1

Ice on the Moon?Science Design of the

Lunar Crater Observation andSensing Satellite (LCROSS) Mission

Andrew Christensen, Howard Eller, Justin Reuter, Luke SollittNorthrop Grumman Corporation, Redondo Beach, CA 90278

Geoff Briggs, Tony Colaprete, Jennifer Heldmann, Antonio RiccoNASA Ames Research Center, Mountain View, CA 94035

ABSTRACT

The design criteria and implementation plan for the Lunar Crater Observation andSensing Satellite (LCROSS) mission is described. The mission is manifest for flightwith the Lunar Reconnaissance Orbiter and set for launch in 2008. The design ofthe LCROSS mission, based on clear and achievable science and exploration goals,is a fast and low cost approach to prospecting for near surface, polar water ice. Themission involves targeting the launch vehicle upper stage to impact the Moon at 2.5km/sec. The impact will be observed by a small ‘shepherd’ spacecraft S-S/C thatwill have separated from the upper stage and will follow it at a distance of ~1000km. Plans have benefited from the lessons learned by previous impact experimentsusing laboratory guns and spacecraft (Apollo impacts, the Deep Impact mission toTempel 1). LCROSS combines a low complexity sensor suite with a simplespacecraft concept that together provides high confidence in mission success. TheLCROSS mission can identify water in lunar regolith ejecta at concentrations as lowas 0.1%. It uses a 2000 kg impactor mass and can accurately target any desired siteat either pole. In addition to the LCROSS payload, Earth and space-basedobservatories will capture the impact event.

I. Introductiona. Background

Interestin thepossible presenceof water iceon the Moonhasboth scientific andoperationalfoundations. It is thoughtthatwaterhasbeen deliveredto theMoonover itshistory from multiple impactsof comets,meteoritesandother objects. The water moleculesmigratein theMoon’sexospheric typeatmosphere thoughballistic trajectoriesand canbecaught in permanently shadowedpolarcold traps thatarecold enough to hold thewaterfor billi onsof years.Verificationof itsactual existence would helpscienceconstrain modelsof theimpact historyof thelunar surface and the effectsof meteoritegardening,photo-dissociation, and solarwind sputtering. Measurementsof theice distributionandconcentrationswould providea quantitative basisfor studiesof theMoon’shistory.

Depositsof iceon theMooncould havepractical implicationsfor future humanactivitieson theMoon. A sourceof water could enable longduration humanactivi tiesand serve asa sourceof oxygen,anothervital material thatotherwisemustbeextractedby melting and electrolyzing thelunar regolith.Hydrogenderivedfrom lunaricecould beusedas a rocket fuel. Theseattractive considerations influencethearchitecture andplansfor mannedactivitieson theMoon. Thus,thedetermination of thenon-existenceof water ice at thepoles would causea re-alignmentof thearchitecture andplans. Operations from a lowlatitudenearsidebasewould lead to substantially simpler communicationsapproach,would focus

Space 200619 - 21 September 2006, San Jose, California

AIAA 2006-7421

This material is declared a work of the U.S. Government and is not subject to copyright protection in the United States.

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exploitationon regolith processinginstead of ice processingandwould negate thechallengeof developingrobotictechnologiescapable of working in verycold cratersand nearlyperpetual darkness.

It has longbeentheorized thatpermanently shadowedregionsnearthelunar polescouldactascold trapsandharborexcesswater ice1,2. Within those partsof the trapsthatare sufficiently cold, icescanbestableto lossby sublimation for billions of years3. Althoughthereareotherlossmechanisms,suchasmicro-meteorite impacts,thedetailedbalance between sourcesand lossprocessesis not well establishedandthepresenceandamount of water ice remainopenquestions.

Observations in theLunar Prospector4,5 mission (Figure1) showedthat anexcessof hydrogenexists in thepolar regions. Theseobservationsare consistent with the presenceof waterice, althoughthewatercouldalsobecontainedin hydratedminerals.

Figure 1. Hydrogenabundancefrom LunarProspectorsuperimposed on the lunar terrain5.

The presence,form, amount anddistributionof water isof scientific interestsinceit bearson theorigin andevolutionof planetary atmospheresincludingtherole of cometary impactsin theformationoftheatmosphereandpresence of water onEarth.Moreover, thequestionshavebeenelevatedin thecontextof the President’s Vision for Space Exploration announcedin Jan2004calling for the extension of thehumanpresenceacrossthesolar systembeginning with a returnto the Moonasaninitial stepin theexplorationof Marsand otherdestinations. Theutilizationof in-situ resourceson the Moon is a keyelementin theexploration architectureand anearly resolutionof the water questionis important.

A componentof theintegratedlunarexploration plan is a seriesof roboticprecursor missionstoaddressbasic scienceandengineering questionsanddemonstrate technologiesrelevant to humanoperationson the Moon. Thefirst of thesemissionsis theLunarReconnaissanceOrbiter (LRO) which isbeingdesignedto identify andcertify futurelandingsitessuitablefor humanandroboticmissions.Siteswhere potential resources,particularly water, thatcould beutilizedto facili tate exploration,areof specialinterest. LRO wil l identify hazardsto landing missionssuch asrocks,pitsand smallcratersandprovidedatafrom which high resolutionterrain mapsof potential sitescanbemade.To providean early, directverification of thepresence of water ice,NASA hasselectedthe LCROSSmission.

b. Impact Missions

In preparation for mannedmissionsto theMoon in the1960’s,boththe U.S.andtheSovietUnionsponsoredrobotic mission to theMoon. TheSoviet’s undertook theLunaseriesof missionsintended toland payloadsandcollect panoramicphotographsof theterrain. Luna-1 missed theMoon,but Luna-2 inSept. 1959became thefirst man-made object to impact the Moon.After a seriesof attempts finally Luna-9became thefirst successfulsoft lander missionin January1966.

TheUS begantheRangerprogramto photograph theMoon with a spacecraftona collision courseandtheSurveyor programto landsoftly andphotographtheterrain.In Jan1964Ranger-4 lost poweronthewayto the Moon, failed in its photographicmissionbut was thefirst US payloadto impactthe Moon. Itwasfollowed by successfulRanger6, 7, 8 and 9 missions.

SP Hydrogen Abundance( LP data)

SP Hydrogen Abundance( LP data)

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Impactson the Mooncontinuedduring theApollo Program(Apollo 10 – 17) from thereleaseof theLunar Module (LM) following ascentfrom theMoonand docking with the CommandModuleprior toreturn to Earth.

Apollo 11 deployedpassiveseismometersto study thelunar interior fromquakesandimpactsincludingtheLM impacts. Later, a geophonenetworkstimulatedby small detonationswasimplemented.

More recently two NASA missions,theLunar Prospector orbiter andtheCometTempel1 DeepImpactmission havecarried out highvelocity impactsto elucidatethepropertiesof thelunarsouthpoleandof a short period comet,respectively. Results for the highly successful DeepImpact6 experimentprovidelessonsfor thedesignof theLCROSSimpactexperiment. Theseinclude:

1. Thecomplementaryvalue of observing the impact using instrumentson the motherspacecraftandonEarthorbitingspacecraft (HST,Chandra, Spitzer, GALEX, FUSE,SWASandRosetta),aswell aswith groundbased observationswith telescopesaround the world.(http://deepimpact.jpl.nasa.gov/science/observations.html)

2. Theuseof extensivemodeling of theexpectedplumecharacteristicsto guidethedesign themission.

3. Theimportanceof choosingprojectile mass,density, velocityand impactangleof incidenceto maximize thequantity of ejectedmaterial.

4. Thevalue of coordinatingthemissionandthe collaborating scienceteams into themissionorganization, planning,and execution.

c. Impact Processes

Several processesoccur whena bodystrikesthe lunarsurfaceat highvelocity, includingthepropagationof a shock wave,theejection of a plume of excavatedregolith and its subsequentre-deposition,andtheexposureof freshsubsurface material. The LCROSSupperstageimpactmayor maynot createa hot enoughimpact to result in aninitial incandescentflashhowever, thepayloadincludesavisible luminancephotometer to observe and characterizeanyimpactflashshould it occur. The ejectawillhave a range of velocities; all will follow ballistic trajectories. The slowestparticleswill bere-depositednear theimpactcrater but a significantfraction wil l riseinto thesunlight to beobservedby theso-calledshepherdspacecraftandother telescopes.The wholeeventwil l beover in a few minutesandtheshepherdspacecraftwill thenalso smashinto theMoon.None of thesolid ejecta wil l orbit theMoon -- importantforthesafetyof LRO andother lunar orbiters. Any water vapor sublimedin thesunlight may,however,forma faint, transient OH exosphere.

Theejectaplumeis expected to form asa conically shaped curtainof material asmodeledin Figure2. Theimpactmodel is basedon widely usedsemi-empirical relations7. Viewedfrom theshepherdspacecraft,it will appear asan expandingring, the spectral characteristicsand brightnessof which willprovideevidenceof water ice and/orhydrated mineralsif theyare presentin thepolar regolith.

Figure 2. Impactmodel simulationsfor a 2000kg lunarimpactareusedto estimatetheimpactplume dynamicsandcharacteristics. Thefiguresshow theplume 0.01secafter impact. (EricAsphaug,private communication,2006)

Density Temperature (T) Speed (v)

1200

120

600

2.5

0.5

2.0

T (K) v (km/s)

1.0

2.0

4

Figure 3. Thelife cycle of a lunar impactcrater andtheimpact observation strategyfor LCROSS.Observationsextend overmany temporal and spatial scalesand includenadirandhorizonviewing sensors.

The impactobservation strategyis ill ustratedin Figure3. The shepherdspacecraft andobservatorieswill monitortheimpact eventsat a varietyof spatial (meters to kilometersto exospherescales)andtemporal scales(secondsto minutesto days).

The amountof material excavated in theimpact scalesapproximatelylinearly with themassof theprojectile. In Figure4, themassof theLCROSSEDUSis takenas2000kg and themassof theS-S/C as700kg. For theexpectedangleof incidence(>60̊ ) and impactvelocityof 2.5km/s, theejectedmass isapproximately 900 and350 metric tons,respectively for stageand S-S/C. Bothof these eventsare100’softimeslargerthanLunarProspector which wassmaller, lesshighspeedand impacted obliquely. Al thoughthere is uncertainty aboutpossible patchinessof anypolarice deposits,thesignificant lateralsizeanddepthof the LCROSSimpact makes it unlikely thatit will excavateunrepresentative material.

Figure 4. Calculatedmassof ejectedmaterialbasedon 2000kg and700kgprojectilesat a velocity of 2.5km/s.TheLunarProspector hit near grazingincidence(~ 6 - 8 degrees).

II. LCROSS Science Design

NIR Specs

Cameras

ShackletonCrater(~20km)

~100

0km

ShackletonCrater(~20km)

~360

kmBoundaryofVaporPlume

ShackletonCrater(~20km)

~70

km

BoundaryofVapor Plume

BoundaryofDebris Plume

T-15 min T-5 min T-1 min

NIR Specs

Cameras

ShackletonCrater(~20km)

~100

0km

ShackletonCrater(~20km)

~360

kmBoundaryofVaporPlume

ShackletonCrater(~20km)

~70

km

BoundaryofVapor Plume

BoundaryofDebris Plume

T-15 min T-5 min T-1 min

0

100

200

300

400

500

600

700

800

900

1000

0 10 20 30 40 50 60 70 80

Impact Incident Angle

Eje

cted

Mas

s(m

etri

cto

ns)

LCROSS EDUSLCROSS S-S/C OnlyLP

LP

LCROSS EDUS

LCROSSS-S/C Only

5

a. Requirements

Drawingheavily on theexperienceand lessons learned from previous impactmissions, theLCROSSmission wasconceivedto advance thestudyof waterin thelunar surfacematerial. Themissionwasselectedby theExplorationMissionDirectorateat NASA to fly asa co-manifest payload with theLunarReconnaissanceOrbiter (LRO) for launchin Oct. 2008.

The science requirements for theLCROSS missionareasfollows:• Createanobservable ejecta plumein a permanently shadowedregionnearthe

polesof theMoon,• Provide context imagesof thetargetedlocation, observationsof the impact

andejectacloud history,• Measuretheconcentrationof water in theejecta cloud, and• Characterizelunar regolithin theejectacloud.

The derivedmeasurementrequirementsfor themissionare:1. Measurethetotal amountof water ice in thelunar regolith.

a. Measuretheamountof water ice in the plume.b. Measurethewatervapor in theplume.c. Measuretheamountof hydratedminerals in theejecta plume.d. Measuretheamountof material in theejecta plume

2. Measurepropertiesof theregolithin theejecta plumea. Temperatureb. Grainsize

3. Verify thelocationof theimpact to ~1 km accuracy

b. Approach

Theexperimental approach (Figure 5) is to use theEarth departureupper stage(EDUS) asa kineticimpactor.The impactcreatesan ejecta plume whoseproperties,includingwater ice contentwill beobservedby theLCROSSspacecraft andEarth- and space-basedtelescopes.

Figure 5. Artistic rendition of theEDUS and shepardingspacecraft impactscenario.

TheEDUScarriesbothLCROSSandtheLunarReconnaissance Orbiter (LRO) ona lunartrajectorywith theLCROSSspacecraft acting asanadapter ring betweentheupperstage and theLRO spacecraft.Following theseparationof the LRO payload earlyin themission, theLCROSSspacecraft actsasa“shepherdspacecraft” (S-S/C) controlling theEDUSanddirecting it ona swing-by of theMoonandtwoorbitsof theEarth(Figure 6). It separatesfrom the EDUSabout anhour beforeimpactandorientsitself to

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Figure 6. LCROSStrajectory

observetheEDUS approachandimpactwith thesurface.The S-S/C, trailing about10 minutesbehind theEDUS,wil l observe theplumeoncetheejectaenterssunlight and will proceedon itsown impact trajectory.About tensecondsbefore impact it will passthroughand,from within, measurespectral propertiesof theplume. Thesunli t plumes fromboth theEDUSand S-S/Cimpactsshould be visible from ground- andspace-basedtelescopes.

Figure 7 showsa mosaic of imagesof thelunarsouthpoleacquired by the Clementinemissionandidentifiesthe Shackletoncrater asa potential target of theLCROSSmission.A SiteSelectionWorkshopwill beheld in Oct 2006to make definit ive impact site recommendations.

The roleof the LRO before andaftertheimpactis underdiscussion. ClearlyLRO will havemuchto offer throughobservationof theimpact and subsequent characterizationof theimpactcrater.

Figure 7. LunarsouthpolecompositeClementine imagesshowing locationof selectedcratersincludingtheShackletoncrater, a possible target. Definitive targetselection will follow a communityworkshoponsite selection.

The S-S/Cinstrumentsuiterequired to meet thescience objectivescomprises:1. Onevisible imager to provide contextandhigh resolution imaging of the impact

locationandobservetheplumeevolution.

60km

150 kmGanswindt

Idelson

Zeeman Schrodinger

Weichert

Shackleton

300kmDia.

Target – Lunar South Pole

60km

150 kmGanswindt

Idelson

Zeeman Schrodinger

Weichert

Shackleton

300kmDia.

Target – Lunar South Pole

2-Month LCROSS Impact Orbit

EarthD=6563 km

MoonD= 3476 km

384,440 km

SUN

140 x 10 6 km

Lunar Orbit

L-Cross Orbit

2-Month LCROSS Impact Orbit

EarthD=6563 km

MoonD= 3476 km

384,440 km

SUN

140 x 10 6 km

Lunar Orbit

L-Cross Orbit

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2. Two Near-IR camerasto obtain spatial distribution of theplumematerial3. Two MID IR Imagers to monitor at 13.8and 7.0micronsin order to determinethe

temperatureof the plumeejecta.4. A visible –nearUV spectrometer to mapthefluorescencefrom OH, a photo-

dissociationproduct of waterin thevaporstate.5. Two near-IR spectrometers to monitor spectral bandsassociatedwith watervapor,

ice,andhydratedminerals(1.35 –2.25microns)covering thefi rst overtonesof H2Oice (bandis freeof interferenceand morebrightly illuminatedby sunlight thanfundamentalsnear3 microns).Onespectrometer pointsalongthe trajectoryandtheotherperpendicular for in situ measurementsmadein thelasttenseconds.

6. Onevisible highspeed photometerto searchfor andmeasureany impactflash8.Groundbasedandspacetelescopes will observethesun-li t ejectaplumescreatedby boththe

EDUSandS-S/Cimpacts whenthematerialrisesabovetherim of thecrater. Theseremoteobservatorieswill beespecially valuable for observing, at near UV wavelengths,anyexosphericOH createdby thephoto-dissociation of water.

UsingtheLCROSSinstrumentsspecif ied in thefollowing section, the expectedSignal/Noisehasbeen calculatedbasedon themodeledejecta plume characteristics. Figure 8 il lustratestheS/N calculationsfor waterversustime after impact.

Figure 8. Signal/Noisefor thedetectionof water versustime afterimpactfor instrumentson theS-S/C andtheKeck telescope in Hawaii. Plumebecomessunlit at 0.1min, theS-S/C encountersthevapor plume at 3min, andencountersthedebris plumeat 10 min aftertheEDUS impact.

c. Design Features

To assurethe successof theLCROSS mission,thedesignhastakenaccount of previous missionapproaches. Table 1 compares a set of LCROSSdesignoptionswith the Lunar ProspectorandDeepImpactmissions.

Other Design Considerations:1. Theneutronspectrometer on Lunar Prospectormeasurementswasconsistent with the

presenceof hydrogen. There is ambiguity whethertheneutronsignatureis fromice,hydratedmineralsor unbound hydrogen.

2. Thereisuncertaintyregarding thepropertiesof deeplyfrozenregolith andthepossiblepresenceof hardrock in thetarget crater sincethefloor cannotbeobservedfromEarth.Observationsby LRO in the80 daysbefore LCROSSimpactmaybeof valuein selectingthetargetsite.

3. Thevertical distribution of anyice deposits is unknown. Estimatesof theconcentrationof Hin theregolith arestrongly model dependent.

4. Thebottom of someshadowedcraterscan befaintly il luminated by earthshinepossiblyimpedingthe accumulationof ice.

0

1

10

100

1000

10000

100000

0.001 0.01 0.1 1 10 100Time After Imapct (min)

Inst

rum

entS

/N

0

10

20

30

40

50

60

70

Eje

cta

Plu

me

Alt

itu

de(k

m)

NIRSPEC, Keck-2 [1%]NIR S-S/C [1%]NIRSPEC, Keck-2 [0.1%]NIR S-S/C [0.1%]Mass weighted altitude

For a 2.5 km/sec, 2080 kg Impact, den = 2000 kg/m3

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TABLE 1 – LCROSS DesignElements

Mission ScienceRequirement

ExperimentOptions

Lunar ProspectorJuly 1999

Deep Impact LCROSS Mission

1. Be CertainofImpactLocation

Camerason theProjectile(Impactor)

NO YES NO

Camerasonadaughterspacecraft

NO YES YES

Camerasona lunarorbiter LRO

NO na YES

Earth-basedTelescopes

YES (HST,Keck1,McDonald),

YES YES

SpaceTelescopesSpitzer,HST

YES YES YES

AirborneTelescopesSOFIA

NO NO YES

2. Makeanejectaplumebig enoughto measureitsproperties

ImpactorMass 168 kg (354lbs) 370 kg 2000 kg

ImpactorVelocity 1.7 km/s 10.2km/s 2.5 km/sAngle of Incidence 6º 90º >70ºCraterSelectionAvoid hard rockfloor impact

(-87.7º lat, 42.35ºlong)

NA TBD(ShackletonCrater)

Massof Ejecta unknown 900 metric tons

3. Select a site withhighexpectationofwaterice

Lunar ProspectorNeutronData

Yes NA YES

PermanentlyShadowedCrater

unknown NA YES

AbsenceofEarthshine

unknown NA TBD

Minimal ReflectedSolar Illumination

unknown NA TBD

4. Measuremorethanoneobservable

Visible ImagingSpectraOH Bands

Yes– Ground&SpaceBased

YES YESYESYES

NIR ImagingSpectra

Yes YES YESYES

MIR ImagingSpectra

NO NO NOYES

UV Yes YES YES

III. LCROSS Implementationa. Instrumentation

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Theinstrumentation selectionsandsupporting observationsprovidemultiple complementarymeasurementtechniquesand, thus, redundancy and robustnessto the LCROSSmission. Moreover,multiple measurementsandplatforms maximize thescience return.

TheS-S/Cpayloadcomprises9 instruments (Table 2): 5 cameras(1 visible,2 NearIR, 2 Mid IR)andthreespectrometers (1 visible, 2 NIR) andone photometer (Tables3 & 4). Instrument checkout,impactrehearsalandcalibration will be performedduring theinitial swing-by of theMoon.Onehourprior toimpactinstrumentswill bepowered onandwil l return data until impactof theS-S/C.

Table 2. LCROSSMeasurementsandInstruments

Measurement Platform Instrument ProductsNIR Spectraλ/∆λ ~ 100

S-S/C NIR Spectrometer(2)

Ice,Vapor,GrainSize,Hydrates

Visible Spectra S-S/C VisibleSpectrometer

H2O+(619nm)OH (308nm)Searchorganics

Thermal Evolution S-S/C Mid IR Camera(2) Pre-impactterrainTotal WaterEjecta Blanket

Ejecta IR S-S/C NIR Camera (2) TotalWaterContext Imagery S-S/C Visible Context

CameraImpactlocationPlumemorphology

ImpactFlash S-SC Visible Photometer Flashlight curve

Table 3. LCROSSPayloadInstrument Parameters

Instrument BandCenter/Range[um]

BandWidth/Resolution[nm]

FOV[deg]

SpatialResolution@ T-15, T-1min [km]

SampleFrequency[Hz]

VisCam 0.65 50 6 0.2, 0.01 0.5NIRCamA 1.3 TBD 6 0.4, 0.02 0.1NIRCamB 1.4 TBD 6 0.4, 0.02 0.1MIRCamA 7 20 10 0.6, 0.04 0.1MIRCamB 12 20 10 0.6, 0.04 0.1VisSpec 0.27-0.65 9 6 1NIRSpecA 1.3-2.4 9 6 1NIRSpecB 1.3-2.4 9 6 1TLP 0.4-0.8 600 6 1000

Table 4. LCROSSInstrumentSuiteincludingDataHandling Unit.

Instrument(totals)

Mass (kg)** Vol (cc)** Power (W)* Data Rate (kbps)*

VisCam 0.1 45.4 2.4 219NIRCams 0.2 249.6 4.8 88MIRCams 2.5 249.6 6.4 88VisSpec 1.5 13.3 0.5 200NIRSpecs 5.0 480.0 5 1.2TLP <0.5 160 2 0.3DHU 1.5 1100 6 N/ATotals 11.3 2298 27.1 598

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Figure 9. Fully integrated NIRspectrometer. Connection to telescopeis via fiber optics.

**In cludes20% contingency.* DuringNominal Operation Mode.

1. Visible and NIR camerasFor thevisible sensor, a high-endbroadcast-quality CCD videocameraoutputting PAL format

(752Hx 582V pixels) will beemployed (Figure9). European-standardPAL camera pixelsare morenearly squarethanpixels for NTSC camerascommonin theU.S.andthusoffer someadvantagesformetrologicalapplicationslike thoseintendedby LCROSS. Thebaseline near-IR sensorsareflight-heritageInGaAs sensors,operated at ambient temperatures,with a 12 bit RS-422output.

2. Visible SpectrometerThe LCROSSS-S/Cwill observe thepre- and post-EDUS-impactedlunar regolith in and outside

thetargetedcrater at a spatial resolution and viewing angleunobtainable fromEarth.Thevisiblespectrometer,developedfor theLCROSSproject by Ocean Optics,shall record thesunlit plumeevolution,andtrackthe evolution of OH radicals from sunlight-dissociatedwatervapormolecules.Thevisiblespectrometer will measuretheOH-1 (308nm)andH2O+ (619nm) transitionssimultaneouswhich shallassessthewatervapor production.

3. Near IR SpectrometersThe LCROSSS-S/Cwill monitor spectral bandsassociatedwith water vapor, ice,and hydrated

mineralsin thenearinfra-red (NIR) spectrum from 1.35– 2.25microns,coveringthefirst overtonesof thesymmetricand asymmetric stretchesof water; thisband, relatively freefrominterferences, is morebrightlyilluminatedby sunlight than the fundamentalsnear3 microns,morethan compensatingtheweakerabsorptionof the overtones. (Sunlightwill illuminate theplume,90 degreesto thedirectionof S-S/Ctravel, from 10 secondsafterimpactuntil theS-S/Citself impacts,~10min later.) The regionsnear1.4and1.9microns, normally obscuredby terrestrialatmospheric backgroundin spectrafrom icy surfaces9, willprovidea sensitive indicationof watervapor fromice or hydrates.Theremainderof thespectral bandwillreveal -- at a levelof detailnot available from Earth-- the natureof ice crystals and mineral hydrates9,10.

Two identical NIR spectrometers will be coupledwith fiber optics to telescopes,onefocusedalongtheimpactor trajectory, thesecondaimedlaterally through theplumetowardsthelimb during thelastten secondsbefore S-S/Cimpact.

The NIR spectrometers utilize a no-moving-partsoptical systemfromPolychromix. Measuring8x6x4 cm3, consuming under2 W, andweighing< 1 kg, each fully integratedspectrometer includesfiberoptic input (NA = 0.22) and integral 2-stageTE detectorcooling (∆T > 55 °C); anelectronicall y tunablegratingcollects the1.35 -2.25micronspectrum (via Hadamardtransform)eachsecond usinga single-elementInGaAsdetector. Spectral resolution,specifiable in the9 - 36 nmrange,will be selectedtomaximizesignal throughputwhile maintainingeffective speciation.Developedfor industrialprocessmonitoringandcontrol,this NIRspectrometer exemplifies leverageof rugged COTSinstrumentation. (SeeFigure 9)

4. Mid IR Cameras

Pre- andpost- impactthermal imagesof the impact terrain wil l beobtained from Mid-IR camerason theS-S/Cto characterizethesurfacematerial(rockvs. regolith), obtain thethermalevolution of theplume(whichis dependent on thewater content), and observetheejecta blanket and freshlyexposedregoli th. Thebaseline mid-IR sensorswill bea fl ight-proven Alpha-silicon uncooledmicro-bolometermostsensitivein the7-14 micronspectralrange,outputting in PAL format (384H x 288V pixels).

5. Total Luminescent Photometer (TLP)A total visible luminancephotometerwil l be used to observea

possibleimpactflash. Thelight flashis due to thermal heating andvaporization or the impactor andsurfacematerial. The shapeof thelightcurve canbe usedto boundcertain initial conditionsof theimpact, and theflashpeakintensity dependson theangleof impact, target,and projectile

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types.

6. Data Handling UnitA Digital Handling Unit (DHU) accommodatesall sensorinterfaces,all digital videosystem

functionality andall interfaceswith theS-S/Cavionics. Both thevisibleand MIR camerasandtheDHUareflight provenhavingflown on bothlaunch systems (MRT KASPABM tests) and spacecraft(GDSpectrumAstro).

7. Ground- space Telescopic ObservationsThere area variety of ground-based and orbital observatoriesthatcanobserve thedust andwater

plumecausedby theimpact into thelunar surface. For impactsnear thepoles,theground-basedtelescopicobservationsof theejectawill be made at thelimb againsta spacebackground-- a fortuitousoptimalgeometry. As in the caseof theDeep Impact mission, appropriate telescopefacilitiesonEarthincludeMaunaKea(including theKeck, Subaru, andGemini North telescopes),Ki tt Peak,Lick Observatory,CerroTololo, Mt. Stromlo, Siding Spring,EuropeanSouthernObservatory, variousUniversityfacilities,etc. Thetiming of the impactswill besuch thattheMoonis simultaneously observable from Hawaii, theContinentalUS andfrom South America. (Appropriate timing wil l alsoensurethatno dustfrom the short-lived eventcanbe intercepted by theLRO spacecraft.) In addition, orbital assetssuchasNASA’s HubbleSpace Telescope(HST), NASA’s Spitzertelescope,NASA’s Galaxy Exploration Explorer, SWAS, andtheCanadianand Frenchagencies’ Far Ultraviolet SpectroscopicExplorer(FUSE)could beused to observetheimpactplume.

b. Space System Description

TheS-S/Cis designedto guidetheEDUSto impacta selectedpolar lunarcrater with high reliability,impactprecision,andeconomy. TheS-S/Cshepherds thedepleted EDUSto a preciseimpacttrajectory,invertsandthenbecomesan in-situ observer of theEDUSimpact plumebeforecreatingansizableplumethroughits own impact.

LCROSShasminimal physical andfunctional impacton theLRO. TheLCROSSS-S/Candits adapter are insertedbetweentheEDUS andtheLRO adapter.LCROSSS-S/C’s62 in. interface replicatestheEDUSinterfacefor theLRO-EDUSadapter.

Figure 10 shows thebasic launchconfiguration with LRO sittingatop thefli ght provenB1194VSPayloadAttachmentFitting (PAF),which in turn is supportedbytheEELV SecondaryPayloadAdapter(ESPA) ring basedS-S/C, which sitson topof a secondexisting fli ght proven highcapacitytwo pieceD1666VS PAF

Functionally, whentheEDUSperformsits LRO divert maneuver it istargetedto provide a 30 m/sdelta-V whichpositionstheEDUS-S-S/C stackfor thelunargravity assistedfly-by of theMoonandprovidesa separation trajectory betweenLRO and theEDUS-S-S/Cstack. Following thisburn theEDUSbegins its ventsequenceand,four hoursinto the mission, theS-S/Ctakestrajectory responsibilit yfor theS-S/C-EDUS stack while LRO proceedsto theMoon.

TheS-S/Cis anextremely simplespacecraft. The S-S/Cconsistsof anESPAring primarystructure,four equipment panel-radiatorassemblies,a singlepropellant tank, two-8-thrusterpods,a nearbuild-to-print copyof the LRO C&DH/PSEavionics,anS-Band Transponder, single TWTA andtwo omnicommunication systems,anda copyof the1553based LRO ACS sensorset. TheS-S/Chasnodeploymentsandno activemechanicalelements,exceptfor a separation band.

Figure 10 Shepherding Spacecraft Launch Configuration

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TheMission Operationsplanis depictedin Figure11: theL-CROSSspacecraft executescommandsreceivedfrom theground, via theDeepSpace Network,andtransmits telemetry to theDeepSpaceMissionSystems (DSMS)elementmanagedby JPLstartingafter LRO separation.

.

Figure 11. LCROSSOperationsSchemeand DataFlow

c. Impact accuracy

Impactaccuracybetterthan3km(3-sigma)expectedfor EDUSandtheS-S/Cwill impactwithin 100mof EDUSandcanretarget if necessary. Figure12 showsanexamplebasedon theShackletoncrater.

Figure 12. Close-up viewof the Shackletoncrater and targeting error elipse.

IV. SUMMARY

ErrorSource

Uncertainty(3-sigma)

Impact Error(3-sigma)

ACSPointing 10 arcsec <1 kmDSN TrackingMeasurements

15 m range1 mm/secrangerate

2.5km

RCSThrusterPerformance

1% <1 km

RSS 2.9km

Figure 2.6-1 LCROSS Operations Scheme and Data Flow

13

The designof theLCROSSmission,basedonclearandachievable scienceand explorationgoals,is a low cost approachto exploring thewatercontent of thepermanently shadowedlunarsurfacematerial. Themissiondesign hasbenefitedfrom thelessons learned onpreviousimpactexperiments.It combinesa low complexity sensorsuitewith a simplespacecraft concept thatgives highconfidencein thesuccessof themission. The LCROSSmissioncan identify waterfrom lunarregolithat concentrationsaslow as0.1%. It usesthelargestpossible impactor massfor theEELVlaunchcapability. It accuratelytargets to any desiredpolar site, and it incorporatesmultipleobserving conceptsandplatformsto maximizethe sciencereturn.

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