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On the Space Station and Prerequisites for the Human Exploration Program On the Space Station and Prerequisites for the Human Exploration Program On March 19, 1993, Space Studies Board Chair Louis J. Lanzerotti sent the following letter, accompanying the report cited, to NASA Administrator Daniel Goldin. It is my pleasure to present to you, on behalf of the Space Studies Board and its Committee on Human Exploration, copies of our new report, Scientific Prerequisites for the Human Exploration of Space. This report surveys and elaborates the key research that must be carried out before a program of human exploration can be undertaken. This research is necessary to establish whether long-duration human spaceflight is possible, and if it is, what technical approaches are most likely to be successful and productive. Substantial preparatory work for Moon and Mars missions can be conducted by robotic probes, but I would like to take this opportunity to elaborate on the special roles of the life sciences and of a piloted space station. NASA has recently announced the intention of conducting a sweeping review of the Space Station Freedom program. Recognizing that the decision to expand human presence into the solar system "must be based on nontechnical factors,"1 the Board has steadfastly maintained that "a properly equipped and configured space station is pivotal"2 to essential preliminary research. The enclosed report states3 that The Space Studies Board strongly affirms the position that a suitably equipped space-based laboratory is required to study the physiological consequences of long-term spaceflight. The Board has summarized the major characteristics of such a space station on several occasions, extracting these from the fundamental guidance provided in the Goldberg report of its Committee on Space Biology and Medicine.4 At the same time that the space station design is being reevaluated, it is apparent that the new administration may be reexamining the position of human space exploration within national priorities. Human return to the Moon or exploration of Mars may not be pursued on an aggressive timetable in our current environment of constrained resources-indeed, the Augustine Committee recommended that the Mission From Planet Earth be undertaken on a "go-as-you- file:///C|/SSB_old_web/chexltr.htm (1 of 3) [6/18/2004 10:36:32 AM]
On the Space Station and Prerequisites for the Human Exploration Program pay" basis.5 However, the Board has noted that "many of the fundamental problems in life sciences research involve a long period of time for their pursuit and solution."6 The enclosed report asserts,7 nonetheless, that the difficulties currently being experienced by the space station project do not negate the essential need for such a facility to perform the enabling research on human adaptation to the microgravity environment necessary for a Moon/Mars program. The current redesign efforts should be based on a realistic assessment of the depth and pace of America's commitment to human exploration of the inner solar system. The body of the Board's work in space biology, together with the efforts of other advisory groups,8 provides comprehensive guidance on the capabilities needed to pave the way for this enterprise. If the goal of human exploration is superseded as the premise for the nation's space station program, planning and implementation of orbital research infrastructure should be adjusted to meet the requirements of the new objectives efficiently and cost-consciously. We must recognize, however, that such decisions might significantly delay the nation's option for human expansion into the solar system. I look forward to the opportunity to meet, at your convenience, with you and your colleagues to discuss our report further. 1Committee on Space Policy, Toward a New Era in Space: Realigning Policies to New Realities, National Academy Press, Washington, D.C., 1988. 2Space Studies Board, letter to NASA Administrator Richard Truly, March 30, 1992. 3Committee on Human Exploration of the Space Studies Board, Scientific Prerequisites for the Human Exploration of Space, National Academy Press, Washington, D.C., 1993, p. 13. 4Committee on Space Biology and Medicine of the Space Science Board, A Strategy for Space Biology and Medicine for the 1980s and 1990s, National Academy Press, Washington, D.C., 1987. 5Report of the Advisory Committee on the Future of the U.S. Space Program, Superintendent of Documents (GPO), Washington, D.C., December 1990. 6Space Studies Board, "Space Studies Board Position on Proposed Redesign of Space Station Freedom," March 14, 1991. 7 Ref. 3, p. 13. 8Aerospace Medicine Advisory Committee of the NASA Advisory Council, Strategic Considerations for Support of Humans in Space and Moon/Mars file:///C|/SSB_old_web/chexltr.htm (2 of 3) [6/18/2004 10:36:32 AM]
On Several Issues in the Space Life Sciences On Several Issues in the Space Life Sciences On April 26, 1993, Space Studies Board Chair Louis J. Lanzerotti and Committee on Space Biology and Medicine Chair Fred W. Turek sent the following letter to Dr. Harry Holloway, associate administrator for NASA's Office of Life and Microgravity Sciences and Applications. At the request of then Acting Director of Life Sciences, Joseph Alexander, the Committee on Space Biology and Medicine has examined and discussed four separate issues of concern to NASA and the Life Sciences Division and has developed comments and/or recommendations on each. Attachments A through D contain the committee's detailed conclusions and recommendations on (1) the use of research animals on Spacelab Life Sciences-2, (2) peer review of research proposals and programs, (3) optimizing the scientific benefits of the U.S./Russian Shuttle/Mir Program, and (4) Russia's biosatellite program (Bion). Following is a brief summary of the committee's thoughts on each. USE OF RESEARCH ANIMALS ON SPACELAB LIFE SCIENCES-2 The use of animals in research has been of fundamental importance to the progress that has been made in biology and medicine. Integral to the scientific success of the upcoming Spacelab Life Sciences-2 (SLS-2) mission will be the use of rodents both as controls on the ground and in-flight as subjects of experiments. Some of the rodents must be sacrificed in space. The results of these studies will, for the first time, allow direct comparison between tissues exposed solely to microgravity and those obtained from ground-based controls, thus providing a basis for the development of measures to counter the effects of microgravity on humans in space. The Committee on Space Biology and Medicine fully endorses NASA's plans to use research animals on SLS-2 and subsequent missions. (See Attachment A.) PEER REVIEW OF RESEARCH PROPOSALS AND PROGRAMS file:///C|/SSB_old_web/lifesci93ltr.htm (1 of 9) [6/18/2004 10:36:37 AM]
On Several Issues in the Space Life Sciences Peer review of research proposals and programs is a long-standing practice of the scientific community that many regard as fundamental to ensuring the integrity of research findings and progress. Because of cultural differences and operational concerns, NASA's life sciences research has not always enjoyed the benefit of rigorous peer review. The Committee on Space Biology and Medicine recommends that all NASA-sponsored extramural and intramural life sciences research proposals and programs be subject to external peer review conducted at regular intervals. Further, in order to guard against a real or perceived conflict of interest, NASA Headquarters should regularly review the policy and management practices applied to extramural research programs by intramural contract and grant administrators and monitors. If any conflicts of interest arise, steps should be taken immediately to resolve them. (See Attachment B.) OPTIMIZING THE SCIENTIFIC BENEFITS OF THE U.S./RUSSIAN SHUTTLE/MIR PROGRAM Recognizing that the upcoming U.S./Russian Shuttle/Mir cooperative missions are largely demonstrations of international cooperation and engineering, the committee nevertheless believes that maximum benefit to the life sciences should also be a goal. The Committee on Space Biology and Medicine thus recommends that NASA Headquarters take all possible measures to ensure that the biomedical science activities on these missions be subject to rigorous peer review. The committee also recommends that NASA solicit assistance from the National Institutes of Health in choosing outside, independent experts to participate in the project to maximize the prospects of achieving scientific goals. The committee understands that there are numerous constraints and uncertainties surrounding this mission. (See Attachment C.) RUSSIA'S BIOSATELLITE PROGRAM Russia's biosatellite program provides the world's only free-flying spacecraft available for conducting extended-duration animal research in space. Over the past 20 years, the United States has provided support to U.S. investigators (approximately $2 million per year) to fly experiments on Cosmos series biosatellites. Current plans call for termination of U.S. participation in this program. Cognizant of both the advantages and disadvantages of the biosatellite program, the Committee on Space Biology and Medicine recommends that NASA maintain the option for future use of the Bion satellites by continuing its dialogue with the Russians about the various options available. In the meantime, NASA should survey its user community to ascertain the extent of the interest in using the Bion satellites and should formally evaluate the relative costs and benefits of different platforms for conducting animal research in space. (See Attachment D.) file:///C|/SSB_old_web/lifesci93ltr.htm (2 of 9) [6/18/2004 10:36:37 AM]
On Several Issues in the Space Life Sciences In addition to requesting an examination of the above four items, Mr. Alexander asked that the committee consider reviewing its 1987 research strategy, A Strategy for Space Biology and Medical Science for the 1980s and 1990s, to assess whether that strategy requires augmentation and whether it accurately reflects the committee's current views and recommendations for NASA's space biology and medicine research program. The committee has discussed this request and plans to begin addressing it at its Spring 1993 meeting. We will keep you informed of our progress. ATTACHMENT A Use of Research Animals on Spacelab Life Sciences-2 Unique insights into modern medicine have been achieved through the humane use of animals in research. To enable the goal of long-duration human presence in space, we must continue to rely on animal experimentation to determine the consequences of, and develop countermeasures to, the effects of gravitational change. For NASA's life sciences program, and specifically the SLS- 2 flight scheduled for August 1993, the use of research animals is critical to the scientific success of the mission. Some of the rodents must be sacrificed in space.1 The Committee on Space Biology and Medicine agrees that this experimental protocol is well justified, for the following reasons: One of the most powerful tools available for the study of physiological processes in space and the development of measures to counter the effects of microgravity is animal research.2,3 Marked advances in biology, physiology, and medicine have been made possible through careful, scientific study of animals in the laboratory.4 The physiological consequences of exposure to microgravity have not yet been separated from those due to reentry forces because, in previous missions, tissue samples were collected only after return to Earth.5-7 In contrast, SLS-2 will, for the first time, offer the unique opportunity to collect tissue samples in the microgravity environment according to the same procedures used in ground-based studies and will allow for direct comparison of the tissue samples collected in both environments. The Committee on Space Biology and Medicine fully endorses the use of animals on SLS-2 and subsequent missions, and it commends NASA for its plans to provide for their optimal care and treatment in flight. Animal subjects will be handled in accordance with the recommendations of the American Veterinary Medical Association panel on euthanasia and the recommendations of other panels.8-11 Having a board-certified veterinarian on the mission will ensure the animals' welfare as well as the humane collection of animal tissue during the mission. file:///C|/SSB_old_web/lifesci93ltr.htm (3 of 9) [6/18/2004 10:36:37 AM]
On Several Issues in the Space Life Sciences ATTACHMENT B Peer Review of Research Proposals and Programs During the past several years NASA has strengthened its peer review of both extramural and intramural life sciences research projects. While recognizing the constraints imposed on mission-oriented science, the Committee on Space Biology and Medicine believes it is nonetheless critical to extend the peer review mechanism to cover all NASA-sponsored biomedical research projects, proposals, and programs, including operationally oriented programs such as the Extended Duration Orbiter Medical Program, the Biomedical Monitoring and Countermeasures Program, and the U.S./Russian Shuttle/Mir Program. A rigorous peer review process is essential to ensure high-quality research projects and programs. In particular, the committee recommends that: Peer review of intramural research programs should take place at regular intervals. Peer review of the content and accomplishments of intramural programs should take place every 3 to 5 years. A process akin to that used by the National Institutes of Health (NIH) for assessing its intramural research programs would be appropriate. The review process used at the NIH has ensured standards of performance respected throughout the biomedical community. Intramural and extramural research projects and programs should be subject to the same peer review standards. Despite the constraints on operationally oriented projects, it is essential to maintain comparable standards for the review of intramural and extramural research projects and programs, to help maintain the quality of both. Review of intramural research programs should be conducted by qualified individuals not associated with that particular program. Intramural projects and programs should not be reviewed by investigators who are collaborators or are affiliated with the programs being reviewed, nor should they be reviewed by NASA grantees who are personally involved with the programs or projects. NASA Headquarters should regularly review the policy and management practices applied to extramural research programs by intramural contract and grant administrators and monitors. In an attempt to use its resources and intramural scientific personnel as effectively as possible, NASA often uses its scientists and group leaders as Research and Technology Operating Plan (RTOP) managers. This practice has led to concern and distrust in the research community about real or perceived conflicts of interest in the awarding and administering of contracts and grants. This practice also potentially compromises the independence of extramural NASA investigators in reviewing intramural projects and programs. Although the involvement of active researchers in file:///C|/SSB_old_web/lifesci93ltr.htm (4 of 9) [6/18/2004 10:36:37 AM]
On Several Issues in the Space Life Sciences program management can be effective and productive, it also includes the potential for conflict of interest, and must therefore be carefully reviewed and monitored. Because even the appearance of a conflict of interest is counterproductive, it is incumbent on NASA Headquarters to institute procedures to regularly review the management of the research program and eliminate any conflicts. In the case of NASA's life sciences program, concerns have been raised by respected members of the community. The Committee on Space Biology and Medicine strongly urges the director of the Life Sciences Division to institute a procedure to regularly review the administration of the research program. If any conflicts of interest are discovered, NASA should take immediate action to resolve them. Such procedures will strengthen both the program and its administration. NASA should adopt the type of program administration that is used so effectively by the National Science Foundation and the National Institutes of Health, whose program officers have no direct personal interest in the research being conducted other than that it be successful. The program officer is judged on the basis of the overall quality and effectiveness of the research program he or she is overseeing. ATTACHMENT C Optimizing the Scientific Benefits of the U.S./Russian Shuttle/Mir Program The Committee on Space Biology and Medicine recognizes that the U.S./Russian Shuttle/Mir Program was initiated primarily to demonstrate international cooperation and that the program has specific engineering goals. It further recognizes that life sciences activities performed as a part of this program face severe time constraints.12 Within this context, the committee offers the following comments and recommendations with the goal of maximizing scientific achievements in the life sciences for both countries. These recommendations are consistent with recommendations made in A Strategy for Space Biology and Medical Science for the 1980s and 1990s13 and Assessment of Programs in Space Biology and Medicineâ1991.14 The committee has been informed by NASA that an investigative team will have responsibility for determining the overall scope and objectives of the program. Members of this team will be selected from a pool of investigators currently involved in operational issues associated with the human space program and from those with approved, peer-reviewed flight investigations. The committee also understands that NASA faces several unusual problems in trying to plan life sciences experiments because of the many uncertainties about the nature of the Shuttle/MIR program and the opportunities it offers for biomedical research. The unique opportunities that may arise from this program, however, require that NASA attempt to maximize the scientific return. Therefore the file:///C|/SSB_old_web/lifesci93ltr.htm (5 of 9) [6/18/2004 10:36:37 AM]
On Several Issues in the Space Life Sciences committee recommends the following: Any opportunities to conduct basic biological experiments during the Shuttle/Mir program should be seized as a means to extend NASA's ongoing physiological studies on humans in space. The best outside experts should be solicited to advise the program. Acknowledging the constraints and uncertainties associated with this program, NASA Headquarters should nevertheless take all possible measures to ensure that biomedical science activities on this mission be subject to rigorous peer review. Outside independent experts should be brought into the project to maximize the likelihood of achieving scientific goals. These experts should be involved in the planning and in the experimentation and analysis phases of the program to ensure that the highest-quality science is performed. To accomplish this, the appropriate National Institutes of Health (NIH) institutes should be asked to recommend specialists. This approach would enhance interactions between NIH and NASA and would provide a model for additional future international collaborations. ATTACHMENT D Russia's Biosatellite Program (Bion) Russia's biosatellite program includes a second-generation, free-flying satellite (Bion) of the Russian Cosmos series that allows for extended-duration animal experiments in space. The United States does not currently have this capability, nor does it have plans to fly biological specimens on free flyers in the future. Up to this point, NASA has sponsored U.S. scientists' use of Cosmos satellites for research, an activity cited as a major factor in the progress made in life sciences research over the last 5 years. However, because of budget pressures, this sponsorship was terminated at the time of the most recent Cosmos flight.15,16 It appears that without international cooperation and support, the Russians may in fact terminate the biosatellite program. The Committee on Space Biology and Medicine concludes that if Russia's biosatellite program is not canceled, Bion offers the following distinct advantages for the U.S. life sciences program: (1) Bion is currently the only vehicle available for extended-duration (30 to 60 days) animal experiments in space; (2) it provides a unique opportunity for follow-up research based on the most extensive set of existing U.S. data, collected on earlier missions, on microgravity's long-term effects on animal systems; and (3) it provides for continued, meaningful research in the period before a U.S. space station becomes available. file:///C|/SSB_old_web/lifesci93ltr.htm (6 of 9) [6/18/2004 10:36:37 AM]
On Several Issues in the Space Life Sciences At the same time, the committee recognizes that Bion has cost uncertainties as well as the following severe limitations: (1) Available power limits the number and type of experiments that can be conducted; (2) problems associated with reentry may compromise the interpretation of some scientific data; (3) there is no opportunity to manipulate the payload in flight; and (4) the instability of the political and economic situation in Russia may compromise the future of the biosatellite program and jeopardize potential U.S.-Russian cooperative activities. Having weighed both the advantages and disadvantages of continued U.S. participation in the biosatellite program, the Committee on Space Biology and Medicine recommends that: NASA should formally evaluate the relative benefits and cost- effectiveness of different platforms for animal research in space. Depending on the outcome of this analysis, NASA should consider providing research support in the 1995 life sciences budget for the biosatellite project. NASA should survey its user community to ascertain the extent of interest in the potential use of the Bion satellites. NASA should continue discussions with the Russians concerning potential U.S. use of the Bion satellites. NASA should indicate an "in principle" interest in the Bion project to the Russians in these continuing discussions. 1"Rationale and Protocol for Animal Sacrifice Onboard SLS-2 Mission," Communication from NASA Life Sciences Division, February 5, 1993. 2"Animal Use on the SLS-2 Mission," Presentation by Ron White, NASA Headquarters, to the Committee on Space Biology and Medicine, January 28, 1993. 3AStrategy for Space Biology and Medical Science for the 1980s and 1990s, Committee on Space Biology and Medicine, National Academy Press, Washington, D.C., 1987. 4Science, Medicine, and Animals, Committee on the Use of Animals in Research, National Academy Press, Washington, D.C., 1991. 5"Cosmos 1887 (Bion 8)," Special Issue, Federation Proceedings, FASEB, Vol. 4, No. 2, January 1990. 6"Cosmos 2044 (Bion 9)," Journal of Applied Physiology, Special Issue, file:///C|/SSB_old_web/lifesci93ltr.htm (7 of 9) [6/18/2004 10:36:37 AM]
On Several Issues in the Space Life Sciences (Supplement) Vol. 73, No. 2, August 1992. 7A Strategy for Space Biology and Medical Science for the 1980s and 1990s, Committee on Space Biology and Medicine, National Academy Press, Washington, D.C., 1987, and Assessment of Programs in Space Biology and Medicineâ1991, Committee on Space Biology and Medicine, National Academy Press, Washington, D.C., 1991. 8"1993Report of the Panel on Euthanasia," Journal of the American Veterinary Medical Association, Vol. 202, No. 2, January 15, 1993. 9Guide for the Care and Use of Laboratory Animals, NIH Publication No. 86-23, U.S. Department of Health and Human Services, Public Health Service, National Institutes of Health, Bethesda, Md., 1985. 10Laboratory Animal Management: Rodents, A Report of the Committee on Rodents, Institute of Laboratory Animal Resources, National Research Council, reprinted from ILAR News, Vol. XX, No. 3, 1977. 11"PositionStatement on Use of Animals in Research," NIH Guide for Grants and Contracts, Vol. 22, No. 8, February 26, 1993. 12"U.S./Russian Shuttle/Mir Program," Presentation by Frank Sulzman, NASA Headquarters, to the Committee on Space Biology and Medicine, January 27, 1993. 13AStrategy for Space Biology and Medical Science for the 1980s and 1990s, Committee on Space Biology and Medicine, National Academy Press, Washington, D.C., 1987. 14Assessment of Programs in Space Biology and Medicineâ1991, National Academy of Sciences, Washington, D.C., 1991. 15"Cosmos Biosatellite Program," Presentation by Frank Sulzman, NASA Headquarters, to Committee on Space Biology and Medicine, January 27, 1993. 16"Research Opportunities Using Cosmos Satellites-A User's Perspective," Presentation by Bernard Cohen, Mt. Sinai Hospital, to Committee on Space Biology and Medicine, May 14, 1992. file:///C|/SSB_old_web/lifesci93ltr.htm (8 of 9) [6/18/2004 10:36:37 AM]
On the Advanced X-ray Astrophysics Facility On the Advanced X-ray Astrophysics Facility On April 28, 1993, Space Studies Board Chair Louis J. Lanzerotti sent the following letter to Dr. Wesley T. Huntress, Jr., associate administrator for NASA's Office of Space Science. In a letter to me dated September 15, 1993, from Mr. Joseph Alexander, Assistant Associate Administrator for Space Science and Applications, NASA requested that the National Research Council (NRC) conduct a scientific evaluation of the restructured Advanced X-ray Astrophysics Facility (AXAF). Working jointly with the NRC's Board on Physics and Astronomy, the Space Studies Board established a Task Group on AXAF to perform this study. I am pleased to enclose the report of this task group. Please contact me if you have any questions about the report. SCIENTIFIC ASSESSMENT OF THE RESTRUCTURED PROGRAM FOR THE ADVANCED X-RAY ASTROPHYSICS FACILITY (AXAF) April 28, 1993 Summary The Task Group on AXAF (TGA), a joint panel of the Space Studies Board and the Board on Physics and Astronomy, finds that the restructured AXAF program-consisting of AXAF-I, to be launched into a high-Earth orbit in 1998, and AXAF-S, to be launched into a polar, low-Earth orbit in 1999-is fully capable of meeting the primary scientific goals of the former AXAF program. Although the need to reduce substantially the total cost of the program has led to shorter mission lifetimes, the expected increase in operating efficiency partly makes up for this shortfall. The TGA concludes that the revised AXAF program continues to meet the scientific expectations set forth in previous NRC reports, which have recommended AXAF as the highest-priority, new, large-scale program in astronomy. Thus the TGA urges NASA to proceed with the implementation of the file:///C|/SSB_old_web/axaf93ltr.htm (1 of 8) [6/18/2004 10:36:44 AM]
On the Advanced X-ray Astrophysics Facility restructured AXAF program and to make every effort to ensure the launch of both AXAF-I and AXAF-S before the end of this decade. Background In a letter dated September 15, 1992, from Joseph K. Alexander, Assistant Associate Administrator for Space Sciences and Applications, to Louis J. Lanzerotti, Chair of the Space Studies Board, NASA asked the National Research Council (NRC) to evaluate the scientific content and the expected scientific return of the restructured AXAF program. In response to this request the Space Studies Board and the Board on Physics and Astronomy jointly established the Task Group on AXAF (TGA) as a subpanel of the newly formed Committee on Astronomy and Astrophysics. Arthur F. Davidsen, of Johns Hopkins University, was appointed Chair of the TGA. The full membership of the task group is attached. The TGA was asked to carry out its review and evaluation of the AXAF reconfiguration by the end of 1992. The TGA held several meetings via teleconference during October and November 1992 and developed a set of questions concerning the reconfigured AXAF. These were addressed to AXAF program officials at NASA Headquarters and AXAF project officials at the Marshall Space Flight Center. In addition, all members of the AXAF Science Working Group were invited to provide to the TGA information and comments concerning the revised program. Martin Weisskopf, AXAF Project Scientist, provided an extensive written response comparing the scientific capabilities of the original and revised AXAF programs, and Peter Ulrich, AXAF Program Manager, provided written materials concerning the programmatic aspects of the restructuring. The TGA discussed all the responses in a teleconference on December 3, 1992, and held a meeting in Washington, D.C., on December 10 and 11, 1992, at which it heard presentations concerning the restructuring and had discussions with the several AXAF scientists and managers who attended part of the meeting. This report presents the TGA's conclusions and recommendations concerning the AXAF program. This report was reviewed and discussed by the parent boards of the TGA, the Space Studies Board and the Board on Physics and Astronomy, as well as by the new joint Committee on Astronomy and Astrophysics of the two boards (membership lists attached). Each of these reviews concurred fully with the substance and findings of the report. Previous NRC Recommendations for AXAF The AXAF mission has been anticipated and endorsed consistently by the decadal studies of astronomy and astrophysics carried out under the NRC's Board on Physics and Astronomy by the Bahcall committee and by the Field file:///C|/SSB_old_web/axaf93ltr.htm (2 of 8) [6/18/2004 10:36:44 AM]
On the Advanced X-ray Astrophysics Facility committee before that, and by several reports of the Space Studies Board (and its predecessor, the Space Science Board) and its committees: In 1979 (just prior to the launch of the Einstein satellite), the Committee on Space Astronomy and Astrophysics of the Space Science Board, in their document entitled A Strategy for Space Astronomy and Astrophysics for the 1980's (National Academy of Sciences, 1979), envisioned and recommended "a semipermanent (several-decade) national observatory facility . . . open to all astronomers and with instrument-changing possibilities . . . . More than an order- of-magnitude improvement in sensitivity over HEAO-2 (Einstein) is required to allow high-resolution spectroscopy and in-depth studies of specific objectives such as clusters of galaxies and active galaxies. This can be achieved by a combination of greater telescope size, better optical surfaces, improved focal- plane instrument sensitivity, and longer mission duration compared with HEAO- 2." (p. 13) The Field Committee report (Astronomy and Astrophysics for the 1980's, Volume I, National Academy Press, 1982) identified four key programs of critical importance for the advancement of astronomy and astrophysics in the 1980s. That committee's top priority was AXAF, which was envisioned as "a permanent national observatory in space, to provide x-ray pictures of the Universe comparable in depth and detail with those of the most advanced optical and radio telescopes. . . . [T]his facility will combine greatly improved angular and spectral resolution with a sensitivity up to one hundred times greater than that of any previous x-ray mission." (p. 15) In the report Long-Lived Space Observatories for Astronomy and Astrophysics (National Academy Press, 1987), the Space Science Board's Committee on Space Astronomy and Astrophysics stated that it "concurred with the recommendations of the Astronomy Survey Committee (1980), which urges the construction of AXAF . . . . [It] will play a fundamental role in the future progress of astronomy and astrophysics." (p. 2) In Space Science in the 21st Century (National Academy Press, 1988), the Space Science Board's Task Group on Astrophysics and Astronomy found that "[t]he powerful capabilities of AXAF and the wealth of fundamental problems it can address suggest that this facility will advance research [in x-ray astronomy] for a long time to come." (p. 27) The Astronomy and Astrophysics Survey Committee of the Board on Physics and Astronomy (The Decade of Discovery in Astronomy and Astrophysics, National Academy Press, 1991) found that AXAF "will return the United States to preeminence in x-ray astronomy . . . [and] have a major impact on almost all areas of astronomy . . . ." That committee reaffirmed the Field Committee decision making AXAF "the highest-priority large program" of the 1990s. (pp. 64-65) The TGA finds that the scientific performance of AXAF that was file:///C|/SSB_old_web/axaf93ltr.htm (3 of 8) [6/18/2004 10:36:44 AM]
On the Advanced X-ray Astrophysics Facility anticipated by these previous studies will still be achieved by the restructured program. It is obvious, however, that the authors of these earlier reports envisioned AXAF as a permanent or at least semipermanent x-ray observatory, with an associated program of maintenance that would include new focal-plane instrumentation. However, because the costs associated with such a program are too high to sustain in the current budget environment, NASA and the AXAF Science Working Group have decided that a pair of limited-life missions is a preferable scenario for accomplishing the scientific goals of the AXAF program. The TGA endorses this view and believes that the revised AXAF program will satisfy the scientific expectations encompassed by previous NRC committee reports, even though it will not provide a permanent x-ray observatory in space. The new program should be designed to ensure that the capabilities of AXAF will still be made available to the broad astronomical community through a vigorous guest observer program. Recent Developments in X-ray Astronomy Since the AXAF program was first conceived in the 1970s, the field of x- ray astronomy has progressed considerably. The TGA finds that recent developments have only strengthened the arguments in previous NRC reports supporting the need for the enhanced imaging and spectroscopic capabilities that the AXAF program can provide. A few examples are cited below. Several important results have recently come from the imaging detectors on ROSAT. A prime example from galactic studies is the detection of multiple low- luminosity x-ray sources in the cores of globular clusters. These may be the long- sought cataclysmic variables (white dwarfs that have captured binary companions in the dense cluster cores) and are only marginally resolved even with the ROSAT High-resolution Detector. Thus, the much higher spatial resolution of AXAF-I will be critical for more detailed studies. There are many new extragalactic results: one is the detection of extended x-ray emission around NGC 1068. Coupled with earlier work on NGC 4151, we now have solid evidence that a hot medium exists around the centers of active galactic nuclei (AGNs) and that spatially resolved, moderate-resolution x- ray spectroscopy will be an important tool for studying both the active nucleus and the surrounding medium. ROSAT has detected substructure in all clusters of galaxies observed. With detectors that provide both imaging and spectroscopic information, AXAF will measure the mass of galaxy groupings within a cluster and trace out the mass distribution. AXAF will provide a consistency check for the assumption of hydrostatic equilibrium, since x-ray-emitting shock waves should be present if hydrostatic equilibrium does not apply. ROSAT has shown that many, if not most, AGNs are strongly absorbed file:///C|/SSB_old_web/axaf93ltr.htm (4 of 8) [6/18/2004 10:36:44 AM]
On the Advanced X-ray Astrophysics Facility below 2 keV. With its higher-energy imaging capability, AXAF will not be impeded in its search for distant objects by the opacity of the circumstellar medium of an AGN. ROSAT, with an energy range below 2 keV, has resolved a large fraction of the x-ray background into discrete objects. AXAF, having significantly more sensitivity and angular resolution than ROSAT, should more completely resolve the x-ray background, if it is indeed entirely composed of discrete sources. Furthermore, AXAF results will apply to energies above 2 keV. The ROSAT all-sky survey has yielded a total of more than 50,000 objects that can be studied in depth with AXAF's broad range of spectroscopic capabilities. The ROSAT catalog is expected to be publicly available by the time AXAF is operating. The Japanese x-ray satellite Ginga detected 6- to 7-keV x-ray lines from nearby AGNs. This implies that iron lines, probably broadened fluorescence lines from circumnuclear material, are common emission features in AGN spectra, and that AXAF will therefore have the capability to measure redshifts of distant AGNs. A very recent result from the Broad-band X-ray Telescope (BBXRT) confirms the existence of an x-ray absorption line in the spectra of BL Lac objects. The greater sensitivity and spectral resolution of AXAF is needed to extend this search to other objects and other lines. The detection of other x-ray absorption lines will resolve ambiguities that currently plague the interpretation of these features. The premier astronomical event of the 1980s was the occurrence of SN1987a, the closest supernova explosion in 400 years. During its planned time in orbit AXAF may have the opportunity to observe an extraordinary phase in the evolution of SN1987a. The expanding shell of debris from the explosion will collide with a slow-moving ring of matter ejected by the star prior to its death. The best estimate for the time when collisions will begin is about the year 2000. Not only will the event be spectacularly bright in x-rays, but it will also be highly variable in intensity and in its spectral line distribution. The resulting display will provide the best determination of the abundances of newly synthesized matter. As collisions of different clumps of ejecta occur, SN1987a will reveal the composition of different parts of the supernova ejecta. AXAF will also have the ability to locate the positions of the discrete clumps as they are heated to temperatures at which x-rays are emitted. By observing how stars make elements, we will better understand how galaxies evolve. Such a direct observational test of nucleosynthesis theory will allow us to apply these models with confidence to abundance patterns in galaxies at high redshift. Comparison of the Original and Revised Programs The restructuring of the AXAF program splits the original, single facility (AXAF-O), a low-Earth-orbit serviceable mission, into two nonserviceable simpler missions: one devoted principally to imaging (AXAF-I), which will be launched into a high, elliptical orbit, and one devoted principally to spectroscopy (AXAF-S), file:///C|/SSB_old_web/axaf93ltr.htm (5 of 8) [6/18/2004 10:36:44 AM]
On the Advanced X-ray Astrophysics Facility which will be in a low, polar orbit. AXAF-I will carry four of the original six mirror- shell pairs that made up the AXAF-O telescope, two imaging cameras-the AXAF CCD Imaging Spectrometer (ACIS) and the High-resolution Camera (HRC)-and two spectrometers-the Low- and the High-energy Transmission Grating Spectrometers (LETGS and HETGS, respectively). AXAF-S will carry a lower- resolution, shorter-focal-length, foil-mirror telescope and the x-ray Spectrometer experiment (XRS). AXAF-O was designed to be serviced at five-year intervals for a total lifetime of fifteen years. The design lifetime of AXAF-I is five years, and the design lifetime of AXAF-S is three years. Since the technical aspects of the various instrument designs remain almost entirely unchanged, the scientific performance of the unified AXAF program is largely preserved. The principal differences are associated with the changes in the telescope complement and in the mission profile. Specifically: The reduction in the number of mirror-shell pairs in the AXAF-I telescope (from six to four) diminishes by about 40% the effective area of the system at low energies. However, this effect is largely offset by the increase in the observing efficiency of the mission brought about by the change to high-Earth orbit. In particular, the number of observations that can be accomplished at fixed sensitivity over an extended period of time is very nearly the same for the original and the revised AXAF missions. At high energies, the effective area of the system has actually been improved, due to the introduction of high-reflectivity iridium coatings in place of the nickel and gold coatings planned for the original telescope's outer and inner mirror shells, respectively. The use of the low-resolution foil telescope for AXAF-S affects both the spatial resolution and the effective area of the XRS investigations. Although some capability for spatially resolved high-resolution spectroscopy still exists with this experiment, measurement of spectral variations on fine angular scales is no longer possible. The foil telescope has very high throughput, and so the net effective area is comparable to that for AXAF-O at high energies and is down by a factor of only about 2 at low energies. Most importantly, the XRS is likely to be more productive during its design lifetime on the AXAF-S mission than it would have been on AXAF-O, simply because it can be operated continuously, thereby utilizing its limited supply of cryogen more efficiently. Another advantage of the restructured program will be the opportunity to conduct simultaneous observations with the two missions. This can be extremely useful for complementary measurements of time-variable sources. As an example, for many sources such as active galactic nuclei, x-ray binaries, and stellar flares, AXAF-S can be used to obtain high-resolution spectra of the Fe K complex near 6 keV (E/ E ~ 500), while at the same time the HETGS experiment on AXAF-I is used to make high-resolution observations of the Fe L complex near 1 keV (E/ E ~ 1000). The comparison of Fe K to Fe L line fluxes and profiles will prove very useful for constraining plasma conditions in these sources. file:///C|/SSB_old_web/axaf93ltr.htm (6 of 8) [6/18/2004 10:36:44 AM]
On the Advanced X-ray Astrophysics Facility Finally, elimination of the servicing aspect of the program reduces net observing time by a factor that is less than 2, since in the restructured mission, AXAF-S and AXAF-I will be operated independently. Perhaps the most serious loss in this regard involves the capability of fielding new instrumentation that might have capitalized on future technological advances or been designed specifically to follow up earlier AXAF discoveries. It seems likely, however, that alternative, post-AXAF mission scenarios could prove equally effective as platforms for fielding new instrumentation, perhaps even in a more cost-effective manner. The restructured AXAF mission maintains essentially all of the outstanding scientific capabilities of the baseline mission. The angular resolution of AXAF-I is more than an order of magnitude better than that offered by any other mission under development or even in the planning stages. The U.S. investment in high-precision x-ray optics makes AXAF-I unique in its capabilities to undertake x-ray investigations on the largest scales and at the earliest epochs of the universe. Similarly, the broad-band, nondispersive spectroscopy enabled by the development of the micro-calorimeter (the XRS) is maintained in the restructured mission. AXAF-S will provide a combination of high sensitivity and high spectral resolution in the important energy region above 4 keV that is unavailable with any other planned missions. Its capabilities for high-resolution spectroscopy of extended sources are particularly notable and unique in comparison with those of dispersive spectrometers. The restructured AXAF program continues to provide unmatched angular resolution, spectral resolution, and sensitivity that will make it the centerpiece of international efforts in x-ray astronomy for the foreseeable future. When the AXAF-I and AXAF-S spacecraft are launched at the end of this decade, they will provide unique capabilities permitting major advances in our understanding of the universe. References 1. Committee on Space Astronomy and Astrophysics, Space Science Board, A Strategy for Space Astronomy and Astrophysics for the 1980s, National Academy of Sciences, Washington, D.C., 1979. 2. Astronomy Survey Committee, Astronomy and Astrophysics for the 1980's, Volume I, National Academy Press, Washington, D.C., 1982. 3. Committee on Space Astronomy and Astrophysics, Space Science Board, Long-Lived Space Observatories for Astronomy and Astrophysics, National Academy Press, Washington, D.C., 1987. file:///C|/SSB_old_web/axaf93ltr.htm (7 of 8) [6/18/2004 10:36:44 AM]
On the Advanced X-ray Astrophysics Facility 4. Task Group on Astronomy and Astrophysics, Space Science Board, Space Science in the 21st Century, National Academy Press, Washington, D.C., 1988. 5. Astronomy and Astrophysics Survey Committee, Board on Physics and Astronomy, The Decade of Discovery in Astronomy and Astrophysics, National Academy Press, Washington, D.C., 1991. Membership Lists Last update 9/5/00 at 9:40 am Site managed by Anne Simmons, Space Studies Board The National Academies Current Projects Publications Directories Search Site Map Feedback file:///C|/SSB_old_web/axaf93ltr.htm (8 of 8) [6/18/2004 10:36:44 AM]
