Grading NASA's Solar System Exploration Program: A Midterm Report (2008)

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C Technology Background The Committee on Assessing the Solar System Exploration Program determined that NASA will be unable to implement the remaining goals of the New Frontiers in the Solar System decadal survey without new technol- ogy. This will require spending on programs to develop the technology. This appendix discusses several important technologies in greater detail and summarizes in Table C.1 at the end of this appendix the advanced technology requirements discussed in the 2003 New Frontiers decadal survey. ADVANCED RADIOISOTOPE POWER SYSTEMS Radioisotope power systems (RPSs) utilize plutonium 238 in the form of plutonium dioxide pellets. Four pel- lets are housed in an assembly referred to as a general-purpose heat source. Such sources have been thoroughly analyzed and tested for appropriate safety standards. Two versions exist: (1) the standard ones previously used in the Radioisotope Thermoelectric Generators (RTGs) employed on Ulysses, Galileo, Cassini, and New Horizons, and (2) modified ones to use with future missions that employ Earth gravity assists for deep space missions. At the time of the 2003 decadal survey, NASA was developing the Alkali Metal Thermoelectric Converter (AMTEC) as part of its X-2000 technology program. AMTEC would have offered substantial gains in specific power that were vital to the original Europa Orbiter. But those performance gains required a technology that could not be developed on the timescale needed for the Europa Orbiter project. The AMTEC technology was essentially abandoned by NASA because of problems with some of the ceramic parts. Subsequently, NASA began the development of two RPSs based on more conservative converter technolo- gies: the Multi-Mission Radioisotope Thermoelectric Generator (MMRTG) using traditional thermoelectric tech- nology, and a higher-risk Stirling cycle technology. Both were designed for operation on the surface of Mars (for the Mars Science Laboratory) and in deep space. NASA also initiated work on advanced converter technologies under the Radioisotope Power Converter Technology (RPCT) program initiated in 2002. Four advanced technologies were pursued, including dynamic (Stirling and Brayton) and static (thermoelectric and thermophotovoltaic). At this time, most remaining work in National Research Council, New Frontiers in the Solar System: An Integrated Exploration Strategy, The National Academies Press, Wash- ington, D.C., 2003. 75 

76 GRADING NASA’S SOLAR SYSTEM EXPLORATION PROGRAM the RPCT is focused on advanced versions of the converters used in the MMRTG and Stirling generators that are currently under development. A shortage of available plutonium fuel has led NASA to pursue the development of the Advanced Stirling Radioisotope Generator (ASRG). Predicted efficiency for the ASRG is 28 percent as compared with ~6 percent for thermoelectric converters. Hence, ASRGs require about one-quarter of the plutonium of thermoelectric con- verters. At the same time, ASRGs produce less reject heat that can be used for other purposes, and they have moving parts that raise reliability, lifetime, and electromagnetic and mechanical system disturbance issues for other spacecraft systems. The work on producing units using Stirling converters is planned out and, if successful, will take pressure off plutonium inventory issues for power supplies and also enable new missions using radioisotope electric propulsion (REP), providing that specific power in excess of ~8 W(e)/kg can be obtained. However, there are three significant issues that do not appear to have been adequately addressed: 1. Even if all design and testing goals are met on schedule by 2012, it is not clear that an ASRG will be baselined as the power unit on a science mission without a technology flight test. 2. Potential failure modes remain poorly understood, as well as ultimate lifetime limits that can be imple- mented in designs. Hence, dynamic systems such as these are viewed as inherently riskier than static systems such as the MMRTG. 3. Stirling converters use moving magnet assemblies, which create electromagnetic and vibrational distur- bances that are transmitted to the rest of the spacecraft. NASA conducted tests of a primitive Stirling converter more than 2 years ago. However, International Traffic in Arms Regulations (ITAR) restrictions have limited the communication of test results to the potential user community. NASA is currently making significant progress on MMRTGs, which will be employed on the Mars Science Laboratory scheduled for launch in 2009. IN-SPACE FISSION-REACTOR POWER SOURCE In-space fission reactor sources would enable significantly more complex spacecraft missions. However, the United States has only operated one, small fission reactor in space, in 1965. The Soviet Union developed and flew more than 30 radar-ocean reconnaissance satellites (RORSATs) in Earth orbit, powered with uranium-fueled fission reactors. NASA began Project Prometheus in January 2003 as a new effort to develop a space fission supply as an integral part of an overall nuclear-electric propulsion (NEP) system that could be used to enable multiple, chal- lenging, high-payoff robotic missions throughout the solar system and beyond. A contractor was selected for the Jupiter Icy Moons Orbiter (JIMO) project in 2004. However, the Jet Propulsion Laboratory (JPL) estimated the life-cycle cost for JIMO at $21.5 billion, and the program was subsequently canceled in 2005. NUCLEAR-ELECTRIC PROPULSION Nuclear-electric propulsion consists of assembling a high-power-density heat source with a high-efficiency thermal-to-electric converter system, and electric propulsion engines. Unlike ground- or ship- and submarine-based reactors used for power production, space-based application concepts typically focus on low-power (~100 kWe) systems with minimum mass. Project Prometheus was initiated to develop NEP as a system for use in robotic solar system exploration in March 2003. The first mission to be flown with this technology was to be the JIMO targeting the Jovian Galilean satellites in general and Europa in particular. Prometheus was a major study effort (~$464 million) involving seven NASA centers and two Department of Energy organizations. See http://www.svengrahn.pp.se/trackind/RORSAT/RORSAT.html. 

APPENDIX C 77 Gridded-ion thrusters compatible with a nuclear power source began development as part of the program in addition to high-power and extreme life systems development consistent with fission power. Development stopped on all of these efforts at a low technology readiness level (TRL). The Prometheus/JIMO effort provided an important benchmark study on the difficulties and costs of imple- menting NEP in general and on robotic missions in particular. Under Prometheus, NASA made significant progress in various spacecraft subsystems that can be used for flight. ADVANCED ION ENGINES Ion engines typically are classified as being either Kaufmann-type ion-bombardment thrusters (ion engines) or Hall effect thrusters (Hall thrusters) with operating powers of ~1 kW to several tens of kilowatts. Ion engines coupled with solar power were used to flight qualify solar electric propulsion (SEP) on the Deep Space-1 (DS-1) mission. Solar electric propulsion is now being used as the prime propulsion system on the Dawn mission. As part of a program under SEP, a flight experiment of a next-generation solar array to power these engines is being developed for flight on ST-8. AEROCAPTURE Aerocapture is the method of using drag in the atmosphere of a planet or moon to reduce the excess speed of a spacecraft sufficiently to be captured into orbit at the target body. This approach saves the equivalent propellant mass for a high-thrust system that can significantly reduce launch mass and therefore overall mission cost. This method has potential applicability to orbital planetary systems missions. NASA has made progress in aeroshell technology and aerocapture systems development. Systems studies have shown the importance of this approach for Mars Sample Return and Titan Explorer. This effort is funded under the In-Space Propulsion program. While there have been advances, flight qualifi- cation of aerocapture is required for its use in planetary missions at an acceptable level of risk. Currently the only approach to such qualification is a flight for the New Millennium Program. As part of that program, an aerocap- ture experiment was proposed to ST-9 to provide flight validation for this approach. The proposal was rejected for development and flight owing to the reduction in the New Millennium budget for FY 2008 to FY 2010. With the budget downturn through FY 2010, there is no mechanism to qualify aerocapture under the current approach prior to the end of 2013. KA-BAND COMMUNICATIONS NASA established the Deep Space Network (DSN) in the 1960s to enable communication with deep space, interplanetary (robotic) spacecraft. The centerpiece of the system consisted of the three 64-meter-diameter antennas established at facilities in the vicinities of Goldstone, Madrid, and Canberra, spread across longitudes to enable 24-hour coverage to a fixed point in the sky. NASA expanded the antennas to 70-meter-diameter to support the Voyager missions. Support of more spacecraft missions has led to the addition of 34-meter-diameter antennas, as well as the introduction of dual X- and Ka-band capability on them in order to improve the system performance. Much of the DSN hardware is now being used more often than originally expected and far past design lifetimes. In particular the 70-meter-diameter antennas are suffering various hardware problems and cannot be upgraded to Ka band owing to structural limitations. However, to meet upcoming needs, Ka band is the next evolutionary step in providing increased data-rate capability. Further increases in performance by using still higher frequencies in excess of Ka band are not feasible owing to water absorption in the atmosphere. NASA has articulated clear plans to increase DSN capabilities by developing higher-power Ka-band transmit- ters for spacecraft (at high efficiency), developing advanced coding and compression, and implementing an array of antennas providing the equivalent of a 240-meter-diameter antenna at each of the three DSN stations. 

78 GRADING NASA’S SOLAR SYSTEM EXPLORATION PROGRAM OPTICAL COMMUNICATIONS Optical communications hold the promise of delivering significantly more spacecraft bandwidth in uplink and downlink for less mass and power than radio-frequency (X- and/or Ka-band) deep-space communications systems. Various proposals have been made for ground-station locations in order to minimize signal interruption from cloud cover. Other concepts include a set of Tracking and Data Relay Satellite System satellites in Earth orbit which can be used as a relay that can rely on existing ground stations. The implementation would require the development of appropriate resilient (radiation-hardened) laser transponders as well as implementation of tighter pointing requirements on the spacecraft itself. NASA has postponed the development of a first-generation optical communications terminal until 2018. The Deep Space Network Roadmap suggests that an optical communications infrastructure may be operational by 2022. SPACECRAFT AUTONOMY Increased autonomy of spacecraft operations can lower mission operations costs. Risk may be increased unless appropriate test protocols are developed and adhered to prior to launch. Differences in spacecraft missions, architectures, and needs make one-size-fits-all developments difficult. Greater spacecraft autonomy is also neces- sitating larger software and data uploads. The New Millennium ST-6 Autonomous Science Experiment on the Air Force’s Tacsat 2 spacecraft validated orders-of-magnitude increases in science per bits downlinked to the ground. However, the narrow focus of this technology limits its future use. The autonomy program was canceled in 2004, with no funding in this area since then. ADVANCED AVIONICS MINIATURIZATION AND PACKAGING Advanced avionics miniaturization and packaging are generally taken to mean increased performance, including increased spacecraft autonomy, increased radiation hardness, increased thermal range of operations, advanced software, and less mass. Previously funded programs made progress in this area, but with the exception of the Mars Technology Program, most of the funding in these areas has ended. NASA’s X2000 program funded radiation-hardened electronics that have been flown on multiple missions. These include the RAD750 from BAE Systems—now flying on Deep Impact and the Mars Reconnaissance Orbiter (MRO)—and a flash-memory-based nonvolatile memory card (from SEAKR Engineering). Under the Prometheus/Deep Space Avionics Program (2003-2005), there was continuation of X2000 power electronics and development of analog/digital converters and focal plane sensors. Because of past funding efforts, all of the pieces for a robotic mission to Europa, with the exception of the nonvolatile memory, are now at a midrange technology readiness level. However, because almost a decade has elapsed since some of this work was done, the fabrication processes may be a generation or more removed from those used for the devices that were fabricated under X2000. The Europa Explorer team is currently putting together a summary of the status of each of the key technologies for Europa Explorer. At this time the lack of dense radiation-hard nonvolatile memory may be close to a solution with the progress in Chalcogenide RAM. The Europa Explorer concept uses existing technologies (mass memory) but requires advanced development for instruments and sensors. Some generic items are or will be qualified under the New Millennium Program: • ST-6 Stellar Compass provides three-axis attitude determination with an accuracy of 0.1 degree (on each axis) at very low power (3.5 W) and mass (2.9 kg); • ST-8 Commercial Off-the-Shelf-Based High Performance Computing for Space is to demonstrate 10 to Randal Blue, “Radiation Hardened Electronics Development,” presentation to Europa Explorer Electronic Parts Radiation Workshop at the Jet Propulsion Laboratory, April 26, 2007. 

APPENDIX C 79 100 times more delivered onboard computational throughput capability than any computer flying in space today and onboard processing throughput density of >300 GOPS/watt; and • ST-8 Miniature Energy Saving Thermal Control Subsystem is a miniature loop heat pipe thermal control system consisting of two evaporators and two condensers/radiators that is capable of reliable start-up and heat load sharing and can maintain operating temperature control from 0°C to 35°C. A recent assessment indicates that 54 technologies have been selected for validation in space by the New Millennium Program, of which 31 have been successfully validated and 7 are still in process.  Seven were lost as a result of the Deep Space-2 failure. A total of 19 of the technology advances have been infused into missions or into flight mission proposals, including the optical navigation used on Deep Impact and Stardust and the Small Deep Space Transponder used on the Mars Exploration Rovers, MRO, Deep Impact, Dawn, Spitzer, and other missions. Electronics tolerant of cold-temperature thermal cycling are being developed as part of the Mars program; hence, any specific requirement tailoring will be focused on Mars conditions. NASA terminated the Cross-Enterprise Technology Development Program (CETDP), which was developing technologies required for Venus lander spacecraft that can withstand high temperatures, high pressures, and cor- rosive environments. NASA has continued some limited work under Small Business Innovation Research programs and the Planetary Instrument Definition and Development Program (PIDDP). INSTRUMENTATION MINIATURIZATION Mass and power will continue to be major constraints on planetary missions. At the same time there will continue to be pressure to make more sophisticated measurements as well as to do more in situ processing in order to maximize and advance science returns. Programs for support of these developments are in place, but funding has been eroding for non-Mars programs. Innovative instruments that will be inserted into the Mars Science Laboratory include Laser Induced Breakdown Spectroscopy (LIBS) that measures elemental abundances without contact. Four continuing Planetary Science Division research and development programs are addressing the instrument technology needs: PIDDP, Mars Instrument Development Program (MIDP), Astrobiology Science and Technology Instrument Development (ASTID), and Astrobiology Science and Technology for Exploring Planets (ASTEP). Only MIDP covers mid-TRL technologies; no comparable program exists for non-Mars technology. Reductions in astrobiology funding have impacted both ASTID and ASTEP. How well the developments under MIDP can be leveraged to support other missions such as Titan remains to be seen. Instrumentation for the South Pole-Aitken Basin and Comet Surface Sample Return missions is apparently not funded. No instruments for the Venus environment are being supported, nor are spectrometry instruments for gas giant in situ missions. Termination of the CETDP Advanced Measurements and Devices program has shut off innova- tion in device technology of the type that is currently making significant contributions, specifically in advanced diffraction gratings used on the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) instrument on the Mars Reconnaissance Orbiter and thermal detectors used on MRO and Lunar Reconnaissance Orbiter. High- power, active, remote-sensing instruments are no longer under development. AUTONOMOUS ENTRY AND PRECISION LANDING Past Mars landing failures have highlighted the risks associated with landings of robotic probes on nonter- restrial bodies. Detailed observations from orbit can locate hazardous and nonhazardous landing sites. However, in the absence of precise targeting, that information cannot be acted upon to reduce the risk of mission failure. At the same time, such detailed observations from orbit also can be used to pinpoint sites of interest either for JohnStocky, Chief Technologist, New Millennium Program, Jet Propulsion Laboratory, “New Millennium Technology Infusion Summary” and “New Millennium Program–Scorecard Summary,” June 1, 2007. 

80 GRADING NASA’S SOLAR SYSTEM EXPLORATION PROGRAM network station deployment, rover deployment for in situ detailed studies, or for sample collection for a sample return mission. Missions beyond Mars will require greater autonomous action, owing both to longer round-trip flight times and to what will likely be less information concerning landing hazards. IN SITU SAMPLE GATHERING, HANDLING, AND ANALYSIS As orbiting spacecraft have given way to landers and rovers, there has been a growing need for more sophis- ticated capabilities in gathering samples, including adequate determination of context and keeping the samples pristine, moving these from the sampling mechanism(s) to instrument ports/receptacles, and subsequently providing analysis either for data transfer back to Earth only or for documenting the state of the sample prior to a sample return to Earth. This effort partially overlaps with the development of miniaturized instrumentation—and for many of the same reasons—and is heavily tied to, but not limited to, surface landers and/or rovers, for example, the Stardust sample return mission. ASCENT VEHICLES The selection and return of samples from a wide number of solar system bodies are required for detailed analysis of pristine material with respect to isotopic, elemental, and mineralogic properties. While comets and asteroids have negligible gravity fields that can easily be overcome with rocket engines that can also be used for interplanetary guidance and control, solid-surface planets and their moons will require dedicated systems to take the samples from the surface to a minimum orbit, from which an interplanetary transfer maneuver can be executed for the return to Earth. A survey of potential sites from which samples can be retuned indicates that the required capabilities fall into four broad classes that can be separated by the equatorial escape speed requirements: (1) 10 to 12 km/s (Venus and Earth), (2) 4 to 5 km/s (Mercury and Mars), (3) 2 to 3 km/s (the Moon, Io, Europa, Ganymede, Callisto, Titan), and (4) 0.5 to 2 km/s (Iapetus, Rhea, Oberon, Titania, Umbriel, Ariel, Triton, Pluto, and Charon). IN-SPACE PROPULSION TECHNOLOGY The In-Space Propulsion Technology (ISPT) program was recently reviewed by external users in the NASA community who found that the program was underfunded for continuing appropriate progress. Several rounds of budget reductions in the FY 2002 to FY 2007 time period led to cuts of ISPT technologies within the portfolio, including solar sails, high-power electric propulsion, and advanced chemical propulsion. Additionally, the focus of ISPT use has shifted to implementation on Discovery, New Frontiers, and other missions of that class. The program began in FY 2002 with $20 million, increasing to $62 million in FY 2003 and continuing at roughly that level through FY 2007. Funding is projected to be in the range of $15 million to $17 million for FY 2008. Current work in advanced chemical propulsion includes a high-temperature bi-propellant thruster. Aerojet is working on high-performance engines for Discovery and New Frontiers missions that use iridium-coated rhenium to enable operation at higher temperatures. High-energy combinations including the use of ozone and fluorine, as well as fluorine including compounds such as oxygen difluoride and chlorine pentafluoride, have been investigated for improved high specific impulse performance. Toxicity, handling, and accident and exhaust safety issues have led to liquid oxygen and liquid hydrogen as the high-energy chemical combination of choice. Paul Wercinski, NASA Headquarters, “An Overview of NASA’s In Space Propulsion Program,” November 19, 2002. Discovery Program Li- brary, NASA Langley Research Center, Hampton, Virginia. Available at http://discovery.larc.nasa.gov/PDF_FILES/ISP_Overview_Wercinski. pdf. 

APPENDIX C 81 TABLE C.1  Advanced Technologies Addressed in the 2003 New Frontiers Decadal Survey Technology Decadal Survey Commentary,a with Current Assessment of Statusb Advanced Advanced RPSs are required to replace the depleted inventory of first-generation RPSs. radioisotope Solar power is generally insufficient beyond the asteroid belt. It provides limited power for spacecraft systems power systems and severely limits the lifetime of landed spacecraft. (RPSs) In the second half of this decade the RPS program can produce advanced flight-qualified radioisotope thermoelectric generators that could be flown on the Europa Geophysical Explorer and the Jupiter Polar Orbiter with Probes, and on the Mars Science Laboratory. In-space Decadal surveya recommendation: “Finally, a compact and efficient (high thrust-to-mass ratio) flight-qualified fission-reactor nuclear-fission reactor should be developed in parallel with the development of second- and third-generation power source ion drives for the high-power NEP [nuclear-electric power] systems required to reach the outer solar system. Development of aerocapture as a means to reduce in-space propulsion requirements will significantly improve mission performance to all planets with atmospheres” (p. 203). The fission-based technology will take a decade to develop. The survey recommends that a series of independent studies be conducted immediately to examine the scientific, technical, and public issues involved in the use of nuclear technologies on planetary spacecraft. The nominal recommendation of the decadal survey will not be achieved during the 2003-2013 decade. A significant amount of work was accomplished that allows better appreciation of the inherent issues in bringing this technology to fruition. Nuclear- In-space chemical propulsion has limited capability, especially for missions to the outer planets, resulting in electric very long flight times and often limiting missions to rare launch windows requiring multiplanet flybys to gain propulsion the necessary energy. (NEP) The development of in-space NEP, including its first qualification flight in space, will take almost the entire decade and will become available for advanced outer-planet missions at the beginning of the next decade. The nominal recommendation of the decadal survey will not be achieved during the 2003-2013 decade. In particular, in-space NEP systems will not be available for advanced outer-planet missions at the beginning of the next decade. Advanced ion For the New Horizons mission, consideration should be given to the use of a solar-electric propulsion stage to engines avoid reliance on a singular Jupiter gravity-assist opportunity in 2007. The use of advanced solar-electric propulsion (coupled with aerocapture) would markedly increase the performance of the Venus In Situ Explorer (VISE) (New Frontiers) mission. Advances in ion propulsion and solar and/or nuclear power sources would improve the performance of the Comet Surface Sample Return (New Frontiers) mission. Aerocapture Development of aerocapture as a means of reducing in-space propulsion requirements will significantly improve mission performance to all planets with atmospheres. The addition of aerocapture technology to next-decadal missions to Neptune, Titan, and Saturn’s rings will yield enhanced capabilities, reduced launch vehicle needs, and/or reduced in-space propulsion system requirements. The use of aerocapture would markedly increase the performance of the VISE (New Frontiers) mission. Spacecraft In the area of spacecraft systems, the key demand is for considerable autonomy and adaptability through autonomy advanced architectures. Advances in automation . . . will improve the performance of the New Frontiers Comet Surface Sample Return mission. Lower-power, lower-mass spacecraft need to be developed commensurate with realistic cost and performance for the available expendable launch vehicles. The autonomy program was canceled in 2004, with no funding for either base of focused technologies in this area since then. continued 

82 GRADING NASA’S SOLAR SYSTEM EXPLORATION PROGRAM TABLE C.1  Continued Technology Decadal Survey Commentary,a with Current Assessment of Statusb Advanced The decadal survey noted a need for more capable avionics in a more highly integrated package to support avionics spacecraft autonomy. The approach recommended advanced packaging and miniaturization of electronics with packaging and a standardized software operating system. Radiation-hardened electronics were noted as required for the New miniaturization Frontiers Jupiter Orbiter with Probes mission as well as for the flagship Europa Geophysical Explorer. In addition to these more generic requirements, called out for outer-planet missions, specific requirements for electronics capable of extreme hot and cold environments were noted. The decadal survey also noted the specific need for the development of high-temperature, corrosion-resistant, and pressure-tolerant systems required for the exploration of Venus within the atmosphere and on the ground. Instrumentation New and increased science measurement capability is needed in planetary science instruments, as is greater miniaturization environmental tolerance for less mass and power. Miniaturization is the key to the reduction of mass and power requirements. In situ instruments: On planetary surfaces, there are requirements for new surface science instruments, including biological measurements; complex organic chemistry and microbiology laboratory packages are needed for exploring organic-rich environments, including Europa and Titan and perhaps even subsurface aquifers of Mars; the South Pole-Aitken Basin mission and future sample return mission need advanced in situ instrumentation, including radiometric age-dating and chemical and mineralogical analysis. In situ instruments—extreme environments: The VISE mission will require in situ instruments that can survive the Venus surface environment and that can accomplish radiometric age-dating and chemical and mineralogical analysis of surface samples; long-lived, high-temperature, and high-pressure systems will be required for Venus sample return and surface stations such as seismic networks; for the Jupiter Orbiter Probe mission, lightweight mass spectrometers for sampling at high pressures with internal gas processing for complex analysis are the key science instrument technology. Remote sensing: Active remote-sensing instruments, including synthetic-aperture radar and laser-activated techniques, will be enabled by fission power sources. Autonomous As planetary exploration moves into the new century with more in situ and sample return missions, it will be entry and necessary to develop planetary landing systems. precision The key requirements for landing systems are autonomous entry, descent, hazard avoidance, and precision landing landing systems. In situ sample Some recommended missions will be sent to planets and satellites that are targets for biological exploration and gathering, will require meeting planetary protection requirements related to forward and back contamination. Technologies handling, and will be required to meet these requirements while reducing the costs to do so. analysis For Mars Sample Return . . . planetary protection technologies (both forward and back) and attendant sample containment, Earth return, and handling [are needed]. The key technologies for the VISE (New Frontiers) mission are those for system survivability, shallow drilling, sample acquisition, and sample transfer at extreme high temperature and pressure in a corrosive environment. The key technology required for the CSSR (New Frontiers) mission is a sample-acquisition system without significant on-surface time, drilling, or sample manipulation and storage at cryogenic temperatures. For the Comet Cryogenic Sample Return mission, drilling and cryogenic sampling will be required for a completely preserved core sample of a comet nucleus. Autonomous Once on the surface, a means for moving about a planet is needed: Rover technology should advance toward mobility long-life and long-range capability, with autonomous hazard avoidance and the ability to operate on large slopes. Aerial platforms for Mars and Venus will be required; they will be the forerunners of systems to be deployed on Titan and the outer planets. Also, subsurface vehicles will be required for the exploration of Mars and perhaps Europa. Advanced autonomy will need to be built in to all of these mobile mechanisms. 

APPENDIX C 83 TABLE C.1  Continued Technology Decadal Survey Commentary,a with Current Assessment of Statusb Ascent vehicles The means to return planetary samples needs to be developed, beginning with small bodies and the Moon, advancing toward Mars, then Venus, and eventually to more distant targets such as Mercury and the satellites of the outer planets. The South Pole-Aitken Basin Sample Return mission to the farside of the Moon could be the first test of sample-return technologies to be used on Mars. The common elements include . . . an ascent vehicle. A Mars-Earth return system, including an ascent vehicle and in-space rendezvous and sample capture, comprises key technologies that can evolve from the vehicles developed for the South Pole-Aitken Basin Sample Return mission. The perfection of Mars sample-return technology should be followed by its adaptation for return of samples from the surface of Venus. Long-lived, high-temperature, and high-pressure systems (including ascent vehicles) will be required for Venus sample return. aCommentary and recommendations drawn from National Research Council, New Frontiers in the Solar System: An Integrated Exploration Strategy, The National Academies Press, Washington, D.C., 2003, pp. 202-206. bThe assessments of the Committee on Assessing the Solar System Exploration Program are shown in italic type.