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Review of NASA's Planned Mars Program 1 Introduction The exploration of Mars has long been a prime scientific objective of the U.S. planetary exploration program. Yet no U.S. spacecraft has successfully made measurements at Mars since the Viking missions of the late 1970s. Mars Observer, which was designed to conduct global observations from orbit, failed just before orbit insertion in 1993. The Russian spacecraft Phobos 2 did succeed in making some observations of the planet in 1989, but it was designed primarily to observe Phobos, the innermost satellite of Mars; the spacecraft failed 2 months after insertion into Mars orbit during the complex maneuvers required to rendezvous with the martian satellite. In fall 1996 NASA plans to launch Mars Pathfinder for a landing on the martian surface in mid-1997. This spacecraft is one of the first two missions in NASA's Discovery program that inaugurates a new style of planetary exploration in which missions are low-cost (<$150 million) and have very focused science objectives. As can be seen in the comparative data presented in Box 1, this mission is considerably smaller in terms of cost, mass, and scope than NASA's previous Mars missions. NASA's FY 1995 budget initiated a continuing Mars exploration program, called Mars Surveyor, that involves multiple launches of spacecraft as small as or smaller than Mars Pathfinder to Mars over the next several launch opportunities, which recur roughly every 26 months. The first mission in the program, Mars Global Surveyor, set for launch late in 1996, is intended to accomplish many of the objectives of the failed Mars Observer. Like the Discovery program, Mars Surveyor is a continuing series of low-cost missions, each of which has highly focused science objectives. See Box 1 for comparative details of those Surveyor missions currently defined. Around the same time that the Mars Surveyor series was chosen as the centerpiece of NASA's solar system exploration program, the Committee on

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Planetary and Lunar Exploration (COMPLEX) designated Mars as one of four scientific targets for emphasis in future studies. It was against this background that the Space Studies Board charged COMPLEX to review whether the Mars Pathfinder and Surveyor programs, as presently conceived, satisfy the highest priorities for understanding Mars as provided in its report, An Integrated Strategy for the Planetary Sciences: 1995-2010. 1 The present document is COMPLEX's assessment of the scientific potential of NASA's new approach to Mars exploration. This assessment considers how well the scientific objectives of the Mars Surveyor program match those of the Integrated Strategy; it also addresses some advantages and disadvantages of the smaller-faster-cheaper approach to the exploration of Mars. The capabilities of the various instruments are not discussed in detail since the Mars Observer instruments, all of which are scheduled for reflight, have already been assessed by COMPLEX 2 and later instruments are, in general, not yet well defined. Box 1 NASA Mars Missions, 1964 to 2005 Past Mariner-Mars 1964 (Mariners 3 and 4): Failure of its launch shroud to open doomed Mariner 3 within minutes of its launch. Mariner 4, however, performed the first flyby of Mars. Its instruments returned the first images of Mars's cratered surface and data on the planet's magnetic and trapped-particle environments. Four additional instruments were dedicated to space-physics measurements made during the journey to Mars. Mission type—2 flybys with 7 instruments each q Launch date—November 1964 q Arrival date—July 1965 q Mass—261 kg (dry), 27 kg (payload) q Cost1—$$ q Operations cost—? q Launch vehicle—Atlas-Agena q Mariner-Mars 1969 (Mariners 6 and 7): The pioneering observations of Mariner 4 were greatly extended by this pair of flyby spacecraft. Both were equipped with sophisticated remote-sensing instruments (including wide- and narrow-angle television cameras, an infrared radiometer, and ultraviolet and infrared spectrometers) mounted on a scan platform. They returned a total of some 200 photographs compared with approximately 20 from Mariner 4. Mission type—2 flybys with 5 instruments each q Launch dates—February and March, 1969 q Arrival dates—July and August, 1969 q Mass—384 kg (dry), 75 kg (payload) q Cost—$$+ q Operations cost—? q

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Launch vehicle—Atlas-Centaur q Mariner-Mars 1971 (Mariners 8 and 9): Although Mariner 8 failed on launch, its twin (Mariner 9) became Mars's first artificial satellite. Despite the loss of Mariner 8, this extremely successful program revolutionized our understanding of martian geologic and climatic history and defined the context in which all subsequent Mars missions were designed. Mission type—2 orbiters with 4 instruments each q Launch date—May 1971 q Arrival date—November 1971 q Lifetime at Mars—11 months q Mass—998 kg (wet), 544 kg (dry), 82 kg (payload) q Cost—$$+ q Operations cost—$$$ q Launch vehicle—Atlas-Centaur q Viking (Viking 1 and 2): This highly capable and expensive program was responsible for the first two successful Mars landings, the only two so far, and the initial search for martian life. Although the life-detection experiments gave ambiguous results, the long-lived Viking landers and especially the orbiters returned a wealth of information about martian meteorology and geology. Mission type—2 orbiters with 4 instruments each and 2 landers with 13 q instruments each Launch dates—August and September, 1975 q Arrival dates—June and August, 1976 (orbit), July and September, q 1976 (surface) Lifetime at Mars—50 and 23 months (orbiters 1 and 2), 76 and 42 q months (landers 1 and 2) Landing system—Parachutes and retrorockets q Landing site—Chryse Planitia (22.3° N, 48.0° W), Utopia Planitia (47.7° q N, 225.7° W) Mass—2330, 1170, 72 and 1043, 650, 65 kg (orbiter and lander: wet, q dry, payload, respectively) Mobility—3-m arm attached to landers q Cost—$$$$+ q Operations cost—$$$ q Launch vehicle—Titan III-Centaur q Mars Observer: Originally called the Mars Geosciences/Climatology Orbiter, this mission was intended to initiate a proposed series of low-cost, Planetary Observer spacecraft. Mars Observer carried a suite of complex remote-sensing instruments to conduct intensive geophysical, geological, and climatological observations of Mars. It failed shortly before entering orbit around Mars. Mission type—1 orbiter with 7 instruments q

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Launch date—September 1992 q Arrival date—August 1993 q Lifetime at Mars—0 years (actual), 3 years (projected) q Mass—2573 kg (wet), 1227 kg (dry), 156 kg (payload) q Cost—$$$- q Operations cost—$$ (projected) q Launch vehicle—Titan III-TOS q Future Mars Pathfinder: One of the inaugural missions in the Discovery series of low- cost planetary spacecraft, Mars Pathfinder will feature the first use of a direct- entry trajectory, an airbag landing system, and the deployment of a minirover. Together, the lander and minirover will carry imaging systems, a meteorology package, and an alpha-proton-x-ray spectrometer. Mission type—1 lander with 3 instruments q Launch date—December 1996 (projected) q Arrival date—July 1997 (projected) q Lifetime at Mars—30 days to 1 year (projected) q Landing system—Parachutes, retrorockets, and airbags q Landing site—Ares and Tiu Vallis (19.5° N, 32.8° W) (planned) q Mobility—Minirover Sojourner2 q Mass—570 kg (wet), 325 kg (lander3), 20 kg (payload) q Cost—$$- q Operations cost—$ q Launch vehicle—Delta II q Mars Global Surveyor: The first of a decade-long series of cost-constrained Mars missions, Mars Global Surveyor is designed to recover much of the science lost with the failure of Mars Observer by reflying five of its predecessor's seven instruments. Among the instruments to be flown are an imaging system, a thermal spectrometer, a laser altimeter, and a magnetometer. The radio system also has scientific functions. Mission type—1 orbiter with 5 instruments q Launch date—November 1996 (projected) q Arrival date—September 1997 (projected) q Lifetime at Mars—2 years plus 3 more as communications relay q (projected) Mass—1050 kg (wet), 670 kg (dry), 75 kg (payload) q Cost—$$- q Operations cost—$+ q Launch vehicle—Delta II q Mars Surveyor 1998: Unlike Viking, the orbiter and lander constituting the second and third flights in the Mars Surveyor series will be launched

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independently and follow separate trajectories to Mars. The orbiter will refly Mars Observer's Pressure Modulator Infrared Radiometer. It will also carry an integrated wide- and medium-angle imager. The lander will be equipped with a descent imager, a lidar, and an integrated science package consisting of a mast- mounted stereo-imager, a meteorological package, a thermal/evolved gas analyzer, and a robotic arm. The lander will also deploy two microprobes prior to entry. Mission type—1 orbiter with 2 instruments q Launch date—December 1998 (projected) q Arrival date—September 1999 (projected) q Lifetime at Mars—2 years plus 2 more as communications relay q (projected) Mass—565 kg (wet), 338 kg (dry), 46 kg (payload) q Cost4—$+ q Operations cost5—$- q Launch vehicle—Med-Lite q Mission type—1 lander with 5 U.S. and 1 Russian instruments q Launch date—January 1999 (projected) q Arrival date—December 1999 (projected) q Lifetime at Mars—86 to 146 days (projected) q Landing system—Parachutes and retrorockets q Landing site—Edge of southern polar cap, 76° S, 210° W (planned) q Mobility—2-m robotic arm (with microscope camera on tip) q Mass—504 kg (wet), 331 kg (dry6), 22 kg (payload), 30 kg (2 q miniprobes) Cost7—$+ q Operations cost8—$- q Launch vehicle—Med-Lite q Mars Surveyor 2001: Undefined at present. Mars Observer's remaining instrument, the Gamma-Ray Spectrometer, will presumably be reflown during this launch opportunity. Mars Surveyor 2003: Although this mission is currently undefined, the Mars Communications/Aeronomy Orbiter and NASA's contribution (three or four small landers) to the European Space Agency's proposed Intermarsnet mission could possibly be flown during this launch opportunity. Mars Surveyor 2005: This launch window represents the earliest possible opportunity for a U.S. sample return mission. The technical feasibility of this goal, within the context of the Mars Surveyor program as currently defined, is far from clear. 1 Costs are based on data supplied by NASA for use in COMPLEX's recent report, The Role of Small Missions in Planetary and Lunar Exploration (Space Studies Board, National Research Council, National Academy Press,

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Washington, D.C., 1995, p. 6), and have been supplemented, where necessary, with new data furnished by the Jet Propulsion Laboratory. Costs are in 1996 dollars and are expressed in terms of cost categories. These categories are as follows: $—Small—<$100 million q $$—Intermediate—>$100 million but <$500 million q $$$—Large—>$500 million but <$1 billion q $$$$—Flagship—>$1 billion but <$4 billion q Operating costs are indicated in a similar manner using the following categories: $—Small—<$25 million q $$—Medium—>$25 million but <$75 million q $$$—Large—>$75 million but <$150 million q The superscripts plus (+) and minus (-) are used to indicate the high and low ends of each category. A question mark (?) indicates that COMPLEX could not identify the cost. 2 See Table 1 in Chapter 3 for specifications. 3 Lander dry mass excludes heat shield and parachute masses, but does include airbags. 4 The total development cost (through launch plus 30 days) for both of the Mars Surveyor 1998 missions is capped at $184 million. COMPLEX has arbitrarily divided this amount equally between the orbiter and lander. 5 COMPLEX has arbitrarily divided the total operations cost for this pair of missions equally between the orbiter and the lander. 6 Lander dry mass excludes heat shield and parachute masses, but does include propellant tanks and associated plumbing. 7 The total development cost (through launch plus 30 days) for both of the Mars Surveyor 1998 missions is capped at $184 million. COMPLEX has arbitrarily divided this amount equally between the orbiter and lander. 8 COMPLEX has arbitrarily divided the total operations cost for this pair of missions equally between the orbiter and the lander. REFERENCES 1. Space Studies Board, National Research Council, An Integrated Strategy for the Planetary Sciences: 1995-2010, National Academy Press, Washington, D.C.,

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1994. 2. Letter report regarding an assessment of the impact on integrated science return from the 1992 Mars Observer mission, from the Committee on Planetary and Lunar Exploration to Geoffrey A. Briggs (NASA), July 12, 1988.