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THE DECADE OF DISCOVERY IN ASTRONOMY AND ASTROPHYSICS Executive Summary THE DECADE OF DISCOVERY In the coming decade astronomers will use telescopes in space, in aircraft, on the ground, and even underground to address fundamental questions concerning our place in the universe. Do planets orbit nearby stars? What triggers the formation of stars? How do life-giving elements such as carbon and oxygen form and disperse throughout the galaxy? Where can black holes be found, and do they power luminous galaxies and quasars? How and when did galaxies form? Will the universe continue to expand forever, or will it reverse its course and collapse on itself? The 1990s promise to be a decade of discovery, providing at least partial answers to known fundamental questions. New instruments will reveal previously unimagined aspects of the universe and will lead to new questions about objects that we do not yet know exist. The National Research Council commissioned the Astronomy and Astrophysics Survey Committee, a group of 15 astronomers and astrophysicists, to survey their field and to recommend the most important new ground-and space-based initiatives for the coming decade. The survey committee obtained advisory studies from over 300 astronomers who participated in one or more of the 15 panels established to represent different wavelength disciplines, as well as solar, planetary, theoretical, and laboratory astrophysics. Many other astronomers provided written advice or participated in organized discussions. More than 15 percent of American astronomers played an active role in some
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THE DECADE OF DISCOVERY IN ASTRONOMY AND ASTROPHYSICS aspect of this study. The committee also consulted with distinguished foreign scientists on future directions in astronomy. In addition to constructing a prioritized list of new instruments based on its assessment of the opportunities for fundamental scientific advances, the committee also evaluated the existing infrastructure, considered the human aspects of the field, including education and international collaborations, explored the consequences of the computer revolution for astronomy, investigated the astronomical opportunities provided by lunar observatories, prepared a popular summary of opportunities for scientific advances in astronomy, and suggested the most promising areas for developing new observational technologies. The committee also examined the ways in which astronomical research contributes to society. For the decade of the 1990s, the committee places the highest priority for ground-based research on increased support for the infrastructure for astronomy and sets as the highest priority for space-based research the establishment of a program that has an appropriate balance between more frequent small and moderate projects and unique large projects. The prioritized list of new equipment initiatives primarily reflects the committee's assessment of the relative scientific potential of the different projects. The committee also took into account cost-effectiveness, technological readiness, educational impact, and the relation of each project to existing or proposed initiatives in the United States and in other countries. RESTORING THE INFRASTRUCTURE The committee's highest priority for ground-based research is to strengthen the research infrastructure at universities and at the national observatories. The committee recommends that the National Science Foundation increase the operations and maintenance budgets of the national observatories to an adequate and stable fraction of their capital cost, thereby repairing the damage caused by a decade of deferred maintenance. The committee recommends an increase in the individual grants program in astronomy at the NSF to permit young researchers to take advantage of the new opportunities for discovery, to utilize appropriately the large amounts of new data, and to enhance support for theoretical astrophysics. ACHIEVING A BALANCED SPACE PROGRAM For space astronomy, the report highlights the need for a balanced program that includes both the Great Observatories and more frequent, smaller missions.
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THE DECADE OF DISCOVERY IN ASTRONOMY AND ASTROPHYSICS The Great Observatories are large facilities that make possible “small science” at institutions distributed across the country, since typically only a few researchers work on each observing project. The committee reexamined the justification for large-scale space astronomy programs, taking into account both the failure to meet specifications for the Hubble Space Telescope and the National Aeronautics and Space Administration 's (NASA's) record of successes in carrying out other complex missions at the frontiers of science and technology. The committee concluded that large telescopes are required to answer some of the most fundamental questions in astronomy. However, smaller telescopes can be built and launched more quickly to answer specific questions, to respond to technological innovations, and to train future generations of scientists. THE PRIORITIZED INSTRUMENTAL PROGRAM Progress in astronomy often comes from technological advances that open new windows on the universe or make possible large increases in sensitivity or resolution. During the 1990s, arrays of infrared detectors, the ability to build large optical telescopes, improved angular resolution at a variety of wavelengths, new electronic detectors, and the ability of computers to process large amounts of data will make possible an improved view of the universe. Paralleling these breakthroughs in observational capability are greater demands on astrophysical theory that are being met with new generations of computers. Modern instruments reveal details that often require sophisticated models for their interpretation. Successfully comparing the results of observations with the constructs of theory, and predicting new phenomena, will require deeper understanding of astrophysical processes, more clever algorithms, more computational power, and improved knowledge of physical constants. The survey committee divided its recommendations for instrumental initiatives into categories of large, moderate, and small programs, depending on the scale of the necessary resources. Ground- and space-based facilities were prioritized in a combined list and also separately. Table 1 presents the recommended list of ground- and space-based equipment initiatives in the large and moderate-sized categories. The four large programs recommended for construction in the 1990s are described below in order of priority. Large Programs The Space Infrared Telescope Facility (SIRTF), which would complete NASA's Great Observatory program, would be almost a thousand times more sensitive than earth-based telescopes operating in the infrared. Advanced arrays of infrared detectors, pioneered in the United States, would give SIRTF the ability to map complex areas and measure spectra a million times faster
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THE DECADE OF DISCOVERY IN ASTRONOMY AND ASTROPHYSICS TABLE 1 Recommended Equipment Initiatives (Combined Ground and Space) and Estimated Costs Initiative Decade Cost ($M) Large Programs Space Infrared Telescope Facility (SIRTF) 1,300 Infrared-optimized 8-m telescope 80 Millimeter Array (MMA) 115 Southern 8-m telescope 55 Subtotal for large programs 1,550 Moderate Programs Adaptive optics 35 Dedicated spacecraft for FUSE 70 Stratospheric Observatory for Far-Infrared Astronomy (SOFIA) 230 Delta-class Explorer acceleration 400 Optical and infrared interferometers 45 Several shared 4-m telescopes 30 Astrometric Interferometry Mission (AIM) 250 Cosmic-ray telescope (Fly's Eye) 15 Large Earth-based Solar Telescope (LEST) 15 VLA extension 32 International collaborations on space instruments 100 Subtotal for moderate programs 1,222 Subtotal for small programsa 251 DECADE TOTAL 3,023 a See Chapter 1 for details. than any other space-borne infrared telescope. Two successful Explorer missions provide an excellent technical heritage for SIRTF. An infrared-optimized 8-m U.S. telescope operating on Mauna Kea, Hawaii, would provide a unique and powerful instrument for studying the origin, structure, and evolution of planets, stars, and galaxies. With diffraction-limited angular resolution better than a tenth of an arcsecond, high sensitivity due to the low telescope background, and instruments capable of high spectral resolution, the infrared-optimized 8-m telescope would complement SIRTF across the limited range of wavelengths transmitted by the atmosphere. Plans for this telescope draw on a decade of progress in the technology of building large mirrors. The Millimeter Array (MMA), an array of telescopes operating at millimeter wavelengths, would provide high-spatial- and high-spectral-resolution images of star-forming regions and distant star-burst galaxies. With spatial resolution of a tenth of an arcsecond at a wavelength of 1 mm, the MMA
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THE DECADE OF DISCOVERY IN ASTRONOMY AND ASTROPHYSICS would bring new classes of objects into clear view for the first time. The MMA utilizes experience and technology developed for the Very Large Array and for two smaller millimeter arrays. An 8-m optical telescope, operating from the Southern Hemisphere, would give U.S. astronomers access to important objects in southern skies. All-sky coverage is essential for pursuing many of the most fundamental astronomical questions. Small and Moderate Programs Small and moderate-sized programs can be carried out relatively quickly in response to new scientific or technological developments, focusing research into the currently most rewarding areas and making possible greater participation by young astronomers. Some of the most exciting scientific results of the past decade have come from modest, cost-effective programs. The committee recommends that an increased emphasis be given in the astronomy research budget to small and moderate programs. SPACE-BASED PROGRAMS Recommendations for moderate-sized space programs include a three-phase augmentation of NASA's Explorer program by purchasing a dedicated spacecraft for the Far Ultraviolet Spectroscopy Explorer (FUSE), increasing the number of astrophysics missions launched on Delta rockets to six for the decade, and increasing the number of astrophysics Explorers launched on Scout-class rockets to five for the decade. The Stratospheric Observatory for Far-Infrared Astronomy (SOFIA), a moderate-sized telescope in a 747 aircraft, would open submillimeter and far-infrared wavelengths to routine observation and would help train new generations of experimentalists. The committee emphasizes that a moderate-class Astrometric Interferometry Mission (AIM) capable of measuring the positions of astronomical objects with a precision of a few millionths of an arcsecond would have a great impact on many branches of astronomy. The committee recommends specific funding for flying U.S. instruments on foreign spacecraft. GROUND-BASED PROGRAMS For ground-based astronomy, the committee judged that two innovative techniques, adaptive optics and interferometry, can greatly enhance the spatial resolution of astronomical images. Adaptive optics can ameliorate the distorting effects of atmospheric turbulence and can be applied to existing or planned telescopes at infrared wavelengths, and eventually at optical wavelengths. The
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THE DECADE OF DISCOVERY IN ASTRONOMY AND ASTROPHYSICS Large Earth-based Solar Telescope (LEST) would provide important information about the sun and test the application of adaptive optics techniques. Optical and infrared interferometry promises spatial resolution better than a thousandth of an arcsecond by linking the outputs of widely separated telescopes. Improvements in the quality and spatial resolution of radio images will be possible with an extension to the Very Large Array. The committee urges the construction of additional 4-m optical telescopes to provide greater access for U.S. scientists to state-of-the-art instrumentation capable of addressing significant astronomical problems. Private and state funds should be sufficient to build and operate such instruments, augmented with modest federal assistance. The committee urges construction of an innovative telescope to determine the characteristics of the most energetic cosmic rays. The committee emphasizes the importance of continued funding for the development of improved detectors at optical and infrared wavelengths, and of instruments to detect neutrinos and “dark matter.” THEORY AND COMPUTERS The success of modern astrophysics illustrates the close interdependence of theory, observations, and experiment. The committee believes that NSF and NASA should increase their support for relatively inexpensive theoretical and laboratory work that is crucial to the interpretation of the results from major observatories. The committee recommends that theoretical astrophysics be funded as a separate program and be given additional resources within the NSF. Within NASA, support for theoretical astrophysics should grow in approximate proportion to the support for the analysis and interpretation of observational data. Astronomers use computers to collect and study billions of bytes of data every 24 hours and to make theoretical simulations of complex phenomena. The committee recommends establishment of national electronic archives of ground- and space-based data, the purchase of desktop and departmental computers, and the development of fast networks to link most astronomical computers together. LUNAR ASTRONOMY A major space exploration initiative could return humans to the moon in the early part of the next century. The committee studied the suitability of the moon for possible astronomical facilities and concluded that a cost-effective and
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THE DECADE OF DISCOVERY IN ASTRONOMY AND ASTROPHYSICS scientifically productive program would require early technology development, including pilot programs with substantial scientific return. The committee recommends that an appropriate fraction of the funding for a lunar initiative be devoted to supporting fundamental scientific missions as they progress from small ground-based instruments, to modest orbital experiments, and finally, to the placement of facilities on the moon. The advanced technology should be tested by obtaining scientific results at each development stage. The committee urges the selection of a modest project for the early phase of the lunar program, such as a 1-m-class telescope for survey or pointed observations, that would provide useful scientific data and valuable experience for operating larger facilities in the future. The committee concluded that, in the long term, the chief advantage of the moon as a site for space astronomy is that it provides a large, solid foundation on which to build widely separated structures such as interferometers. ASTRONOMY AND SOCIETY Answering questions about the universe challenges astronomers, fascinates a broad national audience, and inspires young people to pursue careers in engineering, mathematics, and science. The committee recommends enhancing astronomy's role in precollege science education by increasing the educational role of the national observatories, by expanding summer programs for science teachers, and by setting up a national Astronomy Fellowship program to select promising high school students for summer internships at major observatories. Astronomical research assists the nation, directly and indirectly, in achieving societal goals. For example, studies of the sun, the planets, and the stars have led to experimental techniques for the investigation of the earth's environment and to a broader perspective from which to consider terrestrial environmental concerns such as ozone depletion and the greenhouse effect. Research in astronomy derives its support from the curiosity of human beings about the universe in which we live, from the stimulus it provides to young people to study science, from the synergistic benefits to other sciences, and from the unforeseen practical applications that occasionally ensue. While participating in the thrill of the discovery of new things “out there,” society passes on something of value to future generations.
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