CONCLUSION
The alignment between missions listed in Table 2 and crosscutting themes and priority questions from Vision and Voyages is outlined in Table A.1 of the Appendix.44
CAPS concludes that the missions outlined in Table 2 represent broad areas ripe for further development in preparation for the next planetary science decadal survey. The missions outlined are intended as input to prompt community discussion rather than as specific prescriptive concepts.
Enhancing and Enabling Technologies
Since the release of Vision and Voyages, there have been technological advancements on a number of fronts.45 Although technology is not specifically mentioned in the committee’s charge, CAPS was encouraged to consider technological issues by the following comments in Vision and Voyages: “The scientific harvest from these robotic missions has been sensational, but the extraordinary breadth and depth of these discoveries would not have been possible without parallel technology developments that provided the necessary capabilities.”46 Thus, in addition to identifying priority science mission concepts requiring study prior to the initiation of the next planetary science decadal survey, CAPS also discussed several enabling and/or enhancing technologies that would benefit from further review in the coming years. These technologies are summarized in Table 3 and are described in more detail later in this section. The rationale for examining technological capabilities is that the present status of some of these technologies suggests that they have the potential to enhance the science return for mission concepts studied previously and to motivate the inclusion of individuals with appropriate expertise on future mission study teams. In addition, a review of these technologies could benefit all of NASA’s missions to be launched in the next decade and beyond.
The items highlighted in Table 3 are those CAPS was able to identify in the limited time at its disposal. The chapter “The Role of Technology Development in Planetary Exploration” in Vision and Voyages contains a more complete description of some of those not included in Table 3, such as science instruments (particularly, advancing the technology readiness level of those with the highest potential for making new discoveries), survival in extreme environments, sample handling, and in situ exploration.47
CRYOGENIC SAMPLE ACQUISITION, HANDLING, AND RETURN SYSTEMS
Vision and Voyages commented that the important breakthroughs in understanding of presolar and nebular cosmochemistry would come from the analysis of samples returned directly from the surfaces of comets. But, “the greatest scientific breakthroughs in addressing these questions will come from studying returned surface samples whose volatiles have been cryogenically preserved.”48 The planetary science decadal survey went so far as to say that it was not proposing a flagship-class primitive bodies mission in the current decade so that a technology development program could be initiated to ensure that “such a mission will be possible in the decade after 2022.”49 Since Vision and Voyages was completed, ESA’s Rosetta mission has returned a wealth of new information about comets. In addition, at least one
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44 The crosscutting themes and priority questions are summarized in NRC, Vision and Voyages, 2011, Table 3.1, p. 71.
45 The priority technologies are identified in NRC, Vision and Voyages, 2011, Table 11.1, p. 304.
46 NRC, Vision and Voyages, 2011, p. 303.
47 See NRC, Vision and Voyages, 2011, pp. 303-312.
48 See NRC, Vision and Voyages, 2011, p. 72.
49 See NRC, Vision and Voyages, 2011, p. 87.
TABLE 3 Important Technologies and Other Activities Worthy of Review (not in priority order)
| Area Requiring Study | Notes |
|---|---|
| Cryogenic sample acquisition, handling, and return systems | Cryogenic sampling and sample preservation systems (e.g., for use by comet and lunar-polar sample-return missions) |
| Daughtercraft enhancements to large- and medium-class missions | Substantial planetary science discoveries possible with small craft that expand the scope of their mothership by conducting complementary science and/or exploration of multiple locales |
| Advanced radioisotope power systems | Understand the expected demand for plutonium and associated power-conversion technologies to meet power demands of large-, medium-, and, potentially, small-class missions during the next decade |
| Electric propulsion | Understand the technology development plans for advanced electric propulsion |
| Aerocapture | Understand the technology development plans for aerocapture |
| Optical communication | Understand the technology development plans for free-space optical communication and how far it may be usefully extended into the solar system |
| Autonomous operations | Computing advances allow for more spacecraft autonomy in exploration, improving science return and reducing cost |
proposal for a comet surface (i.e., non-cryogenic) sample return mission is under consideration in the current competition for New Frontiers 4. Moreover, confirmation that frozen volatiles exist in permanently shadowed regions in the polar regions of the Moon and Mercury suggests that the return of cryogenically preserved materials to Earth will be an issue of great interest to the next planetary science decadal survey.
A technology study commissioned in support of Vision and Voyages addressed the challenges of returning rock and ice samples to Earth from the near subsurface of a comet nucleus. The study revealed that a storage temperature of about 125 K was technically feasible and sufficient to maintain the integrity of samples of water ice during the long cruise back to Earth. However, the integrity of more exotic ices, such as hydrogen cyanide and carbon dioxide, would be compromised if the storage temperature was not below 90 K. Maintaining this lower storage temperature would have significant impacts on the cost and complexity of the mission. A reassessment of these results for retrieval of water and other ices from a comet nucleus and the lunar polar regions will likely be of great assistance to the next planetary science decadal survey.
DAUGHTERCRAFT ENHANCEMENTS
A 2016 National Academies report50 highlighted advances in space sciences achievable with CubeSats. Regardless of the use of the CubeSat form factor, two independent advances in capabilities—miniaturization of scientific instrumentation and enhancement of small satellite technology and its
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50 NASEM, Achieving Science with CubeSats: Thinking Inside the Box, The National Academies Press, Washington, D.C., 2016.
reliability—mean that substantial planetary science discoveries are potentially within the capabilities of small craft. Indeed, the 2016 report noted that “CubeSats and platforms taking advantage of CubeSat technology have the potential to make unique contributions to planetary science by creating unique vantage points or multipoint measurements (e.g., in situ package(s) complementary to an orbiter); exploring high-risk or uncharted regions; and serving as low-gravity laboratories.”51 One particular example of the use of CubeSat and related technologies noted in the 2016 report was that deployable, daughtercraft enhancements to large- and medium-class missions “could expand the scope of the mothership with complementary science or site exploration.”52 Communication and propulsion technologies, coordinated operations, autonomous operations, and risk posture are key areas of study in advance of the next planetary science decadal survey that could appropriately capitalize on this emerging technology area in mission concepts.
ADVANCED RADIOISOTOPE POWER SYSTEMS
Radioisotope power systems (RPS) are an enabling technology of particular applicability to future exploration of many solar system environments, including the outer planets, Kuiper belt objects, and nighttime operations.53 As the next planetary science decadal survey sets about its task, its authors will need to be mindful of the expected demand for plutonium-238 and associated thermoelectric conversion technologies to meet the needs of recommended large-, medium-, and, potentially, small-class missions during the next decade. Also important will be consideration of the expected availability of plutonium-238 and the plans to provide advanced RPS to meet the demand. These issues are addressed in the recent comprehensive Nuclear Power Assessment Study to NASA’s Radioisotope Power Systems Program,54 which should prove most useful for the next planetary science decadal survey.
ELECTRIC PROPULSION
Electric propulsion is highlighted in the recent ice giants study55 (see Table 1) as enabling for some of the mission options. The importance of this technology was also identified in Vision and Voyages.56 An advanced electric propulsion system could potentially increase spaceflight transportation fuel efficiency by a factor of 10 over current chemical propulsion technologies and more than double thrust capability compared to current electric propulsion systems.57 The next step will be to demonstrate this new electric propulsion system in space. Development of this technology will advance future in-space transportation capability for a variety of deep-space human and robotic exploration missions.
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51 See, NASEM, Achieving Science with CubeSats, 2016, p. 45.
52 See, NASEM, Achieving Science with CubeSats, 2016, pp. 2, 53, and 84.
53 For a comprehensive review see, for example, NRC, Radioisotope Power Systems: An Imperative for Maintaining U.S. Leadership in Space Exploration, The National Academies Press, Washington, D.C., 2009.
54 Johns Hopkins University Applied Physics Laboratory, Nuclear Power Assessment Study—Final Report, Laurel, Md., 2015, https://solarsystem.nasa.gov/rps/npas.cfm.
55 Solar System Exploration Directorate, Ice Giants Pre-Decadal Study Final Report, JPL D-100520, Jet Propulsion Laboratory, Pasadena, Calif., 2017, http://www.lpi.usra.edu/icegiants/mission_study/Full-Report.pdf.
56 See NRC, Vision and Voyages, 2011, pp. 307-308.
57 See, for example, NASA, “STMD: Tech Demo Missions: Solar Electric Propulsion (SEP),” fact sheet, last updated August 22, 2016, https://www.nasa.gov/mission_pages/tdm/sep/index.html.
AEROCAPTURE
Aerocapture is also highlighted in the ice giants study58 as enabling for some of the mission options. The need to develop this technology was also identified in Vision and Voyages and a recent assessment of its applicability to future missions was conducted by JPL.59,60 The JPL study concluded that no developments are needed for aerocapture at Titan, Venus, or Mars. For other destinations, additional technology development is required. Depending on the destination, this development would involve the formulation of new thermal protection systems or the design of aeroshells with higher lift-to-drag ratios than those currently available. With the possible exception of Neptune, heritage hypersonic guidance and control technologies may be sufficient.
OPTICAL COMMUNICATION
Radio frequency (RF) communications have become a bottleneck for moving data at Internet speeds in space. A free-space optical communication system using lasers offers the promise of breaking through that RF bottleneck by potentially increasing data rates that are 10 to 100 times better than current RF communications systems. Technology demonstrations are currently under way that will pave the way for use of this technology in future deep-space missions. The Laser Communications Relay Demonstration (LCRD),61 sponsored by NASA’s Space Technology and Human Exploration and Operations mission directorates, is the next technology demonstration following the successful Lunar Laser Communications Demonstration,62 a very successful pathfinder mission that flew aboard the Lunar Atmosphere Dust and Environment Explorer in 2013. Launch of LCRD is currently planned for 2018.
AUTONOMOUS OPERATIONS
As instruments become more capable, downlink data volume and the ability to have Earth in the loop become the limiting factors for collecting the best scientific data products. Recent efforts in autonomous operations of landed explorers and spacecraft systems have initiated migration to operation and data processing without Earth in the loop. For example, the Mars rovers are now equipped to autonomously select target types of interest using the so-called Autonomous Exploration for Gathering Increased Science (AEGIS) software.63 As exploration moves to the outer solar system and as high-data-volume products are created by capable instruments, efforts to develop spacecraft avionics and control software that enable feedbacks with the environment will need to be expanded. Future activities, such as
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58 Solar System Exploration Directorate, Ice Giants Pre-Decadal Study Final Report, JPL D-100520, Jet Propulsion Laboratory, Pasadena, Calif., 2017, http://www.lpi.usra.edu/icegiants/mission_study/Full-Report.pdf.
59 See NRC, Vision and Voyages, 2011, pp. 306-307.
60 T.R. Spilker, C.S. Borden, M. Adler, M.M. Munk, R.W. Powell, R.D. Braun, P.M. Beauchamp, et al, An Assessment of Aerocapture and Applications to Future Missions, D-97058, Jet Propulsion Laboratory, Pasadena, Calif., February 13, 2016.
61 See, for example, NASA, “STMD: Tech Demo Missions: Laser Communications Relay Demonstration (LCRD),” last updated May 23, 2017, https://www.nasa.gov/mission_pages/tdm/lcrd/index.html.
62 D.M. Boronson, “The Lunar Laser Communication Demonstration: NASA’s First Step Toward Very High Data Rate Support of Science and Exploration Missions,” pp. 115-128 in The Lunar Atmosphere and Dust Environment Explorer Mission (LADEE) (R.C. Elphic and C.T. Russell, eds.), Springer International Publishing, Switzerland, 2015.
63 For more details about AEGIS see, for example, R. Francis, T. Estlin, D. Gaines, G. Doran, O. Gasnault, S. Johnstone, S. Montaño, et al., “AEGIS Intelligent Targeting Deployed for the Curiosity Rover’s CHEMCAM Instrument,” 47th Lunar and Planetary Science Conference, 2016, https://www.hou.usra.edu/meetings/lpsc2016/pdf/2487.pdf.
