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AI1'visers to t(le Natio11 on Science. Engineering. and Medicine NationalAcademyof Sciences NationalAcademy Engineering 01 Institute01Medicine Space Studies Board NationalResearch Council Coml11ssion on Physical Sdences, Mathematics and Applications April 21, 2000 Dr. Carl Pilcher Science Program Director Solar System Exploration Code S National Aeronautics and Space Administration Washington, DC 20546 Dear Dr. Pilcher: In your letter of January 18, 2000, you reiterated a verbal request made in November 1999 for the views of the Space Studies Board's (SSB ' s) Committee on Planetary and Lunar Exploration (COMPLE:X) on a number of issues concerning the Science and Mission Roadmapl recently prepared as part of the Solar System Exploration science theme's contribution to strategic-planning activities conducted by NASA' s Office of Space Science. In particular, you asked that COMPLEX provide you with the following: .Perspecltives on the degree to which the Roadmap addressesthe priorities outlined in past COMPLEX reports; and .Recom[[lendations for strengthening the scientific rationale and mission priorities contained in the Roadmap. COMPLEX understandsthat you need this assessment becausethe Roadmap, an integral part of the Office of SpaceScience's new strategic plan, is currently undergoing revision prior to publication. Work on this a~isessment began at COMPLEX's November 1-5, 1999, meeting at the I Solar System Explora,tion Subcommittee, Exploration of the Solar System-Science and Mission Strategy, Jet PropulsioJrl Laboratory , Pasadena, California, December 1999. 2101Constitution Avenue, Washington, 20418 Telephone NW, DC (202)3343477 Fax(202)3343701 ssb@nas.edl Office Address:MiltonHarris Building, Room584,2001Wisconsin Avenue, N.W., Washington, 20007 DC

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Arnold and Mable Bec:kmanCenter in Irvine, California, and was conducted in parallel with the preparation of the committee's input to an SSB-wide assessment the strategic plan resulting of from the Office of Space Science's Strategic Planning Workshop held in Galveston, Texas, in November 1999. Sub~)equent your November 1 presentation of the Roadmap, COMPLEX to received additional perspectives from committee member Wendy Calvin and SSB director JosephAlexander bas(:don their role as observers at the Roadmap presentationsheld in Galveston on November 2. In the course of this study COMPLEX reviewed two drafts of the Roadmap: the November 1999 and December 1999 drafts distributed to the committee prior to the November 1999 meeting and in J;a.nuary 2000, respectively. Although in the context of another activity, COMPLEX also was briefed on the technical and programmatic aspectsof one of the new missions featured in the Roadmap, the Venus Surface Sample Return. In addition, the committee reviewed relevant reports issued by COMPLEX and other National ResearchCouncil (NRC) committees (e.g., The Searchfor Life's Origins: Progress and Future Directions in Planetary Biology and Chemical' Evolution [1990], An Integrated Strategyfor the Planetary Sciences: 1995-2010 [1994], Th,eRole of Small Missions in Planetary and Lunar Exploration [1995], Review ofNASA 's Planned Mars Program [1996], "Scientific AssessmentofNASA's Solar System Exploration Roadmap" [1996], Exploring the Trans-Neptunian Solar System [1998], The Exploration ofNear-E:arth Objects [1998], and A ScienceStrategyfor the Exploration of Europa [1999]) and held extensive discussions in closed session. COMPLEX's .assessment the program outlined in the Roadmap is mixed. The of committee is generall)1positive about many of the near- and mid-term flight missions and related activities highlighted in the Roadmap becausethey addresspriorities outlined in the committee's past reports (see attached Assessmentfor full details). COMPLEX is particularly pleasedto seethat NA.SA continues to place a high priority on Mars exploration and that a new initiative relating to Iv[ars sample handling and analysis is proposed. Similarly, COMPLEX is pleasedthat prominent attention is given to a comet nucleus sample-return mission. Moreover, the committee commends NASA for formulating a program of planetary exploration that attempts to systematically addresskey physical and chemical processesrather than merely cataloging and classif:ying planetary environments. Finally, the Roadmap appearsto strike an appropriate balance b(:tween the broad thematic goals of understanding origins and understanding planets advocated in COMPLEX's Integrated Strategy.2 These positives aside, COMPLEX has a number of serious concerns about particular aspectsof the Roadmap and the program of solar system exploration it advocates. These concerns are, in approximate order of priority, as follows: .The Roadmap does not clearly indicate the scientific objectives of solar system exploration and the critical measurementsthat must be made to meet these objectives, nor does it describe how existing or proposed missions will make these measurements. These problems stem in large part fronrl the Roadmap's emphasis on the three broadly scoped "Quests" and are compounded by the document's lack of a coherent structure, a consistent format, a cohesive 2 Space Studies Board, National Research Council, An Integrated Strategy for the Planetary Sciences: 1995-2010" National Academy Press, Washington, D.C., 1994, pages 33-34. 2

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introduction, and a comprehensive supporting text. .The scientific justification for both existing and proposed mission lines is not adequately presented. .The sch(~dulingof, and the rationale for, several of the proposed missions (e.g., Europa Lander, Titan E;xplorer, and Saturn Ring Observer) relative to the flight programs they logically build on (e.g., Europa Orbiter and Cassini/Huygens) need to be clarified. .The Roadmap includes no information concerning the process by which it was assembled,the identity of the authoring group, or the means by which the recommended mission sequenceswere prioritized. .The scie.ntific rationale for the selection of the Venus Surface Sample Return mission is unclear. .Many oj[the major missions in the proposed "To Build a Planet" mission line either are not identified. as high priorities in existing COMPLEX reports or might more properly be justified in other programmatic contexts. .The handling of non-mission activities, such as R&A programs and education and public outreach, does not adequately indicate the importance of these activities. .Important linkages between the Solar System Exploration, Astronomical Search for Origins, and Sun-E;.lrthConnection sciencethemes and Astrobiology either go unmentioned or are obscured. .The asymmetry in the discussion of how the goals of Solar System Exploration relate to the Astronomical Search for Origins and the Sun-Earth Connection science themes, on the one hand, and to A:)trobiology, on the other, might be taken to imply that the latter has a special status. .Any detailed discussion of technological issueshas been excluded. In its 1996 assessmentof the Solar System Exploration Roadmap, COMPLEX commented that it is "important for the Roadmap's scientific objectives to be brought into sharper focus with some'indication of priorities for study and critical measurementsto be made."3 Through a combination of the factors listed above, the new Roadmap's scientific objectives have become even more diffuse than they were in the 1996 edition. Given the structural deficiencies in the current Roadmap, COMPLEX reiterates its 1996 recommendation that this document must clearly indicate scientific objectives and the critical measurementsthat mu:~tbe made to meet these objectives, describe how existing or proposed missions will make the'semeasurements,and indicate relative priorities. Therefore COMPLEX recommends that the next Roadmap team be tasked to define a more scientifically compelling rationale for solar syst(~mexploration than that currently provided by the three Quests. As an intermediate step, COr.APLEX provides some suggestions(see attachedAssessment) as to how the current draft could be reorganized to make a more coherent document. Becausemany of the criticisms outlined in COMPLEX's accompanying Assessment 3 Space Studies Board, National Research Council, "Scientific Assessment ofNASA's Solar System Exploration Roadmap," letter report to Jurgen Rahe, August 23, 1996, pages 2 and 9 3

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result from shortcomings in the Roadmap' s structure and format, they should not detract inordinately from the many favorable aspectsof the program of planetary-exploration missions and supporting activities advocated in this document. The SSB and COMPLEX, in particular, look forward to the implementation of the Roadmap and will be pleasedto review this phaseof the solar system exploration program at an appropriate time. ~ Sincerely, - Claude Canizares .Wood John A Chair Chair Space Studies Board LEX COMP 4

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Scientific Assessment of Exp[oration of the So[ar System-Science and Mission Strategy At its November 1-5,1999, meeting, the SpaceStudies Board's Committee on Planetary and Lunar Exploration (COMPLEX), chaired by John A. Wood of the Harvard-Smithsonian Center for Astrophysic:5,began work on an assessment Exploration of the Solar System- of Science and Mission Strategy,1the most recent update of the Roadmap ofNASA 's Solar System Exploration sciencethe:me. This assessment was made at the specific request ofDr. Carl Pilcher, NASA 's science program director for solar system exploration, and had two purposes. The first was a detailed comparison between the goals and objectives outlined in the Roadmap and those enunciated by COMPLEX and other relevant NRC committees. The secondwas to make recommendationsfor strengthening the Roadmap's scientific rationale and mission priorities. ELEMENTSOFTHEROADMAP The preparation of roadmaps is a key aspect of the strategic planning process currently adopted by NASA's Office of Space Science (OSS). Their primary purpose is to summarize the scientific objectives and programmatic recommendations put forward by each ofOSS's four component groups, or ~)cience themes. The document under review was prepared for use by the Solar System Exploratjlon science theme during OSS' s ongoing strategic planning activities. The Roadmap identifies three overarching goals, or "Quests," for solar system exploration: Explain the formation and evolution of the solar system and of Earth within it; 1 Seek thc~origin of life and its existence beyond Earth; and 2 Chart OlJfdestiny in the solar system. 3 These Quests are addressedby three continuing series of spacecraftmissions-the Outer Planets, Mars Surveyor, and Discovery prograt:ns-and supporting researchand analysis (R&A) programs, technology development, and education and public outreach (E&PO) activities. In addition, the Roadmap recommends that two additional programmatic elements are neededif the three Quests are to be addressedin an adequatemanner. These additions are a new, continuing flight program called "To Build a Planet" and a facilities initiative within the Mars Surveyor program devoted to saJJlple handling and analysis. Within each of the flight programs, current and planned missions are described, explicit priorities for near-term.(2003-2007) to mid-term (2008-2013) new starts are outlined (except for Discovery, which, by its nature, is community driven), and some examples of possible far-term (2013+) missions are indicated. The Roadmap also includes material explaining how solar system exploration activities relate to activities within the purview of OSS' s Astronomical Search for Origins and Sun-Earth Connection science themes.

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The organization of the current Roadmap is significantly different from that of the edition reviewed by COMPLI~X in 1996.2 Although the Quests remain the same,the five subsidiary "Campaigns" and numerous "Portrait" missions featured in the 1996 edition have been replaced by directly linking the Quests to R&A, E&PO, and a relatively small number of prioritized missions within the v3Iious continuing mission lines. STRUCTURE AND FORMAT OF THE ROADMAP In general, COMPLEX found the Roadmap to be an exceedingly difficult document to review, owing, in part, to the Roadmap's format: a hybrid collection of color "vugraph"-style pages,backed up, in part, by facing pagescontaining supplementary text. The Roadmap is clearly intended to be presentedto a reasonably sophisticated audience. Alternatively, its contents could be use(l selectively to provide supporting graphics for display in general presentations about NASA' s planetary-exploration programs. The Roadmap is not an easy read and is likely to be accessibleonly to readers with a strong background in .planetaryissues,processes,and recent discoveries. It is unclear whether non-specialists will urlderstand why, for example, sampling at varying depth and location is important during a comet nucleus sample-retum mission. Brief descriptions of the current state of knowledge might be useful additions to the Roadmap becausethey would provide some context for setting priorities among diverse planetary objects and science goals. Additional stnlctural problems include the lack of a table of contents or outline and the fact that many prograrn elements are scattered seemingly randomly throughout the text. A general discussion of:R&A programs (pages 12-13) is, for example, introduced in the middle of text describing Quest 1. Similarly, the material on E&PO seemsout of place. The document would benefit if the g(~neral text on E&PO (pages 30-34) were moved into an introduction and the remainder (pages :35-37),in the current structure, were integrated into the sections dealing with the relevant Que~)ts. Without a cohc~rent structure and cohesive introductory material the Roadmap appearsto be a haphazard <;;ollec1ion graphics that readers must flip through back and forth in an attempt of to understand the foculs and goals of the proposed program of planetary exploration. GOAJLS, PRIORITIES, AND SCIENTIFIC FOUNDATIONS While the Roadmap appearsto strike an appropriate balance between the brQadthematic goals ofunderstandinj~ origins and understanding planets advocated in COMPLEX's Integrated Strategy,3 the style of presentation is inadequateto convey the detailed goals, priorities, or scientific foundations motivating solar system exploration. Sciencejustification for both existing and proposed mission lines is thin or missing and, as a result, does not substantiateNASA's goals and priorities in solar system exploration. The primary reason for this is that the Roadmap's predomin.mtly vugraph-style format inherently limits the amount of textual information that can be presented. This problem could have been solved in large part by the addition of a narrative:on the pages facing the color graphics. This option, although used in certain places, is not e:xercisedin a consistent manner.

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More seriously, the Roadmap does not provide an adequatelinkage between goals, directly addressablescientific investigations, and missions. While the Campaigns fulfilled this function in the Roadm(lP's 1996 edition, the current version links missions and contributions from the R&A and E&PO programs directly to the three Quests. While these broad overarching statementsare generally consistent with high-Ievel goals enunciated in various SSB reports,4it is not clear that they provide a suitable framework for specifying scientific goals and objectives addressableby specific science investigations and for defining critical measurements. The Roadmap'~;attempt to justify the highly diverse and cross-cutting nature of the program in terms of goals such as "chart our destiny in the solar system" leads to a diffuse and incoherent description of solar system exploration and its sciencejustification. Key elements are fragmented across the l:2uests is seenin the derived outline included as an Appendix to this (as report), and no clear de:scriptionof the proposed program's science priorities is provided. Moreover, there is no s.ynthesisof overall goals and objectives, nor any mention of how specific elements of the prograJll relate to those goals. THE PROCESS OF DEVELOPING THE ROADMAP The Roadmap <:ontains information about the composition of the authoring group or no the process by which i1:was developed. Additionally, with the exception of the Mars Surveyor line, the rationale for prioritization of goals and missions is absent both within and between mission lines. This apparent anonymity of the text is in marked contrast to the previous edition of the Roadmap, which expli,citly included material on how the document was created and by whom it was written, a factor COMPLEX regarded as a plus in its 1996 review.5 Without more information on the process used to draft the Roadmap, COMPLEX cannot comment on its fairness or credibility. The absenceof details concerning the development of the Roadmap is a serious flaw. MISSION LINES The spaceflighl: component ofNASA's solar system exploration program is performed within the context of sl~veralcontinuing line items in NASA' s budget. Their establishment has brought new vitality aJld stability to the solar system exploration program, and NASA deserves much credit for this achievement. Three such lines currently exist, the Outer Planets, Mars Surveyor, and Discove:ry.The Roadmap proposes the addition of a new line, "To Build a Planet." The followinJ~ subsectionsreview what the Roadmap has to say about each of the current lines. Outer Planets Program The Outer Plal1letsprogram, initiated as part of the "Origins" Initiative in NASA' s FY 1998 budget, is, according to the Roadmap, intended to focus on "environments in the outer solar system that can provide insights into prebiotic chemistry and possible habitats for life" (page 43). 3

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The two missions curfi~ntly included in this line are the Europa Orbiter and Pluto/Kuiper Express; both address fundamental scientific goals that are broadly consistent with those outlined in recent COMPLEX reports.6,7 The Roadmap .ldentifies a trio offollow-on missions: the Titan Explorer, Europa Lander, and Neptune Orbiter. The selection of the first two might appear to be premature given that they will logically build on the results from ongoing or planned missions (Cassini-Huygens and Europa Orbiter, respectively) that are still many years from completion. COMPLEX recognizes that a combination of long mission design/development periods and the extended flight times necessaryto reach the outer planets mandatesthat work on follow-on missions must begin promptly if we are to (:xploit the anticipated discoveries from Cassini-Huygens and the Europa Orbiter in a timely manner. These considerations might not, however, be apparentto all readers. The Roadmap does not clearly describe the relationship between the proposed missions and their logical precursors. Wilthout clearly stated scientific priorities and goals, the proposed follow-on missions lack context .and justification. Similarly, the text of the Roadmap makes little or no mention of the fact that major infusions of new kno~rledge about Europa and Titan are expected before the launch of either the Europa Lander or the Titan Explorer. Indeed, the suggestion that, for example, the Europa Lander can be ready for launch in 2008 (page 46), the same year the Europa Orbiter reachesits destination (page 45), implies that there can be little or no synergy between these two missions. (COMPLEX notes that the mission summary chart (page 106) suggestsa more reasonable schedule.) More importarLtly, there is nothing in the Roadmap to suggest how priorities might change if, for example.,the Europa Orbiter finds no evidence for an ocean beneathEuropa' s icy surface. The Roadma]~'sscantjustification for these missions and, in particular, their relationship to ongoin:gand approved missions is a serious flaw. The Roadmap should clearly indicate that planning for these mid-term missions must be sufficiently flexible that they can be ready to exploit new exploratory niches uncovered by earlier missions. It would al~;obe helpful if the Roadmap included some discussion of how mission priorities and sequenc,~s could be adjusted depending on the results from, or failure of, earlier mIssIons. While COMPIJEX has indicated that Triton is the highest-priority target in the trans- neptunian region following the completion of a Pluto-Charon missions and has provided some encouragementfor additional studies of Neptune's magnetic environment,9 the rationale for the emergenceofNeptunt: over, say, detailed study of Jupiter, as recommended by COMPLEX,!O should be justified more fully. In general, as portrayed by the Roadmap this mission line seemsto be suffering from an unresolved split identity. The Outer Planets program becomes "Exploring Organic-Rich Environments" early in the document (page 40) but turns back into the Outer Planets program further on (pages 101 and 103). Is the mission line devoted to organic environments or just to distant objects? The mention of "Interstellar Exploration" (on page 55) and "Interstellar Precursors" (on page 101) in the context of this program is particularly confusing. These mission concepts have deep roots in the space-physicscommunity and have, seemingly, little to do with organic environments.I 1,!2,13 . The outer-plarlets/organic-environments duality seemsto stem from the lack of focused scientific goals as the foundation for exploration and, subsequently, for the mission lines. 11

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Alternatively, this amb'lguity may reflect an unfinished transition from the early approachof cataloging planetary bodies to the more recent science-driven approach. Given COMPLEX's preference for exploration programs formulated in terms ofkey physical and chemical processes rather than distance from the Sun,14 believes that this mission line would be more compelling if it explicitly directed towcLrdthe study of organic environments wherever they are found. Mars Surveyor Intensive exploration of Mars has long been identified as a high-priority activity by COMPLEX,15 and the (:ommittee is encouragedto seethat Mars Surveyor and, in particular, the Mars sample-return program are featured prominently in the Roadmap. Similarly, COMPLEX is pleased to seethat thesl~programs maintain their focus on activities recommendedin previous reports,16accommodatf: some of the recommendations made during the committee's 1998 review of the Mars exploration architecture,17and point to the importance ofa robust communications network. 18COMPLEX: also supports the high priority given to the proposed Mars Sample Handling and Analysis program, since such an initiative is essential both to ensurethe scientific integrity of returned saJmples to maximize the scientific information gleaned from the and analysis of the samples.19The necessaryfacilities and protocols are required to be in place well in advance of the return of the martian samples.2°The description of the Mars Surveyor line does perhaps the best job of linking scientific objectives to specific missions and their sciencegoals. Given the recenltfailures of Mars Polar Lander and Mars Climate Orbiter, it is not clear to what extent the contents of this part of the Roadmap will stand the test of time. Whatever the outcome of the ongoin!~efforts to revise the Mars exploration architecture, the scientific focus for Mars exploration remains the understanding of this planet as a possible abode of past or present life, and this requires a program of comprehensive studies aimed at understanding the origin and evolution of the martian environment.21 A central element of these studies will be the return to Earth of samples of the martian atmosphereand soil, and, more importantly, carefully selected samples from martian rocks.22 It is heartening to seethat the Roadmap outlines a process (page 65) by which future mission goals and strategieswill be reviewed. Whatever changesare made to the Mars Surveyor program in the aftermath of the recent failures, COMPLEX expects that a thorough and open review process will be defined and applied to future Mars missions, be they those outlined in the Roadmap (i.e., Synthetic Aperture Radar, Advanced Sample Return, and Robotic Outposts), or other mission concepts arising from the ongoing architecture-review process.~ Discovery COMPLEX ha:) long maintained that priority objectives in the planetary sciencesare best addressedby a range of mission sizes.23The Discovery program has demonstratedthat reasonablescience can be achieved within the context of small- to mid-size missions!4 While the Roadmap emphasizesDiscovery missions that are defined and led by the planetary-science community, it does not clearly state that selections are made basedon compelling science and technical feasibility. Nor does the Roadmap mention that, in many instances, mission colll~eptsemerge directly from activities supported by the R&A program. Another important asplectof Discovery that goes unmentioned is the program's ability to address 5

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important science goallsthat do not fit within the scopeof the Outer Planets and Mars Surveyor lines. The close identification between Discovery and Quest 1 is probably inappropriate. The study of comets and a~;teroids, example, is of direct relevance to Quests 2 and 3 and is, and for will likely remain, a major focus for Discovery missions. Finally, the Discovery summary chart (page 77) would be ml:>re useful if it clearly indicated which missions had flown, which are in progress, and which aI.estill in preparation. To Build a Planet The Roadmap proposes a new mission line, "To Build a Planet," designed to address questions relating to the formation and development ofplanetary environments. COMPLEX has very mixed feelings about this proposal. The line is justified on the grounds (page 42 and repeatedverbatim on page 81) that Quest 1 is not "adequately addressed"within the current- program structures. This rationale is thin and illustrates the difficulty in using the broadly scoped Quests to justify specific scientific investigations and measurements. The basic .scientific issuesthis line is designedto addressare, however, important items identified in past NRC reports.25,26 Moreover, the first mission in the line, Comet Nucleus Sample Return, is consistent with prior advice from COMPLEX. Indeed, such a mission addressesthe highest-priority goals identified in COMPLEX's Integrated Strategy!7 COMPLEX's most serious problem with this new line is that the suite of proposed missions lacks coherenceand sc~ems be a catchall for large missions. to While the origins and justification for a comet nucleus sample-return mission are well documented, the same'cannot be said for the other two missions proposed for this line, the Saturn Ring Observer and V t~nusSurface Sample Return. The former was featured as a Portrait mission in a Campaign, Astrophysical Analogs in the Solar System, in the 1996 Roadmap.28The latter does not seem to have figured prominently in NASA's recent science-planning activities, although the Europearl SpaceAgency recently published a major study concerning such an endeavor.29Why these missions were selectedover other possible candidates is unclear and highlights the lack of ,discussionon how the Roadmap was created and what process was followed to select the proposed missions. This mission ljlne's apparent lack of coherenceis heightened by the discussion offollow- on missions. Why, for example, is the Mars Geophysical Network not part of the Mars Surveyor line? Similarly, why ~lfethe Jupiter Polar Orbiter and Giant Planet Deep Probes not part of the Outer Planets/Organic:Environments line? R&A PROGRAMS AND OTHER ACTIVITIES The R&A pro!~ramis extremely important becauseit is the origin of both new missions and continued discovt:ry , it supports ground-basedobservational and laboratory studies, and it provides the framework and foundation upon which new information from spacecraft missions is integrated into a comprehensive understanding of solar system processes. As such, its importance has been documented in various SSB reports.30.31 Indeed, in its review of the 1996 Roadmap, COMPLEX specifically noted the 6

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document's failure to rl~cognizethe role ofnon-f1ight activities supported by the R&A program. Therefore, the explicit mention of the R&A program in the context of the Roadmap and, by association, the Office of SpaceScience's strategic-planning activities is an extremely positive factor, one strongly recommended by the SSB.32Unfortunately, the new Roadmap's handling of R&A and other non-mission activities such as E&PO is generally poor and not well integrated with the rest of the text. While the general text on E&PO and that specifically related to the three Quests is consolidated in one place (pages 29-37), the text on R&A is fragmented. General text on R&A is introduced in the middle of the discussion of Quest 1 (pages 12-13) and is followed by specific text relating to Quest 1 (page 14). But the discussion ofR&A activities relating to Quests 2 and 3 is deferred until pages 20 and 26, respectively. SOLAR SY~~TEM EXPLORATION AND OTHER SCIENCE THEMES In the Roadmap, important linkages between the Solar System Exploration, the Astronomical Search fc)r Origins, and the Sun-Earth Connection science themes and Astrobiology either go unmentioned or are fragmented. Text explaining how solar system exploration provides "!~round truth" for the astronomical searchfor origins appearsin the report's brief introductory section (page 6), and additional text linking these two science themes appears in the summary section (pages 108-109). However, text relating the Solar System Exploration and Sun-Earth Connection sciencethemes appearsonly in the summary (pages 110-111). In addition to these linka~~es receiving inconsistent and cursory treatment, discussion of them is not well integrated into tht: preceding text. The discussion of Astrobiology's linkages to solar system exploration is equally brief and fragmented. Astrobiology is discussedonly in the context of the three Quests (pages 15-16, 21- 22, and 27-28). Even 1:hen, discussion is often cryptic. The text, for example, makes the reference to Astrobiology's three fundamental questions (page 22), but nowhere is the reader told what all three questions are. Some introductory material is clearly needed. More importantly, the Roadmap's discuss:ionof the linkages between the exploration of the solar system and Astrobiology in the context of the "Quests" rather than in the context of the "Integration of Space Science" (pages 107-111) could suggestthat Astrobiology has a special status. Similarly, this treatment could be takc~n imply that the goals of the Solar System Exploration theme are being to justified on the basis of their relationship to the goals of Astrobiology. Scientific goals should be judged on their own merit and not on the basis of their connections to other goals of other scientific endeavors. TECHNOLOGY ISSUES The discussion of technological issuesin the 1999 edition of the Roadmap differs significantly from that in the 1996 edition. Almost 25% of the earlier document was devoted to discussion of the key technologies and other capabilities necessaryto enable the featured missions, whereas disc:ussionof technological issues occupies less than 10% of the current document. What discussion there is is divided among the text devoted to the Outer Planets

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(pages 52-53), Mars Surveyor (66-67), and "To Build a.Planet" (96-97) mission lines, and the summary (104-105). llhere is no discussion of the technology development necessaryto enable future Discovery missions. More importantly, there is no indication of how any of the development activities are prioritized, nor is there any mention of the role played by the New Millennium program and the Planetary Instrument Definition and Development Program (PIDDP). To be fair, COJ\1PLEX notes that the Roadmap's introduction (page 2) statesthat "a companion technology roadmap will be published early in the year 2000." Nevertheless, the apparent decoupling of science and missions from technology is unfortunate in that it negates - what COMPLEX vie~'ed as one of the strengths of the Roadmap's 1996 edition:3 FINDINGS AND RECOMMENDATIONS COMPLEX finds that many of the missions and other activities identified in the current Roadmap addresskey priorities identified in reports issued by COMPLEX and other NRC committees. In particular, COMPLEX offers strong support for the Europa Orbiter, Pluto/Kuiper Express, and the Mars Surveyor and Discovery programs. COMPLEX also supports the proposed Comet Nuc1<~us Sample Return (CNSR) mission and the new initiative concerning the handling and analysis of martian samples. Nevertheless, COMPLEX has some significant concerns about the Roadmap and the program it presents. 1nese concerns are, in order of priority, as follows: I. The Roadmap does not clearly indicate the scientific objectives of solar system exploration and the critical measurementsthat must be made to meet these objectives, nor does it describe how existing or proposed missions will make these measurements. As a result, the scientific justification for both existing and proposed mission lines is not adequately presented. These problems stem jm large part from the Roadmap's emphasis on the three broadly scoped "Quests" and are compounded by the document's lack of a coherent structure, a consistent format, a cohesiye introduction, and a comprehensive supporting text. 2. The scheduling of, and the rationale for, several of the proposed missions (e.g., Europa Lander, Titan Explorer, and Saturn Ring Observer) relative to the flight programs they logically build on (e.g., Europa Orbiter and Cassini/Huygens) need to be clarified. Similarly, the priority of these missi,:>ns relative to a number of possible eventualities needsto be spelled out. For example, does the Europa Lander remain in the queue if the Europa Orbiter finds no evidence of liquid water or, worse still, suffers a terminal failure? 3. The Roadmap includes no information concerning the processby which it was assembled,the identit:y of the authoring group, and the means by which the recommended mission sequences were prioritized. 4. The scientific rationale for the selection of the technologically challenging Venus Surface Sample Return (VSSR) mission is unclear.This is the casewhether it is considered within the context of the proposed mission line, "To Build a Planet," or within the context of other possible Venus missions. Moreove.r, other than CNSR, many of the missions in the proposed "To Build a Planet" mission line either are not identified as high priorities in existing COMPLEX reports or might more properly be justified in other programmatic contexts. 8

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5. The haThjling ofnon-mission activities, such as R&A programs and education and public outreach, does not adequately indicate the importance of these activities. Similarly, important linkages betvveenthe Solar System Exploration, Astronomical Search for Origins, and Sun-Earth Connection ~)cience themes and Astrobiology either go unmentioned or are obscured. In particular, discussin!~the relationship between the goals of the Solar System Exploration theme and Astrobiolog:V in the context of the three Quests (pages 15-16,21-22, and 27-28) but deferring much of the d.iscussionof the corresponding relationships with the Astronomical Search for Origins and Sun-Earth Connection themes until later in the Roadmap (pages 107-111) might be taken to impl~r that Astrobiology has a special status. It could even be taken to indicate that the goals of solar system exploration are being justified on the basis of their congruencewith the goals of astrobiolog;y. 6. Detailed discussion of technological issueshas been excluded. Given the deficilencies in the current Roadmap, COMPLEX reiterates the recommendation made in its assessmentof the Roadmap's 1996 edition that this document must clearly indicate scientific objectives and the critical measurementsthat must be made to meet these objectives, must describe how existing or proposed missions will make these measurements,and mu:stindicate relative priorities.34 Therefore COMPLEX recommendsthat the next Roadmap team be tasked to define a more scientifically compelling rationale for solar system exploration thaJl that currently provided by the three Quests. Such a restructtLfing is far beyond the scope of this brief report. Nevertheless, the new structure should, at a minimum, be organized around specific science goals and questions that can be directly related 1:0 critical measurementsand focused priorities. It should, in addition, outline the rationale usl~dfor prioritization and describe how existing and proposed activities can be achieved through R(~A programs, individual missions, and other activities. As an interim s1:ep complete revision of the Roadmap, COMPLEX suggeststhat a to somewhat more cohesive and substantive document could be made if the text relating to R&A programs, E&PO activities, and the cross-linkages between the various sciencethemes were handled in a more consistent and efficient manner. To this end, COMPLEX suggeststhat the Roadmap's introductory text be expanded to include material relating to the following: 1 The org,anizationof the Roadmap (relevant text is not included in the current draft); 2. The process used to create the Roadrnap (relevant text is not included in the current draft); 3. General material on research and analysis programs (appropriate text is to be found on pages 12-13 of the current draft); 4. General material on education and public outreach (appropriate text is to be found on pages 29-34 of the <:urrentdraft); and 5. General material on how the goals of Solar System Exploration relate to the Astronomical Search for Origins (appropriate text is to be found on pages 6 and 108-109 of the current draft) and Sun-Earth Connection (appropriate text is to be found on page 110 of the current draft) science themes, and to Astrobiology (relevant text is not included in the current draft). Particular care :shouldbe taken to ensure that the linkages between the various disciplines are treated in an evenh:mdedmanner. 9

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Addition of this material will help make the existing Roadmap more substantive until such time as a full revision can be undertaken. 10

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APPENDIX Derived Outline of the December 1999 Roadmap Introduction 2 Executive Summary: 3 The Solar Syst(~m Exploration Program: 4 The Search for Origins in Our Solar System: 5 "Ground Truth" for the Astronomical Search for Origins: 6 The Quests Three Quests for Knowledge: 8 Quest I-Goals: 9 Process/Key Destinations: 11 Researchand Plllalysis: 12 Researchand Analysis Contributions to Quest 1: 14 Astrobiology and Solar System Exploration/Quest 1: 15 Quest 2-Goals: 17 Process/Key Destinations: 18 Researc:h and Analysis Contributions to Quest 2: 20 Astrobiology and Solar System Exploration/Quest 2: 21 Quest 3-Goals: 23 Process/Key Destinations: 25 Researc:h and Analysis Contributions to Quest 3: 26 Astrobiology and Solar System Exploration/Quest 3: 27 Education and Publi4= Outreach 29 Infusing Education and Public Outreach into Space Science Programs: 31 Space Science Education and Public Outreach "Ecosystem": 32 Space Education Standards and Benchmarks: 33 Solar System E~xploration Quests: 34 Quest 1-Standard and Benchmarks: 35 Quest 2-Standard and Benchmark: 36 Quest 3-Standard and Benchmarks: 37 The Programs 38 Continuing Programs: 40 Critical New Elements: 41 Why "To Build a Planet..."?: 42 Outer Planets Program-Exploring Organic-Rich Environments: 43 Current Missions: 45 Europa Lander Mission: 46 Titan Explorer Mission: 48 Neptune Orbiter Mission: 50 II

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Technology ReadinessSummary: 52 Future 'Concepts: 54 Mars Surveyor Program-Bringing Mars to Earth: 56 Strategic Elements: 58 Currenl: Missions: 59 Next Sl:eps: 60 Mars Synthetic Aperture Radar/Advanced Sample Return: 61 Mars Robotic Outposts: 62 Earth-Mars Internet: 64 Decision Process: 65 TechnoJogy Developments: 66 Mars Sample Handling and Analysis: 68 Sample Handling Processes: 69 Objectives: 70 Recommendations: 71 Future Concepts: 73 Discovery ProJ~ram: 75 Characteristics: 76 Missio]rls: 77 Future Discovery Missions: 78 To Build a Planet: 79 Why ..To Build A Planet"?: 81 Formation and Evolution of Planetary Environments: 82 Comet Nucleus Sample Return: 84 Key Capabilities/Critical Questions: 85 Science Objectives: 86 New Technologies: 87 Venus Surface Sample Return: 88 Key Capabilities/Critical Questions: 89 Saturn Ring Observer Mission: 90 Key Capabilities/Critical Questions: 91 Other High-Priority Missions: 92 Technology ReadinessSummary: 96 Future Concepts: 98 99 Summary Summary of R.ecommendations: lOO Critical New I~lements: 102 Top Priorities for Continuing Programs: 103 Key Capabilities for Recommended Missions: 104 Mission Timelines: 106 Integration of Space Science 107 Solar System ]~xploration and Astronomical Search for Origins: 108 Solar System ]~xploration and Sun-Earth Connection: 110 12

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REFERENCES I Solar System Exploration Subcommittee, Exploration of the Solar Sy.S'tem-Science and Mission Strategy, Jet Propulsion Laboratory , Pasadena,California, December 1999. 2 Roadmap Development Team, Mission to the Solar System: Exploration and Discovery-A Mission and TechnoloJ:.::Y Roadmap (Version A), Jet Propulsion Labora1:ory, Pasadena, California, June 21, 1996. 3 SpaceStudies Board, National ResearchCouncil, An Integrated Strategyfor the Planetary Sciences: 1995-2010, .National Academy Press,Washington, D.C., 1994, pages 33-34. 4 Space Studies Board, National Research Council, "Scientific Assessment ofNASA 's Solar System Exploration Roadmap," letter report to Jurgen Rahe, August 23, 1996, pages 6- 7. 5 Space Studies Board, National Research Council, "Scientific Assessment ofNASA's Solar System Exploration Roadmap," letter report to Jurgen Rahe, August 23, 1996, page 6. 6 SpaceStudiesBoard, National ResearchCouncil, Exp[oring the Trans-NeptunianSo[ar System, National Academy Pre~;s, Washington, D.C., 1998, pages42-43. 7 SpaceStudiesBoard, National ResearchCouncil, A ScienceStrategyfilr the Exploration of Europa, National Academy Press,Washington, D.C., 1999, page 66. 8 Space Studies Board, National Research Council, Exploring the Trans-NeptunianSolar System, National Academy Pre~;s,Washington,D.C., 1998, page 43. 9 SpaceStudies Board, National ResearchCouncil, An Integrated Strategy for the Planetary Sciences: 1995-2010, National Academy Press,Washington, D.C., 1994, pages 9 and 172. 10SpaceStudies Board, National ResearchCouncil, An Integrated Strategy for the Planetary Sciences: 1995-2010, National Academy Press,Washington, D.C., 1994, pages 193-194. 1 Space Studies Board, National Research Council, Space Science in the Twenty-First Century J Imperatives for the Decades 1995-2015-So1ar and Space Physics, National Academy Press, Washington, D.C., 19~:8, pages 41-43. 12 National Aeronautics and SpaceAdministration, An Interstellar Precursor Mission, JPL77-70, Jet Propulsion Laboratory , Pasadena,California, 1977. 13Sun-Earth Connection 2000 Roadmap Team, Sun-Earth Connection Roadmap-Strategic Planningfor 2000-20~~5, National Aeronautics and Space Administration, Washington, D.C., 1999, pages 152-155. 13

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14Space Studies Boarcl, National Research Council, An Integrated Strategy for the Planetary Sciences: 1995-2010, National Academy Press, Washington, D.C., 1994, page 25. 15SpaceStudies Boarcl, National ResearchCouncil, An Integrated Strategyfor the Planetary Sciences: 1995-2010, National Academy Press,Washington, D.C., 1994, pages 191-193. 16Space Studies Board, National Research Council, Review of NASA 's Planned Mars Program, National Academy Pr{:ss, Washington, D.C., 1996, pages 22-27. 17Space Studies Board, National ResearchCouncil, "COMPLEX's AssessmentofNASA's Mars Exploration Architect\lfe," letter report to Carl Pilcher, November 11, 1998, page 10. 18SpaceStudies Board, National ResearchCouncil, A Scientific Rationale for Mobility in Planetary Environments, National Academy Press,Washington, D.C., 1999, page 3. 19SpaceStudies Boarcl, National ResearchCouncil, "COMPLEX's AssessmentofNASA 's Mars Exploration Architect\lfe," letter report to Carl Pilcher, November 11, 1998, page 8. 20Space Studies Boar(l, National ResearchCouncil, Mars Sample-Return: Issues and Recommendations,Naltional Academy Press,Washington, D.C., 1997, page 31. 21 Space Studies Boardl,National ResearchCouncil, "COMPLEX's AssessmentofNASA's Mars Exploration ArchitectlJfe," letter report to Carl Pilcher, November 11, 1998, page 2. 22 Space Studies Boardl,National ResearchCouncil, "COMPLEX's AssessmentofNASA's Mars Exploration ArchitectlJfe," letter report to Carl Pilcher, November 11, 1998, page 5. 23Space Studies Board, National ResearchCouncil, The Role of Small Missions in Planetary and Lunar Exploration, Niltional Academy Press, Washington, D.C., 1995, page 27. 24SpaceStudies Board, National ResearchCouncil, Assessmentof Mission Size Trade-o.ffs for Earth and Space ScienceMissions, National Academy Press,Washington, D.C., 2000 (in press). 25Space Studies Board, National ResearchCouncil, SpaceScience in the Twenty-First Century- Planetary and Lunar ,E'xploration,National Academy Press,Washington, D.C., 1988, pages83- 84 and 87. 26SpaceStudies Board, National ResearchCouncil, An Integrated Strategyfor the Planetary Sciences: 1995-2010, National Academy Press,Washington, D.C., 1994, pages 13~14. 27Space Studies Board, National ResearchCouncil, An Integrated Strategyfor the Planetary Sciences: 1995-2010, National Academy Press,Washington, D.C., 1994, pages 188-189. 28Roadmap Development Team, Mission to the Solar System: Exploration and Discovery-A Mission and Technology Roadmap (Version B), Jet Propulsion Laboratory, Pasadena,California, September27, 1996, page 47. 29VSR Study Team, J7enusSample Return-Assessment Study Report, SCI(98)3, European ]4

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Space Agency, Paris, June 1998 30Space Studies Board, National ResearchCouncil, An Integrated Strategyfor the Planetary Sciences: 1995-2010, National Academy Press,Washington, D.C., 1994, pages 186-187. 31 Space Studies Board, National Research Council, Supporting Research and Data Analysis in NASA IS Science Programs: Engines for Innovation and Synthesis, National Academy Press, Washington, D.C., 19~~8, pages 1-6. 32Space Studies Board., National Research Council, Supporting Research and Data Analysis in NASA 's Science Programs-Enginesfor Innovation and Synthesis, National Academy Press, Washington, D.C., 19~»8,pages 3-4. 33Space Studies Boardl,National ResearchCouncil, "Scientific AssessmentofNASA's Solar System Exploration Roadmap," letter report to Jurgen Rahe, August 23, 1996, pages 5 and 10. 34Space Studies Boarcl, National ResearchCouncil, "Scientific AssessmentofNASA's Solar System Exploration R,Jadmap,"letter report to Jurgen Rahe, August 23, 1996, pages2 and 9. 15