SSE Decadal Survey Mars Priorities
The National Research Council’s solar system exploration decadal survey enunciated a comprehensive series of goals, priorities, and recommendations relating to the exploration of Mars.1 The decadal survey also described the important role played by R&A programs, technology-development activities, and related undertakings in supporting Mars missions. The following series of extracts from the decadal survey—relating to, for example, the recommendations for small, medium, and large spacecraft missions—are relevant to the topics discussed in this letter report.
Mars Sample Return
While MSR cannot replace certain crucial in situ measurements (e.g., heat flow, seismicity, electromagnetic sounding for water, analyses of labile samples, and determination of atmospheric dynamics), it is scientifically compelling in its own right, and the ground-truth acquired from returned samples will aid the interpretation and greatly enhance the value of data from orbital and robotic lander missions. Spacecraft capabilities that would contribute to effectiveness in sampling include mobility, in situ reconnaissance analytical instrumentation, and a core drilling device. (Under current conditions, it appears likely that living organisms, and more generally all organic material, would be destroyed by oxidizing conditions in the surface layer of Mars. They may be preserved only at depth in the planet. Just what depth—centimeters, meters, kilometers—is unknown.) Necessary capabilities include the ability to manipulate and document samples collected and to package them in a way consistent with requirements placed by the planetary protection protocol imposed on the mission. A radioisotope power system for the mission … would expand the geographic range of sites that could be sampled and would extend the mission’s stay time, allowing the collection of a larger and more carefully selected suite of samples. Ample power undoubtedly will be important if drilling is contemplated.2
Observations by robotic orbiters and landers alone are not likely to provide an unambiguous answer to the most important questions regarding Mars: whether life ever started on that planet, what the climate history of the planet was, and why Mars evolved so differently from Earth. The definitive answers to these questions will require analysis in Earth-based laboratories of Mars samples returned to Earth from known provenances on Mars. Moreover, samples will provide the ultimate ground-truth for the wealth of data returned from remote-sensing and in situ missions. The SSE Survey recommends that NASA begin its planning for Mars Sample Return missions so that their implementation can occur early in the decade 2013-2023.
The Need for Sample Return to Search for Life. At our present state of knowledge and technological expertise, it is unlikely that robotic in situ exploration will be able to prove to an acceptable level of certainty whether there once was or is now life on Mars. Results obtained from life-detection experiments carried out by robotic means can be challenged as ambiguous for the following reasons:
Results interpreted as showing an absence of life will not be accepted because the experiments that yielded them were too geocentric or otherwise inappropriately limited;
Results consistent with but not definitive regarding the existence of life (e.g., the detection of organic compounds of unknown, either biological or nonbiological, origin) will be regarded as incapable of providing a clearcut answer; and
Results interpreted as showing the existence of life will be regarded as necessarily suspect, since they might reflect the presence of earthly contaminants rather than of an indigenous martian biota.
The Need for Sample Return for Geochemical Studies and Age Dating. Rocks contain a near-infinite amount of information on a microscopic scale, some of it crucial to an understanding of the rock’s origin and history. The constituent minerals, fluid inclusions, and alteration products can be studied chemically and isotopically, providing critical information on the age, dates of thermal and aqueous alteration events, nature of the source regions, and history of magmatic processes. In situ instrumentation will always be limited to a fraction of the potential measurement suite and lower levels of precision and accuracy. Information about the Mars climate will be found in the layer of weathering products that we expect to find on rock samples and in the soils. These products will almost certainly be very complex minerals or amorphous reaction products that will tax our best Earth-based laboratory techniques to understand. A critical unknown for Mars is the absolute chronology of the observed surface units. Precise and accurate dating of surfaces with clearly defined crater ages is best accomplished with returned samples.
The Need for Sample Return for Studies of Climate and Coupled Atmosphere-Surface-Interior Processes. Key measurements in modeling the relative loss of portions of the atmosphere to space and to surface reservoirs are surface mineral compositions and their isotopic systematics. Atmospheric loss processes (e.g., hydrodynamic escape, sputtering) leave characteristic isotopic signatures in certain elements. Loss to space and surface weathering (e.g., CO2 to carbonate minerals) are likely to produce isotopic fractionation in different directions. 15N/14N in the martian atmosphere is understood to have evolved over the past 3.8 billion years (it is currently 1.6 times the terrestrial value), and a determination of this ratio in near-surface materials may constrain the time of their formation. Compositional and isotopic analysis of surface minerals, weathering rinds, and sedimentary deposits will establish the role of liquid water and processes such as weathering. The corresponding measurements on volatiles released from near-surface materials are likely to be more heterogeneous and may provide fossils of past atmospheric and chemical conditions that allow the past climate to be better understood.
The SNC Meteorites Do Not Obviate the Need for Sample-Return Missions. SNC meteorites have provided a tantalizing view of a few martian rocks and a demonstration of how much can be learned when samples can be examined in Earth-based laboratories; however, they represent a highly selected subset of martian materials, specifically, very coherent rocks of largely igneous origin from a small number of unknown locations. Thus, SNC meteorites are unhelpful in answering one of our outstanding questions—What is the absolute chronology of Mars?—because although these meteorites can be accurately dated, the geologic units from which they are derived are unknown. While returned samples are also a selected subset of martian materials, we will know their geologic context, and they will be from sites selected because they can provide particularly valuable information.3
It is essential that the site to be sampled be carefully chosen, with the choice drawing upon the large body of orbital and lander data that will be in place by the time the MSR is flown. However, no single sample-return mission will completely satisfy the need for this form of exploration, no matter how carefully it is planned. Mars is highly varied in its geology; prior to returning some martian material to Earth it may be impossible for us to understand which type of site has the highest potential for providing samples that contain evidence of life and other valuable scientific data; sample collection and return represent a new endeavor, one that may not work perfectly the first time. It will be necessary to plan for a series of MSRs over whatever span of time the budget permits.4
Mars Science Laboratory
The Mars Science Laboratory (MSL) is an important mission along the path of “Seek, in situ, and sample.” The science goals are to conduct detailed in situ investigations of a site that is a water-modified environment identified from orbital data. As such, this mission will provide critical ground-truth for orbital data and test hypotheses for the formation and composition of water-modified environments identified through morphological and spectroscopic investigations. The types of in situ measurements possible on MSL are wide ranging, including atmospheric sampling, mineralogy and chemical composition, and tests for the presence of organics. There currently is some debate as to whether this mission will have roving capability on the order of 10 km, or be more focused toward drilling to get below the surface, which is hostile to life. Both strategies have merit in addressing high-priority science goals, though the drilling mission puts a much greater demand on precision landing. Regardless of the ultimate design of the instrumentation, the SSE Survey recommends that while carrying out its science mission, the Mars Science Laboratory mission should test and validate technology required for sample return (e.g., sample handling and storage in preparation for sample return and feed-forward lander design, consistent with the future use of a Mars Ascent Vehicle). In addition, the surface operations of the Mars Science Laboratory mission should feed forward to Mars Sample Return.5
Mars Long-Lived Lander Network
The Mars Long-Lived Lander Network (ML3N) is a grid of science stations that will make coordinated measurements around Mars’s globe for at least 1 martian year. The highest-priority objectives for network science on Mars are the determination of the planet’s internal structure, including its core; the elucidation of surface and near-surface composition as well as thermal and mechanical properties; and extensive synoptic measurements of the atmosphere and weather. In addition, atmospheric gas isotopic observations (to constrain the size of currently active volatile reservoirs) and measurements of subsurface oxidizing properties and surface-atmosphere volatile exchange processes will be valuable.6
The Mars Long-Lived Lander Network (ML3N) would use passive seismometers to explore the structure and activity of Mars. Heat-flow probes also would contribute importantly to our knowledge of the martian interior, but these require the drilling of holes, and they might more logically be emplaced by MSR if that mission has drilling capability; this would avoid placing a drilling requirement on the lander network.
ML3N should also include meteorological stations that measure pressure, temperature, relative humidity, atmospheric opacity, and wind velocity. Also included should be mass spectrometers that permit high-precision, long-lived chemical and isotopic atmospheric analysis of the chemical dynamics of C, H, and O at Mars’s surface. Time variability of isotopic compositions can be interpreted in terms of sources, sinks, and reservoirs of volatiles, and atmospheric evolution. Humidity sensors would track the flux of water vapor into and out of the regolith with time of day and season, providing important insight into the water budget on Mars.
The complement of instruments on the French-led NetLander mission, the four landers distributed around the planet, and the expected lifetime of 1 martian year will be sufficient to constrain the nature and size of the core, seismic activity, seismic velocities of the crust and mantle, and atmospheric properties of pressure, temperature, humidity, and wind speed. They will also have a magnetometer and electromagnetic sounding capabilities to sense crustal structures and to search for subsurface water and ice. While this complement of instruments does not address all of the high-priority goals outlined for the ML3N, it represents a significant step forward.7
Mars Scout Program
The Mars Scout program consists of competed, Discovery-class, principal-investigator-led missions with $300 million [now $475 million] cost caps.8
Mars Scout provides an excellent opportunity for NASA to address science priorities outside the principal objectives of the Mars Exploration Program, and for the broad science community to respond to discoveries and technological advancement. The SSE Survey recommends that the Mars Scout program be managed as is the Discovery program, with principal-investigator leadership and competitive selection of missions. It is essential, therefore, that the measurement goals for the Mars Scout program be directed toward the highest-priority science for Mars and be selected by peer review. The missions-of-opportunity element of the Scout program is also important, as it allows for participation in foreign Mars missions. The SSE Survey strongly recommends that the Mars Exploration Program commit equally as strongly to the Scout program as to sample return.
While Mars sample-return missions will be expensive and consuming of the attention of the MEP, there are sufficient resources in the program as currently structured to achieve both a viable Scout program and sample return. As witnessed by the response to the recent call for Scout proposal ideas (over 40 submissions were received), tremendous enthusiasm has been stimulated by recent Mars discoveries and scientific investigations not covered by the MEP. Scout provides a mission component that is highly flexible and responsive to discovery. The SSE Survey recommends that a Mars Scout mission be flown at every other launch opportunity.9
Mars Upper Atmosphere Orbiter
Mars Upper Atmosphere Orbiter (MAO) is a small mission dedicated to studies of Mars’s upper atmosphere and plasma environment.10
Areas to be addressed by this low-cost mission are the dynamics of the upper atmosphere; hot atom abundances and escape fluxes; ion escape; minimagnetospheres and magnetic reconnections; and energetics of the ionosphere. [MAO] can explicitly explore these issues in the present-day environment and answer a number of important scientific questions. Furthermore, such a mission could quantify present-day escape processes and allow certain backward extrapolations to earlier epochs in martian history.
The instruments needed for a meaningful attack on these questions would require no new, basic instrument development and could be installed as a partial payload complement of an orbiting spacecraft. The neutral winds can be measured by either a “baffled” neutral mass spectrometer or a Fabry-Perot interferometer. The latter instrument, along with a good ultraviolet spectrometer, could address in a meaningful way the hot atom and neutral escape flux questions. The neutral mass spectrometer would also provide neutral composition and temperature information. A plasma instrument complement consisting of a magnetometer, low-energy ion mass spectrometer (capable of measuring flow velocities and temperatures), an electron spectrometer, a plasma wave detector, and a Langmuir probe would go a long way toward resolving the questions of ion escape, minimagnetospheres and magnetic reconnections, and energetics of the ionosphere.11
No plans exist in the current U.S. Mars Exploration Program to address any of the scientific questions identified by previous panels in this area. The Nozomi and Mars Express missions will address them to some extent, but much more data will be needed to meaningfully elucidate these issues. The measurements required for this mission could be accommodated as a science package on an international orbiter mission or as a stand-alone mission in the Mars Scout program.12
RESEARCH AND ANALYSIS PROGRAMS
It is largely through the work supported by [NASA’s] research and analysis (R&A) programs … that the data returned by flight missions are converted into new understanding, advancing the boundaries of what is known. The research supported by these programs also creates the knowledge necessary to plan the scientific scope of future missions. Covered under this line item are basic theory, modeling studies, laboratory experiments, ground-based observations, long-term data analysis, and comparative investigations. The funds distributed by these programs support investigators at academic institutions, federal laboratories, nonprofit organizations, and industrial corporations. R&A furnishes the context in which the results from missions can be correctly interpreted. Furthermore, active R&A programs are a prime breeding ground for principal investigators and team members of forthcoming flight missions.
Healthy R&A programs are of paramount importance and constitute a necessary precondition for effective missions…. The ratio of submitted to funded proposals is typically 3 to 1, which—the SSE Survey believes—is too
high, since at this rate new proposals can rarely be funded. Also, the availability of authorized funds is often subject to delays and, in recent times, the value of the median grant has fallen to below $50,000 per annum, a level generally too small to support a researcher or a tuition-paid graduate student.
The SSE Survey agrees … that NASA should routinely examine the size and number of grants to ensure that the grant sizes are adequate to achieve the proposed research. The Survey supports the budgetary proposals that would steadily expand solar system exploration R&A programs. The SSE Survey recommends an increase over the decade 2003-2013 in the funding for fundamental research and analysis programs at a rate above inflation to a level that is consistent with the augmented number of missions, amount of data, and diversity of objects studied.13
NASA’s Astrobiology program has appropriately become deeply interwoven into the solar system exploration research and analysis program. The SSE Survey encourages NASA to continue the integration of astrobiology science objectives with those of other space science disciplines. Astrobiological expertise should be called upon when identifying optimal mission strategies and design requirements for flight-qualified instruments that address key questions in astrobiology and planetary science.14
Astrobiology as a theme provides a scientific organizational structure that integrates a wide subset of solar system issues and questions that span the origins, evolution, and extinction of life. This theme allows nonexperts to grasp the connections between different component disciplines within planetary science and to do so in a way that most people will appreciate as addressing core themes in human thought. Astrobiology and its connections to space science (and solar system exploration in particular) are the primary means by which NASA tries to implement one of its prime objectives—understanding life’s origins and its distribution in the universe.
… The SSE Survey encourages NASA to continue the integration of astrobiology science objectives with those of other space-science disciplines. Astrobiological expertise should be called upon when identifying optimal mission strategies and design requirements for flight-qualified instruments that will address key questions in astrobiology and planetary science.15
[The] SNC category of martian meteorites plays an important role in studies relating to martian life and the planet’s structure and evolution. Studies of this small group of meteorites in terrestrial laboratories have provided invaluable, if fragmentary, information about the geochemistry and chronology of Mars. NASA, the National Science Foundation, and the Smithsonian Institution have jointly supported an Antarctic meteorite program since 1976, in which teams of experts search areas known to contain a concentration of meteorites for 6 weeks every austral summer; support of this program should continue.16
In anticipation of the return of extraterrestrial samples from several ongoing and future missions, an analogue to the data pipeline must be developed for cosmic materials. The SSE Survey recommends that well before cosmic materials are returned from planetary missions, NASA should establish a sample-analysis program to support instrument development, laboratory facilities, and the training of researchers.17
In addition, planetary protection requirements for missions to worlds of biological interest will require investments, as will life-detection techniques, sample quarantine facilities, and sterilization technologies. NASA’s current administrative activities to develop planetary protection protocols for currently planned missions are appropriate.18
Mars Quarantine Facility
Several NRC studies outline the containment requirements for samples returned from Mars…. The recent NRC report on the Mars Quarantine Facility (MQF) stresses that a minimum of 7 years will be required for the design, construction, and commissioning of the MQF, and that it must be operating up to 2 years prior to the arrival of martian samples. The purpose of the MQF is threefold: to sequester unaltered samples until biohazard testing is complete, to preserve the pristine nature of the samples, and to release samples deemed to be nonhazardous to a sample curation facility for allocation for further scientific study.
The technology required for containment and testing for pathogens is well developed. Biohazard assessment must also consider the potential ecological threats posed by returned samples. Sample containment must preserve the samples in a pristine condition, without inorganic and organic contamination. Technology for the preservation of samples similar to that used for lunar samples in the Lunar Curatorial Facility at the Johnson Space Center is well developed. However, the combination of biocontainment and preservation of samples in their pristine condition requires a unique design for the MQF that no currently existing facility provides. Another important design feature should be the potential for expansion, if early findings of definite evidence of extraterrestrial life warrant the need for all studies to be performed under containment. The cost of building such a specialized quarantine facility needs to be investigated.19
To prevent cross-contamination between samples from different planetary bodies, the samples must be handled in separate facilities. The Mars Curatorial Facility, for example, will be required once the martian samples are shown to be environmentally safe. Construction of such a facility is considered to be consistent with current practice and experience, for example, for lunar samples and antarctic meteorites. Sample allocations from the Lunar Curatorial Facility and from the Antarctic Meteorite Laboratory are under the guidance of advisory committees (the Curation and Analysis Planning Team for Extraterrestrial Materials and the Meteorite Working Group). These advisory committees are the successors of the Lunar Sample Analysis Planning Team, which oversaw the preliminary examination of the returned lunar samples and lunar sample allocations. These committees best exemplify the advisory committee proposed above for the oversight and analysis planning for Mars samples.20
A critical necessity in preparation for the sample returns … anticipated … from Mars … is support for sample curation and handling at a significantly increased level over what exists today. The proper preservation of each returned sample for future investigations is of paramount importance. The samples returned … will have particular handling and storage demands, which must be addressed by separate, specialized facilities. The funding for these facilities, including long-term operating costs, cannot realistically come from each mission’s budget. In particular, development is required in the areas of cryocuration, robotic sample handling, and biological quarantine. The panel recommends that the facilities required for the proper analysis and curation of returned samples be developed and supported.21
Continuing telescopic observation of Mars has played a key role in demonstrating that the surface of Mars changes on a relatively short time scale (as with seasonal changes, dust storms, evolution of the polar caps). Telescopic and spacecraft data are highly synergistic, and each plays a role in supporting the other. Support for future robotic and possible manned missions to Mars will require a long climatological baseline. The long baseline, partially obtained with ground-based and HST telescopic data, will also contribute to an understanding of the water cycles between the atmosphere, regolith, and polar caps, as well as spatially resolved data on volatile cycles of water, carbon dioxide, carbon monoxide, and ozone.22
NASA currently provides support, in widely varying percentages, for planetary science operations at Arecibo, Goldstone, Keck, and the Infrared Telescope Facility, in collaboration with the National Science Foundation (NSF), DSN, a private consortium, and NSF, respectively…. [These] facilities have made major contributions both to planetary science in general and to specific flight missions. The IRTF, the only facility dedicated to NASA planetary astronomy, has provided vital data in support of flight missions. The SSE Survey recommends that the planetary
radar facilities, the Infrared Telescope facility and NASA support for planetary observations at large facilities such as Keck be continued and upgraded as appropriate, for as long as they provide significant scientific return and/or provide mission-critical service.23
Models are an essential component of any scientific endeavor. Examples of theoretical planetary studies are those that treat the geodynamics of Mars, its interior structure, atmospheric loss and fractionation, and global climate and general circulation models.24
OTHER PROGRAMMATIC ELEMENTS
The SSE Survey recommends that NASA commit to significant new investments in advanced technology so that future high-priority flight missions can succeed. Unfortunately, erosion has occurred in the level of investment in technology in the past several years. Flight-development costs have increased over projections, and investments in advanced technologies have been redirected to maintain flight-mission development schedules and performance.
For most of the history of planetary exploration, large-cost flight missions … have carried a large portion of the technology-development burden in their development costs. During the change in the last decade to a larger number of lower-cost flight missions, the consequent loss of technology development by large missions was compensated by adding separate technology-development cost lines to the planetary exploration portfolio … under an understood policy of “no mission start before its technological time.” This mechanism was intended to separate and remove the uncertainties in technological development from early flight-development costs. However, flight-mission costs have been underestimated, and development plans have been too success-oriented, resulting in erosion of technology-development lines by transfer to flight-development costs. This trend needs to be reversed in order to realize [priority] flight missions….25
In the area of spacecraft systems, the key demand is for considerable autonomy and adaptability through advanced architectures. Lower-power, lower-mass spacecraft need to be developed commensurate with realistic cost and performance for the available expendable launch vehicles. Not unrelated is the need for more capable avionics in a more highly integrated package through advanced packaging and miniaturization of electronics and with a standardized software operating system.
New and increased science measurement capability in planetary science instruments and greater environmental tolerance will be required for less mass and power. Miniaturization is the key to the reduction of mass and power requirements….
As planetary exploration moves into the new century with more in situ and sample-return missions, it will be necessary to develop planetary landing systems, in situ exploration systems, and Earth-return technologies. The key requirements for landing systems are autonomous entry, descent, hazard avoidance, and precision landing systems. Once on the surface, sample gathering and analysis become key technologies, with attendant requirements for new surface science instruments, including biological measurements, and means for moving about a planet—on, above, and below the surface. Systems for accessing difficult-to-reach areas will be required.
Rover technology should advance toward long-life and long-range capability, with autonomous hazard avoidance and the ability to operate on large slopes. Drilling techniques on both terrestrial and icy surfaces will be needed, advancing toward deep-ice penetration and submarine exploration in subsurface oceans. Aerial platforms for Mars … will be required…. Advanced autonomy will need to be built into all of these mobile mechanisms.
The means to return planetary samples needs to be developed, beginning with small bodies and the Moon, advancing toward Mars….26
The Deep Space Network (DSN) is suffering from insufficient communications capability and occasional failures as it ages. Limitations on downlink bandwidth restrict the return of data from spacecraft…. While efforts to increase the transmitter power on spacecraft are valuable, likely it will be less expensive to augment both transmitter power and communications capacity on Earth than to correspondingly increase these factors on all spacecraft. Furthermore, additional ground stations would be valuable to provide geographic redundancy for the system as a whole, and they would grant more freedom in the timing of critical spacecraft events….
The SSE Survey recommends upgrades and increased communications capability for the DSN in order to meet the specific needs for this program of missions throughout the decade, and that this be paid from the technology portion of the Supporting Research and Technology (SR&T) line rather than from the mission budgets.27
Some future endeavors are so vast in scope or so difficult (e.g., sample return from Mars) that no single nation acting alone may be willing to allocate all of the resources necessary to accomplish them, and the SSE Survey recommends that NASA encourage and continue to pursue cooperative programs with other nations. Not only is the investigation of our celestial neighborhood inherently an international venture, but the U.S. Solar System Exploration program will also benefit programmatically and scientifically from such joint ventures.28