Full report

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7'ech'd;'icaalMemorandum 4075 Q ovation Studies Technica Report Volume I: Technical Summary National Aeronautics and Space Administration

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This publication is one of four documents describing work performed in fiscal year 7988 under the auspices of the newly formed Office of Exploration. The first in the series, titled, "Beyond Earth's Boundaries . . . Human Exploration of the Solar System in the 27st Century" provides an overall programmatic view of the goals, opportunities, and challenges of achieving a national goal for human exploration. The technical details and analyses are described in a three-volume set titled: "Office of Exploration: Exploration Studies Technical Report (FY 7988 Status)." Volume I is a Technical Summary; Volume I1 is the Study Approach and Results; and Volume Ill is a collection of trade study results, indepth systems assessments, and workshop reports which describe aspects of FY 7988 analyses in more depth.

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NASA Technical Memorandum 4075 , Office of Exploration Exploration Studies Technical Report FY-1988 Status Volume I - Technical Summary December 1988 NASA

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CONTENTS PREFACE EXPLORATION STRATEGY DEFINITION EXPLORATION CASE STUDIES Case Study Approach Human Expedition to Phobos (CaseStudy 1) Human Expeditions to Mars (Case Study 2) Lunar Observatory (CaseStudy 3) Page 1 3 5 5 6 8 10 Lunar Outpost to Early Mars Evolution (CaseStudy 4) 11 THE SEARCH FOR LEVERAGE Extraterrestrial Resources In-Space Vehicle Processing Advanced Propulsion Surface Operations SurfaceSystems Cost Understanding 17 17 18 20 22 23 25 IN HUMAN EXPLOT3ATION MISSIONS 27 SCIENCE OPPORTUNITIES CASE STUDIES 29 COMPARATIVE ANALYSIS OF FY 1988 Earth-toarbit Transportation Low-Earth Orbit Assembly and Operations and ExtraterrestrialResources 32 Impacts of Using Advanced Technology Other Factors PROGRAM INTEGRATION APPROACH Earth-to-Orbit Transportation Life Sciences Research ScientificPrecursor Missions iii P R M ~ PAGE~~ BLANKG NOT FILMED 30 31 33 35 35 35 35

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Space Station Freedom Technology Communications and Data Tracking CONCLUSIONS AND OPPORTUNITIES New Insights Case Studies Prerequisite rkgrams ACRONYMS AND ABBREVIATIONS DEFINITION OF TERMS i v 36 37 37 39 39 40 41 43 44

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TABLES 1. CASE STUDY SHAPING PARAMETERS Page 29 CHARACTERISTICS 34 2. SUMMARY OF CASE STUDY FIGURES 1. Case study methodology 2. Representative split/spnnt trajectory profile Page 5 6 3. Human expeditionto Phobos Earth orbital operations 7 - Mars/Phobos orbital operations 8 4. Human expedition to Phobos- 5. Earth orbital operations 9 Human expeditions to Mars - 6. Mars orbital surface operations 9 Human expeditionsto Mars- 7. Lunar observatory lunar portion 12 8. Lunar Outpost to Early Mars Evolution-- Mars portion (flight 1) 13 9. Lunar Outpost to Early Mars Evolution - 11 10. Lunar Outpost to Early Mars Evolution-Mars portion (flights 2, 3 , 4 -- Earth orbital operations) 13 11. Lunar Outpost to Early Mars Evolution- Mars portion (flights 2 , 3 , 4 -- Mars orbital operations) 14 mass to LEO requirement 30 12. Case studiesmass summary -- annual 13. Typical composite strategy for life sciences research and exploration vehicle development 36 14. Initial LEO mass requirement sensitivity to launch year for human Mars missions V 40

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Preface TheOfficeof Exploration(OEXP)wasestablishedinJune 1987toproviderecammendationsandviablealternatives foran early1990snationaldecisionona focusedprogram of human explorationof the solarsystem, particularlyof the Moon and Mars. The OEXP is also responsible for c steeringAgencyinvestmentsona practical,year-by-year I basis toward providing feasible, defined choices in the I early 1990s. With management centralized at NASA I Headquarters, the OEXP leads a NASA-wide team consisting of all the major program offices and field center organizations that are specifically dedicated to this effort. To accomplish OEXP objectives, a study process was developed that begins with the yearly articulation by OEXP of guidelines and ground rules for human exploration studies. This activity serves to define a I framework of initial concepts within which alternative strategies can be formulated and explored. The methodology used for implementing various strategic approaches, such as expeditions, science outposts, and evolution,istoidentifyreferencemissionstobeexamined as “case studies.” Oncecase studies have been identified by theOEXP,the Mission Analysis and System Engineering (MASE) functionatJSCcoordinatesdevelopmentof detailedcase studydescriptionsand studyinitializationrequirements and data. Detailed technical analyses at the element/ systems level are then performed by designated field center IntegrationAgents(IAs)and SpecialAssessment Agents(SAAs).TherearethreeIAs, eachIAcoveringone of three principal areas of study responsibility: orbital node systems, space transfer vehicle systems, and planetary surfacesystems. SAAs, through direct assignment from OEXP and on their owninitiative,conductindependentassessmentsat an indepth systems analysis and trades level. These studies are usually highly analyticalin nature and focus onmissionor vehiclesystemshavinga highpotentialfor advanced technology exploration mission objectives. RespectiveIA and SAAstudy activitiesare supported as required by technical experts from virtually all of the NASA field centers. Studyprogressforeachcasestudyisreportedat periodic program reviews. These reviews generally include all study agents and support center representatives and Technical Summary often include representatives from each of the NASA Headquarterscodes whose program support would be required in the execution of one or more of the case studies. Each of the affected NASA program offices submits hypothetical case study implementation plans which includeanalyses of each case study’seffecton the office’sstrategicprogram plans and schedules. Theyearlyoutcomeof thisAgency-wideteam effortisan annual report which progressivelymaturesin itsdegree of technical and programmatic legitimacy. This report servesto document specificconclusionsabout the year’s study efforts and provides valuable source material for planning subsequent study year activities. In conjunction with case study definition and development of exploration cases, a parallel effortis to considerwhat thesemissionsmeanintermsof advancing scientific knowledge. The work performed in FY 1988 has been too preliminary to constitute a sciencestrategy but has looked to incorporate some ideas on scientific objectivesintotheengineeringanalysis.In thefuture,the scientific rationale for human exploration missions will be more comprehensivelydeveloped. Thisreportdescribestheprocessthathasbeenformulated to conduct exploration studies and discusses those missions that have formed the backdrop for FY 1988 work. A “casestudy” approachhasbeen developed and used, with the intention not of selecting one case in preference to the others but rather of isolating and identifyingpotential requirements and sensitivitiesthat influencecasestudycomplexity,feasibility,andbenefits. Four case studies were developed during FY 1988: (1) Human Expedition to Phobos, (2) Human Expeditions to Mars, (3) Lunar Observatory, and (4) Lunar Outpost to Early Mars Evolution. Selected to encompassa broad spectrumof objectives, capabilities, and requirements, these cases also cover a variety of potential destinations, emphases for exploration, crew size, and activitieson planetary surfaces. In thecourseof thedetaileddefinitionand assessmentof the case studies, many insights have been gained, regarding both specific case studies and human exploration missions in general. These topics, as well asother results of the Fy 1988 study activity, are summarizedin this volume. 1

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Exploration Stratew Definition Technical Summary ThePresidentialDirectiveonNationalSpacePolicy,signed Each proposed human exploration scenario must be into effect on January5,1988, clearly establishesa posi- examined in terms of how it satisfies the themes or tive thrust to launch the United Statestoward visionary rationales for which such missions are intended and accomplishmentsin space. Of particular significanceis undertaken. Theseconceptsmust be understoodin light the directive that sets the long-range goal "to expand of the fundamentalvaluesheld by our society,in order to human presenceand activitybeyond Earth orbitinto the elicitand sustainwidespread support forour long-range solarsystem." For the firsttimein thehistoryof the space goals. program, theU.S.hasanexplicitnationalpolicymandate that challenges us to move permanent human activity To organize and systematicallyexamine a full range of beyond Earth's boundaries. options for human exploration and development of the Moon and Mars, three strategies were identified for Determining ways in which the civilian space program study in FY 1988. Each strategy presents particular can meet this goal is the responsibility of the Office of opportunities for meeting defined exploration themes Exploration, supported by a NASA-wide effort. Al- and objectives. though national policy directsNASA to expand human exploration, no specific guidelines exist regarding the Thefirststrategyaddresseshuman expeditions, emphapathways, timing, or concentration of purpose. To for- sizinga significant, visible, successfuleffort to establish mulate a logical plan to achieve the goal of human thefirsthumanpresenceon anotherplanetarybody. The exploration, it is important to first identify and compre- expeditionarypathway would lead to explorationwithhend the rich array of possibilities. Developinga philo- out theburden and overhead associatedwith permanent sophicalviewpoint that articulatesthe underlyingmoti- structuresand facilities.Thispathwayhasbeenexplored vation for such a program formsa templatefor themore for missionsto Mars and to its moons. practical aspects of activities to meet exploration objectives. Establishing a science outpost, the second strategy, emphasizesadvancingscientificknowledgeand gaining Tobegin to definethismotivation,sevenmajor"themes" operational experience by building and operating an - national pride and international prestige, advance- extraterrestrialoutpostasapennanentobservatory.This ment of scientific knowledge, technology catalyst, eco- pathway has been explored for a mission to the Moon. nomic benefits, space enterprise,international cooperation, and education and excellence - that have most The third strategy,evolutionary expansion, would susoften been associated with the space program were re- tain a methodical, stepby-step program to open the viewed. An awarenessof the ways in which meetingthe inner solarsystemforexploration,spacescienceresearch, objectivesembodied in thesethemescanbe enhancedby in-situ resource development, and ultimately, permahuman intellect,energy,and participationhelps to guide nent humanpresence. Thisstrategywouldbeginwith an the selection of potential pathways for human explora- outpost on the Moon and progress to a similar base of tion. operationson Mars, establishingsystemsand infrastmcture for further expansion,which is yet to be defined. PRECEDING PAGE BLANK NOT li".,W 3

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Exploration Case Studies Case Study Approach Technical Summary Exploration strategies are developed through a "case themissionand systemconceptsdevelopedinphaseone. study process. The purpose behind developing refer- Threeareasweredeterminedto be significantcase study ence case studies is to define a set of strategies that elements: space transportation systems, orbital nodes, respond to differentobjectivesor modesof implementa- and planetary surface systems. All are, in general,protion, so that a reasonable range of optionscan be under- grammatically independent and can be addressed inistood.Thenumberof potentialcase studiesisvery large, tially as functionallyindependent. The conceptualdeficases nition of theseelementsincludesscalingdata to support but onlya few can be studiedin depth. Additional canbeconstructedbyrearrangingelementsorbyextend- the synthesisin the next phase. ing the referencecases through trade studiesthat examine the effectsof varying assumptions. The third phase is a synthesis of the element concepts back intoan integratedmission and system. The results in nature among and establish a preliminary system concept and a reference The case study process is iterative withinthreedistinctphases(seeFigure1). Thefirstphase configuration that is used to refine the study through addressesconceptual mission and system architectures. severaliterations. Whereuniquescienceand/or technol- As part of this effort, mission and system requirements ogy needs were identified,suchas the possibleimplemare defined to meet the explorationgoalsand objectives entationof nuclearspacecraftpropulsion, specialstudies and user requirements.Themissionand systemrequire- or assessments were made to identify strategies to ments specify functional and performance parameters accommodate those needs. A complementary set of for elements defined by this study, identify environ- broad tradestudies,whicharenot casestudyspecific,but ments in which elements must operate, and identify which identify and assess key sensitivities, is run in element design and operationalconstraints. parallelwiththesethreephases. Therefinedcasestudies, associatedrequirements,anddetenninedbenefitsbome The second phase of the case study process addresses theknowledgebaseofexplorationpathway sensitivities, to which in turn is used to define the explorationinitiative conceptualelement definitions,which are responsive MPLORAlION GOALS a OBJECTIVES +USER REOUIREMENTS MISSIONAND SYSTEM REQUIREMENTS - FUNCTION ALLOCATION PERFORMANCE PARAMETERS . ENVIRONMENTS PATHWAY OPTIONS USER + COMMUNITY ELEMENT PROGRAM SY"ESIS ACCOMMODATIONS * CONCEPTS RBITAL NODECONCEPTS -ADVANCED TECHNOLOGY CASE STUDY CHARACTERISTICS TRANSPORTATION CONCEPTS -HUMANS IN SPACE SURFACE SYSTEMS CONCEPTS -SPACE STATION - ARCHITECTURES FREEDOMEVOL .LoGlsncs -ET0 TRANSPORTATION MASS -PRECURSORS PEOPLE -COMM NRWORK SUPPORTING PROGRAMS Figure 1.- Case study methodology 5

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OEXP Technical Report, FY 1988, Vol. I options, benefits, and risks. A casestudymaybe viewedasa combinationof building blocks: interplanetary trajectory, launch vehicles, transportation node, space transfervehicles, and surfacesystems. Thecombinationof specificelementoptions characterizesthe casestudy in termsof technologyrequired, schedule,capacity, complexity, and cost. The trajectorymaybe consideredthe most basic component. For trips to theMoon, thepathisrelativelystraightforward. The spacecraftis not required to leave Earth's sphere of influence,it only takes three days to get there (orback),andlaunchopportunitiesoccurquitefrequently. Interplanetary transfers,specificallyfrom Earth to Mars, are more complicated. For a given classof trajectory,an opportunity to launch to Mars occursonly onceevery26 months, and mission performance can vary widely, dependingon launch date and round-trip travel time. Three types of round-trip trajectories are employed in Mars explorationcase study design: opposition, sprint, and conjunction.Theoppositionclassischaracterizedby round-trip times of approximately 600 days, and provides the important ability for a Mars-flyby abort. The sprint, a subsetof the opposition, also has the capability for an abort maneuver, and is characterized by roundtrip times of approximately 400 days, with associated I high energy requirements. The conjunctionclass is a much longerround trip, approximately 1,000days,but it has minimum energy requirements. For many human exploration missions, a "split/sprint" technique is em- I ployed to minimize trip time. The cargo is launched on a minimum-energy trajectory (identicalto the outbound leg of a conjunctionclass round trip), whereas the crew carrier makes use of a high-energy sprint trajectory. A typicalsplit/sprint trajectoryprofileisillustratedinFigure 2. In some launch years, a swingby of Venus may be effected to use itsgravity to assist the piloted spacecraft, thereby reducing launch requirements. Another important factor is Earth-to-orbit transportal tion, viewed in terms of both the amount of mass that must be lifted from Earth's surfaceand the number and typeof launch vehiclesneeded. Launch vehiclesthat are assumedforuse in casestudydevelopment aretheSpace Shuttle,a heavy-liftlaunch vehicle, and other proposed 1 reusable and expendable vehicles. An element that enablesor enhancesmost of the casesis an orbiting node for the assembly and servicing of vehicles, transferof crew,and replenishmentof propellant. SpacestationFreedomand itsevolutionaryelementsare used in some case study designs, but other alternatives are being examined as well. ~ Space vehiclesare dependent on the choiceof target and 6 I T S D A Y STAY Figure2.-Representativesplit/sprint trajectoryprofile the plan for post-landing activities. Vehicles must be designed, for example,to transfer the crew and its cargo of suppliesandequipment froma transportation nodeto the ultimate destination and back again. Other vehicles, to descend to and traverse planetary surfaces,must also be developed. Surface systems are also dependent on the choice of target and the plan for post-landing activities. Living quarters, for example,may be required for the crew on the surface. Vehiclesto traverseand exploreextraterrestrial surfacesmust also be developed. The four case studies described below are intended to serve as a backdrop for identifying and examining the larger issuesof human exploration. No order of priority isimplied,nor shoulditbeassumed thatanyonecasewill represent the final goal. In the coming years, the case studieswill be refined, new ones will be added, and the implementationoptionsmaybe narrowed. Theunderlying goal of this effort is to isolate approaches, options, and requirements, to enable an informed choice in the future. Human Extledition to Phobos (Casc: Study 1) A primary objectiveof this mission is the establishment of earlyleadershipin the human explorationof the solar system. To that end, baseline vehicles are designed for minimum dependence on advanced technology, and human presence is extended only to Mars orbit and the surface of Phobos. In this case study, the first human beingswill arriveat theMartianmoonPhobosto explore, conductresourcesurveys,and establisha sciencestation. Other key objectives are to conduc't enhanced robotic explorationof Mars itself from Mars orbit, using rovers,

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Technical Summary penetrators, balloons, and sample collectors, and to re- 2May exploration of the Martian moon. During that turn samples of Mars and Phobos to Earth for detailed time, the crew on Phobos will make observations, conanalysis. The expedition to Phobos combines human ductexperiments,and gathersamplesduringa totalof24 exploration objectives with those of previously studied hoursof extravehicularactivity.The two crew members Mars Rover/Sample Return (robotic)missions, but al- who remain in the orbiting vehicle will teleoperate, or lows different approaches to the exploration of Mars remotelycontrol,roverswhich will gather samplesfrom because of the capability for nearly real-time teleopera- the surfaceof Mars. After spending a total of 30daysin tion of robotic systemsfrom the vicinity of Mars. Mission Description The mission scenario, illustrated in Figures 3 and 4, theMartiansystem,thecrewwillreturndirectlytoEarth, a4-month trip. Thetotallengthof themissionis440days. Results employsa "split/sprint" trajectory: a cargo vehiclecar- ThePhobosmissionispotentiallytheearliestto arriveof rying the Phobos and Deimos exploration equipment, thefour case studies. A number of factorsunique to this Mars rovers, and the crew's return propellant will be missioncontributetothiscapability.Firstof all, it maybe launchedvia an expendableescapestageona minimum- possible for the expedition to Phobos to be completed energy trajectory in February 2001. Upon arrival, this without an assembly node in low-Earth orbit (LEO). vehicle will be placed in Mars orbit to await the piloted However, two operationsmust take placein LEO: matflight. InAugust2002, approximately18monthsafterthe ing of elementsand payloads,and transfer of propellant firstlaunch, a secondvehiclecarryinga crew of four will (eitherfluidtransferorexchangeof tanks)betweenEarthbe launched via an expendableescape stage on a high- to-orbitdeliveryvehiclesand the vehiclescarryingcargo energy sprint-class trajectory, which requires about 9 and crew to Mars. In Mars orbit, a stage exchange or months to reach Phobos. propellanttransferiseffectedbetweencargoand piloted vehicles. Therefore,thesystemsand techniquestoroboti- Upon arrival in Mars orbit, the piloted vehicle will ren- callyjoin elementsand payloadsin low-Earthorbitmust dezvouswith the cargovehicle. Twocrew memberswill be developed, in additionto those for cryogenicpropeltransfer to a Phobos ExcursionVehicle and depart for a lant storageand transferin Earth and Mars orbit. -00 Vehlde I Cargo mission launches Pk(ed mlesh hunchecl Figure 3.-Human expeditionto Phobos-Earth-orbital operations 7

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OEXP Technical Report, FY 1988, Vol. I cargot m f e r ............ .......................... D i m erdty earth return Qpllolb**.) l - S d W n d u .................. Figure4.- Human expeditionto Phobos-Mars/Phobos orbitaloperations Thefactthat thecrewdoesnot landonthesurfaceof Mars structureinLEO.Thisisbecausethemassrequirementin simplifiesboththe scenarioand therequirementsfor the LEO resultsin 20 to 30ETO launches and the resulting mission, and substantially increases the likelihood of integration in orbit. As will be discussed later in this achieving the principal goal of being first. With the report,aerocaptureupon Marsarrivalwasfound to offer exception of the rover systems, no other Mars surface suchasignificantimprovementinIMLE0 that theresults landing systemsare needed, either for equipment or for presented in this report assume the aerocaptureoption crew. This greatly reduces the initial mass to LEO re- for the PhobosExpedition, unless otherwisenoted. quirement, as well as the time required for exploration program development and for the supporting technology and precursor programs. Aprimaryobjectiveofthisthreemissionsetistosendthe to hiasJGw Studv 21 ThePhobosmission could be an excellentprecursorto a first human explorersto the Martian surfacein order to pilotedMarslandingmission. Theroboticexplorationof captureearlyleadershipin thepilotedexplorationof the Mars will provide improved knowledgeof the Martian solar system. Oncethere, the crew would conduct local environment. ThePhobosmissionwill providea unique geologicalreconnaissance,emplacelong-livedgeophysiopportunityto performa systemscheckoutand verifica- cal instruments, and collect samplesfor return to Earth. tion of flight hardware and environment without the Anadditionalkey objectiveisto condiictancillaryexploincreaseddifficultyof a Marslanding. Giventheground ration of the Martian moons,Phobos and Deimos. rules and assumptions for the FY 1988 studies, these considerationsallowa "Marsclass" missiontobeaccom- MissionDescription plished fourand a half yearsbeforethefirstMarslanding of the Mars expedition case. The transportation strategy employed for each of the three missions will be a split/sprint trajectory; an ex- The Phobos Expedition was baselined for the FY 1988 ample of the mission scenario is provided in Figures5 studies to assume propulsive capture into orbit about and 6. Forthe firstexpedition, a cargotransportcarrying Mars. Subsequentanalysisshowedthatsuchlargemasses the landing vehicle (includingMars surface habitat and in LEO were required that it was unlikely that this exploration equipment and the ascent vehicle), and the expedition could be flown without at least some infra- Earth-return propellantwill be launched via an expend- 8

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Propellant Cargo mission hunches Technical Summary Pibted -0 Propellant Pibted mission launches Figure 5.- Human expeditions to Mars-Earth orbital operations Piloted approach aerocapture aerocapture (Mssions 1 L 2 Phobcs 8 Deimos excursbns) Trans-Eanh Injection Refueledpilotedvehicle with 4 crew (w/o Marsaorobrake) Aerocapture returnto earth orbital node Figure 6.-Human expeditions to Mars-Mars orbital/surface operations 9

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OEXP Technical Report, FY 1988, Vol. I able escape stage on a minimum-energy trajectory in ~ m i ceffectsinto the analysis. Substantialvariationsin September2005. UponarrivalatMars,thisvehiclewillbe mission AV requirements, and corresponding IMLEO, placed in Mars orbit to await the piloted flight. In occur as a result of the heliocentric tri3jectory sensitivity December 2006, approximately 15 months after the first to launchyear. Thedoublingof crew size from four (for launch, a vehicle carrying eight crew members will be Phobos) to eight for the Mars Expedition also introduce launched via an expendiable escape stage on a high- a level of complexity to the mission dlesign. energy, sprint-classtrajectory. Due to the extremely large annual IEO mass require- Uponarrivalat Mars, thepiloted vehiclewill rendezvous ments(peakyearmass=l,TOt), two of themapr drivers with thecargovehiclein Marsorbit. Four crewmembers affecting these expeditions are the Earth-to-orbit (ETO) will transfer to the Mars LanderVehicleand depart for a level of activityand LEO assembly techniques. 20-day exploration of the Martian surface. The four remaining crew members will perform the propellant It is important to acknowledge here, however, that the transfer from the cargoto piloted vehicle,conduct Mars- IMLEO estimates to support the three missions associorbitalscience,andmonitorandassisttheactivitiesunder ated with this particular case study are unrealistically way on the surfaceofMars. After a total of 30daysin the high. It isalso importantthatin derivingtheseestimates, Martian system, the surface crew will rendezvous with the supporting analysts obtained i3 cause-andeffect the orbiting piloted vehicle to depart for Earth, amving knowledge base of the various transportationand surabout 5 months later. Total mission length is 440 days. facesystems element/trajectory sensitivitiesthat drove IMLEO to these high levels. This knowledge should Cargo/piloted vehicle pairs will again be launched to enable substantial reductions in IMLEO estimates for Marsduring thenext twolaunchopportunities(2009and future Mars system expeditionaryca:sestudies. 2011). The third piloted flight,in 2011, has a total round- I trip flight time of 500 days. This longer flight time was 1- unar a d_ necessary to avoid prohibitive masspenaltiesassociated with the sprint trajectory in 2011. (The sensitivity of Theobjectiveof thiscasestudyisto understand theeffort Earth-Marstrajectoriestolaunchopportunityisdiscussed required to build and operate a long-duration humanin the CONCLUSIONSAND OPPORTUNITIESsection tended astronomical observatory on the far side of the of thisreport.) Piloted excursionsto Phobosand Deimos Moon, and also to conduct regional lunar exploration. are envisioned as part of the first two Mars expeditions. Theastronomicalfacilitywillconsistof radioand optical Each of the three Mars landing missions will also visit a telescopearrays, stellarmonitoringtelescopes,and radio different site on the Martian surface. telescopes. Such facilities offer the potential of several orders of magnitude improvement in resolution over Results Earth-based or orbital facilities,and, in some cases, provide unique observing environments not available TheMarsexpeditionswilldelivera crewof eightto Mars, anywhere else in the solar system. Also included is a with four landing on the surface, but arrivals will begin program of geophysicalstations, the capability for local almost fiveyears later than the Phobosexpedition. This geologicaltraverses,andamodestlifescienceslaboratory. difference results from the fact that the Mars case is of a much larger scale, with increased dependence on infra- Mission Description structure and new technologies. The Mars expeditions willrequiresignificantLEOinfrastructureand a substan- Thiscasestudyassumesthat fourmissionsto theMoon’s tial degree of on-orbit assembly operations at a LEO far side will be required to set up an operational facility. transportationnode. The four set-up flights will consist of one cargoand one piloted mission per year, in two successiveyears, begin- The Mars expeditions are more complicated than the ningin 2004. Thefourset-upmissionswillbefollowedby Phobos expedition from several standpoints. Separate one operational crew mission per year thereafter. The cargoand piloted vehiclesmustbebuilt to land on (cargo scenariofor this case study is illustrated in Figure 7. and piloted)and ascendfrom (piloted)the Marssurface, significantly increasing the vehicular infrastructure Each piloted mission will carry a crew of four. The complexity (and resultant IMLEO) for these missions. round-tripflighttimewillbe lessthan 20days, including Mars EVA operations will require new pressure suits, a maximum of 14Earth days spent on the lunar surface. portablelifesupport systems,and surfacetransportation No permanenthabitat facilitywillbe deve1oped;because systemswhichcansafelyand productivelyoperatein the of theshortsurfacestaytime, and alsobecauseof the fact Mars one-third gravity, nonvacuum environment. The that subsequent missions will visit different sites, the fact that the Mars Expeditionslaunch to Marsover three crew will live in and work out of the lander vehicle on successiveopportunitiesintroducessignificantastrody- each mission. 10

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mission. every 3rd year dt-sewicing years return Cargo flights (2004 a 2005) <14-day Crew Surface stay-time Lunar tar-side B uSet-upflights Annual operational tli hts (beginning in 20& Technical Summary Aerocaoture LEO F Assembly \ node 0I A I I L Lunar far-side Other lunar shes (tar-side6 near-side) Figure7.- Lunar observatory Nominally, the astronomical facilities will require hu- Thiscaserequires a facilityin LEOto house the crewand man-tended servicing only once every three years after support transfer vehicles and payload assembly opera- In the off-servicing years, tions, including element construction and checkout, they become operational. crewswill explore other lunar sites. During theseexplo- propellant storage and transfer, and payload servicing. ration sorties,crewmembers willmakeseveraltripsinan unpressurized rover for distances up to 10kilometers. Results The major drivers for this scenario are the planetary surfaceactivitiesrequirements,including surfacepower systems and EVA technology. The science facilitieson the Moon require the deployment of large, complex a maximum scientificreturn arrays, and special equipment is required for their em- Thiscasestudyemphasizes using a minimum amount of permanent support facili- placement.Certainly,robotically assisted assemblyand ties. Significanthuman interaction will be required to construction will be promising new technologies to inassemble, deploy, operate, and service the array of in- vestigate. strumentationplanned for this facility. In addition, once will Lunar Oubost to Earlv Mars Evolution (Case Studv 4) the facilityisoperational(in20051, subsequentcrews be utilized for local geological exploration, scientific excursions in rovers for distances up to 10 kilometers, This case study builds a capability that leads to the instrumentation development of a self-sufficient,sustained human presand upgrades and sensor/receiver changeout at the observatory. encebeyond low-Earthorbit.Theevolutionaryapproach provides the basis for continuing technology advance- This scenario can be accomplished for less than one- ment, experience in outpost development and habitafourth the total mass required for the Mars expeditions tion, use of local resources, and the development of a in two facility with opportunities for further growth. This is case. The Lunar Observatorywill be operational as accomplished in two phases: the establishment of a years, usingapproximatelythe samemass investment the Phobosmission. Furthermore,user allocationmassis permanently staffed facilityon the Moon, progressingto years, which is twice the establishmentof a similaroutpost on Mars. The case 100metric tons during the first 10 the allotment for the Mars expeditions. study was constrainedby a limitation of mass to LEO in 11

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OEXP Technical Report, FY 1988,Vol. I qet-rp flights; roubne crew sorb89 T-7-@ LEO Cargo fligM A I I I 1 I I Ealh I Crew flightCrew flight LowLow lunarlunar orbiiorbii ..e.................. I \ A I w.1 I Figure 8.- Lunar Outpost to Early Mars Evolution-lunar portion order to promote creativity in new technology applica- The emphasisin these scenarios is the local-to-regional tions and in-situ resource utilization. geological exploration of the surface of Mars, using piloted and robotic mobility systems, and the exploration Thelunarphaseof themissionincludesthedevelopment of Phobos and Deimos,with the objectiveof establishing of a lunar scienceand resource outpost, which is domi- thecapabilityto extractpropellantfromoneof themoons nated by a lunar liquid oxygen plant, local-to-regional to support subsequent missions. The study envisions geological exploration, and a life sciences laboratory threemissionsto theMarssystem,eachto a differentsite, facility for conducting fractional-gravityresearch. Be- in preparation for the establishment of a permanent cause the location of the outpost may be dictated by outpost on Mars. resource and operationalconsiderations,and not observational science, a far-side site is not mandatory. Mission Description Cargo and piloted lunar space vehicles will be used to Beginningearlyinthenextcentury(approximately2004), optimize delivery of payload and crew exchange. The a series of piloted and cargo flights will embark for the lunar outpost will be capable of permanent habitation, Moon. As illustratedin Figure8, thecrewwill transferto and crews will occupy it for periods of six months to a the Moon aboardchemicallypropelled transfer vehicles, year between rotations. whereasthesurfaceequipmentwillbe transportedvia an Electric Cargo Vehicle. Several years will be spent in Subsequent to the development and operation of the constructing a permanently staffed surface facility. lunar facility, and aftera knowledgebaseforextraterres- Experience will be accumulated in all aspects of longtrialhuman habitationisestablished,humanexploration duration human planetary exploration missions: life missions to Mars will be undertaken.Oxygen produced sciences, psychological effects and human dynamics, on the Moon will be made availablefor the Mars space exploitation of natural resources, and scientific excraft, which depart from the Moon to Mars via an Earth ploration. One goal of the base is to ]m~h.~ce,from the flyby injectionmaneuver. Conjunction-classtrajectories lunarsoil,theliquid oxygenneeded forsubsequentMars are used, with separatecargo and crew vehicles. These flights. trajectories require approximately one year of stay time in the vicinity of Mars, either in orbit or on the surface. In approximately 2010, the branch to Mars will take 12

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Technical Summary Fight11 l-.olbpoape Mifor ..................... mMr*dM U S OuoO NEPcmnrpon I .........................\ -3 ..........................14sm-- .... \ HLV h v l c h a [ = I ............ Figure 9.- Lunar Outpost to Early Mars Evolution-Mars portion ............ LvwM PLOTLD EARTKYARS wn-. YARBcam ..................... .......... D L C A I W U R I ~ ~ ~ L rwIPILOTED ........................... Figure 10.-Lunar Outpost to Early Mars Evolution-Mars portion (flights2 3 4 - Earth orbital and lunar operations) 13 GmG!?$\L, FP(48 !5 OF POOR QUALITY

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OEXP Technical Report, FY 1988, Vol. I - to satie vehicle) Piloted aerocapture Aug 2014 Jul MI6 I Flights #2,3,4 Earth return Aug 2016 Oct 2018 Dec 2020 r Phobos orbit I............ t Figure 11.- Lunar Outpost to Early Mars Evolution-Mars portion (flights2,3,4 - Mars orbital operations) place; the nominal scenario for this phase is depicted in Figures9,10, and 11. Thespecifictimingisleft open, but in general would occur when the lunar capability is sufficient to provide enough propellant to enable the Marsmission. First, an ElectricCargoVehiclewill carry theMarssurfaceequipment,excursionmodulesfortransportation between Mars and Phobos, and varioustypes of scientific equipment to the Mars system. As the spacecraftapproaches the Mars system, it will drop off communications satellites in synchronous orbit, send roboticexplorerstoDeimos,and, uponarrivalatPhobos, deposit a system for producing fuel. Liquid hydrogen and liquid oxygenpropellantsproduced on Phoboswill be used later in the scenario. The evolutionary case study places major demands on a total mission time of nearly three years. Optionsexist forthecrewtoperformaflybyabortnussion(ifaproblem occurs, the mission can return to Earth without landing on Mars, after a total trip time of about 600days), or to limit their stay at Mars to up to 60days. A third option existsfor a two-year stay at Mars. Piloted excursionsto Mars, similar to the first described above, are anticipated in the ensuing launch opportunities. Further cargo flights will be necessary over the duration of the Mars base build-up. Results In the next Earth-Mars launch opportunity, a second the low-Earth orbit operational facilities to assemble, Electric CargoVehicle, reused from the lunar portion of refuel, maintain,and serviceinterplanetaryvehicles. The the mission, will push an (unmanned)crew transport to facilitieswill also be used to transfer :substantialquantithe Moon for fueling with lunar liquid oxygen. After ties of propellantsarrivingfrom Earth, and will serveas fueling, thecargovehicleleaveslunarorbitwith thefully a transfer facility for crews going to and returning from loaded Mars personnel vehicle, and, when in cislunar planetary missions. space, separates and begins its retum to a lower orbit about Earth, where it will await reuse on the next ferry Thiscasestudyalsorequiresorbitalstagingand refueling mission. Thefirstcrewis transportedto the piloted Mars operationsin low lunar orbit, as well ixsin the vicinityof transfervehicle, andaftersystemscheck,theybegin their Phobos. The electric cargo vehicle serves as a mobile journey to Mars. Thenominalplan isfor thecrewto stay node for operations outside low-Earth orbit; therefore, at Marsapproximatelyoneyear,and returntoEarthafter nuclear electricpropulsion system technology to power 14

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Technical Summary theelectriccargovehiclesisamajorrequirement.Systems andtechniquesforaerocaptureatMarsand Eartharealso needed. Life sciences precursor missions and studies must resolvetheissueof zero gravityversusartificialgravityfor extended voyages to Mars. In this case study, that researchisperformedin theone-sixthgravityof thelunar surface and at the LEO node. For permanent lunar and Mars bases, maximum possible closure of life-support systems must be provided, and significant improvements over SpaceStationFreedom life-support systems are desirablefor Mars transfer vehicles. The self-sufficiency embodied in this case levies a r e quirement for the development of technology and systems for mining,processing,and storinglocal resources. Significantpower levelsto operatesurfacehabitats,systems,and roversarerequired;of necessity,nuclearpower sources like that of the SP-100program are the most promisingcandidatetechnologies.However, extensions to the multi-megawatt range must be made. 15

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The Search for Leverage Technical Summary studies Advanced propulsion systems, particularly those that In addition to the system and element definition performed in connection with specific case studies, the derive power from nuclear sources, were applied to the also included special studies, reports, Phobos,Mars,and evolutionarycasestudiesto assessthe FY 1988activities and assessments in areas that offer potential leverage benefit of such systemsto those cases. beyond the baseline scenarios. In the broadest sense, or benefit accrued from Planetary surface operations, the fourth area, covered "leverage" refersto any savings the incorporation of an option into a baseline scenario. technologiesandtechniquesrequiredby casestudyplans of advanced propulsion technolo- for activities conducted on, or in the near vicinity of, For example, the use gies is a strategy for reducing initial mass in low-Earth potential planetary target bodies. Specific emphases be measured included: the feasibility of automating lunar LOX proorbit (IMLEO). The degreeof leveragecan in terms of savings of or benefit to many quantities in duction, teleoperated planetary rovers, and special readdition to mass, such as: power, volume, man-hours, quirementsrelated to theexplorationof Phobos. Closely cost. related to surface operations is the fifth area, surface consumables,datareturned,complexity,and dollar is used to opti- systems, which examined lunar surface power and ad- In a systems engineering sense, leverage mize the objectivefunction. vanced life support. The choice of the objective function(s1will determine Thesixtharea,costunderstanding,wasa specialemphaareas in which the search for leverage will concentrate. sis study. Each of these six topical areas is described in as the objective more detail in the pages that follow. FY 1988 activities focused on IMLEO function; therefore,the search forleverageconcentrated this Extraterrestn'a1 Resourca on strategiesand technologiesthat could minimize parameter. Preliminary study results, detailed in the of broader Propellant Production. Augmenting Earth-supplied pagesthat follow,haveprovided anoverview of a number of potential propellants with those derived from the Moon, Mars, issues involved in the use and technologies. Although final conclusions and/orPhobosand Deimosinherentlyofferspotentialas strategies will require further study and analysis, the process for a high-leverage technology. However, determiningthe doing so in FY 1989has been defined through this effort. viability of extraterrestrialpropellantuse is exceedingly complex,sinceitinvolvesa largenumberof interdiscipli- Several technologies and techniques were selected for MYand tightlyinterrelatedvariables. To analyzethese activitiescan be divided into six variables, it is necessary to understand space developspecialemphasis. These in-space mentoptionsto a levelof engineeringand programmatic topical areas: (1) extraterrestrialresources, (2) surface detail that does not currentlyexist. These variablesalso vehicle processing, (3)advanced propulsion, (4) operations, cost under- tend to change dramatically with each specific case. (5) surface systems, and (6) standing. of the be demonstrated for each case study independently. Extraterrestrialresources addresses the concepts benefit and requirementsof using in-situ resources for Therefore, the viability of the use of extraterrestrialpropellants, and the associated implementation plan, must potential A key finding is that in-situ propellant production is propellantor forcommercialexploitation. The for the extraction and production of fuel exists for all beneficial only for long-termdevelopment: the facilities studies; a preliminary methodol- start-up can take a long time to achievefull production targetsof FY 1988case ogy was formulated through which in-depth analyses capability, and the payback is only realized over a 10- to be initiated. A second area that was examined is the 20-yearhorizon.Not surprisingly,then,lunarLOXusage can a fortheround-tripLLO/lunar surfaceindicatesincreased possibilityofusing helium-3producedon the Moon as fuel for future nuclear fusion reactors on Earth. costs in the short term, but a savingsof about 30percent (in terms of mass) over the long term. Using rough The second general area addressed by this year's trade approximations for surface production facility masses, a topic of great the use of propellants derived from Mars, Phobos/ studies is in-space vehicle processing, and complexity of human Deimos, and the Moon demonstratesvaryingdegreesof significance to the feasibility Study activities examined five benefit as applied to IMLEO. For example, preliminary exploration missions. of the assessmentindicatesthat Phobos/Deimos propellantfor specificaspects: (1) general strategy, (2)assembly issues involved in Mars- the return leg offers more savings for chemical propul- Phobos spacecraft in LEO, (3) launch of cryogenic propellant sion systemsthan lunar LOX for outbound legsto Mars. orbital refueling, (4) storage tanks, and (5)transportationnodes. PREZeDING PAGE BLANK NOT FILMED Also, Phobos/Deimos propellant may be beneficially 17

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OEXP Technical Report, FY 1988, Vol. I exportedtoLE0,whereasexportoflunarLOXtoLEOvia chemicalpropulsion systems may not be beneficial. Further study concerningthe viability of extraterrestrial propellant production must address the issue of the location of a transportation node in Earth-Moon space. Theuse of lunar LOX appears to significantlyreducethe IMLEOrequirementsformanned Marsmissions. However, it also significantly increasesthe amount of lunar LOX required if the transportation node is located in LEO,due to the transportationof the mission LOX from the Moon to LEO.Previousstudieshave concludedthat it would be difficult to deliver lunar LOX to LEO at a lowercost than fromthe Earth's surface. Thissignalsthe obvious linkage between extraterrestrial propellant use and the location of an Earth-Moon transportationnode. Lunar Helium-3 Utilization. A workshop was conducted to provide information assessing the feasibility, practicality, and advantage of using helium-3 (He-3) extracted from the lunar regolith to fuel future nuclear fusionreactorsonEarth. Experts fromthenuclearfusion, mining, and lunar science communities participated. The workshop centered around two topics: terrestrial fusion technology, specifically as it pertains to H e 3 applications, and the technology required to mine He-3 from the lunar surface. Thegroupconcluded that mining, beneficiation,separation, and return to Earth of H e 3 from the Moon are possible, but would require a large-scale infrastructure and improvements in technology. Lunar oxygen production plants would provide an early technology demonstration (2010-2020) for He-3 productionby developing lunar soil mining and processingtechniquesand by providing an opportunity to produce someHe-3as a byproduct of the lunar oxygenproduction process. Thisis in keeping with the estimated timeframe in which deuterium/helium-3 fusion could possibly be ready for commercial terrestrial energy production (circa2015). In-SDaceVehicle Processing General Strategy. Earth-to-orbitdeliveryof spacetransfer vehicles is a mapr architectural, configuration, and operations consideration. When these transfer vehicles become of such a size that it is no longer possible to launch them on a single flight of an established ET0 vehicle, many alternativesexist, each with its own set of specific needs and impacts. A mapr challenge in the design of the architecture(includinginfrastructure)and configurationforeachclassof explorationmissionwillbe the incorporation of the proper emphasis and balance between needsarisingfrommissionobjectivesand those derived fromplacingthe systemintoservice: i.e., assembly. The lessons learned in designing Space Station Freedom will be used to gain initial insight into the ~ 18 1 proper emphasis that should be placed upon a "design for assembly'' philosophy. A trade exists between on-orbit assembly and launch vehiclecapability.Considerationsthat must be included relate to development cost, total operational support cost, and number of vehicles to be produced. A future pursuit will be to determine whether these considerations can be correlated to ET0 delivery capability, and thus, whether a cost-optimizd E l l ) payload-to-orbit capabilitycan be derived. Mosthistoricaldataon thefinalassemblyof spacecraftlie in the flowsconducted for assembly of current and past vehiclesatthelaunchcenter.It wasassumedin thisyear's studiesthat LEOnodeoperationsfor assemblyand verificationwillbesimilarto currentground-basedactivities forsuchtasks. Further,itwasassumedthatalloperations that can be done on the ground will be done on the ground, and extravehicular activity will be used only whennecessary. Flightelementswillbefullytestedprior to launch to LEO,and will be designed and built to facilitateon-orbitassembly. Early analysis indicatesthe need for modularization to enhance in-space vehicle processing. Final installation of hazardous materials is most safely doneoff-nodeand ascloseto stageignitionaspossible. It isalsodesirableforpropellantloadingtobeperformedin thisperiod. Theseconsiderationsnee4tobe examinedin relationtotheproposed Phobosmatingstrategy,inwhich fullyfueled propulsion stagesare launched to orbit and mated, with the entire launch stack build-up requiring more than one year. Processing spacecraft on the ground requires several weeks and several hundred people for each vehicle. Sincethis willbe difficultto duplicateon orbit,it islikely that things must be done differently during LEO transportation node operations, including the use of automation and telerobotics. It is unreasonable to assume that robots in spacewill takeover the assemblytasksthat are currently done on spaceshuttlesat Kennedy SpaceCenter. However,robots may ease the assembly burden for well-designed processes. To date, trades simply assume that many taskscanbe automatedand/or doneby using teleoperation and artificial intelligence. Such assump tionswillrequireconsiderablestudytoassesstheir validity and to determinethe designcharacteristicsnecessary to facilitatethe use of automation and teleoperation. A workshop was held in which participants assessed robotics requirementsfor the OEXP ,casestudies, evaluated thefeasibilityand adequacyof currenttechnologies, projected the magnitudeof advancesovera period of 10 to 15years, and identified barrier, as well as high-leverage, issues in the OEXP case study formulation. There

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Technical Summary was a strongfeelingamong workshop participantsthat, technologies needed to assemble, test, and launch large with appropriatecare in the design of componentsand spacecraftfrom LEOdo not existat present, a lack which the assemblyprocess, many tasks are largelyachievable poses an obstacle for proposed missions carrying huwith robotictechnology. In somecases,automationisan mans to Mars with Earth departure dates on or around enabling technology; i.e., if the tasks cannot be auto- the year 2000. The Space Station Freedom Program’s mated they must be deleted from the flows. In other Evolution WorkingGroup is now workingto charactercases, the use of automation and teleoperationallows a ize the projected use of the phase I1station. Among the simplification of effort and a substitute for crew time; important issuesbeing addressed is how Space Station therefore, these technologies are considered to be en- Freedom might evolve into a transportation node in hancing. support of explorationclassmissions. Anotherfactorinthein-spacevehicleprocessingstrategy It is crucial to long-term program planning that this isthat the LEOnode willstronglyinfluencethecharacter working group closely examine the technical, operaof assembly operations. The amount of functional s u p tional, and scientificresearch ramificationsof using the port that this facility provides to both the vehiclebeing station to support assembly of large space transfer veassembled, and the assembly process itself, will be a hicles in the 1000-trange. From this study a determinasignificantfactorin the overall design. The location of the LEO support crew base will have a tion will be made of whether it would be advantageous to branch to a second LEO node and when to do so. major impact on operations. System functionality re- An OEXP study addressed the potential for assembling quirements will differ significantly, depending on the Phobos cargo and piloted space transfer vehicles in whether the assembly crew is based at Space Station LEO without the use of a transportation node or other Freedomand ferriedto theassemblynode, located at the space-based infrastructureof significance (therequired LEOassemblynodefacilityitself,orlocatedinthepiloted baselinefor thePhobosExpeditionCaseStudy). Various Mars vehicle. If the crew is based at Freedom or in the Phobos vehicleassemblyconceptswere analyzed,and a Marsvehicle, the LEOnode will need to be designedasa list of key issueswas created, the solutionsto which will man-tended system. largely determine the feasibilityof this approach. The generalconsensuswas, however,thatit willbeextremely The flight rate requirements for ET0 transportationfor difficultto assemblethePhobosmissionspacecraftwiththe human expeditions are very high, particularly for out on-orbitstrongback,remotemanipulator,and EVA/ operationssupport. The high flightrate isanticipatedto IVA crew support. impact virtually all major operations phases, including launch vehicle processing and cargo integration, flight Issues Involved in Mars-Orbital Refueling. The expeplanning and reconfiguration, launch preparation, and ditions to Phobos and Mars assume that a cargo vehicle launch and mission support. The utilization of multiple carrying the piloted vehicle’s return propellants has launchsystems, such as an unmanned heavy-liftlaunch preceded the piloted vehicIe into Mars orbit. Cryogenic vehicle in combination with the Space Shuttle, can be fluid transfer between vehicles in Mars orbit is the asexpected to introduce additional complexity. An inter- sumed baseline for these case studies. Several other estingpoint is that the LEOassemblyoperationsmay be potentially viablepropellanttransfer optionswere idenrepresentative of the assembly operations required by tifiedduringthis studyyear but requirefurthertechnical explorationmissions, using similartechnology,en route analysisbefore specificchangesto the baselinecould be to othersolarsystemdestinations.Extrapolationof these recommended. These options include transfer of fully resultsto assemblyoperationsat non-LEO sitesin space loaded propellant tanks between cargo and piloted vemay alsobe possible. hicles as well as transfer of the pressurized crew habitat module to a man-rated cargo vehicle, creating a new Assembly of Phobos Spacecraft in LEO. A variety of piloted vehicle.. Technical areasrequiringfurtherpeneprevious LEO transportationnode studieshave concen- tration for each option include advanced technology and requirements, support equipment and power requiretrated on the problemsof assembling, refurbishing, maintaining fully or partially reusable transportation ments, transfer time requirements and overall operaprevi- tional complexity, vehicle commonality and physical systems for translunaror transMars flight. This on scenarioswhich assumea interfaceconsiderations,and overall impact to IMLEO. ous work has concentrated substantial LEO infrastructure. The capabilitiesfor oncyro- Launch of Cryogenic Propellant Storage Tanks. A orbit bit assemblyand test of spacecraft,as well as genic propellant transfer and storage, are in general question addressed in FY 1988 was whether the better assumed. method of launchingcryogenic fuel to LEO is to launch fully fueled flight tankage or to use separate transfer the other hand, the infrastructure and many of the tanks. Cryogenicflight tanks (integratedto the transfer On 19

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O W Technical Report, M 1988, Vol. I vehiclepropulsionsystem)aretypicallynot designedfor long storage. Therefore,due to the poorer thermalinsulation, boil-off losses are higher, resulting in a mass penalty in terms of additional propellant to accommodate the excess tankage weight and boil-off reserve for a Mars mission. An alternative solution would be to increase the thermal insulation of the flight tankage to reduce boil-off, but this solution, like the first, increases the initial Mars injectionweight of the spacecraft. Thealternativemodeof launchingseparateheavilyinsulated storage tanks with transfer to the lighter weight flighttankagejustprior to stageignitionreducesboththe Mars-injectionweight and the ET0 lift requirementsof the Mars vehicle. However, this mode requires the separate launch of the fully fueled storage tank. The trade-off that needs further study is the assumed higher ET0 requirementsfor this mode versus higher injection mass requirements of the previous mode. Transportation Node. A final topic related to In-Space For the evolutionarycase, theobjectivewas to determine the most desirable location in Earth-Moon space for supportingthe transportationneeds of the Mars portion of thescenario. Thestudyassumed that a transportation node isjustified, based on the specificsof the case study, and that the scope of this trade is to analyze only the locationof thisnode. Otherkey assumptionsinclude: all vehicle traffic@LEOassumesaerocaptureat Earth, and lunar liquid oxygen (LOX)was assumed to be available to fuelthevehiclesbound for Mars, aswell asthetankers carrying fuel to the transportationnode. Fivecandidatenodelocationsarebroadlyrepresentative of themajoroptionsin Earth-Moon space. Theseoptions include: low-Earth orbit, geosynchronous Earth orbit; Earth-Moon libration point (Ll);low lunar orbit (LLO); and an ellipticalorbit, with perigeeat Earth and apogee at lunar distance from Earth. The analysis for this case study assumed the use of lunar LOX even for the LEO node. Vehicle Processingis the need for a transportationnode Within the limitations implied by the validity of the and the choice of its location in Earth-Moon space to specific set of assumptions used, only the following support and/or enhancehuman exploration initiatives. observationwas made: The use of a transportation node, its location, and its assigned functions significantly impact overall mission performance. For FY 1988,this study was conducted for the Lunar Observatory and evolutionarycase studies. For the Lunar Observatory case, four alternativeswere examined: no node, LEO node only, low-lunar orbit (LLO)node only, and nodes in both LEO and LLO. For the baseline mission in which vehicles will require fuel- Positioningthe nodein "near-lunar" space(Ll, LLO, elliptical orbit) appears to be a 'better choice for steady-stateoperationsif lunar LOXisutilized; these locations(theoretically)resultin anadvantageovera node located in "near-Earth" space, in terms of reduction in LEO mass, mission LOX requirements, and LOX transport requirements. ing and assembly onabit, the case without a node is Advanced Protmlsion considered impractical. If any reusable vehicles are employed, a LEO node becomes mandatory for storage Propulsionconceptswith high specificimpulseand high and maintenance between missions. Therefore, a LEO spacecraft thrust-to-weight are very desirable. For the node wasassumedto be required for theLunarObserva- most part, near-term technologiessuch as chemicaland tory case. electric propulsion have one, but not both, of these desired attributes. In the future, "high-leverage" technolo- Because of its location, a low-lunar orbit node cannot gies may be available that will allow large quantitiesof serveasa substitutefor a-LEOnode. Theonly issuetobe cargo to be transported quickly over interplanetarydisconsidered is whether a low-lunar orbit node shouldbe tances. To assessthe leveragethat advanced propulsion included in addition to a LEO node. Since the Lunar technologies could provide to NASA missions, a large Observatory case does not assume the use of local re- numberof nonchemicalpropulsionsystemdesignsrangsources, the principal reason for a node in lunar orbit ing from near-term nuclear electric propulsion (NEP) does not apply, but such a node can perform other systemstosolar-system-classinertialfusionrocketswere functions. However, many of thetasksenvisionedforan examined. LLOnode couldbe more easilyaccommodatedby dedicated lunar orbiters. Furthermore, the LLO node would In general, electric propulsion systems were found to increase costs, integration, and operational complexity, occupy a region of parameter space where the specific requiringan additionalrendezvousand dockingopera- impulseandmassareabout2to10kilosecondsandabout tion upon arrivalin lunarorbit, and it servesno function 10to 50kg/kWj, respectively. With an engine thrust-toatallfor the two cargomissions. Therefore,for theLunar weightof approximatelylo",electricpropulsion systems Observatory case: (1) a LEO node is highly desirable, if appear to be well-suited for flights to the Moon and for not essential,and (2) there is no plausible reason for an interplanetary cargo missions, where short trips are not LLO node. a high priority. Solar and laser thermal rocket concepts 20

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Technical Summary offer someadvantagesinorbitaltransfervehicletriptime propellant requirements for the single stage cargo veover electric propulsion systems, but at the expense of hicle are also reduced by more than by 50 percent when reduced payload fraction. compared to the chemicalcase. With a propellant loadingof approximately136t, thecargovehiclevery closely However, electric propulsion systems are not particu- resembles NTR stages studied in detail by NASA conlarlyeconomicalfor shortflight-timetrajectories,suchas tractors during the 1960sand early 1970sfor lunar and the sprint. A 200 mWe ion/nuclear electric propulsion interplanetary applications. Logistics for the Phobos system, with specific mass and impulse of about 1kg/ mission are also simplified using NTR technology: inkWj and about 20,000 seconds, respectively, was exam- stead of five vehicles/stages, only three are required. ined for its quick trip potential. The system was capable of a 7.5 month round-trip mission to Mars, but its initial Increasingthe specificimpulse from 850 to 950seconds mass was about 1,500 metric tons (t) and the propellant providesa furtherincreasein totalmasssavingsof about and payload fractions were 80 percent and 6 percent, 130 t. At 950 seconds, the IMLEO is 49 percent of the respectively. At a 400 mWe power level, six-month referencechemicalresults. Totalenginebum timeforthe round-trip times could be achieved, but only for a zero 250,000 lbf classNTR used on the cargovehicleis on the payload fraction. order of 15 minutes. The Phoebus-2A rocket/reactor operatedat a thrust levelof 200,000lbf forapproximately Of the variousconceptsthat could bedevelopedoverthe 12.5minutes during its full power test in 1968. next two decades, solid and gas core nuclear thermal rockets offer some of the best prospects for sprint Increasingthe enginethrust level from 100to 250 klbf on missions. Solid coretechnologyand significantresearch the trans-Mars injectionstage increasesthe total mass of intogascorefeasibilityissuesweredemonstratedduring the piloted vehicleby only 14t. Thespacecraft thrust-tothe Nuclear Engine for Rocket Vehicle Application weight is increased, however, by more than a factor of (NERVA)program, adding to the technical maturity of two, and the engine burn time for the transMars injecthese concepts. High-power solar and laser thermal concepts, and tion stage is reduced from 51.0minutes to 21.5 minutes, which minimizesgravity losses during the maneuver. advanced technology solar/nuclear electric propulsion Benefitto Mars Expeditions. With a specificimpulseof (approximately1to5kg/kWj)mayenabletheseconcepts 900seconds,the ”all-propulsive”NTR optionprovidesa to alsobreakinto the sprintclassregion. However,solid total mass savings on the order of 10percemt over the and gas core nuclear concepts (and potential hybrid aerobraked/chemical mission profile results. This savconfigurations) appear to be the leading contenders in ings is accrued totally by the cargo vehicle; the piloted this category at this time. Beyond the year 2020, the vehicle mass is higher than its aerobraked chemical introduction of high thrust/high specific impulse counterpart. However, it is possible to show a mass magnetic and inertial fusion rockets could make solar- savings for the piloted vehicle by eliminating the system-classspacecraft a reality. cooldown propellant for the expendable trans-Marsinjection stage and increasing the specific impulse to 950 In terms of technology maturity, the solid core nuclear seconds. thermalrocket (NTR)istheonly propulsionconceptto be experimentally tested at the power, thrust and specific Benefit to Evolutionary Scenario. For the same trip impulse levels (about twice those of the best chemical times, the use of closed-cycleNuclear Light Bulb (NLB) engine)required fora Marsmission. During theNERVA gas core technology allows the cargo/sprint missionsto to a near-opera- be performed ”all-propulsively” with a lower launch programthis technologywasdeveloped tional status with a total of 19rocket reactorsbeing built mass in Earth orbit than that requiredby the NEP cargo and tested. Included among these systems were a 250 and aerobraked chemical systems launched from lunar and a fully integrated orbit. The mass reduction is approximately414t, which klbf thrust engine (Phoebus-2A) experimentalprototypeengine (theXE-P)both test-fired representsa savingsof approximately21percent.Theloin the late 1960s. Applying NTR with a specificimpulse gistical complexity of the mission and of lunar base to the operationsis also reduced. In the referencecase study,a of 850-950secondsand thrust levelsof 100-250klbf OEXP case studies leads to the followingfindings. totalof sixvehicles/stages areinvolvedin preparingand transportingthecargoand crewfromlunarorbitto Mars. Benefit to Phobos Expedition. Compared to chemical A total of approximately840t of lunar LOX must also be propulsion, the use of NTR technology for the ”all- produced to fuel the logistics landers, excursion modpropulsive” split/sprint Phobos mission resiilts in a 44 ules, and piloted vehicle stages used during the Mars 50 mission. With NLB technology, a single stage cargo percent decrease in total IMLEO. Approximately percent of the mass savings is attributed to reduced vehicle and a two-stage piloted vehicle are all that is The required. Because theN L B requiresonly L%propellant, propellant consumption by the piloted vehicle. 21

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OEXP Technical Report, FY 1988, Vol. I the infrastructureforproducing,storing,andferryingup approximately840t of lunarLOXisunnecessary,andcan be used to support other lunar base activities. A singlecrew/cargo round-tripvehicleemployingspace radiatorcooled, open cycle gas core rocket (SRGCR) technology can perform "all-up," all-propulsive,explorationclassmissionsto Mars in approximately280 days (including a 4O-day stay at Mars) with an IMLXO of approximately 1,OOO t. Increasing mission time to a p proximately450 days (theduration of the split mission sprint leg) lowers the IMLEO to approximately 600 t. With theSRGCR,a separatecargolaunch isunnecessary, and significantreductionsinboth massand in number of required vehicles/stages are possible. The Feasibility of AutomatingLunar LOX Production. In support of extraterrestrialpropellant production, the feasibilityof automating theoperationsof digging,transporting, and processinglunar soil and operating a lunar LOXproduction facilitywasexamined. Theexploitation of lunar resourcesisa high-leverageitembecause: (1)the production of lunar LOX provides an on-site source of oxygenforrocketfueland forlifesupport,and (2)studies indicatethat oxygenexistsin sufficientabundanceat the lunar surfaceto meet these needs. Theoxygen on the Moonappearstobe most oftenbound in the four oxides FeO, SiO,, A40y and TiO,. Oxygen can be extracted by chemical,electrolytic,and pyrolytic processes. The emphasisin this study was to verify the possibility of the automatic acquisition, in sufficient quantities,of theappropriatelunar materialand itsautomaticdelivery to thechemicalplant forthe production of LOX. Lunar soil is generally fine-grained; therefore, heavy digging and crushing appear to be unnecessary. A miningvolume of 12,000 metrictons per year for 15years will require an area of approximately 100,OOO square meters, if theaveragedepthmined isabout 2 meters. The facilities emplaced by the crew would consist of a continuously operating bucket wheel, similar to operations performed in strip mining on Earth. Conveyor belt systemsare used to bring the material to the processing plant. At most, 9 percent of the processed material is extracted and converted to LOX; the remaining 91 percent is redeposited on the lunar surface by a conveyor that moves behind the bucket excavator at the same forward speed.The technologyrequired for continuous autonomous operations is alreadybeing used on Earth. Teleoperated Rovers in Support of Human Planetary Missions. Teleoperated rovers, like humans, can be importantscientificandoperationaltoolsforexploration 22 of lunar,Martian,andMartiansatellitesurfaces. However, it is important when designing misions which utilize both rovers and humans that the rovers' science and operational objectivestake advantageof the synergistic aspects of humans and rovers working together. Whetherthroughacquisitionof qualitysciencedatafrom selectedor serendipitouslocationsbeyond thelandingor crew habitat site, through improvement in the effectivenessand efficiencyof surfaceexploraitionandbasecamp operations by mecahnical or electronic advantage, or through reduction of environmentalrisks to the mission crew, it is important that the man-machine team be assigned taskswhich can be accomplishedbetter pintly than either man or machineis capableof accomplishing individually. Mission planners should capitalize upon the physical and electronic advantages of an immediate crew presence. A surfacecrew in closeproximity to the rover and its environment will be in an excellent position to respondtoboth routineand contingencysituationsrequiring timelyhumanjudgment. Acrew membercanimmediately process and integrate direct visual, electronic,or intellectuallyderived dataand make a decisionbased not onlyonlogicanddeduction,but onjudgment andknowledgeof peripheralmissionsystemsaridoperationsstatus. Additionally, as advances in automation and robotics technology allow rovers to perform more and more 'outside' operational tasks independent or remote from thecrew, totalEVA timeisreducedas isoverallenvironmental risk to the crew. Additional factorswhich may influencethe generalutility of teleoperated rovers are overall mission objectives, rover operational availability, and mission duration. Expedition-classmissions such as those of the Human Expedition to Phobos Case Study allow only about 30 days in the immediate Mars vicinity for a crew of four. During this period, two crew members spend 120days on or in the immediate vicinity of I'hobos. Two other crew membersremain with themothershipin Marsorbit to maintain the spacecraft,conductorbital scienceactivities, and teleoperate the Mars rovers. Assuming that thesetwo crewmeneachseriallydedicate4hoursperday to teleoperation activities (assistedas required by communicationssatellites),a total of 240h~oursof exploration canbe accomplished.Additionalon-linecrewteleoperation time is potentially availableif the Phobos exploration crew reduces its stay time at I'hobos in favor of supporting the acquisition of additional data from the Mars rovers; i.e., assuming two or more crew members can simultaneouslyoperatefrom a singlecontrolstation or assuming there are multiple control stations onboard the mothership.

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Technical Summary However, compared to previously successful (though case study analysis progressed, an option emerged that presumablylesstechnicallysophisticated)Americanand had potential merit for the observatory setup phase: Soviet Mars and lunar robotic missions, this is an ex- allow the crew to stay over for one or two lunar night tremelybrief operationsperiod. Therefore, itwillbe vital periods in order to have more construction time (and thatexplorationsitesbecarefullyselectedthroughanaly- possibly complete construction on one mission). AIsis of precursor mission data and synthesis of desired thoughthiswouldrequiremoremasstobeEarth-launched mission objectives, and that Earth operators complete on the setup missions, it would require fewer Earth checkout, initial placement, and real-time mission launches overall and, consequently, could be signifiobjective"tweaking"activities with the rovers prior to cantly more cost-effective. mission crew involvement.Thebrevity of the operations period may be partially compensated for by beginning One important aspect of lunar observatory operations theteleoperationsprior toMarsorbitinsertionduringthe (includingthe optionof crew stay-over)is that of power final weeks-to-months of the cis-Mars coast period. availabilityfor lunar day and night activitiesincluding However, designingthe rover systems(and trainingthe crew habitation, observatory construction, and instrucrew)to respond to everchanging signal-lagtimespres- mentoperationneeds. Thecrewisassumedto uselander ents an additional complicationto this approach. vehicle power for their habitation needs during the emplacement of the baseline solar photovoltaic (PV) Phobos Exploration. The expedition to Phobos repre- observatorypower system and the initial set of mission sents the first opportunity for humans to explore the science experiments. At this point, the PV system can surfaceof and assessthe operationsfor explorationof an begin supplying power for daytime surface activities, Phobos continuing construction as well as instrumentationopessentially gravity-free, asteroid-type body. presents a unique set of environmental characteristics, erations. The functioningPV system could also be used particularly in terms of its nearly absent gravity, that during the daytime, as power budgets allowed, to s u p planning plement or replace lander power for extended crew mustbeconsideredin missionandcontingency that options can be pre-selected to ensure mission habitation needs. so success. Studies were conducted in FY 1988 to obtain methods of exploring the Phobos Theissueis now: Which energystorage devicesarebest information on (1) the charac- for use during the ensuinglunar night-by the observasurfaceunder low gravityconditions;and (2) teristics of controlled flight in close proximity to the tory instrumentationfor continued science data return, The information, although preliminary, will andby thecrewforextendedconstructionandhabitation surface. help define vehicle and equipment requirements. needs? Conventional power systems (rechargablebatteries) are very massive and are not suitable for pro- Phobos has a small gravity force that would keep a longed use in complementing solar-based power sysbody on the surface. However, the potential tem. However, advances in rechargable hydrogenmotionless (10- oxygen fuel cell technology could make storage for the for leaving the surface for extended periods of time 30 minutes) due to inadvertent pushes or bounding off long lunar night feasible. terrain featuresis high. Thisseemsto indicatea need for anchoring methods to maintain surface contact and to A primary fuel cell (onewhich uses supercooled hydrocreate a stable work platform for sampling. gen and oxygen to produce water and electricity and which is not rechargable) could be used to extend the Flight over Phobos has the benefit of ease of traverse, crew stayperiod over one lunar night without incurring including the ability to alight "anywhere" and to avoid an excessive mass penalty for cryogenic storage tanks. obstacles. Flight trajectorieson the surfaceof Phobos to However, onceused, the fuel cell (andcryogenicstorage both tanks) must be expended. Multiple stay-overs (and be investigatedin greater detail in FY 1989include and multiple primary fuel cells and storage tanks) would short round-trip traverses of less than 2 kilometers long round-trip traversesof up to 10kilometers. Surface S m Case hydrogen and oxygen from the water byproduct for Lunar Surface Power. In the Lunar Observatory require significant additional mass. Technology advances in the regenerable fuel cell (one which uses gaseous hydrogenandoxygento makewaterand electricity, then usespart of the generated power to electrolyze Study, the ground rule for crew stay time on the surface reuse as fuel)could make energystorage for use during for both the obser- the long lunar night feasible: i.e., both fuel cellsand fuel was one lunar day (two Earth weeks) This rule was storage tanks are reused, thereby reducing the mass vatory setup and operations periods. mission objectivesand mani- penaltyforcontinuingcrewandequipmentpowerneeds. intended primarilyto keep fests at a level commensuratewith reasonably low an- LEO Thissolar PV power system consistsof amorphous silinual mass to LEO (and, consequently,manageable infrastructure support requirements). However, as the conrolhut arraysto provideinitialpower. Sun-tracking 23

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OEXP Technical Report, FY 1988,Vol. I fold-out arrays and regenerativefuel cell storage equipment are then deployed/erected. The final stageof constructionwouldconsistof connectingtheinitialarraysto the regenerative fuel cells for nighttime operation. The fold-outPVarraysprovideconstantdaytimeoperational power to the Lunar Observatory. The completesystem can probablybe set up within one 14-daystay. A power system with regenerative fuel cell storage capable of supplying the required continuousday/night power is estimated to have a mass in the 7-8metric ton range. However, once the regenerative fuel cells are operational, extension of the power system construction period into the lunar night is possible. Thisyear's studies also provided a conceptualdesign of a nuclearpower system. Configurationswereselectedto enableand/or enhancea lunarbasemission. Numerous components and coupling techniques were examined, and recommendedoptionswerechosen for safetyimplications, high performance, low mass,and easeof assembly. For power levelsin excessof 60kWe, the nuclear reactor exhibits a mass advantage over the solar PV power system,which increasessignificantly with higher power requirements. As the base expands to include scientific experimentation,roverrecharging,and soilprocessing,a nuclearpower systembecomesthemost viablemeansof meeting the higher power requirements. Thenuclearpower systemexaminedthisyear consistsof a 2300 kWt SP-100reactor coupled to eight free-piston Stirling engines. The reactor is identical to the design currently baselined in the SP-100program, but the Stirling engines replace the thermoelectric power ronversion system.Two Stirlingenginesare held in reserve to provide engine back-up for dependable power generation. Theothersixenginesoperateat91.7percentof their rated capacityof 150kWe. Thedesignpowerlevelforthis system is 825 kWe. The system is modular and can be replicated in increments of 825 kWe to meet higher power requirements. Excludingthemassof requiredconstructionand maintenance equipment,thisnuclear power systemconceptual design offersthe potential fora substantialmasssavings over comparable PV/storage power systems. For example,the pmssof a 50kWe solarPV power systemwith regenerative fuel cell storage for full night capability exceeds the mass of the entire 825 kWe nuclear power plant. The nuclear system also enables continuousday and night operations without the need for energy storage. The 'Bottom line" is that the integrated power system (PV augmented by either primary and/or regenerable fuel cells, or nuclear power)must have a power genera- 24 tion and storagecapabilitysufficienttomeet theongoing setup (20-40kWe) and operational (50-100kWe) power needs of the lunar observatory and must also meet the overall case study objective of minimizing annual IM- LEO during the operational period. Further studiesare required to converge upon the optimum mix of power generation and storage devices with mission strategies and observatory objectives. AdvancedLife SupportSystems. A.spacecraftorplanetary surfacehabitat crew life support system (LSS)providesthefollowingbasic functions: atmosphererevitalization, temperature and humidity ontrol, food supply, personal hygiene, water management, and waste management. Each case study under considerationrequires reliable and efficientLSS technology, for the health and well-beingof themissioncrewaswell asforreduction of mission IMLEO requirements. However, the more complex the mission strategy, the more highly sophisticated must be the LSS. For theLunar ObservatoryCaseStudy,thepiloted space transfer vehiclecan have an LSS that is essentiallyopenloop (food, water, and breathing air supplied as IMLEO with limited onboard water recover]!, air revitalization, and food processing.) This systemclouIdbe developed, in large measure, using existing shuttle LSS physical/ chemicaltechnology.Ontheotherhand, theLSStechnology required to support the crew during the "everyday" extravehicular activity (EVA) operations performed to constructand maintain the observatoryrequires significant enhancementfromthe "current"technologyasused to support the Apollo missions, especiallywith regards to overall system mass and serviceability. Consequently,recent lunar EVA studies were analyzed and toplevel requirements for the lunar EVA system were generated. Basicrequirements for the LSSare that it will need to be both lightweight enough and small enough in volume to allow for easy, convenient EVA in the lunar gravity field, while supporting 6-8hours of EVAperday. Further,post-EVAservicingforreusemust be accomplished within the logistics allowance (spares availability, dedicatedcrew time, etc)for the lunarbase. Thespacesuitassemblymustbe flexibleenoughto allow unaided resumption of footing after a fall, must allow exceptional hand-dexterity to permit extended (multiple-day/week)performance of EVA, and must tolerate the lunar dust environment. Trade studies were identified in these two areas and in the additional areas of support equipment and support vehicles which, when performed, will allow more detailed definition of lunar EVA requirements. Marsexpeditionaryclassvehicles, ontheotherhand, will clearly require a more robust LSS technology that is operablein both the deepspace and nonvacuum plane-

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Technical Summary tary surface environments, is reliable over the length of Hardware: themission(14 monthsor more)and is "closed'(recovers drink- Acquisitioncostrealismand unit productioncostare andreusesor regeneratesconsumablesneeded for practi- significant design requirements. ing, bathing,breathing,etc.)to thegreatestextent cal given the desired mission launchyear, constraintson vehicle mass and volume, and the status of empirically Productimprovementsand maximumuseof proven proven technology. It is anticipated that the partially- componentsand subsystems(especiallycommercial closed, physical/chemical Space Station Freedom LSS items) should be planned. technology, when successfully demonstrated, will suffice for this class of exploration vehicle. However, to A continuousalternativeshould be available. support EVA in the one-third gravityMarssurfaceenvironment, advanced technology suit systems must be Use mass productionas much as possible. developedthat may be significantlydifferentfrom their Subsequent studies will examine Minimizefunctionalcomplexityof individualhardlunar counterparts. Mars EVA requirementsin detail. ware elements. constrain- Seekcommonalityamong hardware elements. Evolutionary-classmissionsplacemuch more ingdemandsontheassociatedLSS: not onlyon thespace transfer vehicle(s)during the months-long transit peri- Designhardwareelementswithsubstantialperformods, but also upon an evolving surface systems infra- ance margins. structure (including increasingly robust EVA support systems) which must support a number of people for Program Management: periods of up to two years or more without benefit of frequent Earth resupply. A space transfer vehicle and Design short, stableschedulesfor development and surface systems LSS technology base characterizedby a high degreeof closure, extremelyhigh reliability,easeof production. maintenance, increased automation, and independence Use experienced, small staffs, with clear channelsof from terrestrial resources will be required if missions of command and limited reporting. thistypearetobesuccessful. Continuingresearchshould includea varietyof LSStechnologiesincludingadvanced Establish effective communication with users for physical/chemical and biological. Qs.t Understanding Thisspecial study was conducted to update the assumptions and art of estimatingcosts of major initiativesthat areat the conceptstage, with implementationfarintothe cost/performancetrade-offs. Seek early development phase funding for production and support considerations. Technology: future,usingexperienceand techniquesthataredifficult Technology should be pushed forward only at reato predict with present information. In traditional cost sonablerates as determinedby the recognized techestimating models, it is assumed that historical trends nology manager. and methods of doing business will continue in the future. This cost understanding analysis takes a fresh lookat theanalytical,political and social"science"of cost estimating, and attempts to isolate the programmatic featuresthat influencecost. A "tailored" methodmustbe developed to include plagrammatic and specificNASA assumptionsontheenvironmentinwhichinitiativeswill be developed. Someof the major program featuresthat impactmission costsare: the wayin whichhardware isdesigned,developed, and built; program management philosophy; and expectationsof rate of technologydevelopment. After a preliminary assessment, the following recommended assumptionsfor incorporationintoa tailored cost model can be made. 15

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Science Opportunitiesin Human Exploration Missions Technical Summary As NASA is exploring potential programs to fulfill the To investigate the potential resources available in nationalpolicyguidelinesof expandinghumanpresence near-Earth space. beyond Earth orbit, it is important to consider what that Al- The specialcapabilitiesof humans as observers, integrameans in terms of advancing scientific knowledge. principal tors, and interpreters provide the greatest leverage in thoughscienceobjectivesmaynotrepresentthe they will performingscience-relatedtaskssuchas: theexploration motivation for undertaking human expansion, generate many of the most visible accomplishmentsas of new environments,searchingforsubtleoruncommon Therefore, in order to features, modifyingexperiments or studies based upon the missions are carried out. of new real-time information,and maintainingand repairmaximizethescientificaccomplishmentsof a program human expansion, a science strategy should be devel- ing mechanicaldevices. oped from the beginning of that program. For the exploration missions themselves, three general The opportunties (or requirements) for science in the types of experiments/investigationscan be considered: proposed OEXP case studies have been developed in an ad hoc manner in FY 1988. The scientific information Investigationsthat make unique use of the capabiliindivid- tiesof people functioningin the space environment. availablehas been derived through inputs from ual scientists, a few workshops, and the literature. Fur- Two examples are: direct exploration, where the of human intellect can contributeto new observations thermore,this content has not undergone the scrutiny performed and react to the unexpected; and the local teleoperaa scientificoversight function. Thus,thework past year does not constitutea sciencestrategy,but tion of machinesby humans. in the has looked to incorporate some ideas on science objectives into the engineeringanalysis. Investigations that take advantage of the opportunitytoemplacescientificpayloadsinnewplaces.For The general science and exploration objectives for the example, the operations to transfer humans to the OEXP case studies are: To study the planetary bodies to understand their Moon and Mars canbe used to transfer major scientific payloads as well. origin, history, and current state, and to understand Opportunities that may come about as ancillary their relation to Earth and the origin of the solar products of non-scientific activities. For example, system. lunar or Phobos mining activities could provide substantialnew opportunitiesfor geologicalinvesti- To seek evidence for the origin and evolution of gations of those areas. living organismsthrough the identificationof envihaveexisted,or through Thecasestudiesdevelopedin FY 1988offerthe following ronmentsin whichlifecould the identification of physical or chemicalremains. potential opportunities in lunar exploration: (1) establishing scientific observatories and exploration base canbeuniquely camps; (2) developingcapabilitiesto produce resources Toconductstudiesoftheuniversethat undertaken utilizing the new environ- for both propellants and life support; and (3) exploring or effectively ments that would be accessiblein the human explo- the potential uses of the Moon as a testbed for the estabration program. lishment of self-supporting human outposts on other planets. In addition,many unansweredgeologicalques- To utilize these newly accessible environments to tions about the origin and history of the Moon can and of science will be addressed by human explorers. conduct important studies in other fields (e.g., high vacuum, very low gravity). Thelunar surfaceisan attractiveplace to establishmajor human astronomical facilities, because of its environmental Tounderstand the abilitiesand limitationsof beings for extended duration spaceflight. qualities: high vacuum, stablebase, extensiveavailable surface,mitigationof structuralproblemsdueto the oneand utility of establish- sixth gravity environment, slow rotation allowing long To determine the feasibility of observationtimes, and thefar sidepermanentlyshielded ing permanent human outposts on the surfaces other planets. 27

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OEXF' Technical Report, FY 1988, Vol. I from the Earth. The current understanding of Phobos and Deimos is meager. The structural complexityand the apparently primitive nature of the surface materials suggest that direct human explorationwill be required to answer the main questionsof originand history. A signficantobjective of Phobos explorationis to establish its characteristicswellenoughtoevaluatewhetherwaterandmaterials useful as rocket propellants are present in sufficient quantities. Samples of Phobos regolith will need to be returned to Earth so that specificextraction techniques can be designed. Theexplorationof Marsin a reconnaissancemode canbe carried out to a large extent by robotic devices. At the current state of understanding about the Martian environment, it is difficultto speculate on the specificscien- 1 tific objectives of a human e x w t i o n . Much will be 28 learned in the next ten years to focusthe objectivesand hazards of human explorationof Mars. In a general sense, there Will be problems or issues identifiedby robotic missionsthat will remain too complex or subtle to be resolved by robotic exploration. For example, a highly important scientificobjectiveof Mars exploration is the search for evidence of existing or ancient life. Although conclusiveevidence could possibly be obtained by robotic missions, it is more probable that theevidenceissubtleenough andscarceenough that human explorationwill be necessary 'tomake the appropriate interpretations to resolvethe i,,c'sue. Thescientificrationalepresentedhere isan initialassessment, which needs to be developed in greater depth, by NASA and the scientific community, to provide guidance to human explorationmissiondlevelopment.

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Comparative Analysis of FY 1988 Case Studies 0. capabilities. The mission strategies range from o n e Theprimaryobjectivefor FY 1988was to developa set Technical Summary case studies with a consistent methodology and to a mission,expeditionaryapproachesto a long-termevolustrate- tionaryapproach. Thetechnologyneedsaredeliberately uniform level of detail so that diverseexploration could paced to include those that will be availablein the near gies (expeditions,science outpost, and evolution) be compared and contrasted. The purpose of this effort term, in addition to assumingthe use of highly sophistithat drive results of cated developments. In order to drive out an underwas to determine the major factors current and future case studies in terms of scale, com- standing of Earth-to-orbitdelivery capabilityand need, and benefits. Broad trade studiesand the requirement for the amount of mass that must be plexity, feasibility, to identify specific, lifted to low-Earth orbit ranges from 250 metric tons in specialassessmentswere conducted innovative techniquesand technologiesthat could be of the peak year for the Lunar Observatory, all the way to example, seven times as much mass, 1,770 metrictons, in the peak significantbenefitto missionperformance. For the scope and potential of various mission designs can year for the Mars Expeditions. realize a significant advantageby the use of advanced technologies; the assessments performed in this year's The selectedgroup of studieslandshuman explorerson to which this thesurfaceof anotherworld any timefrom2003 to 2014, studycyclesoughtto determinethe degree and complex- with planetarysurfacestaytimesfromaslittleas14days istrue.Anotherhigh-level factoristhecost orbit toalmosttwoyears. Gravitationalconditionsgeneratea ity versus the benefit of using a node in low-Earth were examined to unique range of requirements: on Phobos, thegravityis for assembly activities. Case studies explore these extremes. nearly zero; on the Moon, it isone-sixth that of Earth; on Mars, the gravity is one-third that of Earth; and during developa strongknowledgebaseof explorationpath- transit it is zero. The studiesalsocover a wide varietyof To way sensitivities, the case studies were selected to en- trajectoryprofiles, number and frequencyof flights,and and mission duration. compass a broad range of obptives, requirements, Table 1. CASE STUDY SHAPING PARAMETERS Earth-to-Orbit Low-EarthO M other Transportation Assembly ixDed1tions Strateav luman Expedition Large mass per No assembly node to Phobos launch Use then-existing Earliestmission technology Significant assembly Moderate increase Significant precursors luman Expeditions Large mass per year to Mars at node each mission in technology strateav I Minimummass Minimumassembly Moderate increase High science return .unar Observatory per year at node each year in technology IvolutionawStrategy II unar Outpost to Approximately Moderate assembly Advanced Extraterrestrial Early Mars Evolution constant mass at node each year technology resource usage Der year I 29

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I OEXP Technical Report, FY 1988, Vol. I 2000 1800 Lunar-to-Mars 1600 1400 n -w 1200 v v) 10001 I v) 0 I 800 600 400 200 0 2 2 2 2 0 0 0 0 0 0 0 0 0 2 4 6 Calendar Year Large masses not practical; I I I I I I I I I 2 2 2 2 2 0 0 0 0 0 0 1 1 1 1 8 0 2 4 6 Figure 12.- Case studies mass summary-annual mass to LEO requirement Asaresultof this processof developingabroadspectrum of strategiesand approaches, a fairly extensivebase of information has been developed that has enabled some new insightstobegained. The"lessonslearned" overthe I past year are described below; they will be applied, in a continuingprocess of study, to the redirection and definitionof futurework. Oneoverridinglessonhasbecome very clear: this Nation must begin, now, to make the near-term investments that will make human exploration at the turn of the century possible. Thekeyparametersthat shapecasestudiesare: (1)Earthto-orbittransportation; (2) low-Earthorbitassemblyand operations; (3) technology, including concepts of utilizing extraterrestrial resources; and (4) other factors that are unique to each case. A summaryof these case study shapingparametersisshowninTable 1. Aseachof these parametersisappliedtoeachcase,anoverallcomparison of the full set of casestudies and associatedtrades canbe made. - Orbit TransDortation A dependable, high performance Earth-to-orbit (ET01 transportation capability is of fundamental importance to the success of any exploration initiative. Whether 30 derived from current National Space Transportation Systembooster componentsor developed as a separate heavy-lift launch vehicle, new capabilities will be required to enable timely deliveryof massive spacetransfer vehicles, propellant, mission payload components, and support hardware to low Earth orbit for assembly and checkout. For instance, the Human Expedition to Phobos will require a large initial mass to be lifted to orbit, especiallysince this particular case is constrained to minimize low-Earth orbit assembly. On the other hand, the Marsexpeditionscould be accomplished with smaller E T 0 vehicles, since assembly in orbit is not constrained by the case study ground rules. However, issues related to ET0 launch frequency and available accommodationsat the LEO node then become important for Case Study 2. Figure 12 illustrates the annual mass to LEOdeliveryrequirements. ?'his massflowisof fundamentalimportance,sinceitdi~lyaffedsthenature of the required ETO delivery system and Earth-orbital supportfacilities;furthermore,itisa first-orderindicator of total cost. In general, the expeditionary approach is characterizedby very large peaks in inass, corresponding to the year chosen for launch. In contrast, both the LunarObservatoryand theLunarOutpostto EarlyMars Evolutioncasesarecharacterizedby steadyratesofmuch lower magnitude.

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TechNcal Summary Because of the lack of maturity projected to exist in on- delivered vehicle performancefrom concept definition orbit assembly operations at the beginning of the next toflightstatuscouldhavepotentiallysignificantimpacts century, the earlier the mission (i.e., the Phobos case on ongoingactivities,sincethedevelopmentof the space study),the stronger the case for minimizingsuch activi- transfer vehicleswould begin prior to ET0 vehicleflight ties. Thisfactsupportsthedevelopmentof morecapable readiness. ET0 launch vehicles, in order to lift larger, but fewer, currentlyunder Equally important will be the level of automation and componentsto orbit.Heavy-liftvehicles studyassumeamass-to-LEOcapabilityof about91metric robotic technologyavailableat the time to assistwith, or tons. With this performance, the baseline Phobos case perhaps perform all of, the assembly operations. Our requires as many as 20 to 30 separate launches. In addition to factors of cost and availability of ETO vespecial assessments and prerequisite technology programs indicate that complex, detailed assembly operaflights tions will not be ready for robotic application in time to hicles,theimpactsongroundlogisticsformultiple that this nation support our earlier (i.e., 2000) need dates. Thus, our per year are extensive. A mapr decision faces is whether to invest in developing a heavy-lift currentground-basedknowledgearguesforminimizing as those currently and/or simplifymg space assembly operations for the vehicle that isat least twiceascapable under study, to invest instead in a smaller lift capacity early missions, e.g., the Human Expedition to Phobos. extensivecapabil- However, some of the other cases, such as the Lunar withhigherflightratesand developan ityfor in-space assemblyof large structures,or to effecta compromise between heavy-lift capacity and level of Outpost to Early Mars Evolution study, envision adv a n d , reusable vehicles and the use of lunar liquid cannot be oxygen, which impliesa high degreeof readinessfor inassemblyin LEO. Theissueof ET0 capability LEO space operations technologies only a few years later. consideredseparatelyfromthenext functionalarea, assembly and operations. Low-Earth 0rbit Assemblv and ODerations The choice of investment and mission strategies that affect LEO activities is a function of many interrelated Sincethis particular caseevolvesover a longer period of time, it can and must be integrated with development programs. This is consistentwith the forward-thinking philosophy employed in the development of the evolutionary case. As presented in the previous section, it is To reduce the LEO mass to more manageablelevels, an variables. assem- aerobrakedoptionwas analyzed for thePhobosmission. recognizedthat there is a tradebetween on-orbit that the This option resulted in about one-half the LEO mass of bly and ET0capability. In general,it isexpected as the thebaselinecase. It wasintendedtoreducetheLEOmass developmentcostsof ETO transportationincrease the other to the point where major components (i.e., complete requirement for lift capability increases. On hand, asET0 lift capabilityincreases,theexpectedtrend cargo or piloted vehicles) could be assembled on the is for the number of required on-orbit operations (and ground and launched on a very heavy-liftor ”magnum” assumed costs) to decrease. This therefore implies that launch vehicle. Even so,this massis still largeenoughto identified. suggest that someassemblyin LEO is a better approach cost-optimumparametersexistthatneed tobe Manyof theseissueswereaddressedinacursorymanner than a singlemagnumETOlauncher. Reducingthecrew sizefor the Phobos mission further reduces the mass in by trade studies and assessments in and these LEOrequirement and the subsequentE T 0 launchesand FY 1988, analyseswill continuein more depth in FY 1989. However, some observations can be made, based on the preliminary results. Given our current experience in space assembly Operations, it is extremely difficult to spaceassembly operations. Integrating the launch vehicle and spacecraftto synergize the use of upper stagesis oneapproach to minimizproject forward to the level of operations required for ing assembly operations that warrants close scrutiny. these casestudies. Obviously,lessonslearned while we design SpaceStationFreedom will be important. Many Other innovative approaches, such as advanced space propulsion(e.g., nuclear thermalrockets),may be necesof the assembly issues encountered during Freedom’s sary to undertake a major exploration program without ongoingdesignand developmentactivityarecommonto a LEO node. Further study is required to understand, the case studies as well, and the results may be appli- with any certainty, whether or not this mission can be cable. Space Station Freedom’s assembly planning has already experienced constraints imposed by the ETO systems(Shuttle)and by crew (EVA time). accommodatedwithoutanyLEOsupportinfrastructure. At the other extremeof on-orbit assemblyneeds are the Mars expeditions and Lunar Outpost to Early Mars important lesson learned from the Space Station Evolution; these case studies have been structured to AII Freedom experience is that the ETO support functions must commit to transportation performance stabilityin terms of agreed-to E T 0 performance. Degradation in permit a significant amount of activity in LEO, and, therefore, have resulted in very challenging node s u p port and operationsscenarios. To definethe operations 31

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OEXPTechnicalReport, FY 1988, Vol. I for in-space assembly and vehicle processing for these cases, thenatural tendencyhasbeen toattemptto understand our current experiencein ground processing, and extrapolate it to orbital operations. However, current ground processing flows for space vehicles represent a resourceand time requirement that becomes unrealistic to imposeupon on-orbit operations. New ways to process space vehicles that are assembled/nated on-orbit will need to be developed in order to reduce the LEO operations work load and make these cases viable. The resolution to this challenge most likely will be a combinationof revising the vehicle design, eliminating processingfunctions,maximizingvehicle ground processing of resource-intensive tasks, incorporating aut* mation and robotics and other strategies to enhance productivityand capability,and reducingthenumber of on-orbit operations. This strategy will require both a "bottom-up" and a "top-down88approach for FY 1989. The bottom-up approach is one that @ns with the current vehicle ground processingflows. Each function currentlybeing performed needs to be accounted for in some manner (e.g., not required, incorporated into design,integratedwithotherfunctions,etc.)asdonew ones identified for the reference vehicles. The topdown approachis to estabIishan assemblyresource allocation tobe levied asa requirementfor theintegrationagentsto meet. Resultsfrombothmethodswould thenbeusedfor convergence of requirements. For missionsto Marsand Phoboswith short travel times (i.e., split/sprint or opposition),usingaerocaptureasthe means of Mars orbit insertion translates to a savingsof approximately 50% back at initial LEO requires fewer ET0 launchesand has the potential to alleviaterequirements for on-orbit assembly. However, the techniqueof "assembling" the large aerobrake in LEO is not well understood,and it cannotbe unequivocallystatedat this time that a LEOnodewould not still be required in order to assemble the aerobrake. Alternative crew module aerobrake designs that could be smaller, such as nonreusable ablators, could alleviate this problem, as could the use of nuclear thermal rockets. The advantages of using aerobraking are much less for trajectories with longer trip times; therefore, a trade existsbetween missionduration(reliability,human performance)and LEO assembly capability. Impacts of using Advanced =strial Resources The use of one or more key advanced technologiescan cause a significant reduction in Initial Mass to LEO (IMLEO) requirements. As stated earlier, the use of aerocapture for orbit insertion at Mars and Earth can reducetheIMLEOrequirementsby one-half overtheuse of standard chemical propulsion for orbit insertion for 32 split/sprint missions to Mars and Phobos. Advanced propulsion techniquessuch asNuclearThermalRockets canreduceIMLEOforthePhobosExpeditionbyone-half and theMarsExpeditionsbyone-third.'Usinganelectric, low-thrust cargo vehicle in the Lunar Outpost to Early Mars Evolution case can potentially reduce IMLEO by one-third over a standard chemically propelled vehicle. Also,advanced nuclear thermal rocket technology for thepilotedvehicleoffersthepotentialforsimultaneously reducingtrip time,mass toLEO,an.dthe logisticalcomplexity of the evolutionary case study. For the Lunar Observatory,advancedenergystoragecouldextendcrew stay-timethrough the lunar night, and could also eliminate an Earth launch. The use of extraterrestrial propellant is a potentially high-leveragetechnology,and it was incorporated into theLunarOutposttoEarlyMarsEvchtioncasestudy. In thiscase,theuseof propellantfromtheMoonandPhobos (coupledwith the use of electricpropulsionon thecargo vehicle)can reduce the IMLEO by more than one-third compared to the use of all Earth-based propellants. The special assessment study on power showed a substantial mass advantage for nuclear power technology when compared to photovoltaic/regenerative fuel cell technology. Whenthismassadvantageisfoldedintothe total integratedlunar surfacesystems, the end result is a total case study mass reduction at LEO of one-half to threefourths, dependingon mission configuration. These are only a few examples of how advanced technologies are enabling for some areasand enhancing for others. The objectiveis to stimulatethe developmentof technologiesforthe case studiesto build a solidtechnology base from which NASA can select to support a variety of missions. This technological maturity will allow additional manned missionsto other planets. The problem that must be addressed is that different technologiesareoftencompetitivewith respect to developmentalfundingsupport. Thequestionto beanswered iswhichismoreadvantageousto pursue,fromthestandpoint of development cost and risk. Anexample would be that aerospace plane materials technologiesand syst e m designed for the Advanced launch System programcould reduce LEOaccess costs to the point where extraterrestrial propellants would not be competitive with Earth-delivered propellants in LEO. However, whichtechnologydevelopmenthasa greaterprobability of becoming a reality in the planned need time-frame, which has less operationsrisk, and which has the lower developmentcosts? Relatedissuesmustbebetterunderstood through futurecase studies and trades. The use of advanced technologies in a program carries with it an element of risk if the technology is developed

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in serieswith its intended use in the program. To alleviatescheduleimpacts,developmentof enablingtechnologies must be initiated well in advance of their required use. Ideally, technologyshould be at a technologyreadiness level five or six (laboratory-demonstrated or integrated into a hardware subsystem)at the start of Phase C/D. Thetechnologyreadinesslevel at the startofPhase C/D will depend on the perceived risk of the nonavailabilityof the technologyto support the mission; the higher the risk, the higher the technologylevel required. Alternativetechnologiesmust be availablefor eachcase studyor themissionmaybe injeopardy. Thealternative technology may mandate that more massbe required to supportthe mission; forexample,using propulsiveorbit entry as opposed to aerocapture will impose a mass penalty. For all the critical technologies, it must be determined whether an alternative exists and what the impact will be on the mission if that alternative is used. Byallowingforthedevelopmentof the technologieswith proper funding and scheduling, the use of alternatives can be minimized. The technologydevelopment programs were integrated with thecasestudyprograms, and where theseprograms were incompatible, alternative solutions were chosen whereverpossibleandpractical. This wasnot possiblein all cases and outstanding incompatibilities remain in three areas: (1) propellant transfer, (2) nuclear electric propulsion, and (3) Mars-to-Earth aerobraking. Also, some technology areas are not addressed currently in Project Pathfinder, and thus some additional work will need to be accomplished. A majorityof technologiesare commonacrossmost of the casestudies, which indicates thatby developing a coreset of technologiesit ispossible to preservethedecisionoption fora number of missions. Other Factors I In addition to the parameters that pertain to all case studies, each also holds a particular emphasisthat must be considered in the overall planning strategy. These emphases are strictly dependent on the case study scenario itself, and also on thebasic strategy that is selected for exploration. 33 Technical Summary For example,if the major motivation to be stressed is to achieve the earliest and first huinan voyage to another planetary body, then the Human Expeditionto Phobos, which could arrive as early as 2003, becomes a most attractive option. If, however, the strategicemphasis is on the facilitationof opportunitiesfor lunar geophysical and cosmic astrophysical research, the Lunar Observatory Case Study could be considered attractive. The Human Expeditionsto Mars have substantial precursor requirements,both in terms of robotic missionsto characterize the planetary conditions, and life sciences researchto determine the effectson human beingsof longterm exposure to the environment of space. And the Lunar Outpost to Early Mars Evolution case study explores and exploits the use of many new technologies, including those that mine and refine resources on the Moon or Phobos. Clearly, the parameters derived from the studies conducted in FY 1988define a complex and interconnected situation. Many elements must be identified, assessed, planned for, and developed in parallel to enable the successof any mission. At the very heart of case study development is Earth-to-orbit transportation and the need for an ambitious launch schedule and a stable of vehicles that includes the Space Shuttle, a heavy-lift launch vehicle, expendables, and other advanced systems. Also criticalto eachcasestudyis the availabilityof SpaceStationFreedomor another platform in low-Earth orbitforassembly,inadditiontoa heavy-duty LEOspace "tug". The technologydevelopment schedules that are assumed impact all case studies, and each choicefavors a particular exploration strategy. Table 2 provides a summary comparison of key characteristicsfor the casestudies. By studying the data in this figure,such as: arrival date, initial mass, mass delivered to final destination, number of crew members, etc., a relativeassessmentof thecomplexityandcapabilityof all the case studies emerges.

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OEXP Technical Report, FY 1988, Vol. I TABLE 2 - SUMMARY OF CASE STUDY CHARACTERISTICS SCENARIO HUMAN MPEDiTlON iUMAN MPEDlTtONS TO PHOBOS TO MARS o TRANSPORTATION -TRAJECTORY PROFILE Cargo: rninenergy Cargo: minenergy crew: splint crew: sprint LUNAR .UNAR OUTPOST-TO-EARLYMARSEVOLUTION OBSERVATORY LUNAR PORTION MARS PORTION TrpndUnar Cargo: bwthrud 2 c a r g o 2 c l e w C t w t nearfuel min -NUMBER OF FLIGHTS 1cargo.1 crew 3caQo.3crew &-UP); 1 h m per lcaQo.3Crew o CREWSlZE 4(2tOphobOs 8 ( 4 t O M r s sutface) UJff=e) o TOTAL CREWTRIP TIME 440days year thetuafter 4 8 (8to Marssutface) I20 days 1year 35 to 45 mos. days Ma16orbit <14da onsurface 5 1year 1-2years o SURFACE STAYTIME 30 in Marsorbit 30 days in 20 days at Phobos 20 days on aurtaca wrmonly) moons 12 EVA'S EVA%as required 10-km unpress. 4 EVA'Sat Mars 10-km unpress. lo-km unpress. rovertraverse o EVAs (8 hows per EVA;two 4- EVA'Sat Phobos 10EVA'S at unpress. mrer traverses m e r trave- and IOOkm press. crew per EVA) 1o-km EVA%as required rovertraverses rover travefse o MASSTO LEO PEAK YEAR Peak 453182002 Peak: 1 7 7 o t e Peak: 3 t e r n Aemcapture option MOB 1680 o P R O P E U W MASS (1) Cargoveh 234 cargoveh: 1796 Cargoveh: 87 P k t e d v e h 318 Pktedveh: o USERALLOCATION (1) 3363 r r 6 Mars) Pktedveh: 96 12.5. 12.5,6 7 3.3 12 - ORBrAL E (includes Phobose x p :we) 17.5/CargofN. Mars-58 - SURFACE 15. 15 112 7 t Total: 2 teleop 15. explorerson Mars o PROPELLANT PRODUCTION nla nla o YEAR-1STHUMANSTO 2003 2007 SURFACE 34 6.5 I Crew fA. Phobos - 10 nla FouLLOX plants Phobos pmpphnt (40teach) (881) mo4 m 2014

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Program Integration Approach Human exploration strategiesare intimately connected to the plans and schedules of all the NASA program offices. The success of such efforts depends on the integrationof explorationplans with those of programs involvingtransportation,lifesciencesresearch, scientific precursor missions, SpaceStationFreedom,technology, and communicationsand data tracking. Earth-to-OrbitTransDortation All human exploration missionswill require substantial massto low-Earthorbit;clearly,ourpresentlaunchcapability must be augmented. To meet the cargo transport requirementsfor the Mars expedition,the Lunar Observatory, or the evolutionarycasestudies, launch systems with an annual capacity to deliver multimillion-pound payloads are required. These systems must include vehicles with an individual capabilityof at least 91 metric tons (200,000 pounds). This assumes that a significant amount of on-orbit assembly is possible, which must be validated with further study. To minimize on-orbit assembly, a vehicle with even greater capacity is required. The development of the heavy-lift launch vehicle, with capability to deliver up to 91 metric tons, must stay on track andbecomeoperationalby approximately2000.In the interim, to support prerequisitetechnology demonstration missions and science precursor programs, the Shuttle-C(Shuttlecargovehicle)oran equivalentshould be operationalby the mid-to-late1990s. Personneltransport solutionsare stillunder study,but someaugmentationwill probablybe needed. Theexact degreeto which enhancement is required depends on the amount of onorbit assemblyand vehicle processingthat is performed by the crew, but in the near term, various methods of increasing our current capability must be examined. Personnel transport and orbital housing could present a majorissueif morethan 20crewmembersare required in addition to the dedicated SpaceStationFreedom personnel. Life SciencesResearch To permit safe, productive, long stays in space, the life sciences research program to assess, understand, and alleviate the effects of long-duration spaceflight on the human physiologicaland psychological condition is of primary importance. In general, missions to the Moon arefarlessdemandingof prerequisitelifesciencesneeds, i primarilybecauseof short flightsand staytimes, and the ability to use the Moon as a “real-time” life sciences I 35 Technical Summary laboratory, as in the evolutionary scenario (CaseStudy 4). Analysis indicates that with investment in the life sciencesbase researchprogram,combinedwith research definedintheproposedLifeSciencesStrategicPlan,Case Study 3 and the lunar portion of Case Study 4 could be initiated without additional precursor human research. To support direct expeditions to Mars (Case Studies 1 and 21, additionalresearchprogramsmust be planned in areas of artificial gravity and closed loop life support systems. Someof the life sciencesresearch for the Mars portionof CaseStudy4 will be conducted in the Moon’s one-sixth gravityenvironment during the lunar portion of this case. Also,for direct expeditionsto the Mars system, a very significant driver in terms of both vehicle design and crew capability is the long-term gravity environment thatcanbesafelytoleratedbythecrew.Thereiscurrently substantial uncertainty in the assumed success of the zero-gravitycountermeasureprogram forlong-duration spaceflight. Thus, anintensiveartificial-gravityresearch program pursued in parallel with the zerogravity countermeasures program is a high-priority need. Research investmentsmust be made immediatelyto determine whether an artificial-gravityor zero-gravity environment isrequired. Thisinformationmustbe available by 1998 to maintain a first-decade landing schedule; therefore, this research should begin no later than FY 1990. Maintaining cooperation with the U.S.S.R. in life sciencesresearchwouldbemostvaluable,asthiscangive early indications of the zero-gravity/countermeasure program’s probability of success. Since this issue is fundamental to NASA’s ability to executeany of theseexplorationmissions,itisabsolutely critical that an in-depth understandingof the integrated programsand program interactionsbe developed early. Research needs to focuson developingzero-gravity and artificial-gravitystrategies(lifesciencesprogramsaswell asvehicledesign)that maximizethe abilityto respond to all potential outcomesand minimize impactsto vehicle and mission design. A sampleof the type of integrated strategy needed is offered in Figure 13. ScientificPrecursorMissions Thecasestudiesmandatea varyingnumberand scopeof robotic precursors. Suchmissionsare required to define the environment in which spacecraft and crew must function, by acquiringvaluable scientificand engineering data. These missions also serve as technology and engineering demonstrations for such capabilities as

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OEXP Technical Report, FY 1988,Vol. I I P A V I LIFE SCIENCFS COUNTFRMFASURF,SIAWlFlClAELmQmm I I I INITIATE VEHICLE A/B I WILL ZERO-G CM BE EFFECTIVE? INITIATEVGRF a GROUND RESEARCH HUMAN-RATED DEFINITION I - RESEARCH - CENTRIFUGE I - SHUTTLE FLIGHT - ZEROG - I SFLIGHTRESEARCH DEFlhllTlON - INTERNALG I - ROTATING I I I I ZERO4 I CONCEPTS I I PROCEEDW/7!ERO-G VEHICLE =SYSTEMS EXPOSURETO DESIGN U D DEFINITION FOR PARTIAL4 BE NO. CASE STUDY 4 BEGIN DESIGN OF LUNAR GRAVITY RESEARCH FACILITIES WILL TEMPORARY - ACCOMMODATECM + u(pLomnoN EFFECTIVE? EQUIPMENT I VEHICLE I I I I #TERN ALQ I ROTATING CONCEPTS I I CONCEPTS - HUMAN-RATED CENTRIFUGE NO, CONnNUOUSO REWIRED PROCEED WmER0-G VEHICLE I SYSTEMS DEFINITION DESIGN U D I - INTERNAL I - ACCOMMODATE CENTRIFUGE I - ACCOMMODATECM I EQUIPMENT I I I I I CENTRIFUGE BEGINVGRF DEVELOPMENT PROCEED W/ROTATING-G VEHICLE DESIGN WHAT ARE THE ARTIFICIAL-G I CONCEPTS CID I PARAMETERS PARAMETERS? e! - ROTATONRATE VGRF - ACCOMMODATECM - I EQUIPMENT I I ARMLENGTH - G-LEVEL - CORIOI-ISLIMITS - GRADIENTS Figure 13.-Typical composite strategy for life sciences research & exploration vehicle development landingaccuracy,aerocaptureatMarsandEarth, surface mobility, and autonomous rendezvous and docking. Additionally, for the evolutionary case, sample return from the Martian moons is necessaryto plan propellant extractionand processing. Keeping suchmissionsasthe MarsObserver,LunarObserver,andMarsRover/Sample Return on schedule will provide much of the precursor data, demonstrate incremental achievement, and serve to provide important interim milestones in a very long program. An added benefit is that building on the tradition of international cooperation through pintly conducted robotic space sciencemissions can serve as a foundation of near-term experience toward potential cooperation involving longer-term human exploration ventures. SDace Station Freedom As a base to gainlongdurationoperationsexperience,to conductlifesciencesresearch,andto functionasa testbed to demonstrate technology, Space Station Freedom's contributions to human exploration of the solar system are monumental. Bringing these capabilities on line 36 within the current planned schedule will do much to protect our long-term options. Space Station Freedom will most likely serve as a transportation depot; therefore,itiscertainlynottooearly tobeginnowtodefineand develop the evolutionary requirements for Freedom. If SpaceStationFreedomdoesbecome the LEOtransportation node, the possibilityof the on-orbit assembly,staging, and launch operations consuming all of Freedom's resources for extended periods of time must be clearly understood. The scale of these requirements will be driveninlargcmeasurebywhethertheinitialdestination is the Moon or Mars. Therefore, in order to have the appropriate capabilities in place by the time they are needed, a pathwaydecisionin 1991or 1992is important. SpaceStationFreedommay also pl,aya role in the development of artificial-gravity facilities; the life sciences researchmentionedaboveisneededin 1990todetermine this. At this time, the key considerations are to begin to definereferenceevolutionconfigurationsconsistentwith our explorationcasestudy requirennents,and to develop the advanced technology and program planning that ensures readiness to enhance Space Station Freedom's capabilitiesat the turn of the century.

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Key to the near-term investment strategyis to refineand focusthedevelopmentof technologiesrequiredforhuman exploration through the Pathfinder program, which is pushing advanced technology in the areas of surface exploration, in-space operations, propulsion, nuclear power systems, aerobraking, automation and robotics, humans-in-space,spacetransfervehicles, telecommunications,navigation,informationmanagement,andmany others. Because the period between study initiationand actual mission applicationcan run from eight to twelve years, it is imperative that the commitment to this advanced technology endeavor be sustained. It is also important that, as OEXP exploration studies mature, Pathfinder program research is focused on areas that directly feed into theOEXPplans. In order to contribute to eventual mission design, the Pathfinder technologies must achieve the necessary degree of readinessby the mid-1990s. Funding levels currently planned cannot meet case study requirements, and augmentations (or case study schedule adjustments)are necessary. In addition to enhancements, certain technologies will requiremajor ground or flightdemonstrationsaspart of theprogram developmentprocess. Theseinclude: aerobrakingdemonstrationsbeyond theCivilianSpaceTechnology Initiative’s Aerodynamic night Experiment, cryogenic fluid handling in space, closed ecological life supportsystems,fractional-gravityspacecraftprototypes, and nuclear power systems. 37 Technical Summary Communicationsand Data Trackmg. Telecommunications,navigation,and informationmanagement (TNIM)capabilities will require upgrading to supporttheOEXPhuman exploration initiatives. There exist a number of options for the architecture of such support systems. The choice of options to pursue will dependupon a number of factors,includingthe selected exploration scenario and its mission needs, the overall cost-effectivenessof the resulting architecture, NASA life-cycle costs, and the support needs of current unmanned NASA and internationalcooperativemissions at remotebodies. Afinaldecisionon thehuman exploration strategywith which to proceed is planned for early 1990s; therefore, all candidate support options must be identified and analyzed early and the implications of eachoptionmustbeunderstoodforeachexplorationcase study. Our case study approach has demonstrated much of what isneeded to accomplishmissionsto the Moon and Mars. Much detailed research and investment are r e q u i d during the next 10yearsto provide the necessary foundationto enablehuman exploration in the firstdecade of the upcoming new century.

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Conclusions and Otmortunities Technical Summary broad spectrum NERVA learning experience are warranted in future As aresultof thisprocessof developinga of strategies and approaches, a fairly extensivebase of informationhas been developed that has enabled some new insights to be gained. One key finding from this activities. Technology Demonstrations. A major feature of the year's studies is that the strategies and approaches human exploration initiatives is that the eventual sceemployed in somecasestudieswere good choices,and in othercasestudieswere bad choices. For example,for the Mars Expeditions,the choiceof missionprofile, transfer vehicle and surface habitat mass and volume, and LEO forecastingtechnologydevelopment is a complex probpropulsion system, etc., drove the mass in requirement to values that are prohibitive. While the scenarioemployed for the Mars Expeditionsturned out narioormissionproposedtobeflownwillrequiretheuse of several new technologies. The groundrules for the preliminary assessments provide a certain latitude in assumingwhat technologieswillbe availab!e. (Although lem, it is certainlyappropriate at this stage of the analysis.) However, one related issue is that major ground base of and/or flightdemonstrationswillberequired forcertain to be a bad choice,having that result to add to the informationis important. The "lessonslearned" overthe past year will be applied, in a continuing process of technologies, such as aerobraking, cryogenic fuel handling, closed-looplife support systems, fractional-gravstudy, to the redirection and definition of future work. ity spacecraft prototypes, exploration vehicles (such as Some key insights into the human initiatives activities the Phobos ExcursionVehicle), nuclear power systems, and broad issues that need addressing in future studies and Ku-band tclecommunications.Thesedemonstration are discussed below. New InsiPhts Nuclear Power. Nuclear power concepts for both NEP projects are long-lead-timeissues and must be resolved prior to initiation of mission development. In order to preserve schedules 15-20years in the future, these projects must be initiated immediately. and planetary surface applications need further defini- Launch Year Sensitivity. A fundamental aspect of mistion and study. Case Study 4, for example, assumes a sions to Mars is the sensitivity of the Earth-to-Mars initial power level of 5 sprint-classtrajectoryto launch opportunity; this sensi- NEP Cargo Vehicle with an megawattsandspecificmasslevelsof5to lOkg/kWefor tivityisillustrated in Figure 14. TheIMLEOrequirement both lunar and Mars sorties. At this time, the feasibility can vary as much as 60 percent from opportunity to of such multi-megawatt, lightweight nuclear power opportunity. These issues have profound effects on sources is an outstanding issue. Studies and ground- spacecraftdesign resiliency to meet launch delays. The based system tests must be initiated to validate the elec- implicationsto program cost to design a common intertric cargo vehicleconcept for the evolutionary case. planetary transport capable of capturing the mission in severalconsecutiveopportunitiesare enormous. Therehave assumed that nuclear fore, optimum launch opportunities must be protected, The Fy 1988study activities reactors are viable power sources for planetary surface or study activities must be initiated to develop options of the SP-100 technology for these for decoupling the mass performance from launch year activities. The use applications is explicit in Case Study 3, and implicit in CaseStudy4. However, theSP-100program initscurrent fortheEarth-Marsmissionlegs. Potentialsolutionsareto return to the use of conjunction-classtrajectories,which form as a space-based reactor does not enable surface are less sensitiveto celestial geometry,or to use opposipower for either case study. Studies need to be performed to fully conceptualize these nuclear power systemsforplanetary surfaceapplications. Also, theoutput would have to be extended to the multi-megawattrange for the NEP applications envisioned for Case Study 4. Preliminary assessments demonstrated that the applicationof NuclearThermal Rocketsto thecasestudy scenariosresulted in mass savingsin LEOcomparableto the use of aerobraking technology. The feasibilityof the NTR concept was proven with experimental prototype NTR engine test-firing in the late-1960s as part of the NERVA program. Follow-on studiesthatbuild upon the tion-classtrajectories,which haveintermediateperformance demands. Life Sciences. Throughout the FY 1988 studies, the issues of life sciences,i.e., advanced medical care, longduration exposureto zerogravity,long-termexposureto the natural space environment (radiation), life support, and space human factors, have not been specifically addressed. Although these issues have been acknowledged, they have been assumed to be solvable in the timeframeunder consideration;however, they can have significant impacts. In fact, the answers to the life sciences issues will be mission design drivers. Crew size

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OEXP Technical Report, M 1988, Vol. I 50001 1 2003 2005 2007 2009 2011 2013 2016 2018 MUNCH YEAR Figure 14. Initial LEO mass requirementsensitivityto launchyear for human Mars missions and adaptabilityto zero gravity(orthe need for artificial gravity) and space human factors answers will drive spacecraft design. The resiliency of the human body to varyinggravityloadsand radiationhazardsexperienced throughout the mission will determine mission operationsschedulesand the explorationsequencing. Knowledge in allof the life sciencesareasis critical. Phobos Operations. The expedition to Phobos representsthe first opportunityfor human explorationin the Martian system without the associated complexity of landinguponMars.However,Phobospossessesaunique set of environmentalcharacteristicsthat make mission planningfor human explorationof this moon extremely challenging. First, due to the low gravityconditions,the ability of humans to remain on the surface is a major issue. Related to maintaining surfacecontact to createa stablework platform is the issue of surfacemobility for the human explorers. A third area requiring more detailed studyistheissueof dust particlecontaminationas a result of Phobos’s surface conditions in combination with the low surfacegravity. ScienceObjectives. TheScienceobpctivesof thehuman 40 exploration missions were synthesized in FY 1988 and q u i r e more detailed definition than currently exists. Thescientificcommunityatlargeneedstobeinvolvedin order to provide guidance to the definition of the case studies. Once these objectivesare more clearly defined and understood, they will be integrated into the case study mission scenariosfor compatibility. Lunar Helium-3. The use of lunar He3 to provide nuclear fusion power on Earth could become the first truly extraterrestrial commercial venture with application and profit potential back on Earth. This is an area that demandsa more detailed assessmentin FY 1989. If the feasibilityand practicalityof mininglunar regolithto extractHe3can be proven, thiscapabilitywould have a far-reaching impact not only on human exploiation missionsbut also on global commerceas well. Case Studi a Human Expedition to Phobos. The Phobos mission could be an excellentprecursor to a manned Mars landingmission. TheroboticexplorationofMarswillprovide improved knowledge of the Martian environment, and

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i Technical Summary mission also will provide a unique opportu- more probably, it would be carried out in combination the Phobos nity to perform a systems checkout and verificationof withotherlunar utilizationprograms(e.g., lunar oxygen without the increased production for Mars exploration). A formal study of a flighthardwareand environment difficulty of a Mars landing. Therefore, future studies combined program isnot proposed; however, thefundashould consider the .shaping parameters for a Phobos mentalshapingparametersof suchacombinationshould mission as a precursor for a manned Mars landing. Thisdocumentpreviouslyrepottedon the effectsof new technologies, such as aerocapture and nuclear thermal rockets,inreducingtheinitialmasstoLEOforthePhobos be understoodsothatwedo not pursueoptionsthat may not be feasible.Forexample,permanenthabitationfacilities and continuous crew presence could have a major impact on the character of the Lunar Observatory. and any possible consequences, ThesciencefacilitiesontheMoonwillrequirethedeploymission. These effects, stud- ment of large, complex arrays. Although significant shouldbe exploredin greaterdepth in subsequent ies. In addition, reducing the crew size to two, for example,furtherreducesthemassinLEOrequirement,and subsequent ET0 launches and space assembly operations. This crew of two conceptwas addressed at only a cursory level in FY 1988 and the potentially serious operational drawbacks to this approach must be addressed in greater detail in future analyses. At thelevelof detailstudiedin FY 1988,it isnot clearthat the need for a LEOnode has definitelybeen ruled out. If the requirement for no LEO node is maintained for the Phobosmission, then this is a key mission design study. Another area of future work that directly impacts the issue of a LEO node is the evaluation of the impact of artificialgravity/conjunctionclass flight modes for the Phobos Expedition. Human Expeditions to Mars. Of the four case studies analyzedin FY 1988,the Mars Expeditionshave themost LEO. activityperformed in parallel by the Power and Propulextensiverequirements in terms of initialmass to All possibilities of reducingthe mass requirementsfor the wars Expeditionsmust be explored. Onepossibility is to evaluatethe impact on Mars Expeditionsof “scaled down” vehiclesand systems. A second concept requiring further study is the use of the artificial-gravity/ conjunction-classflight mode. Two aspectsof theMarsExpeditionsthat were not studied in detail this year were (1)the requirement for serial visitsto the Martian moonson subsequentmissions; and (2) the requirement for accessing Mars landing sites at latitudesbeyond 45 degrees(northor south). The intent of havingsuchcapabilityisnot only forexpandedexploration purposes, but also because there exists a greater probabilityfornear-surfacewater,a valuablecomponent for life support and propellant production: both necessary ingredients for follow-on missions. The s~enarios human interaction will be required for the assembly, deployment, operation, and servicing, the use of highly automated robotic assistance is a new technology that merits furtherdetailed investigation. Lunar Outpost to Early Mars Evolution. The technical understanding of Case Study 4 did not mature early enoughin the FY 1988 study cycleto enablean in-depth analysis. Consequently, the mission design, element configurationdefinition, and overall case study synthesis were accomplishedwithin the MASE function. The analysis performed this year assumed the use of lunarderived propellants, and, in the later years, of Phobosderived propellants. The use of propellants derivedfromMarsitself wasnot includedin theanalysis and isan interestingoption. Also, the analysisusing the Electric CargoVehicle in this year‘s study activitieswill requireupdatingnextyear,duetothein-depthdefinition sion SpecialAssessment Agents. A thirdrequirementforfuturestudyis to extend thecase study time spanbeyond the first three Marsmissions,in order to investigate the advantages of using Phobos propellants,andalsotherequirementforadditionalelectric cargo vehicles. Prereauisite Pro- In mostcases, theprwequisiteprogramanalysesdemonstrate compatibility between the exploration mission supportneedsandtheabilityof theNASA Headquarters program offices to accommodate those needs. A few areasthatremainoutstandingand haveneed forfocused , attentionin subsequentstudiesare: I required to meet these objectives may have substantial 1. ET0 launch rate and capability versus on-orbit as- 1 impactson missionperformanceand, consequently, initial mass in LEO. Therefore, study activitiesto resolve these two issues must be targeted for futureplanning. I Lunar Observatory. The Lunar Observatorycase study has been defined and studied as an independent proi gram. Viewed realistically, this is not likely to occur; semblyoptions 2. Precursor missionsinteraction with the exploration mission programs; specifically,the development of I planetary environmentsdocuments 3. Strategiestomergezero-gravityandartificial-gravity 41

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OEXP Technical Report, FY 1988, Vol. I Life SciencesPrograms with exploration case study schedules 4. A better understanding of the technology needs of the ExplorationProgramasoutlinedabove,coupled with a technology development program that is compatiblewiththeExplorationProgrammilestones. 5. Further in-depth definition of exploration systems and elementsto uncoverlatentadvancedtechnology needs. ET0 Transportation vs. On-Orbit Assembly Capabilities. It isnot obviousthat theobjectiveof no requirement for a LEOnode has been satisfied by the Phobos mission design. To solve this problem requires a more focused, integrated study of the linkagebetween the ET0 launch vehiclesand the space transfer vehicles. Concepts to be investigatedinclude: common stages, tethered concepts for fuel transfer, and very large launch vehicles. Precursor Missions. The FY 1988 studies identified many areas and opportunitiesfor interactions and mutual support between science missions and exploration missions (e.g., technology demonstration, atmospheric data, etc.). Future work for subsequentstudies needs to be focused in two areas. Oneis to concentrateon further identificationof explorationprogram needs and opportunitiesfor mutual support. Theother is to begin assessment of the value added to the exploration engineering design, mission safety,and system certificationby alternativeprecursorstrategiesin order that optimum strategies can be planned. 42 The background information that facilitates this understandingcan be found in the PrerequisiteRequirements Document(PRD)and the planetarydesign environment document. Future work in the exploration case study area should be focused on developingan accurateset of requirementsforthe PRD. Regardingprecuirsor support programs, attentionshouldbe focused on the planetary design environment documentas well as potential precursor missions. The planetary design environment document should be produced in response to the PRD and shoulddemonstratehow variousprecursormissions can improveknowledge of planetary envircmments. Life Sciences. The Life Sciences Program for development and understanding of zero-gravity countermeasuresand artificial-gravity techniqueshas b~=comemore matureduringFY 1988.Sincethisissueissofiindamental to NASA's ability to execute any of these exploration missions, it is absolutelycritical that an indlepth understandingof the integrated programs and prcgram interactions be developed early. Research needs to focus on developingzero-gravityand artificial-gravitystrategies (both Life Sciences Programs as well as vehicle design) that maximize the ability to respond to all potential outcomes of the Life Sciences Program and minimize impacts to vehicle and mission design. Technology. The Technology support program needs for focused attention and subsequent studies were addressed earlier. Any of these issuescan be resolved through alternative case study strategies,accelerated technology programs, or interim, less optimum, solutions until technology readinessisachieved. Futurework shouldassignspecial trade studiesto investigatethese issuesand recommend solutions.

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1 TechNcalSummary This Technical Summary uses a number of acronyms, abbreviations,and special terms. In order to facilitatethe reader's comprehension of the text, a glossaryis presented here. ACRONYMS AND ABBREVIATIONS ET0 - Earth-to-orbit EVA - extravehicularactivity He-3 - helium-3 IA - Integration Agent IMLEO - Initial mass to low-Earthorbit IVA - intravehicular activity - propulsion system specificmass; power plant mass p e r kilowatt of jet power output kW - kilowatt kWe - kilowatts electric kWt - kilowatts thermal lbf - pound-force LEO - low-Earth orbit LH2 - liquid hydrogen LLO - low lunar orbit LOX - liquid oxygen LSS - Life Support System L1 - Earth-Moonlibration point MASE - Mission Analysis and System Engineering MWe - megawatts electric MWt - megawatts thermal NASA - National Aeronauticsand SpaceAdministration NEP - Nuclear ElectricPropulsion NERVA - Nuclear Engine for Rocket Vehicle Application NLB - Nuclear Light Bulb NTR - Nuclear Thermal Rocket OEXP - Officeof Exploration PRD - PrerequisiteRequirementsDocument PV - photovoltaic SAA - Special IntegrationAgent SRGCR - Spaceradiatorcooled, open cycle gas core rockets t - metric ton TNIM - Telecommunications,Navigation, and InformationManagement 43

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Technical Summary - Aerobrake- Aerodynamic brake foruse in planetaryatmospheres. Aerocapture- A techniqueof capturinga heliocentricspacecraftinto a planetary orbit, using an aerobrake. Beneficiation- Improvingthe chemicalpropertiesof an ore so that metal can be recovered. Cislunar- Of or in the region of spacebetween Earth and the Moon. Crvopenic propellant - Propellant that must be stored at very low temperatures, e.g., liquid hydrogen and liquid oxygen. Earth flyby injection maneuver - Interplanetary trajectory injection technique whereby the spacecraft makes a powered flyby gravity-assistedmaneuver at Earth to reach critical injectionenergy. Electric Cargo Vehicle- Unmanned cargo vehicle propelled by Nuclear Electric Propulsion System. Exploration Requirements Document - Publication produced by the Officeof Exploration that levies,the overall exploration themes and objectivesto initiate the FV 1988studiesactivities. Extraterrestrialprowllant - Rocket fuel produced by the extractionof the appropriateconstituentsfrom a planetary body’s environment. Extravehicular activitv- Any human activity outside protectiveshirt-sleeveenvironment and requiring a spacesuit. Helium-3- The isotope of helium with mass number 3, constitutingapproximately 1.3parts per million of naturally occurring helium on Earth. In sufficient quantities, potential fuel for nuclear fusion reactors. Heaw Lift Launch Vehicle- Earth-to-orbit vehicle with payload lift capabilitygreater than 90 t to low-Earth orbit. in situ - Latin expressionmeaning “in place” used to refer to extraterrestriallocations. Onecommonusage isin situ propellant production, which is synonymouswith extraterrestrialpropellant production. -L1- Libration point; critical point in Earth-Moon space where a body at rest would remain unless disturbed by an external force. Launch stack - The completely assembled interplanetary transport vehicle plus all propulsion stages prior to the departure injection maneuver. Leverage - Used to refer to any savings or benefits accrued through the incorporation of a particular option or capability. Low-Earthorbit- A circularorbit about Earth with an altitude of approximately300 to 500 km. Low-Lunarorbit- A circular orbit about the Moon with an altitude of approximately 100km. Lunar dav/nieht - Approximately 14 Earth days each. The Moon completes one revolution about Earth in approximately 28 days. MametotAasmadvnamics- The generation of electriccurrentby shooting a beam of ionized gas throughL a magnetic field. I ”Mamum” Heaw Lift Launch Vehicle- Earth-to-orbit vehicle with 200-250 metric ton capabilityto low-Earthorbit. 44

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I OEXP TechnicalReport, FY 1988, Vol. I M i s s f i s s- The Mission Analysis and System Engineering (MASE) is a Level 11 implementationfunctionof theofficeof Exploration. TheMASEgroupwilldecomposethescenariorequirementsinto collectionsoftop-level, functionalrequirementsthat must be accomplishedby the IntegrationAgents (IAs). The IAs willdevelopconceptsthatimplementtheserequirementsandfurnishthisinformationto MASE forintegratedsystems synthesisand total scenariooption evaluation. MASEwill alsodevelopscenario-dependentstudyissuesfortheSpecialAssessmentAgents(SAAs)and, asresultsare availablefrom the SAAs, will assesstotal scenarioimpacts. 1 National SpacePolicv and ExplorationGuidelines- Thepolicyspecifiesthat in conjunctionwith otheragencies: NASA will continuethe lead role within the Federal Government for advancing space science, exploration, and appropriate applications through the conduct of activitiesforresearch, technology, development,and related operations. SpaceScience- NASA, with the collaborationof other appropriateagencies,will conducta balanced program to support scientificresearch, exploration, and experimentation to expand understanding of (1) astrophysical phenomena and the origin and evolution of the universe; (2) the Earth, its environment and its dynamic relationshipwith the Sun; (3) the origin and evolutionof the solar system; (4) fundamentalphysical, chemical, and biological processes; (5) theeffectsof thespaceenvironmentonhuman beings;and (6)the factorsgoverning the origin and spread of life in the universe. SpaceExploration- In order to investigatephenomena and objectsboth within and beyond the solar system,the policy statesthat NASA will conduct a balanced program of manned and unmanned exploration. - Human Exploration-To implement the long-rangegoal of expandinghuman presenceand activitybeyond Earthorbitintothesolarsystem,thepolicydirectsNASA tobeginthesystematicdevelopmentof technologies necessary to enableand supporta range of future manned missions. Thistechnology program (Pathfinder) will be oriented toward a Presidential decision on a focused program of manned exploration of the solar system. - Unmanned Exploration- The policy further directs NASA to continue to pursue a program of unmanned explorationwhere such explorationcan most efficientlyand effectivelysatisfy national spaceobjectivesby, among other things, achieving scientific objectiveswhere human presence is undesirable or unnecessary, exploringrealmswheretherisksor costsof lifesupportareunacceptable,and providingdata vital to support future manned missions. Nuclear electricpropulsion - Low-thrust electricpropulsion, with electricpower provided by nuclear reactor. Nuclear liqht bulb- A typeof closedcycle gas core nuclear thermal rocket. Nuclear ThermalRocket- A spacepropulsionconcept in which the heat from a nuclear fissionreactor isused to raise the temperature of the propellant, which is then expanded through a nozzleto provide thrust. Two typesof nuclear thermal rockets have been studied: gascore and solid core. Officeof ExplorationCaseStudies-TheOEXPcase studiesare specificmissionscenariosthat executethe exploration goals according to the objectivecontent of the themes and strategies. Each case study may contain severaloptional I implementationapproaches. The case studieswill be initiative-specific;each case study and its optionalimplementation approacheswill address a single strategy. The fourcase studies analyzed in FY 1988are: I 1. Human Expeditionto Phobos 2. Human Expeditionsto Mars 3. Lunar Observatory i 4. Lunar Outpost to Early Mars Evolution 45

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Technical Summary Office of Exdoration Stratepries- The OEXP strategies present particular opportunities for meeting defined OEXP themes. To organize and systematicallyexamine a full range of optionsfor human explorationand developmentof the Moon and Mars, three strategieswere identified for study in FY 1988: 1)Expeditions, 2) ScienceOutpost, and 3) EvolutionaryExpansion. Officeof Exdoration Themes-TheOEXPthemesdescribebasic, upper-levelobjectivesforspaceexploration: national pride, advancement of scientificknowledge,etc. These themesprovide a synthesisand a translation of the National SpacePolicygoalsinto a set of objectivesthat arecompatiblewith the charter of the OEXP. Thesethemeswill be used to guide the generation of case study development requirements. The OEXP will produce and control the themes. Photovoltaic - Capableof generating a voltageas a result of exposure to visible or other radiation. Precursors Reauirement - Science, technology, or operational data needed as critical path information to enable selection of specific habitation site location, location/objedives of specific user surface activities, systems design options, or specificoperationalapproachesto human exploration. Precursor data are usually obtained via robotic, highly automated missions. PrereauisiteReauirements- A technical space system performance capabilitynecessary for the execution of one or moreexplorationinitiativesor scenarios. Prerequisiterequirementsarepart of the explorationstudyand definecase study-specific technology, space system, and operational support needs at a level of detail sufficient to’enablethe receivingprogramorganizationtoproceed withitsimplementationstrategy:eitherthedevelopmentof newhardware elements, the modification of previously defined or existing hardware elements, or the use of existing hardware elementsin support of the multiprograminitiative implementationeffort. PrereauisiteReauirementsDocument-Publicationproduced by theOEXPlevyingtherequiredsupportingprecursor activitiesupon the other NASA Headquarterscodes. Promllant Tank Farm- Collectionof propellant tanks for on-orbit fuelingof interplanetaryspacecraft. ShuttleC - SpaceShuttlederivativeproposed unmanned cargo vehicle. SP-100- 100-kWe-classof space power systems. Smcial assessment a e n t s - Directors of independent studies targeted toward the identification of high leverage technologies, systems, or operational techniques. SAAs are truly independent and are not used as systems or subsystemdefinition agents for system designers. S M f i c imtmlse- A performance parameter of a rocket engine, expressed in seconds, equal to the thrust in pounds divided by the weight flow rate in pounds per second. Stirling:-eneine- - An engine in which work is performed by the expansionof a gas at high temperature; ‘heatfor the expansion is supplied through the wall of the piston cylinder. Stronzback- Structuralmember that providesrigidity in bending and torsion. Studv Reauirements Document - Publication produced by MASE levying the case study ground rules upon the integration and specialassessment agents. Teleowrator- A general-purpose,remotely controlled, cybernetic,dexterousperson-machinesystem. Telerobotic- Refemng to automated systemsoperated remotely. 46 *U.S .COVER”ENT PRINTING OFFICE:1988-661-008/80846

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REPORT DOCUMENTATION PAGE I 1 . Report No. 2. Government Accession No. 3 . Recipient's Catalog No. TM-4075 4. Title and Subtitle OEXP EXPLORATION STUDIES TECHNICAL REPORT Vol. I: Technical Summary 7. Author(s) 9. Performing Organization Name and Address Lyndon 6. Johnson Space Center Houston, Texas 77508 12. Sponsoring Agency Name and Address National Aeronautics and Space Administration Washington, 0. C. 20546 E u p p l e m e n t a r y Notes 16. Abstract 5. Report Date December 1988 6. Performing Organization Code 8 . Performing Organization Report No. I 10. Work Unit No 11. Contract or Grant No. 13. Type of Report and Period Covered TM - FY 1988 14. Sponsoring Agency Code The Office of Exploration (OEXP) at NASA Headquarters has been tasked with defining and recommending alternatives for an early 1990's national decision on a focused program of human exploration of the solar system. The Mission Analysis and System Engineering (MASE) group, which is managed by the Exploration Studies Office at the Lyndon 6. Johnson Space Center, is responsible for coordinating the technical studies necessary for accomplishing such a task. This technical report, produced by the MASE, describes the process that has been developed study" approach. The four case studies that i n a "case were developed i n FY 1988 include: 1. Human Expedition to Phobos 2. Human Expeditions to Mars 3. Lunar Observatory 4. Lunar Outpost to Early Mars Evolution The final outcome of this effort is a set of programmatic and technical conclusions and recommendations for the following year's work. 17. Key Words (Suggested by Author(s)) 18. Distribiti,on Statement Interplanetary flight Transfer Vehicle Trajectories Lunar Science Robotics Mars Transfer Teleoperation Earth-to-Orbit Transportation Martian Moons Lunar Mining & Oxygen Production Unclassified - Unlimited Category 91 19 Security Classification (of this report) 20. Security Classification (of this page) 21. No. of pages 22. Price Unclassified 47 Uncl assi f ied For sale by the National Technical Information Service, Springfield, VA 22161-21 71 JSC Form 1424 (Rev Jan 88) (Ethernet Jan 88)