This report was requested by the National Aeronautics and Space Administration (NASA) and the National Science Foundation (NSF) to review and assess the current status of planetary science and to develop a comprehensive science and mission strategy that updates and extends the National Research Council’s (NRC’s) 2003 planetary decadal survey, New Frontiers in the Solar System: An Integrated Exploration Strategy.1 As is standard for a decadal survey, the Committee on the Planetary Science Decadal Survey that was established to write this report broadly canvassed the planetary science community to determine the current state of knowledge and to identify the most important science questions to be addressed during the period 2013-2022. The ground- and space-based programmatic initiatives needed to address these important questions are identified, assessed, and prioritized. The committee also addressed relevant programmatic and implementation issues of interest to NASA and NSF.
SCOPE OF THIS REPORT
The scope of this report spans the scientific disciplines that collectively encompass the ground- and space-based elements of planetary science. It also covers the physical territory within the committee’s purview: the solar system’s principal constituents. This territory includes the following:
• The major rocky bodies in the inner solar system,
• The giant planets in the outer solar system,
• The satellites of the giant planets, and
• Primitive solar system bodies.
The committee imposed programmatic boundary conditions, derived largely from its statement of task (see Appendix A), to ensure that this report contains actionable advice:
• The principal findings and recommendations contained in New Frontiers in the Solar System and more recent NRC reports relevant to planetary science activities were assessed, and incorporated where appropriate. Missions identified in those past reports were reprioritized if they had not yet been confirmed for implementation.
• Priorities for spacecraft missions to the Moon, Mars, and other solar system bodies were treated in a unified manner with no predetermined “set-asides” for specific bodies. This approach differs distinctly from the ground rules for the 2003 planetary decadal survey, in which missions to Mars were prioritized separately.
• The committee’s programmatic recommendations were designed to be achievable within the boundaries of anticipated NASA and NSF funding.
• This report is cognizant of the current statutory roles of NSF and NASA, and how these roles may or may not be consistent with current practices within the two agencies regarding support for specific activities—for example, the funding mechanisms, construction, and operation of ground-based observatories.
• This report reflects an awareness of the science and space mission plans and priorities of potential foreign and U.S. agency partners. This report’s recommendations are, however, addressed to NASA and NSF.
To maintain consistency with other advice developed by the NRC and to ensure that this report clearly addresses those topics identified in the committee’s statement of task, the following topics are not addressed in this report:
• Issues relating to the hazards posed by near-Earth objects and approaches to hazard mitigation. However, scientific studies of near-Earth asteroids are discussed in this report.
• Study of the Earth system, including its atmosphere, magnetosphere, surface, and interior.
• Studies of solar and heliospheric phenomena, with the exception of interactions with the atmospheres, magnetospheres, and surfaces of solar system bodies; and magnetospheric effects of planets on their satellites and rings.
• Ground- and space-based studies to detect and characterize extrasolar planets. However, this report does contain a discussion of the scientific issues concerning the comparative planetology of the solar system’s planets and extrasolar planets, together with issues related to the formation and evolution of planetary system.
The committee’s statement of task calls for this report to contain three principal elements: a survey of planetary science; an assessment of and recommendations relating to NASA activities; and an assessment of and recommendations relating to NSF activities. Subsequent sections of this summary address each of these topics in turn.
SURVEY OF PLANETARY SCIENCE
Overview of Planetary Science
Planetary science is shorthand for the broad array of scientific disciplines that collectively seek answers to basic questions such as how planets form, how they work, and why at least one planet is the abode of life. These basic motivations explain why planetary science is an important undertaking, worthy of public support. Though deceptively simple, they have inspired a 50-year epic series of exploratory voyages by robotic spacecraft that have visited almost every type of planetary body in humankind’s celestial neighborhood. These robotic voyages have been complemented by investigations with ground- and space-based telescopes, laboratory studies, theoretical studies, and modeling activities. The resulting grand adventure has transformed humankind’s understanding of the collection of objects orbiting the Sun. Since New Frontiers was published in 2003, ground- and space-based planetary science activities have been particularly productive. Mission after mission, study after study, have uncovered stunning new discoveries. Some especially notable examples include the following:
• An explosion in the number of known exoplanets,
• Evidence that the Moon is less dry than once thought,
• Minerals that must have formed in a diverse set of aqueous environments throughout martian history,
• Extensive deposits of near-surface ice on Mars,
• An active meteorological cycle involving liquid methane on Titan,
• Dramatic changes in the atmospheres and rings of the giant planets,
• Recent volcanic activity on Venus,
• Geothermal and plume activity at the south pole of Enceladus,
• The anomalous isotopic composition of the planets,
• High-temperature minerals found in comet dust,
• Mercury’s liquid core, and
• The richness and diversity of the Kuiper belt.
Current State of Knowledge and Important Science Questions
The deep-rooted motives underlying the planetary sciences address issues of profound importance that have been pondered by scientists and non-scientists alike for centuries. Such questions cannot be fully addressed by a single spacecraft mission or series of telescopic observations. It is likely, in fact, that they will not be completely addressed in this decade or the next. To make progress in organizing and outlining the current state of knowledge, the committee translated and codified the basic motivations for planetary science into three broad, crosscutting themes:
• Building new worlds—understanding solar system beginnings,
• Planetary habitats—searching for the requirements for life, and
• Workings of solar systems—revealing planetary processes through time.
Each science theme brings its own set of questions, based on current understanding of the underlying issues:
• Building new worlds
—What were the initial stages, conditions, and processes of solar system formation and the nature of the interstellar matter that was incorporated? Important objects for study: comets, asteroids, Trojans, and Kuiper belt objects.
—How did the giant planets and their satellite systems accrete, and is there evidence that they migrated to new orbital positions? Important objects for study: Enceladus, Europa, Io, Ganymede, Jupiter, Saturn, Uranus, Neptune, Kuiper belt objects, Titan, and rings.
—What governed the accretion, supply of water, chemistry, and internal differentiation of the inner and the evolution of their atmospheres, and what roles did bombardment by large projectiles play? Important objects for study: Mars, the Moon, Trojans, Venus, asteroids, and comets.
• Planetary habitats
—What were the primordial sources of organic matter, and where does organic synthesis continue today? Important objects for study: comets, asteroids, Trojans, Kuiper belt objects, Enceladus, Europa, Mars, Titan, and uranian satellites.
—Did Mars or Venus host ancient aqueous environments conducive to early life, and is there evidence that life emerged? Important objects for study: Mars and Venus.
—Beyond Earth, are there contemporary habitats elsewhere in the solar system with necessary conditions, organic matter, water, energy, and nutrients to sustain life, and do organisms live there now? Important objects for study: Enceladus, Europa, Mars, and Titan.
• Workings of solar systems
—How do the giant planets serve as laboratories to understand Earth, the solar system, and extrasolar planetary systems? Important objects for study: Jupiter, Neptune, Saturn, and Uranus.
—What solar system bodies endanger Earth’s biosphere, and what mechanisms shield it? Important objects for study: near-Earth objects, the Moon, comets, and Jupiter.
—Can understanding the roles of physics, chemistry, geology, and dynamics in driving planetary atmospheres and climates lead to a better understanding of climate change on Earth? Important objects for study: Mars, Jupiter, Neptune, Saturn, Titan, Uranus, and Venus.
—How have the myriad chemical and physical processes that shaped the solar system operated, interacted, and evolved over time? Important objects for study: all planetary bodies.
Each question represents a distillation of major areas of research in planetary science, and the questions themselves are sometimes crosscutting. Each question points to one or more solar system bodies that may hold clues or other vital information necessary for their resolution. The detailed discussions in Chapters 4 through 8 further explore these questions, dissecting them to identify the specific opportunities best addressed in the coming decade by large, medium, and small spacecraft missions, as well as by other space- and ground-based research activities.
The principal support in the United States for research related to solar system bodies comes from the Planetary Science Division (PSD) of NASA’s Science Mission Directorate. The PSD supports research through a combination of spacecraft missions, technology development activities, support for research infrastructure, and research grants. The annual budget of the PSD is currently approximately $1.3 billion, the bulk of which is spent on the development, construction, launch, and operation of spacecraft. Two types of spacecraft missions are conducted: large “flagship” missions strategically directed by the PSD and smaller Discovery and New Frontiers missions proposed and led by principal investigators (PIs). The choice and the scope of strategic missions are determined through a well-developed planning process, drawing its scientific inputs from advisory groups both internal and external (e.g., the NRC) to NASA. The PI-led missions are selected by a peer-review process that considers the scientific, technical, and fiscal merit of competing proposals submitted in open competition.
The statement of task for this study calls for creation of a prioritized list of flight investigations for the decade 2013-2022. A prioritized list implies that the elements of the list have been judged and ordered with respect to a set of appropriate criteria. Four criteria were used. The first and most important was science return per dollar. Science return was judged with respect to the key science questions described above; costs were estimated via a procedure described below. The second criterion was programmatic balance—striving to achieve an appropriate balance among mission targets across the solar system and an appropriate mix of small, medium, and large missions. The other two criteria were technological readiness and availability of trajectory opportunities within the 2013-2022 time period.
The recommended flight projects for the coming decade were considered within the context of the broader program of planetary exploration. All of the mission recommendations assume that the following basic programmatic requirements are fully funded:
• Continue missions currently in flight, subject to approval obtained through the appropriate senior review process. Ensure a level of funding that is adequate for successful operation, analysis of data, and publication of the results of these missions, and for extended missions that afford rich new science return.
• Continue missions currently in development.
• Increase funding for fundamental research and analysis grant programs, beginning with a 5 percent increase above the total finally approved fiscal year (FY) 2011 expenditures and then growing at an additional 1.5 percent per year above inflation for the remainder of the decade.
• Establish and maintain a significant and steady level of funding (6 to 8 percent of the planetary exploration budget) for development of technologies that will enable future planetary flight projects.
Mission Study Process and Cost and Technical Evaluation
To help develop recommendations, the committee commissioned technical studies of many candidate missions. These candidate missions were selected for study on the basis of white papers contributed by the scientific community and recommendations made by the survey committee’s five panels (Appendix B provides a list of all white papers contributed).
A subset of the mission studies was selected by the committee for further analysis using the cost and technical evaluation (CATE) process, which was performed by the Aerospace Corporation, a contractor to the NRC.
This selection was made on the basis of the four prioritization criteria listed above, with science return per dollar being the most important. The CATE analysis was designed to provide an independent assessment of the technical feasibility of the mission candidates, as well as to produce a rough appraisal of their costs. The analysis takes into account many factors when evaluating a mission’s potential costs, including the actual costs of analogous previous missions.
The CATE analysis typically returned cost estimates that were significantly higher than the estimates produced by the study teams, primarily because CATE estimates are based on the actual costs of analogous past projects and thus avoid the optimism inherent in other cost estimation processes. Only the independently generated CATE cost estimates were used by the committee in evaluating the candidate missions and in formulating its final recommendations. This intentionally cautious approach was designed to help prevent the unrealistic cost estimates and consequent replanning that have sometimes characterized the planetary program in the past. The committee emphasizes that the studies carried out were of specific “point designs” for the mission candidates identified by the survey’s panels. These point designs are a “proof of concept” that such a mission may be feasible, and they provide a basis for developing a cost estimate for the purpose of the decadal survey. The actual missions as flown may differ in their detailed designs and their final costs from what was studied, but in order to maintain a balanced and orderly program, the missions’ final costs must not be allowed to grow significantly beyond those estimated here.
Achieving a Balanced Program
In addition to maximizing science return per dollar, another important factor in formulating the committee’s recommendations was achieving programmatic balance. The challenge is to assemble a portfolio of missions that achieves a regular tempo of solar system exploration and a level of investigation appropriate for each target object. For example, a program consisting of only flagship missions once per decade may result in long stretches of relatively little new data being generated, leading to a stagnant planetary science community. Conversely, a portfolio of only Discovery-class missions would be incapable of addressing important scientific challenges such as in-depth exploration of the outer planets. NASA’s suite of planetary missions for the decade 2013-2022 should consist of a balanced mix of Discovery, New Frontiers, and flagship missions, enabling both a steady stream of new discoveries and the capability to address larger challenges such as sample return missions and outer planet exploration. The program recommended below was designed to achieve such a balance. To prevent the balance among mission classes from becoming skewed, it is crucial that all missions, particularly the most costly ones, be initiated with a good understanding of their probable costs. The CATE process was designed specifically to address this issue by taking a realistic approach to cost estimation.
It is also important that there be an appropriate balance among the many potential targets in the solar system. Achieving this balance was one of the key factors informing the recommendations for medium and large missions presented below. The committee notes, however, that there should be no entitlement in a publicly funded program of scientific exploration. Achieving balance must not be used as an excuse for failing to make difficult but necessary choices.
The issues of balance across the solar system and balance among mission sizes are related. For example, it is difficult to investigate targets in the outer solar system with small or even medium missions. Some targets, however, are ideally suited to small missions. The committee’s recommendations below reflect this fact and implicitly assume that Discovery missions will address important questions whose exploration does not require the capability provided by medium or large missions.
It is not appropriate to achieve balance simply by allocating certain numbers or certain sizes of missions to certain classes of objects. Instead, a scientifically appropriate balance of solar system exploration activities must be found by selecting the set of missions that best addresses the highest priorities among the overarching science questions associated with the three crosscutting science themes listed above. The recommendations below are made in accordance with this principle.
Recommended Program of Missions
Within the category of small missions are three elements of particular interest: the Discovery program, extended missions for ongoing projects, and Missions of Opportunity.
Mission candidates for the Discovery program are outside the bounds of a decadal strategic plan, and this decadal survey makes no recommendations for specific Discovery flight missions. The committee stresses, however, that the Discovery program has made important and fundamental contributions to planetary exploration and can continue to do so in the coming decade. The committee gives the Discovery program its strong support.
The committee notes that NASA does not intend to continue the Mars Scout program beyond the MAVEN mission, nor does it recommend that NASA do otherwise. Instead, the committee recommends that NASA continue to allow proposals for Discovery missions to all planetary bodies, including Mars.
Because there is still so much compelling science that can be addressed by Discovery missions, the committee recommends continuation of the Discovery program at its current level, adjusted for inflation, with a cost cap per mission that is also adjusted for inflation from the current value (i.e., to about $500 million FY2015). So that the community can plan Discovery missions effectively, the committee recommends a regular, predictable, and preferably short (.24-month) cadence for Discovery Announcement of Opportunity releases and mission selections. Because so many important missions can be flown within the current Discovery cost cap (adjusted for inflation), the committee views a steady tempo of Discovery Announcements of Opportunity and selections to be more important than increasing the cost cap, as long as launch vehicle costs continue to be excluded. A hallmark of the Discovery program has been rapid and frequent mission opportunities. The committee urges NASA to assess schedule risks carefully during mission selection, and to plan program budgeting so as to maintain the original goals of the Discovery program.
Other Small Mission Opportunities
Mission extensions can be significant and highly productive, and may also enhance missions that undergo changes in scope because of unpredictable events. In some cases, particularly the “re-purposing” of operating spacecraft, fundamentally new science can be enabled. These mission extensions, which require their own funding arrangements, can be treated as independent, small-class missions. The committee supports NASA’s current senior review process for deciding the scientific merits of a proposed mission extension. The committee recommends that early planning be done to provide adequate funding of mission extensions, particularly for flagship missions and missions with international partners.
Near the end of the past decade, NASA introduced a new acquisition vehicle called Stand Alone Missions of Opportunity (SALMON). In addition to their science return, Missions of Opportunity provide a chance for new entrants to join the field, for technologies to be validated, and for future PIs to gain experience. The committee welcomes the introduction of the highly flexible SALMON approach and recommends that it be used wherever possible to facilitate Mission of Opportunity collaborations.
An important special case of a small mission is the proposed joint European Space Agency (ESA)-NASA Mars Trace Gas Orbiter. The mission would launch in 2016, with NASA providing the launch vehicle, ESA providing the orbiter, and both agencies providing a joint science payload that was recently selected. Based on the mission’s high science value and its relatively low cost to NASA, the committee supports flight of the Mars Trace Gas Orbiter in 2016 as long as the division of responsibilities with ESA outlined above is preserved.
The New Frontiers program allows for competitive selection of focused, strategic missions to conduct high-quality science. The current New Frontiers cost cap, inflated to FY2015 dollars, is $1.05 billion, including launch
vehicle costs. The committee recommends changing the New Frontiers cost cap to $1.0 billion FY2015, excluding launch vehicle costs. This change represents a modest increase in the total cost of a New Frontiers mission provided that the cost of launch vehicles does not rise precipitously; the increase is fully accounted for in the program recommendations below. This change will allow a scientifically rich and diverse set of New Frontiers missions to be carried out. Importantly, it will also help protect the science content of the New Frontiers program against increases and volatility in launch vehicle costs.
The New Frontiers program to date has resulted in the selection of the New Horizons mission to Pluto and the Juno mission to Jupiter. The former is in flight and the latter is in development. A competition to select a third New Frontiers mission is now underway, with selection scheduled for 2011.2 In this report the committee addresses subsequent New Frontiers missions, beginning with the fourth, to be selected during the decade 2013-2022.
On the basis of their science value and projected costs, the committee identified seven candidate New missions for the decade 2013-2022. All are judged to be plausibly achievable within the recommended New Frontiers cost cap (although, for some, not within the previous cap). In alphabetical order, they are as follows:
• Comet Surface Sample Return—The objective of this mission is to acquire and return to Earth a macroscopic sample from the surface of a comet nucleus using a sampling technique that preserves organic material in the sample.
• Io Observer—The focus of this mission is to determine the internal structure of Io and to investigate the mechanisms that contribute to the satellite’s intense volcanic activity from a highly elliptical orbit around Jupiter, making multiple flybys of Io.
• Lunar Geophysical Network—This mission consists of several identical landers distributed across the lunar surface, each carrying instrumentation for geophysical studies. The primary science objectives are to characterize the Moon’s internal structure, seismic activity, global heat flow budget, bulk composition, and magnetic field.
• Lunar South Pole-Aitken Basin Sample Return—The primary science objective of this mission is to return samples from this ancient and deeply excavated impact basin to Earth for characterization and study.
• Saturn Probe—This mission would deploy a probe into Saturn’s atmosphere to determine the structure of the atmosphere as well as abundances of noble gases and isotopic ratios of hydrogen, carbon, nitrogen, and oxygen.
• Trojan Tour and Rendezvous—This mission is designed to examine two or more small bodies sharing the orbit of Jupiter, including one or more flybys followed by an extended rendezvous with a Trojan object.
• Venus In Situ Explorer—The primary science objectives of this mission are to examine the physics and chemistry of Venus’s atmosphere and crust. The mission would attempt to characterize variables that cannot be measured from orbit, including the detailed composition of the lower atmosphere and the elemental and mineralogical composition of surface materials.
The current competition to select the third New Frontiers mission includes the SAGE mission to Venus and the MoonRise mission to the Moon. These missions are responsive to the science objectives of the Venus In Situ Explorer and the Lunar South Pole-Aitken Basin Sample Return, respectively. The committee assumes that the ongoing NASA evaluation of these two missions has validated their ability to be performed at a cost appropriate for New Frontiers. For the other five listed above, the CATE analyses performed in support of this decadal survey show that it may be possible to execute them within the New Frontiers cap.
To achieve an appropriate balance among small, medium, and large missions, NASA should select two New Frontiers missions in the decade 2013-2022. These are referred to here as New Frontiers Mission 4 and New Frontiers Mission 5.
New Frontiers Mission 4 should be selected from among the following five candidates:
• Comet Surface Sample Return,
• Lunar South Pole-Aitken Basin Sample Return,
• Saturn Probe,
• Trojan Tour and Rendezvous, and
• Venus In Situ Explorer.
These five missions were selected from the seven listed above based on the criteria of science return per dollar, programmatic balance, technological readiness, and availability of spacecraft trajectories. No relative priorities are assigned to these five mission candidates; instead, the selection among them should be made on the basis of competitive peer review.
If either SAGE or MoonRise is selected by NASA in 2011 as the third New Frontiers mission, the corresponding mission candidate should be removed from the above list of five, reducing to four the number of candidates from which NASA should make the New Frontiers Mission 4 selection.3
For the New Frontiers Mission 5 selection, the Io Observer and the Lunar Geophysical Network should be added to the list of remaining candidate missions, increasing the total number of candidates for that selection to either five or six. Again, no relative priorities are assigned to any of these mission candidates.
The decadal survey has identified five candidate flagship missions for the decade 2013-2022. In alphabetical order, they are as follows:
• Enceladus Orbiter—This mission would investigate that saturnian satellite’s cryovolcanic activity, habitability, internal structure, chemistry, geology, and interaction with the other bodies of the Saturn system.
• Jupiter Europa Orbiter (JEO)—This mission would characterize Europa’s ocean and interior, ice shell, chemistry and composition, and the geology of prospective landing sites.
• Mars Astrobiology Explorer-Cacher (MAX-C)—This mission is the first of the three components of the Mars Sample Return campaign. It is responsible for characterizing a landing site selected for high science potential, and for collecting, documenting, and packaging samples for return to Earth.
• Uranus Orbiter and Probe—This mission’s spacecraft would deploy a small probe into the atmosphere of Uranus to make in situ measurements of noble gas abundances and isotopic ratios and would then enter orbit, making remote sensing measurements of the planet’s atmosphere, interior, magnetic field, and rings, as well as multiple flybys of the larger uranian satellites.
• Venus Climate Mission—This mission is designed to address science objectives concerning the Venus atmosphere, including carbon dioxide greenhouse effects, dynamics and variability, surface-atmosphere exchange, and origin. The mission architecture includes a carrier spacecraft, a gondola and balloon system, a mini-probe, and two dropsondes.
The CATE analyses performed for these five candidate flagship missions yielded estimates for the full life-cycle cost of each mission as defined above, including the cost of the launch vehicle, in FY2015 dollars. For missions with international components (the Europa Jupiter System Mission, of which JEO is a part; and MAX-C) only the NASA costs are included. The cost estimates are as follows:
• Enceladus Orbiter, $1.9 billion;
• Jupiter Europa Orbiter, $4.7 billion;
• Mars Astrobiology Explorer-Cacher, $3.5 billion;4
• Uranus Orbiter and Probe, $2.7 billion;5 and
• Venus Climate Mission, $2.4 billion.
The committee devoted considerable attention to the relative priorities of the various large-class mission candidates. In particular, both JEO and the Mars Sample Return campaign (beginning with MAX-C) were found to have exceptional science merit. Because it was difficult to discriminate between the Mars Sample Return campaign and JEO on the basis of their anticipated science return per dollar alone, other factors came into play. Foremost among these was the need to maintain programmatic balance by ensuring that no one mission takes up too large a fraction of the planetary budget at any given time.
The highest-priority flagship mission for the decade 2013-2022 is MAX-C, which will begin the NASA-ESA
Mars Sample Return campaign. However, the cost of MAX-C must be constrained in order to maintain programmatic balance.
The Mars community, in their inputs to the decadal survey, was emphatic in their view that a sample return mission is the logical next step in Mars exploration. Mars science has reached a level of sophistication such that fundamental advances in addressing the important questions above will come only from analysis of returned samples. MAX-C will also explore a new site and significantly advance understanding of the geologic history and evolution of Mars, even before the cached samples are returned to Earth.
Unfortunately, at an independently estimated cost of $3.5 billion, MAX-C would take up a disproportionate near-term share of the overall budget for NASA’s Planetary Science Division. This very high cost results in large part from two large and capable rovers—both a NASA sample-caching rover and the ESA’s ExoMars rover—being jointly delivered by a single entry, descent, and landing (EDL) system derived from the Mars Science Laboratory (MSL) EDL system. The CATE results for MAX-C projected that accommodation of two such large rovers would require major redesign of the MSL EDL system, with substantial associated cost growth.
The committee recommends that NASA should fly the MAX-C mission in the decade 2013-2022 only if it can be conducted for a cost to NASA of no more than approximately $2.5 billion (FY2015 dollars). If a cost of no more than about $2.5 billion FY2015 cannot be verified, the mission (and the subsequent elements of Mars Sample Return) should be deferred until a subsequent decade or canceled outright.
It is likely that a significant reduction in mission scope will be needed to keep the cost of MAX-C below $2.5 billion. A key part of this reduction in scope is likely to be reducing landed mass and volume. In particular, it is crucial to preserve, as much as possible, both the system structure and the individual elements of the MSL EDL system. A significant reduction in landed mass and volume can be expected to lead to a significant reduction in the scientific capabilities of the vehicles delivered to the surface.
The committee recognizes that MAX-C is envisioned by NASA to be part of a joint NASA-ESA program of Mars exploration that also includes the 2016 Mars Trace Gas Orbiter. To be of benefit to NASA, this partnership must also involve ESA participation in other missions of the three-mission Mars Sample Return campaign. It is crucial to both parties for the partnership to be preserved. The best way to maintain the partnership will be an equitable reduction in scope of both the NASA and the ESA objectives for the MAX-C/ExoMars mission, so that both parties still benefit from it. The guiding principle for any descope process should be to preserve the highest-priority science objectives of the total Mars program for both agencies while reducing costs to acceptable levels.
The second-highest-priority flagship mission for the decade 2013-2022 is the Jupiter Europa Orbiter. However, as it is currently designed JEO has a cost that is so high that both a decrease in mission scope and an increase in NASA’s planetary budget are necessary to make it affordable.
The Europa Geophysical Explorer, from which the JEO concept is derived, was the one flagship mission recommended in the 2003 planetary decadal survey. The scientific case for this mission was compelling then, and it remains compelling now. Substantial technology work has been done on JEO over the past decade, with the result that NASA is much more capable of accomplishing this mission than was the case 10 years ago.
The difficulty in achieving JEO is its cost. The projected cost of the mission as currently designed is $4.7 billion FY2015. If JEO were to be funded at this level within the currently projected NASA planetary budget it would lead to an unacceptable programmatic imbalance, eliminating too many other important missions. Therefore, while the committee recommends JEO as the second-highest-priority flagship mission, close behind MAX-C, JEO should fly in the decade 2013-2022 only if changes to both the mission and the NASA planetary budget make it affordable without eliminating any other recommended missions. These changes are likely to involve both a reduction in mission scope and a formal budgetary new start for JEO that is accompanied by an increase in the NASA planetary budget.
It is clearly crucial to keep as small as possible the budget increase required to enable JEO. Possible pathways to lower cost include use of a larger launch vehicle that would reduce cost risk by shortening and simplifying the mission design, and a significant reduction in the science payload. NASA should immediately undertake an effort to find major cost reductions for JEO, with the goal of minimizing the size of the budget increase necessary to enable the mission.
The third-highest-priority flagship mission is the Uranus Orbiter and Probe mission. Galileo, Cassini, and Juno have performed or will perform spectacular in-depth investigations of Jupiter and Saturn. The Kepler mission and microlensing surveys have shown that many exoplanets are ice-giant size. Exploration of the ice giants Uranus and Neptune is therefore the obvious and important next step in the exploration of the giant planets.
The committee carefully investigated missions to both Uranus and Neptune. Although both missions have high scientific merit, the conclusion was that a Uranus mission is favored for the decade 2013-2022 for practical reasons. These reasons include the lack of optimal trajectories to Neptune in that time period, long flight times incompatible with the use of Advanced Stirling Radioisotope Generators for spacecraft power, the risks associated with aerocapture at Neptune, and the high cost of delivery to Neptune. Because of its outstanding scientific potential and a projected cost that is well matched to its anticipated science return, the Uranus Orbiter and Probe mission should be initiated in the decade 2013-2022 even if both MAX-C and JEO take place. But like those other two missions, the Uranus Orbiter and Probe mission should be subjected to rigorous independent cost verification throughout its development and should be descoped or canceled if costs grow significantly above the projected $2.7 billion FY2015.
The fourth- and fifth-highest-priority flagship missions are, in alphabetical order, the Enceladus Orbiter and the Venus Climate Mission. To maintain an appropriate balance among small, medium, and large missions, the Enceladus Orbiter and the Venus Climate Mission should be considered for the decade 2013-2022 only if higher-priority flagship missions cannot be flown for unanticipated reasons, or if additional funding makes them possible. No relative priority is assigned to these two missions; rather, any choice between them should be made on the basis of programmatic balance. In particular, because of the broad similarity of its science goals to those of JEO, NASA should consider flying the Enceladus Orbiter in the decade 2013-2022 only if JEO is not carried out in that decade.
As emphasized several times, the costs of the recommended flagship missions must not be allowed to grow above the values quoted in this report. Central to accomplishing this cost containment is avoiding “requirements creep.” The CATE process does not account for a lack of discipline that allows a mission to become too ambitious. To preserve programmatic balance, then, the scope of each of the recommended flagship missions cannot be permitted to increase significantly beyond what was assumed during the committee’s cost estimation process.
Following the priorities and decision rules outlined above, two example programs of solar system exploration can be described for the decade 2013-2022. Both assume continued support of all ongoing flight projects, a research and analysis grant program with a 5 percent increase and further growth at 1.5 percent per year above inflation, and $100 million FY2015 annually for technology development.
The recommended program can be conducted assuming a budget increase sufficient to allow a new start for JEO. It includes the following elements (in no particular order):
• Discovery program funded at the current level adjusted for inflation,
• Mars Trace Gas Orbiter conducted jointly with ESA,
• New Frontiers Missions 4 and 5,
• MAX-C at $2.5 billion,
• Jupiter Europa Orbiter, and
• Uranus Orbiter and Probe.
The cost-constrained program can be conducted assuming the currently projected NASA planetary budget (see Appendix E). It includes the following elements (in no particular order):
• Discovery program funded at the current level adjusted for inflation,
• Mars Trace Gas Orbiter conducted jointly with ESA,
• New Frontiers Missions 4 and 5,
• MAX-C at $2.5 billion, and
• Uranus Orbiter and Probe.
Table S.1 shows how the recommended program is tied to the three crosscutting science themes identified above.
Plausible circumstances could improve the picture presented above. If the mission costs listed above are overestimates, the budget increase required for the recommended program would be correspondingly smaller.
TABLE S.1 Crosscutting Science Themes, Key Questions, and the Missions in the Recommended Plan That Address Them
|Building new worlds||1. What were the initial stages, conditions, and processes of solar system formation and the nature of the interstellar matter that was incorporated?||Comet Surface Sample Return, Trojan Tour and Rendezvous, Discovery missions|
|2. How did the giant planets and their satellite systems accrete, and is there evidence that they migrated to new orbital positions?||Jupiter Europa Orbiter, Uranus Orbiter and Probe, Trojan Tour and Rendezvous, Io Observer, Saturn Probe, Enceladus Orbiter|
|3. What governed the accretion, supply of water, chemistry, and internal differentiation of the inner planets and the evolution of their atmospheres, and what roles did bombardment by large projectiles play?||Mars Sample Return, Venus In Situ Explorer, Lunar Geophysical Network, Lunar South Pole-Aitken Basin Sample Return, Trojan Tour and Rendezvous, Comet Surface Sample Return, Venus Climate Mission, Discovery missions|
|Planetary habitats||4. What were the primordial sources of organic matter, and where does organic synthesis continue today?||Mars Sample Return, Jupiter Europa Orbiter, Uranus Orbiter and Probe, Trojan Tour and Rendezvous, Comet Surface Sample Return, Enceladus Orbiter, Discovery missions|
|5. Did Mars or Venus host ancient aqueous environments conducive to early life, and is there evidence that life emerged?||Mars Sample Return, Venus In Situ Explorer, Venus Climate Mission, Discovery missions|
|6. Beyond Earth, are there contemporary habitats elsewhere in the solar system with necessary conditions, organic matter, water, energy, and nutrients to sustain life, and do organisms live there now?||Mars Sample Return, Jupiter Europa Orbiter, Enceladus Orbiter, Discovery missions|
|Workings of solar systems||7. How do the giant planets serve as laboratories to understand Earth, the solar system, and extrasolar planetary systems?||Jupiter Europa Orbiter, Uranus Orbiter and Probe, Saturn Probe|
|8. What solar system bodies endanger Earth’s biosphere, and what mechanisms shield it?||Comet Surface Sample Return, Discovery missions|
|9. Can understanding the roles of physics, chemistry, geology, and dynamics in driving planetary atmospheres and climates lead to a better understanding of climate change on Earth?||Mars Sample Return, Jupiter Europa Orbiter, Uranus Orbiter and Probe, Venus In Situ Explorer, Saturn Probe, Venus Climate Mission, Discovery missions|
|10. How have the myriad chemical and physical processes that shaped the solar system operated, interacted, and evolved over time?||All recommended missions|
Increased funding for planetary exploration could make even more missions possible. If funding were increased, the committee’s recommended additions to the plans presented above would be, in priority order:
1. An increase in funding for the Discovery program,
2. Another New Frontiers mission, and
3. Either the Enceladus Orbiter or the Venus Climate Mission.
It is also possible that the budget picture could turn out to be less favorable than the committee assumed. This could happen, for example, if the actual budget for solar system exploration is smaller than the projections the committee used. If cuts to the program are necessary, the committee recommends that the first approach should be descoping or delaying flagship missions. Changes to the New Frontiers or Discovery programs should be considered only if adjustments to flagship missions cannot solve the problem. And high priority should be placed on preserving funding for research and analysis programs and for technology development.
Deferred High-Priority Missions
The committee identified a number of additional large missions that are of high scientific value but are not recommended for the decade 2013-2022 for a variety of reasons. In alphabetical order, these missions are as follows:
• Ganymede Orbiter,
• Mars Geophysical Network,
• Mars Sample Return Lander,
• Mars Sample Return Orbiter,
• Neptune System Orbiter and Probe, and
• Titan Saturn System Mission.
Although consideration of these missions is deferred, technology investments must be made in the decade 2013-2022 to enable them and to reduce their costs and risk. In particular, it is important to make significant technology investments in the Mars Sample Return Lander, Mars Sample Return Orbiter, Titan Saturn System Mission, and Neptune System Orbiter and Probe.
Launch Vehicle Costs
The costs of launch services pose a challenge to NASA’s program of planetary exploration. Launch costs have risen in recent years for a variety of reasons, and launch costs today tend to be a larger fraction of total mission costs than they were in the past. These increases pose a threat to formulating an effective, balanced planetary exploration program. Possible ways to reduce launch costs include dual manifesting (launching more than one spacecraft on a single vehicle), making block buys of launch vehicles, and exploiting technologies that allow use of smaller, less expensive launch vehicles.
The Need for Plutonium-238
Radioisotope power systems are necessary for powering spacecraft at large distances from the Sun; in the extreme radiation environment of the inner Galilean satellites; in the low light levels of high martian latitudes, dust storms, and night; for extended operations on the surface of Venus; and during the long lunar night. With some 50 years of technology development and use of 46 such systems on 26 previous and currently flying spacecraft, the technology, safe handling, and utility of these units are not in doubt. Of the more than 3,000 nuclides, plutonium-238 stands out as the safest and easiest to procure isotope for use on robotic spacecraft.
This report’s recommended missions cannot be carried out without new plutonium-238 production or completed
deliveries from Russia. There are no technical alternatives to plutonium-238, and the longer the restart of production is delayed, the more it will cost.
The committee is alarmed at the limited availability of plutonium-238 for planetary exploration. Without a restart of domestic production of plutonium-238, it will be impossible for the United States, or any other country, to conduct certain important types of planetary missions after this decade.
Research and Analysis Programs
The research related to planetary missions begins well before a mission is formulated and funded, and continues long after it is over. Research provides the foundation for interpreting data collected by spacecraft, as well as the guidance and context for identifying new scientifically compelling missions. Ground-based observations can identify new targets for future missions, and experimental and theoretical results can pose new questions for these missions to answer. Research and analysis programs also allow the maximum possible science return to be harvested from missions. And along with analysis of spacecraft data, the portfolios of research and analysis programs include laboratory experiments, theoretical studies, fieldwork using Earth analogs, planetary geologic mapping, and analysis of data from Earth-based telescopes. All of these efforts are crucially important to NASA’s long-term science goals, and all require funding.
Current NASA research and analysis funding in most programs supporting planetary research is distributed as multiple small grants. An unfortunate and very inefficient aspect of this policy is that researchers must devote an increasingly large fraction of their time to writing proposals instead of doing science. The committee strongly encourages NASA to find ways (e.g., by merging related research programs and lengthening award periods) to increase average grant sizes and reduce the number of proposals that must be written, submitted, and reviewed by the community.
The number of good ideas for planetary research surpasses the funding available to enable that research. More funding for research and analysis would result in more high-quality science being done. However, recommendations for increased research funding must be tempered by the realization that NASA’s resources are finite, and that such increases will inevitably cut into funds that are needed to develop new technologies and fly new missions. So an appropriate balance must be sought. After consideration of this balance, and consistent with the mission recommendations and costs presented above, the committee recommends that NASA increase the research and analysis budget for planetary science by 5 percent above the total finally approved FY2011 expenditures in the first year of the coming decade, and increase the budget by 1.5 percent above the inflation level for each successive year of the decade.
Data Distribution and Archiving
Data from space missions remain scientifically valuable long after the demise of the spacecraft that provided them, but only if they are archived appropriately in a form readily accessible to the community of users and if the archives are continually maintained for completeness and accuracy. The Planetary Data System (PDS) provides critical data archiving and distribution to the planetary science community. Over the past 20 years, the PDS has established a systematic protocol for archiving and distributing mission data that has become the international standard. It is crucial that the capabilities of the Planetary Data System be maintained by NASA, both to provide a permanent archive of planetary data and to provide a means of distributing those data to the world at large.
High-level data products must be archived along with the low-level products typically produced by instrument teams. For future missions, Announcements of Opportunity should mandate that instrument teams propose and be funded to generate derived products before missions have completed Phase E. In the interim, separate support should be provided for development of high-level data products in cases where such support cannot be provided by mission funding.
Education and Outreach
The tremendous public interest in planets and planetary exploration points to a deeply rooted resonance between the work done by planetary scientists and the broader populace. Such curiosity can lead to a greater appreciation of the role that science in general, and planetary science in particular, can play in fostering a vigorous and economically healthy nation. Exploration of the planets is among the most exciting and accessible of the scientific activities funded by NASA, and indeed by any government agency. NASA’s planetary program has a special opportunity, and therefore a special responsibility, to reach out to the public.
Much effort is required to transform raw scientific data into materials of interest to the general public, and such efforts should be directly embedded within each planetary mission. The committee strongly endorses NASA’s informal guideline that a minimum of 1 percent of the cost of each mission be set aside from the project budget for education and public outreach activities. Modest additional funding must also be set aside to convey to the public the important scientific results from the longer-term supporting research and analysis programs.
The infrastructure supporting NASA’s spacecraft missions and related research activities includes ground- and space-based telescopes, the Deep Space Network, and sample curation and laboratory facilities.
NASA Telescope Facilities
Most bodies in the solar system were discovered using telescopes. Utilization of the enormous discovery potential of telescopes is an essential part of the committee’s integrated strategy for solar system exploration. Many spacecraft missions, including ones recommended in this report, are designed to follow up on discoveries made using telescopes. Telescopes help identify targets to which spacecraft missions can be flown, and they provide ongoing support for spacecraft missions. NASA’s Infrared Telescope Facility, for example, is specifically tasked to assist with flight missions, and it provides ongoing support for spacecraft such as Cassini, New Horizons, and MESSENGER.
Although most government-supported telescope facilities in the United States are funded by NSF (see the section “NSF Activities” below), NASA continues to play a major role in supporting the use of Earth-based optical and radar telescopes for planetary studies. Ground-based facilities that receive NASA support, including the Infrared Telescope Facility, the Keck Observatory, Goldstone, Arecibo, and the Very Long Baseline Array, all make important and in some cases unique contributions to planetary science. NASA should continue to provide support for the planetary observations that take place at these facilities.
Balloon- and rocket-borne telescopes offer a cost-effective means of studying planetary bodies at wavelengths inaccessible from the ground.6 Because of their modest costs and development times, they also provide training opportunities for would-be developers of future spacecraft instruments. Although NASA’s Science Mission Directorate regularly flies balloon missions into the stratosphere, there are few funding opportunities to take advantage of this resource for planetary science, because typical planetary grants are too small to support these missions. A funding line to promote further use of these suborbital observing platforms for planetary observations would complement and reduce the load on the already oversubscribed planetary astronomy program.
The Deep Space Network
The Deep Space Network (DSN) is a critical element of NASA’s solar system exploration program. It is the only asset available for communications with missions to the outer solar system, and it is heavily subscribed by inner solar system missions as well. As instruments advance and larger data streams are expected over the coming decade, this capability must keep pace with the needs of the mission portfolio. Future demands on the DSN will be substantial. Missions to the distant outer solar system require access to either 70-meter antennas or equivalent arrays of smaller antennas. The DSN must also be able to receive data from more than one mission at one station simultaneously. If new arrays can only mimic the ability of one 70-meter station and nothing more, missions will still be downlink-constrained and will have to compete against one another for limited downlink resources.
Although Ka-band downlink has a clear capacity advantage, there is a need to maintain multiple-band downlink capability. For example, three-band telemetry during outer planet atmospheric occultations allows sounding of different pressure depths within the atmosphere. In addition, S-band capability is required for communications from Venus during probe, balloon, lander, and orbit insertion operations because communications in other bands cannot penetrate the atmosphere. X-band capability is required for communication through the atmosphere of Titan, and also for emergency spacecraft communications. The committee recommends that all three Deep Space Network complexes should maintain high-power uplink capability in the X-band and Ka-band, and downlink capability in the S-, Ka-, and X-bands. NASA should expand DSN capacities to meet the navigation and communication requirements of missions recommended by this decadal survey, with adequate margins.
Sample Curation and Laboratory Facilities
Planetary samples are arguably some of the most precious materials on Earth. Just as data returned from planetary spacecraft must be carefully archived and distributed to investigators, so must samples brought at great cost to Earth from space be curated and kept uncontaminated and safe for continued study.
Samples to be returned to Earth from many planetary bodies (e.g., the Moon, asteroids, and comets) are given a planetary protection designation of “Unrestricted Earth Return” because they are not regarded as posing any biohazard to Earth. However, future sample return missions from Mars and other targets that might potentially harbor life (e.g., Europa and Enceladus) are classified as “Restricted Earth Return” and are subject to quarantine restrictions, requiring special receiving and curation facilities. As plans move forward for Restricted Earth Return missions, including Mars sample return, NASA should establish a single advisory group to provide input on all aspects of collection, containment, characterization and hazard assessment, and allocation of such samples. This advisory group must have an international component.
Sample curation facilities are critical components of any sample return mission and must be designed specifically for the types of returned materials and handling requirements. Early planning and adequate funding are needed in the mission cycle so that an adequate facility is available once samples are returned and deemed ready for curation and distribution. Every sample return mission flown by NASA should explicitly include in the estimate of its cost to the agency the full costs required for appropriate initial sample curation.
The most important instruments for any sample return mission are the ones in the laboratories on Earth. To derive the full science return from sample return missions, it is critical to maintain technical and instrumental capabilities for initial sample characterization, as well as foster expansion to encompass appropriate new analytical instrumentation as it becomes available and as different sample types are acquired. Well before planetary missions return samples, NASA should establish a well-coordinated and integrated program for development of the next generation of laboratory instruments to be used in sample characterization and analysis.
The future of planetary science depends on a well-conceived, robust, stable technology investment program. Ongoing missions such as Dawn and the Mars Exploration Rovers underscore the value of past technology investments. Early investment in key technologies reduces the cost risk of complex projects, allowing them to be initiated with reduced uncertainty regarding their eventual total costs. Continued success depends on strategic investments to enable the future missions that have the greatest potential for discovery. Although the need for a technology program seems obvious, in recent years investments in new planetary exploration technology have been sharply curtailed and monies originally allocated to it have been used to pay for flight project overruns. Reallocating technology funds to cover tactical exigencies is tantamount to “eating the seed corn.” The committee unequivocally recommends that a substantial program of planetary exploration technology development should be reconstituted and carefully protected against all incursions that would deplete its resources. This program should be consistently funded at approximately 6 to 8 percent of the total NASA Planetary Science Division budget. The technology program should be targeted toward the planetary missions that NASA intends to fly, and should be competed whenever possible. This reconstituted technology element should aggregate related but currently uncoordinated NASA technology activities that support planetary exploration,
and their tasks should be reprioritized and rebalanced to ensure that they contribute to the mission and science goals expressed in this report.7
The technology readiness level (TRL) is a widely used reference system for measuring the development maturity of a particular technology item. In general, a low TRL refers to technologies just beginning to be developed (TRL 1-3), and a mid-TRL covers the phases (TRL 4-6) that take an identified technology to a maturity at which it is ready to be applied to a flight project. A primary deficiency in past NASA planetary exploration technology programs has been an overemphasis on TRLs 1-3 at the expense of the more costly but vital mid-level efforts necessary to bring the technology to flight readiness. This failure to continue to mature the technologies has resulted in a widespread “mid-TRL crisis.” A flight project desiring to use a specific new technology must either complete the development itself, with the concomitant cost and schedule risk, or forgo the capability altogether. To properly complement the flight mission program, therefore, the committee recommends that the Planetary Science Division’s technology program should accept the responsibility, and assign the required funds, to continue the development of the most important technology items through TRL 6.
In recent competed mission solicitations, NASA provided incentives for infusion of new technological capabilities in the form of increases to the proposal cost cap. Specific technologies included as incentives were the following:
• Advanced solar-electric propulsion, NASA’s Evolutionary Xenon Thruster (NEXT),
• Advanced bipropellant engines, the Advanced Material Bipropellant Rocket (AMBR),
• Aerocapture for orbiters and landers, and
• A new radioisotope power system, the Advanced Stirling Radioisotope Generator (ASRG).
These technologies continue to be of high value to a wide variety of solar system missions. The committee recommends that NASA should continue to provide incentives for the technologies listed above until they are demonstrated in flight. Moreover, this incentive paradigm should be expanded to include advanced solar power (especially lightweight solar arrays) and optical communications, both of which would be of major benefit for planetary exploration.
A significant concern with the current planetary exploration technology program is the apparent lack of innovation at the front end of the development pipeline. Truly innovative, breakthrough technologies appear to stand little chance of success in the competition for development money inside NASA, because, by their very nature, they are directed toward far-future objectives rather than specific near-term missions. The committee hopes that the formation of the new NASA Office of the Chief Technologist will elicit an outpouring of innovative technological ideas, and that those concepts will be carefully examined so that the most promising can receive continued support. However, it is not yet clear exactly how future technological responsibilities will be split between the new NASA technology office and the individual mission directorates. Given the unique needs of planetary science, it is therefore essential that the Planetary Science Division develop its own balanced technology program, including plans both to encourage innovation and to resolve the existing mid-TRL crisis.
Although the ingenuity of the nation’s scientists and engineers has made it appear almost routine, solar system exploration still represents one of the most audacious undertakings in human history. Any planetary spacecraft, regardless of its destination, must cope with basically the same set of fundamental operational and environmental challenges. As future mission objectives evolve, meeting these challenges will require advances in the following areas:
• Reduced mass and power requirements for spacecraft and their subsystems;
• Improved communications capabilities yielding higher data rates;
• Increased spacecraft autonomy;
• More efficient power and propulsion for all phases of the missions;
• More robust spacecraft for survival in extreme environments;
• New and improved sensors, instruments, and sampling and sample preservation systems; and
• Mission and trajectory design and optimization.
Of all these technologies, none is more critical than high-efficiency power systems for use throughout the solar system. The committee’s highest priority for near-term multi-mission technology investment is for the completion and validation of the Advanced Stirling Radioisotope Generator.
For the coming decade, it is imperative that NASA expand its investment program in all of these fundamental technology areas, with the twin goals of reducing the cost of planetary missions and improving their scientific capability and reliability. Furthermore, the committee recommends that NASA expand its program of regular future mission studies to identify as early as possible the technology drivers and common needs for likely future missions.
In structuring its multi-mission technology investment programs, it is important that NASA preserve its focus on fundamental system capabilities rather than concentrating solely on individual technology tasks. An example of such an integrated approach, which NASA is already pursuing, is the advancement of solar-electric propulsion systems. This integrated approach consists of linked investments in new thrusters, plus new power processing, propellant feed system technology, and the systems engineering expertise that enables these elements to work together. The committee recommends that NASA consider making equivalent systems investments in the advanced Ultraflex solar array technology that will provide higher power at greater efficiency, and in aerocapture to enable efficient orbit insertion around bodies with atmospheres.
Discovery and New Frontiers missions would benefit substantially from enhanced technology investments in the multi-mission technology areas described above; however, two issues have yet to be overcome:
• The nature of the peer review and selection process effectively precludes reliance on new and “unproven” technology, since it increases the perceived risk and cost of new missions; and
• It is difficult to ensure that proposers have the intimate knowledge of new technologies required to effectively incorporate them into their proposals.
While expanding its investments in generic multi-mission technologies, NASA should encourage the intelligent use of new technologies in its competed missions. NASA should also put mechanisms in place to ensure that new capabilities are properly transferred to the scientific community for application to competed missions.
NASA’s comprehensive and costly flagship missions are strategic in nature and have historically been assigned to NASA centers rather than competed. They can benefit from, and in fact are enabled by, strategic technology investments.
An obvious candidate for such investments is the Mars Sample Return campaign. MAX-C’s greatest technology challenge is sample acquisition, processing, and encapsulation on Mars. The two greatest technology challenges facing the later elements of the campaign are the Mars Ascent Vehicle and the end-to-end planetary protection and sample containment system. During the decade of 2013-2022, NASA should establish an aggressive, focused technology development and validation initiative to provide the capabilities required to complete the challenging MSR campaign.
Fortunately, the JEO mission requires no fundamentally new technology in order to accomplish its objectives. However, the capability to design and package the science instruments, especially the detectors, so that they can operate successfully in the jovian radiation environment has not yet been completely demonstrated. A supporting instrument technology program aimed specifically at the issue of acquiring meaningful scientific data in a high-radiation environment would be extremely valuable, both for JEO and for any other missions that will explore Jupiter and its moons in the future.
It is essential that the Planetary Science Division also invest in the technological capabilities that will enable missions in the decade beyond 2022. The committee strongly recommends that NASA strive to achieve balance in its technology investment programs by addressing the near-term missions cited specifically in this report, as well as the longer-term missions that will be studied and prioritized in the future.
The instruments carried by planetary missions provide the data to address key science questions and test scientific hypotheses. At present there are significant technological needs across the entire range of instruments, including the improvement and/or adaptation of existing instruments and the development of completely new
concepts. Astrobiological exploration in particular is severely limited by a lack of flight-ready instruments that can address key questions regarding past or present life elsewhere in the solar system. The committee recommends that a broad-based, sustained program of science instrument technology development be undertaken, and that this development include new instrument concepts as well as improvements in existing instruments. This instrument technology program should include the funding of development through TRL 6 for those instruments with the highest potential for making new discoveries.
One of the biggest challenges of solar system exploration is the tremendous variety of environments that spacecraft encounter. Systems or instruments designed for one planetary mission are rarely able to function properly in a different environment. The committee recommends that, as part of a balanced portfolio, a significant percentage of the Planetary Science Division’s technology funding be set aside for expanding the environmental adaptability of existing engineering and science instrument capabilities.
Human Exploration Programs
The human exploration of space is undertaken to serve a variety of national and international interests. Human exploration can provide important opportunities to advance science, but science is not the primary motivation. Measurements using remote sensing across the electromagnetic spectrum, atmospheric measurements, or determinations of particle flux density are by far best and most economically conducted using robotic spacecraft. But there is an important subset of planetary exploration that can benefit from human spaceflight. These are missions to the surfaces of solid bodies whose surface conditions are not too hostile for humans. For the foreseeable future, humans can realistically explore the surfaces of only the Moon, Mars, Phobos and Deimos, and some asteroids.
If the Apollo experience is an applicable guide, robotic missions to targets of interest will undoubtedly precede human missions. Human exploration precursor measurement objectives focus mainly on issues regarding health and safety and engineering practicalities, rather than science.
A positive example of synergy between the human exploration program and science is the current Lunar Reconnaissance Orbiter (LRO) mission. This project was conceived as a precursor for the human exploration program but ultimately was executed in concert with the planetary science community. By building on lessons learned from LRO, an effective approach to exploration-driven robotic precursor missions can be devised.
Despite the positive recent example of LRO, the committee is concerned that human spaceflight programs can cannibalize space science programs. The committee agrees with the statement in the Human Spaceflight Plans Committee report that “it is essential that budgetary firewalls be built between these two broad categories of activity. Without such a mechanism, turmoil is assured and program balance endangered.”8
Within the planetary science program there have been and will likely continue to be peer-reviewed missions selected that are destined for likely targets of human exploration. The committee believes that it is vital to maintain the science focus of such peer-reviewed missions and not to incorporate human exploration requirements after the mission has been selected and development has begun. If the data gathered by such missions have utility for human exploration, the analysis should be paid for by the human exploration program and firewalled from the science budget. Similarly, if the human exploration program proposes a precursor mission (like LRO) and there is an opportunity for conducting science at the destination, science should be very cautious about directly or indirectly imposing mission-defining requirements, and be willing to pay for any such requirements. The need for caution does not rule out the possibility of carefully crafted collaborations, however.
What should be the roles of humans and robots to meet the goals of planetary exploration? The committee reached the same conclusion as past NRC studies that most of the key scientific lunar and near-Earth object (NEO) exploration goals can be achieved robotically. Scientifically useful investigations should still be developed to augment human missions to the Moon or NEOs. The committee urges the human exploration program to examine this decadal survey and identify—in close coordination and negotiation with the SMD—whereby human-tended science can advance fundamental knowledge. Finding and collecting the most scientifically valuable samples for return to Earth may become, as they were in the Apollo program, the most important functions of a human explorer on the Moon or an asteroid.
For several decades, the NRC has conducted studies of the scientific utility of human explorers or human-robotic exploration teams for exploring the solar system. Invariably, the target of greatest interest has been Mars. The scientific rationale cited has focused largely on answering questions relating to the search for past or present biological activity. On the basis of the importance of questions relating to life, the committee concluded that for the more distant future, human explorers with robotic assistance may contribute more to the scientific exploration of Mars than they can to any other body in the solar system.
Planetary exploration is an increasingly international endeavor, with the United States, Russia, Europe, Japan, Canada, China, and India independently or collaboratively mounting major planetary missions. As budgets for space programs come under increasing pressure and the complexity of the missions grows, international cooperation becomes an enabling component. New alliances and mechanisms for cooperation are emerging, enabling partners to improve national capabilities, share costs, build common interests, and eliminate duplication of effort. But international agreements and plans for cooperation must be crafted with care, because they also can carry risks. The management of international missions adds layers of complexity to their technical specification, management, and implementation. Different space agencies use different planning horizons, funding approaches, selection processes, and data dissemination policies. Nonetheless, international cooperation remains a crucial element of the planetary program; it may be the only realistic option for undertaking some of the most ambitious and scientifically rewarding missions.
In considering international cooperation, the committee drew from the general principles and guidelines laid out in past studies, in particular the joint report of the Space Studies Board and the European Space Science Committee titled U.S.-European Collaboration in Space Science.9 Following consideration of a series of case studies examining the positive and negative aspects of past transatlantic cooperative space science ventures, that report laid out eight essential ingredients that an agreement to engage in an international collaboration must contain; they are (summarized from pp. 102-103 of the 1998 report) as follows:
1. Scientific support through peer review that affirms the scientific integrity, value, requirements, and benefits of a cooperative mission;
2. A historical foundation built on an existing international community, partnership, and shared scientific experiences;
3. Shared objectives that incorporate the interests of scientists, engineers, and managers in common and communicated goals;
4. Clearly defined responsibilities and roles for cooperative partners, including scientists, engineers, and mission managers;
5. An agreed-upon process for data calibration, validation, access, and distribution;
6. A sense of partnership recognizing the unique contributions of each participant;
7. Beneficial characteristics of cooperation; and
8. Recognition of the importance of reviews for cooperative activities in the conceptual, developmental, active, or extended mission phases—particularly for foreseen and upcoming large missions.
The National Science Foundation’s principal support for planetary science is provided by the Division of Astronomical Sciences (AST) in the Directorate for Mathematical and Physical Sciences. Typical awards range from $95,000 to $125,000 per year for a nominal 3-year period. The focus of the program is scientific merit with a broad impact and the potential for transformative research. NSF also provides peer-reviewed access to telescopes at public facilities (see below). In short, NSF supports nearly all areas of planetary science except space missions, which it supports indirectly through laboratory research and archived data.
The annual budget of NSF/AST is currently approximately $230 million. Planetary astronomers must compete
against all other astronomers for access to both research grants and telescope time, however, and so only a small fraction of AST’s facilities and budget support planetary science.
Other parts of NSF make small but important contributions to planetary science. The Office of Polar Programs (OPP) provides access to and logistical support for researchers working in Antarctica. OPP’s activities are of direct relevance to planetary science because OPP supports the Antarctic meteorite collection program (jointly with NASA and the Smithsonian Institution) and provides access to analog environments of direct relevance to studies of ancient Mars and the icy satellites of the outer solar system. The Atmospheric and Geospace Sciences Division provides modest support for research concerning planetary atmospheres and magnetospheres. And the Earth Science Division and Ocean Sciences Division have supported studies of meteorites and ice-covered bodies.
Such grants, although small compared with NASA’s activities in similar areas, are important because they provide a vital source of funding to researchers, mostly to support graduate students and postdoctoral fellows. More importantly, they provide a key linkage between the relatively small community of planetary scientists and the much larger community of researchers studying Earth.
The committee’s overall assessment is that NSF grants and support for field activities are an important source of support for planetary science in the United States and should continue.
Ground-Based Astronomical Facilities
The National Science Foundation is the largest federal funding agency for ground-based astronomy in the United States. NSF-funded facilities of great importance to the planetary sciences include the National Optical Astronomy Observatory (NOAO), the Gemini Observatory, the National Astronomy and Ionosphere Center (NAIC), the National Radio Astronomy Observatory (NRAO), and the National Solar Observatory (NSO). Collectively these are known as the National Observatories. The committee supports the National Observatories’ ongoing efforts to provide public access to its system of observational facilities, and encourages the National Observatories to recognize the synergy between ground-based observations and in situ planetary measurements, perhaps through coordinated observing campaigns on mission targets.
The NOAO operates two 4-meter and other smaller telescopes at the Kitt Peak National Observatory in Arizona and the Cerro Tololo Inter-American Observatory in Chile.
The Gemini Observatory operates two 8-meter optical telescopes, one in the Southern and one in the Northern Hemisphere in an international partnership. The Gemini international partnership agreement is currently under renegotiation, and the United Kingdom, which holds a 25 percent stake, has announced its intent to withdraw from the consortium in 2012. This eventuality would provide a good opportunity for increasing the U.S. share of Gemini, and also presents an opportunity for restructuring the complex governance and management structure.10 The Gemini partnership might consider the advantages of stronger scientific coordination with NASA mission planning needs.
NAIC operates the Arecibo Observatory in Puerto Rico. Arecibo is a unique and important radar facility that plays a particularly important role in NEO studies.
NRAO operates the Very Large Array (VLA) and the Atacama Large Millimeter Array (ALMA), both of which are of great importance to future planetary exploration. The expanded VLA will produce imaging of the planets across the microwave spectrum and also provide a back-up downlink location to the DSN. ALMA will provide unprecedented imaging in the relatively unexplored wavelength region of 0.3 mm to 3.6 mm (84 to 950 GHz).
NSO operates telescopes on Kitt Peak and Sacramento Peak, New Mexico, and six worldwide Global Oscillations Network Group stations. Understanding the Sun is critical to understanding its relationship to planetary atmospheres and surfaces. The committee endorses and echoes the 2010 astronomy and astrophysics decadal survey report’s recommendation that “NSF should work with the solar, heliospheric, stellar, planetary, and geospace communities to determine the best route to an effective and balanced ground-based solar astronomy program that maintains multidisciplinary ties.”11
Many important advances in planetary research have come from access to private facilities such as the Keck, Magellan, and MMT observatories via NSF’s Telescope System Instrumentation Program. The ground-based observational facilities supported wholly or in part by NSF are essential to planetary astronomical obser vations,
both in support of active space missions and in studies independent of (or as follow-up to) such missions. Their continued support is critical to the advancement of planetary science.
One of the future NSF-funded facilities most important to planetary science is the Large Synoptic Survey Telescope (LSST).12 LSST will discover many small bodies in the solar system, some of which will require follow-up observations for the study of their physical properties. Some of these bodies are likely to be attractive candidates for future spacecraft missions. The committee encourages the timely completion of LSST and stresses the importance of its contributions to planetary science, as well as astrophysics, once telescope operations begin.
With apertures of 30 meters and larger, extremely large telescopes (ELTs) will play a significant future role in planetary science. International efforts for ELT development are proceeding rapidly, with at least three such telescopes in the planning stages: the Giant Magellan Telescope, the Thirty-Meter Telescope, and the European Extremely Large Telescope. The committee does not provide specific guidance to NSF on this issue. It endorses the recommendations and support for these facilities made by the 2010 astronomy and astrophysics decadal survey and encourages NSF to continue to invest in the development of ELTs, and to seek partnerships to ensure that at least one such facility comes to fruition with provisions for some public access. The committee believes that it is essential that the design of ELTs accommodate the requirements of planetary science to acquire and observe targets that are moving, extended, and/or bright, and that the needs of planetary mission planning be considered in awarding and scheduling public time for ELTs.
Laboratory Studies and Facilities for Planetary Science
To maximize the science return from NSF-funded ground-based observations and NASA space missions alike, materials and processes must be studied in the laboratory. Needed support for planetary science activities includes the development of large spectroscopic databases for gases and solids over a wide range of wavelengths, including derivation of optical constants for solid materials, laboratory simulations of the physics and chemistry of aerosols, and measurements of thermophysical properties of planetary materials. Planetary science intersects with many areas of astrophysics that receive NSF funding for laboratory investigations. Although laboratory research costs a fraction of the cost of missions, in most areas it receives insufficient support, with the result that existing infrastructure is often not state of the art and required upgrades cannot be made. NSF can make a huge impact on planetary science by supporting this vital area of research. The committee recommends expansion of NSF funding for the support of planetary science in existing laboratories, and the establishment of new laboratories as needs develop. Areas of high priority for support include the following:
• Development and maintenance of spectral reference libraries for atmospheric and surface composition studies, extending from x-ray to millimeter wavelengths;
• Laboratory measurements of thermophysical properties of materials over the range of conditions relevant to planetary objects;
• Investment in laboratory infrastructure and support for laboratory spectroscopy (experimental and theoretical), perhaps through a network of general-user laboratory facilities; and
• Investigations of the physics and chemistry of aerosols in planetary atmospheres through laboratory simulations.
The ties between planetary science and laboratory astrophysics will continue to strengthen and draw closer with the expanding exploration of exoplanets and the development of techniques to study their physical-chemical properties.
NOTES AND REFERENCES
1. National Research Council. 2003. New Frontiers in the Solar System: An Integrated Exploration Strategy. The National Academies Press, Washington, D.C.
2. On May 25, 2011, following the completion of this report, NASA selected the OSIRIS-REx asteroid sample-return spacecraft as the third New Frontiers mission. Launch is scheduled for 2016.
3. On May 25, 2011, following the completion of this report, NASA selected the OSIRIS-REx asteroid sample-return spacecraft as the third New Frontiers mission. Launch is scheduled for 2016.
4. This is the cost of MAX-C only, not the cost of the full Mars Sample Return campaign. Also, the estimate is for the MAX-C mission as currently conceived; in the text below, the committee recommends reductions in scope to keep the cost below $2.5 billion FY2015.
5. This is the version without a solar-electric propulsion stage.
6. National Research Council. 2010. Revitalizing NASA’s Suborbital Program: Advancing Science, Driving Innovation, and Developing a Workforce. The National Academies Press, Washington, D.C.
7. The issue of instrument development problems is a subtler one, given that instrument overruns alone may represent a small fraction of mission cost but can have profound effects on project schedules and induce additional costs beyond those associated with the instrument. This is likely to be a significant problem in the next decade in the wake of the dramatic reductions in technology development spending this past decade that have resulted in fewer mid- to high-TRL instruments being available for flight.
8. Executive Office of the President. Review of U.S. Human Spaceflight Plans Committee. 2009. Seeking a Human Spaceflight Program Worthy of a Great Nation. Washington, D.C.
9. National Research Council and European Science Foundation. 1998. U.S.-European Collaboration in Space Science. National Academy Press, Washington, D.C., pp. 102-103.
10. For additional details concerning Gemini and recommendations for its future, see, for example, National Research Council, New Worlds, New Horizons in Astronomy and Astrophysics, The National Academies Press, Washington, D.C., 2010, pp. 177-179.
11. National Research Council. 2010. New Worlds, New Horizons in Astronomy and Astrophysics. The National Academies Press, Washington, D.C., p. 34.
12. For additional information about and recommendations concerning the LSST, see, for example, National Research Council, New Worlds, New Horizons in Astronomy and Astrophysics, The National Academies Press, Washington, D.C., 2010, pp. 224-225.