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Assessment of NASA’s Mars Architecture 2007–2016 4 A Balanced Mission Portfolio Does the Mars architecture represent a reasonably balanced mission portfolio? Although the committee interpreted this question as relating primarily to scientific balance, other issues of balance are also considered. SCIENTIFIC BALANCE The balance of scientific questions that the proposed architecture can and cannot address was of great interest and concern to the committee. Table 4.1 outlines the three key crosscutting scientific themes defined in the SSE decadal survey and breaks them down into slightly more focused key topics. Table 4.1 also summarizes the extent to which these different topics are satisfied by the proposed missions, based on the descriptions contained in the document Mars Exploration Strategy 2007-2016. As noted above, the lack of sufficient definition of the missions from MSTO onward is such that considerable uncertainty exists as to exactly which topics each mission is likely to address. In particular, the likely capabilities of AFL are far from clear. Table 4.1 clearly indicates that the theme of Mars as a potential abode of life is well served by the proposed architecture, that theme being a primary focus of the Phoenix, MSL, AFL, and Mid Rover missions. Similarly, the second theme, water, atmosphere, and climate on Mars, is also well served and is a focus for the Phoenix, MSL, MSTO, and AFL missions. The third theme, structure and evolution of Mars, is not well addressed by the proposed architecture. The MSL, AFL, and Mid Rover missions will provide some information on crustal compositions. Similarly, detection of localized methane sources by MSTO is likely to indicate ongoing geological activity. However, none of the proposed missions address issues relating to Mars’s deep interior and magnetism, or its absolute chronology. Every proposed mission is focused primarily on either the first or the second of the decadal survey’s crosscutting themes. No mission in the architecture has the decadal survey’s third crosscutting theme as its main focus. The next two subsections explore some of the issues associated with addressing theme three. Network Science Although addressing the key science questions relating to the third theme, the structure and evolution of Mars, is not a priority of the proposed architecture, Mars Exploration Strategy 2007-2016 recognizes the importance of these questions. For instance, the strategy document comments: “The quality and value of scientific results from
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Assessment of NASA’s Mars Architecture 2007–2016 TABLE 4.1 Crosscutting Themes for the Exploration of Mars Identified in the SSE Decadal Survey Compared with the Capability of Proposed Missions SSE Decadal Survey Theme Important Science Topics 2007 Phoenix 2009 MSL 2011 Scout 2013 MSTOa 2016 AFLa 2016 Mid Rovera 2016 ML3Na Mars as a potential abode of life Does/did life exist? X ? Xb XX X How hospitable? XX XX ? XX XX Water, atmosphere, and climate Water XX XX ? X XX XX X Present atmosphere XX X ? XX XX Long-term climate X ? XX X XX Structure and evolution Crust and activity X ? Xb X X X Deep interior and magnetism ? ? XX Chronology ?c ?c ?c NOTE: The comparison is with the capability as described in D.J. McCleese et al., Mars Exploration Strategy 2007-2016, NASA, Jet Propulsion Laboratory, Pasadena, Calif., 2006. Key: X, addressed by the relevant mission as it is currently conceived; XX, very well addressed by the relevant mission as it is currently conceived; ?, potentially addressed given the selection of appropriate instrumentation. Items in roman type are included and/or addressable by the proposed architecture. Items in italic type are not included and/or addressable by the proposed architecture. The ML3N (Mars Long-Lived Lander Network) mission is based on the SSE decadal survey recommendation for a network of geophysical/meteorological packages. MSTO is assumed to include both aeronomy and trace-gas investigations. aMissions that are poorly defined and so may eventually have capabilities somewhat different from those assumed by the committee. bPotential confirmation of localized methane production. cPotentially addressable via in situ techniques. surface missions depend upon the landing site selected and the completeness of the available geological, climatological, and geophysical context…. A network of landers, carrying seismic sensors, heat flow probes and the capability for making high-precision geodetic measurements, is needed to better understand the structure, state and processes of the martian interior in order to ascertain thermal and geological evolution of the planet that is responsible for the surface we see today.”1 In view of the importance of Question 3, and the current imbalance in the proposed architecture, the committee reiterates the recommendation already made to include a geophysical/meteorological network mission as a third possibility for the 2016 launch opportunity. It could be argued that the inclusion of this mission will require significant new technology investments at a time when only limited funding is available. The committee does not think this is the case. The concept of a Mars network was studied extensively by NASA in the early 1990s as part of the Mars Environmental Survey (MESUR) project.2 A prototype of the MESUR landers—MESUR Pathfinder, later renamed Mars Pathfinder—was successfully flown and operated on Mars in 1997. Additional development work has been undertaken in the context of the Pascal Mars Climate Network mission, which has been proposed as a Discovery and a Mars Scout mission.3 Finally, additional developmental activities have been undertaken in Europe in the context of a variety of concepts, including MARSNET, INTERMARSNET, and, most recently, NETLANDER.4 Although the committee has not seen detailed cost studies and is not appropriately constituted to undertake such studies itself, it is of the opinion that the cost of an adequate network mission is comparable with that of the
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Assessment of NASA’s Mars Architecture 2007–2016 other missions under consideration for launch in 2016. If the addition of a network mission in 2016 is not possible, then every effort should be made to make at least some of the highest-priority measurements on the landed missions that are flown in the period 2013-2016. As outlined in Table 4.1, a network mission (envisaged to consist of four stations with seismological, meteorological, and heat flux instruments) has the capability to address the decadal survey’s second and third crosscutting themes.5 Inclusion of this mission in the Mars architecture would be consistent with the SSE decadal survey’s call for the Mars Long-Lived Lander Network mission. The committee anticipates that a moderate amount of technology development (especially of entry, descent, and landing systems), or international collaboration, is required to bring such a network to fruition. Absolute Chronology The committee is concerned that with a Mars sample return mission relegated beyond the current budgetary and planning horizon, the issue of deciphering the absolute chronology of Mars remains unaddressed in the current architecture despite its recognized scientific necessity for unraveling the geophysical, geological, hydrological, and atmospheric history of the planet. This type of historical context is also important for focusing efforts to find life—if it did emerge—and for providing a historical framework within which to evaluate the evolution of any life or suggestions of it on Mars. Chronology can potentially be addressed coarsely through in situ analysis. Even with errors of ±500 million years, such an analysis would greatly improve our understanding of the absolute timing of key events in martian history. Measurement of the age of rocks by a future rover is probably only possible using the potassium-argon (K-Ar) method, but the technical problems in developing such a system are huge. The sample preparation needed would be daunting, especially given the new evidence that rocks on Mars commonly have coatings. Also, the K-Ar system is so easily reset by shock, weathering, and other processes that interpretation of the measured ages will require knowledge about the sample’s petrologic context. The only hope for making an easily interpretable measurement is to go to a landing site with unweathered lava flows uniformly covering a broad area (so that crater-counting data can be obtained for calibration). Unfortunately, such a site will not help to define the boundaries of the martian geological epochs (i.e., the Noachian and Hesperian boundaries are so old that lavas of this age are likely to be altered). Moreover, visiting such a volcanic site would likely require a dedicated mission. On the other hand, an in situ dating technology would find broad applicability to other solar system bodies besides Mars—especially those planets and satellites from which sample return missions cannot now be contemplated, e.g., Venus, Mercury, and the icy bodies of the outer solar system—and so serious consideration should be given to the technical feasibility of developing the appropriate instrumentation. Ultimately, a Mars sample return mission will be required to obtain high-precision dating capable of unraveling the duration of aqueous activity at any single location and the associated implications for extinct or extant life. OTHER ISSUES OF BALANCE The committee also identified four other issues of balance as follows: The balance between different mission types (landers/rovers as opposed to orbiters) was considered reasonable. The exploration of Mars is at a relatively mature stage; most of the necessary orbital measurements have been made, and it is therefore appropriate that the majority of the missions proposed for the coming decade consist of localized, in situ investigations. Careful consideration should be given to achieving the appropriate balance between the use of MSTO as a science platform and as a communications relay. The importance of addressing the long-term climate evolution of Mars, together with uncertainties in Mars telecommunications requirements and the availability of other orbital assets to relay communications, suggests that the balance should be strongly biased toward science. The committee is concerned that MSTO not simply serve as a telecommunications relay, especially in the absence of any quantified, hard telecommunications requirements.
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Assessment of NASA’s Mars Architecture 2007–2016 The committee notes that Scout missions provide a potential additional mechanism for adding balance to the overall architecture (subject to the caveats discussed previously). In particular, the optimum science payload for MSTO may (or may not) alter depending on the outcome of the 2011 Scout competition. Finally, international collaboration, as noted in the document Mars Exploration Strategy 2007-2016, could be another mechanism for adding balance to the Mars architecture. RESPONSE TO QUESTION 3 In response to the question, Does the Mars architecture represent a reasonably balanced mission portfolio?, the committee finds that in the context of the basic types of missions, the Mars architecture is a reasonably well balanced one: both landed and orbital missions are included in an appropriate mix, given the current state of Mars exploration. To the extent that the specific science objectives of the proposed missions are defined, one of the three crosscutting themes for the exploration of Mars identified in the SSE decadal survey is largely neglected, as are very high priority topics related to understanding near-surface and boundary-layer atmospheric sciences, and so, in this respect, balance is sorely lacking. As has already been recommended (see above), a geophysical/meteorological network mission is a key to addressing both of these science areas, although some of the highest-priority science measurements could potentially be made on other surface missions (e.g., the AFL or the Mid Rover missions). These include meteorological, seismic, and heat flow measurements. To optimize efforts to implement a balanced portfolio of missions, the committee offers the following recommendations: Recommendation: Include the Mars Long-Lived Lander Network in the mix of options for the 2016 launch opportunity. Recommendation: If the Mars Long-Lived Lander Network cannot be implemented in the period under consideration, provide for an effort to make some of the highest-priority measurements on the landed missions that are included in the proposed Mars architecture. Recommendation: Ensure that the primary role of the Mars Science and Telecommunications Orbiter is to address science questions, and not simply to serve as a telecommunications relay. This distinction is particularly important with respect to the required orbital parameters that are adopted. NOTES 1. D.J. McCleese et al., Mars Exploration Strategy 2007-2016, NASA, Jet Propulsion Laboratory, Pasadena, Calif., 2006, p. 15. 2. Solar System Exploration Division, MFPE: Mission from Planet Earth, Vol. 2 of Solar System Exploration Division Strategic Plan, NASA, Washington, D.C., 1991, pp. 18-26. 3. See, for example, R.M. Haberle et al., “The Pascale Discovery Mission: A Mars Climate Network Mission,” Concepts and Approaches for Mars Exploration, Lunar and Planetary Institute, Houston, Texas, 2000, available at <www.lpi.usra.edu/meetings/robomars/pdf/6217.pdf>. 4. For more information about NETLANDER, see, for example, <smsc.cnes.fr/NETLANDER/>. 5. Should mission resources permit it, the inclusion of descent and/or surface imagers in each network station would greatly enhance their utility by enabling them to pinpoint the actual landing sites and to perform some assessment of the local geology. With so little information available from specific sites on Mars, the addition of information from four or more network sites would be a significant bonus.
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