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Space Studies Board Annual Report 1995 3 Summaries of Major Reports 3.1 A Strategy for Ground-Based Optical and Infrared Astronomy A Report of the Committee on Astronomy and Astrophysics, under the aegis of the Board on Physics and Astronomy1 EXECUTIVE SUMMARY Astronomy occupies a special place in the research portfolio of this country. Understanding the cosmos is one of the oldest intellectual goals of humanity, and the discoveries of astronomers clearly excite the imagination of the public at large. From primary schools to universities, from planetaria to features in the media, astronomy offers numerous opportunities to improve the scientific literacy of this nation, and astronomers are increasingly engaged in these educational activities. Although for many people astronomy is a clear example of one of the noblest of basic research activities, it is often less recognized that it can and does contribute to other national goals. In particular, its research activities depend on and contribute to the applied development of sophisticated sensors, an essential enabling technology for many scientific fields and for the defense, medical, and commercial sectors. Modern astronomical facilities, and their sophisticated instrumentation, utilizing state-of-the-art detectors, computing resources, and optical design, are expensive. Astronomers are fortunate that the Congress has authorized the construction of numerous major national facilities. National ground-based astronomical facilities are supported primarily by the National Science Foundation (NSF), both in the construction and operations phases. The two 8-meter telescopes of the international Gemini 8-M Telescopes Project (IGP), in which the United States is a 50% partner, are currently under construction and will be completed by the end of the decade. Considerable investment (more than $250 M in the past decade) in large telescopes has also been made with nonfederal support, such that private observatories now provide 81% of the total telescope area (and 76% of the net diameter) available to U.S. astronomers. Still, roughly half of U.S. astronomers must rely entirely on the National Optical Astronomy Observatories (NOAO) for access to telescopes, and nearly all rely on NOAO facilities for some aspects of their work. The Panel on Ground-Based Optical and Infrared Astronomy was convened to determine whether the strategic balance of support by the NSF for all of optical and infrared (OIR) astronomy should be adjusted as these giant new telescopes come on line. In particular, the panel was asked to articulate a new mission for NOAO. In doing so, the 1 “Executive Summary” reprinted from A Strategy for Ground-Based Optical and Infrared Astronomy, National Academy Press, Washington, D.C., 1995, pp. 1–2.
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Space Studies Board Annual Report 1995 panel had to address several complex questions. What is the best role for NOAO in U.S. participation in the IGP? How can the unique resources of both private and NOAO facilities best be deployed? What priorities and strategies should be pursued, recognizing that NSF resources for OIR astronomy will probably be severely constrained? The panel believes that first priority must be given to the development of unique telescopes and instrumentation that advance technology and provide resources of national scope. The Gemini telescopes, the large telescopes at the Cerro Tololo Inter-American Observatory (CTIO), and the Advanced Technologies and Instrumentation (ATI) program of the NSF’s Division of Astronomical Sciences are clearly in this category. The panel finds that the case for increased OIR funding is strong within NSF for operating the Gemini telescopes. However, it is necessary to face the possibility that NSF funding of OIR astronomy will remain level in real dollars for some time. In this eventuality, the panel recommends that the proper instrumentation and operation of the Gemini telescopes should have first priority. The panel also affirms the high priority for the ATI program, which was recommended by the Astronomy and Astrophysics Survey Committee (AASC) report (The Decade of Discovery in Astronomy and Astrophysics, National Academy Press, Washington, D.C., 1991). The panel concludes that, with level funding, major reductions in NOAO operations would be required to meet the priorities stated above. In this constrained situation the Tucson scientific, administrative, and technical services support would have to be scaled back very substantially. The level of support and convenience offered to observers would have to be reduced, and it is very likely that the smaller telescopes at the Kitt Peak National Observatory (KPNO) would need to be closed or privatized. Moreover, to reduce operations costs, the 4-meter Kitt Peak telescope would have to be operated with fewer instruments and used primarily for wide-field or near-infrared applications. In this case, a large number of astronomers whose only access to front-line research tools is through NOAO telescopes would be unable to carry out their research and U.S. science would suffer. The panel has identified a strategy that might alleviate such problems and, at the same time, better utilize the very large recent expenditure by the private sector in the construction of new telescopes. Specifically, the panel recommends the initiation of a new program at a modest level within the NSF for instrumentation of the privately operated telescopes in exchange for national access. In a constrained budgetary scenario, such funds would, of necessity, come from existing NSF OIR astronomy activities, including the existing ATI program. Even with this new plan, some 1200 observer nights would be lost, approximately 40% of the present use by the U.S. astronomy community at NOAO nighttime facilities. The above plan is the best that the panel can envision under a flat-budget scenario. But the panel finds the costs in human, educational, and scientific terms to be unacceptably high. In view of the major capital investments in the Gemini telescopes and other major new telescopes, the panel recommends a second strategy, contingent on the availability of additional funds. Specifically, the panel recommends that $5.5 M/year be added to the NSF astronomy budget for international Gemini project operations. If this recommendation is implemented along with the proposed new instrumentation plan, it would allow for far more efficient utilization of existing telescopes. It would still be necessary to slim down the Kitt Peak/Tucson operations, but the consequences for the U.S. astronomy community would not be as draconian as they would be under the first strategy alone. The panel recommends that a third strategy be pursued, if further funds are available. In this strategy, the NSF astronomy budget would be supplemented by $10 M/year. The first $5.5 M would be used as above for Gemini operations, and the balance would be used to support an augmented program for facility instrumentation grants. Independent observatories would be able to compete for these grants, which would be awarded strictly on the basis of scientific merit, but for which cost sharing, in the form of open access to the astronomical community at large, would be a requirement. Such a program would enable full utilization of the enormous investment in both federal and nonfederal capital in OIR telescopes. The panel recognizes that when new, state-of-the-art facilities are brought on line, older facilities must be retired. All of the options outlined above include such painful downsizing. In the draconian, flat-budget scenario, the community would lose truly first-rate instruments, but even in the optimal plan, major economies in operations would still be required.
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Space Studies Board Annual Report 1995 3.2 Microgravity Research Opportunities for the 1990s A Report of the Committee on Microgravity Research1 EXECUTIVE SUMMARY INTRODUCTION Microgravity research is concerned with the effects of reduced gravitational forces on physical, chemical, and biological phenomena. The scientific disciplines affected by gravity include fundamental physics, fluid mechanics and transport phenomena, materials science, biological sciences and biotechnology, and combustion. It is especially noteworthy that these disciplines are laboratory sciences that inherently use controlled, model experiments. Many experiments require constant attention and frequent intervention by the experimenter, which distinguishes microgravity research from the observational space sciences. Microgravity research also spans both fundamental and applied sciences. Reduced-gravity experimental environments are provided by NASA through drop towers, aircraft in parabolic trajectories, sounding rockets, and Earth-orbiting laboratories. Some of these environments have crews and allow extended periods of time for experimentation and for demonstrating the reproducibility of results. Some of the experimental platforms allow a reduction of the gravity level to 10−6 times that of Earth gravity. In a reduced-gravity environment, the decreases in rates of sedimentation, hydrostatic pressure, and buoyancy-driven flows cause other physical effects to become more important and more readily observable and measurable. The acceleration due to gravity can then be treated as an important and interesting experimental parameter. The exploration of this parameter, through experiments at normal Earth gravity and at reduced gravity, may provide a better understanding of certain physical processes, as well as lead to the identification of new phenomena. The NASA microgravity research program has been widely misperceived as simply a materials processing program with the goal of providing better products for use on Earth. However, the prospects of commercial manufacture in space are limited in the foreseeable future. The justification for the microgravity research program must continue to be the promise of advances in areas of fundamental and applied science. It should be recognized, on the other hand, that manned exploration of space will require increased understanding of transport phenomena, materials processing, and performance in microgravity. There have been a number of previous National Research Council (NRC) reports in this field, of which the following are particularly relevant: Materials Processing in Space2 (the “STAMPS” report, 1978) attempted to provide guidance for the future course of NASA’s program. It assessed the scientific and technological underpinnings of the materials processing in space program and provided a clear understanding of the potential for exploitation of the space environment for processing materials. Space Science in the Twenty-First Century: Imperatives for the Decades 1995 to 2015. Fundamental Physics and Chemistry3 (1988) attempted to identify opportunities for future research efforts in relativistic gravitation and microgravity science (but not including applied research or industrial/manufacturing processes). More recently, the report Toward a Microgravity Research Strategy4 (1992) began to lay a foundation for a more mature research program, and the current report is a continuation of that effort. The research areas discussed in this report are subsets of much broader research disciplines. Only a small fraction of the total activities in each discipline occurs within the microgravity program, and no attempt has been made here to evaluate fully or to prioritize all of the research in a discipline. Only the microgravity component of 1 “Executive Summary” reprinted from Microgravity Research Opportunities for the 1990s, National Academy Press, Washington, D.C., 1995, pp. 1–19. 2 Space Science Board, National Research Council, Materials Processing in Space, National Academy Press, Washington, D.C., 1978. 3 Space Science Board, National Research Council, Space Science in the Twenty-First Century: Imperatives for the Decades 1995 to 2015. Fundamental Physics and Chemistry, National Academy Press, Washington, D.C., 1988. 4 Space Studies Board, National Research Council, Toward a Micro gravity Research Strategy, National Academy Press, Washington, D.C., 1992.
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Space Studies Board Annual Report 1995 each discipline is addressed in detail. Furthermore, the cost-benefit of a microgravity program has not been compared to the cost-benefit of experiments on different subjects in the terrestrial environment. Experiments that can be performed adequately under terrestrial conditions, however, are not given a priority for spaceflight. It should be understood at the outset that in evaluating the costs of doing research on such expensive vehicles as a space station, vehicle expenses are specifically not included. Microgravity research has never been the sole motivation for the space shuttle or other major space missions. These research opportunities have usually been secondary to exploratory, technological, engineering, political, educational, inspirational, and other motives for spaceflight, and until the advent of spacelab, microgravity research has been added on spaceflights launched for other purposes. Thus, in evaluating priorities, the research opportunities are taken into account but not the costs. To date, only a limited number of microgravity experiments have been conducted in space with completed analyses and reports of results. The total experience of U.S., Canadian, Japanese, and Western European scientists is less than 1000 hours for experiments in orbit. Because of the limited results available, the strategic recommendations in this report cannot be highly detailed or exclusive. A number of subjects require further exploratory investigation before detailed objectives can be defined. For the same reasons, it is currently not generally possible to set specific priorities across discipline lines. Assuming experiments are scientifically sound, prioritization across disciplines is largely unnecessary because a wide range of microgravity experiments can be accommodated on shuttle flights without retarding progress in any one discipline. It may even be a mistake to attempt such prioritization since, in many cases, fundamental flight experiments are needed before prioritization can be attempted. Some areas, however, can be identified as more promising than others. This report does not address the NASA commercial program or international programs in microgravity research. These topics will be addressed in future studies of this committee. Finally, although the value and need for manned intervention capabilities and long-duration flights are noted repeatedly in this report, nothing herein should necessarily be interpreted as advocating or opposing any specific NASA spacecraft or space station design initiative. SCOPE OF THE RECOMMENDATIONS The conclusions and recommendations presented in this report fall into five categories: (1) overall goals for the microgravity research program; (2) general priorities among the major scientific disciplines affected by gravity; (3) identification of the more promising experimental challenges and opportunities within each discipline; (4) general scientific recommendations that apply to all microgravity-related disciplines; and (5) recommendations concerning administrative policies and procedures that are essential to the conduct of excellent laboratory science. The overall goal of the research program should be to advance science and technology in each of the component disciplines. Microgravity research should be aimed at making significant impacts in each discipline emphasized. The purpose of this report is to recommend means to accomplish that goal. The essential features of the recommendations are to emphasize microgravity research for its general scientific and technological value, as well as its role in advancing technology for the exploration of space; to deemphasize the research value of manufacturing in space with the intent of returning products to Earth; to modify NASA’s infrastructure, policy, and procedures so as to facilitate laboratory science in space; to establish priorities for microgravity experimentation in scientific disciplines and subdisciplines in accordance with the relative opportunities for scientific and technological impact; and to recognize fluid mechanics and transport phenomena as a central theme throughout microgravity research. The recommendations detailed in this report are based on certain findings that resulted from this study. The findings are as follows: Science can be advanced by the study of certain mechanisms that are masked or dominated by gravitational effects at Earth gravity conditions. Examples include surface tension gradient-driven flows, capillary effects, multiphase flows, diffusive transport processes, and colloidal phenomena. Under terrestrial gravity conditions, these phenomena can often be dominated by effects such as buoyancy and sedimentation. There is a scientific need to understand better the role of gravity in many physical, chemical, and biological systems. To understand the relative importance of certain gravitational effects compared to nongravitational effects under terrestrial conditions, it is helpful to study a phenomenon at more than one gravitational level. Thus, gravitational force can become a controlled experimental parameter. For example, the role of buoyancy versus the role of surface tension gradients in driving a fluid flow could be examined at different gravitational levels.
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Space Studies Board Annual Report 1995 A significant portion of microgravity research programs should be driven by the technological needs of the overall space program. Examples of important engineering issues include the ignition, propagation, and extinction of spacecraft fires; the fluid dynamics and transport associated with the handling, storage, and use in space of water, waste, foods, fuels, air environments, and contaminants; the handling, joining, and reshaping of materials in space; and the dynamics and chemistry of mining or refining resources in extraterrestrial environments. Microgravity research primarily involves laboratory science with controlled model experiments that inherently require attention and intervention by the experimenter. Such experiments also require the opportunity to demonstrate reproducibility. The potential for manufacturing in space in order to return economically competitive products to Earth is very small. The techniques of space manufacturing, however, could prove to be important for materials science and materials processing on Earth. Fluid mechanics and transport phenomena represent both a distinct discipline and a scientific theme that impacts nearly all microgravity research experiments. The ground-based research program is critically important for the preparation and definition of the flight program. The need for an extended-duration orbiting platform has been identified as critical in many microgravity research experiments because of the time required for experimentation, the wide parametric ranges, and the need to demonstrate the reproducibility of results. In developing this report, it has been assumed that a space station will be available within a decade. The recommendations have value and should be implemented, however, even if a space station does not materialize and the microgravity research program continues only with the current facilities. Although this report does not set out a complete strategy for microgravity research, it presents some of the important elements of such a strategy, including: A summary of the current state of knowledge of microgravity science; A discussion of some of the fundamental questions to be answered; A presentation of the goals in this field; The science objectives within each discipline; An evaluation of the potential for microgravity research to provide advances within each discipline; The experimental requirements for achieving the science objectives of each discipline; A description of the other resources required for a successful microgravity science program; and A limited prioritization of research topics within each discipline. The two aspects of a strategy for microgravity research that are not presented in this report are (1) a prioritization of microgravity research objectives across disciplines and (2) a cost-benefit analysis of anticipated microgravity results. Experience has shown how difficult it is to set research priorities, even within a single homogeneous science discipline. Reaching agreement on priorities for microgravity research relative to all other science research was judged so unlikely that it has not been attempted in this report. The other practical reason for not setting stricter priorities stems from the nature of shuttle flights. Frequently, pay loads are assigned to a flight because their requirements for space, power, and so on, fit what is available, and scientific priority is less important. No cost-benefit analysis was attempted because the assumption is that orbiting platforms will be available for microgravity research. Decisions on the availability of platforms such as a shuttle or space station are essentially programmatic issues in which microgravity research is only one of many considerations. RECOMMENDATIONS FOR THE SCIENCE PROGRAM The disciplines of microgravity research discussed in this report include fluids and transport, combustion, biological sciences and biotechnology, materials science, and microgravity physics. Materials science is further categorized by constituent subfields: metals and alloys, organic materials and polymers, inorganic crystals, epitaxial layer growth, and ceramics and glasses. The expected degree of scientific success in each of these areas naturally varies.
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Space Studies Board Annual Report 1995 General Priorities Fluids and transport, combustion, metals and alloys, microgravity physics, and certain areas of biotechnology offer the greatest likelihood for substantial advances. In these areas, focused experiments can be performed that will expand our knowledge of fundamental phenomena and processes. The areas of polymers, ceramics or glasses, inorganic crystals, and epitaxial layer growth, on the other hand, do not at present offer great promise of new advances. Limited support is still warranted, however, for certain fundamental studies. Certain areas of the biological sciences and biotechnology should be viewed from a different perspective. Much of the work in these areas is phenomenological. Such research should be pursued to discover the scope and potential for utilizing the microgravity environment. Areas Recommended for Emphasis Major prospects and opportunities in each of five disciplines are summarized in the following sections. Fluid Mechanics and Transport Phenomena Fluid mechanics and transport phenomena play a dual role in the microgravity research program. They stand as distinct disciplinary areas but also appear as themes running through other disciplines. The presentation in this report reflects the role of fluids and transport in the support of other microgravity disciplines. Most physicochemical transport phenomena are influenced significantly by gravity. As a consequence, unusual behavior is expected in low-gravity environments for many fluid configurations. Also, the reduction of gravitational forces leads to dominance by other forces normally obscured in terrestrial environments, such as surface tension and electrohydrodynamic effects. Basic research is required to understand and describe the unusual characteristics of transport phenomena under low-gravity conditions. Transport phenomena also play essential roles in many processes that are important to mission-enabling technologies. Predictive models for low-gravity performance and operation of those technologies are frequently inadequate. New models are needed. Strictly empirical approaches are not preferred for low-gravity applications because they are costly and time consuming, and can result in products or systems that are unreliable or inefficient. Priority should be given to the study of phenomena that are prominent in the low-gravity environment and to those that are critical to space mission-enabling technologies and commercial developments. Among the basic topics that may be studied uniquely with special advantages in the low-gravity environment are the following: Surface tension gradient-driven flows and capillary effects. These are frequently obscured in a terrestrial environment but may become significant or dominant in reduced gravity. These topics warrant investigation because they are not well understood and because surface tension-driven flows are ubiquitous for many spaceflight-enabling technologies. Multiphase flows. Many processes involve multiphase flows. Gravity imposes a specific orientation on multiphase fluids and structures (e.g., gas-liquid, liquid-solid). In a reduced-gravity environment, multiphase flows and associated transport phenomena become significantly different because of the altered orientation of the various phases. Diffusive transport processes. At 1 g, multicomponent fluids experience various modes of thermosolutal convection. In addition, there are other effects due to different diffusivities for heat and mass. With reduced-buoyancy convection, these complex interactions can be separated and analyzed. Furthermore, transport effects masked at 1 g, such as Soret and Dufour phenomena, can become important. Colloidal phenomena. At 1 g, the nature of surface and short-range forces, and their consequences in colloidal systems, are often difficult to study because of the complications associated with competing gravitational effects. Microgravity provides an opportunity for study of colloidal systems in which short-range forces are dominant, which can contribute in an important way to the understanding of these physicochemical interactions.
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Space Studies Board Annual Report 1995 The above topics appear prominently in many areas of science including combustion, biotechnology, materials science, and physics. Therefore, fluid mechanics and transport phenomena should be viewed as a common theme throughout many of the microgravity disciplines. The following topics deserve attention for both their intrinsic scientific importance and their applications to space technologies: Convective processes at low Reynolds number. Investigation of low Reynolds number flows with density variations, at reduced-gravity levels, will reveal the altered nature of transport phenomena in a new range of parametric conditions. Transport processes with a phase transition. The modified processes of condensation, evaporation, and boiling in a low-gravity environment with dominant interfacial forces require study. Complex materials. Porous, granular, colloidal media, and foams are complex materials whose structures and functions can differ in microgravity. Research is necessary to understand the behavior of such materials in a low-gravity environment and may also lead to a better understanding of their behavior at 1 g. Materials processing. Buoyancy, sedimentation, and interfacial phenomena influence such processing methods as fluidized-bed hydrogenation, electrowinning, and vapor-phase pyrolysis and therefore should be investigated. Physical processes in life- and operating-support systems (enabling technologies). Some of the effects indicated above apply to processes such as power generation and storage, water purification, oxygen production, and fuel and fluid storage and management. Numerous parameters govern the topics listed above. Judicious choice of the parameter ranges and configurations will be required to ensure that the information obtained is directly applicable to the reduced-gravity environment. Clearly, fluids and transport phenomena appear as critical technical issues in many spaceflight-enabling technologies. Combustion Combustion involves fluid mechanics, mass and heat transport, and chemical reaction—all directly or indirectly subject to numerous gravitational effects. The number of parameters to be investigated is large. Several phenomena require long-duration observations and measurements (e.g., smoldering and flame spread). The following research areas are recommended for emphasis according to rank-order: The highest-priority area, and one of intense practical interest, is that of fires in spacecraft and potential extraterrestrial bases. Microgravity and reduced-gravity research is required because of the potential for disaster posed by fires. Much is still unknown about fires in altered gravity conditions. A variable gravity capability would be useful for a full understanding of gravitational effects and for implementation of fire safety measures in spacecraft. In fire research, several subfields of combustion need to be investigated under microgravity conditions. Ignition, flammability limits, smoldering, flame spread, and extinguishment are all deserving of detailed study. Variables should include fuel type and phase, fuel:oxidizer ratio, ambient oxidizer concentration, forced and free convection, ignition source, and extinguishment methodology. Turbulent combustion processes are highly important on Earth but cannot be probed at 1 g at the small size scales that typically occur. Laboratory scale-up at 1 g introduces unwanted buoyancy. Reduced gravity would allow a scale-up in overall size without the introduction of major buoyancy effects, thus permitting access to the smallest scales of turbulence that are important to the problem. Here, the Reynolds number based on a forced flow velocity would remain fixed in the scaling process. Even though gravity is not an important parameter for many practical devices, the laboratory study of combustion processes is often impeded at 1 g. Research on laminar premixed and diffusion flames and spray-flow interactions should be conducted, again because of the importance of these processes on Earth. The same problem occurs here as with turbulent flames. That is, scale-up to allow study at 1 g introduces unwanted buoyancy effects.
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Space Studies Board Annual Report 1995 In addition, other general recommendations are noteworthy. Reproducibility must be verified. Many combustion phenomena require a survey of a wide range of parameters. Also, some combustion phenomena are long-duration events. Consequently, an extended orbiting platform capability will be required for many combustion experiments for complete and serious study. Relevant to all areas above, ground-based experiments should be undertaken to develop miniaturized diagnostics and experimental apparatus and techniques for performing multiple repetitions of a specific experiment. Biological Sciences and Biotechnology The biological sciences and biotechnology are experimental disciplines that are highly dependent on empirical approaches to the solution of problems and on the continued discovery and development of useful research systems. Unlike many other branches of microgravity science such as fluid dynamics or materials science, there may be no firm foundation of theory, only a limited accumulation of experience. Thus, a reasonably high tolerance for scientific risk (which is clearly distinct from safety risk) should be allowed in investigations in the biological sciences. The science community should be prepared, however, to support research in this area on the basis of its long-term potential and importance, especially its relevance to human spaceflight. Since research on biological topics commonly requires experiments that take a long time to complete, an extended-duration orbiting capability is necessary. Priorities should be given to scientific issues in biological sciences and biotechnology in the following order: In studies to improve methods of crystallization of macromolecules for use in diffraction studies, additional experiments should focus on defining quantitatively those macromolecular crystal properties and growth mechanisms affected by gravity. There is demonstrated success in this research area and it is recommended for the highest priority. Further experimentation is needed in both terrestrial and microgravity environments to develop new methods, materials, and techniques to exploit the potential of microgravity, where it exists, for improvements in biochemical separations. These separations are important both in terrestrial applications and in materials processing to support human spaceflight. A dedicated effort should be made to evaluate the potential advantages of the microgravity environment for the study of cellular interactions, cell fusion, and multicellular assembly and to identify candidate cell systems that show maximum response to being cultured in such an environment. Efforts should also be made to identify and characterize subcellular mechanisms that sense and mediate responses to the magnitude and direction of gravitational forces. A systematic effort should be made to identify those cellular and biomolecular processes, structures, assemblies, and mechanisms that may be affected by gravity, and to design and carry out experiments to explore the effects of microgravity on appropriate systems. Materials Science and Processing Metals and Alloys. The microgravity environment provided by an orbiting spacecraft offers new opportunities in the control of melting and solidification processes. Reduction of convective velocities permits, in some cases, more precise control of the temperature and composition of the melt. Body force effects such as sedimentation, hydrostatic pressure, and deformation are similarly reduced. Weak noncontacting forces derived from acoustic, electromagnetic, or electrostatic fields can be used to position specimens while they are being processed, thus avoiding contamination of reactive melts with their containers. Since many experiments in this field require long time scales for completion, the capability of an extended-duration orbiting platform is needed to obtain full benefits from microgravity research. Topics in the metals and alloys area that would benefit from a focused effort include the following prioritized items: Nucleation control and the achievement of metastable phase states, such as metallic glasses and nanostructures, are areas that could benefit from achieving deep supercooling in the microgravity environment, by elimination of container surfaces, and from the reduction of melt flows due to buoyancy-driven convection.
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Space Studies Board Annual Report 1995 Microgravity experiments on Ostwald ripening and phase coarsening kinetics would add quantitative, fundamental information about the key metallurgical issues of interfacial dynamics during thermal and solutal transport, and the question of micro structure evolution in general. Observations of aligned microstructures processed reproducibly under quiescent microgravity conditions should help to provide well-defined thermal processing limits for polyphase directional solidification of eutectics and monotectics. Studies of the formation of solidification cells and dendrites under well-defined microgravity conditions can add to our expanding knowledge of complex metallurgical pattern formation and, more generally, of the fundamental physics of nonlinear dynamics. Microgravity conditions can be useful in these instances for the pursuit of sophisticated tests of theory and the quantification of metallurgical pattern dynamics. Some thermophysical properties can be measured advantageously in microgravity. Accurate data on such properties, frequently essential for the modeling of metallurgical processes and materials responses, are often not available from standard terrestrial measurements. Polymers. Polymers potentially represent the broadest classes of engineered materials, permitting great innovation and precision in design, including control at the molecular level. Although the viscous character of most high polymer melts greatly desensitizes their response to gravitational acceleration, nonetheless some polymer solutions have relatively low viscosities. Moreover, some of these organic systems provide materials with interesting applications in the fields of nonlinear optics and metrology. A few initial experiments on the vapor- and solution-phase processing of organic and polymer films in microgravity have shown improved texture and smoothness over terrestrial counterparts, suggesting that this area of research merits further study. Growth of Inorganic Single Crystals. The microgravity environment will be particularly useful for the study of transport phenomena in the liquids from which bulk crystals are grown, and priority should be given to these studies rather than to the growth of large crystals. Such studies probably require a steady, very-low-gravity environment such as that obtainable in a free-flyer and will provide useful data without requiring growth of bulk crystals. Precise transport data will become particularly useful for fluid dynamics computations, which are rapidly improving for terrestrial melt and solution growth. Any experiments on bulk crystal growth must be judged by their potential to contribute to the scientific understanding of the fundamental processes of crystal growth. The recommendations for this area of research are as follows: The design and execution of microgravity experiments that lead to a better fundamental understanding of crystal growth have proved elusive, and the committee recommends against the growth of large inorganic crystals under low gravity. The best approach to understanding the details of such growth will likely derive from fluid dynamical modeling and the modeling of processes at the fluid-solid interface, along with terrestrial studies of crystal growth. This analytical approach may provide the rationale for the growth of benchmark-quality inorganic crystals in microgravity. Assuming that some of the versatility of terrestrial experimentation can be achieved in the microgravity environment, there are opportunities for microgravity research that will have an impact on terrestrial bulk crystal growth. Priority should be given to transport studies, including studies of solute and self-diffusion, heat diffusion, and Soret diffusion. All of these involve the fluid from which crystals are grown, and they are amenable to routine study with repeatedly used apparatus. However, they may require a more stable environment than that provided by the space laboratory. Indeed, since such studies will undoubtedly be sensitive to the acceleration environment, they may also be useful for the study of this environment as a variable in the low-gravity range. Precise transport data will become particularly useful since fluid dynamical computational capabilities (for which these data are required) are improving rapidly for terrestrial melt and solution growth, as well as other industrial processes. Furthermore, transport measurements in industrially important fluids may be an important microgravity application outside the realm of large inorganic crystal growth. Growth of Epitaxial Layers on Single-Crystal Substrates. During the terrestrial growth of epitaxial layers by vapor deposition, an effort is made to minimize the effects of flow, buoyancy, and boundary layer uniformity by rotating
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Space Studies Board Annual Report 1995 or spinning substrates during the growth process. In addition, attempts are under way to calculate precise flow patterns and resulting growth rates in model systems. The calculations are complex, and it is uncertain whether they will be able to predict occurrences in real systems that are useful for industrial production. Since the manufacture of heterostructures by vapor deposition methods will be accomplished terrestrially, it is not clear whether any relevant data can be obtained solely under microgravity. A low priority is recommended for chemical vapor deposition studies under microgravity conditions. For molecular beam epitaxy (MBE) methods, great gains in purity can, if necessary, be made on Earth, if sufficient attention is given to reducing contamination and increasing pumping speed. The committee concludes that epitaxial layers will be too costly to manufacture in space and that, at a reasonable cost, much improvement in the vacuum environment can be achieved terrestrially. Molecular beam epitaxy studies in orbiting vehicles are not appropriate until the limits of ground-based alternatives have been clearly reached. Ceramics and Glasses. As discussed above, a low-gravity environment will reduce buoyancy-driven convective flows in liquids. Most ceramic synthesis and processing is done at high temperature either by solid-state processes exclusively or by processes in which there are only small amounts of viscous liquid phases. Glasses are formed from high-temperature melts, where the suppression of convective mixing is generally undesirable because convection promotes compositional homogeneity. A second case in which liquids are important to ceramics is in the synthesis of ceramic powders or films from aqueous solutions or colloidal suspensions. Frequently, the requirement is to achieve a high density of nuclei and consequent fine particle sizes of the precipitated powders. Thus, rapid mixing is used, and there is no reason to suppress convection. For these reasons, low-gravity studies are of limited advantage in this discipline. Nonetheless, a low-gravity environment might be of benefit to ceramics research and development in the following prioritized areas: There is interesting potential for containerless melting. Processing of ceramics at high temperature requires refractory containers that remain unreactive with the specimen. Availability of a general capability for container-less, high-temperature processing (to at least 1600°C) would allow contamination-free synthesis of glasses and ceramics, such as those being considered for optoelectronic applications, as well as the study of glass nucleation and crystal growth without heterogeneous nucleation on a container wall. A fundamental study of crystal nucleation and growth in glass melts in microgravity would be interesting. Crystallization is an important process, desirable in glass-ceramics and undesirable in optical glasses, that requires further characterization and understanding. Mass transport and diffusion studies of glass and ceramic melts under microgravity conditions should generate more precise data than those available from terrestrial measurements. One area of research that might be aided by reduction of convection is obtaining accurate data on diffusion in ceramic melts. The suppression of free evaporation from melt surfaces could allow synthesis at higher temperatures than can be performed on Earth. The epitaxial growth of films from solution, including biomimetic synthesis (self-assembling monolayers) of ceramics, should be studied. Microgravity Physics Experiments in this area, with the exception of the general relativity test Gravity Probe-B (GPB), all represent extensions of work that is, or can be, conducted in Earth-based laboratories. Much of the scientific value of the proposed space experiments will depend on the strength of the connection to Earth-bound research. Given the long time scale for the ground-based development through flight of a space experiment, there is concern that the scientific goals of the experiment might be bypassed by new developments or by major shifts in the value ascribed to the work.
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Space Studies Board Annual Report 1995 The topics of microgravity physics fall into two general categories: (1) development of new instruments (e.g., superconducting gyroscopes for the GPB experiment and the mass balance for the equivalence principle test), and (2) preparation and study of unique samples such as uniform fluid free from gravity-induced density gradients or low-density granular materials near a percolation limit. This program can include such important studies as fundamental physics measurements (e.g., verification of the equivalence principle), critical phenomena, dynamics of crystal growth, and low-density aggregate structures. A recent successful experiment in this area is the Lambda Point Experiment (LPE) that was flown on the shuttle in October 1992 (USMP-1). Analysis of the data indicates an improvement of nearly two orders of magnitude over previous data obtained on Earth. This has been done in an unbiased way, and heat capacity data have been obtained approaching a few nanokelvin of the Lambda point. This experiment demonstrates clearly that highly sophisticated experiments involving the most sensitive and advanced instrumentation can be profitably performed in the microgravity environment. The quality of the microgravity environment must be examined critically in the context of each possible experiment. Minimum acceleration is the most obvious parameter of concern for many of the contemplated experiments; however, the time span over which a high-quality, low-gravity environment can be maintained may be of equal importance. For some experiments, accidental large accelerations (perhaps resulting from sudden movements of personnel or the firing of small thrustors) might destroy the object of study, for example, a low-density granular structure. With regard to the quality of the microgravity environment available for experiment, only the center of the orbiting spacecraft is in true free-fall and then only to the extent that orbital drag effects and other external influences are negligible. In a gravity gradient-stabilized spacecraft, there will be a steady rotation of any experiment about the center of mass of the entire spacecraft once each orbit. For a low Earth orbit, this will result in accelerations on the level of 10−7-g level at a distance 1 meter from the center of mass of the entire orbiting system. On both the space shuttle and the space station, only a few experiments will be located close enough to the center of mass to ensure acceleration levels below the 10−6-g level. A number of scientifically meritorious projects, such as the equivalence principle experiment and GPB, will require spaceflight independent of any manned space facilities. In the future, we may anticipate a continued requirement for low-temperature facilities in space, since low temperatures are important for the highest-resolution measurement techniques, particularly those based on SQUID (Superconducting Quantum Interference Device) technology. If a space station is to be a useful contributor to the area of fundamental science, access to liquid-helium facilities will be mandatory. GENERAL SCIENTIFIC RECOMMENDATIONS FOR MICROGRAVITY RESEARCH Following are a number of general science recommendations that are important for microgravity research: The reproducibility of results is a crucial element of laboratory science, and flight investigators should be given the opportunity to address reproducibility in their research. Nonetheless, a balance should be established between the reflight opportunities necessary for reproducibility and the flight of experiments that address new scientific issues. The need for scientific judgment, trained observation, and manned intervention and participation in certain laboratory microgravity experiments requires a greater use of payload specialists with expertise and laboratory skills directly related to the ongoing experiments. Some flight experiments would also benefit from the direct investigator interaction made possible by teleoperation capabilities, and NASA should support the development and deployment of such techniques in future microgravity experiments. As a rule, microgravity experiments should be designed and conducted to provide specific explanations for meaningful scientific questions. Scientific objectives should be clear and specific. In addition, NASA must
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Space Studies Board Annual Report 1995 The following expands key recommendations of the report: Institute for Space Science—In response to direction in the FY 1994 Senate appropriations report, the committee considered a space sciences umbrella organization within NASA to coordinate and oversee all space science activities, functioning like the National Institutes of Health (NIH) within the Department of Health and Human Services. The committee reviewed the advantages and disadvantages of such a model and concluded that the NIH model, while effective in the arena of health research, is not appropriate for the space sciences. NASA space science benefits from close coordination with other elements of NASA, such as hardware development, launch services, and tracking and data operations, which have no counterparts in the NIH model. The committee believes the required coordination would be hampered by the creation of a quasi-autonomous space science institute. The committee therefore does not recommend establishment of such an umbrella institute. The Role of the Chief Scientist—The role of the Chief Scientist was found to be a critical one from many perspectives, leading the committee to recommend expanding the authorities and responsibilities of this position. Despite the central role of the science associate administrators in the management of their respective science areas, the committee finds a need for greater integration and coordination of these programs. To achieve this, the position of Chief Scientist should be strengthened, particularly by the addition of concurrence authority in key matters affecting space science. The Chief Scientist should be a person of eminent standing in the scientific community with a significant record of accomplishment. A proposed “functional statement” for the Chief Scientist is given in Chapter 4. A major component of this official’s integration responsibility is coordination and oversight of the recommended science prioritization process. Another component is coordination of the technology development programs that support space science. The Prioritization Process—The committee believes that peer review is the most effective form of merit review for the selection of scientific research. A clear set of criteria, known and understood by all parties, is crucial to the prioritization of scientific goals. The relative ranking of science and mission plans will be most strongly affected by scientific factors at the entry level, where proposals from the same discipline or subdiscipline compete against one another. As the arena of competition broadens to the interdisciplinary and then to the agency-wide level, other programmatic and political influences become increasingly important. It is essential, however, that all proposals being considered at progressively higher levels retain the heritage of scientific merit that comes from successful confrontation with their peers at lower levels. The office of the Chief Scientist should oversee these prioritization processes, especially as they cross disciplinary boundaries. NASA management should cancel those programs or projects that are failing or whose priority has dropped substantially in this prioritization process. The committee found that peer review and the above corollary principles apply generally to technology research as well. Technology Planning—New technologies are important as agents of change, enhancing the quality of scientific output and the ability to accomplish more with less. Technology development is undertaken both by NASA’s science program offices and by its Office of Space Access and Technology (OSAT). The committee recommends that NASA establish an agency-wide strategy and plan for the technologies that support the space sciences. These technologies may be characterized as near-term or far-term technologies (the latter defined as requiring more than five years to be ready for flight demonstration). The space science offices should have primary responsibility for identifying and reviewing near-term technologies, giving them greatest control of the technologies that most immediately affect the success of their programs. Each science office should allocate a significant fraction of its resources to Advanced Technology Development activities and should be willing to pool resources to achieve shared objectives. Most importantly, the implementation of all categories of technology development should be undertaken by the best-qualified individuals or teams within NASA, other government laboratories, industry, or academia, as determined by peer review. Promising far-term technologies should be identified, funded, and managed by OSAT. Projects in these areas should be reviewed jointly by the science offices and by OSAT. Like near-term technology development, far-term projects should be carried out by the best-qualified individual or teams, as determined by peer review. These projects should stimulate exploratory development of possibly unconventional technologies having the potential of producing breakthroughs in capability. Finally, a rigorous review process should be put in place to identify those projects that ought to be terminated in the present constrained budgetary environment. “Industrial Funding”—The committee examined the advantages and disadvantages of an explicit full-cost accounting system in which all charges, including salaries and facilities, are charged against projects (so-called “industrial funding”). This approach permits ready assessment of comparative costs that might otherwise be hidden
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Space Studies Board Annual Report 1995 in an institutional funding environment. The committee endorses NASA’s decision (stated in the “Zero Base Review” briefing to the Congress) to identify, budget, and manage by total program costs, including civil service labor costs. The committee recommends that NASA change the funding of its field centers to an industrial funding arrangement. The committee believes that decisions on program priorities and budgets would be more rational if based on full-cost accounting, and program accountability and discipline in personnel management would thereby be enhanced. A similar recommendation was made in the NASA Federal Laboratory Review report.4 The Downsizing of Headquarters—NASA is currently “re-engineering” its organization. This re-engineering entails a very large downsizing of its Headquarters staff and a concurrent transfer of functions to the centers. The result is expected to be the analog of a lean “corporate management” model. While the committee endorses the intent, it notes that an unintended consequence could be a center-dominated model as opposed to the desired enterprise-focused one. Several recommendations are offered to avert this outcome. Not all program management functions should be transferred to centers. Those complex programs that cut across centers should be retained at Headquarters and integrated with enterprise management. Support of scientific disciplines, management of peer review, and oversight and integration across center boundaries should remain Headquarters functions. Likewise, creation of a strategy and plan for the technologies that support space science should be a Headquarters responsibility. The adoption of industrial funding will further emphasize the importance of a suitably strong Headquarters organization. Research in New Fields—The committee recognizes the competitive obstacles faced by smaller, newer, or less well-established fields of science. The committee recommends that NASA science budgets include dedicated funding for innovative, high-risk, high-return ideas falling outside current frameworks of inquiry or design. This research is highly important and deserves special management attention, including that of the Chief Scientist. This recommendation is not intended to allow circumventing of peer review for the major parts of any science program. Science Institutes—Creation of contractor-operated institutes may be advantageous in specific instances. However, the committee recommends that, as NASA proceeds with arrangements for the first focused science institutes, it give due attention to the processes by which these institutes are selected and created, and by which, over a few years, their guaranteed base funding will be transformed into competed programmatic funding. Further, there should be consideration of a review process that will ensure either (1) that they compete successfully to maintain or increase their size, or (2) if less successful, that they are phased down in an orderly fashion. The committee recommends that additional initiatives along these lines be deferred until the above processes have been defined and the success of the two proposed institute pilots can be evaluated. The committee’s recommendations are gathered together by main theme in Chapter 7. The NASA space science programs, from the dawn of the space age to the present, have produced an unprecedented flow of discoveries. The fiscal, political, and technological environment of the agency is now in a state of rapid change. It is vital that NASA respond to its challenges and opportunities in the most constructive manner to ensure the success of its future space science endeavors. The committee believes that the recommendations made in this report, if accepted by NASA, will aid in this objective. 4 Federal Laboratory Review Task Force, NASA Advisory Council, NASA Federal Laboratory Review, February 1995.
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Space Studies Board Annual Report 1995 3.7 The Role of Small Missions in Planetary and Lunar Exploration A Report of the Committee on Planetary and Lunar Exploration1 EXECUTIVE SUMMARY The last 30 years have seen remarkable progress in our understanding of the solar system and its diverse constituents. But this period has also seen an upheaval in the political and economic circumstances that have been among the prime drivers of planetary and lunar exploration. The motives that led the United States, the former Soviet Union, and, to a lesser extent, various European nations and Japan to explore the solar system during the past three decades were political as well as scientific. Now, with the end of the Cold War, the political motive has virtually disappeared. With such strong roots in the former East-West confrontation, the space program in general and planetary exploration in particular have become vulnerable to changing national priorities. Some observers question the utility of a space program as an instrument of national policy, and others point to the nation’s altered economic fortunes and ask if space exploration is a luxury we can no longer afford. Against this backdrop, the past successes of the planetary exploration program are, paradoxically, endangering its future vitality. Telescopic observations combined with the Apollo lunar landings and a string of highly successful robotic missions, including Vikings, Magellan, and the Voyagers, have given us a first-order understanding of all the planets and major satellites in the solar system from Sun-scorched Mercury to frigid Neptune; even Pluto’s gross characteristics are known from ground-based and Earth-orbital measurements. Thus we have finished the preliminary reconnaissance of the major bodies in the solar system and have entered an era of intensive study of the physical phenomena that shape our planetary neighbors. Increased knowledge and comprehension lead us to pose more fundamental questions requiring increasingly sophisticated and expensive investigations to answer. Thus—quite naturally—the small, simple, and inexpensive spacecraft sufficient 20 to 30 years ago to record basic data about the planets have given way to multibillion-dollar robots capable of performing multidisciplinary investigations in the farthest reaches of the solar system. But the increased scale and scope of planetary missions have a cost other than that measured in dollars. With a planetary program composed only of a few large missions, each spaceflight becomes precious. This is especially true in an environment of declining status and budgets for space exploration, where the failure of any given mission is no longer tolerable. A result is engineering conservatism, with engineers forced to seek the “perfect” design. At the same time, in a program of few spaceflights, scientists—fearing that no other missions will fly soon—will attempt to take the maximum advantage of available opportunities and potential gains from synergistic measurements, something that could, uncharitably, be interpreted as “trying to cram as much aboard as possible.” As we have slowly come to understand, deep-space missions are inherently difficult. Thus it is impossible to ever reduce the risk of failure to zero. With a space program built on occasional comprehensive missions, a simple mechanical failure (as with Galileo), or a breakdown with an uncertain cause (as with Mars Observer), or a budgetary problem (as with the Comet Rendezvous/Asteroid Flyby) can prematurely end—or at least seriously degrade—a large fraction of the nation’s effort in planetary exploration. The most widely proposed solution to break this vicious cycle is to return to simpler, cheaper missions. With an assured, steady stream of small missions, occasional failures become, if not acceptable, at least tolerable. Since early in the space program, NASA’s astrophysics and space physics programs have built and flown a highly effective series of Explorer spacecraft. These low- to moderate-cost missions have transmitted a virtually continuous stream of important scientific data for more than three decades. NASA’s earth science program recently instituted a similar series, the Earth Probes, to fill a comparable niche in its activities. Several attempts have been made over the last decade and a half to introduce a comparable line of small planetary missions. For a variety of reasons, these efforts have all failed. Undaunted, NASA recently proposed again to begin such a program, now called Discovery. Two small planetary missions, the Near-Earth Asteroid Rendezvous (NEAR) and Mars Pathfinder, received new starts in the FY 1994 budget as “Discovery” missions, although, as mentioned in the main report, they do not satisfy NASA’s present guidelines for this program. Given this situation, the Space Studies Board charged its Committee on Planetary and Lunar Exploration (COMPLEX) to: 1 “Executive Summary” reprinted from The Role of Small Missions in Planetary and Lunar Exploration, National Academy Press, Washington, D.C., 1995, pp. 1–3.
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Space Studies Board Annual Report 1995 Examine the degree to which small missions, such as those fitting within the constraints of the Discovery program, can achieve priority objectives in the lunar and planetary sciences; Determine those characteristics, such as level of risk, flight rate, target mix, university involvement, technology development, management structure and procedures, and so on, that could allow a successful program; Assess issues—such as instrument selection, mission operations, data analysis, and data archiving—to ensure the greatest scientific return from a particular mission, given a rapid development schedule and a tightly constrained budget; and Review past programmatic attempts to establish small planetary science mission lines, including the Planetary Observers and Planetary Explorers, and consider the impact management practices have had on such programs. In the course of its deliberations, COMPLEX found that rather than representing a fall from past glories, the initiation of a series of small missions presents the planetary science community with the opportunity to expand the scope of its activities and to develop the potential and inventiveness of its members in ways not possible within the confines of large, traditional programs. Some researchers may use the opportunities raised by a program of small missions to enhance or augment comprehensive studies of particularly interesting objects such as Mars and Jupiter. Others may employ them to perform reconnaissance of classes of relatively unknown objects such as comets and asteroids, to pursue aspects of intensive study of the terrestrial planets and the Moon, or to investigate planetary phenomena from Earth orbit. The rapid development schedules achievable with small missions should allow the possibility of exploiting targets of opportunity, should permit greater use of current technology, and should enhance the involvement of all sectors of the educational system in space research. COMPLEX also realized, however, that a program of small planetary missions (such as Discovery) was, in and of itself, incapable of meeting all of the prime objectives contained in its report An Integrated Strategy for the Planetary Sciences: 1995–2010.2 As explained in that report, a responsive planetary exploration program demands a mix of mission sizes ranging from comprehensive missions with multiple objectives (such as Galileo and Cassini) to small missions with highly constrained scientific objectives. For a program of small planetary missions to fulfill its promise, COMPLEX believes that it must satisfy certain criteria. These include the following: A continuing budget line should be initiated that is dedicated to a series of small planetary missions that focus on specific, well-defined objectives and are capable of yielding significant scientific results. The chosen missions should address key scientific questions and objectives as outlined in the report An Integrated Strategy for the Planetary Sciences: 1995–2010. This budget line for small planetary missions should be funded at a level that will permit the launch of at least one mission per year, with approximately half of the accepted missions supported at a level close to the currently announced budget cap of $150 million (FY 1992 dollars), not including inflation. Each mission must be selected through open competition from proposals presented as an integrated package by a principal investigator. This individual should have full authority to decide the appropriate balance among science performance, mission design, and acceptable risk. NASA should not impose on mission design arbitrary constraints such as preselection of launch vehicle, spacecraft bus, payload, or data rate, nor should NASA specify a particular management structure or a specific institution to run mission operations. The budget, schedule, and risk envelope must be identified in the conceptual and definition phase of mission planning. It is essential for NASA to adhere to the agreed-upon funding profile. Past NASA practices must change in order to foster the development of a streamlined approach to management of each complete mission. As soon as they have been calibrated and validated, data and all subsidiary information (e.g., spacecraft ephemerides) needed for their interpretation should be archived expeditiously to ensure their prompt availability to the entire research community. NASA’s Planetary Instrument Definition and Development Program should be augmented to produce highly capable science instruments that are appropriate for use in the Discovery program. The option of using elements of the small-mission philosophy for Mars Surveyor and future large missions should be studied. 2 Space Studies Board, An Integrated Strategy for the Planetary Sciences: 1995–2010, National Academy of Sciences, Washington, D.C., 1994.
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Space Studies Board Annual Report 1995 3.8 Setting Priorities for Space Research: An Experiment in Methodology A Report of the Task Group on Priorities in Space Research1 EXECUTIVE SUMMARY In 1989, the Space Studies Board created the Task Group on Priorities in Space Research to determine whether scientists should take a role in recommending priorities for long-term space research initiatives and, if so, to analyze the priority-setting problem in this context and develop a method by which such priorities could be established. After answering the first question in the affirmative in a previous report, Setting Priorities for Space Research—Opportunities and Imperatives (National Academy Press, Washington, D.C., 1992), the task group set out to accomplish the second task. The basic assumption in developing a priority-setting process is that a reasoned and structured approach for ordering competing initiatives will yield better results than other ways of proceeding. The task group proceeded from the principle that the central criterion for evaluating a research initiative must be its scientific merit—the value of the initiative to the proposing discipline and to science generally. But because space research initiatives are supported by public funds, other key criteria include the expected contribution to national goals (including the enhancement of human understanding), the cost of the initiative, and the likelihood of success. To be effective, a priority-setting process must also reflect the values of the organizations using it, be sensitive to political and social contexts, be efficient, and provide a useful product. The key elements of such a process include determining the categories of candidate initiatives that will be considered, specifying explicitly the criteria that will be used to evaluate initiatives, providing a mechanism for advocacy of initiatives, and providing a mechanism for evaluating the initiatives. Evaluation schemes can range from informal, subjective approaches to formal, quantitative methods. This general outline of a priority-setting process was expanded by the task group into a specific schematic sequence of distinct steps for selecting and ranking initiatives. The task group developed a two-stage methodology for priority setting and constructed a procedure and format to support the methodology. The first of two instruments developed was a standard format for structuring proposals for space research initiatives. The second instrument was a formal, semiquantitative appraisal procedure for evaluating competing proposals. To help guide the development of the priority-setting process and instruments, the task group conducted two trials of preliminary versions. In the first, a small informal group of practicing scientists was convened at a workshop to evaluate a set of strawman initiative proposals prepared with the help of Board discipline committees. The results of this trial were used to refine the instruments. In a second trial, the Board itself exercised revised versions of the instruments and assessed their utility. The Board concluded that the method was not fully suitable for adoption on an operational basis. Reasons given by individual Board members for not supporting the proposed process included philosophical differences with the scope or approach of the method, reservations about the instruments themselves, and concerns about the ability of the Board and its committees to successfully implement them. Notwithstanding the reluctance of some members to adopt the proposed methodology, the Board remained broadly in accord with the task group’s earlier finding that researchers should participate actively in priority setting. This report makes available complete templates for the methodology, including the advocacy statement and evaluation forms, as well as an 11-step schema for a priority-setting process. From the beginning of its work, the task group was mindful that the issue of priority setting increasingly pervades all of federally supported science and that its work would have implications extending beyond space research. Thus, although the present report makes no recommendations for action by NASA or other government agencies, it provides the results of the task group’s work for the use of others who may study priority-setting procedures or take up the challenge of implementing them in the future. 1 “Executive Summary” reprinted from Setting Priorities for Space Research: An Experiment in Methodology, National Academy Press, Washington, D.C., 1995, pp. 1–2.
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Space Studies Board Annual Report 1995 3.9 A Science Strategy for Space Physics A Report of the Federated Committee on Solar and Space Physics, Space Studies Board, and Committee on Solar-Terrestrial Research, Board on Atmospheric Sciences and Climate1 SUMMARY This report by the Committee on Solar and Space Physics and the Committee on Solar-Terrestrial Research recommends the major directions for scientific research in space physics for the coming decade. As a field of science, space physics has passed through the stage of simply looking to see what is out beyond Earth’s atmosphere. It has become a “hard” science, focusing on understanding the fundamental interactions between charged particles, electromagnetic fields, and gases in the natural laboratory consisting of the galaxy, the Sun, the heliosphere, and planetary magnetospheres, ionospheres, and upper atmospheres. The motivation for space physics research goes far beyond basic physics and intellectual curiosity, however, because long-term variations in the brightness of the Sun vitally affect the habitability of the Earth, while sudden rearrangements of magnetic fields above the solar surface can have profound effects on the delicate balance of the forces that shape our environment in space and on the human technology that is sensitive to that balance. The several subfields of space physics share the following objectives: To understand the fundamental laws or processes of nature as they apply to space plasmas and rarefied gases both on the microscale and in the larger, complex systems that constitute the domain of space physics; To understand the links between changes in the Sun and the resulting effects at the Earth, with the eventual goal of predicting the significant effects on the terrestrial environment; and To continue the exploration and description of the plasmas and rarefied gases in the solar system. Significant progress has been made in the more than three-decade history of space research. Many space plasma and rarefied gas phenomena have been characterized and are well understood, but many others are still under investigation and new discoveries continue to be made. Space physics asks fundamental questions about how plasmas are energized; about how the energy is redistributed with the result that a few particles are taken out of a near-thermal distribution and accelerated to superthermal or very high energies; about the specific roles played by magnetic fields in transferring energy from plasmas to particles and vice versa; about instabilities and interactions between waves and particles in a plasma; about the generation of magnetic fields through convection and rotation; and about the complex physical processes that operate in boundary layers between regions of different types of plasmas and rarefied gases. Some plasma configurations or particle distributions are known to be unstable and to relax spontaneously to a more stable state with the release of free energy, but there are many others for which the instabilities and wave-particle interactions are not yet understood. Determining the physics of such relaxation processes is fundamental to understanding and eventually being able to predict disturbances such as solar eruptions and geomagnetic storms, both of which can have important impacts on a technological society. This strategy identifies five key scientific topics to be addressed in space physics research in the coming decade. For each of these topics, the report presents the scientific background and discusses why the topic is important, describes the current program for research on the topic, and then recommends, in priority order, research activities for the future. As is made clear in the main text, each of these five diverse topics is linked by a number of basic themes. Even though this strategy does not address specific proposals for future programs or missions, consideration is given to the practical aspects of carrying out the recommended investigations. The rationale for the research priorities is driven not only by scientific priority, but also by considerations such as current plans, near-term budget constraints, technological readiness, and balance between large- and small-scale endeavors. The five topics [box omitted], which are not prioritized, and the prioritized recommendations for research in each topic are briefly summarized as follows. 1 “Summary” reprinted from A Science Strategy for Space Physics, National Academy of Sciences, Washington, D.C., 1995, pp. 1–7.
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Space Studies Board Annual Report 1995 THE KEY TOPICS IN SPACE PHYSICS RESEARCH Mechanisms of Solar Variability The Sun is a variable star on time scales of milliseconds to centuries or more. These variations occur not only in visible light, but also at radio, ultraviolet, x-ray, and y-ray wavelengths and in the emission of the solar wind and energetic particles. Although solar variability ultimately arises from the interaction of magnetic fields and differential rotation inside the Sun, the Sun’s interior dynamics are largely unknown. The new tool of helioseismology is being used to probe the solar interior; it has shown that the Sun’s rotation rate does not increase inward as had previously been postulated and thus rules out the “standard” model of the dynamo that generates the solar magnetic field. At least at the solar surface, and perhaps in the interior as well, the magnetic fields are confined to rope-like structures with diameters of about 100 km, which are too small to be resolved from Earth. It has been suggested that the twisting and shearing of these flux tubes lead to bursts of high-speed solar wind, called coronal mass ejections, and to solar flares, but the trigger mechanisms for those violent events are not yet known. On longer time scales, complacency about the simplicity of the Sun has been upset by the discovery and documentation in the historical record that the Sun has undergone periods of low activity. The association of the Maunder Minimum period (~1645 to 1715), when few sunspots appeared on the solar surface for roughly 70 years, with the Little Ice Age, when Europe experienced exceptionally cold winters, has potentially serious implications for society should a similar episode occur under current conditions. In addition, confidence in current understanding of the solar interior was upset by the discordantly low flux of solar neutrinos observed in several experiments. It is not yet known whether this disagreement derives from errors in neutrino physics or from errors in understanding of the solar interior. The research priorities for advancing the understanding of solar variability are as follows: Use helioseismology to study the structure and dynamics of the solar surface and interior over a full solar cycle, to obtain information on the interior changes that cause solar cycles. Assure continuity of total and spectral irradiance measurements, supported by spatially resolved spectrophotometry, to investigate correlations between solar magnetic activity and solar output variations and thereby to understand how they are coupled. Measure high-energy radiation and particles from flares and coronal mass ejections with good angular resolution, good spectral resolution, and wide spectral coverage to determine what drives each of those phenomena and how they contribute to the solar output at high energies. Observe surface magnetic fields, velocities, and thermodynamic properties with enough spatial resolution (<150 km, with an ultimate goal of <100 km) to study small-scale structures such as flux tubes that may play a decisive role in solar activity and the generation of solar outputs. Make global-perspective measurements of the solar surface magnetic and velocity fields and solar oscillations to measure the three-dimensional structure and long-term evolution of active regions and to detect weak but coherent global oscillations. Measure active regions with angular resolution of ~1 arc sec and temporal resolution of ~10 min for a duration of ~10 days without nighttime gaps to determine the magnetohydrodynamic history of their emergence, development, and decay and the physical scenario behind it. The Physics of the Solar Wind and the Heliosphere Some of the energy transported from the solar interior goes into heating the Sun’s outer atmosphere, called the corona, to over a million degrees by processes that are currently the target of intense study. The hot corona in turn becomes the source of the solar wind, but there are still major questions about how this occurs. Further observations and numerical simulations are required to determine the relative importance of magnetic reconnection, explosive jets, tiny active regions called bright points, hydromagnetic waves, and the topology of the magnetic fields in the corona in accelerating the quasi-stationary solar wind. There are additional questions about the acceleration of the nonstationary or transient solar wind arising from explosive events called coronal mass ejections. New observations of the variable elemental composition and ion charge states of the solar-wind plasma are providing valuable clues concerning the acceleration of both types of solar wind.
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Space Studies Board Annual Report 1995 As the solar wind flows out through the solar system, it blows a big bubble, called the heliosphere, in the interstellar medium. Because of its very large scale (~100 AU), the heliosphere provides a unique laboratory for studying plasma processes in relative isolation from boundary effects; from heliospheric studies it is possible to learn much about instabilities in expanding plasmas, the interaction of colliding plasmas, the generation and evolution of plasma waves and magnetohydrodynamic turbulence, and the acceleration and propagation of energetic particles in turbulent fields. Within the decadal time frame considered by this report, it will be possible to measure the latitudinal variations of heliospheric particles and fields over the full range of solar activity and to test theories about the interaction of the solar wind with the interstellar gas and plasma. The following priorities are identified for future research on the solar wind and the heliosphere: Continue to obtain and synthesize the data from the present constellation of heliospheric spacecraft and from the interplanetary cruise phases of planetary missions in order to characterize the global and solar-cycle-dependent properties of the heliosphere and its interactions with the interstellar medium. Carry out in situ observations of the solar corona to explore and characterize the region of acceleration of the solar wind and the physical processes responsible for that acceleration. Obtain new types of data required to reveal the mechanisms responsible for the transport of energy, including wave motions (periods of 1 to 10 s), from the solar surface into the chromosphere and corona to understand how these are heated. Carry out stereo imaging of the solar corona to reveal the three-dimensional structure of coronal features without the ambiguity caused by integration along the line of sight. Develop and use techniques for the remote sensing of the coronal magnetic field in order to improve knowledge of the acceleration of the solar wind and of the initiation of coronal mass ejections. Make in situ measurements of the outer heliospheric boundaries and the interstellar medium with instruments specifically designed for those purposes. The Structure and Dynamics of Magnetospheres and Their Coupling to Adjacent Regions Some of the most visually awe-inspiring, yet poorly understood, terrestrial phenomena are a direct consequence of the interaction of the variable Sun and solar wind with the Earth. Auroral displays, usually confined to high latitudes, episodically descend into the temperate zones during periods of extreme solar activity. The aurora is only one manifestation of the complex chain of physical events and connections that link the energy output of the Sun with the Earth’s magnetosphere, ionosphere, and atmosphere. As the solar wind reaches the Earth, some of it enters the magnetosphere via several different processes and paths and affects the circulation and dynamics of the plasma within the magnetosphere. The interplanetary magnetic field can become temporarily connected to the geomagnetic field, but the physics of the reconnection process is not yet well understood. Once within the magnetosphere, the energy from the solar wind cascades through the system and some is released catastrophically in events whose trigger mechanisms and extent are not well known. Flows of thermal and energetic plasma, large-scale current systems, magnetic perturbations, and imposed electric fields provide the basic links between the magnetosphere and the ionosphere. The ionosphere provides feedback to the magnetosphere in the form of ion outflow, conductivity changes, and dynamo fields. There is a continual reconfiguration of this system as the solar wind and its embedded magnetic field change in response to solar and interplanetary dynamics and energetics. The past and current program, based primarily on in situ measurements, is providing an understanding of the magnetosphere that is strong in terms of local phenomena and a statistical picture of the global structure, but weak in terms of global dynamics. Researchers now know that most transport processes take place within narrow boundary layers connecting regions with very different plasma conditions. The frontier issues for the future center on the global magnetospheric dynamics in response to the solar wind driver, and the physical mechanisms that determine the coupling between regions. Many of the outstanding questions in magnetospheric physics will be addressed by global magnetospheric imaging, a new addition to the techniques available for magnetospheric research. In addition, studies of the magnetospheric environments of other planetary bodies can also yield important physical insights into the mechanisms that drive the dynamical behavior of the Earth’s magnetosphere. The following priorities are identified for future progress on this topic:
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Space Studies Board Annual Report 1995 Reap the full scientific potential of the International Solar-Terrestrial Physics program and its coordinated programs to advance understanding of the transport of mass, momentum, and energy throughout the solar wind, and the magnetosphere and ionosphere systems. Simultaneously image the plasma and energetic particle populations in the aurora, plasmasphere, ring current, and inner plasma sheet to study the global structure and large-scale interactions of magnetospheric and ionospheric regions during different levels of solar and geomagnetic activity. Maintain the full complement of particle and field instruments on current and future planetary missions to gain increased understanding of the formation and dynamics of diverse magnetospheres and ionospheres. Further develop and exploit ground-based facilities that image the ionospheric manifestations or “foot-points” of solar wind/magnetosphere coupling processes to complement the magnetospheric imaging initiative aimed at studying the global properties of the magnetosphere. Explore Mercury’s magnetosphere to understand the role of an ionosphere in coupling between the solar wind and planetary magnetospheres. Target localized regions that require greater understanding of the small-scale physical processes occurring there with high-resolution, multispacecraft measurements that take advantage of new smaller, lighter, more capable instruments and more sophisticated data-compression schemes. The Middle and Upper Atmospheres and Their Coupling to Regions Above and Below A complex interface exists between Earth’s space environment and the lower atmosphere or troposphere where weather and climate occur. This interface includes the highly variable middle and upper regions of the atmosphere extending upward from a lower boundary at 10 to 15 km altitude. The middle and upper atmospheres have considerable practical as well as intellectual interest because most ozone resides there and because disturbances in the upper atmosphere and ionosphere caused by solar wind and magnetospheric variations can disrupt technological systems through their effects on satellite drag, communications, and induced ground currents. The middle and upper atmospheres are strongly influenced by inputs of mass, momentum, and energy from both above and below. The absorption of variable solar ultraviolet and x-radiation and of energetic particles not only heats the atmosphere, but also initiates chains of photochemical reactions and ionizes the upper atmosphere to form the ionosphere. Highly variable electric fields and currents originating above and below the upper atmosphere are major sources of energy and momentum to that region. Gravity, planetary, and tidal waves that originate partly from the lower atmosphere grow in amplitude as they propagate upward, where they contribute to the momentum and energy budgets of the middle and upper atmospheres and produce turbulence that influences mixing processes. There are major deficiencies in our knowledge of many of these inputs to the middle and upper atmospheres as well as of the multiple interactions and feedbacks that occur there. The following priorities are identified for future research aimed at understanding this important interface between Earth’s lower atmosphere and space: Exploit the exciting new capabilities of UARS,2 FAST, and CEDAR to provide the foundation for future advances in our understanding of the middle and upper atmospheres. Investigate the reaction of the middle and upper atmospheres to upward propagating waves from the lower atmosphere and energy inputs from space so that the sources of important features such as the quasi-biennial and semiannual oscillations and the causes of mesosphere/lower-thermosphere structure and variability can be understood. Study the long-term variations in the middle and upper atmospheres using a combination of consistent long-term satellite and ground-based measurements together with three-dimensional radiative-chemical-dynamical modeling to understand natural and anthropogenic changes in these regions. Develop methods to observe the time-dependent electrodynamics operating on microscales to global scales, both in the upper atmosphere-ionosphere-magnetosphere coupling regions so that feedback processes can be characterized, and in the regions above thunderstorms so that the effects of electrified clouds on the “global circuit” and on middle atmosphere chemistry and energetics can be characterized. 2 A glossary of acronyms is included as the appendix, and the principal programs identified by the acronyms are described in the main text.
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Space Studies Board Annual Report 1995 Take advantage of opportunities to include carefully chosen, appropriate instruments on planetary orbiter missions to make measurements critical to understanding planetary aeronomy and its relation to terrestrial aeronomic processes. Plasma Processes That Accelerate Very Energetic Particles and Control Their Propagation Many of the plasma processes responsible for phenomena within the heliosphere probably also play a role in determining the properties of galactic cosmic rays, which are the only available sample of matter from outside the local solar neighborhood. Mass, charge, and energy spectrometers on existing and planned spacecraft can make in situ measurements of energetic particles throughout the heliosphere to study particle acceleration, fractionation, and transport in a variety of space plasma environments. Theories of acceleration mechanisms in larger-scale galactic structures such as supernova remnants make specific predictions about compositional changes that should take place at the highest energies attainable in those objects, but the theories have not yet been tested observationally. Cosmic rays are confined to the galaxy by turbulent magnetic fields. Measurements of radioactive “clock” nuclei can be used to distinguish diffusive trapping in the galactic halo from the simpler phenomenological models used for many years. Gamma ray measurements can be used to trace the radioactive parent elements of positrons that should be accelerated by the shocks presumed to be the source of the galactic cosmic ray nuclei. Although fluxes of antiprotons and positrons produced in collisions of cosmic rays with gas in the interstellar medium can be calculated with some precision, a full understanding of the sources of antimatter in the cosmic radiation requires a new generation of measurements. Nuclides heavier than nickel are produced by accretion of neutrons either in supernova explosions or during certain other phases of stellar evolution. Knowledge of the abundance of different cosmic ray elements and isotopes will allow the use of nucleosynthesis models to determine quantitatively the fraction of cosmic rays synthesized in each type of source. The abundance of actinide elements can be used as a radioactive clock to determine the time delay between the synthesis of these elements and their acceleration to cosmic ray energies. The measurements necessary to address scientific issues concerning particle acceleration and propagation are, in priority order: Complete the observations from the current and planned network of interplanetary spacecraft to study particle acceleration, fractionation, and transport. Extend direct composition measurements to 1015 eV to probe the limits of acceleration and trapping mechanisms. Measure abundances of radioactive isotopes above 1 GeV/nucleon to search for evidence of an extended galactic magnetosphere and wind. Measure the spectra of positrons (10 MeV to 100 GeV) and antiprotons (100 MeV to 100 GeV) to determine where those particles are created and how they are accelerated. Measure isotope abundances for nuclei heavier than nickel and elemental abundances through the actinides to probe the plasma regions where the nuclei are synthesized and to measure the time scales involved. RECOMMENDED RESEARCH EMPHASES The specific programs required to obtain answers to the questions raised under each of the five key topics outlined above are quite different. However, they are united by four common elements or themes that the CSSP and CSTR consider to be the most important research emphases for space physics in the next decade. 1. Complete currently approved programs. The space physics community must reap the benefits of the existing approved programs. A stable program permits the most efficient management and execution of high-priority research. In addition to the obvious scientific return, these ongoing programs provide the basis for developing future research directions. Space physicists will gain the maximum benefit from ongoing and approved missions by:
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Space Studies Board Annual Report 1995 Completing the diverse components of the International Solar-Terrestrial Physics program; Enhancing data analysis and interpretation efforts; Streamlining mission operations for all space physics missions; Carrying out extended missions for the uniquely placed Voyager (to the greatest possible heliocentric distance) and Ulysses (through the solar polar passes at solar maximum); Supporting essential observational programs that require long-duration databases; and Enhancing the effectiveness of some of the longer-duration programs by soliciting new ideas and analysis techniques from guest investigators and by ensuring easy access to archived data resulting from the various programs for use in “small science” research tasks. 2. Exploit existing technologies and opportunities to obtain new results in a cost-effective manner. Much technology is already in place to take the next observational steps required to address many of the important questions in space physics outlined here. These steps include: Adapting existing instrumentation to the new generation of smaller spacecraft and more focused space missions; Placing space physics instruments on planetary, Department of Defense, and other spacecraft of opportunity; Utilizing suborbital platforms such as rockets and long-duration balloons for both science objectives and instrument development; and Supporting, where appropriate, activities at unique ground sites such as in the polar cap. 3. Develop the new technology required to advance the frontiers of space physics. In order to achieve several high-priority objectives, or to lower the cost of projects, the limits of technology must be pushed in the following ways: Developing methods to approach the Sun ever more closely to open one of the most exciting new frontiers of space science; Producing new spacecraft and instruments based on lightweight structure and miniature electronics; Extending capabilities in suborbital techniques for both experimentation and instrument development; Exploiting infrared instrumentation for solar physics; and Devising techniques to explore the region between the altitudes reached by balloons and those reached by spacecraft. 4. Support strongly the theory and modeling activities vital to space physics. Special emphasis should be given to the following topics: Designing a new generation of instrumentation for remote global imaging of magnetospheric, ionospheric, and solar wind plasmas; Recognizing that synergy between observations, modeling, and theory provides the optimum way of addressing the principal questions in space physics; Making numerical simulations of space physics systems more realistic by extending them to three dimensions, longer time durations, and a greater range of scale sizes, and by incorporating additional physical and chemical processes; Ensuring access to state-of-the-art computational facilities; Exploiting new insights gained from theory, especially the theory of nonlinear processes; and Revisiting earlier efforts to predict solar activity, such as coronal mass ejections and flares, using simulations combined with solar observations.
Representative terms from entire chapter: