Technology Development and Testing forEnhanced Mars Rover Sample Return Operations

�

RichardVolpe Eric Baumgartner PaulSchenker SamadHayatiMailstop198-219 Mailstop82-105 Mailstop125-224 Mailstop180-603

818-354-6328 818-354-4831 818-354-2681 818-354-8273

JetPropulsionLaboratoryCaliforniaInstituteof Technology

Pasadena,California91109Email: firstname.lastname@jpl.nasa.gov

Abstract—ThispaperdescribesseveralJetPropulsionLabo-ratoryresearcheffortsbeingconductedto supportMarssam-plereturnin thecomingdecade.After describingthe2003/05missionscenario,we provide an overview of new technolo-gies emerging from three complementaryresearchefforts:LongRangeScienceRover, SampleReturnRover, andFIDORover. Theresultsshow improvementsin planning,naviga-tion, estimation,sensing,andoperationsfor smallroversop-eratingin Mars-likeenvironments.

TABLE OF CONTENTS

1. INTRODUCTION2. MARS SAMPLE RETURN M ISSION SCENARIO3. LONG RANGE SCIENCE ROVER TECHNOLOGIES4. SAMPLE RETURN ROVER TECHNOLOGIES5. FIDO ROVER TECHNOLOGIES6. SUMMARY7. ACKNOWLEDGMENTS

1. INTRODUCTION

EvenbeforeSojournermadeits first wheeltracksonMarsin1997,it wasanticipatedthatthis roverwouldbeonly thefirstin a seriesof surfaceexplorationspacecrafttargetedfor theplanet. While it will be Sojourner’s flight sparethat driveson Marsin 2002,thenext leapin technicalcapabilityexhib-itedby roverswill bein the2003/05missionset,wheremuchlargerroverswill performrockandsoil samplecollectionforreturnto Earth. Theseroverswill have greaterinnatecapa-bilities, openingthe door for the insertionof new roboticstechnologiesthathave beenin developmentsincethe incep-tion of the Pathfindermissionfive yearsago. Among theseare on-boardstereovision processing,autonomouslander-lessoperations,manipulationandinstrumentpositioningbyarms,precisionnavigation for rover/landerrendezvous,anddistributedgroundoperations.

Of fundamentalimportanceto the incorporationof the newcapabilitieson next-generationrovers is the useof a morecapableelectronics,sensing,andinstrumentationinfrastruc-ture locatedon-boardthe rover. For instance,asSojournerwas being preparedfor flight, JPL was constructinga newprototype,Rocky 7 [16]. Severalkey featureswereaddedtosupportlongtripsawayfrom thelander:adeployablemastto

�0-7803-5846-5/00/$10.00c

�2000IEEE

raisecamerasandtake panoramicimagesof thesurroundingterrain,a shorterarm for sampleacquisitionandinstrumentplacement,anda sunsensorto accuratelydetermineheadingwhile driving. Thesefeaturesweredemonstratedduringfieldtestsin theMojave Desertin 1997,which led directly to theacceptanceof the03/05missions[15].

Theselected03/05missionconcept,however, requiresanen-largedroverthathastheaddedfunctionalityof carryingadrillfor rock sampling,largerwheelsfor enhancedmobility, andasignificantlyupgradedscienceinstrumentsuite(asopposedthe Sojournerrover). Therefore,to supportcontinuedfieldtestswith the selectedscienceteamfor the 03/05 mission,a new Field IntegratedDesignandOperations(FIDO) roverwasconceived, designed,integratedduring a 12-monthpe-riod, anddemonstratedin deserttestsin April 1999[14]. TheFIDO rover reflectsthe currentengineeringsensorsandsci-enceinstrumentsuitethatareplannedfor the03/05mission.While this roverwill continueto actasanoperationstestbedfor missionscientists,it hasa secondfunctionasanintegra-tion testbedfor new technologiesthat continueto be devel-opedby ongoingresearchefforts.

The JPL core robotics technologyprogramhas beensup-porting theseresearchefforts, which include the Rocky 7rover aswell asanotherplatform, the SampleReturnRover(SRR) [13]. Each rover has beendedicatedto increasingautonomyin two respective halvesof the explorationprob-lem: autonomousmotionaway from andbackto the lander.New techniquesusedincludeestimationandvisual localiza-tion,on-boardpathandsequencere-planning,andnaturalandman-madetargetrecognitionandtracking.

This paperdescribesthesetechniques,aswell asthe detailsof the missionscenarioin which they will be used. Sec-tion 2 describestheMarsSampleReturn’sAthenarovermis-sion.Thetechnologydevelopmentsassociatedwith theLongRangeSciencerover taskarediscussedin Section3, whiletheSampleReturnRoverandthedevelopmentof rendezvoustechniquesaredescribedin Section4. TheAthenaterrestrialprototyperover, FIDO, is discussedin Section5, andsum-maryremarksareprovidedin Section6.

Figure 1. Preliminarydrawing of theMarsSampleReturnAthena-Rover.

2. MARS SAMPLE RETURN M ISSIONSCENARIO

Launchingin 2003andagainin 2005,NASA’s MarsSampleReturn(MSR)spacecraftwill placetwo scienceroversonthesurfaceof theplanet.Theseroverswill becarriedto thesur-faceon the top deckof a three-leggedlanderthat is roughly1 m tall and3 m in diameter. This size,substantiallylargerthanpreviouslandersof the1996,1998,and2001missions,makesit possibleto carry a sample-returnMars AscentVe-hicle (MAV) aspart of the landerpayload. The landersizealsoenablestheuseof aroverthatis approximatelytwicethesizeof the Pathfindermissionrover, Sojourner, in every di-mension. (Sojournerwas60 x 40 x 35 cm.) A preliminarydrawing of this “Athena-class”rover is shown in Figure1.

The largersizeof this MSR rover is neededto supportrocksamplingoperationsand to carry the seven scienceinstru-mentsthat make up its payload. Rock samplingis accom-plishedusingacoringdrill, whichrelieson therovermasstoprovide the force behindit in its vertical operatingconfigu-ration. Thescienceinstrumentsareusedto selectthe targetrocksfor sampling,to determinethecompositionof therocksamplesobtained,andto studyrocksin thesurroundingarea.Fourof theinstruments,locatedonafivedegrees-of-freedomarm, requirecloseproximity to the sampleto be measured.Two others,locatedon a 1 m mast,requireonly line of sightto thetarget.Thedrill, itself, is theseventhinstrument.

The rover will begin its missionon the landertop deckbyobtaininga panoramaof thesurroundingterrainfor science,engineering,andpublic outreachpurposes.From theseim-ages,arampdeploymentdirectionwill beselected,aswell asinitial travel routesandgoalsfor thefirst rover traverse.Af-ter rampdeployment,the rover will drive to thesurfaceandbegin navigating the terrain. The maximumdistancedriveneachdaywill be100m,andoftenmuchless,especiallywhentherover is positioningitself for scienceoperations.

During themission,communicationwith theroverwill nom-inally take placetwice perday, relayedby the lander. Eachcommunicationwindow will allow a limited set of imagesanddatato be transmittedto operatorson earth,while newinstructionsareprovided to the rover basedon the previouscommunicationcycle. Typically the rover will receive in-structionsfor thedayin themorning,andtransmittheresultsandstatusat theendof theday.

After obtainingits first setof rocksamples,theroverwill re-turn to thelanderanddepositthemin theMAV. Thismustbeaccomplishedby successfullyaligning with the baseof theramp,driving up its two narrow rails, andaccuratelydetect-ing theproperpositionfor sampletransfer. At this location,theMAV payloaddoorwill beopenedandthesampletransferwill be completedrobustly andautonomously;thermalcon-siderationsrequirethat the payloaddoor be openlessthanthatof thetypical communicationscycle.

Sincemissionconstraintslimit surfaceoperationsto lessthan90days,thesampleacquisitionandreturnto MAV cycle canbeperformedonly threetimesat most. It is likely, however,that eachcycle will seethe rover venturingfartherfrom thelander.

After thelastsamplereturnoperation,theroverwill moveoffthe landerdeckandfar enoughaway from the landerto pre-ventits beingdamagedduringtheMAV lift-of f. This launchis expectedto damagethelandercommunicationsystemandprevent it from acting as a relay for the rover. Therefore,the rover will useauxiliary communicationto an orbiter, toenableit to perform the extendedmissionof exploring thesurface.

Obviously, the complexity andaccuracy of the autonomousoperationsdescribedabove directly influencethe amountofscienceoperationsthat will be performed. For this reason,JPLresearchprojectsaim to introducenew functionalityandfeaturesinto Mars rovers to enablegreatersciencereturnfrom all upcomingMarsrovermissions.Techniquesfor moreautonomousandrobust explorationandreturnto the landerhave beendevelopedandimplementedin field tests.Eachoftheseefforts is describednext.

3. LONG RANGE SCIENCE ROVERTECHNOLOGIES

To improverovernavigation,exploration,andautonomy, theLong RangeScienceRover (LRSR) researchtaskhasbeenimproving therover’sability to navigatethroughtheenviron-ments,while maintainingan accuratesenseof its position.This sectiondescribesadvancesin four pertinentareas:dy-namic sequencegeneration,autonomouspath planning,vi-suallocalization,andstateestimation.All researchwascon-ductedwith theprototyperover, Rocky 7, shown in Figure2.

DynamicSequencePlanning

On-boardplanningwith dynamicsequencegenerationallowsgroundcontrollersto provide muchhigherlevel commands,while increasingtheoptimalityandrobustnessof roveropera-

Figure 2. TheRocky 7 researchprototype.

tionson thesurface.For instance,duringthePathfinderMis-sion, the Sojournerrover [10] wasprovided with extremelydetailedsequencesdaily, fatiguingoperatorswhile alsodis-allowing contingency operationswhentheflow of executionwasnon-nominal.Contraryto this,wehavebeenexperiment-ing with on-boardreplanningthat canchangethe executionof daily activitiesbasedonunanticipatedvariationsin quanti-tiessuchasposition,terrain,power, andtime. To accomplishthis,wehaveusedadynamicon-boardplaningsystemcalledCASPER(ContinuousActivity Scheduling,Planning,Execu-tion, andReplanning)[5], [6].

Figure3 showsanexamplescenarioin mapform,wheredarkorangeshapesrepresentobstaclesknown a priori (e.g. fromlanderdescentimagery). In this case,the initial planfor thetraversewill bring the rover to an unexpectedobstaclenearthefirst goal,representedasalight orangeshadedshape.Cir-cumnavigationaroundthisobstaclewill movetherovercloserto othergoals,triggeringCASPERto recognizethesituationand re-planto visit the closestgoal first. We arecurrentlyevaluatingthisandsimilarscenariosexperimentally.

AutonomousPathPlanning

For the longertraversesrequiredof upcomingmissions,au-tonomouspathplanningis desirablesinceoperatorswill notbe able to seethree-dimensionalterrain featuresout to themoredistantgoallocations.WhereasSojournerdrovea totalof 84m duringits entiremission,theMSRAthenaroverwillbecapableof driving this distancein a singleday. However,stereoimageryof the terrainprovidedto operatorswill onlyhave an envelopeof 20 m at bestresolution.Therefore,thepathplanningadvancesdescribedherewill allow therovertobeits own operator. It canimagetheterrainfrom periscopic

Re-planned path

Original planned path

Figure 3. After encounteringapreviouslyunknownobstacleshown in light orange,CASPERreplansthe sequenceof targets.Bluecrossesarethegoallocations,anddarkorangeshapesareobstaclesknown apriori.

cameras,selecta paththroughthe terrainto the edgeof theeffective stereorange,andrepeatthe processuntil the goalis achieved. A representative exampleof a partialpanoramaand the resultingelevation mapof the terrainareshown inFigure4.

Rocky 7 usesa localsensor-basedpathplannercalledRover-Bug [8], [9]. This algorithmwasdevelopedfor vehiclesthathave limits on sensorrange,field of view, and processing.The two main modesof operationare motion-to-goalandboundary-following, which areusedto provide global con-vergence.

Rover-Bug works by using the local elevation map to con-structa mapof convex hulls aroundall obstaclesin thesens-ing range.Thesehullsarethenmergedandgrown to providea configurationspacerepresentationof thesensedterrain. Atangentgraphis constructedto determineif thereis an un-obstructedpath to the envelopeof the sensedregion in thedirectionof thegoal. If oneexists,it is followed,andthepro-cessis repeatedat theendof thepathsegmentto thesensoryenvelope.

If a free path doesnot exist, stereoimagesareobtainedtothemostpromisingsideof thecurrentview, andtheprocessis repeated.In somecases,the free pathplacesthe rover attheedgeof thesensoryenvelopebut still obstructedfrom thegoalby anobstacle.In this case,therover will begin to useits body-mountedcamerasto reactivelyboundaryfollow untilthereis aclearpathto thenext goal.

Figure 5 shows experimentaldata obtainedfrom Rocky 7while usingthisalgorithmto traverseourMarsYardtestarea.The startpositionis in the lower left corner, 21 m from thegoalin theupperright. Foursetsof sensorydataareshown as

Figure 4. Stepsof on-boardterrainsensing:panoramicmosaicview from rover maststereoimager, compositerangemapextractedfrom stereoviews,andelevationmapcreatedfrom rangedata.

Figure 5. Experimentalresultsfrom a multi-steprun usingRover-Bug in theJPLMarsYard.

orangewedgesalongthepath.Projectedon to thesedatasetsarethepink convex hull representationsof thesensedobsta-cles. The greenandblue lines passingthroughthe obstaclefield are the plannedandexecutedpaths,respectively. Thegapbetweendatasetsis dueto alackof mergingof datafromboth the mastandbody-mountedcameras,and is currentlybeingcorrected.Thesuddenchangesin thepathdirectionatthefarsideof eachwedgedoesnotindicatedactualrovermo-tion; ratherit is anartifactof theestimatedroverpositionthatis updatedby localizationat this point in the traverse. Thislocalizationis discussednext.

VisualLocalization

Visual localization usesthe sameterrain imagery as pathplanning,but for thepurposeof monitoringtheapparentmo-tion of three-dimensionalgroundfeaturesafter therover hascompleteda move. In this way, the on-boardpositionesti-mateof the rover can be updatedto compensatefor errorscausedby wheelslippageor rock bumping. On Pathfinder,thislocalizationfunctionalitywasperformedmanuallybyop-eratorsviewing Sojournerfrom thefixedpositionlandercam-eras,restrictingtheupdateto onceadayandpermittingoper-ationsonly within thestereoenvelopeof the lander. In con-trast,the terrain-basedlocalizationdescribedherehasappli-cationto many forms of landerlessoperations:incrementallong traverses,local operationswithin rangeof a prior stereopanorama,localizationin descentimagery, andclosedchainrovermoveswith estimatesmoothing.

Goal position

Localization target

Figure 6. Exampleof automatictargetselectionfor local-ization.

Thetechniquereliesonobtainingastereoelevationmapfromtheinitial roverposition,asshown in Figure4. This imageryis automaticallyanalyzedbasedontherangedataquality, andthequality expectedto beseenat thegoalpoint specifiedbypathplanning[11]. Typically, therewill bea prominentrockbetweenthe two locations. From the analysis,it will be se-lectedasthelocalizationtarget,andviewedby theroverafterreachingthe endof the local pathsegment. Figure6 showsanexampleof theautomatictargetselection,with four imagesconcatenatedto provideareasonablenumberof potentialtar-gets.

To match the two stereo views of the terrain, a multi-resolutionsearchtechniqueis usedto provide the bestesti-mateof thedisplacementof theoriginal elevationmapfromthe final one[12]. Typical resultsprovide positionerror es-timatesthat are1% of the distancetraveled. However, thesearchusestheon-boardestimateof therover positionasitsstartingpoint,somorereliableresultsareobtainedif theini-tial estimateis moreaccurate.Therefore,to obtainbettercon-tinuouspositionestimates,we have beendevelopinga newestimationtechnique,discussednext.

0 2 4 6 8 10−10

0

10

20

ξ1

(deg

) ESTSIM

0 2 4 6 8 10−10

−5

0

5

10

ξ2

(deg

) ESTSIM

0 2 4 6 8 10−10

−5

0

5

10

t (s)

ξ3

(deg

) ESTSIM

0 2 4 6 8 10−20

−10

0

10

ξ4

(deg

) ESTSIM

0 2 4 6 8 10−10

−5

0

5

ξ5

(deg

) ESTSIM

0 2 4 6 8 10−5

0

5

10

t (s)

ξ6

(deg

) ESTSIM

Figure 7. Simulationresultsshowing truevaluesandesti-matesfor wheelcontactpositions,wherethe left/rightthree wheelsanglesare shown by the left/right sidegraphs.

KinematicStateEstimation

In addition to periodic visual localizationof the rover, wehavedevelopedreal-timepositionandheadingestimationus-ing all othersensorson thevehicle:angularrate,accelerom-eter, sunsensor, wheelanglerates,andmobility systemlink-age(rocker-bogey) configuration.This techniquemovesfarbeyondthesimpledeadreckoningof Sojournerandimprovesuponour previous advancesin positionestimationwith sunsensing[15]. The resultsaid navigation during pathexecu-tion, provide betterinput to localization,andreplacebothinvisually featurelessterrain(e.g.,sanddunes)or in thecaseofvisualsensingfailure.

Theestimatorusesa Kalmanfilter framework, with thepro-cessmodelchosensothattheinertial sensordataareusedasaninput to drive theprocessequation.Theprocedureavoidsthe difficulty of modelingthedetailedprocessdynamics[1]by exploiting the ability of the Kalmanfilter to performtheappropriateleast-squaresaveragingof theactionof eachkine-maticchainin therover. Theseforwardkinematicchainshavevelocitycomponentsdefinedby thesequenceof links joiningthe rover frame to eachestimatedwheelcontactpoint, anda componentgiven by the slip betweenthe wheel and theground. The deterministiccomponentof the slip is usedtocapturetheeffectsof a known steeringactionor a known av-erageslip rateoverdifferentkindsof terrain.

Bothsimulationandexperimentalresultswith thisestimationtechniquehavebeenconducted.Figures7showstheability oftheestimatorto correctlytrack thewheelcontactangleoveranundulatingterrain.Thesimulationis particularlyvaluablesincegroundtruthcanbeknown exactly. For instance,usingsimpleintegrationof thewheelvelocity resultsin a 2% errorin measuredposition,while theestimatorreducestheerrorbyanorderof magnitude.

Experimentalresultsfurthersupporttheseconclusions.Fig-ure8 shows theresultsfrom Rocky 7 driving over anobsta-cle on the right sideof the vehicleonly. While the left side

0 5 10 15 20 25−10

−5

0

5

ξ1

(de

g)

0 5 10 15 20 25−2

−1

0

1

ξ2

(de

g)

0 5 10 15 20 25−1

0

1

2

t (s)

ξ3

(de

g)

0 5 10 15 20 25−20

−10

0

10

ξ4

(de

g)

0 5 10 15 20 25−10

0

10

20

ξ5

(de

g)

0 5 10 15 20 25−20

−10

0

10

t (s)

ξ6

(de

g)

Figure 8. Experimentalresultsfrom Rocky 7 showing theestimatesfor wheelcontactangles.

Figure 9. TheSampleReturnRover.

wheel contactpoints changeonly slightly, the much largerchangesin the right sidearecorrectlydetermined.Note, inthefinal configuration,thebogey wheelswerestill on theob-stacle,while thesteeringwheelhadcompletelytraversedtheobstacle. The estimatedwheel contactangleswere within5 degreesof thetruevaluesmeasuredindependently. Furtherexperimentsarein progress,aswell asintegrationof visualpositionestimation,asdescribedin thenext section.

4. SAMPLE RETURN ROVER TECHNOLOGIES

In 1997,JPLbegandevelopmentof theSampleReturnRover(SRR),a small, lightweight rover that investigatedfocusedtechnologyadvancesin theareasof rover-to-roverandrover-to-landerrendezvous. SRR, shown in Figure 9, is a 7 kgrover with a 4-wheel rocker mobility systemthat is capa-ble of traversingover obstaclesup to 15 cm in height. Therover includes4-wheelsteeringandcarriesa threedegrees-of-freedommanipulatorarmwith a1degree-of-freedomgrip-per. This robot arm is usedfor panoramicimaging alongwith samplepick-up and transfer. The rover also includesaposablerockerjoint for variablegroundclearanceandroverreconfigurationin difficult terrain. SRR carriesa PC104+derived electronicssystem,including a 300 MHz AMD K6processor, motioncontrolI/O boards(D/A andencoderread-erswith closed-loopcontrolrealizedin software),A/D board,PCIcolor framegrabbers,andawirelessEthernet.

Theoriginal conceptfor SRRderivedfrom thepreviousver-sion of the MSR missionwherean Athena-classrover tra-

versedlongdistances,stoppedatinterestingsciencesites,andacquired� andstoredrock andsoil samples.During a secondmission,asmall,lightweightroverwouldlandontheMartiansurfaceandrendezvouswith thesciencerover to retrieve thesamplecollectedduring the primary sciencemission. Sucha rover-to-rover rendezvous was demonstratedby the SRRtechnologyteamduring thesummerof 1998[13]. This ren-dezvouswas accomplishedusing an RF beacontransmitterand receiver pair for non-line-of-sitenavigation to the sci-encerover, visual trackingof thestaticsciencerover duringline-of-sightnavigation,determinationof rover-to-roverposeusingman-madefeatureslocatedon the sciencerover, and,terminalguidanceto thesamplecachecontainerandpickupof thiscontainerusingtheon-boardmanipulatorarm.

In 1999, the SRR task turned its attentionto the rover-to-landerrendezvousproblemin supportof the MSR missionandthe requirementthat the Athenarover return its cachedsamplesto the landerand the awaiting MAV, as describedin Section2. Someof the technologydevelopmentsestab-lishedduringtherover-to-roverrendezvousapplicationweretransferredto the rover-to-landerrendezvousproblem. Therequirementsof theAthenarover mission,however, necessi-tatedthe developmentof new techniquesfor the robust andaccuratenavigation of SRRwith respectto the landersuchthat autonomouslanderacquisition,landerrendezvous,andrampclimbingarepossiblewith minimal, if any, groundsup-port. Figure10depictsthescenarioassociatedwith therover-to-landerrendezvousproblemin termsof themulti-phaseop-erationsandtechnologiesusedduringthereturnto thelander.The rover-to-landerrendezvousproblemis divided into thefollowing phases:

� Longdistancevisualtrackingusinglandertexturefeaturesderivedin thewaveletspace

� Multi-point tracking of lander featuresfor headingandrangeestimationof theroverrelative to thelander

� Ramplocationdeterminationusinglanderfeatures� Ramp recognition using cooperative ramp featuresfor

headingand rangeestimationof the rover relative to thebottomof theramps

Thelong-distancenavigationof SRRrelative to thelanderisaccomplishedwith anovelwavelet-baseddetectionalgorithmfor thelong-rangevisualacquisitionof a landerfrom greaterthan 100 m using a single, black-and-whiterover imagingsystem(20 degreefield of view) [4]. This informationen-ablesautonomouscorrectionthe rover headingwith respectto the lander, andto guidanceof SRRto within 25 m of thelander. Sucha navigation sequenceis shown in Figure11.Within 25 metersof the lander, a visual techniquethat takesadvantageof the known geometryof the landerstructureisusedto trackmultiple features(e.g.,landerleg struts,landerdeck,etc.) to determinetheposeof the rover relative to thelander. Preliminaryresultsindicatethatprecisionontheorderof 50cmin rangeand1 to 2 degreesin orientationis possibleusingthisapproach.

Likewise,theknown rampgeometryallowsfor thevisualac-quisition of the landerrampsandthe relative positioningoftherover relative to theramps.Thesetechniquescombinetoproducea navigation strategy for the autonomousguidance

of the rover from 25 m from the landerto 5 m in front ofthe ramps.Finally, visual acquisitionof the landerrampsisaccomplishedusingcooperativemarkingsfrom which rover-to-ramppositionandheadinginformation is obtained. Thesuccessive visual acquisitionof the landerrampsbringstherover from 5 metersto within 5 cm of thebottomof the lan-der ramps.Many successfulexperimentshave beenaccom-plishedin bothlaboratoryandoutdoorsettings.Theseresultsindicatethattherovercanreliableandrobustlynavigateto thebottomof therampswith anabsoluteprecisionof 1 cmin lat-eralandlongitudinaloffsetandlessthan1 degreeorientationerrorwith respectto theramps.As such,thecombinationoftheserovernavigationtechniquesleadsto a single-commandautonomoussequenceassociatedwith thereturnto thelanderandtheregressof theroverupthelanderrampsto depositthesamplecachein theMAV.

Finally, theSRRtaskhas,over thepasttwo years,developedanalternative form of rover stateestimationfor theaccurateandreliabledeterminationof rover positionandorientationrelativeto afixedreferenceframe.Thistechniqueusesanex-tendedKalmanfilter framework basedonthework describedin [3]. Within theSRRdevelopment,theregistrationof suc-cessive rangemapsgeneratedby therover’s forward-lookinghazardavoidancecamerasareutilizedtodeterminetheframe-to-frametranslationandrotationof the rover. This informa-tion is combinedwith deadreckonedestimatesof therover’stranslationandrotationto producean optimizeddetermina-tion of therover pose.This work is describedin [7] and[2]andillustratedin Figure12 for a 6+ m traversewithin a soft-soil, rock-filled indoorsandpit.

5. FIDO ROVER TECHNOLOGIES

As describedin Section2, the2003/05MSR’s Athenarovermissionrepresentsa significantincreasein complexity overtherecentSojournerrovermission.TheAthenarovercarriesseven sciencepayloadelements,including a multi-spectralimagingsystem,amicroimager, asampleacquisitionsystem,andfour differentspectrometersascomparedto Sojourner’ssinglescienceinstrument,theAlpha ProtonX-ray spectrom-eter. In addition,the Athenarover hasover eight timesthevolumeand six times the massof the Sojournerrover. Assuch,theAthenarover representsa truesciencecraftandful-fills theneedfor a roboticfield geologistonMars.

To facilitatethesuccessfuloperationof theAthenaroverdur-ing the 2003/05Mars SampleReturnmissions,a terrestrialprototypeof theAthenaroveris beingusedby theAthenasci-enceteamfor scienceandengineeringtestingassociatedwithflight missionoperations. The developmentof this roboticvehicle,known as FIDO (for Field Integrated,Design,andOperations)rover began in early 1998 with the conceptualdesignof thevehicleandculminatedninemonthslaterwiththefull-scaleintegrationof theroverandits sciencepayload[14]. In April 1999(lessthan14monthssincetheinitial paperdesigns),theFIDO roverwassuccessfullyoperatedattheSil-ver Lake field testsiteoutsideBaker in California’s Mojavedesert. Figure13 shows FIDO operatingduring this desertfield test.

FIDO’s mobility subsystemconsistsof a 6-wheel rocker-

Figure 10. Theoperationsscenarioassociatedwith thereturnto thelander.

Figure 11. Wavelet-basedlanderdetectionandnavigation.

Kalman FilteredDead Reckoned

0 10 20 30 40 50 60 70 800

0.5

1

1.5

2

2.5

3Position Est. Error wrt. Ground Truth, K.F. vs. D.R.

Time (Navigation Iterations)

Pos

ition

Err

or (

m)

Figure 12. Stateestimationfor roverposedetermination.

Figure 13. TheFIDO roverduringtheSilverLakefield trial.

bogiesuspensionsystemthathasbeenscaledup by a factorof 20/13 from the Sojournerdesign. This suspensionsys-temallows for thesafetraverseoverobstaclesup to 30cminheight. Eachwheel is independentlydriven andsteeredus-ing a Sojourner-derivedactuationandencodersystem. Thetop groundspeedof the vehicle is 9 cm/sec. Approximaterover dimensionsare1 m in length,0.8m in width, 0.5m inheight,and0.23m groundclearance.Therovercarriesafourdegrees-of-freedomdeployablemastthat stands1.94 m offthegroundsurfaceat full extent.Thismastprovidesthenec-essarypan-and-tiltcontrol for panoramicimagingandpointspectroscopy. FIDO alsocarriesa four degrees-of-freedominstrumentarmthatis usedto placethein situsuiteof instru-mentson rockandsoil targets.

TheFIDO electronicsaresimilar in natureto theSRRelec-tronicswith theCPUbeinga 80586AMD processorrunningat a 133 MHz clock speed. The rover usesa PC104-basedplatform for all I/O functions, including a motion controlsystem(D/A and encoderreaderswith closed-loopcontrolin software) that can control up to 30 actuatorssimultane-ously, two monochromaticandonecolor framegrabbers,dig-ital I/O boards,A/D boards,low-passfilter andanalogmul-tiplexerboards,andawirelessEthernet.Engineeringsensorsinclude front and rear stereohazardavoidancecamerasys-tems,aninertialnavigationsystem,andasunsensorfor abso-luteheadingdetermination.A differentialGPSunit is alsoin-tegratedwithin theroverelectronicsfor ground-truthingpur-posesonly.

Figure 14. Theminiaturecoredrill acquiringacoresamplefrom a carbonaterockatSilverLake

ThesciencepayloadonFIDOis analogousto theAthenapay-load. In particular, the remotesensingsuite locatedon theFIDO mast includesa multi-spectral,narrow field-of-viewPancam stereo imaging system; a monochromatic,widerfield-of-view Navcamstereoimagingsystem;andtheopticsfor a near-IR point spectrometerthatoperatesin the1200to2500 nm wavelengthregion. The multi-spectralcapabilityassociatedwith the Pancamsystemis realizedusinga Liq-uid CrystalTunableFilter (LCTF) that is tunedto the threenear-IR wavelengthsof 650, 750 and 850 nm. The in situinstrumentsuiteattachedto theend-effectorof theFIDO in-strumentarm consistsof a color microimageranda Moess-bauerspectrometerthatareusedto determinetheiron contentof targetrocks.A miniaturecoredrill system,body-mountedto therover, providesthecapabilityto acquireandcacherockandsoil samples.All of theseinstruments,with theexceptionof the near-IR point spectrometer(the flight missionusesaminiaturethermalemissionspectrometerin themid-IR wave-length region), arebreadboardsof the Athenaflight instru-ments.

In total,thescienceinstrumentandengineeringsensingsuitesand the resultingFIDO rover systemrepresenta terrestrialanalogof theAthenarover thatcanbeusedto testandvali-datetheAthenamissionscenarioandassociatedengineeringfunctions.As such,theAthenascienceteamledby ProfessorSteven Squyres,AthenaPI, andProfessorRaymondArvid-son, AthenaCo-I, has worked with the FIDO engineeringteamsinceMarch1999to performroveroperationstestinginsupportof theAthenarovermission.In particular, thedesertfield trial at theSilverLake testsiterepresentedthefirst everdemonstrationandvalidationof thesampleacquisitionphaseof theAthenarovermissionthroughtheidentificationof tar-getrocks,approachto thetargetrock,placementof theminia-turecoredrill over the target rock, successfulacquisitionofa core sampleusing the miniaturecore drill, and return ofthesesamplesto a simulatedlandingsite. Figure14 showstheFIDO rover andassociatedcoredrill duringthesuccess-ful acquisitionof acoresamplefrom acarbonaterock. Futurefield trials in 2000and2001will focusonflight-likeroverop-erations,with therover andscienceteamsbeingsequesteredat JPLwhile therover is locatedat a remotetestsite. Duringsuch“blind” field trials,thefull Athenamissionscenariowillbethefurthervalidated,includingsampleacquisitionandre-turn to the landeraswell as long-rangescienceexplorationanddiscovery.

6. SUMMARY

This paperhasreviewed several recentresearchefforts thatsupportupcomingMSR missionscenarios.Threeresearchtasks,LRSR,SRR,andFIDO,havebeendevelopingandtest-ing new capabilitiesin prototyperover platforms.LRSRre-searchwith Rocky 7hasdevelopedfournew techniquestoen-hancethefunctionalityof autonomouslong-rangeMarsrovernavigation: intelligent sequencing,sensorconstrainedpathplanning,naturalterrainvisual localization,andKalmanFil-ter stateestimation. SRR hasdevelopeda return-to-landercapabilitywith visual trackingat variousranges,usingtech-niquessuitableto thoseranges.It hasalsodisplayedvisualodometrytechniques.Finally, FIDO representstheculmina-tion of thetwo corerobotictechnologyprogramssinceits de-velopmentis basedon the experiencesgainedwithin LRSRandSRR.As aresult,it hasbecomeastandardintegrationandtestsystemfor thevalidationof rover navigationandcontrolstrategies.

7. ACKNOWLEDGMENTS

Largesystemslike theserequirethesupportof many peoplebeyondtheauthors.We would like to recognizethe follow-ing individualsfor their invaluablecontribution to the workdescribedin this paper: the LRSR teamincludesJ. (Bob)Balaram,Clark Olson,SharonLaubach,TaraEstlin,RichardPetras,DarrenMutz, Greg Rabideau,and Mark Maimone;theSRRteamincludesHrandAghazarian,TerryHuntsberger,YangCheng,MikeGarrett,andLeeMagnone;theFIDOteamincludesHrandAghazarian,TerryHuntsberger, Anthony Lai,RandyLindemann,Paul Backes,Brett Kennedy, Lisa Reid,MikeGarrett,andLeeMagnone.

The researchdescribedin this paperwascarriedout by theJetPropulsionLaboratory, CaliforniaInstituteof Technology,underacontractwith theNationalAeronauticsandSpaceAd-ministration. Referenceherein to any specificcommercialproduct,process,or serviceby tradename,trademark,man-ufacturer, or otherwise,doesnot constituteor imply its en-dorsementby theUnitedStatesGovernmentor theJetPropul-sionLaboratory, CaliforniaInstituteof Technology.

REFERENCES

[1] J. Balaram. Kinematic State Estimation for a MarsRover. Robotica, Special Issue on Intelligent Au-tonomousVehicles, Acceptedfor publication,1999.

[2] E. T. Baumgartner, P. C. Leger, P. S.Schenker, andT. L.Huntsberger. SensorFusedNavigationandManipulationfrom a PlanetaryRover. In SensorFusionand Decen-tralizedControl in RoboticSystems,SPIEProceedings3523, Boston,November, 1998.

[3] E. T. Baumgartnerand S. B. Skaar. An AutonomousVision-BasedMobile Robot. IEEE Transactionson Au-tomaticControl, 39(3):493–502,March1994.

[4] J-K. Changand T. L. Huntsberger. Dynamic MotionAnalysisusingWavelet Flow SurfaceImages. PatternRecognitionLetters, 20(4):383–393,1999.

[5] S.Chien,R. Knight, R. Sherwood,andG. Rabideau.In-tegratedPlanningandExecutionfor AutonomousSpace-

craft. In IEEEAerospaceConference, AspenCO,March1999.

[6] T. Estlin, G. Rabideau,D. Mutz, andS. Chien. UsingContinuousPlanningTechniquesto CoordinateMultipleRovers.In IJCAIWorkshoponSchedulingandPlanning,Stockholm,Sweden,August1999.

[7] B. D. Hoffman, E. T. Baumgartner, T. L. Huntsberger,andP. S.Schenker. ImprovedRover StateEstimationinChallengingTerrain.AutonomousRobots, 6(2),1999.

[8] S. Laubach. Theoryand Experimentsin AutonomousSensor-BasedMotion Planning with Applications forFlight PlanetaryMicrorovers. PhDthesis,CaliforniaIn-stituteof Technology, May 1999.

[9] S. Laubachand J. Burdick. An AutonomousSensor-BasedPath-Plannerfor PlanetaryMicrorovers. In IEEEInternationalConferenceon Roboticsand Automation,DetroitMI, 1999.

[10] J. Matijevic et al. Characterizationof theMartianSur-faceDepositsby the Mars PathfinderRover, Sojourner.Science, 278:1765–1768,December5 1997.

[11] C. Olson. Subpixel LocalizationandUncertaintyEsti-mationUsing Occupancy Grids. In IEEE InternationalConferenceon Roboticsand Automation, pages1987–1992,Detroit,Michigan,May 1999.

[12] C. OlsonandL. Matthies. Maximum-likelihoodRoverLocalizationby MatchingRangeMaps. In IEEE Inter-nationalConferenceonRoboticsandAutomation, pages272–277,Leuven,Belgium,May 1998.

[13] P. S. Schenker et al. New PlanetaryRovers for LongRangeMars ScienceandSampleReturn. In IntelligentRobotsand ComputerVision XVII, SPIE Proceedings3522, Boston,November, 1998.

[14] P. S. Schenker et al. FIDO Rover and Long-RangeAutonomousMars Science. In Intelligent RobotsandComputerVisionXVIII, SPIEProceedings3837, Boston,September, 1999.

[15] R. Volpe.NavigationResultsfrom DesertFieldTestsoftheRocky 7 MarsRover Prototype.InternationalJour-nal of RoboticsResearch, 18(7),1999.

[16] R.Volpeetal. Rocky 7: A Next GenerationMarsRoverPrototype. Journal of AdvancedRobotics, 11(4):341–358,1997.

Richard Volpe, Ph.D., is the Principal Investigatorfor theLongRangeScienceRoverResearchProject,andtheSystemTechnologistfor the Athena-Rover samplecollection robotfor the 2003Mars SampleReturnProject. His researchin-terestsincludereal-timesensor-basedcontrol, robot design,softwarearchitectures,pathplanning,andcomputervision.

Richardreceived his M.S. (1986)and Ph.D. (1990) in Ap-plied Physicsfrom Carnegie Mellon University, where hewasa US Air ForceLaboratoryGraduateFellow. His the-sisresearchconcentratedon real-timeforceandimpactcon-trol of robotic manipulators.SinceDecember1990,he hasbeenat theJetPropulsionLaboratory, CaliforniaInstituteofTechnology, wherehe is a SeniorMemberof the TechnicalStaff. Until 1994,hewasamemberof theRemoteSurfaceIn-spectionProject,investigatingsensor-basedcontrol technol-ogy for teleroboticinspectionof theInternationalSpaceSta-tion. Startingin 1994,he led thedevelopmentof Rocky 7, anext generationmobilerobotprototypefor extended-traversesamplingmissionson Mars. In 1997,he received a NASAExceptionalAchievementAwardfor thiswork, whichhasledto thedesignconceptsfor the2003Marsrovermission.

Eric T. Baumgartner, Ph.D., is a group leaderin the Me-chanicalandRoboticsTechnologyGroupanda seniormem-ber of engineeringstaff in the ScienceandTechnologyDe-velopmentSectionat NASA’s JetPropulsionLaboratoryinPasadena,CA. At JPL,heservesin asystemsengineeringca-pacityfor thedevelopmentof advancedplanetaryroversandalsocontributesto technologydevelopmentsin the areasofrobotic sensingand control. Prior to his tenureat JPL, hewasan AssistantProfessorin the MechanicalEngineering-EngineeringMechanicsDepartmentat MichiganTechnolog-ical University in Houghton,MI. He haspublishedover 30articlesin the areaof robotic, controls,andstateestimationandis activein theSPIEandASME.HereceivedhisB.S.de-greein AerospaceEngineeringfrom theUniversityof NotreDame,the M.S. degreein AerospaceEngineeringfrom theUniversityof Cincinnatiin 1990,andthePh.D.in Mechani-calEngineeringfrom theUniversityof NotreDamein 1993.

Paul S. Schenker, Ph.D., is Supervisorof the Mechani-cal andRoboticsTechnologiesGroup,MechanicalSystemsEngineeringandResearchDivision, JetPropulsionLabora-tory. His current work emphasizesplanetaryrover devel-opmentandrobotic samplingtechnologies;he is taskman-agerfor NASA/JPL’s SampleReturnRover (SRR)andEx-ploration TechnologyRover Design, Integration, and FieldTest R&D efforts (”ET Rover/FIDO” – a Field IntegratedDesign& Operationsrover prototypesupportingthe NASAMars ’03-’05 samplereturn missions, and related terres-trial missionsimulations),as well as new NASA tasksonuseof cooperatingroboticassets/roversfor Marsexplorationand future humanhabitation. Schenker also recently ledJPL’s PlanetaryDexterousManipulatorsR&D underNASAfunding, work that proto- typed a robotic sampling con-cept which flies on the NASA Mars Polar Landermissionnow in route to the red planet. Schenker’s other recentroboticsR&D activities includea role asfoundingco-PI forNASA/MicroDexterity SystemsInc. developmentof aRobotAssistedMicrosurgeryhigh-dexterity tele-operativeworksta-tion andalongerstandinginvolvementin varioustele-robotictechnologyand systemdevelopmentsfor orbital servicingandautonomousroboticexploration. Schenker is a memberof AAAI, IEEE, and SPIE;he is a Fellow and1999Presi-dentof thelast. Schenker is widely active in externaltechni-cal meetings,publications,and university collaborationsinthe areasof roboticsand machineperception,having con-tributedabout100 archival articlesto same. Dr. Schenkerreceivedhis B.S. in EngineeringPhysicsfrom Cornell Uni-versity, andcompletedhisM.S.,Ph.D. andpostdoctoralstud-ies in ElectricalEngineeringat PurdueUniversity. Prior tojoining JPL/Caltechin 1984,Schenker waswith theElectri-calSciencesfaculty, BrownUniversity, andlatertheResearchSectionChieffor Signal& ImageProcessing,Honeywell Inc.

Samad Hayati received his M.S. andPh.D. in MechanicalEngineeringwith a specialtyin controlsfrom theUniversityof CaliforniaatBerkeley in 1972,and1976,respectively. Hejoined the JetPropulsionLaboratoryin 1979andworked intheguidanceandcontrolof theJupiterorbiterGalileospace-craft, currently orbiting Jupiter. From 1983-1999he per-formedresearchin roboticsat JPL.He wasalsoa lecturerofroboticsat theCalifornia Instituteof Technologyfrom 1986to 1988.He haspublishednumerousconferenceandjournalpapersandholdstwo US patentsrelatedto roboticscontrol.His pioneeringwork in robotcalibrationwasusedto developtechniquesto utilize manipulatorsasan aid in brain neuro-surgery at the Long BeachMemorial Hospital in Californiain 1986.His mostrecentresearcheffortswerein thedevelop-mentof long rangescienceroverandrendezvousandsampleretrieval technologiesfor NASA’splannedmissionsto Mars.

Currently, Samadis the managerof RoboticsandMars Ex-plorationTechnologyProgramsatJPL.

In April 2004, two mobile robots named Spiritand Opportunity successfully completed their primarythree-month missions on opposite sides of Mars andwent into bonus overtime work. These twin vehiclesof NASA’s Mars Exploration Rover project continuedtheir pursuit ofgeological cluesabout whetherparts of Mars for-merly had envi-ronments wetenough to be hos-pitable to life.

Opportunityhit the jackpotearly. It landedclose to a thinoutcrop of rocks.Within twomonths, its versa-tile science instru-ments found evi-dence in thoserocks that a bodyof salty waterdeep enough tosplash in onceflowed gentlyover the area.Preliminary inter-pretations point to a past environment that could havebeen hospitable to life and also could have preservedfossil evidence of it, though these rovers are notequipped to detect life or to be fossil hunters.

As Opportunity’s primary mission ran out and anextended mission began, the rover was headed forthicker layers of exposed bedrock that might bear evi-dence about how long or how often water covered theregion.

Spirit, duringits primary mis-sion, explored aplain strewn withvolcanic rocksand pocked withimpact craters. Itfound indicationsthat smallamounts of watermay have gotteninto cracks in therocks and mayalso have affect-ed some of therocks’ surfaces.This did not indi-cate a particularlyfavorable pastenvironment forlife.

Spirit’sextended missionbegan with therover starting a

long trek toward a range of hills on the horizon whoserocks might have come from an earlier and wetter eraof the region’s past.

Mars Exploration Rover

NASA FactsNational Aeronautics andSpace Administration

Jet Propulsion LaboratoryCalifornia Institute of TechnologyPasadena, CA 91109

Shadow of rover Opportunity in “Endurance Crater,” July 26, 2004.

Second Extension as Adventure Continues

In late September 2004, NASA approved a secondextension of the rovers’ missions. The solar-poweredmachines were still in good health, though beginningto show signs of aging. They had come through theworst days of the martian year from a solar-energystandpoint. Also, they had resumed full operationsafter about two weeks of not driving in mid-September while communications were unreliablebecause Mars was passing nearly behind the Sun.

Spirit had driven 3.6 kilometers (2.25 miles), sixtimes the goal set in advance as a criterion for a suc-cessful mission. It was climbing hills where its exam-inations of exposed bedrock found more extensivealteration by water than what the rover had seen inrocks on the younger plain. During the long trek,Spirit’s right front wheel developed excessive friction.Controllers found a way to press on with the explo-ration by sometimes driving the rover in reverse withthe balky wheel dragging.

Opportunity had driven about 1.6 kilometers (1mile). It was studying rocks and soils inside a craterabout 130 meters (142 yards) wide and 22 meters (24

yards) deep. The rover entered this crater in June aftercareful analysis of its ability to climb back out.Inside, Opportunity examined layer upon layer ofbedrock with characteristics similar to those of theoutcrop inside the smaller crater where it landed. Thisindicated a much longer duration for the watery por-tion of the region’s ancient past. The rover also foundsome features unlike any it had seen before, evidenceof changes in the environment over time.

Whether the rovers’ unpredictable life spanswould extend only a few more days or several moremonths, they had already racked up successes beyondthe high expectations set for them when the MarsExploration Rover project began.

Favorable Time to Build on Experience

Mars came closer to Earth in August 2003 than ithad in thousands of years. NASA decided in the sum-mer of 2000 to take advantage of this favorable plane-tary geometry to send two rovers to Mars.

The design began with some basics fromSojourner, the rover on NASA’s 1997 Mars Pathfindermission. Some of the carried-over design elements are

2

Artist’s simulation of a Mars Exploration Rover at work on Mars.

six wheels and a rocker-bogie suspension for drivingover rough terrain, a shell of airbags for cushioningthe landing, solar panels and rechargeable batteriesfor power, and radioisotope heater units for protectingbatteries through extremely cold martian nights.However, at 174 kilograms (384 pounds), each MarsExploration Rover is more than 17 times as heavy asPathfinder. It is also more than more than twice aslong (at 1.6 meters or 5.2 feet) and tall (1.5 meters or4.9 feet). Pathfinder’s lander, not the Sojourner rover,housed that mission’s main communications, cameraand computer functions. The Mars ExplorationRovers carry equipment for those functions onboard.Their landers enfolded them in flight and performedcrucial roles on arrival, but after Spirit andOpportunity rolled off their unfolded landers ontomartian soil, the landers’ jobs was finished.

NASA’s Jet Propulsion Laboratory, Pasadena,Calif., designed and built the two new rovers plus thelander and the cruise stage for each. The cruise stageprovided capabilities needed during the journey fromEarth to Mars. In early 2003, the hardware arrived atNASA’s Kennedy Space Station in Florida for finalassembly, testing and integration with Boeing Delta IIlaunch vehicles.

While the twin spacecraft were being built, scien-tists and engineers winnowed a list of 155 candidatelanding sites to a final pair best suited to the mis-sions’ goals and safety. More than 100 Mars expertsparticipated in evaluating the sites. They made heavyuse of images and other data from NASA’s MarsGlobal Surveyor and Mars Odyssey orbiters.

The rover project’s science goal has been to assessthe history of environmental conditions at sites thatmay once have been wet and favorable to life. Eachof the two selected landing sites showed evidencedetectable from orbit that it may have once been wet.For Spirit, NASA chose Gusev Crater, a Connecticut-size basin that appears to have once held a lake, judg-ing from the shapes of the landscape. A wide channel,now dry, runs downhill for hundreds of kilometers ormiles to the crater and appears to have been carved bywater flowing into the crater. For Opportunity, NASAchose part of a broad plain named Meridiani Planumbased on a different type of evidence for a possiblywatery past. A mineral-mapping instrument on MarsGlobal Surveyor had identified there an Oklahoma-

size exposure of gray hematite, a mineral that usuallyforms in the presence of liquid water.

Getting to Mars

Both rovers were launched from Cape CanaveralAir Force Station on central Florida’s Space Coast.Spirit ascended in daylight on June 10, 2003.Opportunity followed with a nighttime launch on July7 after several days of delays for repairing cork insu-lation.

During the cruise to Mars, Spirit made four trajec-tory correction maneuvers. Opportunity performedthree. The two spacecraft survived blasts of high-energy particles from some of the most intense solarflares on record. To prevent possible problems fromthe flares’ effects on computer memory, mission con-trollers commanded rebooting of the rovers’ comput-ers, a capability originally planned for use on Marsbut not during the cruise.

Each rover made the trip tightly tucked inside itsfolded-up lander, which was encased in a protectiveaeroshell and attached to a disc-shaped cruise stageabout 2.6 meters (8.5 feet) in diameter. The cruisestage was jettisoned about 15 minutes before thespacecraft reached the top of Mars’ atmosphere.

With the heat-shield portion of the aeroshellpointed forward, the spacecraft slammed into theatmosphere at about 5.4 kilometers per second(12,000 miles per hour). Atmospheric friction in thenext four minutes cut that speed by 90 percent, then aparachute fastened to the backshell portion of theaeroshell opened about two minutes before landing.About 20 seconds later, the spacecraft jettisoned theheat shield. The lander descended on a bridle thatunspooled from the backshell. A downward-pointingcamera on the lander took three pictures during thefinal half-minute of the flight. An onboard computerinstantly analyzed the pictures to estimate horizontalmotion. In the final eight seconds before impact, gasgenerators inflated the lander’s airbags, retro rocketson the backshell fired to halt descent speed, and trans-verse rockets fired (on Spirit’s lander) to reduce hori-zontal speed. The bridle was cut to release the landerfrom the backshell and parachute. Then the airbag-encased lander dropped in free fall.

Spirit landed on Jan. 4, Universal Time (at 8:35p.m. Jan. 3, Pacific Standard Time). It bounced

3

about 8.4 meters (27.6 feet) high. After 27 morebounces and then rolling, it came to a stop about 250to 300 meters (270 to 330 yards) from its first impact.Spirit had journeyed 487 million kilometers (303 mil-lion miles). JPL navigators and engineers successfullyput it only about 10 kilometers (6 miles) from thecenter of its target area. Coordinates of Spirit’s land-ing site are 14.57 degrees south latitude and 175.47degrees east longitude.

Opportunity landed on Jan. 25, Universal Time (at9:05 p.m. Jan. 24, Pacific Standard Time). It traveledabout 200 meters (220 yards) while bouncing 26times and rolling after the impact, with a 90-degreeturn northward during that period. It came to restinside a small crater. One scientist called the landingan “interplanetary hole in one.” Opportunity hadflown 456 million kilometers (283 million miles)from Earth and landed only about 25 kilometers (16miles) from the center of the target area. The landing-

site crater, later informally named “Eagle Crater,” isabout 22 meters (72 feet) in diameter, 3 meters (10feet) deep. Its coordinates are 1.95 degrees south,354.47 degrees east.

Science Instruments: A Geology Toolkit

Like a human field geologist, each MarsExploration Rover has the capabilities to scout its sur-roundings for interesting rocks and soils, to move tothose targets and to examine their composition andstructure.

Spirit and Opportunity have identical suites offive scientific instruments: a panoramic camera pro-vided by JPL; a miniature thermal emission spectrom-eter from Arizona State University, Tempe; aMoessbauer spectrometer from the JohannesGutenberg University, Mainz, Germany; an alpha par-ticle X-ray spectrometer from Max Planck Institutefor Chemistry, also in Mainz, Germany; and a micro-

4

Spirit’s landing site on a plain inside Gusev Crater, viewed with the rover’s panoramic camera before leaving the lander.

Opportunity’s landing site inside “Eagle Crater,” looking back at the empty lander after leaving the crater.

scopic imager from JPL. These are augmented by arock abrasion tool from Honeybee Robotics, NewYork, N.Y., for removing the weathered surfaces ofrocks to expose fresh interiors for examination. Thepayload also includes magnetic targets provided byNiels Bohr Institute in Copenhagen, Denmark, tocatch samples of martian dust for examination. Thespectrometers, microscopic imager and abrasion toolshare a turret at the end of a robotic arm provided byAlliance Spacesystems Inc., Pasadena, Calif.

� Panoramic Camera — Providing thegeologic context: This high-resolution stereo camerareveals the surrounding terrain at each new locationthat the rover reaches. Its two eyes sit 30 centimeters(12 inches) apart, atop a mast about 1.5 meters (5feet) above the ground. The instrument carries 14 dif-ferent types of filters, allowing not only full-colorimages but also spectral analysis of minerals and theatmosphere. Its images are used to help select rockand soil targets for more intensive study and to picknew regions for the rover to explore.

� Miniature Thermal Emission Spectrometer— Identifying minerals at the site: This instrumentviews the surrounding scene in infrared wavelengths,determining types and amounts of many differentkinds of minerals. A particular goal is to search fordistinctive minerals that are formed by the action ofwater. The spectrometer scans to build up an image.Data from it and from the panoramic camera are usedin choosing science targets and new areas to explore.Scientists also use it in studies of Mars’ atmosphere.

� Moessbauer Spectrometer — Identifyingiron-bearing minerals: Mounted on the rover arm,this instrument is placed against rock and soil targets.It identifies minerals that contain iron, which helpsscientists evaluate what role water played in the for-mation of the targets and discern the extent to whichrocks have been weathered. The instrument uses twocobalt-57 sources, each about the size of a pencileraser, in calibrating its measurements. It is a minia-turized version of spectrometers used by geologists tostudy rocks and soils on Earth.

� Alpha Particle X-Ray Spectrometer —Determining the composition of rocks: Animproved version of an instrument used by theSojourner rover, this spectrometer is also similar toinstruments used in geology labs on Earth. It uses

small amounts of curium-244 in measuring the con-centrations of most major elements in rocks and soil.Learning the elemental ingredients in rocks and soilshelps scientists understand the samples’ origins andhow they have been altered over time.

� Microscopic Imager — Looking at fine-scalefeatures: The fine-scale appearance of rocks and soilscan provide essential clues to how those rocks andsoils were formed. For instance, the size and angulari-ty of grains in water-lain sediments can reveal howthey were transported and deposited. This imager pro-vides the close-up data needed for such studies.

� Supplemental Instruments — Engineeringtools aid science: Each rover also has other toolsthat, while primarily designed for engineering use inthe operation of the rover, can also provide geologicalinformation. The navigation camera is a wider-anglestereo instrument on the same mast as the panoramiccamera. Hazard-avoidance cameras ride low on thefront and rear of the rover in stereo pairs to producethree-dimensional information about the nearby ter-rain. The front pair provides information to aid posi-tioning of the tools mounted on the rover’s arm.Rover wheels, in addition to allowing mobility, areused to dig shallow trenches to evaluate soil proper-ties.

5

Picture from Opportunity’s microscopic imager showing aniron-rich spherule embedded in layered rock. The areacovered in this image is 3 centimeters (1.2 inch) wide.

Names of Rovers and Features

The names of the rovers, Spirit and Opportunity,were selected in a student essay contest that drewnearly 10,000 entries.

After the spacecraft reached Mars, NASA dedicat-ed the landers as memorials to astronauts who per-ished in space shuttle accidents. Spirit’s landerbecame Columbia Memorial Station. Opportunity’sbecame Challenger Memorial Station.

A committee of the International AstronomicalUnion designates official place names on Mars, suchas the names Gusev Crater and Meridiani Planum.NASA and members of the rover science team haveput unofficial names on many natural features seen bythe rovers.

A range of hills that Spirit saw on the easternhorizon from the rover’s landing site is unofficiallycalled the “Columbia Hills,” with seven individualhilltops named for members of the Space ShuttleColumbia’s last crew: Anderson, Brown, Chawla,Clark, Husband, McCool and Ramon. Spirit drovemore than three kilometers (about two miles) to reachthose hills and begin climbing them.

As in earlier Mars surface missions — Viking andPathfinder — scientists assign informal names tosmaller features, such as rocks and patches of soil in

order to avoid confusion when talking about plansand results related to those features. The named fea-tures range from stadium-size craters to coin-sizespectrometer targets on rocks.

Persistent Spirit

Spirit’s first photos looking around its landing siterevealed a rock-strewn plain. A few shallow, dustyhollows lay nearby and a few hills and crater rimsinterrupted the flat horizon. Even before the rover hadrolled off its lander platform, scientists chose“Bonneville Crater,” about 300 meters (328 yards) tothe northeast, as a destination that might offer accessto underlying rock layers. They eyed the ColumbiaHills, about 2.6 kilometers (1.6 miles) to the south-east, as a tempting but probably unreachable goal forlater.

An airbag that was not fully retracted under thelander presented an obstacle to simply driving Spiritforward off the lander. Engineers had practiced manyscenarios for getting the rover off. They chose to tellSpirit to turn in place about 120 degrees before dri-ving down a side ramp. The rover rolled onto martiansoil on Jan. 15. The next day, it extended its roboticarm to a patch of soil and took humankind’s firstmicroscopic image of the surface of another planet.Scientists chose a nearby, football-size stone dubbed“Adirondack” as the first rock to get full researchtreatment with all four tools on the arm. Spiritreached out to the rock on Jan. 20, but the examina-tion was interrupted by a computer and communica-tion crisis.

Spirit stopped communicating on Jan. 21. For two

6

Spirit’s robotic arm reaching to a rock informally named“Adirondack” for examining the rock with tools on the arm.

Map of Spirit’s travels through Sept. 3, 2004, from landingsite at left northeastward to rim of “Bonneville Crater” thensoutheastward into the “Columbia Hills.” Scale bar is 500meters (1,640 feet).

worry-filled days, it sometimes failed to send signalsat all and other times sent signals without meaningfuldata. Engineers began to coax some helpful data fromSpirit on Jan. 23. They learned the onboard computerhad rebooted itself more than 60 times in three days.They developed a strategy to stabilize the rover whilecontinuing to diagnose and remedy the problem overthe next several days. The diagnosis was a flight-soft-ware glitch that obstructs proper management of theonboard computer’s flash memory when the memoryis too full. The main remedy was to clear Spirit’sflash memory and, from that point on, to avoid get-ting the memory too full on either rover.

Spirit finished with “Adirondack,” where the rockabrasion tool provided the first-ever look inside arock on Mars. Then the rover set out toward“Bonneville Crater,” examining “Humphrey” andother rocks on the way. It reached the crater rim onMarch 11 and looked inside. No bedrock layers werevisible to tempt the team into sending Spirit downinto the bowl. On March 31, the rover completed aneight-day inspection of a wind-scalloped bouldercalled “Mazatzal” just outside the crater. That rock,like all others examined on the plain Spirit was cross-ing, came from a volcanic eruption. However, thincoatings on the rock and veins inside it suggest that itmight have been affected by water at some point.

The rover spent 10 weeks driving from near“Bonneville” to the edge of “Columbia Hills” whilesurveying soils, rocks and smaller craters along theroute. Its longest single-day advance was 123.7meters (135 yards) on May 10, about 20 percent far-ther than Sojourner drove during its entire threemonths of operations on Mars in 1997. As becametypical for long-drive days, the feat combined a blind-drive portion, in which Spirit followed a route thatrover planners at JPL had determined in advanceusing stereo images, and an autonomous navigation

portion, during which the rover watched ahead forhazards and chose its own path to avoid them.

Spirit reached the base of the hills on June 11.There, it examined an oddly knobby rock dubbed“Pot of Gold” and other eroded features beforeascending a ridge called “West Spur.” Climbing thatridge in early August, Spirit reached exposed bedrockfor the first time, seven months after landing.

Well-Placed Opportunity

Opportunity drove up to exposed, layered bedrockin “Eagle Crater” on Feb. 7, just two weeks afterlanding. It spent most of the next six weeks examin-ing this outcrop, which arcs about halfway around theinner slope of the crater but stands only about as highas a street curb.

The rover discovered BB-size gray spheresembedded in the rock like blueberries in a muffin.These spherules are also plentiful in the soil of thearea, apparently set loose when erosion wore awaysofter rock material around them. They containhematite, the mineral whose detection from orbit hadmade Meridiani a compelling landing site.

Spectrometers on the rovers found that the out-crop is rich in sulfate-salt minerals, evidence that the

7

Spirit’s view after climbing into “Columbia Hills,” part of a full-circle panorama taken between Aug. 9 and Aug. 19, 2004.

Map of Opportunity’s travels through Aug. 21, 2004, fromlanding site on left eastward to “Endurance Crater,” theninto that crater. Scale bar is 100 meters (328 feet).

rock had been drenched with salty water. Thespherules are distributed throughout the rocks, ratherthan only in particular layers. This observation con-tributed to a conclusion that they are concretions,another sign of mineral-rich water soaking throughthe rocks. The microscopic imager revealed rippledbedding patterns in some of the finely layered rocks,indicating that the rocks not only were exposed towater after they formed, but actually formed fromsediment particles laid down in flowing water.

Opportunity climbed out of Eagle Crater onMarch 22. It examined some rocks and soil on thedark surrounding plain, then headed east toward a sta-dium-size crater called “Endurance.” It set a one-daymartian driving record of 140.9 meters (462 feet) onApril 17 and reached the rim of the crater on April30.

The rover’s panoramic camera and miniature ther-mal emission spectrometer surveyed the interior of“Endurance” from two overlook points about a thirdof the way around the rim from each other. Thatinformation helped the rover team plot the safestroute to the most interesting targets accessible. Therover drove into “Endurance Crater” on June 8. Itfound that as far down as outcrops extended, theybore evidence of extensive exposure to water.

Project/Program Management

The Mars Exploration Rover program is managedfor NASA by JPL, a division of the CaliforniaInstitute of Technology, Pasadena, Calif.

At NASA Headquarters, David Lavery is the pro-gram executive and Dr. Curt Niebur is the programscientist. Dr. Catherine Weitz was the program scien-tist through August 2004. At JPL, Peter Theisingerwas project manager until February 2004, followedby Richard Cook and, currently, Jim Erickson. JPL’sDr. Joy Crisp is the project scientist. The principalinvestigator for the science payload is Dr. SteveSquyres from Cornell University, Ithaca, N.Y. Deputyprincipal investigator is Dr. Ray Arvidson fromWashington University, St. Louis.

On the Internet

Additional information and images are availableon Web sites for the Mars Exploration Rover Missionat http://marsrovers.jpl.nasa.gov and for the suite ofscience instruments at http://athena.cornell.edu .

10-04

8

Portion of the outcrop in “Eagle Crater,” where Opportunity landed. The rocks are about 10 centimeters (4 inches) tall.

Opportunity’s view northeastward into “Endurance Crater,” combining frames taken with the panoramic camera betweenMay 23 and May 29, 2004. The crater is about 130 meters (about 425 feet) in diameter.