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Review of NASA's Planned Mars Program Executive Summary Although Mars has been a primary target for space science missions over the past three decades, the record of success in the last few years has been poor. Indeed there has not been a completely successful Mars mission since the Viking project in the late 1970s. The failure of the Mars Observer mission in 1993 was a particularly hard blow for the planetary science community, because this spacecraft was scheduled to address many of the highest-priority investigations of the Red Planet. To recover from the loss of Mars Observer, NASA initiated Mars Surveyor, an extended program aimed at sending two small spacecraft to Mars during every launch opportunity between now and 2005. Mars Surveyor is cost-capped at $156 million (including operations and launch vehicles) per year, and its announced goals are the study of martian climate, life, and "resources." The first mission, the 1050-kg Mars Global Surveyor, will be launched in November 1996 and will carry duplicates for much of Mars Observer's payload. A Discovery mission, Mars Pathfinder, consisting of a 360-kg lander and a 10-kg roving vehicle, will also be sent to Mars during this launch window. Subsequent missions in the Mars Surveyor program are expected to carry the remaining two instruments from Mars Observer and to conduct more complex observations, both on the surface and from orbit, perhaps in cooperation with international partners. Given that Mars is one of the highest-priority objects for study identified in the Committee on Planetary and Lunar Exploration's (COMPLEX's) 1994 report, An Integrated Strategy for the Planetary Sciences: 1995-2010, 1 the Space Studies Board asked COMPLEX to review whether the Mars Surveyor and Mars Pathfinder programs, as presently conceived, satisfy the highest priorities for understanding Mars as provided in the committee's Integrated Strategy. Given that Mars Surveyor's "smaller-faster-cheaper" philosophy is very different from that of past NASA planetary missions, the current report's emphases concern not just the planned scientific objectives but also the effectiveness of using numerous, small missions with focused goals to explore Mars; COMPLEX does not assess the specific details of the program, which, especially in the out-years, is more conceptual than specific.
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A complete exploration of Mars would require measurements of the planet's atmosphere, soil, rocks, and interior, as well as the surrounding near-Mars space environment. The missions in the Mars Surveyor program should be able to conduct fruitful experiments on the characteristics of the soil and atmosphere, since these are everywhere available. If a network of miniature meteorology stations were emplaced, then a major objective of atmospheric science could be accomplished. While studies of Mars's upper atmosphere are currently absent from the Mars Surveyor program, many of this field's objectives might be achieved through NASA's planned participation in Japan's Planet B mission. Cost and payload limitations imposed on Mars Surveyor's small landers might prevent the flight of advanced rovers capable of adequate sampling of the rock record. Because evidence for past climate changes and ancient life, if any, is most likely embedded in the rocks, this is a major shortcoming. Sounding of the interior requires simultaneous operation of at least three widely spaced seismology stations. This may be accomplished in the Mars Surveyor program as currently defined only if sophisticated landers, having less mass than Mars Pathfinder, can be developed; if not, it may become feasible in cooperation with the European Space Agency. A coordinated program with the Russians, in which they land an advanced rover, may alleviate the problem of access to solid rocks; alternatively NASA might develop advanced rovers on its own. The missions currently planned do, within the Mars Surveyor program, have the potential of adding significantly to our understanding of Mars. Not only does Surveyor recover essentially all of Mars Observer's objectives, which are essential first steps according to the Integrated Strategy, but it also initiates a challenging program of surface exploration by small landers with highly focused science goals. In addition, some aspects of COMPLEX's strategy not addressed by Mars Surveyor are being or can be addressed by judicious cooperation with international partners. Spacecraft instrumentation is of great concern to COMPLEX. Because the Mars Surveyor program is on a fast track, there is inadequate time to allow some instruments to be developed to a sufficient level so that risk is small. Furthermore, although plans are being formulated outside the Surveyor program to reduce significantly the size of spacecraft, schemes to produce complementary and innovative miniaturized instruments are absent. Yet the success of the Mars Surveyor program will depend to a considerable extent on how sophisticated a payload can be flown within the program's stringent constraints on cost, schedule, and mass. Because funding within the Surveyor program is too limited to foster significant development of so-called microinstruments, the scientific objectives of the program could be seriously undermined unless instrument development is externally supported. Thus, to ensure important scientific advancement either microinstrument development should become an essential component of NASA's New Millennium spacecraft technology program, or some activity comparable to the existing Planetary Instrumentation Definition and Development Program (PIDDP) should be initiated for microinstruments.
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A longer-term concern is that as the program progresses it may become increasingly difficult to make major discoveries with the small landers currently envisaged. In any transition to more ambitious missions, including sample return, long-range rovers equipped with significant instrumentation may be necessary for the definitive resolution of questions concerning past climates and history. Despite these potential problems, the Mars Surveyor program (as long as NASA continues to interpret "resources" to include martian geology, geophysics, and geochemistry) provides a major opportunity to broaden and deepen our understanding of Mars-its atmosphere and climate, its geochemistry and geophysics, and, to a somewhat lesser extent, its present and past potential for harboring life. Because the program includes many launches over many years, it- like the Discovery program-can, in principle, afford to be bolder and take greater scientific and technological risks than the more restrictive programs of the past. This opportunity for innovation should not be missed. However, substantial technological innovation will occur only if NASA adopts a new attitude toward risk management. As COMPLEX has emphasized previously, the ability to accept the occasional but inevitable disappointments that come with trying innovative solutions must be an integral feature of NASA's emphasis on small missions. 2 While long-established, hard-earned attitudes cannot be expected to change overnight, the smaller-faster-cheaper approach will demand that some additional risk be accepted. In summary, although NASA's Mars exploration program does not meet all scientific requirements (e.g., in aeronomy, internal structure, and seismic activity, or with respect to a sophisticated exploration for extant or extinct life), it will be broadly consistent with a significant subset of the scientific priorities outlined in the Integrated Strategy provided that: q The program of global mapping planned to start with Mars Global Surveyor in 1996 is completed by flying the Pressure Modulator Infrared Radiometer in 1998 and the Gamma-Ray Spectrometer in 2001; q The mobility of landers and other vehicles is enhanced beyond that exemplified by Mars Pathfinder's rover so as to allow measurements to be made on a wide variety of rocks and terrains; q The Mars Surveyor program is kept flexible so that it can respond to scientific and technological opportunities and can encompass a broad range of mission modes; q International partners continue to be involved in order to supplement U.S. capabilities and leverage U.S. resources committed to the program; q An aggressive program for development of miniaturized instruments is initiated; and q The goal of returning samples of martian soil, atmosphere, and, most importantly, rocks remains a central element of NASA's planning. REFERENCES
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1. Space Studies Board, National Research Council, An Integrated Strategy for the Planetary Sciences: 1995-2010, National Academy Press, Washington, D.C., 1994. 2. See, for example, Space Studies Board, National Research Council, The Role of Small Missions in Planetary and Lunar Exploration, National Academy Press, Washington, D.C., 1995, pp. 18-19.