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2 Summary of Planned Future Missions The following is a brief summary of upcoming or planned missions to Mars. The only approved missions are the U.S. Mars Observer mission to be launched in October 1992 and the Soviet Mars 1994/96 mission. Both NASA and ESA are studying a network mission that involves placing numerous small stations on the surface of the planet. In addition, both the United States and the former Soviets have been studying various sample return missions that may also involve the use of rovers. APPROVED MISSIONS U.S. Mars Observer Mission Mars Observer will arrive at the planet in September 1993. After a checkout period, the spacecraft will be placed in a high-inclination mapping orbit and will start to systematically observe the planet.1 The mapping orbit is such that the spacecraft will have less than 1 chance in 10-4 of impacting the planet before 2038. The spacecraft will have a variety of instruments directed at characterizing both the surface and the atmosphere. An altimeter will determine surface elevations to a vertical precision of a few meters, and the surface will be imaged at a resolution of roughly 100 meters per pixel. a magnetometer will determine if the planet has an intrinsic magnetic field, map any crustal remnant field, and follow variations in the magnetic field induced by the solar wind or surface anomalies. The surface chemistry and mineralogy will be mapped by two 18

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instruments: (1) a gamma-ray spectrometer will determine all major elements and most minor elements with spatial resolution of roughly 300 kilometers per pixel, while (2) a thermal emission spectrometer will map variations in surface mineralogy at a spatial resolution of roughly 3 kilometers per pixel. An on-board camera will be used to assess daily variations in cloud patterns, as well as to image small areas of the surface at a resolution of 1.5 meters per pixel. A pressure modulated infrared radiometer will repeatedly sound the atmosphere to characterize changes in the vertical structure of the atmosphere with time and location. Finally, on-board transponders will permit extremely precise determination of the planet's gravitational field. The nominal mission will last for 1 Mars year, or roughly 2 Earth years. The spacecraft has a relay antenna designed to receive data from Soviet surface stations to be launched in 1994 and 1996; after completion of the nominal mission, the spacecraft will be used in part to support these surface stations. It is also expected to continue to make observations of the planet, perhaps focusing on areas of special interest identified during the nominal mission. Soviet Mars 94/96 Mission The former Soviets are planning to launch a spacecraft to Mars in 2 1994. It will be primarily an orbiter instrumented to make a variety of observations of the surface, atmosphere, and ionosphere. Among these instruments, those of greatest biological interest are an imaging system that will image large regions of the planet at a resolution of 10 meters per pixel, a near-infrared imaging spectrometer for determination of surface mineralogy, and ground-penetrating radar that could detect anomalies caused by the presence of water near the surface. Of concern from the point of view of planetary protection are stations that will land on the surface. The spacecraft will carry two penetrators designed to be released from the spacecraft 3 to 4 days before arrival at Mars. The penetrators will separate on impact with the ground. the forebody will penetrate the ground to a depth on the order of meters, while the aft body will remain resting on the surface still wired to the forebody. Within the forebody will be various analytical instruments such as a gamma-ray spectrometer and a seismometer. The aft body will have an array of meteorological instruments, a camera, and a transmitter. The parent spacecraft will also release two small stations 3 to 4 days before arrival at Mars. These stations will land on the surface and deploy an array of instruments similar to those in the penetrators. Both the penetrators and the small stations are planned to last for 1 Mars year. The landing sites are restricted to latitudes from about 20°S to 60°N. In 1996, the former Soviets plan to launch a second spacecraft similar to that launched in 1994, except that it will place in Mars orbit a 19

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module from which will be launched a balloon and small rover.3 Both the balloon and the rover will be released to the surface simultaneously and are expected to land in the same part of the planet. The preferred landing sites are at high latitudes (50 to 60°N) for reasons of balloon safety. The balloon will be 30 meters high, constructed of 6-micron mylar, and designed to land at night and float during the day. It is expected to last for as long as 10 days, during which it could travel as far as 1000 kilometers. During the night it will drag an instrumented guide rope along the ground. The gondola of the balloon will carry a camera and various instruments to measure the chemistry and mineralogy of the soil, as well as any water present, and to monitor the atmosphere and magnetic field. One concern is that it will be difficult to reduce the bioload because of the balloon's fragility and size, and there is no information available on what decontamination procedures will be used. Since the balloon will move large distances dragging a guide rope and instruments along the ground, the potential for contamination is significant. The Mars 96 rover will weigh roughly 100 kilograms and be about a meter in height.4 In addition to imaging instruments, it will carry instruments to measure soil mineralogy and chemistry, the water content of the soil, and trace gases in the atmosphere, and it may include capabilities for analyzing organic materials. It will have a drill that can bring to the surface, for analysis, material from a depth of as much as 2 meters below the surface. The lifetime is nominally 1 Mars year. The distance that it can travel in this time will depend on the terrain it encounters, but could be as much as several hundred kilometers. CONTEMPLATED MISSIONS U.S. MESUR Mission The United States has been studying the feasibility of placing a network of simultaneously operating stations on the martian surface.5 The objectives of the network are (1) to determine the chemistry and mineralogy of martian soils and rocks at different locations representative of martian heterogeneity, (2) to observe the fine-scale structure of the surface in different geologic environments, (3) to determine the seismicity and internal structure of the planet, and (4) to improve our understanding of the circulation of the atmosphere and the structure of the boundary layer. The network will be built by launching four to eight small (1.3- meter diameter), relatively inexpensive spacecraft on successive launch opportunities spanning a 4-year period, possibly starting in the late 1990s. The plan is that 16 stations will be operating simultaneously on the surface at the end of the launch period and that they will survive for 1 full Mars year after all are in place. The MESUR mission will thus have a total 20

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lifetime of about 7 Earth years. The stations will fly independently to Mars and will have the ability to land almost anywhere on the planet. Each will carry a seismometer, a camera, instruments for determination of the chemistry and mineralogy of rocks and soil, and a meteorology package. The mode of instrument deployment and whether the subsurface can be accessed are aspects still being studied. The stations will be widely distributed, and some will be sent to places such as the poles that are unlikely to be visited by other types of landers in the foreseeable future. ESA Marsnet Mission The European Space Agency has been independently studying a network mission called Marsnet.6 The design is very similar to that of the MESUR mission except that fewer stations are involved, and the mechanism for delivery of the stations to the martian surface is uncertain. The array of instruments proposed for Marsnet is similar to that proposed for MESUR. Preliminary discussions have been undertaken to determine how the two concepts might be merged. Sample Return and Rover Missions The return of samples from Mars has had high scientific priority but has been deferred in favor of other missions because of its high cost. A U.S. sample return mission before 2000 is extremely unlikely, but the former Soviets have at times suggested that they would like to launch such a mission by that year. There are many ways to implement a sample return mission. In the late 1980s, several types of sample return missions were studied. They involved the return of 5 to 10 kilograms of sample and the use of large (1000-kilogram) rovers to collect and document samples from many different locations. Such missions would be so expensive that conducting them would require major changes in the way planetary science is funded. More recently, simpler sample return techniques have been studied.7 These techniques take advantage of the miniaturization of spacecraft components and analytical instruments, as well as the reduced amount of sample that is required by modern analytical techniques. The general philosophy is to send small sample return missions to several locations to obtain a variety of samples, rather than relying on an elaborate rover to provide a range of samples. The missions could still carry rovers to acquire samples, but the rovers might weigh on the order of 10 kilograms rather than 1000 kilograms. These approaches reduce the projected cost of sample return missions by a factor of 10. Which, if any, of these missions will actually fly is uncertain in light of the current worldwide economic situation. 21

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REFERENCES 1. Albee, A.L., and Palluconi, D.F. 1990. "Mars Observer's Global Mapping Mission." EOS 71:1099-1107. 2. Friedman, L.D. 1991. "What Now with the Soviets?" The Planetary Report XI(4):4-7. 3. Anderson, C.M. 1991. "Wind, Sand and Mars: The 1990 Tests of the Mars Balloon and SNAKE." The Planetary Report XI(1):12-15. See also, Friedman, L.D., 1991. 4. See Friedman, L.D., 1991. 5. National Aeronautics and Space Administration (NASA). 1991. Mars Environmental Survey (MESUR): Scientific Objectives and Mission Description. NASA Ames Research Center, Moffett Field, Calif., July 19. 6. European Space Agency (ESA). 1991. Marsnet Assessment Study Report. SCI(91)6. ESA, January. 7. National Aeronautics and Space Administration (NASA). 1991. Solar System Exploration Division Strategic Plan: Preparing the Way to the New Frontier of the 21st Century. NASA Headquarters, Washington, D.C., July. 22