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Space Studies Board: Annual Report 1995 (1996)

Chapter: 3 Summaries of Major Reports

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Suggested Citation:"3 Summaries of Major Reports." National Research Council. 1996. Space Studies Board: Annual Report 1995. Washington, DC: The National Academies Press. doi: 10.17226/9039.
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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

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“Executive Summary” reprinted from A Strategy for Ground-Based Optical and Infrared Astronomy, National Academy Press, Washington, D.C., 1995, pp. 1–2.

Suggested Citation:"3 Summaries of Major Reports." National Research Council. 1996. Space Studies Board: Annual Report 1995. Washington, DC: The National Academies Press. doi: 10.17226/9039.
×

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.

Suggested Citation:"3 Summaries of Major Reports." National Research Council. 1996. Space Studies Board: Annual Report 1995. Washington, DC: The National Academies Press. doi: 10.17226/9039.
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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.

Suggested Citation:"3 Summaries of Major Reports." National Research Council. 1996. Space Studies Board: Annual Report 1995. Washington, DC: The National Academies Press. doi: 10.17226/9039.
×

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.

Suggested Citation:"3 Summaries of Major Reports." National Research Council. 1996. Space Studies Board: Annual Report 1995. Washington, DC: The National Academies Press. doi: 10.17226/9039.
×
  • 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.

Suggested Citation:"3 Summaries of Major Reports." National Research Council. 1996. Space Studies Board: Annual Report 1995. Washington, DC: The National Academies Press. doi: 10.17226/9039.
×
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.

Suggested Citation:"3 Summaries of Major Reports." National Research Council. 1996. Space Studies Board: Annual Report 1995. Washington, DC: The National Academies Press. doi: 10.17226/9039.
×

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:

  1. 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.

  2. 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.

  3. 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.

  4. 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.

Suggested Citation:"3 Summaries of Major Reports." National Research Council. 1996. Space Studies Board: Annual Report 1995. Washington, DC: The National Academies Press. doi: 10.17226/9039.
×

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:

  1. 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.

  2. 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.

  3. 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.

  4. 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:

  1. 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.

Suggested Citation:"3 Summaries of Major Reports." National Research Council. 1996. Space Studies Board: Annual Report 1995. Washington, DC: The National Academies Press. doi: 10.17226/9039.
×
  1. 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.

  2. 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.

  3. 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.

  4. 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

Suggested Citation:"3 Summaries of Major Reports." National Research Council. 1996. Space Studies Board: Annual Report 1995. Washington, DC: The National Academies Press. doi: 10.17226/9039.
×

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:

  1. 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.

  2. 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.

  3. 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.

  4. The suppression of free evaporation from melt surfaces could allow synthesis at higher temperatures than can be performed on Earth.

  5. 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.

Suggested Citation:"3 Summaries of Major Reports." National Research Council. 1996. Space Studies Board: Annual Report 1995. Washington, DC: The National Academies Press. doi: 10.17226/9039.
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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

Suggested Citation:"3 Summaries of Major Reports." National Research Council. 1996. Space Studies Board: Annual Report 1995. Washington, DC: The National Academies Press. doi: 10.17226/9039.
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continue to support ground-based experiments and the development of underlying theories. Theoretical understanding and ground-based experimental results should support the need for microgravity experiments and the likelihood that experimental objectives will be met. Notwithstanding this, exploratory experiments can be valuable in advancing understanding of some complex systems (e.g., biological systems).

  • There are scientific reasons to augment microgravity research in certain areas with a variable-gravity capability of extended duration that covers the microgravity to 1-g range. In a laboratory science where controlled model experimental systems are essential, the ability to vary an important parameter continuously should be developed whenever feasible. Therefore, if a space station centrifuge is to be developed, it is desirable to evaluate shared utilization for microgravity research.

  • NASA should categorize experiments according to their minimum facility requirements to maximize scientific return and cost-effectiveness. Drop towers, aircraft on parabolic trajectories, sounding rockets, and orbiting platforms supply a range of acceleration levels, acceleration spectra, and experimental durations and provide opportunities for manned interaction and demonstration of reproducibility. Some facilities are more suitable than others for precursor experiments to evaluate instruments and procedures and to demonstrate feasibility.

  • General-purpose facilities (versus experiment-specific equipment) should not be imposed on principal investigators if it might degrade the scientific results. Costs are not necessarily lowered when equipment is designed for a wide range of experiments. The scientific benefits could be substantially reduced by the inherent compromises.

  • For each flight experiment, the acceleration vector should be accurately measured locally, frequently (or continually), and simultaneously with other experimental measurements. Since the magnitude and direction of the net local acceleration environment can significantly affect experiments, they must be correlated with the primary experimental data. The net acceleration vector varies temporally and with position relative to the spacecraft center and can have major effects even at small magnitudes.

  • Materials studied in microgravity experiments should be adequately characterized on Earth. For some materials, there is a lack of the thermophysical data essential for both experimental design and modeling. These data should be obtained by ground-based research, where possible, or from microgravity measurements, when necessary.

  • The qualitative effects of the acceleration environment on certain types of experiments should be studied. These effects are not generally understood and characterized.

FLIGHT OPPORTUNITIES AND CHALLENGES

The peculiar character of microgravity research as a laboratory science in space requires real-time interactions between scientists and their experiments. This special requirement indicates another role for humans in space, in addition to the traditional use of astronauts for exploration and the deployment and repair of satellites. Moreover, a laboratory-based researcher should be able to carry out a large number of experiments to cover required ranges of the experimental parameters and demonstrate the reproducibility of results. The researcher should be able to modify the apparatus and diagnostics, when necessary, to ensure successful experimentation.

An assortment of facilities is available for research in a low-gravity environment. These range from drop towers and aircraft to orbiting platforms. The duration required for experiments in some of the subdisciplines of microgravity research may exceed the flight time available on some platforms. Additional spacelab missions, particularly those with extended-duration capability, might adequately serve those subdisciplines. For other subdisciplines such as some aspects of biotechnology and materials science, however, longer flight times would provide significant benefits in terms of the quality of scientific yields. Even for those subdisciplines with shorter-duration experiments, the limited number of spacelab flights and the high costs associated with them severely limit the experimenter with regard to demonstration of reproducibility, time for readjusting or repairing equipment, and reflight opportunities. These limitations, inherent to the spacelab system, can be obviated only by the longer flight durations available on a space station or a recoverable satellite. It is important, however, that the design of a space station or recoverable satellite provide a stable microgravity environment that minimizes unacceptable disturbances.

The present microgravity research infrastructure does not readily accommodate the needs of laboratory research. Although drop towers and airplanes flying parabolic trajectories can be used for special or precursor experiments and some materials processing can be done on free-flyers, the spacelab and space station are better suited for microgravity laboratory research. Experience with spacelab for microgravity research, however,

Suggested Citation:"3 Summaries of Major Reports." National Research Council. 1996. Space Studies Board: Annual Report 1995. Washington, DC: The National Academies Press. doi: 10.17226/9039.
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indicates that (1) it is likely to take years to develop an experiment that can yield high-quality scientific data and (2) it is an extremely expensive process.

The time required from the selection of the principal investigator to launch with new hardware is 5 to 6 years for mid-deck (noninteractive) experiments and 6 to 8 years in spacelab. Reflights with minimal modifications to the equipment require 1 year for mid-deck and 2 years for spacelab experiments. Minute elements of an experiment must be documented in detail and subjected to safety tests. Experiments are often delivered up to a full year before launch for integration into the spacelab and then into the orbiter. Because the number of spacelab missions is limited, as many experiments as possible are scheduled for each flight. Thus, the number of experimental runs is limited even if all goes as planned on the mission. As a result, compromises are made that might be favorable for one experiment but not others. For those experiments that suffer in the compromise process, essential science might be sacrificed. Also, because of heavy demand, experimenters are often guaranteed only one flight.

Surmounting the various administrative hurdles confronting an experiment requires interaction with three different NASA centers. The conditions imposed on the experiment by various centers are not always mutually consistent. The principal investigator is often excluded from the discussions. Most of this complexity results from concern for the safety of the crew and spacecraft, and results in long times for experiment development and flight and, consequently, increased cost. Concern for safety in human spaceflight missions should always remain a primary consideration, but safety issues could be fully addressed in a streamlined administrative process that does not compromise the scientific objectives of the mission. The requirement for laboratory science is that human participation in the experimental process be guaranteed, although in some cases, unmanned flights with remote control of experiments are effective substitutes for physical human presence. Human presence, however, will be necessary for many spaceflight experiments in the foreseeable future.

The entire infrastructure and extensive procedures that are currently extant have been developed essentially for missions in space with purposes other than laboratory science. They should now be reassessed and perhaps modified extensively to take full advantage of the unique microgravity environment.

The biotechnology program has been affected by some confusion concerning its administrative oversight. Biotechnology is tied strongly to other microgravity programs because it shares fluids and transport phenomena as the common scientific theme through which gravity becomes an important parameter. The administrative issue concerns the need for cooperation and coordination between the microgravity research administration and the life sciences administration for research on cellular and subcellular processes and mechanisms.

In summary, the major administrative challenges before NASA in the microgravity research domain are the following: (1) interactions among centers and between centers and headquarters should be simplified and unified; (2) principal investigators should be continually involved with the development of experiments; and (3) biotechnological research and life sciences programs should be well coordinated.

ADMINISTRATIVE RECOMMENDATIONS

The following recommendations do not directly address the scientific issues, but rather summarize administrative issues that profoundly affect the quality and quantity of the scientific content of the microgravity program.

  • Meaningful interaction should be maintained between the principal investigators and NASA staff during experiment development and integration, and communication among these groups must be continued following flight. It is essential to minimize the overlap of responsibilities in the NASA infrastructure to accomplish this goal.

  • It is essential that the overlap of responsibilities among NASA centers and between centers and headquarters be substantially reduced in order to optimize the influence of the principal investigators and the likelihood of successful experiments.

  • Measures should be taken to improve coordination and cooperation between the life sciences administration and the microgravity research administration concerning biological and biotechnological research on cellular and subcellular processes and mechanisms. The strong scientific coupling between biotechnology and other microgravity disciplines through the fluids and transport theme should be recognized in any administrative reorganization.

  • All data, including acceleration measurements, should be made available immediately to the principal investigator. Current delays in providing data extend many months beyond the flights. NASA should coordinate the operations of various offices so that priority is given to the processing of experimental data.

Suggested Citation:"3 Summaries of Major Reports." National Research Council. 1996. Space Studies Board: Annual Report 1995. Washington, DC: The National Academies Press. doi: 10.17226/9039.
×
  • It is necessary to increase substantially the number of ground-based investigations to ensure the future supply of high-quality flight experiments. Consequently, the budget for ground-based research should be increased as a fraction of the entire microgravity program. To the maximum extent feasible, funding for ground-based research in the microgravity program should be protected from temporary budgetary fluctuations.

  • In addition to its role in developing flight experiments, the ground-based program can provide important scientific and technical data for other purposes. A ground-based study can therefore be judged successful even if a flight experiment does not result.

  • Microgravity research is much broader than the topic of materials processing in space and should be identified as microgravity research in all official documents, including the federal budget. Microgravity research better describes the activity and its actual and potential accomplishments. Materials processing in space characterizes only a fraction of this research activity and promotes a misleading impression of the potential benefits and scope of the program.

  • The microgravity sciences and applications program and the commercial development program have a large area of overlap and common interest. Coordination between these programs and an equally stringent review process for each should be fostered by NASA for their mutual benefit.

  • NASA should establish mechanisms for continuous, unrestricted submission of research proposals in order to optimize quality and take advantage of scientific advances. Unrestricted submission of research proposals would parallel approaches of other funding agencies and enable continual scientific advance.

  • To manage the diverse disciplines in microgravity research, it is necessary to increase the breadth and experience of the scientific staff at NASA headquarters. A rotation of prominent scientists on leave from universities, national laboratories, and industry is one mechanism to be explored. Introduction of active scientists in the administration of the program would be highly beneficial.

  • Prompt documentation of experimental results should be required and enforced. Reports of all experiments, including unsuccessful efforts, should be accessible to all interested parties. A concern is that some investigators might not report results because they are proprietary or inconclusive. The lack of an available report could lead to unnecessary duplication of efforts.

  • NASA should organize and maintain an accessible archive of microgravity research results. This archive should contain a bibliography of all published scientific papers and reports on microgravity subjects and should preserve the original spaceflight data sets, such as photographs and electronically recorded data.

An additional point of concern is that given the long time scale for the development through flight of a space experiment, there is a real danger that the scientific goals of the experiment might be bypassed by new developments or by major shifts in the value ascribed to the work. There is also the possibility that the principal investigator may lose contact with the field. Several of the above recommendations may be useful in this regard. Anything that NASA can do to shorten this time frame would be beneficial.

Suggested Citation:"3 Summaries of Major Reports." National Research Council. 1996. Space Studies Board: Annual Report 1995. Washington, DC: The National Academies Press. doi: 10.17226/9039.
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3.3 Review of Gravity Probe B

A Report of the Task Group on Gravity Probe B1

SUMMARY

BACKGROUND

The experiment now known as Gravity Probe B (GP-B) was conceived more than 30 years ago. Bold and daring in concept, it has been under continuous development ever since. The aim of the experiment is to measure, rather precisely, an effect that is predicted by all viable relativistic theories of gravity but has not yet been observed. Just as Newton’s law of gravity is paralleled by Coulomb’s law of electricity, so also it is expected that the force between currents of electrical charge, described by Ampere’s law, should be paralleled by a force between “currents” of flowing matter. It is this force that has never been directly observed.

A useful perspective on the GP-B experiment can be obtained from a historical profile of its funding. Until the late 1980s, the project was funded at a level of $1 M to $2 M per year to develop and demonstrate the necessary technology. Funding was then increased to permit detailed engineering of the various subsystems and thorough ground testing. The funding level reached about $30 M/yr in FY 1992, when the project entered a “science mission” phase involving development of an appropriate spacecraft to carry the experiment. Since then the funding has been approximately $50 M/yr.

When the project was last reviewed for NASA 4 years ago, the Parker Committee, an ad hoc review committee convened by NASA Associate Administrator for Space Science and Applications Lennard A. Fisk and chaired by Eugene N.Parker of the University of Chicago, recommended that if GP-B were to go forward, it must be properly funded. That committee considered an appropriate funding level to be about $50 M/yr until the time of launch, which was anticipated to be late in the 1990s. Subsequent funding has in fact been at this level, and has allowed highly skilled teams to address thoroughly various technical details of the experiment and to start building the flight instrument package and integrating it into a spacecraft. By the end of FY 1995 about $240 M will have been spent on the project. NASA estimates that another $340 M will be needed for completion, including launch and subsequent data analysis.

SCIENTIFIC MOTIVATION

Like most other fields of science, Einstein’s theory of gravity, the general theory of relativity or GR, has developed its own notation and jargon. Despite the simplicity and economy of its underlying assumptions, the theory in full glory leads to intensely complicated nonlinear equations. Indeed, the equations have been fully solved only in a few special instances. However, much of the mathematical complication can be removed by assuming that all gravitational fields are weak. The equations then reduce to a form remarkably similar to those governing electromagnetism. Terms appear that are analogous to the electric field caused by charges (the gravitoelectric field, produced by masses), and to the magnetic field produced by the flow of charge (the gravitomagnetic field, produced by the flow of matter). A spinning ball of electrical charge produces a well-prescribed static magnetic field, and correspondingly a spinning mass such as the Earth is expected to produce a static gravitomagnetic field. Of course, general relativity has important differences from electromagnetism, as well: in particular, it represents gravitational forces as arising from geometric curvature in the structure of space and time.

Gravity Probe B aspires to detect and measure, at the 1 percent level, the gravitomagnetic field produced by the spinning Earth through a spin-spin interaction with an orbiting gyroscope. This effect of the gravitomagnetic field is often referred to as “frame dragging,” or the Lense-Thirring effect. In addition, GP-B will accurately measure the much larger “geodetic” precession, a combination of the effects of spin-orbit coupling and space-time curvature.

In the quarter century since inception of the GP-B project, many other tests of Einstein’s theory of gravity have been made. The delay and deflection of light signals passing close to massive objects have been measured with increasing precision and found to agree with the predictions of GR at the 0.1 percent level. Geodetic precession has

1  

“Summary” reprinted from Review of Gravity Probe B, National Academy Press, Washington, D.C., 1995, pp. 1–4.

Suggested Citation:"3 Summaries of Major Reports." National Research Council. 1996. Space Studies Board: Annual Report 1995. Washington, DC: The National Academies Press. doi: 10.17226/9039.
×

been detected and measured with 2 percent accuracy by laser ranging to the Moon. Gravitational radiation from accelerated masses in a binary pulsar system has been shown to be consistent with GR at the 0.4 percent level. Some of these tests involve gravitomagnetic effects related to the translational flow of matter, in combination with other relativistic gravitational effects, and therefore they provide indirect evidence for the existence of gravitomagnetism. By contrast, GP-B proposes to provide a direct test of gravitomagnetism caused by rotation, in isolation from other relativistic gravitational effects.

The past quarter century has also seen the development of exquisitely sensitive new instruments based on developing technologies and located both on Earth and in space. Some of them have provided the means to probe more and more deeply into the nature and evolutionary history of the universe. Observations with such instruments have yielded one surprise after another, and they raise perplexing questions about missing mass, the age of the universe, and the circumstances giving rise to the large-scale distribution of matter in space. In the past, laws of nature previously considered sacrosanct have sometimes been found deficient when subjected to much closer scrutiny or applied to new phenomena. As long as some discoveries defy understanding, it is important to continue testing nature’s most fundamental laws.

CONCLUSIONS
Scientific Importance

The frame-dragging effect predicted by our principal theory of space and time, general relativity, has a deep conceptual significance involving the connections between rotation, distant matter, and absolute space. Frame dragging is a direct manifestation of gravitomagnetism. Its consequences have found important astrophysical applications in, for example, models of relativistic jets observed streaming from the cores of quasars and active galactic nuclei. A 1 percent measurement of the predicted frame-dragging effect would be a significant and unique test of GR. Gravity Probe B is one of the few space missions NASA has conducted with relevance to fundamental physics. If successful, it would assuredly join the ranks of the classical experiments of physics. By the same token, a confirmed result in disagreement with GR would be revolutionary.

Since GP-B was conceived, significant progress has been made through experimental studies of gravity, both in improved precision and in performing qualitatively new tests. These tests are so constraining that there are now no examples of alternative theories that are consistent with the experimental facts and predict a frame-dragging effect different from that predicted by GR at a level GP-B could detect. Yet the basic weakness of the gravitational force means that GR has been tested much less thoroughly than the other fundamental theories of physics. Nevertheless, along with most physicists this task group believes that a deviation from GR’s prediction for frame dragging is highly unlikely.

In addition to detecting the new gravitomagnetic effect of frame dragging, Gravity Probe B should be able to measure the geodetic precession of its gyroscopes to an unprecedented accuracy of about 75 parts per million (ppm). This result would provide a factor-of-20 improvement in the measurement of space curvature per unit mass (now known to about 2 parts in 1000) and would tightly constrain the deviations from GR predicted by other theories of gravity in the weak-field limit.

Technical Feasibility

The task group is highly impressed with the extraordinary talents and abilities of the technical team assembled to create Gravity Probe B. The group has consistently solved technical problems with great inventiveness and ingenuity. Moreover, in the course of its design work on GP-B the team has made brilliant and original contributions to basic physics and technology. Its members were among the first to measure the London moment of a spinning superconductor, the first to exploit the superconducting bag method for excluding magnetic flux, and the first to use a “porous plug” for confining superfluid helium without pressure buildup. They invented and proved the concept of a drag-free satellite, and most recently some members of the group have pioneered differential use of the Global Positioning System (GPS) to create a highly reliable and precise aircraft landing system.

The task group finds progress in construction of the actual GP-B apparatus to be very impressive, as well. Working in concert with a team from the Lockheed Missiles and Space Company, the Stanford group is well on its way toward putting GP-B into space before the end of the decade, providing that the funding level is sustained. The

Suggested Citation:"3 Summaries of Major Reports." National Research Council. 1996. Space Studies Board: Annual Report 1995. Washington, DC: The National Academies Press. doi: 10.17226/9039.
×

task group has found no serious technical impediments to meeting the existing launch schedule. The spacecraft, experimental package, and projected methods of operation are well designed to meet the scientific requirements and prove the results valid. The team is well prepared to cope with a wide range of unanticipated phenomena. The task group considers the overall complexity of GP-B to be somewhat greater than that of the Cosmic Background Explorer (COBE) but much less than that of the Hubble Space Telescope (HST). An ordinary hardware failure is no more likely than in other comparable space missions. Furthermore, GP-B has been designed with extensive in-flight testing of all parts, four independent sensor gyros to provide immediate confirmation of results, and in-flight calibration using observations of the aberration of light caused by the motion of the satellite.

Nevertheless, the extraordinary experimental requirements and the impossibility of ground tests of some critical systems at the necessary level of accuracy introduce significant risks. Despite an extensive list of detailed questions put to the GP-B team by the task group, no specific weakness or likely points of failure have been identified. A majority of the task group believes that GP-B has a reasonably high probability of achieving its design goals and completing the planned measurements. However, based on their experience with complex scientific experiments on the ground, several members remain skeptical about the large extrapolations required from ground testing to performance in space. This minority believes it likely that some as yet unknown disturbance may prevent GP-B from performing as required. The task group notes that in any event, should the GP-B experiment be completed successfully but yield results different from those predicted by general relativity, the scientific world would almost certainly not be prepared to accept them until confirmed by a repeat mission using GP-B backup hardware, or by a new mission using different technology.

Comparison with Other Proposed Programs

The scientific objectives of GP-B involve testing one of the fundamental laws of nature. The goals are therefore quite different from the objectives of a common situation in which natural laws, as inferred theoretically and tested in terrestrial laboratories, are used to interpret observations of astrophysical phenomena. In particular, the ambitions of GP-B are qualitatively different from those underlying most astronomical work, including NASA projects such as the HST, the Stratospheric Observatory for Infrared Astronomy (SOFIA), the Space Infrared Telescope Facility (SIRTF), and the Advanced X-ray Astrophysics Facility (AXAF). Tests of nature’s laws are the ultimate foundation of physical science and are the only rational basis for belief that these laws are, at least in part, “understood.” Despite its omnipresence, gravity remains the least well tested of all the fundamental forces.

NASA’s highly successful COBE satellite was designed primarily to answer certain astrophysical and cosmological questions. Nevertheless, its results have implications in fundamental physics as well, particularly for questions concerning the origin of the universe. The task group’s considered judgment is that the most likely of successful outcomes of the GP-B experiment—the measurement and confirmation of two specific effects predicted by general relativity—will be an important milestone, but will have less impact on the scientific world than the cumulative results of COBE. The reason is simple: there is no serious alternative to the general theory of relativity that predicts effects differing from those of general relativity by amounts that GP-B could detect. The GP-B experiment has been exciting for many scientists because of the need for confirmation of gravitomagnetism and the possibility of a great surprise, but the latter chance now seems more remote than before.

Other proposed satellite tests of frame dragging or spatial curvature, such as LAGEOS III, are intrinsically an order of magnitude less precise than GP-B. Another proposal claiming to offer higher accuracy is now in the conceptual stage and might eventually become a worthy successor to GP-B. It is discussed briefly in the section “Other Tests of Frame Dragging or Geodetic Precession” [in Chapter 2].

NASA estimates that $340 M will be required to complete the construction, launch, and data analysis phases of GP-B. If the experiment delivers as promised, so that the frame-dragging effect is measured to 1 percent accuracy and the geodetic term to 75 ppm, is it worth the cost? This question must be viewed in the context of other NASA projects of comparable magnitude, and necessarily its answer involves subjective scientific judgments. The task group was not able to achieve a clear consensus on the question of competitive value, even after extensive discussion and deliberation. Its members agree unanimously that all scientists would find it appealing to see a clean and direct demonstration of the frame-dragging effect, and that a confirmed discrepancy between the result of the GP-B experiment and the prediction of general relativity would fully justify the mission’s cost, including the additional expense of a confirming experiment. However, in light of existing tests of gravitation theories such a discrepancy is considered highly unlikely.

Suggested Citation:"3 Summaries of Major Reports." National Research Council. 1996. Space Studies Board: Annual Report 1995. Washington, DC: The National Academies Press. doi: 10.17226/9039.
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Consequently, the task group’s members hold a range of opinions on the relative cost-effectiveness of GP-B. A significant minority judge that the purpose of the mission is too narrow in comparison with missions that explore wide-open scientific issues and have a high probability of making new discoveries. This minority assigns high weight to the fact that essentially all experts believe that gravitomagnetism must exist, and consequently it does not appear likely that unexpected new knowledge will be gained.

In contrast, the task group’s majority judgment gives higher weight to the importance of experimental verification in GP-B’s unique and direct test of general relativity. Considering also the possibility of a revolutionary discovery, however remote, the majority judges the GP-B project well worth its remaining cost to completion.

Suggested Citation:"3 Summaries of Major Reports." National Research Council. 1996. Space Studies Board: Annual Report 1995. Washington, DC: The National Academies Press. doi: 10.17226/9039.
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3.4 Earth Observations from Space: History, Promise, and Reality

A Report of the Committee on Earth Studies1

EXECUTIVE SUMMARY

The ability to make earth observations from space is one of the great successes of the space age. For both scientists and operational users of the data, however, this success has been tempered with disappointment. The promise of the technology has not yet been realized, nor is it evident that current activities are leading toward a timely realization of that promise. The civil earth observations programs of the National Aeronautics and Space Administration (NASA) have been in a state of annual redesign for more than 5 years. The early momentum that led to the laudable concept of NASA’s Mission to Planet Earth (MTPE) is being dissipated.

In this report the Committee on Earth Studies (CES), a standing committee of the Space Studies Board (SSB) within the National Research Council (NRC), reviews the recent history (nominally from 1981 to 1995) of the U.S. earth observations programs that serve civilian needs. The principal observations programs examined are those of NASA and the National Oceanic and Atmospheric Administration (NOAA). The Air Force’s Defense Meteorological Satellite Program (DMSP) is discussed, but only from the perspective of its relationship to civil needs and the planned merger with the NOAA polar-orbiting system.

The report also reviews the interfaces between the earth observations satellite programs and the major national and international environmental monitoring and research programs. The monitoring and research programs discussed are the U.S. Global Change Research Program (USGCRP), the International Geosphere-Biosphere Program (IGBP), the World Climate Research Program (WCRP), related international scientific campaigns, and operational programs for the sharing and application of environmental data.

It is not the intent of the CES to make detailed reviews of every aspect of this broad scope of activities, nor is it the intent to provide detailed findings and recommendations for action by responsible agencies. Instead, the purpose of this report is to provide a broad historical review and commentary based on the views of the CES members, with particular emphasis on tracing the lengthy record of advisory committee recommendations. Any individual topic could be the subject of an extended report in its own right. Indeed, extensive further reviews are already under way to that end. If the CES has succeeded in the task it has undertaken, this report will serve as a useful starting point for any such more intensive study.

The report is divided into eight chapters: (1) an introduction, (2) the evolution of the MTPE, (3) its relationship to the USGCRP, (4) applications of earth observations data, (5) the role that smaller satellites can play in research and operational remote sensing, (6) earth system modeling and information systems, (7) a number of associated activities that contribute to the MTPE and the USGCRP, and (8) organizational issues in the conduct of civil earth observations programs. Following the body of the report is a series of appendixes: after a list of acronyms and abbreviations and collected short biographies of CES members, six brief tutorials discuss several scientific topics important to the science and applications of earth observations. Highlights from the eight chapters follow.

EARTH SCIENCE FROM SPACE AND THE EVOLUTION OF THE MISSION TO PLANET EARTH

The NASA effort in earth observations is called the Mission to Planet Earth. It includes (1) a number of intermediate-size satellites that are collectively called the Earth Observing System (EOS); (2) a series of smaller satellites called Earth Probes; (3) a major information system named the EOS Data and Information System (EOSDIS); (4) associated research, data analysis, and mission operations activities; and (5) the Landsat-7 satellite, which will be the joint responsibility of NASA and NOAA. In addition, the MTPE relies on the availability of data from NOAA’s operational satellites, the DMSP satellites (up to the point of their merger with the NOAA polar-orbiting satellites), and numerous foreign satellites—some wholly foreign owned, others carrying NOAA or NASA instruments in cooperative ventures.

1  

“Executive Summary” reprinted from Earth Observations from Space: History, Promise, and Reality, National Academy Press, Washington, D.C., 1995, pp. 3–10.

Suggested Citation:"3 Summaries of Major Reports." National Research Council. 1996. Space Studies Board: Annual Report 1995. Washington, DC: The National Academies Press. doi: 10.17226/9039.
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The Mission to Planet Earth began as a scientific initiative called Global Habitability, which had its origins in the research and operational earth observations missions of the 1960s and 1970s. The Global Habitability effort culminated in the report of a NASA workshop chaired by Richard Goody entitled Global Change: Impacts on Habitability (JPL, 1982). The next step in the advancement of the idea came in the report of an NRC workshop chaired by Herbert Friedman entitled Toward an International Geosphere-Biosphere Program (NRC, 1983). The concept continued to evolve and took much of its present form from the seminal work of the Earth System Science Committee (ESSC), which was chaired by Francis Bretherton (NASA, 1986, 1988). These three pivotal efforts became known colloquially as the Goody, Friedman, and Bretherton reports.

The MTPE was allied early with the Space Station program. As a result of that tie, the program took the initial form of a satellite design using very large, highly complex, astronaut-tended, polar platforms that would be serviced from the Space Shuttle, which was required to fly in a polar orbit for this purpose. After planning for launches of the Space Shuttle into polar orbit and astronaut servicing of platforms there was eliminated, the separation of the MTPE from the Space Station program soon followed. A continuous series of reviews, redesigns, budget reductions, and changes in scope has led to the current configuration that employs intermediate and smaller satellites. Reviews are ongoing in 1995, with Congress calling for a reexamination of the program by NASA, the General Accounting Office (GAO), the Marshall Institute, and the NRC.

The continuing redesign has led to (1) large amounts of discarded work, (2) a reduction in the scientific and technical scope of the effort, (3) a retreating series of dates for the achievement of the originally stated scientific and technical goals, and (4) a continuous distraction for the scientists and administrators attempting to carry out the program. It is the CES’s perception that a substantial fraction of the overall effort conducted over a period of 5 years, particularly that by people within NASA, has been devoted to responding to calls for changes to the program from the Administration, the agency, and Congress.

Approximately 6 years prior to the present report, a blue-ribbon panel was formed to examine the future of the U.S. civil space program; it was chaired by one of the nation’s most prominent industrial leaders. The panel’s report noted (Augustine, 1990),

“Management turbulence” [is] defined as continual changes in cost, schedule, goals, etc…. Each change induced has a way of cascading through the entire project execution system, producing havoc at every step along the way…. At each step, contracts must be renegotiated, people reassigned, designs changed and schedules revised. Soon a disproportionate amount of time is spent in the pursuit of these change practices instead of producing the end product itself.

The report also noted,

The impact of excessive revisions in research contracts conducted by universities has much the same effect. In this case, substantial effort is devoted by academic researchers to the preparation of proposals for research support. When the presumed funds to support the work are subsequently diverted to other objectives, the productive talents of some of the nation’s most able people are largely wasted.

The CES finds the Augustine panel’s language to be an accurate and troubling description of what has overtaken the MTPE.

MISSION TO PLANET EARTH AND THE U.S. GLOBAL CHANGE RESEARCH PROGRAM

The U.S. Global Change Research Program (USGCRP) was created in response to public concerns regarding environmental change and stemmed from earlier national and international programs (e.g., the WCRP, United Nations Environmental Program (UNEP), IGBP, and NASA’s work leading up to the MTPE). An early characteristic of the USGCRP was the tendency to include under its umbrella nearly all preexisting environmental programs within federal agencies, whether or not they were part of an organized, coherent program of research on global change.

In the context of this report, climate change refers to changes on time scales from a few years to a few centuries in the climate. Following Lorenz (1975) and Peixoto and Oort (1992), climate is defined as “the mean physical state of the climate system…, consisting of the atmosphere, oceans, and cryosphere. The ‘mean physical state’ is

Suggested Citation:"3 Summaries of Major Reports." National Research Council. 1996. Space Studies Board: Annual Report 1995. Washington, DC: The National Academies Press. doi: 10.17226/9039.
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defined as a set of averaged quantities complete with higher moment statistics…that characterize the structure and behavior of the atmosphere, hydrosphere, and cryosphere.” Peixoto and Oort make an important distinction between climate and weather: “The climate…can be considered as ‘average weather,’ complete with some measures of the variability of its elements and with information on extreme events.” Some variables that are relevant in weather and in other branches of meteorology are also important in the characterization of climate.

In spite of its title, agency budget pressures and prioritization decisions have greatly reduced the scope of the USGCRP from global change to the narrower global climate change. Some areas of scientific research and remote sensing that have near-term scientific importance or serve practical applications have been reduced in scope or eliminated (e.g., land surface and vegetation research employing high-spatial-, high-spectral-resolution electrooptic sensors and microwave and laser sensing of oceans and ice).

When the current program was formulated, it was assumed that Landsat-like data would continue to be available. Now, however, it is the view of the CES that the combination of the loss of Landsat-6 and the cancellation of other advanced electrooptical sensors leaves a substantial gap in medium- to high-spectral-resolution and high-spatial-resolution measurements needed to meet the USGCRP objectives. Global surveys of vegetation class, land use, and surface minerals, as well as contributions to cartography, are not included in current plans. As structured, the USGCRP will also not generate some other data of substantial value to the earth applications community, such as systematic regional and global topography, digital elevation maps, and magnetic and gravitational fields.

The active microwave oceanographic and cryospheric measurements for the USGCRP (altimetry, scatterometry, and synthetic aperture radar, or SAR) are not integrated into a coherent plan either for their eventual transfer to long-term research or operational status on future NOAA satellites or for securing the timely availability of these data from foreign and/or internationally cooperative systems.

Alterations in vegetation class and extent are obviously changes in surface properties of great human interest; they are also changes that can be monitored from space. Such changes may develop because of climate change. The reduction in scope of the USGCRP to focus more narrowly on global climate change reduces the capability to make these measurements. At the same time that reductions in scope have been directed, policymakers are asking for nearer-term answers upon which to base decisions—in effect, re-expanding the scope of the effort.

The previously mentioned reductions now make the United States increasingly reliant on other nations for spacecraft, sensor systems, and data in some areas in which the United States was preeminent, notably high-spectral-and high-spatial-resolution electrooptical and microwave measurements. The CES enthusiastically endorses the concept of sharing the burden for the conduct of earth observations among as many nations as possible. However, the diminution of the ability of the United States to obtain required data from its own systems places a greater importance on the reliability of international agreements than in the past. In the past, these agreements have been difficult to reach and have not always resulted in ready data availability. This difficulty has been present in even such commonplace data as coarse-spatial-resolution meteorological measurements.

The USGCRP includes efforts of NASA, NOAA, the Department of Interior (DOI), Department of Agriculture (USDA), Department of Energy (DOE), Environmental Protection Agency (EPA), National Science Foundation (NSF), and others. As a result, responsibility for the USGCRP involves more than a dozen agencies, their respective budget examiners, and several dozen congressional committees, making efficient management improbable, or at least quite difficult.

USGCRP oversight is carried out by an interagency committee, which has provided useful coordination, but which also has little authority, offers inadequate means to review progress against milestones, and must rely on its powers of persuasion to conduct normal program management functions. For example, reallocation or redirection of program elements in an efficient manner (in response to changing needs or new discoveries) is hampered by the number of agencies and budget processes involved.

APPLICATIONS PROGRAMS

Advancing the operational utility of civil earth observations has not been given national priority in the current efforts. In the environmental satellite programs of NOAA, no systematic program has been formed to replace the NASA Operational Satellite Improvement Program (OSIP), which was abruptly terminated early in the 1980s and upon which NOAA had relied. In its stead, the U.S. operational weather satellite program has only a limited internal

Suggested Citation:"3 Summaries of Major Reports." National Research Council. 1996. Space Studies Board: Annual Report 1995. Washington, DC: The National Academies Press. doi: 10.17226/9039.
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research and development arm addressing needed improvements in the current generation of sensor systems and requirements for the next generation of sensors. New sensors are being pursued under the EOS program, but—despite some NOAA participation—with relatively little consideration for their affordability or practicality for transfer to operational use.

Under current NOAA planning, only small or incremental improvement of operational capabilities will take place over the next decade or even longer, even though the nations of the world plan to launch some 50 new observation satellites in that period (BNSC, 1992). Indeed, the polar-orbiting satellites of NOAA are little changed since the launch of the Advanced Tiros-N (ATN) in 1978. Thus, a period of some 27 years has elapsed between generations during a time of great technological advancement.

Of particular significance, no plans yet exist for the incorporation in the operational U.S. weather satellite fleet of advanced microwave instrumentation for altimetry, measurement of sea surface winds and waves, and imaging of polar ice fields—or, if not carried on U.S. satellites, for ensuring the routine availability of these data to operational users from foreign satellite systems. The CES questions the absence of an organized, advanced R&D program for the systematic introduction of these appropriate new technologies.

Landsat-like data are a necessary element in global change research and in operational applications. In spite of that, the future availability of these data is not ensured as of early 1995. The current U.S. role in this area rests solely with the aging Landsats-4 and -5. The future availability of these data to U.S. users rests on a Landsat-7 satellite planned to be launched in 1998 and on the commercial and data exchange practices of foreign countries. Similarly, as noted in the preceding section on the USGCRP with regard to research, no plans exist for the exploitation of space-based imagery in the preparation of topographic maps, digital elevation models, global vegetation inventories, mineral and soil surveys, or updated standard maps. Such products are among the greatest benefits to be derived from the nation’s investment in its space program.

The problems associated with space applications in general, and with earth observations in particular, are of long standing. Ten years ago, the NRC’s Space Applications Board (SAB) wrote (SAB, 1985),

The civil space program of the United States is a study in contrasts. The shuttle program is now operational; funding for the space station has been included in the President’s FY 1986 budget. In the field of science, the NASA program in physics and astronomy (for example) is strong and has received increases in funding. Several NASA research programs involving earth observations, the Upper Atmosphere Research Satellite (UARS), the Earth Radiation Budget Experiment (ERBE), and the development of an instrument to measure wind speed at the ocean surface are moving ahead vigorously.

There is, however, one major sector of the space program that is in disarray: the operational remote sensing of the earth. The successful weather satellite system in NOAA has been severely affected by programmatic reductions, by stretch-outs in satellite procurement, and by reduced cooperation between NOAA and NASA. The land remote sensing effort is endangered as the attempt to turn the program over to the private sector threatens to flounder because of limitations placed on federal support. No civil operational program in ocean remote sensing is in place or planned, although the Navy (with the cooperation of NASA and to a lesser degree NOAA) plans to mount a significant effort, the Navy Remote Ocean Sensing Satellite (NROSS).

Information from operational earth remote sensing systems is needed for a host of practical purposes, such as weather forecasting, ocean transportation and utilization, land management, and mineral exploration. This information is also required to improve understanding of various earth sciences—meteorology, oceanography, geology, and geophysics. Not only practical applications of substantial economic importance but also the advance of earth-oriented science are inhibited by the inadequacies of this sector of the space program.

Why should such a practical program be floundering? Why is it that earth-oriented activities are being outdistanced by other, less applicable sectors of the space program? It is true that the surge into space is largely an investment in the future, but one might assume that we as a nation would make every effort to reap the benefits of our investment as soon as it became possible to do so. This is not being done. Indeed, the situation is even less logical than has already been stated: In at least one critical area of earth remote sensing, the United States is marking time as other countries move toward world leadership and prepare to reap the benefits of our investment—using technology developed in this country.

…We do not condone or accept as appropriate the disarray in operational earth remote sensing.

These observations remain valid a decade later.

Suggested Citation:"3 Summaries of Major Reports." National Research Council. 1996. Space Studies Board: Annual Report 1995. Washington, DC: The National Academies Press. doi: 10.17226/9039.
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SMALLER SATELLITES AND EARTH PROBES

The CES believes that it is desirable for the nation’s civil earth observations program to include both long-term elements and other elements that permit quick-response, rapid-turnaround measurements. Satellites of all sizes are likely to be required, with each filling a particular niche.

Smaller satellites can play a scientifically important role in the MTPE and can also play important operational roles. The CES and other bodies within the NRC have long endorsed the use of smaller missions (see, e.g., SSB, 1988a,b, 1991; ASEB, 1994). The CES notes, however, that the choice of satellite size should be made by applying well-understood systems engineering procedures to the task to be accomplished. The very large polar platforms proposed for the MTPE in the early 1980s were a mistake. In retreating from that mistake, however, the pendulum must not be allowed to swing so far in the opposite direction that we lose sight of the function the satellite is intended to serve. The program should not be detrimentally driven by the pursuit of still another technological objective.

Furthermore, the CES sees no pressing need within the domain of civil earth observations to fly satellites as a management demonstration simply to prove that small, modestly capable satellites can be launched quickly. Well-crafted experimental technology satellites, however, can serve as engineering testbeds to qualify new subsystems for later use in research and operational observation systems; but such testbeds are quite likely to be of a different character than satellites intended to observe long-term changes in climate variables. NASA’s Advanced Communications Technology Satellite (ACTS) is illustrative of the difference: it demonstrates new technologies for later adoption, but is not itself in a form that would permit its use or replication as an operational commercial communications satellite. CES concerns arise only when mission objectives are mixed and demonstrations of new technology are appended as a requirement for the conduct of a mission in such a manner as to thwart scientific objectives or add unwarranted costs and delays. Astronaut-serviceable platforms should not be mandated as a requirement, and the use of microsatellites should not be mandated either.

It is important to recognize that technology changes and that the boundary between what measurement requires a larger satellite and what can be accomplished with a smaller satellite is not static. Some technological areas will be advanced with ease, making the boundary quite dynamic, while other areas will prove more resistant to advances—or will encounter basic limits likely to be of long standing. Sound and objective engineering judgment must be applied to determine the location of the boundary in individual cases.

EARTH SYSTEM MODELING AND INFORMATION SYSTEMS

Large information systems and accurate earth system models are easier to imagine than they are to build. Constructing earth system models possessing predictive skill of a useful degree is among the most challenging research tasks humans have undertaken. As with information systems, the state of earth system modeling is rudimentary, and the production of models must proceed incrementally, allowing for frequent adjustments in approach. The mathematical methods, algorithms, visualization approaches, software design, and other aspects of earth system modeling all have major embedded research tasks. Furthermore, present and probable future modeling capabilities should be factored into the design of observational systems. Both models and observational systems should be designed such that—as far as is reasonably possible—continuity, sampling frequency, and accuracies are commensurate with the needs for understanding and simulating the behaviors of the components of the earth system.

The subject of earth system modeling has received considerable attention by NRC bodies. The CES has itself addressed this issue frequently (SSB, 1982, 1985). The U.S. Committee for the IGBP (the Committee on Global Change, or CGC) has written extensively on the complexities of the problem of modeling (CGC, 1986, 1988, 1990). The Bretherton report contains comprehensive diagrammatic representations of the earth system model (NASA, 1988). The NRC’s Board on Atmospheric Sciences and Climate (BASC) has addressed modeling in a number of its reports, but perhaps the most significant is its 1991 data assimilation report (BASC, 1991), which addressed the integration of asynchronous, irregularly distributed measurements of varying quality and character. NASA also convened a special climate modeling workshop whose final report provided a broad survey of the challenges and requirements alluded to above (Unninayar and Bergman, 1993). All of these reports have stressed the intellectual challenge of the tasks before the MTPE and USGCRP.

Suggested Citation:"3 Summaries of Major Reports." National Research Council. 1996. Space Studies Board: Annual Report 1995. Washington, DC: The National Academies Press. doi: 10.17226/9039.
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Perhaps fittingly, in light of the difficulty of the research it supports, the EOS Data and Information System (EOSDIS) is the most complex civil data and information system yet conceived (Dutton, 1989). The task before NASA is not one of preparing a system specification, hiring the software and hardware systems specialists, and then awaiting the completion of a “turnkey” system, although there are elements of each of these. Instead, the task involves major, continuing research efforts as well. While some overall structures can be beneficially proposed and followed, the CES believes that development must proceed incrementally and must allow for frequent adjustments in direction as lessons are learned.

Data systems have been a perennial problem for the space and earth sciences for the entire history of the space program (see, e.g., Zygielbaum, 1993). The CES’s choice to limit this historical review to the period beginning in the early 1980s neglects much of that history. The lessons learned have often been painful ones, with the early Landsat experience being particularly noteworthy. As a result, the NRC has written numerous reports and critiques of information systems (see, e.g., SSB, 1982, 1985, 1986, 1988a,b; CODMAC, 1982, 1986, 1988; NRC, 1990; and many others). Most recently, the NRC was asked to form a panel specifically to review the plans for EOSDIS. It was chaired by Charles Zraket, and its report called for a major revision of EOSDIS (NRC, 1994). The CES concurs with the Zraket panel’s recommendations. In brief, the recommendations call for a user-driven design that is logically distributed and based on an open and fully extensible architecture. Those recommendations have been accepted by NASA.

ASSOCIATED ACTIVITIES

There are a number of topics that do not fit neatly into the above categories. They include magnetic and gravitational field measurements, the use of the Global Positioning System (GPS), the importance of coordinated in situ measurements, and the role of the research and analysis (R&A) line in the NASA budget.

Over the long term, an enhanced measurement of the Earth’s magnetic and gravitational fields will be a vital ingredient in global change research and operational applications. The history of the measurement of these fields by satellite is populated by more failed proposals than successful missions. The current USGCRP largely neglects the solid earth and its associated fields.

The advances being made in the application of the GPS may offer a lower-cost way to achieve important earth science and applications objectives. These include applications in many areas of the earth sciences. The NRC has considered some of these applications in analyzing GPS enhancements (ASEB, 1995).

No space-based system is entirely self-sufficient; all rely on in situ measurements, and all rely on advanced R&A for the interpretation of the results of space-derived data. Support for in situ measurements and experimental campaigns is widely dispersed in the government. The CES believes that it is vital that in situ measurements and campaigns be closely coordinated with the deployment of space-based systems, and that each is less effective if technical or budget problems thwart their parallel deployment where necessary. For example, intended support from the NASA Scatterometer (NSCAT) to investigations of the El Niño was precluded when NSCAT’s launch was delayed until after the period of deployment of the in situ sensors.

The NASA budget contains a category termed R&A. R&A has customarily supplied funds for enhancing fundamental understanding in a discipline and stimulating the questions from which new scientific investigations flow. R&A studies also enable conversion of raw instrument data into fields of geophysical variables and are an essential component in support of the research required to convert data analyses to trends, processes, and improvements in simulation models. They are likewise necessary for improving calibrations and evaluating the limits of both remote and in situ data. Without adequate R&A, the large and complex task of acquiring, processing, and archiving geophysical data would go for naught. Finally, the next generation of earth scientists, the graduate students in universities, are often educated by performing research that has originated in R&A efforts.

THE ORGANIZATION OF CIVIL EARTH OBSERVATIONS PROGRAMS

As noted above, the United States is funding a variety of experimental and operational earth observations programs. They include EOS, Earth Probes, NOAA’s polar-orbiting and geostationary operational satellites, Landsat, and the DMSP. Of these, only the NOAA and DMSP polar orbiters are currently planned to be merged, although Vice President Gore’s National Performance Review recommended the further merger with the NASA

Suggested Citation:"3 Summaries of Major Reports." National Research Council. 1996. Space Studies Board: Annual Report 1995. Washington, DC: The National Academies Press. doi: 10.17226/9039.
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MTPE satellites as well (Gore, 1993). At present, systems engineering practices are not being applied to the total U.S. satellite constellation. Overlapping functions suggest that economies of scale may be found in mergers of several or all of these systems. In addition, the oversight of both the earth sciences and operational applications support provided by these systems is fragmented. A full spectrum of options exists for reducing this fragmentation, ranging from maintaining the status quo (no improvement) to forming a single entity to oversee all civil earth observations.

International collaborations are an important part of both NASA and NO A A programs. In the area of international telecommunications, similar interdependencies led to the formation first of Intelsat and then of Inmarsat. Were the United States to take the step of creating a designated entity for civil earth observations, it might prompt other nations to do the same and possibly lead to a sharing of responsibilities analogous to that in the telecommunications industry. While there seems little prospect of near-term movement in this direction, it nevertheless seems unlikely that nations will permanently accept the high costs of orbiting national systems, when the same data could be gained from shared systems at lower cost.

REFERENCES

Aeronautics and Space Engineering Board (ASEB), National Research Council. 1994. Technology for Small Spacecraft, National Academy Press, Washington, D.C.

Aeronautics and Space Engineering Board (ASEB), National Research Council. 1995. The Global Positioning System: A Shared National Asset, National Academy Press, Washington, D.C.

Augustine, Norman (Chair). 1990. Report of Advisory Committee on the Future of the U.S. Space Program, U.S. Government Printing Office, Washington, D.C.


Board on Atmospheric Sciences and Climate (BASC), National Research Council. 1991. Four-Dimensional Model Assimilation of Data: A Strategy for the Earth System Sciences, Panel on Model-Assimilated Data Sets for Atmospheric and Oceanic Research, National Academy Press, Washington, D.C.

British National Space Centre (BNSC). 1992. The Relevance of Satellite Missions to the Study of the Global Environment, report for the United Nations Conference on Economic Development, Rio de Janeiro, Committee on Earth Observations Satellites (CEOS).


Committee on Data Management and Computation (CODMAC), National Research Council. 1982. Data Management and Computation, Volume 1: Issues and Recommendations, National Academy Press, Washington, D.C.

Committee on Data Management and Computation (CODMAC), National Research Council. 1986. Issues and Recommendations Associated with Distributed Computation and Data Management Systems for the Space Sciences, National Academy Press, Washington, D.C.

Committee on Data Management and Computation (CODMAC), National Research Council. 1988. Selected Issues in Space Science Data Management and Computation, National Academy Press, Washington, D.C.

Committee on Global Change (CGC), National Research Council. 1986. Global Change in the Geosphere-Biosphere: Initial Priorities for an IGBP, U.S. Committee for an International Geosphere-Biosphere Program, National Academy Press, Washington, D.C.

Committee on Global Change (CGC), National Research Council. 1988. Toward an Understanding of Global Change: Initial Priorities for U.S. Contributions to the International Geosphere-Biosphere Program, U.S. National Committee for the IGBP, National Academy Press, Washington, D.C.

Committee on Global Change (CGC), National Research Council. 1990. Research Strategies for the U.S. Global Change Research Program, National Academy Press, Washington, D.C.


Dutton, John. 1989. “The Eos Data and Information System: Concepts for Design,” IEEE Trans. Geosci. Remote Sensing, vol. 27, no. 2, pp. 109–116.


Gore, Al. 1993. Creating a Government That Works Better and Costs Less, Report of the National Performance Review, Times Books, New York.


Jet Propulsion Laboratory (JPL). 1982. Global Change: Impacts on Habitability, a Scientific Basis for Assessment, a report by the Executive Committee of a workshop held at Woods Hole, Mass., June 21–26, 1982, submitted on behalf of the Executive Committee on July 7, 1982, by Richard Goody (Chair).


Lorenz, E.N. 1975. “Climate Predictability,” in The Physical Basis of Climate and Climate Modelling, World Meteorological Organization, Geneva, Switzerland, GARP, vol. 16, pp. 132–136.


National Aeronautics and Space Administration (NASA). 1986. Earth System Science, Overview, a Program for Global Change, report of the Earth System Science Committee (Francis Bretherton, Chair), NASA Advisory Council.

National Aeronautics and Space Administration (NASA). 1988. Earth System Science: A Closer View, report of the Earth System Science Committee (Francis Bretherton, Chair), NASA Advisory Council.

Suggested Citation:"3 Summaries of Major Reports." National Research Council. 1996. Space Studies Board: Annual Report 1995. Washington, DC: The National Academies Press. doi: 10.17226/9039.
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National Research Council (NRC). 1983. Toward an International Geosphere-Biosphere Program: A Study of Global Change, report of a National Research Council workshop held at Woods Hole, Mass., July 25–29, 1983, Herbert Friedman (Chair).

National Research Council (NRC). 1990. The U.S. Global Change Research Program: An Assessment of FY 1991 Plans, National Academy Press, Washington, D.C.

National Research Council (NRC). 1994. Panel to Review EOSDIS Plans: Final Report, National Academy Press, Washington, D.C.


Peixoto, J.P., and A.H.Oort. 1992. Physics of Climate, American Institute of Physics, New York.


Space Applications Board (SAB), National Research Council. 1985. Remote Sensing of the Earth from Space: A Program in Crisis, Committee on Practical Applications of Remote Sensing from Space, National Academy Press, Washington, D.C.

Space Science Board (SSB), National Research Council. 1982. A Strategy for Earth Science from Space in the 1980’s, Part I: Solid Earth and Oceans, Committee on Earth Sciences, National Academy Press, Washington, D.C.

Space Science Board (SSB), National Research Council. 1985. A Strategy for Earth Science from Space in the 1980’s and 1990’s, Part II: Atmosphere and Interactions with the Solid Earth, Oceans, and Biota, Committee on Earth Sciences, National Academy Press, Washington, D.C.

Space Science Board (SSB), National Research Council. 1986. Remote Sensing of the Biosphere, Committee on Planetary Biology, National Academy Press, Washington, D.C.

Space Science Board (SSB), National Research Council. 1988a. Space Science in the Twenty-First Century, Imperatives for the Decades 1995 to 2015, Mission to Planet Earth, Task Group on Earth Sciences, National Academy Press, Washington, D.C.

Space Science Board (SSB), National Research Council. 1988b. Strategy for Earth Explorers in Global Earth Sciences, Committee on Earth Sciences, National Academy Press, Washington, D.C.

Space Studies Board (SSB), National Research Council. 1991. Assessment of Satellite Earth Observation Programs—1991, Committee on Earth Studies, National Academy Press, Washington, D.C.


Unninayar, Sushel, and Kenneth H.Bergman. 1993. Modeling the Earth System in the Mission to Planet Earth Era, review of presentations at the NASA Climate Modeling Workshop, November 13–15, 1991, Alexandria, Va., NASA, July.


Zygielbaum, Arthur (editor). 1993. Earth and Space Science Information Systems, American Institute of Physics Conference Proceedings 283, AIP, New York.

Suggested Citation:"3 Summaries of Major Reports." National Research Council. 1996. Space Studies Board: Annual Report 1995. Washington, DC: The National Academies Press. doi: 10.17226/9039.
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3.5 A Scientific Assessment of a New Technology Orbital Telescope

A Report of the Task Group on BMDO New Technology Orbital Observatory1

EXECUTIVE SUMMARY

The end of the Cold War and a decline in the fortunes for space research have gone hand in hand. If the space sciences are to continue advancing and not slip into a decline matching their dwindling budgets, new and innovative ways will have to be found to perform space missions. This is particularly true for space astronomy, given that certain features of spacecraft design (e.g., telescope apertures and detector sizes) are constrained by the laws of physics and cannot be miniaturized and still carry out their scientific tasks.

Not all of the events of recent years have been detrimental for space science. The decline in superpower rivalries has opened new avenues for international cooperation. Similarly, once-secret military technology has become available for civilian applications. Indeed, declining defense and space budgets have given rise to hybrid projects with both military and scientific goals. Prime among these was the recent Clementine lunar orbiter. This report assesses another such project, a large space telescope. In addition to demonstrating technology of interest to the Department of Defense (DOD), this mission has significant scientific capabilities, both in enabling direct astronomical observations and in demonstrating technology that may drastically alter the cost/performance ratio of future NASA missions.

At the height of the Cold War, the DOD’s Strategic Defense Initiative Organization (SDIO) actively sponsored development of the technology needed to make space-based laser weapons feasible. As part of this program, SDIO developed many components of an agile, ultra-lightweight, 4-meter space telescope, equipped with an advanced active-optics system. Budgetary shortfalls and program redirection led to the cancellation of any tests of laser weapons in space. However, many components of the system had other applications of interest to both the DOD and the scientific community, and so development of the space-based telescope continued under the so-called Advanced Technology Demonstrator (ATD) program of SDIO’s successor, the Ballistic Missile Defense Organization (BMDO).

To assist in the evaluation of the ATD’s scientific potential, BMDO asked the Space Studies Board to provide advice on instrumentation, data management, and science operations to optimize the scientific value of a 4-meter mission. Following the initiation of the study by the Task Group on BMDO New Technology Orbital Observatory, however, a combination of budgetary pressures and redirected defense priorities forced BMDO to defer the ATD mission. Nevertheless, BMDO reaffirmed that “planning advice and recommendations [about the scientific aspects of the 4-meter mission] would still be valuable in formulating future joint experiments should this program or a similar one be funded in a subsequent Defense Plan.”2

Despite the uncertain future of a flight-test of the 4-meter telescope and the currently unknown national security goals of such a mission, the task group proceeded to analyze the astronomical potential of the deferred mission. Given the potential scientific aspects of the 4-meter telescope, this project is referred to as the New Technology Orbital Telescope (NTOT), or as the ATD/NTOT, to emphasize its dual-use character. The task group emphasizes that it was specifically charged to assess the astronomical capability of the ATD/NTOT and therefore included only people with competence for that specific assessment.

The ATD/NTOT mission was conceived as a low-cost demonstration of technology, intended for use in future national security spacecraft, but having implications for astronomy. As such it is:

  • Designed to cost (~$350 million, including launch);

  • Uses existing technology and/or designs wherever possible;

  • Has a 3-year development schedule and a nominal orbital lifetime of 1 year; and

  • Is not driven by specific astronomical requirements.

1  

“Executive Summary” reprinted from A Scientific Assessment of a New Technology Orbital Telescope, National Academy Press, Washington, D.C., 1995, pp. 1–6.

2  

Payton, Gary E., Deputy for Technology Readiness, BMDO, memorandum to the Space Studies Board, October 24, 1994.

Suggested Citation:"3 Summaries of Major Reports." National Research Council. 1996. Space Studies Board: Annual Report 1995. Washington, DC: The National Academies Press. doi: 10.17226/9039.
×

Given these characteristics, the task group adopted the basic philosophy that any potential involvement of the astronomical community in the ATD/NTOT should, at least initially, be predicated on the assumption that the ATD/ NTOT is primarily a test of new technology for astronomy and is not a mission driven by any particular astronomical requirements. In this light, the ATD/NTOT’s greatest benefit to the astronomical community will be to show whether or not it is possible to break the Hubble paradigm—that is, to demonstrate that it is possible to obtain large space optics at low cost. While doing this, it could carry out major astronomical studies not possible with the HST even with its currently planned improvements in instrumentation.

The basic features of the ATD/NTOT are the following:

  • A 4-meter-aperture, 17-mm-thick, primary mirror equipped with some 260 actuators for on-orbit refiguring;

  • Afocal optics with an image-stabilization mirror located at an image of the entrance pupil to adjust the pointing anywhere within a ±5.7-arc-minute region without moving the spacecraft;

  • Graphite polycyanate (graphite epoxy) structures for the entire telescope assembly;

  • Use of an on-board inertial reference to maintain pointing stability over a bandwidth from 1 to 300 Hz;

  • The ability to track stars, as faint as 19th magnitude, through the full aperture of the telescope to maintain pointing stability against disturbances at frequencies of less than about 10 Hz;

  • A design optimized for agility and rapid slewing from one part of the sky to another; and

  • A highly eccentric orbit with a 12-hour period allowing continuous viewing of targets over much of the sky for periods up to about 8 hours.

Estimates of the performance of the ATD/NTOT suggest that it approaches the diffraction limit at near-infrared wavelengths. In the optical, its full width at half maximum (FWHM) is better than that for any current or planned facility, while the diameter for 50% encircled energy is comparable to the HST’s. The reason for this is the relative roughness of the primary mirror. In fact, the primary mirror dominates all other sources of wavefront errors in the ATD/NTOT’s error budget. This suggests an obvious enhancement: improving the figure of the primary mirror by a factor of two so that its contribution to the telescope-level error budget is comparable to that of the other components. Not only could this improvement be achieved at relatively low cost, but it would also have a dramatic impact on the ability of the ATD/NTOT to do both the technology demonstrations and the observing projects outlined in this report.

The baseline instrument package for the ATD/NTOT consists of a variety of optical- and infrared-array detectors. The one of most interest is a 1024×1024 indium antimonide (InSb) infrared array that would have state-of-the-art astronomical capabilities if operated at a cold enough temperature. The two passive, visible, fine-tracking arrays would have some astronomical applications. These would, however, be limited because their charge-coupled devices (CCDs) are line-transfer devices, and the arrays and their amplifiers are not optimized for low readout noise. The obvious deficiency in the instrument package is the absence of an optical framing camera of astronomical quality. The addition of such an instrument would have a very significant impact on the astronomical capabilities of the ATD/NTOT.

Understanding the areas in which the ATD/NTOT might have significant advantages over existing and planned facilities is critical to deciding which scientific projects and technological demonstrations to emphasize. To do this the task group considered two aspects of the ATD/NTOT: its optical and near-infrared performance, and the operational modes in which it can be used most cost effectively. Consideration of performance factors led to the conclusion that the ATD/NTOT has major advantages:

  • In the near infrared (2 to 4 microns), where the sky background is reduced by several orders of magnitude;

  • In the far red (>0.7 micron), where the sky background is reduced by one order of magnitude;

  • For programs that depend on high contrast between a point source and its neighborhood, or those that require subarc-second spatial resolution; and

  • For programs that are photon-starved, that is, receive little attention with the HST.

Consideration of operational factors led to the conclusion that the ATD/NTOT is best suited to large surveys because repeated use of the telescope in a single mode, by a small team of scientists, is the most cost-effective operating procedure. In addition, large surveys make less than optimum use of complex, multiuser facilities such as the HST.

Suggested Citation:"3 Summaries of Major Reports." National Research Council. 1996. Space Studies Board: Annual Report 1995. Washington, DC: The National Academies Press. doi: 10.17226/9039.
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In determining what scientific and technological projects the ATD/NTOT is most suited to perform, the task group’s overriding priority has been to minimize cost while still ensuring the capability to do exciting science. The first astronomical goal of an ATD/NTOT flight should be to test the applicability of its technology for use in future space science missions. Prime among these tests are (in no particular order):

  • Demonstration by actual astronomical application of the ability to adequately refigure a large mirror in orbit to obtain astronomical-quality images, both with and without ground-based intervention;

  • Evaluation of image quality and its consistency both across the field of view as the fast-steering mirror stabilizes the telescope’s line of sight and in a variety of thermal environments;

  • Characterization of the likely degree of passive cooling by establishing the thermal emission from the optical and other components of the system in both the initial low Earth orbit and the eventual highly elliptical (or Molniya) orbit;

  • Investigation of the stability of field distortions, particularly as the figure of the primary mirror responds to its control actuators and, also, as the fast-steering mirror stabilizes the telescope’s line of sight;

  • Exploitation of the ATD/NTOT’s agility and large fuel reserves to actively maneuver the spacecraft so that it is in the right place, at the right time, to observe ephemeral events such as occupations;

  • Exploration of the possibilities presented by the Molniya orbit to conduct very long integrations in a cost-effective manner; and

  • Utilization of the facility as an experimental testbed for various modes of ground operations that may be needed for future space science missions.

The implementation of some of the task group’s suggested enhancements to the baseline ATD/NTOT would significantly improve the evaluation of both the technology and the astronomical significance of a program of technology demonstrations. Two of the most important enhancements are enhancing the figure of the primary mirror and adding an optical framing camera. These improvements would allow far more rigorous tests of, for example, the image quality that can be realized with the ATD/NTOT technology. Addition of just the optical framing camera would permit studies of the system’s photometric stability. Also of great importance is enhancing the cooling of the InSb array, since this would allow a better evaluation of the ATD/NTOT’s infrared performance.

If the ATD/NTOT’s technology passes its key tests and can exceed its 1-year design lifetime, then it will have a significant capability for astronomical research. An area in which the ATD/NTOT should excel is in studies of origins. The creation and evolution of the universe and its component galaxies, stars, and planets is a topic of great scientific and popular interest and one in which large-scale surveys play major roles. To highlight the ATD/ NTOT’s potential in these areas, the task group discusses four possible observing programs:

  • A series of deep surveys of the early universe at near infrared wavelengths to study the evolution of galaxies, define the magnitude/number-count relation, and search for new “standard candles” at intermediate redshifts. All of these projects are consistent with the baseline mission but would benefit significantly from the addition of an optical framing camera and enhancement of the primary mirror.

  • A survey of the outer solar system to define the size- and radial-distributions of the primitive bodies constituting the Kuiper Disk (down to ~1 km bodies at ~40 AU). This project requires an optical framing camera and would benefit significantly from the use of an enhanced primary mirror.

  • High-resolution optical studies of the disks, jets, and winds associated with young stellar objects during the embedded, accretion-dominated, and post-accretion phases of their evolution. The success of this project depends critically on enhancement of the primary mirror and the addition of an optical framing camera.

  • Synoptic occultation observations of Pluto and Triton to monitor global atmospheric variations due to seasonal variations in insolation. Although compatible with the baseline mission, this project may be expensive in terms of operations and use of spacecraft resources because it would involve extensive spacecraft maneuvering and orbital changes.

In the course of the task group’s deliberations, a number of items arose that raise questions about the astronomical utility of the ATD/NTOT. In particular:

Suggested Citation:"3 Summaries of Major Reports." National Research Council. 1996. Space Studies Board: Annual Report 1995. Washington, DC: The National Academies Press. doi: 10.17226/9039.
×
  • Little or no systems analysis has been performed to verify that the ATD/NTOT’s individual components can be combined to form a working astronomical telescope.

  • There is some doubt about the ability of the baseline ATD/NTOT to track guide stars as faint as would be needed for certain observations. Although there are solutions to this problem, the problem may be moot if the telescope is devoted to surveys.

  • Aspects of the ATD/NTOT’s design, particularly that of the tripod supporting the secondary mirror, may scatter stray light into the focal plane.

  • The rate at which the figure of the primary mirror will need correction as it deforms due to thermal and other drivers, and the impact corrections may have on observing overhead, are not clear.

  • Software problems of the type that ultimately doomed the Clementine mission must be avoided.

  • The effect of cosmic-ray events on the ATD/NTOT’s imaging arrays when the spacecraft is operating in the highly eccentric Molniya orbit is a significant factor.

  • Although building to cost is becoming a key feature of NASA’s present and future missions, neither NASA nor the space science community has much experience with this mode of operation.

While the resolution of these issues is beyond the scope of this study, they must nevertheless be resolved as the ATD/NTOT mission is further defined.

The task group’s analysis shows that the ATD/NTOT mission uses advanced technology that has important potential applications for future space astronomy missions. Furthermore, its advertised cost-effectiveness is crucial to NASA’s ability to carry out significant space astronomy missions in an era of tightly constrained budgets. Both of these factors have not escaped the notice of other groups. Thus, both the High-Z and Polar Stratospheric Telescope concepts draw heavily on the capabilities of the ATD/NTOT’s technology. The task group’s basic conclusion is that the ATD/NTOT mission does have the potential for contributing in a major way to astronomical goals. It is equally clear that if the ATD/NTOT performs as advertised, it could undertake astronomical observations that could not be matched by any other facility now in existence or under development. Thus the task group’s first and foremost recommendation is as follows:

  1. To optimize the return to astronomy from the ATD/NTOT, the astronomical community should be directly involved in the continued study and development of this mission, including system engineering and complete mission analysis. These community representatives should be selected by NASA, and their role should be to advise NASA on the continuing value of this mission for astronomy. The group should include not only astronomers proposing specific observing programs, but also individuals with particular expertise in the design of large telescopes and space missions.

Since any scientific applications of the ATD/NTOT are a bonus, the task group further recommends the following:

  1. If the ATD/NTOT mission flies, a suite of tests of the suitability of its technology for astronomical applications should be carried out. Some of these tests can be conducted concurrently with DOD’s demonstration mission, but others require an astronomical phase of the mission.

  2. Although scientific goals must be kept in mind and accommodated insofar as possible during the planning of the ATD/NTOT mission, these goals should not impose requirements that would have a major impact on development or operations costs.

  3. The ATD/NTOT’s astronomical promise is sufficient, even at this preliminary stage, that it is appropriate to plan for a mission phase devoted to astronomical observations. The resources devoted to planning an astronomical mission should be kept to a minimum until such time as the ATD/NTOT’s scientific and technological capabilities are better defined.

A mission phase dedicated to astronomical observations, while highly desirable, could be extremely expensive if not managed appropriately. Given the philosophy of designing to cost, the development costs for astronomical

Suggested Citation:"3 Summaries of Major Reports." National Research Council. 1996. Space Studies Board: Annual Report 1995. Washington, DC: The National Academies Press. doi: 10.17226/9039.
×

research programs must be kept to an absolute minimum. In order to minimize operational costs, the task group recommends the following:

  1. The astronomical phase of the ATD/NTOT mission should be carried out by a principal investigator and a science team, with rotating membership to accommodate a range of scientific expertise. No provision should be made for a traditional guest observer program.

  2. An extended ATD/NTOT mission should concentrate on extensive surveys that repeatedly use the ATD/ NTOT in a single mode.

  3. Astronomical data collected in the ATD/NTOT mission should be delivered promptly to an existing public archive that is independent of and expected to outlive the mission.

Because DOD sponsorship of the ATD/NTOT is uncertain, the mission’s exact specifications are unclear. The task group has assumed a baseline performance predicated on the requirements necessary to perform the mission that BMDO has now deferred. This analysis revealed several areas in which enhancements beyond the baseline specifications would have a significant impact on the ATD/NTOT’s astronomical capabilities. Some of these enhancements may ultimately be required by, or at least be consistent with, a DOD mission if and when it is finally defined. Although the task group has not evaluated the cost-effectiveness of all of these enhancements (something that must be done during the system engineering phases of the mission), it has discussed their potential impact with representatives of Lockheed and Itek. In one case the costs are well defined and the performance benefits reasonably determined. In other cases, neither the costs nor the actual improvements in performance are very well determined. It is, however, the sense of this task group that these enhancements are likely to be very cost-effective and important for the astronomical aspects of the mission. In particular:

  1. The figure of the ATD/NTOT’s primary mirror should be improved by roughly a factor of two to reduce its surface error to ~17 nm, and, thus, the total system’s wavefront error to roughly 50 nm rms. Itek estimates that this enhancement would cost ~$100,000.

  2. A large-format, framing, optical CCD of astronomical quality should be included in the ATD/NTOT’s focal-plane package. A less expensive but clearly less desirable option would be to replace the baseline line-transfer CCDs in the fine-tracking sensors with frame-transfer CCDs.

  3. The ATD/NTOT’s baseline infrared detector, an InSb array, should be optimized for sensitivity by, for example, additional cooling and by minimizing the number of emitting surfaces in the optical path.

The task group briefly discussed other enhancements that could significantly improve the scientific return from an extended mission dedicated to astronomical observations. Unlike those discussed above, however, all of these modifications would add significantly to the cost of the mission and/or perhaps be incompatible with the national security objectives of the mission. These enhancements include:

  • Modifying the ATD/NTOT’s orbit to minimize and/or stabilize the thermal load on the spacecraft;

  • Optimizing the design to enhance the passive-cooling characteristics of the telescope and focal-plane instruments; and

  • Adding additional instruments (e.g., a dedicated infrared focal plane) for scientific research.

Even if the ATD/NTOT mission is not eventually funded by BMDO and does not find another sponsor in the national security community, the task group believes that the time devoted to this study has been of use. While the complete package of technologies embodied in the ATD/NTOT proposal promises exciting advances in astronomical capabilities, it should be remembered also that much of its hardware already exists. A complete adaptive-optics system and examples of thin primary mirrors, for instance, currently sit gathering dust in testing chambers. Many of these subsystems are themselves interesting additions to the tools at the disposal of astronomers and may find scientific applications very different from those for which they were designed. The ATD/NTOT may never fly, but if this report does nothing more than illuminate some of the capabilities lurking in the shadows of the Cold War, it will have achieved something worthwhile.

Suggested Citation:"3 Summaries of Major Reports." National Research Council. 1996. Space Studies Board: Annual Report 1995. Washington, DC: The National Academies Press. doi: 10.17226/9039.
×

3.6 Managing the Space Sciences

A Report of the Committee on the Future of Space Science1

EXECUTIVE SUMMARY

In April 1994 the National Research Council received a request from NASA Administrator Daniel S.Goldin that the NRC’s Space Studies Board provide guidance on several questions relating to the management of NASA’s programs in the space sciences.2 The issues raised in the Administrator’s request closely reflect questions posed in the agency’s fiscal year 1994 Senate appropriations report. These questions included the following:

  • Should all the NASA space science programs be gathered into a “National Institute for Space Science”?

  • What other organizational changes might be made to improve the coordination and oversight of NASA space science programs?

  • What processes should be used for establishing interdisciplinary science priorities based on scientific merit and other criteria, while ensuring opportunities for newer fields and disciplines to emerge?

  • What steps could be taken to improve utilization of advanced technologies in future science missions?

Since the creation of NASA in 1958, space science has been a key element of its mission. Indeed, the Augustine Committee report,3 submitted at the end of 1990, asserted that science was NASA’s most important mission. The committee responsible for the present report has proceeded on the same premise. A balanced and healthy program of space science is crucial to the future of NASA, regardless of the overall level of support available to the agency.

The most important recommendations of this report are listed below. They are further elaborated following the list.

  • NASA should not establish a “National Institute for Space Science” that would pull together the three present science program offices.

  • NASA should augment the responsibilities and authorities of the NASA Chief Scientist.

  • NASA should establish a set of fair, open, and understandable processes to be used in the prioritization of space science research. These processes will ensure that major project proposals considered at progressively higher levels within the agency have the heritage of scientific merit that comes from a successful confrontation with competing proposals at lower levels.

  • NASA should create a comprehensive strategy and plan for the technologies that support the space sciences, with the responsibility for near-term technology development residing in the science programs to be served and the responsibility for longer-term technology strategy and development residing in the Office of Space Access and Technology.

  • NASA should change the funding of its field centers to full-cost accounting (“industrial funding”). Cost accounting should be based on full program costs, including civil service salaries. The committee endorses NASA’s intentions to move in this direction.

  • NASA should exercise caution in downsizing its Headquarters staff and transferring functions to the centers; this process could be carried too far and have unintended consequences. The committee identified a number of areas where it believes control should be retained at Headquarters.

  • NASA science budgets should include a limited amount of dedicated funding for innovative ideas in high-risk, high-return areas lying outside the current framework of inquiry or design.

  • NASA should take a cautious approach to the recently proposed establishment of focused science institutes. There should be a well-defined process for their selection and creation, and a clear plan for the phased transfer of base funds to programmatic funding.

1  

“Executive Summary” reprinted from Managing the Space Sciences, National Academy Press, Washington, D.C., 1995, pp. 1–4.

2  

In this report, “space sciences” refers to all of NASA’s science programs conducted in or from space, including space astronomy, space physics, planetary exploration, microgravity research, space life sciences, and Earth science.

3  

Advisory Committee on the Future of the U.S. Space Program, Report of the Advisory Committee on the Future of the U.S. Space Program, December 1990.

Suggested Citation:"3 Summaries of Major Reports." National Research Council. 1996. Space Studies Board: Annual Report 1995. Washington, DC: The National Academies Press. doi: 10.17226/9039.
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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

Suggested Citation:"3 Summaries of Major Reports." National Research Council. 1996. Space Studies Board: Annual Report 1995. Washington, DC: The National Academies Press. doi: 10.17226/9039.
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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.

Suggested Citation:"3 Summaries of Major Reports." National Research Council. 1996. Space Studies Board: Annual Report 1995. Washington, DC: The National Academies Press. doi: 10.17226/9039.
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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.

Suggested Citation:"3 Summaries of Major Reports." National Research Council. 1996. Space Studies Board: Annual Report 1995. Washington, DC: The National Academies Press. doi: 10.17226/9039.
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  1. 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;

  2. 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;

  3. 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

  4. 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:

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. Past NASA practices must change in order to foster the development of a streamlined approach to management of each complete mission.

  7. 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.

  8. 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.

  9. 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.

Suggested Citation:"3 Summaries of Major Reports." National Research Council. 1996. Space Studies Board: Annual Report 1995. Washington, DC: The National Academies Press. doi: 10.17226/9039.
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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.

Suggested Citation:"3 Summaries of Major Reports." National Research Council. 1996. Space Studies Board: Annual Report 1995. Washington, DC: The National Academies Press. doi: 10.17226/9039.
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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.

Suggested Citation:"3 Summaries of Major Reports." National Research Council. 1996. Space Studies Board: Annual Report 1995. Washington, DC: The National Academies Press. doi: 10.17226/9039.
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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.

Suggested Citation:"3 Summaries of Major Reports." National Research Council. 1996. Space Studies Board: Annual Report 1995. Washington, DC: The National Academies Press. doi: 10.17226/9039.
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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:

Suggested Citation:"3 Summaries of Major Reports." National Research Council. 1996. Space Studies Board: Annual Report 1995. Washington, DC: The National Academies Press. doi: 10.17226/9039.
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  • 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.

Suggested Citation:"3 Summaries of Major Reports." National Research Council. 1996. Space Studies Board: Annual Report 1995. Washington, DC: The National Academies Press. doi: 10.17226/9039.
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  • 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:

Suggested Citation:"3 Summaries of Major Reports." National Research Council. 1996. Space Studies Board: Annual Report 1995. Washington, DC: The National Academies Press. doi: 10.17226/9039.
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  • 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.

Suggested Citation:"3 Summaries of Major Reports." National Research Council. 1996. Space Studies Board: Annual Report 1995. Washington, DC: The National Academies Press. doi: 10.17226/9039.
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