Assessment of Planetary Protection Requirements for Venus Missions

This assessment by the Task Group on Planetary Protection Requirements for Venus Missions (the members of the task group are listed in Attachment 1) was carried out at a meeting held at the Southwest Research Institute in Boulder, Colorado, on October 3-5, 2005. The assessment was conducted at the specific written request of Dr. John D. Rummel, NASA’s Planetary Protection Officer, who asked the National Research Council (NRC) to address three issues in terms of their implications for planetary protection:

  1. Assess the surface and atmospheric environments of Venus with respect to their ability to support Earth-origin microbial contamination, and recommend measures, if any, that should be taken to prevent the forward contamination of Venus by future spacecraft missions;

  2. Provide recommendations related to planetary protection issues associated with the return to Earth of samples from Venus; and

  3. Identify scientific investigations that may be required to reduce uncertainty in the above assessments.

VENUS MISSIONS

The United States and the former Soviet Union (with France) have been sending spacecraft to Venus since the beginning of the space age.1 Missions to land on Venus began with the Soviet Venera 3 atmospheric probe, which lost communications before atmospheric entry in March 1966. Atmospheric probes Venera 4, 5, and 6 also crashed on Venus. On December 15, 1970, Venera 7 made the first successful landing of a spacecraft on another planet and survived for 23 minutes before succumbing to heat and pressure. Venera 8 landed July 22, 1972, and survived for 50 minutes. Between 1975 and 1982, Venera probes 9 through 14 made successful landings.

In 1978, NASA sent two Pioneer spacecraft to Venus. The Pioneer Venus Multiprobe carried one large and three small atmospheric probes. The large probe was released on November 16, 1978, and the three small probes on November 20, 1978. All four probes entered the Venus atmosphere on December 9, 1978, followed by the delivery vehicle. Although not expected to survive the descent through the atmosphere, one probe continued to operate for 45 minutes after reaching the surface. The Pioneer Venus Orbiter was inserted into an elliptical orbit around Venus on December 4, 1978. It carried 17 experiments and operated until the fuel used to maintain its orbit was exhausted and atmospheric entry destroyed the spacecraft in August 1992.

The Soviet Union’s Vega 1 and Vega 2 probes encountered Venus on June 11 and June 15, 1985. Landing vehicles carried experiments focusing on cloud aerosol composition and structure. The Vega 1 and 2 spacecraft each deployed a balloon-borne aerostat that floated at about 53 km altitude for 46 and 60 hours, respectively, traveling about one-third of the way around the planet. These probes measured wind speed, temperature, pressure, and cloud density.

Although the most recent spacecraft sent to Venus ceased operating over a decade ago (the last mission was NASA’s Magellan radar mapper, which operated until 1994), scientific interest in Venus has not waned. The 2003 NRC report New Frontiers in the Solar System: An Integrated Exploration Strategy2 recommended the Venus In Situ Explorer as one of eight high-priority planetary exploration projects for the period 2003 to 2013. As a result, NASA is considering possible space missions to Venus, including orbiters, landers, and atmospheric probes. Moreover, several other nations and space agencies are planning to launch missions to Venus in the near future. The European Space Agency’s Venus Express spacecraft was successfully launched on November 9, 2005, and the Japan Aerospace Exploration Agency plans to launch a Venus orbiter, Planet-C, in 2008.

1

For more details of missions to Venus, see, for example, A.A. Siddiqi, Deep Space Chronicle: A Chronology of Deep Space and Planetary Probes 1958-2000, Monographs in Aerospace History 24, National Aeronautics and Space Administration, Washington, D.C., 2002. The brief summary that follows here was adapted from Wikipedia contributors, “Observations and Explorations of Venus,” Wikipedia, The Free Encyclopedia, available online at <en.wikipedia.org/w/index.php?title=Observations_and_explorations_of_Venus&oldid=28480484>. Last accessed February 7, 2006.

2

National Research Council, New Frontiers in the Solar System: An Integrated Exploration Strategy, The National Academies Press, Washington, D.C., 2003.



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66 Space Studies Board Annual Report—006 Assessment of Planetary Protection Requirements for Venus Missions This assessment by the Task Group on Planetary Protection Requirements for Venus Missions (the members of the task group are listed in Attachment 1) was carried out at a meeting held at the Southwest Research Institute in Boulder, Colorado, on October 3-5, 2005. The assessment was conducted at the specific written request of Dr. John D. Rummel, NASA’s Planetary Protection Officer, who asked the National Research Council (NRC) to address three issues in terms of their implications for planetary protection: 1. Assess the surface and atmospheric environments of Venus with respect to their ability to support Earth- origin microbial contamination, and recommend measures, if any, that should be taken to prevent the forward contamination of Venus by future spacecraft missions; 2. Provide recommendations related to planetary protection issues associated with the return to Earth of samples from Venus; and 3. Identify scientific investigations that may be required to reduce uncertainty in the above assessments. VENUS MISSIONS The United States and the former Soviet Union (with France) have been sending spacecraft to Venus since the beginning of the space age.1 Missions to land on Venus began with the Soviet Venera 3 atmospheric probe, which lost communications before atmospheric entry in March 1966. Atmospheric probes Venera 4, 5, and 6 also crashed on Venus. On December 15, 1970, Venera 7 made the first successful landing of a spacecraft on another planet and survived for 23 minutes before succumbing to heat and pressure. Venera 8 landed July 22, 1972, and survived for 50 minutes. Between 1975 and 1982, Venera probes 9 through 14 made successful landings. In 1978, NASA sent two Pioneer spacecraft to Venus. The Pioneer Venus Multiprobe carried one large and three small atmospheric probes. The large probe was released on November 16, 1978, and the three small probes on November 20, 1978. All four probes entered the Venus atmosphere on December 9, 1978, followed by the delivery vehicle. Although not expected to survive the descent through the atmosphere, one probe continued to operate for 45 minutes after reaching the surface. The Pioneer Venus Orbiter was inserted into an elliptical orbit around Venus on December 4, 1978. It carried 17 experiments and operated until the fuel used to maintain its orbit was exhausted and atmospheric entry destroyed the spacecraft in August 1992. The Soviet Union’s Vega 1 and Vega 2 probes encountered Venus on June 11 and June 15, 1985. Landing ve- hicles carried experiments focusing on cloud aerosol composition and structure. The Vega 1 and 2 spacecraft each deployed a balloon-borne aerostat that floated at about 53 km altitude for 46 and 60 hours, respectively, traveling about one-third of the way around the planet. These probes measured wind speed, temperature, pressure, and cloud density. Although the most recent spacecraft sent to Venus ceased operating over a decade ago (the last mission was NASA’s Magellan radar mapper, which operated until 1994), scientific interest in Venus has not waned. The 2003 NRC report New Frontiers in the Solar System: An Integrated Exploration Strategy2 recommended the Venus In Situ Explorer as one of eight high-priority planetary exploration projects for the period 2003 to 2013. As a result, NASA is considering possible space missions to Venus, including orbiters, landers, and atmospheric probes. Moreover, several other nations and space agencies are planning to launch missions to Venus in the near future. The European Space Agency’s Venus Express spacecraft was successfully launched on November 9, 2005, and the Japan Aero- space Exploration Agency plans to launch a Venus orbiter, Planet-C, in 2008. 1For more details of missions to Venus, see, for example, A.A. Siddiqi, Deep Space Chronicle: A Chronology of Deep Space and Planetary Probes -000, Monographs in Aerospace History 24, National Aeronautics and Space Administration, Washington, D.C., 2002. The brief summary that follows here was adapted from Wikipedia contributors, “Observations and Explorations of Venus,” Wikipedia, The Free Encyclo- pedia, available online at . Last accessed February 7, 2006. 2National Research Council, New Frontiers in the Solar System: An Integrated Exploration Strategy, The National Academies Press, Wash- ington, D.C., 2003.

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6 Short Reports SCIENTIFIC CONSIDERATIONS AND PAST NATIONAL RESEARCH COUNCIL REPORTS Despite Venus’s being Earth’s near twin in terms of its mass, radius, and other bulk properties, the surface of Venus represents perhaps the most hostile planetary environment ever explored by robotic spacecraft. The average surface temperature of Venus is more than 737 K, hot enough to melt lead. The surface pressure is 92 bar, about equivalent to 1 km deep in Earth’s ocean. The surface is desolate, water is absent, and sulfur is abundant. More than 85 percent of the surface is covered by volcanic rock. Venus’s atmosphere is more than 96 percent carbon dioxide, with 3 percent nitrogen and traces of other gases. Three distinct cloud layers shroud the entire planet, at altitudes from 45 to 60 km. The clouds occupy the “Earth-like” part of Venus’s atmosphere, with pressures ranging from 2 bar to 10 mbar and temperatures ranging from ~240 to 390 K. Water vapor ranges from a few parts per million at the top of the cloud deck to a few tens of parts per million at the base. However, the cloud droplets are formed of extremely concentrated sulfuric acid. A high flux of solar ultraviolet radiation exists throughout the cloud deck.3 Although the surface environment of Venus is clearly inimical to terrestrial life, some researchers have argued that conditions in Venus’s clouds may be potentially conducive to life.4 Indeed, some authors have suggested that chemical disequilibrium among trace constituents of Venus’s atmosphere is evidence for microbial life in the planet’s lower cloud layers.5,6 In particular, supporters of this conjecture point to the coexistence of chemical species—such as H2 and O2 and H2S and SO2—not normally found in association and the existence of relatively benign regions in the atmosphere where the temperature is 300 to 350 K, and where pressures of 1 bar and water vapor concentrations as high as several hundred parts per million may exist.7 Such organisms, presumably, would have evolved when Venus’s climate was more like that of Earth and then migrated to the clouds as Venus lost its surface water. Irrespective of such speculations, the evolution and present states of Venus’s atmosphere have a direct bearing on the history and evolution of both biotic and abiotic organic compounds in the solar system. For example, given the similar location in the solar nebula of Mars, Earth, and Venus, these planets are likely to have had roughly similar bulk chemical compositions 4.5 billion years ago and would have been exposed to similar early radiation processes. The extent to which the atmospheres have evolved and diverged since that time yields information on the evolution of Earth’s atmosphere and the couplings of atmospheric composition with biology and life. Venus may also provide clues to the composition of past atmospheres on Earth that ultimately would have influenced the distribution of ter- restrial organic compounds in the form of, for example, carbon reservoirs in the atmosphere compared with those at the surface, in the interior, and in the oceans. The Space Studies Board (SSB) has a long track record of assessing the biological potential of Venus and making recommendations concerning appropriate planetary protection guidelines for Venus missions. In 1970, for example, the SSB’s predecessor, the Space Science Board, commented as follows:8 A slight possibility exists that terrestrial organisms could grow on airborne particles near to the cloud tops of Venus. The problem was discussed at the 1970 COSPAR [Committee on Space Research of the International Council for Science] meeting, and some interest was expressed in investigations of airborne life. Life on Venus is no more than a remote contingency, but the possibility of contamination by terrestrial organisms must be considered. The saving feature of all Venus missions is that there is no longer any doubt that a temperature of about 700 K prevails over the entire surface of the planet. There is no possibility that terrestrial organisms can grow at such temperatures, and we are therefore at worst concerned with a short period of transit through the cooler regions of the atmosphere. According to the COSPAR agreements, the cumulative probability up to 1988 of contaminating the planet must be less than 10−3. With 20 missions, the probability per mission must then be less than 5 × 10−5. We are satisfied that this constraint is readily met, even if the bus or orbiter should enter the atmosphere. These unshielded vehicles will mostly vaporize in the upper atmosphere, and at most a few charred members may fall rapidly through the temperate 3See, for example, . Last accessed February 7, 2006. 4D. Schulze-Makuch and L.N. Irwin, Life in the Unierse: Expectations and Constraints, Springer-Verlag GmbH, Berlin, 2004, pp. 128-132. 5D.H. Grinspoon, Venus Reealed: A New Look Below the Clouds of Our Mysterious Twin Planet, Perseus Publishing, Cambridge, Mass., 1997. 6D. Schulze-Makuch and L.N. Irwin, “Reassessing the Possibility of Life on Venus: Proposal for an Astrobiology Mission,” Astrobiology 2: 197-202, 2002. 7D. Schulze-Makuch, O. Abbas, L.N. Irwin, and D.H. Grinspoon, “Microbial Adaptation Strategies for Life in the Venusian Atmosphere,” Abstract 12747, NASA Astrobiology Institute General Meeting, Tempe, Arizona, 2003. 8National Research Council, Venus: Strategy for Exploration, Report of a Study by the Space Science Board, National Academy of Sciences, Washington, D.C., June 1970, pp. 12-13.

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6 Space Studies Board Annual Report—006 region of the cloud tops. For numerical estimates we may start with the figures given in the Planetary Explorer, Phase A Report (Goddard Space Flight Center, October 1969, Section 6 and Appendix C). The number of spores is taken as 104. The probability of release in the atmosphere under the above circumstances is estimated to be less than 10−3; we regard the Goddard figure of 0.3 as far too high for atmospheric release, because it was based on a hard-surface impact. The probability of growth was given as 10−4, but this assumes the presence of a stable particle or droplet to grow on. However, droplets are subject to evaporation, while solid particles must be subject to rapid mixing to support them against fallout; they will therefore reach a hot region in a short time. We believe that the probability of growth in the atmosphere should be amended to less than 10−6 for a total probability of contamination per impact of less than 10−5. We therefore see no reason why the bus or orbiter should not be permitted to impact the planet whenever a scientific benefit is to be gained thereby. Low-periapses orbiters should also be open to consideration. Surface-sterilized entry probes, hermetically sealed and with a fully sterilized heat shield, present a far lower probability of contamination than do the bus or orbiter, and risk of contamination from them may be neglected. We therefore recommend that, with some precautions, spacecraft be allowed to impact the planet when scientific benefit is to be gained thereby. The most recent NRC study of the planetary protection requirements for Venus missions was issued in 1972.9 It commented as follows: Two values of probability of growth are used for Venus, one for the planet surface, the other for its atmosphere. Prior to the proposed new quarantine policy these values stood at Pg(surface) ≤ 10−6 and Pg(atmosphere) ≤ 10−4. The proposed new values use Pg(surface) = 0; Pg(atmosphere) ≤ 10−9. There is now general agreement that the surface temperatures of Venus are much too high for any known terrestrial microorganism to survive. Consequently, the proposed value Pg = 0 is acceptable. Regarding the atmosphere, there are some uncertainties on the likely presence of sufficient nutrients, a high water activity and the convective rate by which water droplets containing microorganisms are transported downwards and pyrolyzed at the higher temperatures. The probability of contaminating the Venus atmosphere was treated in the SSB 1970 summer study;* in that study, a probability of growth for the atmosphere ≤ 10−6 was recommended and approved by the Space Science Board (a recommendation which superseded the previous value of Pg ≤ 10−4). The committee recommends that NASA evaluate their sterilization standards for the Pioneer Venus mission (surface probe) in the light of the Pg(atmosphere) number recommended in the Venus 1970 study report. If further elucidation or interpretation on the application of these numbers is needed, the SSB would be willing to review the matter again. For the Venus/Mercury 1973 flyby mission, the committee recommends a Pg(atmosphere) ≤ 10−9 (Venus atmosphere). _____________________ ∗National Research Council, Venus: Strategy for Exploration, Report of a Study by the Space Science Board, National Academy of Sciences, Washington, D.C., June 1970, pp. 12-13. Since these reports were issued, the approach to planetary protection adopted by the Committee on Space Research (COSPAR) of the International Council for Science—the de facto guardian of the planetary protection provisions mandated by the United Nations’ 1967 Outer Space Treaty10—has been significantly revised. The quan- titative, statistical approach—based in part on the probability of growth (Pg) of terrestrial organisms transferred to an extraterrestrial environment—has been abandoned.11 In its place is a simpler, more straightforward methodology 9National Research Council, Space Science Board Ad Hoc Committee for Review of Planetary Quarantine Policy, Report (Final), February 14, 1972, pp. 3-4. 10United Nations, Treaty on Principles Goerning the Actiities of States in the Exploration and Use of Outer Space, Including the Moon and Other Celestial Bodies, U.N. Document No. 6347, United Nations, New York, N.Y., January 1967. 11The quantitative planetary protection methodology was based on the concept of a probability that a particular mission will contaminate a particular planet. The probability of contamination (Pc) was determined by a formula linking such factors as the measured bioburden on the spacecraft at launch, the likelihood that terrestrial organisms on the spacecraft will survive transit to their planetary destination, the probability that organisms will be released into the planet’s environment, and the probability that these organisms will grow and reproduce (Pg). For a recent discussion of this approach, see, for example, Space Studies Board, National Research Council, Preenting the Forward Contamination of Mars (Prepublication Text), The National Academies Press, Washington, D.C., 2005, pp. 25-27. For a detailed, quantitative discussion, see, for example, S. Schalkowsky and R.C. Klein, Jr., “Analytical Basis for Planetary Quarantine,” pp. 9-26 in L.B. Hall, ed., Planetary Quarantine: Principles, Methods, and Problems, Gordon and Breach, New York, N.Y., 1971.

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6 Short Reports based on the type of mission (e.g., flyby, orbiter, lander, or sample return) and the degree to which the mission’s destination is of interest to the process of chemical or biological evolution (see Attachment 2). The planetary protection characterization resulting from the two NRC studies conducted in the 1970s was that although Venus was of some interest with respect to issues of chemical and biological evolution—for example, to studies relating to the divergent evolutions of Earth, Mars, and Venus—the chances of contaminating Venus with ter- restrial organisms are so slight that no special requirements need be levied on spacecraft missions to that planet. As such, missions to Venus are currently assigned to planetary protection Category II (see Attachment 2 for details). Much new information about the origin and evolution of Venus’s surface and atmospheric environment has, however, been revealed in the past three decades. In the same period, there has been an explosion of new findings concerning the ability of terrestrial microorganisms to survive in extreme conditions. These two strands of new in- formation have been woven together by various authors, who have proposed plausible theories suggesting how life may have arisen on the early Venus, when environmental conditions were much more like those of Earth.12 Then, as Venus gradually lost its initial inventory of water and its climate became increasingly dominated by a runaway greenhouse effect, microbial life might have been able to adapt to changing conditions and survive to this day in the more clement temperature and pressures found in Venus’s clouds. Thus, a reexamination of the planetary protection requirements for Venus missions is appropriate at this time. TOPICS CONSIDERED BY THE TASK GROUP The task group considered the following topics: • Origins of life—What does our current understanding of the origins and early evolution of life on Earth tell us about the possible origins of life on Venus? • Surial of life on Venus—What can the study of terrestrial extremophiles tell us about the survival of life on Venus, whether it is indigenous or inadvertently transported from Earth? • Planetary protection issues—What can planetary protection studies for other solar system objects tell us about likely issues concerning Venus? • Venus’s enironment—What can our current understanding of the origin and evolution of Venus tell us about the likely environmental conditions and potential habitable niches on the planet through time? • Life in Venus’s atmosphere—What is the environment in Venus’s clouds, could life exist there, and what is the likelihood that life exists there? Origins of Life It is generally agreed that surface conditions on early Venus were much more Earth-like and far more conducive to life than they are on Venus today. A liquid-water ocean and significant atmosphere are thought to have existed, and many of the processes that have been considered to be relevant to the origin of life on Earth could equally well have occurred on Venus. These include the formation of aqueous solutions of organic compounds that may have originated from meteoritic infall, atmospheric spark-synthesis, the mineral-catalyzed reduction of carbon dioxide or oxidation of methane, and hydrothermal synthesis in submarine vents. Even if life did independently arise on the surface of Venus, it is very clear that it must have eventually become extinct or migrated to the cloud environment as the runaway greenhouse effect heated up the surface of the planet and evaporated most of the volatiles, except for those that recondensed in the global cloud deck. Any life remaining in the cloud deck would have had to adapt to conditions that do not overlap the range of conditions inhabited by life on Earth. Consequently, considerations of a possible origin of life on Venus are not relevant to considerations of the possibility that life currently exists on the surface of Venus or that living organisms of Earth origin could survive there. The origin of life within the Venus cloud deck must be considered to be highly improbable. While in principle a living cell could maintain an intracellular environment of neutral pH, higher free-water concentration, and higher ionic strength than that persisting in the sulfuric acid droplet within which it exists, little in the way of protection from these harsh conditions will be available to molecules constituting a newly emerged, minimal self-replicating 12C.S. Cockell, “Life on Venus,” Planetary and Space Science 47: 1487-1501, 1999.

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0 Space Studies Board Annual Report—006 system. It seems therefore inevitable that cells would be quickly destroyed (or not exist in the first place) rather than continue to replicate. In principle, life in the Venus ocean could have been transported to the clouds and then persisted there after the point at which life on the surface became impossible and even until the present day. While this hypothesis overcomes the problems inherent in an origin of life within the clouds, it does not overcome the formidable problems that would face an organism living in this hostile environment, which include the following: • The extremely acidic, dehydrating, and oxidizing environment of the cloud droplet environment, which will lead to the destruction of organic matter; • The very high energetic cost of recruiting water from concentrated sulfuric acid; • The high temperatures of the droplets at the cloud base, through which all droplets inevitably cycle; • The lack of persistence of individual droplets, which have a probable life span of months to, at most, a few years; • The loss of nonvolatile elements that fall to the surface of Venus; and • The absence of biogenic elements that do not have volatile forms (e.g., Na, Mg, K, Ca, Mn, Fe, and most other metals). Although these elements could be introduced into the atmosphere by volcanic eruptions and by meteoritic infall, there is no obvious mechanism by which they could become widely distributed among all cloud droplets. Survival of Earth-Life on Venus The identification of extremophiles on Earth has expanded knowledge of the physicochemical limits at which life as we know it can exist. Organisms have been shown to grow at temperatures as high as 121°C,13 in chronic radiation fluxes of 60 gray/hour,14 in extreme pressures at the bottom of oceans, and in acidities as extreme as pH 0.15 However, none of these extreme but life-supporting environments approaches the severity of surface and atmospheric conditions present on Venus. In particular, the ambient surface and atmospheric conditions on Venus render all currently known extremophilic phenotypes on Earth irrelevant. Concentrated sulfuric acid is sterilizing for all known organisms. Thus, genetic and other physiologic determinants necessary for life on Earth could not function on Venus, nor would biological determinants that evolved on Venus be expected to function on Earth. Planetary Protection Issues Past planetary protection studies have repeatedly addressed the importance of a scientifically sound assessment of what is known and a conservative approach to the unknowns. In the case of Venus, there are many unknown de- tails, particularly about the past, but also about present conditions. In its deliberations, the task group found that the known aspects of the present-day environment offer compelling arguments against there being significant dangers of forward or reverse biological contamination, regardless of the unknowns. Individual points, discussed in more detail elsewhere, merit emphasis. In particular, it is not necessary to know whether life is present in the atmosphere of Venus to conclude that no terrestrial life would be capable of persisting, much less replicating, in any of Venus’s extant atmospheric regimes. The dominant factor in this assessment is the concentration of sulfuric acid (and cor- responding lack of free water) in cloud droplets in Venus’s atmosphere. No region of present atmospheric models is even close to habitable by life carried from Earth. In terms of chemical contamination of Venus biosignatures by terrestrial material, organic material delivered to the surface of Venus will be rapidly destroyed. Biogenic material deposited in the planet’s atmosphere will be either destroyed in situ or eventually (on the timescale of years) carried to lower atmosphere levels, where it will be destroyed. Thus, without biological replication, forward contamination with biomarkers is not a significant issue. The reverse cannot be demonstrated, but is also hard to escape; life consistent with the environmental conditions in the atmosphere of Venus is not going to find a corresponding niche on Earth. The closest equivalent might be acid 13K. Kashefi and D.R. Lovley, “Extending the Upper Temperature Limit for Life,” Science 301: 934, 2003. 14A. Venkateswaran, S.C. McFarlan, D. Ghosal, K.W. Minton, A. Vasilenko, K. Makarova, L.P. Wackett, and M.J. Daly, “Physiologic Deter- minants of Radiation Resistance in Deinococcus radiodurans,” Applied Enironmental Microbiology 66: 2620-2626, 2000. 15K. Edwards, P. Bond, T. Gihring, and J. Banfield, “An Archaeal Iron-Oxidizing Extreme Acidophile Important in Acid Mine Drainage,” Science 287: 1796-1799, 2000.

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 Short Reports mine drainage sites, which can be extremely acidic. However, even these sites are much less acidic than any portion of the Venus atmosphere. In addition, the acid mine drainage sites are generally characterized by extremely high metal-ion concentrations. Venus’s clouds, while apparently containing some metallic contaminants, remain poorly characterized in terms of composition and certainly do not possess these high metal-ion concentrations. In terms of metal content, some terrestrial acidic fumaroles or solfataras might be a better match, but none comes close to the acidity of the Venus environment. Venus’s Environment Our best current understanding of the origin and evolution of Venus suggests that Venus formed with much more water than it has at present, although the water abundance is not well constrained. Venus probably possessed liquid- water oceans during its early evolution, before the main-sequence evolution of the Sun led to warming and the loss of the oceans owing to a moist greenhouse atmosphere, photodissociation of water, and the subsequent thermal and nonthermal escape of hydrogen. The lifetime of Venus’s oceans is not known or well constrained but may have been as short as a few hundred million years or as long as several billion years. When the oceans were lost and the surface temperature rose, the potential for life as we know it was completely destroyed on the surface of Venus. The only remaining habitable niche would then have been the clouds. Current understanding of the chemistry and formation of the clouds indicates that the persistence of the global cloud deck depends on continuing surface volcanic activity, as SO2 is outgassed and oxidized to SO3, which reacts with water vapor to form sulfuric acid. If volcanic activity ceases, the clouds will be destroyed in roughly 30 million years, as atmospheric SO2 is destroyed by reaction with surface minerals. It is not clear whether or not the surface has been continuously volcanically active, and therefore it is not clear whether or not the clouds have persisted throughout the history of the planet. There may well have been periods when Venus was entirely cloud free. If this has occurred, any cloud-based microbial ecology would have been permanently extinguished. Life in Venus’s Atmosphere The clouds occupy the “Earth-like” part of Venus’s atmosphere, with pressures ranging from 2 bar to 10 mbar and temperatures ranging from ~240 to 390 K. Water vapor ranges from a few parts per million at the top of the cloud deck to a few tens of parts per million at the base. However, the cloud droplets are formed of extremely concentrated sulfuric acid, with weight percents ranging from 85 percent at the top of the cloud deck (with a slight dip to 82 percent within the upper cloud layer) to 98 percent at the bottom of the lower cloud layer. At these concentrations, the molar ratio of H2SO4 to H2O is ≥ 1, so that all water is protonated (H3O+) and tightly bound to the sulfuric acid. Such concentrations dehydrate and oxidize organic compounds. There is also a high flux of ultraviolet radiation throughout the cloud deck of Venus. The likelihood that life exists in the cloud deck is impossible to assess, given the complete lack of knowledge of the prospects of life in nonterrestrial environments. It has been suggested that some form of life may have evolved that takes advantage of the ultraviolet energy or the chemical disequilibria in the cloud-level gases, which include the coexistence of H2 and O2, as well as sulfur in varying oxidation states, including H2S and SO2. Such a cloud-based microbial biosphere, if it exists, would need to have evolved mechanisms for surviving in extremely acidic conditions that are unknown in any natural environment on Earth. Given the requirement for adaptation to this extreme environment, such or- ganisms would not have the capacity to survive in the very different conditions found on Earth, as they would have experienced no selective pressure to evolve (or retain) such capacity. PLANETARY PROTECTION CONSIDERATIONS In accordance with international treaty obligations, NASA maintains a planetary protection policy to avoid the cross-contamination of Earth and extraterrestrial bodies by spaceflight missions (see Attachment 2). NASA develops implementation regulations based on recommendations from both internal and external advisory groups, but most notably these regulations have been developed on the basis of recommendations provided by the National Research Council. Historically, constraints on missions—where deemed necessary—have ranged from the cleaning of a spacecraft to reduce its surface bioburden to the heat sterilization of an entire spacecraft prior to launch. In addition, there

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 Space Studies Board Annual Report—006 may be constraints on spacecraft orbits and operating procedures, requirements for the inventory and archiving of samples of the organic constituents of the spacecraft, and the need to document the locations of landing sites and impact points. NASA has a clear need to obtain external guidance on the planetary protection requirements for Venus missions that is based on a careful assessment of the most recent planetological and biological information. Without such guidance, NASA cannot provide the appropriate guidelines to mission designers, nor can it establish operational procedures for future Venus missions. NASA states that its planetary protection policy serves the following goals: • To preserve planetary conditions for future biological- and organic-constituent exploration; and • To protect Earth and its biosphere from potential extraterrestrial sources of contamination. Obligations imposed by the United Nations’ Outer Space Treaty16 mandate that spacecraft missions be conduct- ed in such a way as to minimize the inadvertent transfer of living organisms from one planetary body to another. CONCLUSIONS AND RECOMMENDATIONS The cloud layers in the atmosphere of Venus provide an environment in which the temperature and pressure are similar to surface conditions on Earth. However, the chemical environment in the clouds, and specifically in the cloud droplets, is extremely hostile. The droplets are composed of concentrated (82 to 98 percent) sulfuric acid formed by condensation from the vapor phase. As a result, free water is not available, and organic compounds would rapidly be destroyed by dehydration and oxidation. Therefore, any terrestrial organisms having survived the trip to Venus on a spacecraft would be quickly destroyed. It is not possible to demonstrate conclusively that a spacecraft returning to Earth after collecting samples of Venus’s surface and atmosphere will not come into contact with hypothetical aerial life forms and inadvertently carry them back to Earth; however, this has to be considered an extremely unlikely scenario. At any rate, any life forms that had adapted to living in the extremely acidic envi- ronment of Venus’s cloud layer would not be able to survive in the environmental conditions found on Earth. No special procedures are warranted beyond those required to maintain the sample integrity necessary for scientific studies of the returned samples. Conclusions The task group’s assessment of the likely planetary protection implications of Venus missions is as follows: • Landers—The prospects for indigenous biological activity on or below Venus’s surface are negligible owing to the high temperature of the surface, the absence of water, and the toxic chemical environment.17 Similarly, the prospects for the survival of terrestrial organisms deposited by probes on Venus’s surface are nonexistent. There- fore, the task group concluded that no significant risk of forward contamination exists in landing on the surface of Venus. • Atmospheric probes, including balloons—Venus’s cloud layers are an environment of moderate temperature and pressure. However, because the cloud droplets consist of concentrated sulfuric acid, any terrestrial organisms would be rapidly destroyed by chemical degradation. Therefore, the task group concluded that no significant forward-contamination risk exists regarding the exposure of spacecraft to the clouds in the atmosphere of Venus. • Surface or atmospheric sample returns from Venus to Earth—The task group discussed in detail the recent arguments for the potential for life in the Venus cloud decks. Although it is impossible to completely rule out the possibility that life might exist in such an environment, the task group considers this possibility to be extremely low because of the hostile chemical nature of the cloud environment. Specifically, concentrated sulfuric acid is a strong dehydrating and oxidizing agent that causes the rapid destruction of complex organic molecules. And, conversely, 16United Nations, Treaty on Principles Goerning the Actiities of States in the Exploration and Use of Outer Space, Including the Moon and Other Celestial Bodies, U.N. Document No. 6347, United Nations, New York, N.Y., January 1967. 17National Research Council, Ealuating the Biological Potential in Samples Returned from Planetary Satellites and Small Solar System Bodies: Framework for Decision Making, National Academy Press, Washington, D.C., 1998, pp. 31 and 77.

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 Short Reports any organisms that had managed to adapt to such a chemical environment would not find a comparable environment on Earth and would not be expected to survive. Therefore the risk to Earth posed by organisms indigenous to Venus is considered to be negligible. Therefore, the task group concluded that no significant back-contamination risk exists concerning the return of atmospheric samples from the clouds in the atmosphere of Venus. Similarly, no significant risk exists concerning back contamination from Venus surface sample returns. Recommendations In light of the above conclusions, the task group recommends that the Category II planetary protection classification of Venus be retained. Although there are many important scientific investigations to be carried out to improve understanding and knowledge of Venus, the task group does not recommend any scientific investiga- tions for the specific purpose of reducing uncertainty with respect to planetary protection issues.

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 Space Studies Board Annual Report—006 6.2 A Review of NASA’s 2006 Draft Science Plan On September , 006, A. Thomas Young, Chair of the Ad Hoc Committee on Reiew of NASA Science Mission Directorate Science Plan sent the following letter to Mary Cleae, NASA’s Associate Administrator for the Science Mission Directorate. In your letter of April 12, 2006, to Space Studies Board (SSB) Chair Lennard Fisk, you requested that the Space Studies Board conduct a review of the Science Mission Directorate’s (SMD’s) draft Science Plan1 and provide its assessment and recommendations for how the draft might be improved. You asked for comments in the following areas: • Responsiveness to National Research Council (NRC) recommendations in recent reports; • Attention to interdisciplinary aspects and overall scientific balance; • Utility to stakeholders in the scientific community; and • General readability and clarity of presentation. In response to your request, the ad hoc Committee on Review of NASA Science Mission Directorate Science Plan was established and met July 11-13, 2006, in Washington, D.C., to review the draft Science Plan. This report discusses the committee’s findings and offers related recommendations. The committee found the draft Science Plan to be an informative document demonstrating that a major NASA objective is to conduct scientific research to advance the fundamental understanding of Earth, the solar system, and the universe beyond. Some portions of the plan, such as that concerning astrophysics, do a truly excellent job of outlining why NASA carries out its science missions. The committee also found that the draft plan outlines a defensible set of rules for prioritizing missions within each of SMD’s discipline divisions, and it believes that SMD has made a serious effort to base its plans on the mis- sion priorities established by the scientific communities that undertake and benefit from the missions that NASA conducts. Many of these priorities were established in NRC reports such as the decadal surveys, NASA’s respon- siveness to which the committee evaluates in the attached report. Historically, NASA has benefited from the advice provided by its several scientific advisory structures, and their health is vital to the agency’s success in implementing its mission. Although NASA was asked by Congress to develop a single prioritized list for missions across all four science disciplines (astrophysics, Earth science, heliophysics, and planetary science), for various reasons outlined in the report the committee does not believe that NASA should or could produce a prioritized list across disciplines at this time. However, the committee does have some concerns about the draft plan. The committee found that the lack of a comparison of the current plan to plans produced in 2003 obscured the fact that NASA’s space science plans have been significantly scaled back due to budget changes, and it recommends that NASA include a comparison between the current plan and those produced in 2003 for the Earth and space sciences. The committee further notes that the NRC’s recent report An Assessment of Balance in NASA’s Science Pro- gram2 is largely neglected in the draft Science Plan. Although the NRC report was released shortly before the completion of the draft Science Plan, NASA representatives informed the committee that they had sufficient time to consider it. The committee acknowledges that the draft plan is based on the assumptions contained in the FY 2007 budget request and that the Balance report was critical of the adequacy of the budget to accomplish the total NASA plan. Nevertheless, the committee believes that the Balance report’s recommendations are worthy of consideration and, where appropriate, incorporation in the NASA Science Plan. The committee found that the current plan overemphasizes mission-specific work at the expense of strategies and steps for achieving goals in mission-enabling areas such as research and analysis, maintaining the Deep Space 1NASA Science Plan, Draft 3.0, June 23, 2006. 2National Research Council, An Assessment of Balance in NASA’s Science Programs, The National Academies Press, Washington, D.C., 2006.

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 Short Reports Network, and technology development. In addition, the committee noted that the draft plan often declares an inten- tion to implement a program or identifies a goal or mission as a top priority, but then does not indicate what steps NASA will take to achieve the goals or what strategies it will pursue to accomplish its priorities. The committee is concerned about the problem of mission cost growth and believes that if it is not successfully addressed, NASA will face the possibility of having to abandon either flagship missions or the ability to execute a balanced program. Mission cost growth and other factors identified in the attached report threaten the execution of the NASA Science Plan. The committee believes that addressing the issue of executability is a prerequisite for confidently defining a robust Science Plan, and it offers several recommendations on this subject. The committee recognizes that NASA is awaiting the forthcoming NRC decadal survey on Earth sciences. How- ever, the committee wishes to express its concerns about recent developments in Earth science, particularly recent decisions concerning the National Polar Orbiting Environmental Satellite System (NPOESS) program, whereby climate science instruments were deleted from the satellites. Many of these instruments are crucial to understanding the changing Earth system, and a strategy is needed to deal with their deletion from NPOESS. By design, the draft plan addresses only those science programs that are conducted by SMD. The committee notes that an appreciation of the full extent of NASA’s science activity requires a look at a number of programs outside SMD, in particular, the lunar precursor and robotic program, and the life and microgravity science activities within the Exploration Systems Mission Directorate (ESMD). The committee understands that Congress directed NASA to produce a Science Plan only for SMD. The committee concludes that the document would be improved if the introduction made clear the boundaries of the Science Plan’s scope and also acknowledged that science is performed elsewhere within NASA as well, and the extent to which these other science programs are sensibly complementary to those within SMD. Some of the committee’s recommendations are broad and apply to all four of SMD’s science disciplines, but the difficulties underlying the committee’s concerns are more acute in some disciplines than in others. For example, the problems associated with controlling mission cost growth and preserving proper balance between large and small missions are now particularly pressing in astrophysics and, prospectively, in planetary science. The need to develop strategies for meeting future computing and modeling capabilities is particularly noticeable for Earth science and heliophysics. In addition, although the committee makes discipline-specific recommendations for the planetary and Earth sciences, it stresses that the astrophysics and heliophysics sections of the draft plan are also addressed in the more general recommendations and require equal attention. The committee’s recommendations on the implementation and viability of the draft NASA Science Plan follow: 1. The NASA Science Plan should compare the key aspects of its 2003 Earth and space science plans with the 2006 plan in a list or table that shows how the current plan differs from the previous ones. This comparison would also provide some indication of the starting point for the new Science Plan, and the changes that have occurred since 2003. 2. NASA/SMD should provide some indication of the strategy it will use to determine how critically needed technologies will be developed for future missions and their proposed timescales. The committee recommends that NASA outline a strategic technology plan, providing an indication of the resources needed and the schedule that must be met to enable the ambitious goals of the plan. But NASA should also seek to protect general R&A funding from encroachment by technology R&A. 3. The NASA Science Plan should explicitly address realistic strategies for achieving the objectives of the mission-enabling elements of the overall program. The committee recommends that NASA: a. Undertake appropriate studies through its advisory structure in order to develop a strategic approach to all of its R&A programs (this strategy should include metrics for evaluating the proper level of R&A funding relative to the total program, the value of stability of funding levels in the various areas, and metrics for evaluat- ing the success of these programs); and b. Develop a strategic plan to address computing and modeling needs, including data stewardship and in- formation systems, which anticipates emergent developments in computational sciences and technology, and displays inherent agility. 4. NASA should improve mechanisms for managing and controlling mission cost growth so that if and when it occurs it does not threaten the remainder of the program, and should consider cost-capping flagship missions.

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6 Space Studies Board Annual Report—006 Although NASA already does seek to manage and control mission cost growth, these efforts have been inadequate and the agency needs to evaluate them, determine their failings, and improve their performance. NASA should undertake independent, systematic, and comprehensive evaluations of the cost-to-complete of each of its space and Earth science missions that are under development, for the purpose of determining the adequacy of budget and schedule. 5. NASA/SMD should move immediately to correct the problems caused by reductions in the base of research and analysis programs, small missions, and initial technology work on future missions before the essential pipeline of human capital and technology is irrevocably disrupted. 6. For planetary science, the committee recommends as follows: a. NASA/SMD should incorporate into its Science Plan relevant recommendations from the NRC interim report on lunar science,3 when they are available, in such a way as to maintain the overall science priorities advocated by previous NRC studies, while recognizing that science advice will change as scientific understand- ing and technology improve. b. Although Mars should remain the prime target for sustained science exploration, the NASA Science Plan should acknowledge that missions to other targets in the solar system should not be neglected. c. Where the question of habitability (i.e., the ability of a planet to support life) is determined to be the main focus for exploration, a proper hierarchy of scientific goals and objectives should be developed, stronger pathways between the concept of habitability and proposed missions should be articulated and maintained, and basic discovery science should not be ignored. d. Life detection techniques should be clearly identified as an astrobiology strategic technology develop- ment area. 7. For Earth science, the committee recommends as follows: a. NASA/SMD should incorporate into its Science Plan the recommendations of the NRC Earth science decadal survey interim report,4 and should incorporate the recommendations of the Earth science decadal survey final report when it is completed. b. NASA/SMD should develop a science strategy for obtaining long-term, continuous, stable observations of the Earth system that are distinct from observations to meet requirements by NOAA in support of numerical weather prediction. c. NASA/SMD should present an explicit strategy, based on objective science criteria for Earth science observations, for balancing the complementary objectives of (i) new sensors for technological innovation, (ii) new observations for emerging science needs, and (iii) long-term sustainable science-grade environmental observations. The committee elaborates on its findings and recommendations in the attached report. Signed by A. Thomas Young, Chair of the Ad Hoc Committee on Reiew of NASA Science Mission Directorate Science Plan 3National Research Council, The Scientific Context for the Exploration of the MoonInterim Report, The National Academies Press, Washington, D.C., 2006. 4National Research Council, Earth Science and Applications from Space: Urgent Needs and Opportunities to Sere the Nation, The National Academies Press, Washington, D.C., 2005.

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 Space Studies Board Annual Report—006 The committee finds that the Science Plan is responsive to the NRC decadal surveys, with the notable exception that the mission-enabling elements, which are critical to an integrated science plan, are much less integrated and emphasized than the missions themselves. The NASA FY 2007 budget request, upon which the draft Science Plan is based, illustrates the pitfalls of addressing budgetary shortfalls without also considering the relative benefits of mission-specific and mission-enabling programs. Although NASA is primarily a mission-based agency, supporting activities that involve building and maintaining the technology, workforce, and scientific infrastructure necessary to ensure the success of these missions are essential, as pointed out in the NRC Balance report. The committee recom- mends that the mission-enabling elements important to the integrated plan receive greater emphasis in the NASA Science Plan. The agency should review the decadal surveys, and particularly the Balance report, for further guid- ance on the importance of mission-enabling elements. The committee acknowledges the difficulty that the agency faces in determining the proper levels of R&A funding and addresses them in the section titled “Balance” in this report, including offering a recommendation about the need to determine proper levels of R&A.9 The committee does note, however, that although Mars Sample Return was rated as a top priority in the plan- etary decadal survey, it is mentioned only once in the draft Science Plan, and only in reference to planetary protec- tion, not as an actual planned mission. Although the Science Plan is generally responsive to the decadal surveys, there is one notable exception. The NRC released an interim report for its Earth sciences decadal survey over a year ago. As already noted, with the exception of the reinstatement of the Glory mission, the draft Science Plan does not reflect the recommendations made in this interim report. The draft plan responds well to other recent NRC reports, and the committee commends NASA for this. Ex- amples include the instigation of the decadal survey for Earth sciences and applications from space, recommended by the NRC in 2003.10 The agency also adopted 2005 NRC advice to conduct senior reviews of extended Earth observing missions to determine if such missions were worth continuing or had outlived their usefulness.11 The committee commends NASA for responses by the agency to issues raised in previous recent NRC reviews of NASA science plans. Two prior reviews of Space Science Enterprise plans12 and the 2003 review of the Earth Science Enterprise plan all cited the lack of explicit discussion of priorities and resources in those plans as weaken- ing their utility for decision making.13 The 2006 NASA Science Plan does address explicit priorities for spaceflight missions, and it does indicate that the plan is based on budget projections outlined in NASA’s FY 2007 budget re- quest. While the committee remains concerned about aspects of these elements of the Science Plan, it nonetheless applauds the fact that NASA has included priorities and relationship to the budget as key features of the plan. In 2003, the NRC assessment of NASA’s Space Science Enterprise strategy’s balance of astrobiology across the enterprise’s scientific themes expressed concern that the search for life had been referred to in many places in the strategy but lacked any real scientific substance. The current draft Science Plan does a better job of integrating the subject into the two most relevant discipline areasastrophysics and planetary exploration. Notably, the draft does not overstate the role of astrobiology as a scientific driver in these two discipline areas. However, the committee be- lieves that further refinements are possible. These are discussed in greater detail in the next section of this report. The 2005 NRC report Science in NASA’s Vision for Space Exploration emphasized the need for better inte- gration of NASA’s science program and the objectives of the Vision for Space Exploration. The committee notes that this is a challenging objective and that the agency has made good progress by evaluating science programs in terms of how they support the agency’s broad science mission. The committee applauds this approach. However, the committee finds that in some areas the integration of science objectives into the exploration program remains ambiguous and could be improved. The committee further notes that the NRC’s Balance report is largely neglected in the draft Science Plan. The committee acknowledges that the plan is based on the assumptions contained in the FY 2007 budget request and that 9The decadal surveys refer to the importance of mission-enabling programs. For example, see: “The committee emphasizes that telescopes alone do not lead to a greater understanding of the universe. . . . The committee recommends a vigorous and balanced program of astrophysical theory, data archiving and mining, and laboratory astrophysics.” Astronomy and Astrophysics in the New Millennium, National Academy Press, Washington, D.C., 2001, p. 96. 10National Research Council, “Assessment of NASA’s Draft 2003 Earth Science Enterprise Strategy,” letter report, 2003. 11National Research Council, Extending the Effectie Lifetimes of Earth Obsering Research Missions, The National Academies Press, Washington, D.C., 2005. 12National Research Council, “On the Space Science Enterprise Draft Strategy Plan,” letter report, 2000; National Research Council, “As- sessment of NASA’s Draft 2003 Space Science Enterprise Strategy,” letter report, 2003. 13National Research Council, “Assessment of NASA’s Draft 2003 Earth Science Enterprise Strategy,” letter report, 2003.

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 Short Reports the Balance report was critical of the adequacy of the budget to accomplish the total NASA plan. The committee believes that the Balance report’s recommendations are worthy of consideration and, where appropriate, incorpora- tion in the Science Plan. This aspect is discussed in greater detail in the next section of this report. The committee found no rationale for the agency’s allocation of R&A funding, or the fraction devoted to tech- nology development, computational capabilities, modeling, and data analysis. Both in the summary chapters and in the various discipline chapters, the Science Plan emphasizes the need for R&A, suborbital, and facilities programs. There is a clear description of the intrinsic role of these programs as mission enablers and as cost-effective methods for achieving science and technology advances. This aspect of the draft Science Plan is completely consistent with the recommendations of numerous NRC documents such as the recent Balance report, and with the recommenda- tions of every NASA-commissioned community roadmap. What the draft plan does not do is outline how NASA will prioritize the programs in terms of budgets, or how it will achieve its goals in these areas. The committee recommends that the NASA Science Plan explicitly address realistic strategies for achieving the objectives of the mission-enabling elements of the program. 3 ATTENTION TO INTERDISCIPLINARY ASPECTS AND OVERALL SCIENTIFIC BALANCE Some of NASA’s scientific projects are, such as Mars exploration, are significantly more interdisciplinary than others, or cross administrative boundaries. Often it is difficult to conceptualize, prioritize, communicate, and budget for these projects because of the problems of crossing divisions within NASA, government organizations, and sci- entific disciplines. Although many of NASA’s scientific undertakings are interdisciplinary, the committee identified three areas of NASA’s science planning that are particularly challenging because of their interdisciplinary nature and/or the fact that they also cross administrative (i.e., bureaucratic) boundaries: lunar exploration, astrobiology, and Earth sciences. The committee believes that all three need additional attention within the draft Science Plan. Lunar Science Chapter 8 of the draft Science Plan, “Science Enabling & Enabled by Human Exploration,” states that SMD and ESMD are “working closely.” However, based on statements made by NASA officials at the committee’s July meeting, it appears to the committee that enhanced consultation and communication between the two directorates are needed to optimize the broader science benefits that could be derived from these ESMD exploration-related, and potentially science-related, activities. The committee notes that Chapter 8 of the Science Plan is especially general and lacks specifics on how NASA intends to incorporate science into the agency’s lunar exploration plans. Robotic lunar missions currently planned by NASA are the responsibility of ESMD because such investigation has as its primary purpose the characterization of the lunar environment in preparation for eventual human activity on the surface of the Moon. However, given that one of the goals of the Vision for Space Exploration is “to advance U.S. scientific . . . interests,” the science community should have the same opportunity to influence the planning and prioritization of ESMD’s exploration science activity as it has to influence other space science activity conducted by NASA. The committee is pleased to see that NASA has requested that the NRC identify science opportunities and establish priorities for exploration-enabled science activities on the Moon.14 That committee will produce an interim report by fall 2006 and a final report in 2007. The committee supports this planning activity as a means to improve the science benefits of NASA’s exploration activity. The committee recommends that NASA incorporate relevant recommendations from the NRC interim report on lunar science into its Science Plan in such a way as to maintain the overall science priorities advocated by previous NRC studies, while recognizing that sci- ence advice will change as scientific understanding and technology improve. Astrobiology Astrobiology crosses multiple disciplines, creating unique challenges for science management, especially in terms of mission prioritization. Thus, the planetary section of the draft Science Plan emphasizes assessing “habit- 14National Research Council, The Scientific Context for the Exploration of the MoonInterim Report, The National Academies Press, Wash- ington, D.C., 2006.

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 Space Studies Board Annual Report—006 ability” in the solar system. Habitability is loosely defined by the astrobiology community as the ability of a planet to support life, based on the presence of the key requirements: water, nutrients, and energy. NASA’s exploration of Mars is focused on the search for evidence of life, and this issue is important for future missions to Europa and eventually to Titan and Enceladus. In the astrophysics chapter of the plan, astrobiology is presented in a narrower contextexploring the habitable zones around other stars, primarily through missions like the Terrestrial Planet Finder (TPF) and the Space Interferometry Mission (SIM). The draft plan discusses the astrobiology field largely in the context of solar system exploration, although it acknowledges the importance of astrobiology as a driver in other disciplines. In the draft Science Plan, astrobiology is highlighted in a text box at the end of the planetary science chapter. The committee believes this presentation un- deremphasizes the interdisciplinary nature of astrobiology and sets limiting boundaries that are inconsistent with the actual subject matter. The committee notes, for instance, that even subjects that appear to have no direct connection to astrobiology can be relevant to the field. For instance, lunar studies can provide information on the impact flux of asteroids in the early solar system and therefore the hazards they present to the formation of life. The committee suggests that the draft plan would be improved by the addition of an overarching section that includes a balanced discussion of the connections between astrobiology, planetary science, and astrophysics. In the present draft, this discussion would benefit from a deeper treatment of astrobiology as a science, its value as a unifying theme, and a few of the many scientific advances in this field since its inception over a decade ago. The draft plan does not mention or take account of NASA’s Astrobiology Roadmap, which is the primary source of information on the field and its scientific objectives, as defined by the community. The committee suggests that this roadmap be included in the Science Plan as a list or table.15 The text box in Chapter 6 of the draft plan asserts that while the Planetary Science Division provides the insti- tutional home for the core astrobiology R&A program, integrating its efforts, answers are pursued in the research programs and flight missions of “all four SMD Divisions.” The committee could find no explicit mention of astro- biology programs or missions in the Earth science or heliophysics sections. In this context, it is worth noting that the NRC’s 2003 assessment of NASA’s science plan found no indication of how the Sun-Earth Connection program could advance the agency’s strategic goal to “understand the origin and evolution of life and search for evidence of life elsewhere.”16 Potentially strong links could be made through studies of the origin and evolution of terrestrial life, both of which are active research areas in astrobiology. For example, access to the historical record of climate change (a major focus of the Earth science enterprise), through studies of the fossil record and the impact of long- and short-term environmental changes on biosphere diversity and evolution, are logical connections. Such research is certainly consistent with current R&A efforts in evolutionary biology under the astrobiology program. Also worrisome is the omission of any discussion of the needs of astrobiology in the context of overall technol- ogy development goals, despite the implicit requirement to develop reliable approaches for life detection within the next 6 to 8 years in order to support proposed investigations of the Astrobiology Field Laboratory (launch of which is anticipated in 2016). Efforts to develop life detection technologies and protocols are in fact being funded under two key astrobiology technology development programsAstrobiology Science and Technology for Exploring Planets (ASTEP) and Astrobiology Science and Technology Instrument Development (ASTID). Neither program is mentioned in the draft. Indeed, there seems to be a general unawareness of the immaturity of the field of life de- tection and of the time required to develop and adequately test the technologies needed to actually explore for life elsewhere.17 The committee recommends that life detection techniques be clearly identified as an astrobiology strategic technology development area. Finally, although the draft plan raises the important topic of planetary protection, the area of backward contami- nation is insufficiently discussed, even though it could prove to be a serious consideration for future sample returns from Mars. The committee notes that the NRC recently published a report on planetary protection and Mars and encourages NASA to incorporate the recommendations of that report into the Science Plan.18 15Office of Space Science, National Aeronautics and Space Administration, “Astrobiology Roadmap,” Ames Research Center, Moffett Field, Calif., 1999. 16National Research Council, “Assessment of NASA’s Draft 2003 Space Science Enterprise Strategy,” letter report, 2003. 17National Research Council, Assessment of NASA’s Mars Architecture 00-06, The National Academies Press, Washington, D.C., 2006. 18National Research Council, Preenting the Forward Contamination of Mars, The National Academies Press, Washington, D.C., 2006.

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 Short Reports Earth Science Another example of interdisciplinary science within SMD is the field of Earth system science, which was initi- ated by NASA. Conceived in the 1980s and implemented in the 1990s with the Earth Observing System Interdis- ciplinary Science Program, Earth system science is uniquely suited to the global perspective of the interconnected nature of the atmosphere, oceans, land, cryosphere, and biosphere of our planet that Earth observing satellites provide. NASA is unique in this field. No other U.S. government agency has the discipline breadth, or requisite technological, observational, and modeling capabilities, to nurture and develop such an important field of science. Although still in its infancy, over the past 15 to 20 years Earth system science has produced new and significant insights of atmosphere-ocean, land-atmosphere, and physical-biogeochemical coupling and cycles. The committee believes that the draft Science Plan does not adequately explain or illustrate the impressive developments in this field. For instance, global altimeter, scatterometer, ocean color, and rain radar observations of phenomena such as El Niño were not possible until relatively recently. The Science Plan could incorporate this and other examples to illustrate the evolution from inconsistent and spot observations to the development of highly integrated, global views of the Earth system (e.g., 30 years of observations of sea ice concentration and extent or space-based observations of the ozone hole). NASA has been at the forefront of these developments, and the draft Science Plan should adequately reflect the agency’s impressive achievements. In short, the Earth science section does not provide the historical context for Earth remote sensing and does not appropriately capture the significance of NASA’s accomplishments to date in Earth remote sensing. The committee notes that the Earth science section of the draft plan appears to reflect less community input than other sections, and trusts that this will be rectified following publication of the Earth science decadal survey. The extraordinary progress in Earth system science has altered dramatically the capabilities and requirements to conduct leading-edge science and has unlocked a wealth of applications of immediate social relevance. Today scientists and Earth science stakeholders expect and depend on data for climate science and broader climate R&D applications. This has created a frequently unrecognized change in the types of data about Earth that satellites col- lect. In addition to requirements for data such as weather observations and “science” data, there is now a requirement for long time series of scientific observations. Traditionally NOAA has performed weather-related data collection and NASA has conducted scientific data collection. Today, however, the scientific community expects NASA to conduct long-term collection of scientific data that has no immediate use for decision making but is needed to study and understand natural climate fluctuations on interannual to decadal time scales, and is necessary for the develop- ment of integrated climate models, and thus requires long-term programmatic and funding commitments.19 Recent developments in the NPOESS program reflect the wide gap between community expectations for data collection and current plans. When NPOESS experienced severe development problems and cost overruns, the climate research and monitoring instruments were deleted from the NPOESS satellites whereas the weather instru- ments were preserved. Many of the instruments removed from NPOESS are crucial to understanding the changing Earth system, and some strategy is badly needed to deal with their elimination from NPOESS. Unless this is done, when the current fleet of Earth Observing System (EOS) satellites expires, there will be nothing to replace them. The Earth science portion of the draft Science Plan is relatively vague with respect to the strategy for pursuing Earth system science beyond the EOS era. It states that the program will “exploit the vast wealth of new data from EOS,” “promote interdisciplinary research . . . identified as emerging sciences areas in the Strategic Plan of the U.S. CCSP [Climate Change Science Plan],” and “pursue innovative interdisciplinary research in new topical areas.” These statements begin to convey what the agency will do and why. But they do not indicate how these goals will be achieved, or when they will be achieved. The draft NASA Science Plan lacks a strategy for an integrated synthesis of the ariety and olume of Earth obserations generated by NASA. The plan mentions but does not describe the unique modeling, prediction, and computational capabilities and requirements for Earth science. In addition, the plan lacks a science strategy for the deelopment of Earth system models and a discussion of a strategy for deeloping understanding to enable a predic- tie capability for the Earth system. Finally, the committee found no indication of NASA’s strategy for linking and crosscutting the six interdisciplinary science focus areas: atmospheric composition, carbon cycle and ecosystems, climate ariability and change, Earth surface and interior, water and energy cycle, and weather. The committee 19National Research Council, Climate Data Records from Enironmental Satellites: Interim Report, The National Academies Press, Washington, D.C., 2004, p. 95; National Research Council, Issues in the Integration of Research and Operational Satellite Systems for Climate Research: Part I. Science and Design, National Academy Press, Washington, D.C., 2000, pp. 8-9.

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6 Space Studies Board Annual Report—006 recommends that NASA begin immediately to develop a science strategy for obtaining long-term, continuous, stable observations of the Earth system that are distinct from observations to meet requirements by NOAA in support of numerical weather prediction. The committee recognizes that the Earth science decadal survey to guide NASA’s research priorities in this area will not be completed until the end of 2006 and that, at that time, the agency expects to incorporate decadal survey report recommendations into a revised Science Plan. However, other than the reinstatement of the Glory mission, the committee is troubled to see no reference in the current plan to the findings and recommendations in the Earth sciences decadal survey interim report that was issued more than one year ago. By addressing in the current Science Plan the recommendations from the interim report, NASA could establish the framework for accommodating the recommendations to come from the decadal survey. The committee is concerned that the draft Science Plan suggests that NASA is waiting for the expected decadal survey, when the agency needs a more coordinated effort to develop its Earth systems science strategy now. The Earth science fiscal situation has deteriorated since the interim report was released, specifically due to cuts to R&A programs, degradation of existing missions, and the current turmoil in the NPOESS program. NASA needs to have an observing strategy in Earth sciences that balances technological innovation (new sensors), emerging science needs (new observations), and the foundational requirements of long-term sustainable science-grade environmental observations. Balance The NRC report An Assessment of Balance in NASA’s Science Programs defined several different dimensions of “balance.” One key aspect is scientific balance, meaning that at least the minimum health of major scientific dis- ciplines is maintained so that each discipline can make progress toward its major scientific goals. A second dimen- sion involves balance between the support of ongoing programs and missions, on the one hand, and opportunities for new initiatives, capacity building, and longer-term scientific development, on the other. A third, particularly important, aspect of balance is the ability to sustain a mix of large, medium, and small programs and missions and a core program of research, data analysis, technology development, theoretical studies, and modeling. Scientific Balance With respect to scientific balance, the committee has not found any serious imbalance across the four major discipline areas. There are specific concerns within each discipline, which are addressed here, but no particular discipline area appears to be placed at a disadvantage with respect to the others; for instance, the disciplines receive generally similar levels of funding. Furthermore, the draft Science Plan correctly notes that each discipline area can look forward to making notable scientific progress over the period covered by the plan. Nevertheless, the committee has several concerns about scientific balance within the disciplines. Because fiscal realities do not allow NASA to maintain continuity in flagship missions, the small missions are increasingly im- portant. However, the mix of small missions in astrophysics and planetary science has been drastically curtailed, as has the opportunity to participate in foreign missions. Under the current plan the astrophysical community faces an extended period with no access to short wavelengths on NASA’s major instruments. Such gaps are probably unavoid- able, but when they have occurred in the past a strong program of international participation, supporting research, and technology development sustained a healthy community, ready to support the next major NASA mission when it finally took place. This makes the current loss of such balance particularly troubling at this time. In the past decade, planetary exploration has increasingly been divided into two parts, Mars exploration and exploration of the rest of the solar system. This has presented unique challenges for balancing efforts between these two areas. The committee notes that the NRC recently produced a report on the future of robotic Mars exploration and suggests that the Science Plan incorporate the recommendations of this report.20 The committee recommends that Mars should remain the prime target for sustained science exploration; the NASA Science Plan should acknowledge that missions to other targets in the solar system should not be neglected. Furthermore, the committee wishes to repeat the recommendations of the 2006 NRC report Reiew of Goals for 20National Research Council, Assessment of NASA’s Mars Architecture 00-06, The National Academies Press, Washington, D.C., 2006.

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 Short Reports NASA’s Space and Earth Sciences, which reviewed NASA’s science roadmaps, concerning the role that habitability should serve as an objective for exploration. The committee recommends that where habitability is determined to be the main focus for exploration, a proper hierarchy of scientific goals and objectives should be developed and stronger pathways between the concept of habitability and proposed missions be articulated and main- tained. The committee notes that basic discovery science should not be ignored in the Science Plan. As noted above in the discussion of interdisciplinary aspects of the plan, the Earth science section of the plan does not provide a strategy for ensuring that there will be continuity of measurements that will provide the long-term data sets needed for scientific studies of the Earth system, including climate. No strategy is provided for how such observations will enable prediction of the Earth system. Lastly, the funding situation and programmatic priorities permit only the next new start for an Earth System Science Pathfinder (ESSP), which is the small-mission compo- nent of the Earth science program, to be launched in 2014. Although two ESSP missions are currently in develop- ment, the nearly decade-long gap between the selection of new ESSP missions undercuts the entire purpose of the program, which was to produce missions rapidly, taking advantage of new scientific discovery. Balance Between Mission and Mission-Enabling Elements A second aspect of balance about which the committee has serious concerns relates to the balance between spaceflight missions and non-flight elements of the program, especially R&A. This problem was discussed at length in the Balance report, which found that under NASA’s FY 2007 budget request the proposed “cuts to the R&A grants program cause disproportionately large damage to the viability of the space sciences disciplines as well as to future programs.” Because the Science Plan is based on funding levels proposed in the administration’s budget for FY 2007-2011, including the proposed reductions in R&A and other small programs, the draft plan also suffers from the problems that are cited in the Balance report. These small programs are vital for the training and develop- ment of the scientific and engineering workforce. Furthermore, new technology development both enables future missions and makes them more cost-effective. Consequently, the committee fully concurs with the findings in the Balance report and reiterates that report’s recommendation that “NASA should move immediately to correct the problems caused by reductions in the base of research and analysis programs, small missions, and initial technology work on future missions before the essential pipeline of human capital and technology is irrevocably disrupted” (p. 3). While the draft Science Plan presents good arguments for the importance of these programs, it does not present a strategy for how they will be integrated into the overall program or how NASA will respond to concerns raised in the Balance report. Balance of Mission Sizes A third important balance issue in the plan relates to the mix of mission sizes and to problems that confront NASA over the feasibility of sustaining a properly mixed portfolio of mission sizes. In the plan, the Heliophysics and Planetary Sciences divisions have managed to maintain a degree of balance with respect to mission sizes—i.e., there are small and medium missions in the plan. However, the number of Explorer missions, which constitute the small mission component in astrophysics and heliophysics, and which are vital for training the scientists and engi- neers of the future, have been reduced substantially, creating problems that call into question the long-term health of the disciplines. As noted above, there is a similar problem with respect to opportunities for new ESSP missions in Earth science. The committee notes that the draft Science Plan makes almost no mention of suborbital and bal- loon programs. Perhaps the greatest current threat to the feasibility of a mixed portfolio of flight mission sizes is the cost of execution of currently approved missions. Cost growth for NASA’s large flagship missions has drawn considerable attention, but the problem has occurred across all mission sizes. SMD now faces a situation in which the overall balance of the program has been distorted by escalating costs for flight missions. The Balance report concluded that “the major missions in space and Earth science are being executed at costs well in excess of those estimated at the time when the missions were recommended in the National Research Council’s decadal surveys for their disci- plines. Consequently, the orderly planning process that has served the space and Earth science communities well has been disrupted, and balance among large, medium, and small missions has been difficult to maintain” (p. 3). This problem is especially acute in astrophysics, where the costs for the division’s two highest-priority missions—HST

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 Space Studies Board Annual Report—006 and JWST—and funding requirements for near-term missions such as SOFIA, GLAST, and Kepler are threatening the overall program balance. The longer-term implications of the mission cost growth problem are particularly alarming. If the problem is not successfully addressed, the committee beliees there are ery real prospects that SMD will be faced with haing to abandon either flagship missions or the ability to execute a balanced program. Therefore the committee fully concurs with and reiterates the recommendation of the Balance report that “NASA should undertake indepen- dent, systematic, and comprehensive evaluations of the cost-to-complete of each of its space and Earth science missions that are under development, for the purpose of determining the adequacy of budget and schedule” (p. 3). This assessment should be the first step in a strategy for resolving the current mission cost growth problem and ensuring that future missions can be executed within manageable costs, schedules, and content.21 The committee further recommends that NASA improve mechanisms for managing and controlling mission cost growth so that if and when it occurs it does not threaten the remainder of the program, and also that NASA consider cost-capping flagship missions. Although NASA already does seek to manage and control mission cost growth, these efforts have been inadequate and the agency needs to evaluate them, determine their failings, and improve their performance. The committee notes that a number of past missions have been successfully descoped. Examples include the Grand Tour (Voyager), the original Voyager (Viking), the Venus Orbiter Imaging Radar (Magellan), AXAF (Chandra) and SIRTF (Spitzer), where descoping and scientific reassessment were successfully used to control mission cost while preserving the most important science capabilities. As eloquently stated in the draft plan, SMD cannot achieve its stated objectives with missions alone. Additional programs are needed in order to provide necessary infrastructure for performing the missions and in order to real- ize the science advances that lead to and are derived from the missions. These mission-enabling components of the strategy include R&A programs, including supporting research and technology and suborbital investigations, that consist of regularly competed principal-investigator-led projects covering the whole range of SMD disciplines and science techniques (theory, data analysis, and instrumentation). The mission-enabling components include essential facilities, such as the Deep Space Network and other space communications systems. Essential facilities include information technology infrastructure, such as the virtual observatories for accessing and storing data, and compu- tational resources for analyzing the vast amounts of data gathered by the missions and for developing and running the models that are the expected products from the flight missions. Although the draft Science Plan contains impressive language about the importance of mission-enabling programs, the committee found that a number of crucial elements are missing from the draft Science Plan in the following areas: 1. The plan does not present a strategy for determining the size and adjustments to the R&A programs. The lack of such a strategy can lead to arbitrary and potentially damaging decisions such as the 15 percent cut to R&A in NASA’s FY 2007 budget submission. The committee notes that even small increases in data analysis budgets are frequently difficult to obtain, whereas the actual missions themselves are expensive and prone to cost increases that dwarf data analysis budgets. The committee recognizes that developing a strategy will require more time than is available for this particular Science Plan. The committee further recognizes that while past reports have called explicitly for such a strategy, this will be a difficult task for which there has been no specific guidance from previ- ous NRC or community reports concerning the optimum size for the mission-enabling programs.22 The committee recommends that NASA immediately undertake appropriate studies through its advisory structure in order to develop a strategic approach to all of its R&A programs. This strategy should include metrics for deter- mining the success of the programs. 2. The plan identifies a number of critically needed technologies for future missions (e.g., in the planetary, Earth sciences, and heliophysics sections), but it does not present a mechanism or schedule for achieving these technologies. It is not clear, for example, if the technologies are to be developed in the R&A program or via some 21A number of previous NRC reports have commented on the need for descoping and/or reprioritization of major missions (see National Research Council, “Review of Progress in Astronomy and Astrophysics Toward the Decadal Vision,” letter report, 2005; “Review of the Rede- signed Space Interferometry Mission,” letter report, 2002; and “Scientific Assessment of the Descoped Mission Concept for the Next Generation Space Telescope,” letter report, 2001). 22“The more the R&DA activities are integrated into the strategy and managed the implementation and evolution of the strategy, the stronger is the overall program.” National Research Council, Supporting Research and Data Analysis in NASA’s Science Programs: Engines for Innoa- tion and Synthesis, National Academy Press, Washington, D.C., 1998, p. 42.

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 Short Reports other dedicated technology program. The committee notes that placing technology development under R&A may lead to an erosion of the scientific R&A programs. The plan is unclear if technologies are being sought in an inte- grated SMD-wide manner, or are only being developed in each separate division. The committee recommends that NASA provide some indication of the strategy it will use to determine how critically needed technologies will be developed for future missions and their proposed timescales. The committee recommends that NASA out- line a strategic technology plan, providing an indication of the resources needed and the schedule that must be met to enable the ambitious goals of the plan. NASA should also seek to protect general R&A funding from encroachment by technology R&A. In addition, the committee notes that NASA support of technology development within the science program needs to be tightly coupled to evolving science needs. 3. The plan clearly identifies the need for extensive computational technologies and facilities in order to achieve the science and application goals. This is especially true for Earth science and heliophysics, which are working toward developing operational models, but the draft plan does not present a plan and a schedule for achieving them. The committee recommends that NASA develop a strategic plan to address computing and modeling needs, including data stewardship and information systems. 4. The plan identifies needed enhancements to communications infrastructure such as the Deep Space Network, but again no strategy is presented as to how these enhancements will be obtained. Finally, the committee notes that the launch rate for new missions continues to decrease, an indication of unhealthy trends for the overall program and a situation that the agency experienced before, in the 1980s. NASA faces the problem of rising launch costs, which is a situation that is largely beyond the agency’s control. These increases pose a serious threat to the overall science program. The committee endorses NASA’s efforts to address this problem. 4 UTILITY TO STAKEHOLDERS IN THE SCIENTIFIC COMMUNITY The committee believes that the NASA Science Plan will be useful to scientists and graduate students as a broad overview of the agency’s space science portfolio. However, scientists and graduate students are primary recipients of R&A funds, and it is therefore important that they understand the agency’s strategy for allocating R&A funds, something that is lacking in the current draft. Furthermore, the committee notes that if the Science Plan clearly indicates how cost overruns will be addressed in the future, this will provide clarity that will be useful to industry when developing spacecraft and developing cost estimates for projects. The committee believes that the draft Science Plan does not explain how NASA’s Science Mission Director- ate can partner with other government agencies to achieve its goals. For instance, the Department of Energy has some interests that overlap with NASA’s Beyond Einstein program. The Department of Defense and the National Reconnaissance Office have technology that has been adapted to scientific uses. The plan should acknowledge these resources in other government agencies and explain how SMD can make use of them. The committee commends the draft plan’s positive assessment of the benefits of international cooperation and the plan’s endorsement of playing both senior partner and junior partner NASA roles in international Earth and space science programs. International cooperation is not to be undertaken for its own sake, but rather where value is added to the NASA program and the benefits to be gained warrant the risks in taking on an external partner. The draft plan’s recognition of the importance of carefully selecting, structuring, and managing cooperative programs represents a balanced statement about the legal and policy issues that NASA faces. Joint planning can ideally lead to the coordination of national programs via the identification of synergies and the development of interdependencies among programs. The goal would be to minimize gaps and overlaps in discipline areas, while maximizing the leveraging among one another’s programs. All partners should be seeking to complement one another’s scientific work rather than duplicating it or competing with it. Historically, the launching of Explorer and Discovery missions has been frequent enough to accommodate missions of opportunity, which have often included international participation. If the interval between such oppor- tunities becomes too long, their utility as a mechanism for international involvement degrades, and an alternative

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0 Space Studies Board Annual Report—006 strategy needs to be identified in the plan. The committee encourages NASA to seek an alternative strategy to ac- complish such cooperation.23 5 GENERAL READABILITY AND CLARITY OF PRESENTATION The draft NASA Science Plan is a lengthy document, and it could benefit from an executive summary that concisely outlines the contents of the report. The committee suggests that the Science Plan include graphics such as roadmap timelines and checklists, in each of its four disciplines—astrophysics, Earth science, heliophysics, and planetary exploration. The committee suggests that the report include the NASA astrobiology roadmap as well. When discussing such a broad subject as NASA’s science goals and plans, it is necessary to provide the reader with information to make comparisons. The committee suggests that NASA include a chart comparing and defining the different size missions across disciplines. This chart could compare the cost ranges of missions such as Explorers (MIDEX and SMEX), ESSPs, Discovery, Scout, New Frontiers, and flagship missions. Furthermore, it would be useful to provide the reader with an indication of the average development times for these missions. The committee finds that the overall length of the Science Plan is appropriate, considering the amount of information that must be discussed. However, the committee recommends that the report strive to achieve a more uniform tone and quality of presentation. The astrophysics section does an especially good job at explaining the wonder of scientific discovery and the breadth of the program, and serves as an excellent model for the other chap- ters to emulate. During its July 2006 meeting, the SMD Heliophysics division representative presented a table indicating the decadal survey priorities for heliophysics. The committee recommends that each of the section chapters include such a table to give the reader easy access to the decadal priorities within the document. It would be helpful for the table to indicate the status of each decadal priority in the current Science Plan. 6 FINDINGS AND RECOMMENDATIONS Findings 1. The committee finds that the draft NASA Science Plan successfully demonstrates that a major NASA objec- tive is conducting scientific research to advance the fundamental understanding of the Earth, the solar system, and the universe beyond. Portions of the plan do an excellent job of outlining the reasons that NASA carries out sci- ence missions. The draft outlines a defensible set of rules for prioritizing missions within each of SMD’s discipline divisions. 2. The committee supports the plan’s treatment of priorities on a discipline-by-discipline basis and concludes that NASA should not or could not produce a prioritized mission list across disciplines. 3. In the committee’s view, the current draft plan overemphasizes mission-specific work at the expense of strategies and steps for achieving goals in mission-enabling areas. The value of space missions to the nation is not determined merely by successful launches, but by the scientific return from those missions. The research and analysis portion of the program is where the public receives its return on investment in the missions. The committee reiterates the findings in the Balance report and that report’s recommendation that “NASA/ SMD should move immediately to correct the problems caused by reductions in the base of research and analysis programs, small missions, and initial technology work on future missions before the essential pipeline of human capital and technology is irrevocably disrupted” (p. 3). 4. The draft Science Plan often declares an intention to implement a program or identifies a goal or mission as a top priority, but it does not indicate what steps it would take to achieve the goals or strategies it would pursue to accomplish its priorities. Based on recent NASA experience, the committee believes that unless the agency takes a stronger approach to managing program cost, risk, and schedule, the current Science Plan is not executable. Clear strategies are required to ensure that the plan can be executed, and in some cases these are missing. While some 23Seealso, National Research Council, Reiew of Goals and Plans for NASA’s Space and Earth Sciences, The National Academies Press, Washington, D.C., 2006.

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 Short Reports disciplines are in better shape in the plan than others, each division has some parts of its plan that cannot be executed in the manner that the draft Science Plan presents. If the problem of mission cost growth is not successfully addressed, the committee believes there are very real prospects that SMD will be faced with having to abandon either flagship missions or the ability to execute a balanced program. Therefore the committee fully concurs with and reiterates the recommendation of the Balance report that “NASA should undertake independent, systematic, and comprehensive evaluations of the cost-to-complete of each of its space and Earth science missions that are under development, for the purpose of determining the adequacy of budget and schedule” (p. 3). 5. The Science Plan lacks a strategy for an integrated synthesis of the variety and volume of Earth observations generated by NASA. The plan mentions but does not describe the unique modeling, prediction, and computational capabilities and requirements for Earth science. In addition, the plan lacks a science strategy for the development of Earth system models and a discussion of a strategy to develop understanding for enabling a predictive capability for the Earth system. Finally, the committee found no indication of NASA’s strategy for linking and crosscutting the six interdisciplinary science focus areas: atmospheric composition, carbon cycle and ecosystems, climate variability and change, Earth surface and interior, water and energy cycle, and weather. Recommendations Some of the committee’s recommendations are broad and apply to all four of SMD’s science disciplines, but the difficulties underlying the concerns reflected in the recommendations are more acute in some disciplines than others. For example, the problems associated with controlling mission cost growth and preserving proper balance between large and small missions are now particularly pressing in astrophysics. The need to develop strategies for meeting future computing and modeling capabilities is particularly noticeable for Earth science and heliophysics. In addition, although the committee makes discipline-specific recommendations for the planetary and Earth sciences, it stresses that the astrophysics and heliophysics sections of the draft plan are also addressed in the more general recommendations and require equal attention. The committee’s recommendations on the implementation and viability of the draft NASA Science Plan are as follows: 1. The NASA Science Plan should compare the key aspects of its 2003 Earth and space science plans with the 2006 plan in a list or table that shows how the current plan differs from the previous ones. This comparison would also provide some indication of the starting point for the new Science Plan, and the changes that have occurred since 2003. 2. NASA/SMD should provide some indication of the strategy it will use to determine how critically needed technologies will be developed for future missions and their proposed timescales. The committee recommends that NASA outline a strategic technology plan, providing an indication of the resources needed and the schedule that must be met to enable the ambitious goals of the plan. But NASA should also seek to protect general R&A funding from encroachment by technology R&A. 3. The NASA Science Plan should explicitly address realistic strategies for achieving the objectives of the mission-enabling elements of the overall program. The committee recommends that NASA: a. Undertake appropriate studies through its advisory structure in order to develop a strategic approach to all of its R&A programs (this strategy should include metrics for evaluating the proper level of R&A funding rela- tive to the total program, the value of stability of funding levels in the various areas, and metrics for evaluating the success of these programs); and b. Develop a strategic plan to address computing and modeling needs, including data stewardship and infor- mation systems, which anticipates emergent developments in computational sciences and technology, and displays inherent agility. 4. NASA should improve mechanisms for managing and controlling mission cost growth so that if and when it occurs it does not threaten the remainder of the program, and should consider cost-capping flagship missions. Al- though NASA already does seek to manage and control mission cost growth, these efforts have been inadequate and the agency needs to evaluate them, determine their failings, and improve their performance. NASA should undertake

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 Space Studies Board Annual Report—006 independent, systematic, and comprehensive evaluations of the cost-to-complete of each of its space and Earth sci- ence missions that are under development, for the purpose of determining the adequacy of budget and schedule. 5. NASA/SMD should move immediately to correct the problems caused by reductions in the base of research and analysis programs, small missions, and initial technology work on future missions before the essential pipeline of human capital and technology is irrevocably disrupted. 6. For planetary science, the committee recommends as follows: a. NASA/SMD should incorporate into its Science Plan relevant recommendations from the NRC interim report on lunar science,24 when they are available, in such a way as to maintain the overall science priorities advo- cated by previous NRC studies, while recognizing that science advice will change as scientific understanding and technology improve. b. Although Mars should remain the prime target for sustained science exploration, the NASA Science Plan should acknowledge that missions to other targets in the solar system should not be neglected. c. Where the question of habitability (i.e., the ability of a planet to support life) is determined to be the main focus for exploration, a proper hierarchy of scientific goals and objectives should be developed, stronger pathways between the concept of habitability and proposed missions should be articulated and maintained, and basic discovery science should not be ignored. d. Life detection techniques should be clearly identified as an astrobiology strategic technology develop- ment area. 7. For Earth science, the committee recommends as follows: a. NASA/SMD should incorporate into its Science Plan the recommendations of the NRC Earth science decadal survey interim report,25 and should incorporate the recommendations of the Earth science decadal survey final report when it is completed. b. NASA/SMD should develop a science strategy for obtaining long-term, continuous, stable observations of the Earth system that are distinct from observations to meet requirements by NOAA in support of numerical weather prediction. c. NASA/SMD should present an explicit strategy, based on objective science criteria for Earth science ob- servations, for balancing the complementary objectives of (i) new sensors for technological innovation, (ii) new ob- servations for emerging science needs, and (iii) long-term sustainable science-grade environmental observations. 24National Research Council, The Scientific Context for the Exploration of the MoonInterim Report, The National Academies Press, Wash- ington, D.C., 2006. 25National Research Council, Earth Science and Applications from Space: Urgent Needs and Opportunities to Sere the Nation, The National Academies Press, Washington, D.C., 2005.