1
Introduction

SCIENTIFIC AND PROGRAMMATIC BACKGROUND

The United States and the former Soviet Union have been sending spacecraft to Mars since the beginning of the space age.1 Indeed, as early as 1966, the exploration of Mars was highlighted as a priority target for NASA spacecraft.2 After several unsuccessful prior attempts, the Soviet Union achieved partial success when its Mars 1 spacecraft made a distant flyby of the Red Planet in 1963. A NASA spacecraft, Mariner 4, made the first successful close flyby of Mars in 1965 and returned images of the planet’s cratered surface. Numerous additional spacecraft were dispatched from both sides of the Cold War divide during the remainder of the 1960s and early 1970s. Although there were many failures on both sides, there were some notable firsts, included the first attempted landing (unsuccessful) by Mars 2 in 1971 and the first successful Mars orbiter, NASA’s Mariner 9, also in 1971. The culmination of this first era of Mars exploration was the successful landing of NASA’s Viking 1 and 2 on the martian surface in 1976. The twin landers, supported by twin orbiters, operated successfully for many years. Although the primary experiments on the landers were designed to search for evidence of life—a task that was unsuccessful—additional, non-biological experiments did return a treasure trove of scientific data. Nevertheless, Viking was widely regarded as a programmatic failure because the life detection experiments did not return evidence of life on Mars. The lack of clear positive results from the life detection experiments undercut political support for additional Mars missions in the United States until the launch of NASA’s Mars Observer in 1992. Perhaps the key lesson learned from the Viking experience was that the search for life on Mars should be undertaken only in the context of a comprehensive understanding of the origin and evolution of the martian environment. In the absence of a clear understanding of key parameters of the martian environment—e.g., the chemistry of the martian regolith—the design of biological experiments and the interpretation of the results from such experiments will be fraught with difficulties.

The failure of Mars Observer shortly before entering orbit about the Red Planet in 1993 led to a fundamental revision of NASA’s Mars exploration strategy. Rather than relying on large spacecraft with comprehensive, multidisciplinary payloads as was the case with Mars Observer, future missions would embody the faster-cheaper-better design philosophy. That is, missions would be smaller, would be more focused on a narrow set of scientific goals, and would be launched at every possible Mars launch opportunity. Mars Global Surveyor and Mars Pathfinder, both launched in 1996, were the first missions to embody this new approach.3 The programmatic and scientific success of both missions—combined with the political impetus fueled by claims of evidence of past life



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Assessment of NASA’s Mars Architecture 2007–2016    1 Introduction SCIENTIFIC AND PROGRAMMATIC BACKGROUND The United States and the former Soviet Union have been sending spacecraft to Mars since the beginning of the space age.1 Indeed, as early as 1966, the exploration of Mars was highlighted as a priority target for NASA spacecraft.2 After several unsuccessful prior attempts, the Soviet Union achieved partial success when its Mars 1 spacecraft made a distant flyby of the Red Planet in 1963. A NASA spacecraft, Mariner 4, made the first successful close flyby of Mars in 1965 and returned images of the planet’s cratered surface. Numerous additional spacecraft were dispatched from both sides of the Cold War divide during the remainder of the 1960s and early 1970s. Although there were many failures on both sides, there were some notable firsts, included the first attempted landing (unsuccessful) by Mars 2 in 1971 and the first successful Mars orbiter, NASA’s Mariner 9, also in 1971. The culmination of this first era of Mars exploration was the successful landing of NASA’s Viking 1 and 2 on the martian surface in 1976. The twin landers, supported by twin orbiters, operated successfully for many years. Although the primary experiments on the landers were designed to search for evidence of life—a task that was unsuccessful—additional, non-biological experiments did return a treasure trove of scientific data. Nevertheless, Viking was widely regarded as a programmatic failure because the life detection experiments did not return evidence of life on Mars. The lack of clear positive results from the life detection experiments undercut political support for additional Mars missions in the United States until the launch of NASA’s Mars Observer in 1992. Perhaps the key lesson learned from the Viking experience was that the search for life on Mars should be undertaken only in the context of a comprehensive understanding of the origin and evolution of the martian environment. In the absence of a clear understanding of key parameters of the martian environment—e.g., the chemistry of the martian regolith—the design of biological experiments and the interpretation of the results from such experiments will be fraught with difficulties. The failure of Mars Observer shortly before entering orbit about the Red Planet in 1993 led to a fundamental revision of NASA’s Mars exploration strategy. Rather than relying on large spacecraft with comprehensive, multidisciplinary payloads as was the case with Mars Observer, future missions would embody the faster-cheaper-better design philosophy. That is, missions would be smaller, would be more focused on a narrow set of scientific goals, and would be launched at every possible Mars launch opportunity. Mars Global Surveyor and Mars Pathfinder, both launched in 1996, were the first missions to embody this new approach.3 The programmatic and scientific success of both missions—combined with the political impetus fueled by claims of evidence of past life

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Assessment of NASA’s Mars Architecture 2007–2016 in the martian meteorite, ALH 84001—prompted the federal government to devote greater resources to NASA’s Mars Exploration Program.4 The failure in 1999 of both of NASA’s next two Mars missions—Mars Polar Lander and Mars Climate Orbiter—led to major revisions in the Mars Exploration Program and to the abandonment of many aspects of the faster-cheaper-better philosophy.5 Despite the two failures, scientific interest in Mars did not wane; nor did political and financial support for a robust program of Mars Exploration. The lander mission planned for launch in 2001 was canceled, but the 2001 orbiter mission, Mars Odyssey, proceeded on schedule and has, subsequently, provided much valuable scientific data concerning Mars’s global geochemistry. Interest in Mars exploration is not confined to NASA. In 1998, Japan’s Institute for Space and Astronautical Science launched Nozomi, a small orbiter designed to focus on studies of Mars’s upper atmosphere and interactions with the solar wind. Unfortunately, this spacecraft suffered multiple failures and was unable to enter orbit around Mars. In 2003, the European Space Agency launched Mars Express and NASA launched the twin Mars Exploration Rovers. Finally, in August 2005 NASA launched the Mars Reconnaissance Orbiter, and this spacecraft successfully entered orbit around Mars in March 2006. As a result of this unprecedented level of activity, there are currently six operating spacecraft on or in orbit about Mars. The resilience of the Mars Exploration Rovers, Spirit and Opportunity, and the wealth of data that they and their companion spacecraft have gathered on Mars, are opening a new chapter in understanding of the Red Planet. Discoveries of stratigraphic layers, evaporite deposits, and mineral forms show clearly that Mars experienced a somewhat Earth-like warmer and wetter era.6,7 Questions remain as to how this era came to be and how Mars changed to its current cold and dry climate. Another significant set of results from Mars concerns the putative spectroscopic detection of methane in the planet’s atmosphere by ground-based telescopes8,9 and the Mars Express spacecraft.10 Although the result obtained from Mars Express is still somewhat controversial, all three sets of observations indicate methane at concentrations of about 10 parts per billion. This is significant in that methane is unstable in the martian atmosphere and would disappear in ~300 years if not replenished. Although the origin of the methane has not yet been determined, possible sources include volcanic activity, chemical reactions between water and iron-bearing minerals in a hydrothermal system, and biological activity.11 These and other recent advances are not the only factors influencing NASA’s Mars Exploration Program. Other factors include the following: The development of a highly effective, community-based group, the Mars Exploration Program Analysis Group (MEPAG), which devised a comprehensive series of Mars exploration goals and priorities and has drafted topical reports on specific Mars exploration opportunities;12 The publication in 2003 of the NRC’s first solar system exploration (SSE) decadal survey report, New Frontiers in the Solar System: An Integrated Exploration Strategy,13 which places the exploration of Mars in the context of other SSE activities and also provides specific recommendations and priorities for a variety of Mars exploration activities; The enunciation on January 14, 2004, of the Vision for Space Exploration, President Bush’s overarching plan for “a sustained and affordable human and robotic program to explore the solar system and beyond”;14 and Changes in the Mars Exploration Program’s budgetary expectations for fiscal years 2006 and 2007, which resulted in various programmatic adjustments, including the cancellation of the planned 2009 launch of the Mars Telecommunications Orbiter, the loss of several Mars Scout missions in the post-2011 period, the termination of a series of robotic human-precursor missions, and the deletion of a variety of technology-development activities.15 These factors and, in particular, the last, compelled NASA’s Science Mission Directorate to revisit the sequence of missions the agency plans to launch to Mars in the period 2007-2016. After several months of study, consideration and incorporation of the guidance from NRC studies and the Vision for Space Exploration, and community consultations via individual inputs and a MEPAG-sponsored working group, the Jet Propulsion Laboratory’s Mars Advanced Planning Group developed a revised program architecture for the coming decade of Mars robotic exploration. This architecture is embodied in the report Mars Exploration Strategy 2007-2016.16

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Assessment of NASA’s Mars Architecture 2007–2016 THE MARS EXPLORATION ARCHITECTURE 2007-2016 NASA’s Mars Exploration Program seeks to understand whether Mars was, is, or can be an abode of life. The key to understanding the past, present, or future potential for life on Mars can be found in the overarching goals for Mars exploration: determine if life ever arose on Mars, characterize the climate and geology of Mars, and prepare for human exploration of Mars.17 The Mars exploration architecture proposed by NASA envisages the launch of a mission to Mars at every possible launch opportunity, i.e., every 26 months. The missions considered for the period 2007-2016 are as follows: 2007, Phoenix (the first competitively selected Mars Scout); 2009, Mars Science Laboratory; 2011, Mars Scout (the second competitive selection for flight); 2013, Mars Science and Telecommunications Orbiter; and 2016, Astrobiology Field Laboratory or two Mid Rovers. Phoenix The Phoenix mission, scheduled for launch in August 2007, is the first of NASA’s principal-investigator (PI)-led, competitively selected Mars Scout missions. When Phoenix lands on Mars in May 2008, it will begin a program of investigations specifically designed to measure volatiles (especially water) and complex organic molecules in the arctic plains of Mars, where the Mars Odyssey orbiter has discovered evidence suggesting ice-rich soil very near the surface. Its science objectives are to study the history of water in all its phases, to search for evidence of a habitable zone in the near-surface regolith, and to assess the biological potential of the ice-soil boundary. Mars Science Laboratory The Mars Science Laboratory (MSL) is an advanced rover mission designed to follow the highly successful Mars Exploration Rovers, Spirit and Opportunity. The primary goal of the mission is to assess Mars’s potential as a past or present abode of life, i.e., to determine whether Mars ever was, or is still today, an environment able to support microbial life. The mission’s specific scientific objectives are as follows: Determine the nature and inventory of organic carbon compounds; Inventory the chemical building blocks of life (i.e., carbon, hydrogen, nitrogen, oxygen, phosphorus, and sulfur); Identify features that may represent the effects of biological processes; Investigate the chemical, isotopic, and mineralogical composition of the martian surface and near-surface geological materials; Interpret the processes that have formed and modified rocks and regolith; Assess long-timescale (i.e., 4-billion-year) atmospheric evolution processes; Determine the present state, distribution, and cycling of water and carbon dioxide; and Characterize the broad spectrum of surface radiation, including galactic cosmic radiation, solar proton events, and secondary neutrons. The Mars Science Laboratory mission was not well defined at the time the SSE decadal survey was drafted. Nevertheless, its importance to addressing key Mars science goals was recognized, and this mission was determined to be the highest-priority medium-cost Mars mission for the decade 2003-2013.18 Since then the scope and cost of the mission have grown significantly. The combination of MSL’s highly capable science payload, its long expected lifetime, and its use of as-yet untested entry, descent, and landing systems has led some observers to suggest that it would be prudent to send

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Assessment of NASA’s Mars Architecture 2007–2016 two. Indeed, NASA’s 2005 Roadmap for the Robotic and Human Exploration of Mars recommends that two MSL spacecraft should be launched “to ensure mission success and maximize the science return.”19 Such an approach might be an appropriate risk-reduction strategy. However, its implementation at such a late stage in the development of a large and complex mission seems ill advised, irrespective of its financial implications for the rest of the Mars program. The committee notes that a recent Space Studies Board review—focusing “on the scientific balance implications for the overall program and the capacity of the program to maximize scientific return”—found no scientific justification in the 2005 Mars Roadmap for two MSLs.20 Mars Scout 2011 NASA proposes to launch the second of the PI-led, competitively selected Mars Scout missions no later than January 2012. Given the programmatic scope of the Scout missions, the nature, goals, and capabilities of this mission are currently unknown. NASA released an announcement of opportunity for this mission in early May 2006. The importance of Mars Scout missions rests in their ability to address high-priority science goals related to unexpected discoveries and in the opportunity they provide for maintaining program balance. These factors led the SSE decadal survey to rank the Mars Scout program as the highest-priority activity in the small Mars mission category. Mars Science and Telecommunications Orbiter The Mars Science and Telecommunications Orbiter (MSTO) is envisaged as being comparable in size, scope, and cost with the Mars Reconnaissance Orbiter and capable of addressing a broad range of scientific objectives associated with the study of Mars’s atmosphere and space-plasma environment. Its scientific goals and instrument complement are only partially defined at the moment. Science goals endorsed in the recently completed study by MEPAG’s Mars Science and Telecommunications Orbiter Science Analysis Group include the following:21 Determine the interaction of the solar wind with Mars; Determine diurnal and seasonal variations of Mars’s upper atmosphere and ionosphere; Determine the influence of the crustal magnetic field on ionospheric processes; Measure thermal and non-thermal escape rates of atmospheric constituents and estimate the evolution of the martian atmosphere; Measure composition and winds in the middle atmosphere; and Address in detail the issue of methane in the atmosphere. As currently conceived, this mission will also have a secondary role of serving as a telecommunications relay to enhance the data return from surface missions such as MSL (if it is still operating) and/or the Astrobiology Field Laboratory (AFL) or the Mid Rovers. The dual science and mission-support role of MSTO presents issues concerning the selection of appropriate orbits. Those mission goals related to studies of the martian thermosphere, ionosphere, and solar wind interactions suggest an orbit that dips into the atmosphere to altitudes as low as 130 km. On the other hand, the mission goals that seek to delineate the dynamics of the neutral atmosphere would benefit from a 400-km to 500-km circular orbit. The mission’s role as a telecommunications orbiter also suggests a circular orbit. The just-completed MEPAG study of MSTO presents a plan for orbit changes during the course of the mission, which does represent a reasonable compromise among the different requirements. A likely scenario would include an initial 130-km-by-4000-km orbit followed by a circular orbit near 400 km. Although this mission concept postdates the publication of the SSE decadal survey, its aeronomy goals are similar to the survey’s second-highest-priority small Mars mission, the Mars Upper Atmosphere Orbiter. Astrobiology Field Laboratory The Astrobiology Field Laboratory mission is conceived as being a highly capable rover derived from the Mars Science Laboratory. Its principal goals are to assess the biological potential of sites, interpret the paleo-

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Assessment of NASA’s Mars Architecture 2007–2016 climate record, and search for biosignatures of ancient and modern life. It is generally recognized that the viability of the mission depends on results obtained by MSL in its search for organics. This mission concept postdates the publication of the SSE decadal survey. Mid Rovers The Mid Rovers are conceived as being more capable than the Mars Exploration Rovers but less complex, costly, and heavy than the Mars Science Laboratory. Their principal purpose is to serve as geological explorers, i.e., to evaluate the geological context of specific sites and search for organic compounds at targets identified by prior missions. As currently envisaged, NASA’s goal is to fly two rovers for a cost approximately equal to that of the Mars Science Laboratory. The Mid Rovers would be equipped with a modest yet capable payload and be capable of landing in an error ellipse < 50 km long. This mission concept postdates the publication of the SSE decadal survey. NASA’s plan for flying two such missions at the same launch opportunity appears to be an appropriate strategy. TOPICS CONSIDERED BY THE COMMITTEE Given the short duration of this study, it was not possible for the committee to develop its conclusions and recommendations ab initio. Nor, given its composition and expertise, was it possible for the committee to speak definitively on topics other than those concerning scientific goals, priorities, and investigations. Given these caveats, the committee adopted an approach to addressing the three questions posed by NASA that relies heavily on the interpretation and reiteration of advice contained in past NRC reports and, in particular, New Frontiers in the Solar System, the SSE decadal survey. The committee’s reliance on past advice is limited to the extent that this advice is still valid in the light of new discoveries. The SSE decadal survey was completed 4 years ago, and since then there have been significant advances in our understanding of Mars. Thus, the committee’s first step was to determine whether or not the decadal survey’s advice and recommendations concerning the exploration of Mars are still valid. In summary, the committee’s approach to answering the three questions posed by Dr. Cleave was to break them down, and to consider the subtopics listed under each question as follows: Question 1: Is the Mars architecture reflective of the strategies, priorities, and guidelines put forward by the NRC’s SSE decadal survey and related science strategies and NASA plans? The exploration of Mars in a solar system context Major new discoveries since the SSE decadal survey report was issued The Mars architecture and the SSE decadal survey’s Mars exploration goals The Mars architecture and related science strategies The Mars architecture and other NASA plans Question 2: Does the revised Mars architecture address the goals of NASA’s Mars Exploration Program and optimize the science return, given the current fiscal posture of the program? The Mars architecture and the goals of NASA’s Mars Exploration Program Optimizing the science return Question 3: Does the Mars architecture represent a reasonably balanced mission portfolio? Subsequent chapters address each of these topics in turn. Where appropriate, conclusions are drawn and recommendations are made. NOTES    1. For more details on missions to Mars, 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.

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Assessment of NASA’s Mars Architecture 2007–2016       2. National Research Council, Space Research, Directions for the Future, National Academy of Sciences, Washington, D.C., 1966.    3. For a review of NASA’s Mars Exploration Program at this point in its development see, for example, National Research Council, Review of NASA’s Planned Mars Program, National Academy Press, Washington, D.C., 1996.    4. For a review of NASA’s Mars Exploration Program at this point in its development see, for example, National Research Council, Assessment of NASA’s Mars Exploration Architecture, National Academy Press, Washington, D.C., 1998.    5. For a review of NASA’s Mars Exploration Program at this point in its development see, for example, National Research Council, Assessment of Mars Science and Mission Priorities, The National Academies Press, Washington, D.C., 2003.    6. S.W. Squyres et al., “The Spirit Rover’s Athena Science Investigation at Gusev Crater Planum, Mars,” Science 305: 794-799, 2004. Also see subsequent papers (pp. 800-845) in this issue of Science.    7. S.W. Squyres et al., “The Opportunity Rover’s Athena Science Investigation at Meridiani Planum, Mars,” Science 306: 1698-1703, 2004. Also see subsequent papers (pp. 1703-1756) in this issue of Science.    8. M.J. Mumma, R.E. Novak, M.A. DiSanti, and B.P. Bonev, “A Sensitive Search for Methane on Mars,” AAS/DPS 35th Meeting, September 1-6, 2003.    9. V.A. Krasnopolsky, J.P. Maillard, and T.C. Owen, “Detection of Methane in the Martian Atmosphere: Evidence for Life,” European Geophysical Union Meeting, Nice, May, 2004.    10. V. Formisano, S. Atreya, T. Encrenaz, N. Ignatiev, and M. Giuranna, “Detection of Methane in the Atmosphere of Mars,” Science 306: 1758-1761, 2004.    11. J.S. Kargel, “Proof for Water, Hints of Life?” Science 306: 1689-1691, 2004.    12. For more information about MEPAG and its activities see, for example, <mepag.jpl.nasa.gov>.    13. National Research Council, New Frontiers in the Solar System: An Integrated Exploration Strategy, The National Academies Press, Washington, D.C., 2003.    14. See, for example, National Aeronautics and Space Administration (NASA), The Vision for Space Exploration, NP-2004-01-334-HQ, NASA, Washington, D.C., 2004.    15. J. Douglas McCuistion, Mars Exploration Program, NASA Headquarters, presentation to the committee, March 29, 2006.    16. D.J. McCleese et al., Mars Exploration Strategy 2007-2016, NASA, Jet Propulsion Laboratory, Pasadena, Calif., 2006.    17. D.J. McCleese et al., Mars Exploration Strategy 2007-2016, NASA, Jet Propulsion Laboratory, Pasadena, Calif., 2006, p. 9.    18. National Research Council, New Frontiers in the Solar System: An Integrated Exploration Strategy, The National Academies Press, Washington, D.C., 2003, p. 194.    19. NASA, Science Mission Directorate, A Roadmap for the Robotic and Human Exploration of Mars, NASA Headquarters, Washington, D.C., 2005, p. ES-3. Available at <images.spaceref.com/news/2005/srm2_mars_rdmp_final.pdf>.    20. National Research Council, Review of Goals and Plans for NASA’s Space and Earth Sciences, The National Academies Press, Washington, D.C., 2006, p. 11.    21. MEPAG’s study of MSTO is available at <mepag.jpl.nasa.gov/reports/MSTO_SAG_report.doc>.