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Approved, Continuing, and Previously Recommended Programs AS emphasized in Chapter 2, the achievement of the goals for as- tronomical research presented in Chapter 3 depends heavily on the maintenance of support for approved and continuing programs; these, together with programs previously recommended in other National Academy of Sciences reports for implementation in fiscal year 1982 and earlier, form the base of present and planned resources from which the recommendations of the Astronomy Survey Committee proceed. Their role in the research of the 1980's is discussed below in the following order, which carries no implication of priority: A. Space Telescope and the associated Space Telescope Science Institute; B. Second-generation instrumentation for Space Telescope; C. The Gamma Ray Observatory; D. Level-of-effort observational programs within the National Aeronautics and Space Administration: The NASA Explorer satellite program, with a substantial aug- mentation, Research with balloons, aircraft, and sounding rockets, at enhanced levels of support, and The Spacelab program, reaffirming NASA'S original strong commitment to research with the Space Shuttle; E. Two major astrophysics facilities for Spacelab: The Shuttle Infrared Telescope Facility (STRTF) and 101

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102 ASTRONOMY AND ASTROPHYSICS FOR THE 1980's The Solar Optical Telescope (SOT); F. Facilities for the detection of solar neutrinos; G. Federal grants in support of basic astronomical research at U.S. . . . unlverslhes; H. Programs at the National Astronomy Centers; and I. The 25-Meter Millimeter-Wave Radio Telescope. The remainder of the present chapter illustrates the role that these programs will play in addressing the major scientific problems of the coming decade. A. SPACE TELESCOPE AND THE ASSOCIATED SPACE TELESCOPE SCIENCE INSTITUTE The Astronomy Survey Committee regards Space Telescope (ST) as a project of extreme importance for all of astronomy and rec- ommends that NASA complete its development and place it into operation at the earliest possible date. This facility will represent one of the most momentous advances in astronomical instru- mentation since Galileo's first telescope. The launch of ST, now planned for 1985, will provide the first permanent optical observatory in space. This facility, carrying a 2.4-m telescope of superb optical quality, will take full advan- tage of the benefits of observing above the Earth's atmosphere: sharp images unaffected by clouds or atmospheric turbulence, elimination of airglow, and extension of the spectral range into the ultraviolet (uv) and near-infrared wavelength regions. ST will be the first orbiting telescope large enough to carry out studies of extragalactic objects at the limits of the observable Universe. The first complement of instruments on ST will obtain digital photometric images over the wavelength range 1200-12000 A, spectra from 1200 to 8000 ~ with a large range of resolutions, and visible and uv photometry with fast time resolution. The European Space Agency will provide one of these instruments as part of a planned international collaboration in the ST program. The results of ST will profoundly affect every branch of as- tronomy. Identification and photometry of stars fainter than the twenty-seventh magnitude in the visible and uv regions will revolutionize extragalactic astronomy. Studies of stellar popula- tions down to the main sequence can be made in nearby galax- ies and in almost all of the globular clusters of our Galaxy. Bright stars suitable as distance indicators can be observed individually

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Approved, Continuing, and Previously Recommended Programs 103 ,~ in galaxies out to the Virgo cluster, allowing the cosmic expan- sion to be studied with unprecedented accuracy. The high an- gular resolution of ST will permit morphological classification of galaxies with red shifts up to order unity, allowing direct stud- ies of the evolution of galaxies over the past 5 billion to 8 bil- lion years. What kinds of galaxies may be associated with qua- sars is likely to be determined from an analysis of ST images. The question of whether some galaxies harbor giant black holes in their nuclei may be settled. Galactic astronomy will utilize the ability to measure the very faint stars in globular clusters and the Galactic bulge to determine, for example, the mass function of star formation in various regions of the Galaxy. The imaging ca- pability of ST will also open an important new range of investi- gations within the solar system; for example, diffraction-limited images at high spatial resolution will permit detailed views of the structure and dynamics of atmospheric circulation on other planets. The spectroscopic capabilities of ST are equally impressive. Our understanding of the interstellar medium, revolutionized by ob- servations with the Copernicus satellite and rocket surveys of soft x rays, will be further advanced by ST measurements down to 1200-A wavelength: new observations will be made at much higher spectral resolution and in much more heavily obscured regions all over the Galaxy. Most of the known quasars can be studied spectroscopically in the uv region, permitting critical comparisons of distant and nearby objects and the use of qua- sars as probes of the intervening medium. In planetary astron- omy, the w spectroscopic capability will permit searches for new molecules in planetary atmospheres and comets and delineate their structure. The surface chemistry of planets and asteroids can also be explored. The Committee strongly approves NASA'S commitment to oper- ate and support ST through an associated but independent Space Telescope Science Institute, which will include international par- ticipation. The Institute will be responsible for the scientific di- rection of ST, for data-reduction facilities, for education concern- ing use of the instrumentation, and for meeting all research expenses incurred by the ST user community; it will also be the liaison between NASA and the scientific community on matters concerning the management and improvement of this powerful instrument.

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104 ASTRONOMY AND ASTROPHYSICS FOR THE 1980's B. SECOND-GENERATION INSTRUMENTATION FOR SPACE TELESCOPE Space Telescope is designed to employ interchangeable instru- ments that can be replaced either in orbit or when ST iS re- turned to Earth. Since ST should exploit all the benefits of the latest technology, the Astronomy Survey Committee regards timely upgrading as extremely important. Major changes that can cur- rently be foreseen include improvements to the ST spectrographs and the implementation of ST'S potential infrared capability. These two changes are sufficiently important to merit further discus slon. Both of the first-generation spectrographs on ST employ Digi- con detectors with one-dimensional diode arrays behind a pho- tocathode. The power of a spectrograph can be increased dra- matically through use of a two-dimensional detector; in an echelle format, for example, a wide spectral range is then available in one high-resolution exposure; for extended objects, spatial infor- mation is then obtained along the entire slit image. It seems likely that two-dimensional, charge-coupled-device-type detectors with very low read-out noise and high uv sensitivity will become available within a few years. This combination of two-dimen- sional coverage with high quantum efficiency constitutes an up- grading of very high priority. Present ST instruments do not allow observations at wave- lengths much longer than 1 ~m. Although the infrared region will also be covered by the ERAS Explorer satellite and the powerful SIRTF Shuttle facility, the large aperture of ST gives it a great advantage in two crucial areas of scientific investigation. One is imagery in the near infrared, for which detectors of high quan- tum efficiency will almost certainly soon become available. The other is high-resolution spectroscopy throughout those extensive regions of the infrared to which the Earth's atmosphere is opaque; this work requires the greater collecting area and angular reso- lution of ST. Infrared capability in each of these areas is com- plementary to both ground- and space-based programs and will be valuable for a wide variety of critical programs ranging from planetary science to cosmology. For example, since the expan- sion of the Universe shifts the well-studied optical region into the infrared for very distant objects, evolutionary studies of galaxies cannot be complete without infrared data. The Committee there

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Approved, Continuing, and Previously Recommended Programs 105 fore recommends that NASA develop appropriate infrared instru- ments to be flown aboard ST. C. THE GAMMA RAY OBSERVATORY The Astronomy Survey Committee believes that the Gamma Ray Observatory (GRO) will yield results on high-energy processes that will be of fundamental importance to the advance of astrophys- ics during the coming decade. The 1979 report of the Space Sci- ence Board's Committee on Space Astronomy and Astrophysics (CSAA) recommended that GRO be the next new space-astronomy mission beyond those already approved by Congress at that time (A Strategy for Space Astronomy and Astrophysics for the 1980's, Na- tional Academy of Sciences, Washington, D. C., 1979~. The Sur- vey Committee joins with CSAA in endorsing this important fa- cility and is pleased that GRO iS now an approved component of the U.S. space-science program. Gamma-ray astronomy permits the study of energy transfor- mations in critically important processes, such as cosmic explo- sions, acceleration and interactions of high-energy particles, gravitational accretion by superdense objects, nucleosynthesis in stars, and matter-antimatter annihilation. Because gamma rays have high penetrating power, they can reach the Earth from parts of the Universe whose optical or low-energy x-ray emission may be obscured by intervening matter, such as the center of our own Galaxy and the central regions of active galaxies. Observations with GRO will address many important astro- nomical questions. The SAS-2 satellite and, in Europe, the COS-B satellite have demonstrated the rich character of the diffuse Gal- actic radiation, believed to be a result of cosmic-ray interactions with the interstellar medium. Observations of this emission on a finer scale with GRO will help to determine the origin and dy- namic-pressure effects of cosmic rays, to identify large concen- trations of interstellar gas, and to study Galactic structure. Numbers of discrete gamma-ray sources have been detected in previous surveys. While some of these are associated with known supernova remnants and pulsars, others have not yet been identified at longer wavelengths and may thus represent a new class of objects. Additional gamma-ray observations are required to clarify why some sources are more complex than anticipated. The Vela pulsar, for example, exhibits two gamma-ray pulses per

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106 ASTRONOMY AND ASTROPHYSICS FOR THE 1980's cycle, while only one pulse occurs in the radio region; more- over, neither gamma-ray pulse is in phase with the radio pulse. Another puzzle is a strong source in the general direction of the Galactic center, which is indicative of pair annihilation; further observations are needed to investigate the nature of this source. GRO can obtain information relevant to nucleosynthesis by de- tecting nuclear-decay gamma-ray lines of recently synthesized elements in our own and other nearby galaxies. In the most in- tense sources it may be possible to record line profiles, from which one can infer the current rate of heavy-element produc- tion and information relevant to the densities, temperatures, and flow velocities in supernova remnants. Regions in which mas- sive stars are forming may be found through observations of the lines of isotopes such as 26A1. GRO will permit the study of cosmic gamma-ray bursts with much greater sensitivity and energy resolution than provided by any previous or other currently planned mission, thus shedding new light upon the nature of gamma-ray burst sources. GRO will also obtain detailed information on the spatial uni- formity and energy spectrum of the diffuse extragalactic gamma radiation, providing clues to its origin. Since gamma radiation may reflect most directly the primary emission process in active galaxies, GRO observations will contribute to an improved under- standing of these objects. Studies of time variability at gamma-ray (and other) wavelengths will yield insight into the active vol- umes and associated energy densities. High-energy gamma rays may also be observed from nearby normal galaxies; if so, GRO data will furnish information on the distributions of cosmic rays and matter in such galaxies as well. The Committee agrees with CSAA that the continued develop- ment and timely launch of GRO iS essential to the pursuit of these important scientific objectives during the coming decade. ~ {Jet 1 D. LEVEL-OF-EFFORT OBSERVATIONAL PROGRAMS WITHIN THE NATIONAL AERONAUTICS AND SPACE ADMINISTRATION NASA has developed three modes for carrying out observational space astronomy within level-of-effort programs: the Explorer program; balloons, aircraft, and sounding rockets; and the Spacelab program. Each of these modes provides a highly effec- tive and in some cases unique mechanism to address particular observational problems in astronomy and to test instrument con

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Approved, Continuing, and Previously Recommended Programs 107 cepts employing state-of-the-art technology. The Astronomy Sur- vey Committee regards these level-of-effort programs as the backbone of observational space astronomy and astrophysics for the 1980's. The Committee therefore urges the continued, vigor- ous support of the Explorer program and of research with bal- loons, aircraft, and rockets, together with a speedy reaffirmation of NASA'S original strong commitment to the Spacelab program. The Explorer Program The Explorer program has been one of the most productive and cost- effective elements of the NASA space-science program. Its level-of- effort character has encouraged both frugal management and rela- tively rapid response to newly perceived scientific opportunities, providing a highly effective mechanism to exploit new observational techniques, to explore newly accessible wavelength intervals, or to study a particular class of objects. Nearly all of the branches of space astronomy have had or will soon have their beginnings in Explorer missions. For example, the present International Ultraviolet Explorer (lUE) program has provided essentially all of the intermediate-reso- lution uv spectra available to the world of astronomy. The future astronomy Explorers now under development or planned give prom- ise of continuing this high level of pioneering achievement: The Infrared Astronomy Satellite THRASH, a project based on in- ternational collaboration, will provide a detailed and comprehensive reconnaissance of those components of the Universe that radiate most strongly at relatively low temperatures (100-1000 K). Millions of sources that emit substantially in the 10-100-m wavelength range should be detected and their positions determined by ERAS, providing a wealth of material for an initial survey of regions of active star formation as well as of the brightest extragalactic sources. ERAS will also be able to determine the surface composition of thousands of asteroids within the solar system. The Cosmic Background Explorer (COBE) will make definitive measurements of the 3 K cosmic background radiation, now generally accepted to be a relic of the radiation generated in the big bang. COBE will test this conclusion through precise measurements of the inten- sity throughout the spectrum and of the anisotropy of the radiation. Deviations from isotropy on the largest angular scales reflect the motion of our Galaxy with respect to the large-scale structure of the

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108 ASTRONOMY AND ASTROPHYSICS FOR THE 1980's Universe, while deviations on angular scales of the order of 10 carry unique information about the inhomogeneity of the early Universe. The Extreme Ultraviolet Explorer (EUVE) will open for study an- other major region of the electromagnetic spectrum, from 100 to 912 wavelength (from soft x rays to the uv region below the Lyman limit), a primary objective being the completion of an unbiased, all- sky survey of sources of EUV radiation. EUVE iS expected to reveal a large number of new sources with temperatures in the range 105- 106 K, furnish broadband spectral information on many other already known sources, and provide new information on the structure and ionization state of the interstellar medium over a wide range of distances from the Sun. This mission can also yield new information about the Jovian magnetosphere and cometary atmospheres. The X-Ray Timing Explorer (XTE) will provide important new opportunities for observations of variability in x-ray sources on time scales ranging from milliseconds to years. The scientific objectives of this mission include investigations of the mass, magnetic moment, and internal structure of neutron stars and degenerate dwarfs; the physics of accretion disks, plasmas, and stellar magnetospheres; the geometry of source emission regions; the nature and evolution of normal stars, through studies of mass loss; the nature of variable sources, such as x-ray bursters and transient x-ray sources; and the underlying physics and emission mechanisms in compact extraga- lactic objects. The Committee endorses the above mission concepts, which have been carefully studied and highly recommended by other review groups. Our concern is primarily for the future of this highly pro- ductive program. We believe that it is vitally important for NASA to maintain a strong Explorer program; over the past decade, however, inflation and other factors have doubled the dollar cost charged to the Explorer budget for the same real level of effort. The Committee therefore recommends an augmentation to the Explorer program to restore it at least to the level of effort of the previous decade. Such an augmentation will ensure not only the timely flights of the mis- sions described above but also opportunities for pursuit of many other exciting new scientific objectives, as discussed in Chapter 6. Balloons, Aircraft, and Sounding Rockets The balloon, aircraft, and sounding-rocket programs have been vi- tally important to the progress of astronomy and to the development

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Approved, Continuing, and Previously Recommended Programs 109 and testing of new detector systems later used on satellites. The Greenstein report recommended a doubling of support for balloons, rockets, and aircraft; balloon research has received strong support by the Balloon Study Committee of the Geophysics Research Board (The Use of Balloons for Physics and Astronomy, National Academy of Sciences, Washington, D.C., 1976~; and balloons, aircraft, and rockets have been supported by CSAA in its recent report (`A Strategy for Space Astronomy and Astrophysics for the 1980's, National Academy of Sci- ences, Washington, D.C., 1979~. Unfortunately, funding for such programs has not grown, although the need is ever more acute. The present Committee supports a vigorous effort in all three areas during the 1980's to encourage innovative experiments and to obtain promptly the initial scientific results from recently developed instruments. The balloon program has been of particular value to infrared, x- ray, gamma-ray, and cosmic-ray astrophysics, yielding important contributions to the study of cosmic rays, energetic x-ray spectra, low-energy gamma-ray bursts, gamma radiation from the Galactic center, and far-infrared emission from ionized H ~ regions. Balloon detector systems were prototypes for instruments on HEAo-3 and SAS-2 and for several of those planned for COBE, Spacelab, and GRO. The balloon program will continue to provide important new sci- entific results and permit new instruments to be tested in an envi- ronment similar to that of space. In order to remain productive, this program should receive an augmentation in funding to compensate for inflation, to provide larger balloons for heavier instruments, and to develop a new balloon system to allow flights of longer duration. The NASA aircraft program-including the U2 aircraft, the Lear let Observatory, and especially the Kuiper Airborne Observatory (KAO: has achieved scientific results of great importance, including the first observations of far-infrared emission from other galaxies; an impor- tant series of infrared observations of our own Galactic center; the study of internal energy sources in Jupiter, Saturn, and Neptune; the probing of interstellar molecular clouds and ionized regions in new ways; a primary role in the discovery of rings around Uranus; and studies of water vapor in the atmosphere of Jupiter and of sulfuric acid droplets in the clouds of Venus. The KAO and Lear let Observatory not only continue to serve as test facilities for many of the research instruments and techniques being developed for space- science applications but also provide the reconnaissance of the field necessary for future major missions. For example, first-generation instrumentation for far-infrared and submillimeter-wavelength spec- troscopy is now being used on KAO to probe the spectral lines that

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110 ASTRONOMY AND ASTROPHYSICS FOR THE 1980's are believed to govern the energy balance in the bulk of the inter- stellar medium. The full potential of these aircraft observatories un- fortunately has not been achieved because of a lack of funds for operations and personnel. A substantial increase in funding should be provided for KAO operations in particular, not only to compensate for increased fuel costs but also to permit the greater numbers of flights required for a more intensive and hence more efficient use of this outstanding facility. The U.S. sounding-rocket program has played a key role in ad- vancing the frontiers of x-ray, ultraviolet, and infrared astronomy, with achievements including the discovery of the first cosmic x-ray source (Sco X-1), discovery of x-ray pulsations from the Crab pulsar, the first measurement of the uv spectrum of a nearby quasar, the first soft x-ray sky survey, and the first ~20-~m all-sky survey, which yielded new information about classes of previously unobserved in- frared sources. Sounding rockets will continue to provide economical and effective means for developing new instruments, for testing new observational techniques, and for exploratory investigations. A strong sounding-rocket program should therefore be maintained. The Com- mittee also endorses the extension of observing time for rocket pay- loads through their placement in temporary orbit by the Space Shuttle as part of NASA'S Experiment of Opportunity Program (EOP). The Spacelab Program The Spacelab program will provide new flight opportunities for large payloads that require servicing and will facilitate observational pro- grams demanding higher altitudes or flights of longer duration than . . . ~ . . ~ . . ~ ~ . ~ . ~ can ne achieved by aircraft or balloons. Spacelab flights will be par- ticularly suitable for those facilities (both large and small) that can gather substantial quantities of data within the relatively short initial flights of the Space Shuttle; the Solar Optical Telescope and Shuttle Infrared Telescope Facility described in Section E below are examples. On its recent report, cited in the preceding section, CSAA recom- mended a vigorous program of astronomy and astrophysics on Spacelab with an annual level of effort exceeding that of a typical moderate ~ . . c. .ass mission. It is therefore of serious concern that funding for Spacelab exper- iments and facilities has not yet reached substantial levels; support for experiments that have already been approved has been signifi

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Approved, Continuing, and Previously Recommended Programs 111 cantly reduced, and the selection of additional PI experiments has been deferred. The Committee is cognizant of the programmatic and technical problems that have contributed to these decisions. How- ever, now that flights of the Space Shuttle have begun, we urge NASA to re-establish its original strong commitment to a vigorous Spacelab program as soon as possible. The Spacelab program will also facilitate the development of large instruments designed to make initial observations on Shuttle flights and later to be placed in orbit to carry out more comprehensive scientific programs, possibly aboard a long-duration space platform. The augmentation of Spacelab capability by such a space platform would allow the Shuttle to realize its full potential as a scientific tool. We therefore support NASA plans for the development of a long- duration space platform operated in conjunction with Spacelab and the Shuttle (see Appendix A, Statement Concerning a Space Plat- form). We furthermore endorse the pursuit of means to extend the observing time available to rocket-sized payloads through the de- velopment of a standard module that will allow such payloads to be placed in temporary orbit during Spacelab missions, without incur- ring the substantial costs of an active Shuttle interface, such as may be required for larger payloads. The Committee also encourages the development of a Solar Shuttle Facility, composed of several advanced facility-class instruments, to be used in a coordinated group on the Space Shuttle. These instru- ments will obtain data critical to an understanding of the fundamental plasma processes underlying cyclic activity and transient high-energy phenomena on the Sun and other stars; their development should proceed as part of the ongoing Spacelab program, with the Solar Optical Telescope (SOT) as the first such instrument. A plan for the addition of succeeding instruments is expected to emerge from the recommendations of other advisory groups, particularly the cssP. Among the other instruments proposed for inclusion are a Solar Soft X-Ray Telescope Facility (SSXTF), a Grazing Incidence Solar Telescope (GRIST, selected for advanced study by the European Space Agency), and a Pinhole/Occulter Facility for hard x-ray imaging and for the study of the corona at high resolution (currently under study by NASA). Still other solar instruments-such as those for EM and gamma- ray observations and for specialized observations of the extended corona, long-period photospheric oscillations, and large-scale circu- lation should be considered for development as PI instruments or as additional facilities within the Spacelab program.

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2 ASTRONOMY AND ASTROPHYSICS FOR THE 1980's E. TWO MAJOR ASTROPHYSICS FACILITIES FOR SPACELAB The Astronomy Survey Committee endorses both the Shuttle In- frared Telescope Facility (SIRTF) and the Solar Optical Telescope (SOT) as the first major astrophysics facilities planned for Space- lab; the order of the following discussion carries no implication of priority. The Shuttle Infrared Telescope Facility (SIRTF) The proposed SIRTF will be the cornerstone of research in infrared astronomy during the 1980's. The Astronomy Survey Committee joins with the Space Science Board's Committee on Space Astronomy And Astrophysics (A Strategy for Space Astronomy and Astrophysics for the 1980's, National Academy of Sciences, Washington, D.C., 1979) in recommending this facility as the first major infrared telescope in space. STRTF will permit investigations over the enormous range of wave- lengths from 2 to 300 ~m. For some important types of observations it will, because of its cryogenically cooled optics, yield a sensitivity gain of 1000 over the largest existing ground-based and airborne infrared telescopes; this gain in sensitivity is so large that it is not unreasonable to expect that SIRTF will make important and unex- pected discoveries. The multiple, interchangeable focal-plane instru- ments planned for SIRTF will moreover greatly increase our ability to explore the evolution of distant extragalactic sources, the physical properties and chemical composition of molecular clouds and regions of star formation, the nature of cometary nuclei and asteroids, and the structure of planetary atmospheres. For example, STRTF will be able to detect infrared sources at the limits of the observable Universe; on one Shuttle flight, it could gather information on sources of both large and small red shift, thus permitting a comparison of the en- ergetics of quasars and galaxies at the earliest epochs of the Universe with those at the present epoch. Because of its relatively wide field of view, SIRTF will also be able to carry out efficient surveys of infrared sources that will help to optimize the observing programs of larger instruments, such as the New Technology Telescope (NTT), the VERB Array, and a Large Deployable Reflector (LDR) in space, which have narrower fields of view. STRTF should be an early and frequently flown payload on Shuttle sortie missions. It has such high sensitivity that very extensive in- frared observations can be accomplished even within the relatively

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Approved, Continuing, and Previously Recommended Programs 113 brief, 7-day profile of an early Shuttle flight; reflight on the Shuttle makes it possible to fly STRTF with continually improved focal-plane instrumentation and detectors. Eventually, however, SIRTF flights of longer duration will be needed to realize the full potential of this remarkable facility, and the study of such flights is recommended in Chapter 7. The Solar Optical Telescope (SOT) The SOT will carry out solar observations from 1100-A wavelength into the near-infrared wavelength region with high angular resolu- tion 0.1 arcsec at 5000 ~ (70 km on the Sun) and nearly 0.02 arcsec at 1100 ~ (14 km) together with very high spectral resolution. Fol- lowing the recommendations of the Space Science Board's Committee on Space Astronomy and Astrophysics ( OCR for page 101
114 ASTRONOMY AND ASTROPHYSICS FOR THE 1980's dynamics of the solar convection zone; the dynamo responsible for the solar magnetic field and the solar activity cycle; and the ther- modynamic structure and dynamical behavior of the solar photo- sphere, chromosphere, transition region, and corona. A more com- plete understanding of these solar properties should also lead to a better understanding of physical processes in high-temperature plas- mas, energy-release mechanisms in other objects such as quasars, and activity cycles in other stars. F. FACILITIES FOR THE DETECTION OF SOLAR NEUTRINOS The Astronomy Survey Committee recommends continued, vig- orous support for programs to detect and measure the flux of neutrinos from the interior of the Sun. Additional facilities are needed to supplement the data currently being obtained by 37C1 detectors at underground sites, and the use of a neutrino detec- tor employing substantial quantities of gallium presents a partic- ularly attractive opportunity to broaden our knowledge of the solar-neutrino energy spectrum. Detectors employing 7Li and win may also become feasible during the coming decade. The observation of neutrinos produced in the interior of the Sun is our only direct source of information about the process of stellar energy generation, which is of fundamental importance to an understanding of the structure and evolution of the Sun and other stars. Experiments of the past decade emplovinz 37C1 de v~ ~ , . ~ ~ v sectors at underground sites suggest strongly that relatively high- energy neutrinos from the solar interior are arriving at the Earth at no more than one third of the rate predicted by theory. A1- though this finding has prompted searching re-examination of the theory of stellar energy generation, of currently accepted models for solar structure, and of neutrino physics itself, no generally accepted explanation for the discrepancy has yet been found. The revision of present concepts in any one of these three areas of inquiry would have profound implications for astronomy and astrophysics. It is important that the 37C1 experiments be continued and re- fined so that they may yield more precise data. At the same time, it is essential to pursue the solar-neutrino problem with additional, complementary experiments aimed at recording those neutrinos produced in other chains of nuclear reactions inside the Sun. The use of substantial quantities of gallium as a detector

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Approved, Continuing, and Previously Recommended Programs 115 offers an outstanding opportunity in this regard and permits the concurrent test of relevant neutrino properties as well. For a conclusive measurement of the solar-neutrino flux in the coming decade, approximately 50 tons of gallium will be required; how- ever, the gallium will not be consumed during the experiment envisaged and may be sold at its completion. A pilot experiment employing 1.3 tons of gallium was suc- cessfully completed during the summer of 1980. The U.S. De- parl~ent of Energy and the Max Planck Institutes in Germany are now supporting the development of a larger detector that will be calibrated with a laboratory source of neutrons produced in a reactor. The Committee urges continued financial support of the gallium-detector experiment by this international collaboration and the completion and operation of the full gallium neutrino detec- tor at the earliest opportunity. G. FEDERAL GRANTS IN SUPPORT OF BASIC ASTRONOMICAL RESEARCH AT U. S. UNIVERSITIES The Astronomy Survey Committee recommends the continuation of programs of federal grants in support of basic astronomical research at U.S. universities. The most important of these are the grants program of NSF'S Astronomy Division and grants awarded through NASA'S Research and Analysis Program (formerly the Supporting Research and Technology Program); the research needs of the 1980's will require substantial increases in both of these funding sources. U.S. astronomical research is carried out in a number of dif- ferent types of organizations, including federal laboratories, the National Astronomy Centers, privately endowed research insti- tutes, private industry, and private and state universities. The diversity of these organizations is one of the strengths of the national research effort in astronomy; for example, U.S. research in radio, x-ray, and uv astronomy was initiated at federal and industrial laboratories, while optical astronomy started much ear- lier in universities and research institutes. Vigorous programs of basic astronomical research at U. S. universities are of special importance in this overall effort be- cause universities are responsible for the training of future re- search scientists and teachers of astronomy and, through their teaching programs, for the dissemination of the latest scientific . . .

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116 ASTRONOMY AND ASTROPHYSICS FOR THE 1 980's results to students and the general public. In this process, the interaction of established astronomers with bright young people stimulates many new ideas for research and for the develop- ment of new techniques. The great majority of visiting astrono- mers who use the National Astronomy Centers are university scientists; the overall scientific productivity of the Centers is thus itself heavily dependent on the quality of the university research environ- ment. The strength and vigor of university research in turn depends decisively on federal support through grants to university scientists. Federal support of university research in astronomy flows from a number of sources. The most broadly distributed and critically needed support of university research comes from grants awarded through NASA'S Research and Analysis (R&A) Program, which is essential to the health of U.S. space astronomy, and from the grants program of NSF'S Astronomy Division, which provides support to greater numbers of U.S. university astronomers than any other federal funding source. NASA'S R&A program has been highly effective in supporting basic research of importance to the planning of space-science missions. Those fields of astronomy that are restricted to obser- vations from balloons, rockets, aircraft, or space vehicles such as gamma-ray, x-ray, and uv astronomy, together with cosmic-ray stud- ies rely almost totally on R&A funding for initial research efforts. The R&A program has been critical for the\ development of instru- mentation, detectors, and other hardware for space astronomy and will continue to play this key role throughout the coming decade; R&A support of theoretical astrophysics should also increase sub- stantially in the years ahead. NSF'S mission to support U.S. ground-based astronomy finds a particularly effective expression at the universities through the Astronomy Division grants program, which is the primary source of operating funds for many of the nation's major university-op- erated radio-astronomy observatories and which also provides extensive support for instrumentation at many ground-based op- tical observatories operated by universities. Most theoretical as- trophysics in the United States is also supported through the NSF grants program (with a small but increasingly important contri- bution by NASA). The purchase of computers, the development of detectors, the construction of instrumentation, and the support of technical personnel are other examples of the critically important needs met by NSF grants program. Finally, both the R&A program of NASA and the NSF grants

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Approved, Continuing, and Previously Recommended Programs 117 program are essential for the effectiveness of university research activities, providing funds for travel, publication costs, and com- putation, together with student, postdoctoral, and in the sum- mer faculty salaries. These funds, which are awarded on the basis of merit, reach an extremely wide range of the U.S. astro- nomical community and foster a cooperative spirit that benefits all involved. The universities provide the research environment and academic-year salaries to scientists; NASA and NSF provide these scientists with the appropriate tools for research. For these reasons, the NASA and NSF grants programs will continue to be essential to the health of basic astronomical re- search at U.S. universities in the coming decade. Substantial in- creases above present funding levels in both programs will be necessary to provide for expanded needs for instrumentation and detectors, theory and data analysis, computational facilities, lab- oratory astrophysics, and technical support at ground-based ob- servatories, as discussed in Chapter 5. H. PROGRAMS AT THE NATIONAL ASTRONOMY CENTERS The Astronomy Survey Committee recommends the vigorous support of programs carried out at the National Astronomy Centers. Five of the Centers receive support from NSF'S Astron- omy Division: Sacramento Peak Observatory, one of the nation's leading in- stitutions for ground-based observational research in solar physics; Kitt Peak National Observatory, operator of the most heavily utilized and broadly instrumented collection of optical and infrared telescopes generally available to American astronomers; Cerro Tololo Inter-American Observatory in Chile, a vital optical/ infrared window on the southern hemisphere of the sky, operated with the cooperation of Chilean astronomers, who share in the ob . , . serving time; National Astronomy and Ionosphere Center, operator of the world's largest (300-m) single-dish radio telescope at Arecibo, Puerto Rico; and National Radio Astronomy Observatory, operator of the nation's most varied collection of radio-astronomy facilities, including the Very Large Array (VLA) and, in the future, the 25-Meter Millimeter- Wave Radio Telescope.

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118 ASTRONOMY AND ASTROPHYSICS FOR THE 1980's The three remaining Centers receive federal funding through other channels: High Altitude Observatory of the National Center for Atmos- pheric Research, funded by NSF'S Atmospheric Sciences Division for studies of solar physics; The recently completed 3-m Infrared Telescope Facility on Mauna Kea, operated as a national facility by NASA; and The Space Telescope Science Institute, recently established by NASA at The Johns Hopkins University and charged with the future scientific direction of Space Telescope (ST), together with oversight of support for ST users. The continued health of U.S. astronomy depends on the proper balance between programs carried out at private and state observa- tories and those at the National Astronomy Centers. The National Center programs must weigh fairly in this balance for a number of reasons. The Centers furnish the only facilities available to all the nation's astronomers without the necessity of contract or grant sup- port. They are able to provide resources on the scale needed to operate the largest telescopes as nationally accessible facilities. Be- cause the user community is able to exert a decisive influence on the initiation and guidance of scientific research efforts, the National Center programs are highly responsive to the needs of the astro- nomical community. Finally, the National Centers design and de- velop instrumentation that later benefits research groups across the nation. It is thus essential to preserve and strengthen the research capabilities of the National Astronomy Centers. The decade of the 1970's saw a major expansion and upgrading of the observational facilities operated by the National Astronomy Centers for the benefit of the astronomical community. During the 1980's, however, the operations budgets of those centers serving as sites for additional new instruments will have to be increased if the potential of these new facilities is to be realized. Although in some cases economies could be effected through the closing of older Center facilities as new ones become operational, it must also be borne in mind that telescopes do not "wear out." When equipped with mod- ern instrumentation and detectors, older telescopes will continue to provide excellent research opportunities at low cost. Moreover, re- search opportunities for many Center facilities, both new and old, will expand during the coming decade in response to the scientific challenges to be presented by the next generation of astronomical

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Approved, Continuing, and Previously Recommended Programs 119 observations from space. Meeting these challenges will require a vigorous, coordinated program of observations from ground-based observatories covering both hemispheres of the sky. Critically im- portant in such a program will be the contribution of the Cerro Tololo Inter-American Observatory; this facility and the privately operated Las Campanas Observatory are the only two major southern-hemi- sphere observatories regularly available to U.S. astronomers. The Committee believes that the National Centers must have strong resident scientific staffs to initiate and guide instrument-development efforts, to assess the performance of observatory equipment, and to assist visiting scientists. To maintain their expertise, such staff mem- bers should be encouraged to engage in forefront research of their own and given adequate opportunities to do so. The National Centers face a difficult task in responding to the diverse needs of a heterogeneous user community. They will con- tinue to need the strong support and encouragement of sponsoring federal agencies in the decade ahead. The Centers must be funded at a level that not only provides for the maintenance of existing facilities and staff but also permits the acquisition of appropriate new equipment in addition to the major capital expenditures recom- mended by the Astronomy Survey Committee. I. THE 25-METER MILLIMETER-WAVE RADIO TELESCOPE The Astronomy Survey Committee supports the construction of a 25-Meter Millimeter-Wave Radio Telescope as provided in the long-range plan of the Astronomy Division of the National Sci- ence Foundation and as had been recommended, in an earlier form, in the Greenstein report (Astronomy and Astrophysics for the 1970's, National Academy of Sciences, Washington, D.C., 1972~. The rapid completion of this facility and its associated instru- mentation will be important to continued U.S. progress and leadership in millimeter-wave astronomy during the coming dec- ade. Studies of star formation, mass loss from stars, the interaction of galaxies with their environment, changes in the nonthermal luminosity of energetic objects, and other important astrophysi- cal processes provoke questions that can be best addressed by observations made at millimeter wavelengths, from 1 to 10 mm, or 30-300 GHz in frequency. For example, the study of star for- mation benefits from millimeter-wave observations because even optically opaque interstellar clouds are transparent to radiation at

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120 ASTRONOMY AND ASTROPHYSICS FOR THE 1980's millimeter wavelengths, and many of the emission lines of the molecules found in clouds lie in the millimeter spectral region. These molecular radiations provide detailed information about the obscured regions containing the molecules, including the extent, motions, densities, and temperatures of interstellar clouds. This information-particularly when supplemented by the results of infrared photometry and spectroscopy can provide remarkable insights into the star-formation process itself. The discovery at millimeter wavelengths of more than 50 mo- lecular species in interstellar clouds has generated a new field of astronomical research, astrochemistry, directed toward under- standing the formation and chemistry of interstellar molecules and elucidating the role they play in the collapse of interstellar clouds to form stars. Millimeter-wave continuum observations provide an important probe of the Universe as a whole. For example, x-ray observa- tions show that many clusters of galaxies are pervaded by dif- fuse gas having temperatures between 107 and 108 K; millimeter- wave observations of the microwave background toward such clusters may reveal depressions in the intensity arising from in- verse-Compton scattering of the microwave background by the electrons in the hot gas. X-ray and millimeter-wave observations of the same objects can be combined to provide a determination of the value of the Hubble constant that is independent of other methods. Because of the importance of such studies to astronomy, the Committee believes it essential to undertake a greatly expanded program of millimeter-wave astronomy during the coming dec- ade. Unfortunately, present u . a. s~ng~e-a~sn m~merer-wave telescopes have inadequate angular resolution and collecting area, are not sufficiently precise to allow observations at the shortest wavelengths desired, and have restricted sky coverage because of their northerly locations. The 25-Meter Millimeter-Wave Tele- scope will largely remove such restrictions. The Committee notes that Great Britain, France, West Germany, and Japan are also planning or constructing major new millimeter-wave facilities; these initiatives reflect a worldwide recognition of the impor- tance of this area of research. The United States 25-m telescope will be larger, or will have greater sky coverage, or will operate at shorter wavelengths than these other new instruments, per- mitting the United States to maintain its leadership in this excit- ing and highly productive field. ~T ~ 1 1 1 11 lo_

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