser—several hundred mph faster than a nuclear warhead. It was not unreasonable to speculate that it would someday be possible to

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build a defense system with enough precision to intercept slower-moving space targets such as missiles and warheads.51 The 1985 shuttle test was the first to propagate a laser from the ground to a spacecraft. Although this was an important step forward, the wavefront distortion data it acquired were not completely integrated into an adaptive optics system—the experiment had not attempted to send an outgoing compensated beam from the ground back up to the shuttle. Phase three of the ACE experiments would take on that challenge.52 Several months after the shuttle test, Lincoln Lab scientists on Maui under the direction of Darryl Greenwood began the third phase of the ACE. It consisted of four separate launches of Terrier-Malamute two-stage sounding rockets—at a cost of $750,000 each—developed by a Sandia National Laboratory team headed by Richard Eno. Each rocket took off from the Navy’s Barking Sands launch site on the island of Kauai and reached its apogee of 372 miles (599 kilometers) as it passed south of the Maui site. The rockets’ altitude was roughly three times that of the altitude of the lowest earth-orbiting satellite and twice that of the shuttle Discovery’s orbit during the SDIO experiment—making them realistic targets for testing the capability of Lincoln’s adaptive optics system under operational conditions.53 The purpose of the experiment was to compensate a laser beam traveling from the ground to the rocket. That required sending a 4-watt argonion blue illuminator laser from the Maui site to a retroreflector on the nose of the rocket. The reflected beam returned to the ground, where distortions caused by atmospheric turbulence were measured. These in turn drove the settings on the 69-channel deformable mirror. The plan called for a second outgoing “scoring” green laser beam (1 watt) to reflect off the deformable mirror and strike a diagnostic array of 20 sensors aligned in a row near the center of the rocket. Those sensors would measure the quality of the scoring beam to determine if it had been compensated—properly corrected—as it moved through the atmosphere to the rocket.54 Scientists aimed the second (compensated) beam along the same path that the first beam had traveled to hit the retroreflector. (The direction of the outgoing beam automatically took into account point-ahead angle.) Between the time the first beam returned to Earth and the second beam was transmitted to the rocket, the rocket had moved forward slightly. The second laser would thus hit a detector array in the middle of the rocket

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Photo 31. The Atmospheric Compensation Experiment demonstrated the first compensated laser beam from the ground to rockets in space. At left is the Terrier-Malamute two-stage sounding rocket, at center is a laser beam transmitted from the Maui site to the rocket, and at right is a schematic showing the rocket’s flight path.

rather than on its nose, because the rocket had moved slightly forward so the array now occupied the position where the retroreflector had been previously located a fraction of a second earlier.55 The ACE sounding rocket experiments were 75 percent successful. After launch of the first rocket on 27 September 1985, the Maui ground station’s tracking system malfunctioned and failed to acquire the missile. Although launch of the first rocket was flawless, the inability to track it meant the mission had to be aborted. Since tracking was a critical element for directing the laser to the rocket, the Maui ground team never projected a beam to target.56 Lincoln’s Dan Murphy was in charge of the experiments for sounding Strategic Defense Initiative

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rockets 2, 3, and 4. Each rocket launched successfully and was accurately tracked during its 10-minute flight before it crashed into the ocean 496 miles (793 kilometers) downrange from its launch point. (The plan did not call for the rockets to be recovered.) One of the major improvements for this test was that Lincoln had developed a faster and more accurate digital computer for processing wavefront measurements to replace the Itek analog computer used in previous experiments.57 Greenwood and Primmerman reported all three rocket tests clearly showed “a dramatic increase in irradiance when the beam is compensated. The ACE sounding rocket tests were the first to demonstrate atmospheric compensation of a beam propagating from the ground to space.” Also, SDIO officials told the press that the experiments furthered the understanding of physics in terms of “projecting high-power, ground based lasers through the atmosphere to space for application to a ballistic missile defense.” DARPA officials were pleased and encouraged. Secretary Weinberger sent a congratulatory message to the director of Lincoln Lab, praising the ACE team for conducting “the first successful demonstration of the propagation of a compensated visible laser beam from ground to space at Maui on 27 Sept 1985. This result is a significant achievement which supports the feasibility of SDI.” Phase three produced more evidence that adaptive optics worked under realworld conditions. The sounding rocket experiments were completed and the resulting data processed by the end of 1985; this marked the end of the atmospheric compensation experiments conducted by Lincoln Laboratory.58 There was no immediate follow-on program to the ACE experiments. The adaptive optics system used on Maui was subsequently transferred to the Mount Wilson Observatory and used to conduct astronomical experiments to acquire improved images of stars, planets, galaxies, and other space images—a prime example of technology transfer by the military to the civilian sector, in which Mount Wilson benefited from the state-of-theart technology and realized considerable cost savings.59 Not everyone agreed that Lincoln Lab, the Air Force, and other government agencies were making significant progress with lasers and adaptive optics. Critics pounded away at the weakness of SDIO’s vision, calling for directed-energy weapons as the ultimate ballistic missile defense weapon. They argued it would be decades at least before these “pie-in-the-sky” weapons could be deployed. The American Physical Society and the Union

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of Concerned Scientist led the charge, claiming that Star Wars was unrealistic, technically immature, and easy to defeat using relatively simple countermeasures. The Union of Concerned Scientists was an independent nonprofit organization that assessed the impact of technology on society and carried substantial weight among scientists outside the government.60 Although many physicists outside the Defense Department expressed pessimism about the success of SDIO, they did not have access to all the facts. During the 1980s, most adaptive optics research was classified, as was much laser research. The announcement of adaptive optics laser guide star progress at the American Astronomical Society’s meeting in Seattle in 1991 was an eyeopener to astronomers and other scientists, some of whom had a hard time accepting that the military had led the way on laser guide stars.61 A second consideration that critics did not always take into account was that it is not unusual for laboratories to experience more failures than successes, given the nature of scientific research. In most cases, it took large financial investments and decades of work to accomplish a major scientific breakthrough. There was no such thing as instant scientific success, especially when large, complex military systems were involved. A good example was the Air Force’s development of the Airborne Laser Laboratory. During the 1970s and early 1980s, critics insisted that the system would never work. For 13 years they were right, but in 1983 the ALL succeeded in shooting down five air-to-air missiles over the China Lake test range in California. This success influenced the decision to proceed with the development of a second-generation airborne laser, which is under way today.62 A third issue critics did not anticipate was that SDIO evolved more into a political venture than a scientific enterprise, and as such had significant and lasting consequences for the entire world. Opponents of strategic defense technologies in the 1980s had no way of predicting that SDIO’s commitment to developing a ballistic missile defense system would contribute to the demise of the Soviet Union and the end of the Cold War. At the Reykjavik Summit in October 1986, Ronald Reagan and Mikhail Gorbachev addressed the sensitive issue of arms reduction of ballistic missiles. Gorbachev asked Reagan to abandon SDI, but Reagan refused, because he believed that this new defensive strategy would be a military insurance policy against future Soviet aggression. The truth was that the struggling Soviet economy was too weak to match the huge U.S. financial Strategic Defense Initiative

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investments in SDIO, and the Soviets knew it. Severe economic instability in the Soviet Union led to political unrest in the late 1980s that changed the course of that nation dramatically. By June 1987 Gorbachev had introduced perestroika to move the Soviet Union away from the traditional communist model of a planned and centrally controlled economy. Gorbachev believed perestroika, in combination with glasnost or political openness, would lead to the revitalization of the Soviet Union. But his economic and political reforms failed. By December 1991 the Soviet Union had splintered into 15 separate and independent republics.63 At a conference at Princeton University in February 1993, former Soviet foreign minister Alexander Bessmertnykh declared that the inability of the Soviet Union to develop economically and sustain its own SDI program contributed greatly to its downfall. When Reagan died in June 2004, many around the world praised him most for his tough rhetoric and unswerving stand against the Soviet Union. Gennady Gerasimov, one of the top spokesmen for the Soviet foreign ministry in the 1980s, remembered the powerful impact Reagan’s SDI program had on the balance of world power. Gerasimov recalled that “Reagan bolstered the U.S. military might to ruin the Soviet Union, and he achieved his goal.” Describing SDI as a form of “successful blackmail,” Gerasimov explained, “The Soviet Union tried to keep up pace with the U.S. military buildup, but the Soviet economy couldn’t endure such competition.” Even though SDI never deployed a single piece of operational hardware, its specter hastened the collapse of the Soviet Union.64 Although many believed that SDI contributed to the demise of the Soviet Union, others argued that the country collapsed naturally under its own deteriorating economic conditions. Since the 1970s, the Soviet Union had suffered a steady decline in its economy. Gorbachev tried to reverse this trend through economic reform, but that change did not begin to take root until long after he was forced out of office. The Soviet Union continued to maintain a robust research and development program, but it never created its own ballistic defense program to compete on the same level as SDI.65 One other criticism of SDI was that it cost too much. But the DoD argued that when put in perspective, SDI’s costs were rather modest and consumed only a small fraction of the federal budget. For example, in fiscal year 1989, the federal budget totaled $1,119.0 billion. The DoD spent $282.4 billion or about 25 percent of the federal budget. SDI’s budget was $3.8 billion—0.34 of

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one percent of the overall federal budget. Of course, these funds were spent primarily on research; any operational weapons systems to come out of the program (none had been built yet) would cost significantly more.66 Regardless of the Soviet Union’s response to SDI, and in spite of the criticism that SDI would never work, the Air Force and Lincoln Laboratory pressed on. After the ACE experiments, Lincoln personnel became heavily involved in a space satellite experiment called LACE, which stood for LowPower Atmospheric Compensation Experiment.

Low-Power Atmospheric Compensation Experiment Lou Marquet and his directed-energy group at SDIO started planning for LACE in the mid-1980s. On 7 April 1984, the shuttle Challenger launched from its cargo bay NASA’s Long Duration Exposure Facility (LDEF) satellite. The original plan had called for the Challenger to retrieve the LDEF satellite in 1986, strip it of its experimental hardware, and turn it into a satellite platform for LACE, which would be launched from a future shuttle flight. But the Challenger disaster of 28 January 1986, in which seven crew members died, intervened. When shuttle launches were put on hold pending an investigation of the disaster, deployment of LACE was delayed and LDEF was left in orbit, leaving LACE without a vehicle to fly on. Consequently, SDIO decided to deploy LACE on its own satellite and not wait for LDEF or the shuttle. It would take nearly 4 years before LACE was ready to be launched into space aboard an expendable Delta rocket.67 LACE was the last part (the ground-to-space phase) of Lincoln Lab’s Short-Wavelength Adaptive Techniques or SWAT program, which explored ways to compensate for atmospheric distortions. The Naval Research Laboratory in Washington, DC, built the LACE satellite, which took 3 years. LACE experiments were similar to the ACE program, except that a laser beam engaged the LACE satellite at a lower altitude than the ACE sounding rockets. LACE’s cross-sky velocities were also greater, making it more difficult to track.68 The LACE plan called for Lincoln Lab scientists to demonstrate that a laser beam propagated from the ground to a satellite could be compensated for atmospheric turbulence. To accomplish that first required measuring Strategic Defense Initiative

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Photo 32. Technicians prepare the LACE satellite for launch on 14 February

1990. The square sensor array located in the center of the satellite measured the intensity of the compensated scoring beam.

wavefront distortions in one of the lasers used in the experiment—called a beacon light—which was projected from a beam director on the ground and reflected from the LACE target satellite back to the ground, where information on the beam’s makeup could be analyzed. Based on the data analysis, Lincoln’s 241-channel SWAT adaptive optics system would make the required adjustments on its deformable mirror so it would pre-distort an outgoing laser beam—designated the scoring beam—that could then be sent from the ground back up to the satellite. If scientists could show that a compensated beam was feasible, then SDIO would be a step closer to the enabling technology it needed to develop a powerful ballistic missile defense system.69 LACE experienced numerous delays because of technical and administrative problems. Launches scheduled for August 1989, December 1989,

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January 1990, and 8 February 1990 were all canceled for various reasons. For example, the 8 February launch delay occurred because a contractor employee dropped a 4-inch spacecraft connector tool into a constricted area between the protective shroud of the rocket and the LACE satellite. Why the tool was not tethered to the worker as required by standard operating procedures was never fully explained. One Air Force officer held the contractor (McDonnell Douglas) responsible because “quality assurance was not vigilant.” The dropped tool caused no damage to any of the satellite components. But because it lodged in an inaccessible place, technicians had to remove a detector array panel and other components to retrieve it. That delayed the launch of LACE by 6 days.70 On 14 February 1990 at 11:15 a.m., a Delta II rocket lifted off smoothly from Pad 17B at Cape Canaveral Air Force Station and launched the 3,175pound (1,428.8-kilogram) LACE satellite into a 547-kilometer (340-mile) circular orbit over the Indian Ocean. Once in orbit, the $130 million LACE satellite served as a target for a laser beam fired from the ground. The goal of the experiment was to verify the ability of the ground-based adaptive optics hardware to correct for atmospheric turbulence and then to send the corrected or compensated laser beam from the ground to the target spot on LACE. Two of the most important components of the satellite were the retroreflector beacon and the diagnostic detector array, called the sensor array subsystem.71 Dan Murphy, Lincoln Lab’s principal investigator for LACE, explained that the retroreflector was made up of an array of 252 cornercube retroreflectors—each an inch in diameter—precisely packed together and arranged in different positions so light from the ground of any frequency striking the array from any direction would reflect back to its source on the ground. Mounted at the end of a lightweight boom in front of the satellite, the retroreflector represented the correct point-ahead distance from the “sweet spot” of the detector array, which was located at the center of the LACE satellite.72 A continuous wavelength argon-ion laser transmitted from the Maui site illuminated the retroreflector as it passed overhead. It also served as a tracker. When the beam exited the beam director, it measured only 2.5 centimeters (1 inch) in diameter. By the time it reached the LACE satellite, the beam had expanded to 15 meters (16.5 yards) in diameter. As in the earlier ACE tests, the beam flooded the entire retroreflector, making it Strategic Defense Initiative

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Figure 12. The Low-Power Atmospheric Compensation Experiment (LACE) demonstrated for the first time a compensated laser beam transmitted from the ground to a low-earth-orbiting satellite.

relatively easy to hit the target and get a reflected beam transmitted back to the Maui site. A wavefront sensor on the ground measured distortions in the reflected beam and, based on those measurements, adjusted the surface of the deformable mirror. A second beam—the outgoing scoring beam— traveled along the same path of atmospheric turbulence as the first beam, which had reflected off the satellite less than a second earlier. In the time it took light to make the round trip from the satellite to the ground and back to the satellite, the body of the satellite had moved forward to occupy the previous location of the retroreflector. That meant that the scoring beam hit the detector array, a 4-meter (4.4-yard) square target board located in the center of the body of the satellite. Two hundred sensors in the detector array measured the intensity of the beam on the target board and transmitted the data to the ground station on Maui for analysis.73

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Figure 13. The LACE satellite deployed three booms: the retro-reflector boom (lower right), a counterweight boom for balance (left), and a gravity gradient boom (center) to keep the sensor array pointed down facing the Earth.

This process—sending the first beam to the retroreflector and back, changing the deformable mirror settings, and then sending a compensated beam back to the LACE satellite—made up the closed-loop feature of the SWAT adaptive optics system. Most experiments lasted under 2 minutes, which was the viewing time of the satellite as it passed above Maui once every 24 hours. For that brief period the adaptive optics system was continually receiving feedback and making up-to-date corrections to the deformable mirror, thereby allowing a compensated beam to propagate through the atmosphere to the detector array. This was the first cooperative atmospheric compensation of a laser beam propagating to a satellite.74 Although Lincoln Laboratory ran the LACE SWAT experiments, Starfire Optical Range responded to Lincoln’s request for assistance on short notice once the LACE satellite was in orbit. Lincoln was concerned Strategic Defense Initiative

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that the cross section of the LACE cornercube array might not be positioned correctly, which could jeopardize the success of the experiments. To evaluate the situation, an SOR team used a laser to illuminate the satellite as it passed over the Kirtland site and imaged the array. Results confirmed that the array was properly positioned. The Naval Research Laboratory— sponsor of the Lincoln’s LACE—sent a letter of appreciation to the SOR team applauding the timeliness of their work.75 The LACE satellite in the work done thus far was a cooperative target. However, under hostile conditions, an operator would not have this luxury— an enemy would not install retroreflectors on its missiles or satellites. Some other technique would have to be found to measure atmospheric turbulence in order to accurately aim a beam from the ground to an enemy satellite or mi