The Space Launch System's Enablement of Crewed Lunar Missions and Architectures

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CrewedLunarMissionsandArchitecturesEnabledbythe
NASASpaceLaunchSystems
BenjaminDonahueandSheldonSigmon
BoeingExplorationLaunchSystems,Huntsville,Alabama,35806
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Abstract
TheNASASpaceLaunchSystems(SLS)outstandingcapabilitiesforlaunchingheavy,largediameterpayloads
willenablerobustHumanLunarandMarscampaigns.Lunararchitecturescurrentlybeinganalyzedinclude
bothmulti‐launchvehicleandSLSonlycampaigns.FortheLunarArchitecturetheNearRectilinearHaloOrbit
(NRHO)isus eda san agg regationnodeforth ela nde r,t ran sferstageandOrionelements.TheSLScapabilities
toLaunchLanderelementsisdiscussed,asisthestatusoftheSLS,andthenewlargeExplorationUpper
Stage,currentlyindevelopment,whichwilloptimizetheSLSCoreandBoosterStages.
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I.
TheNASASpaceLaunchSystem
SLS consists of a series of increasingly
capable vehicles to incrementally
expand Beyond Earth Orbit (BEO)
exploration from lunar space and then
to Mars. The SLS Block 1 utilizes the
Interim Cryogenic Propulsion Stage
(ICPS) and the Block 1B features the
new,largeExplorationUpperStage
(EUS).TheICPSisaderivativeofthe
Delta‐IV upper stage; the EUS is in
development. Only the SLS can deliver
the 27.5 mt Orion Crew Vehicle to the
Moon; it delivers significantly more
payloadtoLEOandBEOdestinations
thananyotherexistingorplanned
launch system. Payload capabilities to
Trans‐Lunarinjection(TLI)are shownin
Fig.1fortheFalconHeavy(left),theSLS
Block1B,Block2andtheVulcan(right).
The Block 1B/EUS has a TLI capability
between39and43mt.Thelater2030’s
eraSLS Block 2would provide a53 mt
TLIcapability.Byenablinglargermargins
inthedesignofexplorationplatformsand
theabilitytosendmultiplecopiesofatmosphericandsurfaceprobes,higherresolutionspatialandtemporaldatacan
becollectedinasinglemission. Missionriskcanbereducedbyincreasing theredundancyofeachindividualsystem
andthearchitecturebyusingmultiplecopiesofthesamesystems.
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II.
SLSCoreStageDevelopment
TheSLSBlock1isprogressingtowardaFY2020launch.MajorassemblesareinmanufactureandtestatNASAMichoud
AssemblyFacility(MAF)andacompleteCorestagewillentertestingatNASAStennisSpaceCenter(SSC)in2020.InFig
2theCoreStage’sforwardsection(Forwardskirt,LO2tank,andintertank)isshownjoinedtotheAftLH2Tank.InFig4
Figure1LaunchVehicleLunarPerformanceinMetricTons(mt)

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theCoreStageForwardSkirtisshown.TheCoreIntertankisshowninaNASAMSFCteststandinFig.5.
Figure2SLSCoreStageatMichoudAssemblyFacility(MAF)
Figure3InspectionofSLSBarrelSection
TheEngineSectionutilizesfourhighIspLO2/LH2RS‐25enginesprovidingover2millionpoundsofthrustatliftoff.The
fourRS‐25engineswillconsumeapproximately4,500lbofpropellantpersecond.

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Figure4SLSCoreStageForwardSkirtatMAF
Figure5SLSCoreStageIntertankStructureinTestatNASAMSFC

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III.
InterimCryogenicPropulsionStage(ICPS)
Theinitial Block 1 versionof the SLS usesthe Interim Cryogenic Propulsion (ICPS) Upper stage, whichis a close
derivativeoftheDelta‐IV5.0mdiameterUpperstage.TheICPS and Orion is supported by the Launch Vehicle
SpacecraftAdaptor(LVSA).TheICPSispoweredbyasingleRL10‐C1engine.ThefirstflightoftheBlock1isscheduled
forlate2020,andwillcarryanuncrewedOrionspacecraftaroundtheMoon.
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Figure6SLSICPSUpperStageatNASAKSC
Fig.6SLSCoreStageLiquidOxygenTankStructuralTestArticleArrivingatMSFC

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IV.
ExplorationUpperStage(EUS)
TheEUSisthenextevolutioninthedevelopmentoftheSLS.TheEUSoptimizesthepowerfulSLSCoreandBooster
Stages and greatly increases the SLS injected payload capability. The EUS is a multi‐mission stage with
accommodationsformissionmodificationkitsandvariablepropellantloadingcapability;itisasuspended stage
poweredby4RL‐10enginesandincreasesthecapabilityofSLSvstheBlock1withtheICPS.TheEUSisroughlyfour
timesthemassandfourtimesthethrustofICPS.RelativesizesofupperstagesaregiveninTables1and2.TheEUS
isdesignedtoprovide43.0mttotheMoon,enablingrobust,sciencerichexplorationmissions.
Table1LargeUpperStagesComparison
Table2ICPSandEUSParameters

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TheEUSconsistsof7 major elements (Fig. 8), including theForwardSkirt,
LH2 Tank, Mid‐body, LOX Tank, Equipment Shelf, Thrust Structureand
Engines. These elements support an array of systems including avionics,
pressurization,RCS,mainpropulsionsystems(MPS)andsensors.
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TheEUSForwardSkirtactsastheinterfacetotheIntegratedSpacecraftand
PayloadElementandtheEUSLH2Tank.Theforwardskirtstructureisan8.4
mdiameter,1.8mlongOrthogridbarrel.
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TheEUSLH2Tankisusedtostoreuptoapproximately78,000gallonsofLH2
at cryogenic temperatures of −423˚ F (−253˚C). The primary structure is
madeoffrictionstirwelded,ellipticallyshapeddomesandOrthogridbarrel
section.Keepingthetankatcryogenictemperaturesandtopreventicing,the
tankiscoveredwithspray‐onfoaminsulation(SOFI).
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TheEUSMid‐bodyiscomposedofanaftadapterandmetallicV‐strutswhich
providetheprimarystructuralconnectionbetweentheLH2andLOXtanks.
The Mid‐body is also the primary support for the vehicle pressurization
system,communicationshardwareandantenna.
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The5.5 mdiaEUSLOX tankholdsup to 25,000gallonsof ‐297˚F(‐183°C)
LOX.Th eLOXtan kisalso theinterfacefo rthethruststru cturewhichattaches
tothedomeandanequipmentshelfwhichattachestotheaftflangeofthe
tank.
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The EUS equipment shelf is a honeycomb panel,ortho‐grid plate and bracketed design to support the avionics and RCS
structuralneeds.TheshelfisattachedtotheLOXtankflangebystruts.Avionicscomponentsthataresupportedontheshelf
areflightcomputers,guidanceandnavigation,powerdistributionsystemandRL‐10enginecontrols.Propulsioncomponents
supportedincludetheRCSanditshydrazinepropellanttanks.
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Figure8SLSExplorationUpperStage
Figure9SLSICPSandEUSTLICapabilityBreakdown

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TheEUS ThrustStructureis anI‐beamand strutconstructionattachedtothe LOXtankdome.Thestructureistheprimary
structuresupporting4RL10engineswhichprovideacombinedthrustcapabilityof99,000lbf.
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TheInterstageattachestheEUStotheCoreandsupportstheEUSduringCoreflight.Thisstructuremustsupporttheweight
ofeverythingontopoftheCoreStage,whichcouldbeinexcess180mt.Theinter‐stageisanisogridpaneldesign;contained
withitistheseparationsystemthatutilizesapushersystemtoseparatetheEUSafterCoreStagemainenginecutoff(MECO).
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Fig.10containsacomparisonofLaunchcapabilitiestoTLI.TheSLSprovidessignificantlymorepayloadtothemoonthanany
othervehicle. The Block 1BprovidesasignificantimprovementoverBlock1. The 2030’s era Block2willfacilitateCrewed
Marsmissions.InFig12SLSFairingsizesarelisted.InFig.13aLarge,8mdia.monolithicopticSpaceTelescopeisillustrated.
Figure10Trans‐LunarInjection(TLI)PayloadCapabilitiesforEightLaunchVehicles
Figure11Block1B:IllustrationofOrion/USA/EUSatIgnitionjustafterCoreStageJettison

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Figure12SLSBlock1Band2FairingSizesandVolumes
Figure13SLSEUSand8.0mdiaVeryLargeSpaceTelescopeafterFairingJettison

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V.
NASAHumanLandingSystem(HLS)Architecture
NASA’sreturntotheMoonplaninvolvesaggregatinglanderandtransferstage elements in a Near Rectilinear Halo
Orbit(NRHO).TheretheOrionwillhostthelunarlander.InsomeplanningscenariostheOrionissupportedbyaNRHO
Gatewayplatform (Fig. 14 middle); the Gateway would consist of (ata minimum) a habitation module, Powerand
Propulsion Element (PPE) and a Logistics Module. In addition to the Gateway, thisarchitecture would include four
transportationelements;theAscentElement(AE)(topleft,Fig14),theDescentElement(DE)(middleleft),theTransfer
Element(TE)(bottomleft)and,forlatermissions,aRefuelingElement(RE)(notshown).
In this scenario, the 4 elements are flown out separately and aggregatedinNRHO.Onceready,thecrew
transfersfrom the Orion to the Lander, and the3stage(AE/DE/TE)combinationtransfersfromNRHOto Low Lunar
Orbit(LLO)withtheTEprovidingthedelta‐Velocity(dV).OnceinLLO,theTEseparatesandreturnstoNRHO.Thecrew,
intheDE/AE,descendtothesurface.Afterasurfacestay,theAEascendsdirectlybacktoNRHO.TheREmaybeused
intwoways;first,toreplenish(topoff)theDEtanksinNRHO;andsecond,torefueltheAEandTEforreuse.Foreach
newlunarsortiemissionanewDEandREarelaunched.
IntheNASAdiagram(Fig.14),threetypes of launchers inject theAE,DE,TEandREintoTLI.Includingthe
Orion,thereare5transportationelementsthat operatefromNRHO inthisarchitecture.This scenariocarrieswith it
somedegreeofcomplexityand,toreducethecomplexity,asimplifiedversionofthisarchitecturewasdevelopedand
ispresentedhere.ThesimplificationkeepstheNRHOasastaginglocationandtheaggregationofelementsthere,but
reduces the number of transportation elements, the number of launch vehicle types and the number of launches
required.Forthissimplifiedarchitectureacrewedlunarlanderconceptwasdeveloped.

InFig.15,NHRO orbitisdepicted andmissiondVsarelisted foreachlegofthejourneyfromtheEarthtotheMoon.
AfterinjectionintoTLI,transferdVtotheNRHOis458m/s.Afteraggregationofelements,the(1daytransit)NRHO‐
to‐LLOtransferrequires750m/sdV.ThedescentfromLLOdVis2,100m/s.(Totalone‐way,post‐TLItosurface(through
NRHO)is3,308m/s).AEascenttoNHROrequires2,700m/s.TotaldVis6,008m/s,splitamongTE,DEandAEelements.
As mentioned, the HLS architecture depicted in Fig. 14 is a “3 launch” scenario. For this architecture, In NRHO,
Figure14NASAHLSArchitectureDiagram.TransportationElements(left),LaunchedSeparately,
areAggregatedinNearRectilinearHaloOrbit(center),ThenProceedtotheSurface(right)

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propellant transfer is required to
replenish (top off) the DE tanks.
Thisis because neither of thetwo
non‐SLS Launch vehicles (Fig. 14)
are capable of injecting a fully
fueled DE to NRHO. (Early
estimates of the DE mass place it
over16mtfullyfueled).Thusthe
DE (in this scenario) must be
launched with a partial propellant
off‐load to remain within the TLI
capabilityof thelauncher.Onceat
NRHO, the DE is and RE must
autonomously rendezvous, and
oncepropellant line interconnects
aremadeandverified,propellantis
transferred into the DE’s partially
filledtanksuntiltheyarefully
fueled.
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VI.
SLS“2Launch”SimplifiedNASAHLSArchitecture
ThesignificantlyhigherTLIlaunchcapabilityoftheSLSwillenablethethreeprimaryHLSElements(AE,DEandTE)to
belaunchedin2launchesratherthan3,andwillallowtheDEtobelaunchedfullyfueled.This SLS“Twolaunch”scenari o
eliminatesoneLaunchperLunarSortiemission,andeliminatestheneedtotransferpropellanttotheDEatthegateway.
Itwouldalso,eliminate,or postpone, the necessity for aREfortheinitial series of missions. Once the Architecture
reachesits“sustainability”stage,theREwouldbebroughtintorefueltheAEandTEattheNRHOtoallowthemtobe
reused.In Fig. 16the EUS, Orionand SLS Lander are illustrated.  InFig 17, a SLSlaunchedAE/DE lander conceptis
illustrated(left,inthe8.4mdiafairing).ThisAEconcepthasasingleenginelocateddirectlyunderneathitscylindrical
Ascent Cabin (F ig.17 ‐18).Similarly ,theSLSlau nchedDE conceptalsoutilizesasingleengine.Centrallypositioned,single
engineconfigurationsarelesscomplexthanmultipleenginedesigns;placingasingleengineatbottomcenterensures
thrustisdirectlybelowthevehicle’scenterofgravityatalltimes.Otherconfigurationsareunderstudy,includingthose
thatusemultipleengines;eitherasclusterscentrallypositioned,orindividualenginespositionedaroundtheperimeter
ofthestage.Forthisconcept,theAE’senginenozzleisembeddedinthetopoftheDE.AtthebottomcenteroftheDE
isitsdescentengine.Asshown,theSLSlaunchedAEconcepthasfoursphericalsidemountedtanksattacheddirectly
totheCrewCabin(Fig18).TheDE’s4tanksarepositionedtoallowtheaccommodationoftwoside‐mountedpayload
pallets(Fig16,17)whichallowforeaseofdownloading.Pallets,attachedatahingepointnearthebottom,arerotated
Figure15NASAHLSArchitecture
TrajectoryPhasesandMission
Delta‐Velocities

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downtoahorizontalposition,foreasyaccesstopayloads.Thelarge8.4mdiafairingprovidesthewidthtomakethis
sideplacementpossible;ifconstrainedto5.0mfairing,sidemountingcouldnotbereadilyachieved.Oneofthepallet
positionsmayb eoc cup ied bya rover.TheSL SBlock 1B“ Two Launch”conceptLanderisshowninFig.16(right).Because
neitherof the elements (AE, DE or TE) areconstrainedtofitwithinasmaller5mdiafairing,their geometry can be
optimized;thelanderforeaseofsurfacepayloadoff‐loadingandlowstageheight.ShowninFig.17aretheAEandDE;
theAECrewcabinisaverticalcylinderwithadockingportontop,anda singleengineonthebottom.TheAEengine
nozzlefitsdownintothetopportionoftheDE.TheDE’sbottomcenter engineissurroundedby 4 cylindricaltanks,
structureandpayloads.TheLanderisshown with landing legs stowed (Fig.17 left), and (right)deployed.TheAEis
illustratedinFig.18;itsengineisimmersedintothecabin.TheDEcanalsobeflowninacargoonlymode.Inthatcase
anadditionalpayloadispositionedontopinplaceoftheAE.Thatpayload might be a surfacehabitat,solarpower
station, nuclear surface power unit, insitu propellant plant, powerbeamingstation,‘FarSide’Astronomyassetor
mining/excavationmachinery.TheSLSBlock1BCargoversionTLIcapabilityis43.0mt;thiscapabilityissufficientto
launchHLSlanderelements,withexcesscapabilitytocoverweightgrowth,increasesinpayload,increasesincrewsize,
orstaytime.
Landersizinganalysisusedthefollowingassumptions:
1) AECabinsizedforCrewof3,butcarriescrewof2initially,5daysurfacemission,50kgsamples
2) Crewcabin3.25mt,plus0.45mtforcrew,consumablesandonboard(AE)scienceequip.
3) DEsurfacepayload0.5mt,SeparateAirlock,mass0.85mt(including2EVAsuitsandsupplies)
4) Propellantresidualsandflightperformancereserves(FPR)of4%,Drymassmargins15%
5) Cryocoolersarecarriedtopreventboiloffforthesoftcryogenoptions(LO2/LCH4)
6) Hepressuranttanks:CompositeOverwrapPressureVessel(COPV)4,000psia
7) OutboundtoNRHOis5days,NRHOtosurface1day,surfstay5days,NRHOreturn1day
8) AEthrustrequired7,500lbf,DEthrust19,200lbf,pervehicleT/Wof1.8(local)atignition
9) RCSstorablebipropellant290secIsp,AERCSthruster50lbf,DEthruster100lbf
10) SLSBlock1BCargoinjects43.0mttoTLI,Block1BCrewinjects12.5mttoTLIinadditiontoOrion.

TheTE(notillustrated)willrideasaco‐manifestedpayloadwiththeOrionintheCrewSLSlaunchandtravelswiththe
OriontotheNRHO.Theun‐crewedlanderisthenlaunched,andtransferstoNRHO.There itwillbejoinedtotheTE;
oncecheckedout,thecrewwillboard and the Lander/TE combination will separate. Lander propulsiontradestudy
Figure16SLSTwoLaunchArchitectureTransportationElements(TransferElement(TE)notshown)

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resultsaregiveninSectionXII,whereSLSlaunchedAE,DEandTEmassesareexplainedandlaunchmarginsaregiven
forseveralvariationsofthelander.TheApolloLunarExcursionModule(LEM)andthe2008NASAConstellationprogram
AltairlanderconceptarereviewedinSectionsVIIandVIII.CandidatelanderenginesarereviewedinSectionsIXandX.
TheseSectionsset the context forthe SLS lander trade studyforthesetofassumptionsandgroundrulesthatare
appropriateforaNRHObasedLunarsortiearchitecture.

Fig.17SLSTwoLaunchCrewedLunarLanderConcept.TheSLSwide8.4mdiaFairingallowstheDescent
ElementsGeometrytobeoptimizedforEaseofCargoOff‐loadingandLowStageHeight.
Figure18AscentElement(AE)Configuration
VerticalCylinder,withSingleImmersedEngine.MoreDetailsonpage20.
InternalVolumeVarieswithCrewSizeandStayTime.

TheSLS Lander is designedtothelarge8.4 m diafairingandtakesadvantageofthatwidediametertolocatethesurface
cargoattheouterperimeteroftheDE,eitherastwosidepallets(Fig.17)oras4smallerpayloadbays(notshown).Ineither
option,surfacecrews,atgroundlevelwouldhaveeasyaccessto thecontents.LimitingaLandertoasmaller 5.0mfairing
mightpreventsidemounting.ThetwincargopalletscontainequalmassesofpayloadtokeeptheLanderCenterofGravity
(Cg)centered.Payloadelementscouldbeloadedontothelanderin NRHO;oroff‐loaded fromtheLandertotheNRHOas
missionneedsmaydictate.ConfiguringtheDEforasingle,centerenginefacilitatesthedualpalletcargoapproach.

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VII.
ApolloLunarExcursionModule(LEM)
TheApolloCommandModule(CM)andLunarExcursionModule(LEM) areillustratedinFig.19; theLEMfortheApollo14
missionmassed15.3mt.TheLEMDEprovidedonlythedescentfromLLOtoSurfacedV.TheLEMwascapturedintoLLOby
theCM Service Module. Fig. 20 lists LEM DE, AE andRCSEngineinformation.Boththe LEM and CM ServiceModuleused
storablepropellants(NTO/AZ50).Isp’swere311secfortheLEMAscentElementand305secforDescent.
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Figure19ApolloCommandModuleandLunarExcursionModule(LEM)
Figure20ApolloLEMEngineInformation

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VIII.
2008NASAConstellationProgramAltairLanderConcept
NASA’s2008‐09 Constellation Program Altair Lander Concept is illustrated inFig.21.TheAltairDEfeatureddeep cryogen
(LO2/LH2)propellants; it’sAEused storablepropellants.Due toverylowdensityLH2,coupledwiththefactthattheAltair
wasrequiredtodotheLunarOrbitInsertion(LOI)burn(capturingbothitselfandtheOrion),itsDEwasverylarge.Totalmass
oftheAltairwas45.6mt,3timestheLEM(Fig.22).Altair’sDEfeatured4RL‐10engines,8proptanks,ajoinedtrussstructure
andmassed38mt.Altairwouldhavestood3storieshighmakingcrewegressachallenge.TheCargoonlyversionlocatedits
payloadsontop;off‐loadingthesetothesurfacewouldhavebeendifficult.Boeingevaluatedalternativestothisconfiguration
andpublishedsomeofthefindingsinRef.2,3and4.
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Figure21NASAAltairLanderConceptIllustration
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Fig.22SizeComparisonAltairandApolloLunarExcursionModule(LEM).
TheLEMuseddenseStorablepropellant;Altairtheleastdenseofpropellants(LH2).AltaircapturedbothitselfandtheOrion
intoLowLunarOrbit(LLO)beforedescenttotheSurface;theLEMwascapturedintoLLObytheApolloServiceModule.

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IX.
PumpFedStorablePropellantLanderEngineCandidates
Aerojet‐RocketdyneXLR‐132andAestus‐IIenginedataarelistedinFig.23.Bothenginesuseddensestorablepropellant,but
unlike the LEM engines, they feature a higher Isp pump fed cycle.ARXLR‐132,demonstratedinflight,andAestusII,
demonstratedintest,bothachieved340Isp,asignificantimprovementvsthe315secpressurefedusedbyApollosystems.
Fig.23PumpFedStorableEngineCandidates(AestusIIupperleft,XLR‐132bottomright)
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X.
MethanePropellantLanderEnginePerformance
TheAerojet‐RocketdyneRS‐18LO2/CH4(methane)pumpfedengineispicturedontheteststandinFig.24.Expandercycle
methaneenginesarecapableof375secIsp,anotableimprovementoverstorablesystems.Methane,asoftcryogen,isless
densethan mono‐methylhydrazine(MMH)but significantly moredensethanLH2. In Table3,variationof Isp withEngine
ChamberPressure(Pc)islisted.Isp’sof368,371and375scorrespondtoPcof600,750and1000psia,forfixednozzleexit
diameterof65inches,andthrustlevelsof16,000lbf.InthisanalysisaconservativeIspof365secwasused,corresponding
toaPcof600psia;arelativelylowPc,identicaltothePcoftheLO2/LH2RL‐10engine.
Table3PumpFed,ExpanderCycleMethaneEnginePerformance

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XI.
SLSLaunchedLanderConceptPropulsionTradeStudy
Asizing evaluation was done foraprospectiveSLSlaunchedCrewed Lunar lander and TE appropriate for aNRHOcrewed
lunarprogram.Thetradestudycomparesfivepropellant/enginecombinationsfortheAE,DEandTE.TheSLScargolaunch
(Block1B, with fairing)injectstheLander (integratedAEandDE)toTLI;theDEprovidesthedvfortheoutboundtransfer
NRHO.That launch is followed by a secondSLS Crewed Block 1B,which injects theOrion and theTE as a co‐manifested
payload,also to NRHO. The Orion’s Service Module (SM) provides dv for the combination on the outboundtrip.Allthree
transferelementswereevaluatedwitheachofthe5propellantcombinations.WhatistobedeterminedintheTradeStudy
arethemassesoftheAE,DEandTEasafunctionofthefivepropellantselections(Table4),aswellastheSLSlaunchmargins
foreachofthesecombinations.Twoofthefivearepressure‐fedoptions,withpropellanttankpressuresof270psia;threeof
thefivearepumpfedoptionswithtankpressuresof40psia.EngineSpecificImpulse(Isp)rangefrom320‐385sec.
Figure24MethaneEngineinTest2009
Table4FivePropellant/EngineCombinationsforLanderTradeStudy

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Forthemissionscenariosgiveninthisreport,theTEdoesthetransfertoLLOburnstoplacetheLanderintoLLO,butitdoes
notcarryanyreturn‐to‐NRHOpropellant;itoperatesinanexpendablemode.Inotheranalysis(notincludedinhere)theTE
carriesthemodestadditionalpropellantneededforittodepartLLO,byitselfandreturntoNRHO.
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XII.
SLSLaunchedLanderMassasaFunctionofPropellantandEngineOptions
TheobjectiveofthelanderandTEevaluationistoestimatestagemassesandtodeterminehowmuchSLSlaunchmarginis
available.VehiclemassesarelistedinTable6.DataisincludedfortheAE(row10),theDE(row11),landersummary(sumof
AEandDE,row12)andTE(row16).Thesemassesincludeallpayloadsand airlockmass.Thesummed AEandDE(lander)
massesarecomparedtotheavailableSLS Block1BCargoTLIinjectionmass(43.0mt,row14).Thedifferenceinthesetwo
valuesandthepayloadattachfitting(PAF,adaptor)isthe“launchmargin,”i.e.thesurplusmassavailableinthesystemfor
launchingthelander.A negativelaunchmargin meansthelandermassisgreaterthantheamounttheCargoBlock1Bcan
injecttoTLI;marginsarelistedinRow14. AlsotheTE massiscomparedtotheavailableBlock1BOrionco‐manifestedTLI
injectedmass(12.5mt,bottomrow),thesemarginsaregiveninrow18.
Table6containsdataforsevenlanderandTEcombinations;thefirst5columnscorrespondtothe5propellantsdescribedin
Table4.(Ineachofthese5,propellantandenginechoicesarethesamefortheAE,DEandTE).Thesixthandseventhcolumns
haveAE’s and DE’s with differentpropellants(TEis same as DE).Column 6 data is forapressure‐fed storable propellant
(“storable”)AEcoupledtoapump‐fedmethane(CH4)DEandTE.Theseventhcolumnappliestoapump‐fedstorableAEand
amethaneDEandTE.Resultsindicatethatfor4ofthe7options,significantSLSlaunchmarginisavailable.Columns2,4,5
and7ofTable6showmarginsof8.4,9.1,12.1and8.7mtrespectively;landermassforthese4casesare33.7,32.9,29.99,
and33.2mt.Thesystemchosenasareferenceamongthese5optionsisthe340sIspstorablepump‐fedoption(Col.2Table
6).UsingXLR‐132demonstratedtechnologyanddensestorablepropellants,theSLSBlock1Bcanlaunchthisreference33.7
mtlanderwithalaunchmarginof8.4mt(Col.2,Fig.26‐26)).FortheSLSOrionlaunch,aStorable9.4mtTEiscarriedwitha
marginof2.76mt.Thehighestperformingofthe7optionsisthestagedcombustionmethaneoption;withalanderof29.99
Table5MissionandVehicleParameters:ApolloLEM,AltairandSLSLaunchedLanders

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andTEof7.75mt,availableSLSmarginsare12.1and4.3mt(Col.5). Another high performing option isexpander cycle
methane(Col. 4); which achieves a landerof32.9mt,alaunchmargin of 9.1 mt, and a TE mass of 8.86 mtwitha3.4mt
margin.Although providing slightly less margin than the two pump‐fedCH4 systems, the storable option would eliminate
boiloffconcerns.(Forallmethaneconcepts,activecryocoolersandadvancedcryogenicfluidmanagement(CFM)systemsare
carriedtominimizeboiloff).Fig.25listsmassforTE,DEandAEofthe340secIspStorablesystem.InFig.26theAEisshown
atliftoff; also listed is ‘as launched’ massfor the referencepump‐fed Storable option (Col.2), including surface payload,
airlock,inertandpropellantmasses.ThedataindicatestheBlock1B/EUSenablesthetwolaunchlunarmissions.
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XIII.
ArchitecturalLevelFindings
The‘TwoLaunch’SLSGatewayarchitectureisrobust,i.e.hassignificantmarginformassgrowth,increasesinpayload,crew
size,staytimeorsomecombinationofthese,andsimplifiestheHLSarchitecturebyreducingthenumberoflaunchesfrom3
to2.ThisArchitectureisalsorobustinthesensethatitcandeliverallelementsfullyfueled.
Forthecaseofthe‘3Launch’architecture(Fig.14),theDEisflownseparatelyinasmallerlauncherthatiscapableof15mt
toTLI(Fig.1left).EarlyindicationsarethattheDEforthe‘3Launch’architecturewillmassmorethan15mt,andthustheDE
mustbelaunchedoff‐loaded,requiringalaterrendezvouswiththeRefuelingElement(RE),forpropellanttransfertotopoff
its tanks. Listing the total number of elements in the ‘3 launch’ architecturewould begin with the (at least 3) Gateway
elements,ifitisutilized–(habitat,PPEandlogisticsmodule);theOrion;andthe4separatelylaunchedTransferelements(if
theREisincluded),distributedamong3differentlaunchers.Thetotalamountsto8individualelementsandprocurements.
Tosummarize,theTwoLaunchSLSapproachwouldsimplifythearchitecturebyeliminatingtherequirementforpropellant
transfer,reducingthenumberof launches, while providing robustness to massgrowth, crew size, stay time, andmission
evolution.Eitherthepumpfedstorable(Col.2)orpumpfedexpandercycleMethaneoption(Col.4)wouldprovidesufficient
performance;thestagedcombustionmethane(Col.5)providesthelowestmassoftheoptionsconsideredhere.Thepump‐
fedstorablesystem(XLR‐132technology)maybepreferredasitwouldeliminatethedevelopmentofactiveCFM.
Table6MassSummariesforSLS‘TwoLaunch’ArchitectureLanderPropulsionTradeStudy

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Figure25TE,DE,AEmasses(lefttoRight):Propellant,Inert,CrewCabin(AE)andSurfacePayload(DE)
StorablePump‐FedPropulsion.These,alongwithOrion,arelaunchedwith2SLSBlock1Blaunchers.
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Fig.26AscentLiftoff(left),andAE,DE,TEMassStatement(right).AECabinSizedfor3,Carries2forthismission.
StorablePump‐FedPropulsionOption.SLSLaunchMargins(bottomright)

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AlternateAscentStageConfigurations
FourconfigurationvariationsoftheAEareillustratedinFig.27.Thevariationsinvolveengine,tankagepositioningandcrew
cabincylinderorientation.Fig.27farleft,showsaverticalcylindercabin,withasingleengineand4verticallystackedtanks;
leftmiddle,ahorizontalcylindercabin,singleenginewith4horizontallyalignedtanks;middleright,ahorizontalcylindercab
withasingleimmersed(slotted)engineand4verticaltanks;farright,ahorizontalcylindercab,4sideengines(2arevisible)
and4horizontaltanks.TheReferenceAEshownearlier(Fig.17‐18,26)andinTable8,consistsofahorizontalcylindercab,
singleimmersedengineand4verticallystackedtanks.AEmassesarelistedinTable8.Thisisa‘minimum’Crewcabinasitis
sizedforacrewof3fora5daysurfacestaytime,initialmissionscarry2crew.TheAEascendsthroughatotalof2,890m/s
dVtoreachNRHO,andhaspropellantmargins(unusablesandflightperformancereserves)of4%.


Table
7
LanderandTransferElementPropulsionTradeStudySummary

Fig.27LanderCrewedAscentElement(AE)ConfigurationVariations

Table8
A
E:Sizedfor3,Carries2,5DaySurfaceStay,StorablePump‐fedPropellant,AscendstoNRHO

PublicDomain/AdministrativeData
–
NotExportControlled
21


Conclusions
TheNASASLSFamilyofLaunchVehiclesprovideagame‐changingcapabilityforBeyondEarthOrbitExplorationMissions.The
EUS Upper Stage is sized to optimize the powerful SLS Core and Booster stages, providing a significant improvement in
performanceovertheinterimICPSupperstage.WiththeEUS,theSLSBlock1Bcan providerobustcrewedlunarmissions.
TheSLSBlock1BcandeliverallprospectiveNASAHLSLanderelementsintwolaunchesratherthanthree,whilemaintaining
launchmarginformassgrowth,increasesinpayloads,andmissionevolution.

References
1. NASA,SpaceLaunchSystem(SLS)MissionPlanner’sGuide,ESD30000InitialBaseline,ReleaseDate:04/12/17

2. Benton,M.,Caplin,G.,Reiley,K.,Donahue,B.,Messinger,R.,Smith,D.,BoeingDesignTradesinSupportoftheNASA
AltairLunarLanderConceptDefinition,AIAA2008‐7798,AIAASpace2008Conference,SanDiego,CA,9Sept2008

3. Donahue,B.,Grayson,G.,Caplin,G.,Reiley,K.,Smith,D.,LunarLanderAscentModuleConfigurationandPropulsion
Study,AIAA2009‐6406,AIAASpace2009Conference&Exposition,Pasadena,CA,14Sept2009

4. Donahue,B.,Caplin,G.,Smith,D.,Maulsby,C.,Behrens,J.,LunarLanderConceptsforHumanExploration,AIAAJournal
ofSpacecraftandRockets,Vol.45,No.2,March‐April2008
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