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THE EXPLORER PROGRAM FOR ASTRONOMY AND ASTROPHYSICS Committee on Space Astronomy and Astrophysics Space Science Board '\ Commission on Physical Sciences, Mathematics, and Resources 1 ) National Research Council ( tf,S, ), ...__ - .. /I PROPERTY OF NAS- NAE: DEC 161986 LISRAfft Order from National Technical Information Servic ï¿½ NATIONAL ACADEMY PRESS Springfield. Va. Washington, D.C. 1Q86 22161 Ordlf Mo. '
Â· ' J. IL' ' 79ï¿½,5 NOTICE: The project that is the subject of this document was approved by the t.ï¿½f.t.c 9 â¢ Governing Board of the National Re11evch Council, whose members are drawn from /J,Â£!'} the Councils of the National Academy of Sciences , the National Academy of EngineerÂ ing , and the Institute of Medicine. The members of the committee that cosponsored I &JJJ, the workshop were chosen for their special competences and with regard for appropriÂ ate balance. (' I, This report has been reviewed by a group other than the authors according to procedures approved by a Report Review Committee consisting of members of the National Academy of Sciences , the National Academy of Engineering, and the Institute of Medicine . The National Research Council was established by the National Academy of SciÂ ences in 10 16 to associate the broad community of science and technology with the Academy's purposes of furthering knowledge and of advising the federal government. The Council operates in accordance with general policies determined by the Academy under the authority of its congressional charter of 1863 , which establishes the Academy as a private, nonprofit, self-governing membership corporation. The Council has become the principal operating agency of both the National Academy of Sciences and the National Academy of Engineering in the conduct of their services to the governÂ ment, the public, and the scientific and engineering communities. It is administered jointly by both Academies and the Institute of Medicine. The National Academy of Engineering and the Institute of Medicine were established in 1064 and 1070 , respecÂ tively, under the charter of the National Academy of Sciences. Frontispiece: The IRAS sky survey in the infrared (1983) showing many Blue represents emission at 12 microns, green represents emission at 60 striking features of solar-system and extrasolar point and diffuse sources. microns and red represents emission at 100 microns. The plot is in galactic to be bright at 60 and 100 microns. Warm dust in the solar system (the sideÂ coordinates, and shows the Milky Way (the bright yellow band in the figure) ways S-shaped blue curve in the figure) emits strongly at 12 microns. CourÂ tesy: Infrared Processing and Analysis Center, Jet Propulsion Laboratory, California Institute of Technology. Available from Space Science Board 210 1 Constitution Avenue, N.W. Washington, D.C. 204 18
COMMITTEE ON SPACE ASTRONOMY AND ASTROPHYSICS BLAIR D. SAVAGE, University of Wisconsin, Chairman ERIC E. BECKLIN, University of Hawaii JOSEPH P. CASSINELLI, University of Wisconsin ANDREA K. DUPREE, Harvard-Smithsonian Center for Astrophysics JAMES L. ELLIOT, Massachusetts Institute of Technology WILLIAM F. HOFFMANN, University of Arizona HUGH S. HUDSON, University of California, San Diego MICHAEL JURA, University of California, Los Angeles JAMES KURFESS, Naval Research Laboratory STEPHEN S. MURRAY, Harvard-Smithsonian Center for Astrophysics SAUL A. RAPPAPORT, Massachusetts Institute of Technology ANTHONY READHEAD, California Institute of Technology CRAIG L. SARAZIN, University of Virginia NICHOLAS Z. SCOVILLE, California Institute of Technology ADRIENNE PEDERSEN, BDM Incorporated MARK E. WIEDENBECK, University of Chicago RICHARD C. HART, Executive Secretary Liaison Representatives STEPHEN S. HOLT, Goddard Space Flight Center BERNARD F. BURKE, Massachusetts Institute of Technology iii
SPACE SCIENCE BOARD THOMAS M. DONAHUE, University of Michigan, Chairman DON L. ANDERSON, California Institute of Technology D. JAMES BAKER, Joint Oceanogr)i.phic Institute ROGER D. BLANDFORD, California Institute of Technology JAY M. GOLDBERG, University of Chicago DONALD HALL, University of Hawaii DONALD M. HUNTEN, University of Arizona WILLIAM KAULA, NOAA HAROLD KLEIN, University of Santa Clara STAMATIOS M. KRIMIGIS, Johns Hopkins University ROBERT M. MacQUEEN, National Center for Atmospheric Research CARL E. MciLWAIN, University of California, San Diego ROBERT PEPIN, University of Minnesota CHRISTOPHER RUSSELL, University of California, Los Angeles BLAIR D. SAVAGE, University of Wisconsin J. WILLIAM SCHOPF, University of California, Los Angeles JOHN SIMPSON, University of Chicago DARRELL STROBEL, Johns Hopkins University ANTHONY L. TURKEVICH, University of Chicago RAINER WEISS, Massachusetts Institute of Technology DEAN P. KASTEL, Staff Director iv
COMMIS S ION ON PHYSICAL SCIENCES, MATHEMATICS, AND RES OURCES HERBERT FRIEDMAN, National Research Council, Chairman CLARENCE R. ALLEN, California Institute of Technology THOMAS D. BARROW, Standard Oil Company, Ohio (retired ) ELKAN R. BLOUT, Harvard Medical School BERNARD F. BURKE, Massachusetts Institute of Technology GEORGE F. CARRIER, Harvard University CHARLES L. DRAKE, Dartmouth College MILDRED S. DRESSELHAUS, Massachusetts Institute of Technology JOSEPH L. FISHER, George Mason University JAMES C. FLETCHER, University of Pittsburgh WILLIAM A. FOWLER, California Institute of Technology GERHART FRIEDLANDER, Brookhaven National Laboratory EDWARD D. GOLDBERG, Scripps Institution of Oceanography MARY L. GOOD, Allied Signal Corporation J. ROSS MACDONALD, University of North Carolina, Chapel Hill THOMAS F. MALONE, Saint Joseph College CHARLES J. MANKIN, Oklahoma Geological Survey PERRY L. McCARTY, Stanford University WILLIAM D. PHILLIPS, Mallinckrodt, Inc. ROBERT E. SIEVERS, University of Colorado JOHN D. SPENGLER, Harvard School of Public Health GEORGE W. WETHERILL, Carnegie Institution of Washington IRVING WLADA WSKY-BERGER, IBM Corporation RAPHAEL G. KASPER, Executive Director LAWRENCE E. McCRAY, Associate Executive Director v
FOREWORD The Space Science Board's ( SSB ) Committee on Space Astronomy and Astrophysics ( CSAA ) prepared the following report in order to provide NASA with a strategy for proceeding with Explorer-class programs for research in space astronomy and astrophysics. With this report and its companion, A Strategy for the Explorer Program for Solar and Space Physics ( National Academy Press, 1 984), prepared by the Space Science Board's Committee on Solar and Space Physics ( CSSP ) , the SSB has now completed its study of NASA's Explorer Program. These two reports strongly endorse a vigorous Explorer Program, but are necessarily different in ways that reflect the needs of the respective disciplines. Solar and space physics requires direct access to a large volume of space and frequent opportunities in order to keep the science vital. Space astronomy also requires frequent access to space and often needs technologies (i.e., those enabling accurate pointed observations) that are inherently costly and result m more expensive missions. The needs of these different areas of science require a flexible program to support many different approaches. The great strengths of the Explorer Program-easy, frequent, and inexpensive access to space-have not been fully exploited in recent years. Although more advanced technologies and some scientifically ambitious missions have vii
been developed within the program, the main reason for the loss of vigor of the Explorer Program has been the erosion of buying power by a budget that has not kept pace with inflation. The program could serve most of the requirements of the space physics, solar physics, and astronomy and astrophysics communities if NASA would make a strong effort to ensure the program proceeds expeditiously and if a major augmentation of the budget is provided. The CSSP and CSAA reports document in a convincing way that the health of space physics, solar physics, and astronomy and astrophysics requires a total Explorer budget of approximately $130 million (1986 dollars) per year ($80 million for astronomy and astrophysics and $50 million for solar and space physics). Even in an era of space stations and Great Observatories, Explorers will play an important role in furthering the objectives of space physics, solar physics, and astronomy and astrophysics. They will continue to be the primary tool for exploring new regions or phenomena, a means of demonstrating new design concepts and hardware for scientific instruments, the bridge between sounding rocket/Spartan experiments and major missions, and an opportunity to develop the scientific research and engineering capabilities of individuals and organizations. We believe it is imperative that the tremendous potential of the Explorer Program to the United States space research effort not be lost-NASA must make the effort to revitalize the program and provide the necessary funding. Thomas M. Donahue, Chairman Space Science Board viii
PREFACE In its first 25 years the Explorer Program has produced an outstanding record of discoveries that impact nearly all aspects of the scientific study of the Universe. However, looking to the future there are major problems within the Explorer Program. The number of Explorer flight opportunities is rapidly diminishing and an exceedingly long interval of time now passes between initial acceptance and the actual launch of an Explorer mission. Missions selected in 1974 will probably not fly until the early 1990s. Because of concern over the future viability of the program, the Committee on Space Astronomy and Astrophysics (CSAA) under the Chairmanship of Jacques M. Beckers began a study in November 1 984 of NASA's Explorer Program in order to evaluate the future role of Explorer-class missions for astronomy and astrophysics. The CSAA Explorer study was chaired by Andrea K. Dupree and was charged with addressing the following points: â¢ The role of Explorers in astronomical research. â¢ Scientific objectives for Explorers. â¢ Cost, capability, and frequency of astronomy missions. â¢ Examples of possible missions. ix
â¢ Selection process for new Explorers. â¢ Relation to other programs, e.g., Spartans, Space Station, Space Observatories. In our study of the Explorer Program for the past two years, we consulted many members of the space astronomy and astrophysics community and listened to presentations by scientists, project managers, and engineers to learn of their experiences and to profit from their advice. Draft versions of the CSAA Explorer report were discussed extensively at three meetings of the full CSAA between February 1985 and March 1986. In order to have a broad ranging discussion within the science community, draft versions of the report were presented and discussed at meetings of two NASA advisory committees (Astrophysics Management and Operations Working Group and Astrophysics/Relativity Management and Operations Working Group). Our report was in preliminary draft form when the Space Shuttle Challenger exploded on January 28, 1 986. Our Committee shares with the nation a deep grief over the loss of the seven exceptional people aboard that mission. In the reassessment of the United States space program which is now occurring, it is very appropriate to consider how the Challenger disaster will influence the Explorer Program. In the short term ( the next 4 years), it appears that launch opportunities for space science payloads will be severely limited. This will undoubtedly delay the launch of several Explorer missions. Since a vigorous healthy Explorer Program requires frequent and timely access to space, we hope there is a careful reevaluation of. the most cost effective way to provide that access in the future. Astronomy and Astrophysics Explorers have produced spectacular advances in our knowledge of the universe. Future Explorers currently in the queue will also certainly produce fundamental new knowledge. However, the rate of progress in the future will be greatly slowed unless there is a substantial augmentation in the funding of the Explorer Program. X
The task of producing this report involved the help of many of our scientific and technical colleagues. Even though we cannot acknowledge all individually, we are grateful for their thoughtful contributions. We especially wish to acknowledge the assistance we received from NASA headquarters, particularly from C. Pellerin and E. Weiler. Richard Hart as Executive Secretary was an invaluable resource and source of support. Stephanie Deeley of the Center for Astrophysics produced a superb manuscript. Andrea K. Dupree, Chairman CSAA Explorer Report Blair D. Savage, Chairman Committee on Space Astronomy and Astrophysics xi
CONTENTS I. EXECUTIVE SUMMARY 1 Introduction 1 Recommendations 2 II. THE ROLE OF EXPLORERS IN ASTRONOMY AND ASTROPHYSICS 7 Goals of the Explorer Program 7 Developmental Components of Space Astrophysics 10 Relation to Other Flight Opportunities 12 III. ACCOMPLISHMENTS OF ASTRONOMY AND ASTROPHYSICS EXPLORERS 15 Explorer 11: Gamma-Ray Astronomy 15 Explorer 38: RAE-I 18 Explorer 42: SAS-1 ( Uhuru) 18 Explorer 48: SAS-2 18 Explorer 49: RAE-2 19 Explorer 53: SAS-3 19 International Ultraviolet Explorer 20 Infrared Astronomical Satellite 21 Astrophysics Experiments on Other Missions 23 1. Cosmic-Ray Research 23 2. Gamma-Ray Research 24 xiii
I. EXECUTfVESUï¿½Y INTRODUCTION The Explorer Program has established an outstanding record of scientific accomplishments in a variety of space sciÂ ence fields including astronomy and astrophysics, space plasma physics, and solar physics. This report reviews the accomplishÂ ments and continuing promise of the Explorer Program for Astronomy and Astrophysics. It describes the unique character of Explorer opportunities and presents anÂ· assessment of the funding requirements necessary to maintain an effective scienÂ tific program for astronomy and astrophysics. The needs of the solar and space physics community have been addressed in a previous report (A Strategy for the Explorer Program for Solar and Space Physics, National Academy Press, 1984). Experiments in the Explorer line offer well-defined, problem-oriented opportunities to achieve observations and measurements in space. Continuity and stability of the Explorer budget line enable reasoned scientific programs to be developed and carried out. The success of the program stems also from the flexible mix of Principal Investigator ( PI ) class instruments and of moderate experiments using both free-flying spacecraft and "piggyback" instruments. Guest Observer proÂ grams have captured individual talents and the imagination of many hundreds of astronomers per year. Explorers also proÂ vide the opportunity for free-flying spacecraft to be located in regions of space that are optimum for the scientific goals. 1