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Space Studies Board: Annual Report 1999 3 Summaries of Major Reports 3.1 A Scientific Rationale for Mobility in Planetary Environments A Report of the Committee on Planetary and Lunar Exploration 1 EXECUTIVE SUMMARY For the last several decades, the Committee on Planetary and Lunar Exploration (COMPLEX) has advocated a systematic approach to the exploration of the solar system; that is, the information and understanding resulting from one mission provide the scientific foundations that motivate subsequent, more elaborate investigations. COMPLEX’s 1994, An Integrated Strategy for the Planetary Sciences: 1995-2010, 2 advocated an approach to planetary studies emphasizing “hypothesizing and comprehending” rather than “cataloging and categorizing.” More recently, NASA reports, including The Space Science Enterprise Strategic Plan 3 and, in particular, Mission to the Solar System: Exploration and Discovery—A Mission and Technology Roadmap, 4 have outlined comprehensive plans for planetary exploration during the next several decades. The missions outlined in these plans are both generally consistent with the priorities outlined in the Integrated Strategy and other NRC reports, 5 , 6 and are replete with examples of devices embodying some degree of mobility in the form of rovers, robotic arms, and the like. Because the change in focus of planetary studies called for in the Integrated Strategy appears to require an evolutionary change in the technical means by which solar system exploration missions are conducted, the Space Studies Board charged COMPLEX to review the science that can be uniquely addressed by mobility in planetary environments. In particular, COMPLEX was asked to address the following questions: 1 “Executive Summary” reprinted from A Scientific Rationale for Mobility in Planetary Environments, National Academy Press, Washington, D.C., 1999, pp. 1-4. 2 Space Studies Board, National Research Council, An Integrated Strategy for the Planetary Sciences: 1995-2010, National Academy Press, Washington, D.C., 1994, p. 25. 3 National Aeronautics and Space Administration, The Space Science Enterprise Strategic Plan: Origin, Evolution, and Destiny of the Cosmos and Life, National Aeronautics and Space Administration, Washington, D.C., 1997. 4 Roadmap Development Team, National Aeronautics and Space Administration, Mission to the Solar System: Exploration and Discovery. A Mission and Technology Roadmap, Version B, Jet Propulsion Laboratory, Pasadena, Calif., 1996. 5 Space Studies Board, National Research Council, “Scientific Assessment of NASA’s Solar System Exploration Roadmap,” letter report to Jurgen Rahe, NASA, August 23, 1996. 6 Space Studies Board, National Research Council, letter report to Wesley T. Huntress, Jr., NASA, concerning the draft Office of Space Science strategic plan, August 27, 1997.
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Space Studies Board: Annual Report 1999 What are the practical methods for achieving mobility? For surface missions, what are the associated needs for sample acquisition? What is the state of technology for planetary mobility in the United States and elsewhere, and what are the key requirements for technology development? What terrestrial field demonstrations are required prior to spaceflight missions? APPROACH Mobility may be achieved by a variety of techniques, including balloons, aircraft, rovers, and hoppers. In addition, the concept of mobility can be thought to encompass devices for instrument positioning, digging, drilling, and sample manipulation. Indeed, the history of planetary exploration contains a number of examples of the application of mobility. Conventional flybys and orbiters, together with entry probes, are explicitly excluded from consideration in this study because these mission modes have already been discussed extensively. Given that COMPLEX’s expertise is in the planetary sciences rather than engineering or robotics, and that the primary reason for employing mobility is to enhance the return of valuable scientific data, this report is focused on scientific rather than technological issues. COMPLEX therefore restricted its attention to six case studies, representative of the goals, environments, disciplines, and technologies drawn from previous COMPLEX and NASA reports: What is the nature of the circulation in the lower atmosphere on Venus? What tectonic processes are responsible for the structural and topographic features present on Venus? Is there evidence for extinct or extant life on Mars? What is the physical and chemical heterogeneity within small bodies such as asteroid 4 Vesta? What drives the zonal winds in the jovian atmosphere? What is the internal structure of Europa? These six case studies are discussed in Chapter 2 . CONCLUSIONS AND RECOMMENDATIONS The most important conclusion from this study is that mobility is not just important for solar system exploration—it is essential. Many of the most significant and exciting goals spelled out in numerous NASA and National Research Council documents cannot be met without mobile platforms of some type. A second conclusion is that the diversity of planetary environments that must be explored to address priority scientific questions requires more than one type of mobile platform. Thus, the simultaneous development of some combination of wheeled rovers, aerobots, aircraft, touch-and-go orbiters, and cryobots is not only justified but is also necessary, as long as there is a scientific justification for the development of each mobile platform. Technology development funds are likely to be scarce and so should be allocated only after a vigorous peer review of the proposed mobility device’s technical feasibility and the scientific applications for which it will be used. Technology development activities should be undertaken by the best-qualified individuals and teams within NASA, industry, and academia, as determined by peer review. With some exceptions, the current technical development efforts are appropriate and well focused. However, it is instructive to compare the tenor of recommendations in science-oriented presentations and of science-centered working groups with the thrust of technical development efforts. The science sources emphasize the need for very capable mobile platforms with these characteristics: Synergy of instruments, that is, a suite of mutually complementary instruments rather than either a small number of instruments or many instruments that are independently conceived and developed; Extensive range and long lifetime; and One or more manipulative devices, such as claws, drills, and the like, some of which are likely to be complex and difficult to develop. These characteristics define a mobile platform that is fairly large and potentially rather complex. In contrast, the main thrusts of technical development, especially of rovers, are directed at reducing their size and increasing
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Space Studies Board: Annual Report 1999 their autonomy. These tendencies create a tension between a model-driven approach to mobility and a technology-driven approach. Reconciling these apparently contradictory priorities and minimizing their impact on the scientific productivity of mobility missions will require close cooperation between engineers and scientists. Most science objectives defined for future solar system missions call for mobile platforms, manipulative devices, and instruments with significant capabilities. Attaining this level of capability will require reducing the total mass of mobile platforms while maintaining acceptable functional capabilities. The size of a mobile platform needs to be considered as part of a systems optimization based on scientific needs and mission constraints. Although very small mobile systems, such as the micro- and nanorovers currently under development, involve a significant reduction of mass, their payload capacity may be too limited for widespread application unless particular attention is paid to the development of appropriate micro- and nano-instrumentation. Long-range mobility, whether with rovers, aerobots, or other devices, poses significant navigational challenges. This is in part due to the constraints imposed by long, two-way communication times and in part to the limited data downlink capacity available. The more time and downlink capacity are used for navigation, the less they will be available for returning scientific data. Lessons learned in the Marsokhod field tests and during the operation of Sojourner suggest that descent imagers should be included on lander and rover missions to provide critical information on the context of the landing site for use in rover navigation and science-operations planning. Navigational tools for long-range mobility should be available in as near real time as feasible. The hardware and software for intelligent autonomous operation and efficient operational planning should be actively developed. Many planned and possible future missions will require spacecraft and mobility devices to operate in hostile environments. An environment can be hostile because of the high levels of radiation (e.g., the surface of Europa), high pressure (e.g., the atmospheres of the giant planets), high temperatures (e.g., the lower atmosphere of Venus), low temperatures (e.g., the surface of Titan), and very low gravity (e.g., the surfaces of comets and asteroids). Such environments place unusual constraints on spacecraft and instruments, indicating the need for long-range advanced planning and development. These conclusions suggest two fundamental recommendations: Technological development of mobile platforms must be science driven. Available funds will never be adequate to develop all possible types and variants of platforms, and these scarce funds should not be wasted on devices of limited scientific utility no matter how technologically intriguing they may be. Thus, there should be science input into technology development from the very beginning. Mobile platforms, ancillary devices, instruments, and operational procedures must be thoroughly tested on Earth. This involves laboratory tests of instruments, field trials of individual components of space missions, and field trials of complete systems (mobile platform and instruments) and all relevant personnel (operators, design engineers, and scientists). To be fully effective, such field trials require thorough testing and calibration of instruments in the laboratory before they are mounted on a mobile platform, extensive field testing of mobile platforms both with and without instruments aboard, and full operational field testing of total systems. Proposals to conduct field tests should be peer reviewed in advance, and the test results should be promptly published in peer-reviewed journals. In addition, several more-specific recommendations derive from the six case studies: Data downlink rates must be significantly increased, perhaps through the use of new technologies, such as the ongoing efforts to upgrade the Deep Space Network to operate in the Ka band or an eventual transition to optical communications. This is a problem that is not unique to mobile platforms. A means to control aerobot motion, both vertically and horizontally, needs to be developed. The capability to obtain descent images should be included on all lander and rover missions to provide critical context for navigation and science. Navigation tools and operational plans should be developed so that the impact of navigational needs on science return can be minimized. In summary, the various disciplines interested in solar system exploration and research have many common needs for mobility, and, thus, generally need not consider themselves as competitors for payload mass. For example, a rover carrying a suite of instruments designed to carry out a predominantly exobiology mission will differ very little from one designed to carry out a geology/geochemistry mission. Likewise, an aircraft or balloon
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Space Studies Board: Annual Report 1999 mission designed to measure important atmospheric parameters at various altitudes can also collect surface spectral data important to geologists, geochemists, and exobiologists. Obviously, not all missions will satisfy all persons, but it seems clear that differences in mobile platform type and design are linked more to the target of the mission than to the interests of the scientists involved.
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Space Studies Board: Annual Report 1999 3.2 Size Limits of Very Small Microorganisms: Proceedings of a Workshop Steering Group for the Workshop on Size Limits of Very Small Microorganisms 1 OVERVIEW How small can a free-living organism be? On the surface, this question is straightforward—in principle, the smallest cells can be identified and measured. But understanding what factors determine this lower limit, and addressing the host of other questions that follow on from this knowledge, require a fundamental understanding of the chemistry and ecology of cellular life. The recent report of evidence for life in a martian meteorite and the prospect of searching for biological signatures in intelligently chosen samples from Mars and elsewhere bring a new immediacy to such questions. How do we recognize the morphological or chemical remnants of life in rocks deposited 4 billion years ago on another planet? Are the empirical limits on cell size identified by observation on Earth applicable to life wherever it may occur, or is minimum size a function of the particular chemistry of an individual planetary surface? These questions formed the focus of a workshop on the size limits of very small organisms, organized by the Steering Group for the Workshop on Size Limits of Very Small Microorganisms and held on October 22 and 23, 1998. Eighteen invited panelists, representing fields ranging from cell biology and molecular genetics to paleontology and mineralogy, joined with an almost equal number of other participants in a wide-ranging exploration of minimum cell size and the challenge of interpreting micro- and nano-scale features of sedimentary rocks found on Earth or elsewhere in the solar system. This document contains the proceedings of that workshop. It includes position papers presented by the individual panelists, arranged by panel, along with a summary, for each of the four sessions, of extensive roundtable discussions that involved the panelists as well as other workshop participants. CONSENSUS AND CAVEATS The discussions forming the basis of this document sought to address three distinct but related issues: (1) What are the theoretical, observable, and empirically testable limits on the minimum size of organisms living on Earth today? (2) What, in theory, are the size limits on organisms not constrained by the biochemistry of extant cells? and (3) How can we recognize traces of ancient and potentially unfamiliar life in samples from other bodies in the solar system? As is evident from the summaries, there was strong consensus on the first issue, but the others remain open. The six geneticists and cell biologists in Panel 1 reached consensus on the smallest size likely to be attained by organisms of modern biochemical complexity. Free-living organisms require a minimum of 250 to 450 proteins along with the genes and ribosomes necessary for their synthesis. A sphere capable of holding this minimal molecular complement would be 250 to 300 nm in diameter, 2 including its bounding membrane. Given the uncertainties inherent in this estimate, the panel agreed that 250 ± 50 nm constitutes a reasonable lower size limit for life as we know it. At this minute size, membranes have sufficient biophysical integrity to contain interior structures without the need for a cell wall, but only if the organism is spherical and has an osmotic pressure not much above that of its environment. Panel 2 consisted of microbial ecologists asked to elucidate the smallest sizes actually observed in free-living organisms. Once again, consensus emerged from the panel’s discussion. Consistent with the theoretical limits articulated by Panel 1, members of Panel 2 reported that bacteria with a diameter of 300 to 500 nm are common in oligotrophic environments, but that smaller cells are not. Nanobacteria 3 reported from human and cow blood fall 1 “Overview” reprinted from Size Limits of Very Small Microorganisms: Proceedings of a Workshop, National Academy Press, Washington, D.C., 1999, pp. 1-3. 2 Contributors to the workshop have usually described relevant scale sizes or dimensions in units of nanometers (nm) or micrometers (µm), depending on the context and the features being described. For an indication of the range of relevant scale sizes, see Figure 1 in the paper by Jack Farmer, Panel 3, p. 94. 3 While biologists have yet to agree on a precise meaning for this term, it is generally used to refer to any single-celled microorganism proposed to have a maximum diameter in the range of tens to a few hundreds of nanometers.
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Space Studies Board: Annual Report 1999 near the lower size limit suggested by cell biologists; however, the much smaller (ca. 50 nm) bodies found in association with these cells may not, themselves, be viable organisms. Observations on archaea indicate that, in general, they have size limits similar to those for bacteria. Two problems constrain discussions of minimal cell size in natural environments. Commonly used methods of measuring cell size have inherent uncertainties or possibilities of error. Perhaps more important, most cells found in nature cannot be cultivated. Thus, ignorance about biological diversity at small sizes remains large. These problems notwithstanding, it appears that very small size in modern organisms is an adaptation for specific environmental circumstances, including stress and scarcity of resources. Primordial organisms may or may not have been tiny, but the smallest organisms known today reside on relatively late branches of the RNA phylogeny. Whereas Panels 1 and 2 indicated that a cell operating by known molecular rules—with DNA or maybe RNA, ribosomes, protein catalysts, and other conventional cell machinery—would have a lower size limit of 200 to 300 nm in diameter, Panel 4 suggested that primitive microorganisms based on a single-polymer system could be as small as a sphere 50 nm in diameter. There is no assurance that primordial cells would have been this small or, if they were, that such minute cells would have been more than transitory features of early evolution. Nonetheless, unless one is willing to posit that everywhere it has arisen, life has evolved a biochemical machinery comparable to that seen on Earth, the rules that govern minimum cell size may not be universal. In fact, as explored by Panel 3, there are a number of ways that living cells or fossils might fall below the minimum size deemed likely by cell biologists and ecologists. On Mars or Europa, fossils might preserve a record of biological systems different from those we understand—perhaps early products of evolution that made do with a small complement of functional molecules. Organisms of modern biochemistry might become small by being pathogens or living in consortia—that is, by using the products of another organism’s genes. Or, fossils might preserve remains that shrank after death, or parts of organisms rather than complete cells—both are common in the terrestrial record. Of course, fossil morphologies are but one of several types of biological signature preserved in rocks. Experience with ancient terrestrial rocks shows that extractable organic molecules, minerals, fractionation in isotopic or elemental abundances, and distinctively laminated sedimentary structures can all provide indications of past life. Many of these features, however, can be mimicked by physical processes. Panel 3 concluded that a much better understanding of biological pattern formation is needed before intelligently chosen martian samples are returned to Earth. The panel also emphasized that this must go hand in hand with improved knowledge of the limits of morphological and chemical pattern formation by non-biological processes. Indigenous features of extraterrestrial samples can be accepted as biogenic only if they are incompatible with formation by physical processes. THINKING ABOUT THE FUTURE In 2008, a small (<1 kg) sample of martian rock and soil is scheduled to be delivered to Earth by a robotic spacecraft that will be launched to Mars in 2005. Among the important questions that will be asked of these samples is, Has Mars ever been a biological planet? Our ability to address this question is directly related to our understanding of the range of morphological features that can be produced by life and by physical processes, as well as the ranges of organic chemicals, mineral forms, and sedimentary rock features that can be generated by biological and by nonbiological processes. As the results of the workshop made clear, welcome consensus has emerged among the participants regarding the size and chemical limits on modern life on Earth. But, given reasonable uncertainty about whether such features are particular products of terrestrial evolution or universal features of life, the meter stick by which the biogenicity of martian or other planetary samples is measured will likely be knowledge of the limits on physical processes—knowledge that needs to be developed before samples from Mars arrive in the laboratory.
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Space Studies Board: Annual Report 1999 3.3 A Science Strategy for the Exploration of Europa A Report of the Committee on Planetary and Lunar Exploration 1 EXECUTIVE SUMMARY Since its discovery in 1610, Europa—one of Jupiter’s four large moons—has been an object of interest to astronomers and planetary scientists. Much of this interest stems from observations made by NASA’s Voyager and Galileo spacecraft and from Earth-based telescopes indicating that Europa’s surface is quite young, with very little evidence of cratering, and made principally of water ice. More recently, theoretical models of the jovian system and Europa have suggested that tidal heating may have resulted in the existence of liquid water, and perhaps an ocean, beneath Europa’s surface. NASA’s ongoing Galileo mission has profoundly expanded our understanding of Europa and the dynamics of the jovian system, and may allow us to constrain theoretical models of Europa’s subsurface structure. Meanwhile, since the time of the Voyagers, there has been a revolution in our understanding of the limits of life on Earth. Life has been detected thriving in environments previously thought to be untenable—around hydrothermal vent systems on the seafloor, deep underground in basaltic rocks, and within polar ice. Elsewhere in the solar system, including on Europa, environments thought to be compatible with life as we know it on Earth are now considered possible, or even probable. Spacecraft missions are being planned that may be capable of proving their existence. Against this background, the Space Studies Board charged its Committee on Planetary and Lunar Exploration (COMPLEX) to perform a comprehensive study to assess current knowledge about Europa, outline a strategy for future spacecraft missions to Europa, and identify opportunities for complementary Earth-based studies of Europa. CURRENT UNDERSTANDING Perhaps the most exciting aspect of Europa revealed by recent studies is the possible existence of liquid water beneath a surface covering of ice. Although no unique evidence for such an ocean exists yet, very intriguing indications have been seen from spacecraft. Europa’s reflectance characteristics indicate that its surface is almost-pure water ice. Local- and global-scale ice tectonics dominates the geology, with a very large number of cracks criss-crossing Europa’s surface. Seen at kilometer-scale resolution from the Galileo spacecraft, large “rafts” of ice appear to have broken up and moved with respect to each other; the appearance is similar to that of sea ice on Earth. Contaminants have been detected within the ice, including sulfur dioxide (SO2) frost, hydrogen peroxide (H2O2), and a variety of salts. The salts, in particular, may provide additional evidence for a global ocean, as they are easily dissolved in and transported by water. The presence of hydrogen peroxide suggests that Europa’s surface chemistry is dominated by radiolysis. Gravity measurements obtained from the tracking of Galileo indicate that Europa’s interior is differentiated. The outermost layer is predominantly water and/or water ice and is perhaps 100 km thick. Below the water exists a “rocky” interior, which also has differentiated into a dense core and a less-dense mantle; these are thought to be analogous to the iron core and silicate mantle of the terrestrial planets. Europa’s magnetic “signature” indicates the presence of a conducting layer near the satellite’s surface, most likely owing to water containing dissolved salts. Europa also has a thin atmosphere, likely composed primarily of materials ejected from its surface. To date, molecular oxygen and atomic sodium have been identified, although other species are expected to exist. These species are thought to have been emplaced into the atmosphere as a result of the collisions of highly energetic particles from the jovian magnetosphere; some of the sodium, however, may come from Io, where it is ejected by similar processes. The gases reside in an extended atmosphere until they are ionized by solar ultraviolet light or magnetospheric electrons and picked up by Jupiter’s magnetic field. As a result of the likely existence of liquid water, at least on a transient or intermittent basis, Europa has the potential for life to exist below its surface. The other requirements for life—access to the biogenic elements and to 1 “Executive Summary” reprinted from A Science Strategy for the Exploration of Europa, National Academy Press, Washington, D.C., 1999, pp. 1-6.
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Space Studies Board: Annual Report 1999 a source of energy—are present at the water-rock boundary at the bottom of the water layer. While no evidence for life exists, the potential for life makes Europa an exciting target for additional exploration following the completion of the Galileo mission. OUTSTANDING QUESTIONS AND ISSUES At our current level of understanding, then, the outstanding questions and issues to be addressed for Europa include the following: Is there liquid water on Europa today, or was there liquid water in the geologically recent past? Are the ice rafts seen in Galileo’s images of Europa the result of movement atop liquid water or through a warm, soft (but not necessarily melted) ice? What is the composition of the deep interior of Europa, below the water/ice layer? What is the composition of the non-ice component of the surface materials (such as the salts)? What is the nature of the ice-tectonic processes that have affected the surface? What is the composition of the atmosphere and of the ionosphere? What are the characteristics of the surface radiation environment and what are the implications for organic/ biotic chemistry? What is the abundance of geochemical sources of energy that could support life? KEY MEASUREMENTS The outstanding questions and issues for Europa can be addressed through a series of spacecraft missions that, together, can contribute to an integrated understanding of the nature of Europa, the possibility that liquid water exists there, and the potential for life. In particular, important measurements will include: Measuring Europa’s global topography and gravity, and determining how Europa’s shape changes as it orbits Jupiter; Characterizing Europa’s geology and surface composition on a global scale; Mapping the thickness of Europa’s ice shell and determining the interior structure; Distinguishing between any intrinsic europan magnetic field and induction and/or plasma effects; and Sampling the geochemical environment of Europa’s surface and possible ocean. CONCLUSIONS AND RECOMMENDATIONS Priority Status of Europa Exploration With the likelihood that it has vast quantities of liquid water beneath its icy surface, Europa is one of the places in our solar system with the greatest potential for the existence of life. Along with Mars, it appears to possess all of the environmental conditions necessary to support the origin and the continued existence of biota. As a result, finding evidence that might indicate whether life had existed on either Mars or Europa would help us to understand whether our theories for the origin of life on Earth are correct and would help us to understand whether life might be widespread outside our solar system. Thus, COMPLEX concludes that Europa is an exciting object for additional study following the completion of the Galileo mission. It offers the potential for major new discoveries in planetary geology and geophysics, planetary atmospheres, and, possibly, studies of extraterrestrial life. In light of these possibilities and the equal priority given to the exploration of Mars and the Jupiter system by COMPLEX’s Integrated Strategy, 2 COMPLEX feels justified in assigning the future exploration of Europa a priority equal to that for the future exploration of Mars. This equality must, however, be tempered by the uncertainty as to whether liquid water is actually present and the technological challenges posed by the exploration of Europa. 2 Space Studies Board, National Research Council, An Integrated Strategy for the Planetary Sciences: 1995-2010, National Academy Press, Washington, D.C., 1994, pages 8 and 191.
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Space Studies Board: Annual Report 1999 The two highest-priority overall science goals identified by COMPLEX for exploration of Europa reflect the emphasis on the potential for life as a major driver in Europa’s exploration: Determining whether liquid water has existed in substantial amounts subsequent to the period of planetary formation and differentiation, whether it exists now, and whether any liquid water that is present is globally or locally distributed; and Understanding the chemical evolution that has occurred within the liquid-water environment and the potential for an origin of life and for its possible continuation on Europa. The Need for a Systematic Program of Exploration COMPLEX recognizes the frustration that will inevitably result from following a well-conceived strategy for conducting a thorough and detailed investigation of the potential for life on Europa that likely will take one or two decades to carry out. With the excitement today about searching for life elsewhere, it is tempting to advocate a spacecraft mission that will immediately search for europan life or return samples of surface ice to Earth for such analyses. However, the history of space exploration suggests that a phased approach, in which the results of one mission provide the scientific foundation for the next incremental advance, is more productive in the long term. We need only look to the history of the search for life on Mars to see the wisdom of an incremental approach. Although the Viking missions seemed very well conceived in 1970, they look naive today in the light of current understanding of the martian environment, and of the diversity of life on Earth and its ability to survive in extreme conditions. As a result, Viking did not sample the most appropriate environments in its search for extant life on Mars. The results from the Viking biology experiments, though, have provided a remarkable foundation for understanding of martian geochemistry that is playing a key role in knowing how and where to look for life on Mars today. In a similar vein, the absence of identifiable surface environments that might support life or contain evidence of life on Europa and our complete lack of understanding of the chemical environment of the icy surface layer, the liquid water layer that may or may not underlie it, and the rocky interior of Europa suggest that a detailed exploration of the satellite will provide the best opportunity to answer these exciting questions. In other words, understanding the history of the satellite and the potential for life requires a detailed investigation into the geochemistry of the surface and subsurface ice or water, and of possible organic molecules or biological activity. Measurements of the atmosphere, ionosphere, the rocky interior, and the ice- or water-rock interface will also be important. Therefore, COMPLEX recommends that Europa be explored within the framework of a well-conceived and planned strategy designed to create a scientific base of information that is sufficient to provide a global context for interpreting data pertaining to the possible presence of life on Europa. A comprehensive understanding of the geology, geochemistry, and geophysics of Europa, and of the nature of its atmosphere, is not strictly necessary in order to determine if liquid water is present. Knowledge of these is necessary, however, to assess the potential for life, to determine whether life is present, and to understand the chemical evolution of Europa. COMPLEX concludes that, should it turn out that liquid water is not present on Europa and has not been present in geologically recent times, the strong evidence for comparatively recent or ongoing geologic activity still makes it an appropriate target for exploration. However, the priority accorded Europa in the solar system exploration program and the sequence of exploration activities would have to be reassessed at that time. Europa and the Search for Life in the Solar System The search for extinct or extant life on Mars, and the geophysical and geochemical analyses that are a fundamental part of the search, will provide substantial new insights into the environments in which life might exist and the precursor and resulting molecules that might obtain. Similarly, the search for life in extreme environments on Earth is providing key new insights into the potential for life elsewhere in the universe. In both cases, the new results need to be integrated into the ongoing Europa program to ensure a solid basis for investigation and analysis.
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Space Studies Board: Annual Report 1999 Thus, COMPLEX recommends that the search for evidence of present or past life on Europa, or for evidence of chemical evolution that has the potential to lead to life, should be coordinated with other aspects of the search for possible abodes of life in the solar system. Elements of a Comprehensive Exploration Program A comprehensive exploration of Europa that can address the major scientific goals will require a combination of spacecraft missions, ground-based telescopic observations, technology development, and supporting research and analysis. The scientific priorities for exploring Europa should proceed from the global to the local scale in searching for liquid water, determining the composition of the surface and near-surface ice, and exploring any pockets or oceans of liquid that may be discovered. The set of subsequent spacecraft missions to Europa that follows from this, then, likely should proceed from a polar orbiter, to landed experiments, to subsurface devices that can penetrate to depths necessary to reach liquid water. COMPLEX recognizes that implementation of such an ambitious sequence of spacecraft, with each being able to take advantage of results from the earlier missions, may require decades. COMPLEX recommends that a staged series of missions be utilized to explore Europa, with the scientific focus of the first mission being to determine whether liquid water exists at the present epoch or has existed relatively recently. If liquid water is present, the focus of follow-on missions should be to characterize surface materials and to access and study the liquid water. Priorities for the Initial Europa Mission COMPLEX recommends that the primary goals for the first Europa mission should be determining whether a global ocean of liquid water exists beneath the icy surface, determining if possible the spatial and geographical extent of liquid water, determining the bulk composition of the surface material, and characterizing the global geologic history and the nature of any ongoing surface and atmospheric processes. These science objectives can best be met by observations from polar or near-polar orbiting spacecraft. Specific measurement objectives include, in priority order: Obtaining measurements of the time variations of Europa’s global topography and gravity field over a period of several tens of orbits of Europa around Jupiter, with a precision and accuracy of ±2 meters to uniquely distinguish between tidal distortions of several meters (expected for a completely solid ice cover) and several tens of meters (expected if a global layer of liquid is present). The results of these efforts will allow a unique conclusion regarding the present-day existence of a global liquid-water layer; Imaging Europa’s surface, with resolution of at least 300 m/pixel for global coverage and with higher resolution (< 50 m/pixel) for selected regions, to understand the global geologic history and identify regions where liquid water may be readily accessed; Performing radar sounding of Europa’s subsurface structure to a depth of 5 to 10 km, to identify possible regions where liquid water might exist close to the surface. If the ice is less than 5 to 10 km thick, use of ice-penetrating radar may allow determination of the vertical extent of the surface ice layer (and possibly a direct detection of any underlying liquid water), as well as the local structure of the ice; Mapping the near-infrared reflectance spectrum of Europa’s surface materials globally at kilometer-scale resolution, supplemented by 300-m resolution in selected areas, and using the results to identify the bulk composition of the surface materials, their abundances, and their spatial distributions. A spectral resolution of 10 to 15 nm will be required; Measuring the magnetic field to a precision of 0.5 nT under a variety of different background conditions (i.e., at different jovian longitudes), combined with coordinated measurements of the plasma environment, to determine whether there is an intrinsic magnetic field and what the properties of either the intrinsic or induced field are. Such measurements may provide important information about the structure of and dynamical processes operating in Europa’s deep interior, and Determining the composition and properties of the atmosphere using both in situ and remote-sensing experiments.
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Space Studies Board: Annual Report 1999 Priorities for Follow-on Europa Missions Following the systematic orbital characterization of Europa, the focus of follow-on missions should shift to studies of the nature of Europa’s surface materials and the means to access and study any liquid water present. Therefore, COMPLEX recommends that: The science objectives for follow-on experiments designed to elucidate the properties of Europa’s surface materials should include in situ determination of the composition of the ice and of any non-ice surface components, including the bulk material, trace elements, isotopes, and mineralogy; analyses of any organic molecules at or near the surface, and identification of endogenic or exogenic sources; determination of the composition and properties of the atmosphere and of any materials sputtered from the surface; and estimation of the absolute ages of surface materials. These science goals probably can best be met using a landed package of instruments on Europa’s surface. If subsurface liquid water is detected and found to be accessible with an instrumented probe, the science objectives of subsequent missions should include determination of the physical and chemical properties of the water, including salinity, acidity, pressure and temperature profiles within the water, abundances and chemical gradients in key redox compounds, and existence and abundances of organic materials; determination of the composition and abundance of suspended particles; exploration of the properties at the water-ice interface; and a search for extant life in the water. Earth-based Studies, Technology Development, and Other Issues Much additional laboratory and theoretical work, together with field studies and associated technical developments, is required in a program designed to pursue the exploration of Europa. As a result, COMPLEX recommends that: A vigorous program of laboratory measurements and supporting theoretical analyses be carried out, to encompass the nature of materials at temperatures, pressures, and irradiation conditions likely to be found on Europa. NASA support a program of theoretical analysis of the geophysical and geochemical environment at Europa, including the nature of the interior, surface, atmosphere, and magnetospheric interactions. New large telescopes and instrumentation that are being developed incorporate, from the beginning of the design stages, the ability to observe relatively bright targets moving with respect to the background stars, and that these capabilities be implemented in a timely manner. For new ground- and space-based facilities, a non-sidereal tracking capability with an accuracy analogous to that of the Hubble Space Telescope would be appropriate. Low-mass, radiation-hardened instruments be developed for use on orbiting and surface spacecraft. Devices that can penetrate through any surface ice and explore the subsurface ice and possible liquid water ocean on Europa be developed, on a schedule that will allow them to be launched on possible spacecraft missions a decade from now. Appropriate diagnostic remote tests and instrumentation for determining the physical and chemical properties of a sub-ice ocean and for detecting the presence or potential for life be developed. NASA continue its collaborative efforts with other government agencies to explore sub-ice freshwater lakes (such as Antarctica’s Lake Vostok) and sub-ice-shelf ocean environments as a means of understanding scientific, technological, and operational issues associated with the exploration of isolated environments. Peer review be used to select Earth-analog programs and investigators to ensure a significant and appropriate level of participation by all of the relevant scientific communities. NASA, to avoid “reinventing the wheel,” should look to other federal agencies to deal with some of the scientific and technological issues and develop mechanisms for cooperating with governments of other countries in exploring Earth analogs. Appropriate planetary protection measures be determined and implemented on all relevant spacecraft missions. 3 3 Appropriate planetary protection measures are currently being determined by the Space Studies Board Task Group on the Forward Contamination of Europa.
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Space Studies Board: Annual Report 1999 reviews of preliminary design, critical design, and safety—all conducted by NASA. Prelaunch hardware integration and specimen preparations (if any) are conducted by the principal investigator, assisted by the payload developer, working with the ISS prime contractor and the space station program office at JSC. Following launch, flight operations are supported by the NASA discipline lead center. Data analysis and archiving are the responsibility of the principal investigator working under the oversight of the discipline lead center and NASA headquarters. GUIDING PRINCIPLES On the basis of discussions with NASA officials and its own deliberations, the task group concluded that the principal use of ISS would be for research. While there certainly will be other uses, both early in the program and over its lifetime—examples cited include education, staging for human space exploration expeditions, delivery of certain commercial services, possibly some manufacturing on a limited scale of very high-value products, or even advertising or tourism—none of these other uses appears to be ready to demand or justify a major fraction of ISS resources. Instead, for the foreseeable future they are candidates for secondary uses, or they remain unproven, or it is unclear how they will be handled. Research is the one clearly defined application that is ready to begin immediately and to be sustainable for a long time. For the purposes of this report, “research” includes basic scientific studies, applied research directed toward beneficial applications and commercial interests, engineering research, and advanced technology development. It does not include performance testing or monitoring of operational systems on the ISS or the installation or evaluation of systems to upgrade ISS operational capacity. Nor does it include use of the ISS as an operational site in support of human exploration missions beyond low Earth orbit. Given that research is the main use of the ISS and recognizing that safety is the highest priority at all times, the following principles should guide the character and operations of any organization charged with facilitating the research use of the ISS: High-quality basic and applied research should be paramount. Responsibility for managing and supporting research would not require that the organization manage other ISS activities. The research user community should have early, substantive, and continuing involvement in all phases of planning, designing, implementing, and evaluating the research use of the ISS. The organization must be flexible and capable of adapting over time in response to changing needs and lessons learned. Basic and applied scientific and engineering users should be selected on the basis of their scientific and technical merit, as determined by peer review. The selection processes for space technology development and for commercial R&D would not need to be the same as those for scientific and engineering research, but they would have to meet similar standards. NASA officials indicated, and the task group agrees, that there are important operational objectives for the research support organization. Meeting those objectives would lead to a number of improvements with respect to the space shuttle and Spacelab programs: Enhanced understanding of and sensitivity to research users and uses; Shorter selection-to-flight cycle times; Streamlined processes and procedures; and Simpler investigator interfaces for initiation and conduct of research activities. Lower end-to-end investigation costs; The task group examined a range of alternative organizational approaches. One model entailed a minimal-change, process-improvement approach inside NASA; another entailed the creation of an independently chartered corporation that would take over the full ISS program. The task group concluded that the guiding principles and objectives noted above called for an intermediate approach: the establishment of an NGO, under the direction of institutions able to represent the broad research community, that would manage the research utilization aspects of the ISS.
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Space Studies Board: Annual Report 1999 The task group does not recommend continuing the current arrangements inside NASA, for three reasons. First, NASA’s past practice—focusing its efforts on advanced R&D and transferring long-term operations to the private sector—makes good sense for the long-term support of research on the ISS, especially since NASA’s own workforce is shrinking. Second, research use of the ISS can be optimized with an organization run by and for researchers. Finally, the interests of the extraordinarily diverse set of research communities need to be coordinated by a single organization. At the other extreme, the concept of an independently chartered corporation that would have full responsibility for the entire ISS program was viewed as too broad and ambitious and too disruptive of some activities that are now being handled satisfactorily to be appropriate for the time scale within which NASA needs to act. The NASA reference model provided an excellent starting point for an intermediate approach. Many of the components of the NASA reference model would be appropriate for the NGO envisioned by the task group, and they were incorporated into the model recommended in this report. The task group also concluded that an appropriate approach for NASA is to plan an NGO whose role would be rather narrowly focused in the near term but able to expand in the long term to comprise a broader set of tasks. The task group recommends that the following three operational principles guide the establishment of the new organization in the near term: The proposed organization should concentrate its efforts on support of research needs and leave basic systems operations and maintenance activities to NASA. To fulfill its responsibilities, the organization must have clear authority and adequate funding. NASA must act promptly on the recommendations in this report to ensure that the NGO is actively involved before ISS “assembly complete.” STRUCTURE AND RESPONSIBILITIES OF THE ORGANIZATION To facilitate the broad utilization of the ISS for high-quality basic and applied research and technology development, the organization should be able to fill four key roles: Provide the highest caliber scientific and technical support to enhance research activities; Provide the research community with a single point of contact through which it can utilize the capabilities of the ISS; Promote the infusion of new technology for ISS research; and Stimulate new directions in research, for both established and new user communities. NASA should use a competitive process to select a consortium led by a research institution or group of institutions, governed by an independent board of directors, managed by a strong scientific director, and guided by an advisory process that is broadly representative of the research community. Locating the NGO near a major research facility (for example, near or on a campus) would have many advantages. The NGO should house a cadre of support scientists and engineers who would function in a number of ways: As points of contact for investigators in dealing with the NGO and other implementing ISS organizations both within and external to the government; As facilitators for investigators who are new to the complex world of using the ISS as well as for more experienced investigators; and As advocates who represent the interests of the investigators through the entire process of interface definition, payload development, testing and documentation, flight planning and operations, and postflight processing of results (where required). This cadre should include ISS crew members, selected by the NGO, who would serve in much the same way as Spacelab payload specialists or mission specialists. The NGO should be responsible for fostering commercial research uses of the ISS as well as research by the academic science and engineering communities. To that end, the organization should:
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Space Studies Board: Annual Report 1999 Proactively explore and stimulate potential commercial uses; Assist the community of NASA commercial space centers (CSCs) in their use of the ISS; Include commercial representation in user groups and, where appropriate, broker funds between NASA and other sources to advance commercial research; and Establish clear policies and procedures for the protection of proprietary information and intellectual property. The task group recommends that for the organization to meet its responsibilities and to accomplish its mission effectively, it must have adequate authority and resources. The NGO would need to do the following: Manage the research utilization budget for experiments conducted by U.S. investigators; Participate in all decisions regarding the allocation and operational use of resources available for the ISS; Allocate ISS resources among government-sponsored and privately sponsored users, although it would not administer private-sector research funds; and Disburse funds not only to research investigators but also to research support organizations such as research hardware developers, payload integration contractors, and operations support organizations. NASA headquarters should continue to set policy, define top-level strategy, advocate and defend budgets in the federal budget process, and allocate overall funding for ISS operation and utilization. For the near term, headquarters also should retain responsibility for the coordination of research planning with other federal agencies and the international partners and should continue to solicit research proposals, conduct peer reviews, and select and prioritize investigations for research payloads for the ISS. The NGO would play a key role in assisting headquarters in these activities. Under the recommended model, the NGO would be responsible to NASA headquarters, through its governing board, for all other functions affecting the utilization of the ISS for U.S. research payloads. The NGO would also assume responsibility for coordinating joint or shared utilization of international payloads for which NASA had accepted any responsibility for development, launch, operations, maintenance, or recovery and would establish and maintain a close working relationship with all non-U.S. organizations approved for research on the ISS. Specifically, the NGO should be responsible for tactical and payload operations planning for all payloads under NASA management, for testing and analytical and physical integration of all NASA-approved payloads, for payload interface development and control, and for training crew to conduct research programs. It should take the lead in identifying new technologies and approaches to enhance the research utilization of the ISS and in planning for maintenance and upgrades of research equipment and ISS support capabilities. It also should play an active role, on behalf of the user community, in areas where other organizations may have the lead, such as payload safety, transportation, station operations and maintenance, crew selection, and education and outreach. IMPLEMENTATION Because planning for the early phases of research use is already under way, it is urgent to bring an NGO on board. In the view of the task group, it will be very important to move expeditiously in FY 2001 to begin the transition and implementation process. NASA should plan on establishing an NGO in three phases: A near-term phase during which the NGO is selected and a director, science support staff, and scientific advisory council are recruited and brought on board; A transition phase during which roles now performed by the government are handed off to the NGO, the NGO takes the lead in planning for research activities that will begin at “assembly complete,” and the NGO begins to restructure and streamline the investigation flow process; and A longer-term phase during which the NGO might take on additional responsibilities and authority as the program reaches a steady state. In the view of the task group, the institutional approach recommended in this report would ensure an effective and efficient program to advance the research capabilities and other objectives of the ISS while preserving capabilities already established within NASA headquarters and field centers. The recommended organization is
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Space Studies Board: Annual Report 1999 optimized to provide strong support for research utilization of the ISS because it will be established and run by the research community for the research community. The responsibilities for research support will be integrated in a single organization of critical mass that can attract high-caliber staff and that can integrate and coordinate the activities of a diverse collection of disciplines. The recommended organization would be an entity that is explicitly charged with providing service and advocacy on behalf of ISS research. There would be a clear and logical division of roles and functional responsibilities. First, the recommended approach leaves inherently governmental functions inside NASA and permits the NGO to provide assistance where appropriate. Second, it leaves unchanged other activities that are already being carried out effectively and that do not elicit any pressing arguments for reassignment. The recommended approach also has well-focused sets of responsibilities. Long-term research operations are placed in the private sector, leaving NASA free to pursue its traditional high-technology R&D roles. The recommended NGO is given the responsibility and authority to restructure and streamline the process of developing and integrating the scientific investigations. Finally, the recommended approach offers the flexibility for the organization to evolve as the ISS program itself evolves and matures. The recommended approach to implementation is incremental and anticipates transitions through immediate, mid-term, and long-term phases. By concentrating first on certain critical tasks and functions rather than trying to assume a large set of responsibilities all at once, the NGO can gain experience and assume other duties if and when this is warranted. REFERENCE National Aeronautics and Space Administration (NASA) . 1998 . Commercial Development Plan for the International Space Station . November 16 .
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Space Studies Board: Annual Report 1999 3.5 U.S.-European-Japanese Workshop on Space Cooperation: Summary Report A Report of the Board’s Committee on International Space Programs, the Space Research Committee of the Science Council of Japan, and the European Space Science Committee of the European Science Foundation 1 PREAMBLE A trilateral workshop on space cooperation hosted by the Space Research Committee (SRC) of the Science Council of Japan—and including representatives of the Committee on International Space Programs (CISP) of the Space Studies Board (SSB), National Research Council (NRC), and the European Space Science Committee (ESSC) of the European Science Foundation (ESF)—was held in Tokyo at the Science Council of Japan on May 19-21, 1999. The purpose of the workshop was to: Assist independent space science advisory bodies in Europe and the United States to establish a relationship with like bodies in Japan; Begin this relationship by examining the nature of trilateral, cooperative space missions conducted during the last decade; Understand better the primary factors that led to successful collaboration, explore the benefits and costs of cooperation, and identify major problems; and Review the status of several embryonic projects and consider broader issues such as the possibility of coordinated, international strategic planning for space science and other policy issues likely to be significant in the future. INTRODUCTION The trilateral workshop originated, in part, from a joint SSB/CISP-ESSC study, U.S.-European Collaboration in Space Science, which recognized the need to consider interactions with other spacefaring partners such as Russia and Japan. 2 Following publication of the joint study in 1998, both the ESSC and the SSB/CISP began to pursue relations with space science entities in Japan and agreed to initiate communications together. The SSB and ESSC identified the SRC under the Science Council of Japan as a similar entity with which to establish relations. Initial discussions among representatives of the SRC, SSB, and ESSC were held at the 32nd Scientific Assembly of the Committee on Space Research (COSPAR) on July 16, 1998, in Nagoya, Japan, and led to an agreement to hold a tripartite workshop on space cooperation. The general scope of the workshop, which was to include surveys of three cooperative missions, analysis of the lessons learned from such missions, and discussion on how to improve future cooperative missions, was agreed upon in Nagoya. Specifically, the workshop would include U.S., European, and Japanese perspectives on each of the missions to be surveyed. In addition, the workshop would focus on space science (astronomy and astrophysics, planetary sciences, and space and solar physics), recognizing that other disciplines and areas of cooperation might be studied later. The workshop agenda and a list of participants are included in Appendix B. Professor A. Nishida, chair of the SRC and director general of the Institute of Space and Astronautical Science (ISAS), selected Geotail, Yohkoh (previously Solar-A), and the Advanced Satellite for Cosmology and Astrophysics (ASCA; previously Astro-D) as the three cooperative missions to be examined. 3 Planning for the workshop entailed identifying individuals from the United States, Europe, and Japan who had worked on these missions and 1 “ Preamble ,” “ Introduction ,” and “ Lessons Learned ” reprinted from U.S.-European-Japanese Workshop on Space Cooperation: Summary Report, National Academy Press, Washington, D.C., 1999, pp. 1-2. 2 See National Research Council and European Science Foundation, U.S.-European Collaboration in Space Science, National Academy Press, Washington, D.C., 1998, p. 11. 3 Geotail, launched in July 1992, is exploring the geomagnetic tail of Earth. Yohkoh was launched on August 31, 1991, as an observatory to study X rays and gamma rays from the Sun. ASCA, launched on February 20, 1993, is Japan’s fourth cosmic X-ray astronomy mission; it is conducting X-ray spectroscopy of astrophysical plasmas and features such as emission lines and absorption edges.
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Space Studies Board: Annual Report 1999 would share their insights on the cooperative experience. Speakers were asked to focus on the lessons learned from the missions and on aspects of mission success and to elaborate on any problems within the collaboration, as well as on other concerns and issues that might affect future cooperative activities. Speakers were provided with a template of questions to guide them in preparing their remarks. The speakers at the workshop rated collaborations on all three missions as successes, although there were also lessons learned. LESSONS LEARNED Framework Lessons extracted from the mission surveys were sorted into five general categories: Personal issues such as trust, openness, language, leadership, cultural differences, sharing of credit within a joint project, and the equality of the relationship; Legal, political, and institutional issues such as negotiation of memoranda of understanding (MOUs) and cross-waivers of liability, the role of umbrella science and technology agreements, 4 export controls, data management agreements, continuity of resources, up-front planning funds, and differing policy processes; Organizational patterns including relations among scientists, engineers, and operational personnel; project initiation and development; data access and publication norms; initiation of the cooperative activity; and the process for conceiving and developing new collaborative projects; Scientific interest and technical issues including community interest in the subject; equality or complementarity of capabilities among partners; the eight criteria for successful cooperative missions identified in the U.S.-European report; 5 and the payoffs of cooperation (e.g., exposure to different approaches and expanded opportunities); and Other issues such as privatization; the impact of the National Aeronautics and Space Administration’s (NASA’s) “faster, better, cheaper” philosophy on international cooperation; the effect of differing patterns of inhouse versus contract development and NASA centers versus universities; the validity of cost savings from cooperation; and relationships to military activities. 4 The Department of State negotiates bilateral framework or umbrella agreements on science and technology with foreign governments. These agreements are formulated to be consistent with U.S. foreign policy objectives. (See U.S. General Accounting Office, Information on International Science and Technology Agreements, Government Printing Office, Washington, D.C., April 1999.) 5 U.S.-European Collaboration in Space Science, pp. 102-104.
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Space Studies Board: Annual Report 1999 3.6 Radiation and the International Space Station: Recommendations to Reduce Risk A Report of the Board’s Committee on Solar and Space Physics and the Board on Atmospheric Sciences and Climate’s Committee on Solar-Terrestrial Research1 EXECUTIVE SUMMARY INTRODUCTION This report originated with a request from the National Aeronautics and Space Administration (NASA). To construct the International Space Station (ISS) and maintain it during construction, astronauts and cosmonauts will work in space suits outside their spacecraft in shifts, each of which is projected to last for 6 hours, for a total amount of time estimated to exceed 1,500 hours. According to the present construction schedule, these extravehicular activities (EVAs) will occur over a 4-year period that straddles the peak in activity of the current solar cycle. After the 4-year period, one or two EVAs per month will probably continue for the life of ISS. The peak in the solar cycle combines with the station’s high-inclination orbit to add a new concern for managers of radiation risk. Unlike the originally planned low-inclination orbit (28 degrees), the finally approved high-inclination orbit (51.6 degrees) cuts through high-latitude radiation environments that are sometimes quite harsh, as was noted when the redesign was contemplated in the early 1990s. These high-latitude radiation environments (energetic particles from solar storms and relativistic electrons in Earth’s outer radiation belt) vary greatly over time, from benignly calm to severely stormy. At the height of their storminess, they can be intense enough to pose a radiation hazard to astronauts engaged in EVAs, although doses estimated for even worst-case scenarios fall short of life threatening. The principal risk to astronauts that increased exposure to radiation in ISS orbit poses is the increased probability of developing cancer later in life. The principal concern for flight directors that increased exposure of astronauts to radiation raises is the potential impact on flight schedules and crew rotation if a radiation event pushes an astronaut over an allowable radiation limit. Astronauts are also concerned that crossing an allowable radiation limit will restrict flight opportunities. Storms bearing intense radiation are relatively rare, but EVAs during ISS construction flights are relatively frequent, which raises a concern that the two might by chance coincide. Information obtained during the course of this study puts at near-certainty the likelihood that on one or more occasions an ISS construction flight will be in progress when a high-latitude radiation event (described below) occurs. This finding naturally raises the question, What is the status of radiation risk management as it pertains to ISS construction? It would seem to be a simple matter, for example, for the Space Environment Center (SEC) of the National Oceanic and Atmospheric Administration (NOAA) or for NASA’s own satellites to identify solar events that could cause radiation problems and to get such information to the flight director in time to take appropriate action. But an overly restrictive flight rule and the lack of operationally calibrated models bar the path between the flight director and such sources of information. The problematic (albeit unofficial) flight rule is the “real-time, on-site data” rule, which says that changes in flight plans in response to a radiation situation must be based on real-time, on-site data only. The first recommendation of CSSP/CSTR addresses this flight rule. Recommendation 1: Because it denies access to valid information and thus unnecessarily restrains flight-director options, flight directors should not adhere rigidly to the (unofficial) real-time, on-site data rule. As mentioned, the second obstacle in the path between the flight director and data sources is the lack of operationally calibrated models. In important cases, however, the state of radiation modeling is advanced enough, or with directed effort could quickly become advanced enough, to justify a flight rule that allows use of validated procedures to infer and, in some cases, to predict on-site radiation conditions from off-site data. The report cites such cases. CSSP/CSTR notes that Russians performing EVAs will be directed out of the Russian mission control center in Moscow. Further, it is likely that U.S. and international crew members on ISS will also participate in EVAs directed out of mission control-Moscow. However, flight rules at mission control-Moscow pertaining to radiation
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Space Studies Board: Annual Report 1999 may differ from those at NASA’s mission control center. Although this report is directed at NASA, CSSP/CSTR believes that some of its recommendations could also be implemented by mission control-Moscow. SOLAR PARTICLE EVENTS AND THE INTERNATIONAL SPACE STATION Based on the assumption—the best now available—that the radiation characteristics of the current solar cycle will resemble those of the last cycle, there is nearly a 100 percent chance that at least 2 out of 43 planned ISS construction flights will overlap a significant solar particle event (SPE) and a 50 percent chance that at least 5 flights will overlap such an event. Moreover, the high-latitude zones to which solar energetic particles have access show a marked tendency to widen over the polar latitudes reached by the ISS orbit when SPEs are in progress, a tendency that becomes more pronounced as SPEs intensify. Two storms during 1989, near the maximum of the last solar cycle, illustrate the point. The areas around the poles accessible to SPE particles enlarged until they engulfed more than a quarter of the ISS orbit, and the flux of particles was high enough to have pushed an astronaut over the short-term limit for irradiation of skin and eyes during a single ill-timed 6-hour EVA. These results would seem to call for an aggressive program aimed at reducing solar radiation risk to astronauts during ISS construction. Recommendation 2 addresses means of implementing the elements of such a program. Recommendation 2: For real-time SPE risk management, carry out the steps needed to make usable by SEC and the Space Radiation Analysis Group (SRAG) at Johnson Space Center (JSC) models that use real-time data to specify the intensity of SPE particles and the geographical size and shape of the zones accessible to them. NASA, NOAA, the U.S. Air Force (USAF), and the distributed space physics community have the capability for implementing this recommendation. The project implied in this recommendation is one of the important projects that could be implemented early enough to have an impact on SPE radiation risk management during ISS construction. It should receive high priority for early implementation. RELATIVISTIC ELECTRONS AND THE INTERNATIONAL SPACE STATION For a portion of nearly every day, some fraction of the ISS orbit lies within the outer radiation belt, where relativistic electrons reside. At its maximum, this fraction is about 20 percent. During occasions called relativistic electron events, which happen on average about once per month and last several days, the intensity of relativistic electrons in the belt increases by up to four orders of magnitude. When the intensity of relativistic electrons is greatest, a single ill-timed EVA could deliver a radiation dose big enough to push an astronaut over the short-term limit for skin and eyes. To minimize the possibility of scheduling EVAs during such events, procedures can be implemented to specify and forecast at least approximately the intensity of relativistic electrons in the outer belt. NOAA Polar-Orbiting Operational Environmental Satellites (POES) provide measurements of relativistic electron fluxes that can be used to calculate with reasonable accuracy the relativistic electron environment at ISS. These measurements are available only about every hour and a half, however. NOAA Geostationary Operational Environmental Satellites (GOES), on the other hand, provide relativistic electron measurements continuously, but these measurements are not so directly transferable to the ISS orbit. Nonetheless, the intensity of GOES measurements tracks the intensity of POES measurements in the outer belt. Thus, in combination, POES and GOES measurements would allow radiation risk managers to quantitatively follow variations of electron intensity in the outer belt. A crucial piece of hardware that the ISS project should provide is an electron dosimeter attached outside the station. This would allow SRAG to test the quality of the specifications and forecasts that are possible from measurements taken by POES and GOES. These considerations lead to three related recommendations. Recommendation 3a: NASA should implement a procedure for using POES and GOES measurements of relativistic electrons in the outer radiation belt to specify and forecast the electron radiation environment at ISS. (Such a procedure is outlined in Section 3.3 .)
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Space Studies Board: Annual Report 1999 Recommendation 3b: As soon as possible, JSC should install an electron dosimeter and an ion dosimeter outside the ISS that can return data in real time to SRAG at JSC. Recommendation 3c: A project should be initiated to develop a protocol for identifying the conditions that produce highly relativistic electron events based on the demonstrated good correlation between changes in solar wind conditions and the onset of such events. The recommended project might be a candidate for support by one of the affiliated agencies of the National Space Weather Program (NSWP). SPACECRAFT SOURCES OF OPERATIONAL RADIATION DATA Data that could contribute to reducing radiation risk are currently being acquired by a strategically placed multiagency fleet of research and operational spacecraft. This fleet can provide information on the radiation environment of ISS orbit in real time and in advance of real time. Some spacecraft monitor the Sun and its corona in multiple wavelengths and so can diagnose the X-ray potency of solar flares and warn of oncoming material spewed from the Sun by solar storms. They also monitor SPE fluxes to give direct information on the radiation intensity within zones accessible to SPE particles. Other spacecraft monitor solar wind parameters, which can be used to compute the size and shape of SPE-accessible zones. Spacecraft in relatively low-altitude, polar orbits monitor the flux of relativistic electrons in the outer radiation belt, which the ISS orbit transects. Recommendation 4 addresses a need to channel the relevant information to SRAG at JSC. Recommendation 4: Promptly convene a meeting of pertinent NASA Space Science Enterprise, SRAG, and SEC managers with the principal investigators of satellite instruments. The meeting would (1) consider ways to extend the capabilities of the current spacecraft fleet to provide real-time radiation data for driving models and specifying the ISS radiation environment and (2) formulate an implementation plan for swiftly channeling such data to radiation risk managers at JSC. INTERAGENCY CONNECTIONS A major obstacle stands in the way of implementing any of the improved scientific data and modeling resources that are currently available from research programs in NASA and the National Science Foundation (NSF). Both SEC and SRAG are fully tasked in maintaining their daily program of data collection and analysis. Ongoing operations require that these be maintained. Incorporation of improvements thus becomes a secondary activity, and the lack of adequate resources and agency support in both organizations limits the rate at which improvements can be made. The next two recommendations address this condition. Recommendation 5a: NASA, NOAA, and the USAF should cooperate to support the activities that would lead to an operational space weather forecasting capability. Recommendation 5b: NOAA should extend the range of its SPE predictions from the present ≥10 MeV to biologically effective energy ranges. Forecasts of particle energies at several steps between 10 and 100 MeV would be a significant improvement for space radiation use as well as for other users who operate satellites and systems in space. INTRA-NASA CONNECTIONS There are other major programs at NASA besides the manned flight program that require an accurate knowledge of Earth’s radiation environment. The kind of knowledge required varies from program to program, but the range of knowledge needed extends from the basic science, physical processes, and generation mechanisms of the radiation belts and particle events, to net integrated radiation doses averaged over a long period of time. The trend in recent years at NASA has been toward smaller and cheaper spacecraft with heavy use of microelectronics, smaller instruments, and more onboard data processing. For this and other reasons, the working knowledge of Earth’s radiation environment (models, forecasts of particle events and disturbances, integrated doses, etc.) needs to be improved to address current planning and development requirements in just about every area of NASA activity.
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Space Studies Board: Annual Report 1999 Recommendation 6: To coordinate intra-NASA activities and concerns related to radiation, NASA should establish an agency-level radiation plan and task force. It should also establish a multidisciplinary steering committee to advise the task force. SPACE WEATHER MODELS APPLIED TO RADIATION RISK REDUCTION The above recommendations address means to exploit currently available resources to allow a rapid augmentation of the tools available for radiation risk management during ISS construction. Looking beyond these recommendations, there are actions of a tactical nature that can be taken to strengthen radiation risk management in the late phases of ISS construction and during ISS operations. These actions entail the selective implementation of space weather modeling efforts. Space weather modeling is the discipline responsible for developing models that take information from where instruments happen to be and use it to specify and forecast the space environment at places where the information is wanted. Appendix A identifies research projects that address specific elements of an effort that would provide high-quality information on the parameters most crucial to assessing radiation risk. Two projects deserve particular attention, the first because its potential impact on radiation risk reduction is especially crucial, the second because the maturity of its models promises early, tangible results: Mapping latitudes at which SPE particles can penetrate under a variety of geomagnetic conditions to the altitude of ISS. Several methods have been proposed; these should be critically evaluated and the best should be implemented. Developing operational space weather nowcast and forecast codes. Several of the existing advanced, databased space weather nowcast and forecast codes could be transformed relatively quickly into operational codes to give SRAG the ability to forecast at least some radiation-risk parameters during most of the ISS construction period. These projects could be undertaken in the near term by one or more of the affiliated agencies of the NSWP. TIMELINE FOR IMPLEMENTING RECOMMENDATIONS Figure ES.1 gives a timeline keyed to the ISS construction schedule (as it was known in July 1999) for the implementation of the recommendations of this report. As shown in the figure, there are recommendations that should be implemented immediately (R1, R3a, R4, R5b, and R6), recommendations that will require 1 or 2 years to implement (R2 and R3b), and recommendations that will take several years to implement (R3c and R5a). The research needed to improve space weather services in support of manned missions is also shown in Figure ES.1 . Research activities are organized into two groups: (1) those that can be implemented within 5 years (A1), with some of these activities being implemented within 1 year, and (2) those requiring more time to implement (A2).
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Space Studies Board: Annual Report 1999 Figure ES.1 Timeline for implementing the report’s recommendations, which are denoted R1 through R6. A1 and A2 refer to priority research activities (see Appendix A). The timeline is keyed to the ISS assembly sequence, which is available from NASA on the World Wide Web at < http://spaceflight.nasa.gov/station/assembly/flights/chron.html >. The first crew—a U.S. astronaut and two Russian cosmonauts—will be launched on a Russian Soyuz spacecraft in March 2000 to begin a 3-month stay on flight 2R (the letter “R” in the flight designation denotes a Russian mission). From that point on, the ISS is planned to be permanently staffed.
Representative terms from entire chapter: