Acta Astronautica 59 (2006) 742–749www.elsevier.com/locate/actaastro

A low-cost approach to the exploration of Mars through a robotictechnology demonstrator mission

Alex Ellerya,∗, Lutz Richterb, John Parnellc, Adam Bakerd

aSchool of Engineering, Kingston University, Roehampton Vale, London SW15 3DW, UKbDLR, Institute of Space Simulation, D-51170 Cologne, Germany

cDepartment of Geology & Petroleum Geology, University of Aberdeen, Kings College, Aberdeen B24 3UE, UKdSurrey Satellite Technology Ltd., Centre for Satellite Engineering Research, University of Surrey, Guildford, Surrey G2 5XH, UK

Abstract

We present a proposed robotic mission to Mars—Vanguard—for the Aurora Arrow programme which combines an exten-sive technology demonstrator with a high scientific return. The novel aspect of this technology demonstrator is the demon-stration of “water mining” capabilities for in situ resource utilisation (ISRU) in conjunction with high-value astrobiologicalinvestigation within a low-mass lander package of 70 kg. The basic architecture comprises a small lander, a micro-roverand a number of ground-penetrating moles. This basic architecture offers the possibility of testing a wide variety of generictechnologies associated with space systems and planetary exploration. The architecture provides for the demonstration ofspecific technologies associated with planetary surface exploration, and with the Aurora programme specifically. Technologydemonstration of ISRU will be a necessary precursor to any future human mission to Mars. Furthermore, its modest massoverhead allows the re-use of the already built Mars Express bus, making it a very low-cost option.© 2005 Published by Elsevier Ltd.

1. Introduction

The European Space Agency’s (ESA) Aurora pro-gramme has recently stimulated interest in the explo-ration of Mars with a view to a human flight around2030. Prior to this human venture, an extensive ar-ray of robotic missions must be flown in order to

∗ Corresponding author.E-mail addresses: a.ellery@kingston.ac.uk (A. Ellery),

Lutz.Richter@dlr.de (L. Richter), j.parnell@abdn.ac.uk (J. Parnell),A.Baker@sstl.co.uk (A. Baker).

0094-5765/$ - see front matter © 2005 Published by Elsevier Ltd.doi:10.1016/j.actaastro.2005.07.052

increase our scientific understanding of the Martianenvironment to which such humans would be ex-posed, and to demonstrate a large diverse set of tech-nologies required to realise such an ambitious project.To that end, we propose a small but highly capablescientific exploration and technology demonstrationmission—Vanguard [1]. By utilising the currentlyexisting Mars Express bus, re-built for the Vanguardlander, very low costs are incurred. Furthermore, thismission would be ideally suited as one of the ear-lier proposed Aurora Arrow missions. Vanguard candemonstrate the basic technology of borehole drilling,

A. Ellery et al. / Acta Astronautica 59 (2006) 742–749 743

water extraction and water storage from near sub-surface regolith layers. These techniques will be ofcritical importance to the demonstrating feasibility ofa human mission to Mars. The surface package has amass of only 70 kg including a small base station lan-der, a micro-rover and three ground-penetrating moles.The entry descent and landing system baselined tobe similar to that for Beagle 2 (scaled for total en-try mass 140 kg). The 140 kg mass budget currentlyallows 36 kg of orbiter instruments to the Mars Ex-press bus. The lander itself has a mass of 36 kg toprovide communications relay services to the orbit-ing Mars Express during its perigee overhead pass(nominally once per day). The lander also mounts anumber of low-mass scientific instruments similar tothose on Beagle 2 including a meteorological packageand a set of environment sensors. The Mars micro-rover has a mass of 28 kg which carries the majorityof the scientific instruments. As well as the requiredonboard navigation systems, it carries almost 7 kg ofscientific instruments dominated by a laser-based sci-entific package of Raman spectrometer (for the detec-tion of organic materials and mineral species), laserplasma spectrometer (for chemical element determi-nation) and infrared spectrometer (for water detectionand mineral species determination) — this represents acompletely complementary scientific payload to Bea-gle 2 [2]. The micro-rover carries three rear-mountedground-penetrating moles similar to the PLUTO moleto be flown on Beagle 2. The deployment of each ofthese moles is supported by the inclusion of a rover-mounted ground-penetrating radar (GPR) to select ap-propriate sites for their deployment. Currently, themoles carry only sensor heads to the rover-mountedlaser instruments, though the option exists to includesmall instruments such as a magnetometer, a numberof advanced sensors, and a biotechnology-based assayinstrument. The moles are connected by tethers to therover which is paid out during deployment to allowsub-surface depths of 5 m to be reached. The moles arenot recovered eliminating much of the robotic com-plexity invoked in such a process. Although the sci-entific instruments offer a very high scientific returnwith a strong exobiology focus, the primary missiongoal is to provide a demonstration of “water-mining”to support a human mission. Each mole has zeolitecaps mounted to the rear which remain on the surfacecapping the top of the mole borehole. As the mole

descends, the borehole opens the sub-surface to am-bient atmospheric pressure allowing any ice depositsto sublime and be captured by the zeolite caps. Theefficiency of this “water-mining” technique may bedetermined by cross-correlation with the water con-centration with depth profile measured by the infraredspectrometer. We submit that the Vanguard conceptoffers a high scientific return in conjunction with ademonstration of one of the most important enablingtechnologies for a human mission—demonstration ofwater mining for consumables and for Mars Sabatierreactors—and that this makes it ideal as a candidateArrow mission.

2. Vanguard architecture

We briefly outline the Vanguard mission architecturebefore reviewing its potential for technology demon-stration. We emphasise the low-cost nature of this mis-sion by virtue of its low-mass imposition, and theuse of a pre-existing Mars bus—the European MarsExpress. Indeed, the payload capacity of the MarsExpress bus—nominally 176 kg—provided the majorconstraint for the design of the Vanguard lander. Es-sentially, the Mars Express bus may be re-built withminimal re-design. As the spacecraft bus is the majorelement in driving the costs of planetary missions, thisapproach drastically minimises this component of thecost of the Vanguard mission. The overall design phi-losophy is to minimise robotic complexity, mass andcost.

The entry descent and landing system (EDLS) isconceived to be similar to that of Beagle 2—a ballis-tic entry followed by ablative deceleration, parachutedescent, and airbag impact landing. The landing siteis required to be relatively rock-free, but this does notrestrict the scientific mission as the scientific missionis astrobiology focussed. The landing error ellipsoidfor such an EDLS is large ∼ 75 × 150 km cross-trackand along-track, respectively, but this can be readilyfitted into the baseline landing site—the 166 km di-ameter Gusev palaeolake crater (14◦S 184◦ W). Sucha large landing ellipse does eliminate targetting ofpotential palaeo-hydrothermal vent sites (typicaldimensions ∼ 1.102 m) except by serendipity. Thisnow-traditional approach to EDLS option is currentlybeing investigated for comparison with the adoption of

744 A. Ellery et al. / Acta Astronautica 59 (2006) 742–749

Fig. 1. Vanguard micro-rover with three vertically mounted moles(courtesy Ashley Green).

inflatable entry technology [3]. Assume a linear scal-ing, the EDLS will comprise ∼ 50% of the entry massof the entry probe. The total mass of the entry probeincluding EDLS is 140 kg, landing 70 kg of surfaceassets onto Mars. This leaves a payload of 36 kg fororbiter instruments which may be used to providestrategic support for the lander.

The Vanguard architecture comprises a triad ofrobotic support devices—a base station lander (36 kg)to support communications as a relay to the orbiter,a Sojourner-class micro-rover (28 kg) to provide sur-face mobility across ∼ 1 km range for the delivery ofa drill and scientific instruments, and three ground-penetrating moles (2 kg each) mounted verticallyon the rover to be deployed independently at threeseparate drill sites to a depth of up to 5 m (Fig. 1).

The depth of penetration was selected in orderto penetrate beneath the oxidising layer (which willdegrade organic material) with an estimated depthof 2–3 m [4–6]. The PLUTO (planetary undergroundtool) mole to be deployed by Beagle 2 is a self-contained percussive device with a length of 0.3 mand diameter of 0.02 m within a mass of 0.4 kg[7]. The force delivered by the internal percusion isaround ∼ 0.1 N m per shock which can provide a fullpenetration depth within one Martian day. There isa limitation to the depth of penetration of ∼ 5.10 mdue to an increase in the resistive forces due to soilcompaction with depth. Issues relating to Martiansub-surface penetration technology are outlined in

[8]. Each of the modified Vanguard moles deploys atether carrying fibre optic cables for data transmissionand electrical wiring for power transmission from therover to the mole. The fibre optic cabling couplesthe laser-based scientific instruments mounted on therover to the moles which carry the side-scanning sen-sor heads. Each mole carries the sensor head of theoptical instruments into the sub-surface whilst exca-vating its borehole. Three moles delivered at threedifferent sites will result in a triplicate depth profile.Although five boreholes would have been preferablefor replicability, the mass and volume constraintslimit the Vanguard payload to three.

The lander carries only small instruments whosedata may be corrupted by mobility:

(i) a meteorological/environment package similar tothat on Beagle 2;

(ii) a passive seismometer to be embedded in the soilas a complement to a seismic network.

As well as the required onboard navigation systems,the micro-rover carries the 7 kg of scientific instru-mentation onboard the rover, including a confocalmicroscope for sub-micron imaging, a laser Ramanspectrometer for biomolecule and mineral character-isation, an infrared spectrometer for water detectionand mineral characterisation, and a laser plasma spec-trometer to determine the elemental composition (thisinstrument renders the alpha-proton-X-ray spectro-meter (APXS) obsolete). The advantages of theseinstruments are three-fold:

(i) they require minimal integration times ∼ secondsto minutes;

(ii) they are “remote” sensing instruments whichmay be separate from the sensor heads renderingphysical sampling unnecessary;

(iii) they may be integrated into a single primary in-strument package utilising the same, single opti-cal chain through the tether [9,10].

This adoption of four instruments within a single pack-age represents a highly useful planetary instrumentpackage within a small mass ∼ 2.3 kg. The use ofsuch “remote” sensing instruments eliminates the needfor physical soil samples and so the requirement forretrieval of the mole to the surface, eliminating much

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robotic complexity. In addition, a GPR is baselined onthe micro-rover for dual use—as an electromagneticsounder and as a sub-surface site mapper [11, Hall D,2003 private communication]. Indeed, it is generallyreckoned that GPR represents a superior technologyto seismology for Martian-type conditions [12]. Dueto power limitations, this would be operated whilststatic. The GPR may be used as a tool for drill siteselection so that submerged boulders can be avoided.The moles themselves may be instrumented to carrysmall instruments such as thermal probes, pressuresensors and instruments such as a magnetometer.

Details of the systems design and sizing of the struc-tural, thermal, power, computer, and communicationssystems for the Vanguard lander and rover are outlinedin [13]. The scientific case for Vanguard as an astrobi-ological mission are presented in [14–16]. The massand power budgets are detailed in Table 1.

Although Vanguard may superficially resemblethe larger EXOMARS mission—the first Auroraflagship—its purpose and scientific return is verydifferent. Indeed, it more closely resembles an earlyversion of the Beagle 2 lander [17].

3. Technology demonstration

The Vanguard platform may be utilised as a platformfor a number of demonstrations of technology. Alreadymentioned are:

(i) the use of inflatable technology for EDLS;(ii) the development of high-value integrated scien-

tific packages of low mass and volume;

Technology demonstration may be based around fourmajor themes:

(i) generic spacecraft technologies such as advancesin ground station control systems, propulsiontechnology, onboard computing and avionics,communications and data compression, electricpower generation and storage, thermal controlsystems, and structural materials and designs;

(ii) specific planetary spacecraft technologies suchas EDLS, robotics technology, and autonomousnavigation;

(iii) scientific technology such as advanced sensorsand instruments with an emphasis on miniaturi-sation;

(iv) specific technologies required for the Aurora pro-gramme to support human missions to Mars suchas long duration life support systems and in situresource utilisation (ISRU).

Almost any mission can be used to demonstrate tech-nology of the first type—we shall not consider thiscategory further, but suffice to say that robotic plan-etary missions can be used and enhanced to demon-strate technologies such as distributed computingarchitectures, multi-functional materials, smart ma-terials, advanced control systems, and biomimetictechnologies. Specific planetary space mission tech-nologies such as EDLS can be demonstrated on mosttypes of planetary lander mission, though the wisdomof doing so on a large, expensive mission is debatable.The third category of scientific instruments is ideal forsmall scientific missions as they are a good metric forscientific value-for-money in defining the efficiencyof scientific return. Our focus here is on two ma-jor themes for advanced technology—miniaturisationand autonomy. Although each of these themes havewide applicability, we shall examine each withinspecific contexts—autonomy in robotic rovers andminiaturisation of scientific instruments.

Planetary exploration imposes unique constraintson mobile robotics by imposing a hostile planetarysurface. Such robust environments and the nature oftraverse offer a considerable challenge and are an im-portant, if oft-neglected, aspect of robotic autonomy.There are a number of options for mobility acrossa planetary surface which may broadly be classifiedinto three categories—wheels, tracks, and legs. Plan-etary exploration thus provides a driver to robotictechnology development for robust environments. Wehave proposed a novel tracked vehicle concept calledthe elastic loop mobility system (ELMS) based on theuse of the shape memory alloy, Nitinol (49/51) [18].This is a hybrid approach that combines the perfor-mance advantages of tracked locomotion with the lowpower requirement of wheels [19,20]. We have usedBekker theory analysis for analysing the performanceof a number of different mobility systems—Bekkertheory represents the only theoretical model ofvehicle–terrain interaction currently available whichalthough limited in accuracy (but can be used in con-junction with experimental calibration methods) canprovide insights into the issue of traction and mobility

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Table 1Mass and power budgets for Vanguard (modified from [13])

Surface element Sub-system Mass (kg) Power (W)

Mars lander Instruments 0.5 2.02Computer/electronics (ERC32) 1.8 5 (8)Telecommunications 0.83 3 (20)Structure 6.63Battery 2.1Solar panels 10.5Power conv/dist 1.3Thermal control 6.0Rover support 3.0Miscellaneous (e.g. wh, etc.) 1.5 2Sub-total 34.2 12.02 (32.02)Plus 5% margin 35.9 12.62 (33.62)

Mars rover Structure 2.0Solar panels 7.4Power dist/conv 0.8Thermal control 2.0Nav camera stereo-pair 0.5 3Panoramic stereo-camera pair (1.8 m) 0.5 3Autogyros 0.25 3SEO LRF-200 laser rangefinders 0.5 5Proximity/contact sensors 0.1 1Mobility/chassis system 2.5 6Computer/electronics (ERC32+2xT865) 1.8 5 (8)Telecommunications 0.83 3Miscellaneous (wh, etc.) 0.5 3Scientific instruments 6.8 22Sub-total 26.5 32 (35)Plus 5% margin 27.8 33.6 (36.8)

Moles × 3 Structure 0.7Tether (5 m) 0.5Percussion mechanism 3 (5)Zeolite caps 0.2Instruments 0.43 4.1Sub-total 1.8 7.1 (9.1)Plus 5% margin 1.9 7.5

Surface segment Total 69.2EDLS 69.2Entry probe Total 138.4

on planetary surfaces [21]. ELMS represents a firstattempt to utilise smart materials as a major struc-tural component. The use of legged locomotion hasbeen generally avoided due to the control complexitybut this is an active research area, particularly withregard to compliant materials to provide “preflexes”.The central problem with all-terrain environmentsis in the control of robot–environment interactionforces. This brings us to the more traditional focusof autonomy–autonomous navigation. Although there

exist a number of approaches, we favour the poten-tial field approach which provides a natural meansfor integrating servo-level control of the locomo-tion system and the integration of behaviour controlstrategies [22,23]. However, approaches to robustautonomy must take into consideration the hostileenvironment.

Autonomy of scientific instrument operation is keyto the development of intelligent sensors. Vanguard’sspectrometers must be augmented by onboard intelli-

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gent decision-making in order to react to “interesting”data generated quick-look analysis to deploy instru-ments for more detailed survey. The current mode of“blind” instrument deployment and operation is waste-ful. For instance, if the Vanguard Raman spectrometerdetected mineral substrates (e.g. calcium oxalate) thatindicate biogenic activity within the borehole, Van-guard must adopt onboard decision-making to stopthe mole’s drilling in order to take multiple scansand proceed more slowly to depth. This may take theform of an expert system. Such expert systems add“intelligence” to scientific instruments.

The Vanguard scientific instrument suite representsa subset of those desired for full astrobiological inves-tigation [24]. Advanced sensor technologies that maybe demonstrated on Vanguard include:

(i) fibre-optic sensors (such as the fibre-optic mag-netometer based on the Mach-Zender interfer-ometer);

(ii) photonic crystal fibres which can enhance Ra-man spectroscopy;

(iii) chromatographic “labs-on-a-chip”;(iv) redox sensors such as fibre-optic pH meters and

gas sensors;(v) microtechnology-based accelerometers and gy-

roscopes based on micromachined cantileversand vibrating combs (for use in micro-rovers);

(vi) surface acoustic wave (SAW) sensors sensitiveto a range of physical properties and chemicalspecies;

(vii) electronic nose arrays sensitive to a wide rangeof gas mixtures, to augment or even possiblyreplace gas chromatography–mass spectrometry(GCMS);

(viii) humidity sensors with high sensitivity to watervapour;

(ix) biotechnology-based immunological assays.

A step in this direction regarding advanced sensorswas taken by the Mars 96 Mars Oxidant Experiment(MOx) [25]. These low-mass, low-volume, advancedsensors with high sensitivities will have a profoundimpact on the future of planetary exploration missions.Their demonstration on Vanguard would enhance thescientific return of the mission, and offer the possi-bility of distributed array instrumented robotics forgreater autonomous reactivity.

We next examine the use of Vanguard as an ISRUtechnology demonstrator as one of the critical tech-nologies for the fourth category.

4. ISRU demonstrator

Given the overall goal of ESA’s Aurora programme,we suggest that the human aspect of the Aurora pro-gramme deserves early consideration. One of the mostimportant technological factors in minimising the fi-nancial cost for a human mission to Mars will be theability to exploit indigenous resources. Such ISRU hastypically been focussed on the Sabatier reactor, whichis a well-characterised chemical process for producingmethane and water from carbon dioxide and hydro-gen feedstocks. A Sabatier reactor represents feasibletechnology for transporting to Mars and operating re-motely, but suffers from two substantial drawbacks.Firstly, it requires hydrogen input, and secondly it pro-duces a low ratio of oxygen to methane, insufficientfor in situ propellant production and life support ap-plications. Methods of additional oxygen productionto augment the Sabatier reactor will not be coveredhere as we will be addressing the issue of providinghydrogen feedstock. There are substantial difficultiesincurred in attempting to transport hydrogen feedstockfrom Earth, not least being the problem of storage[26]. The extraction of water from the sub-surface ef-fectively eliminates the need for carrying hydrogenfeedstock from Earth for the Sabatier reactor, and pro-vides the basis for supporting human beings on Marsand on their return at a much reduced mass penalty.

The Mars reference mission and variants thereofare generally based on a 500 day surface mission for4–8 astronauts. A human being requires a daily inputof 3.9 kg of water for consumption plus 2.3 kg ofwater for sanitation, less 1.8 kg of water which maybe recovered through recycling (total 4.4 kg), 0.9 kgof oxygen to breathe, and 0.7 kg of dehydrated food.Water is the most critical resource and oxygen can berecovered from the electrolysis of water. Hence, util-isation of local water resources represents a consid-erable asset to a human Mars mission. Furthermore,the human mission will require significant mobilitycapabilities imposing a need for propellant (such asmethane/carbon dioxide) for rovers and aircraft in-ternal combustion engines—the Martian atmosphere

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of 95% CO2 represents a bountiful resource. Bipro-pellant methane/oxygen with a specific impulse of350–375 s will be required for the Mars ascent vehicle(MAV), and perhaps, sub-orbital hoppers. Methaneand oxygen can be produced through the Sabatierreaction with a Ni catalyst at 400 ◦C: CO2 + 4H2 →CH4+2H2O and 2H2O → 2H2+O2 (water electroly-sis). More efficient electrolysers are composed of lay-ers of solid electrolyte impregnated plastic separatedby metal meshes. Ruthenium-on-alumina catalyst of-fers superior performance below 300 ◦C and does notproduce toxic nickel carbonyl products evolved withNi catalysts. Prior to the Mars Odyssey mission, ithad been assumed that the initial hydrogen feedstock(which is recycled) would have to be transportedfrom Earth under cryogenic storage. Furthermore, theSabatier reaction yields a stoichimetric ratio of 1:2 formethane to oxygen while a ratio of 1:3 is required formaximum fuel efficiency. The only other alternativeto the Sabatier reaction is direct reduction of CO2 at1100 ◦C which is energetically expensive—indeed,a further 500 ◦C increase in temperature to 1600 ◦Cwould enable closed cycle carbothermic reduction ofmetal silicate minerals for metal and silicon extrac-tion: Fe2SiO4 +4CH4 → 4CO+8H2 +Fe+Si. How-ever, given that water ice may reside as close as ∼ 1 mfrom the surface, such resources solve many problemsin the support of a human mission—water, hydrogenand oxygen (by water electrolysis) become readilyavailable.

Vanguard provides an ideal platform for an initialISRU investigation for the mapping and extractionof sub-surface water deposits. Mars Odyssey has re-vealed that there may be extensive water ice depositsas close as ∼ 1 m from the surface. Obtaining localdata on this distribution and its extractability will becritical in determining the feasibility of water min-ing to support human missions as both consumablesand as feedstock for a Sabatier reactor for producingfuel. The GPR instrument may be deployed to provideinitial surveys prior to mole deployment. The chiefdifficulty will be in the robotic acquisition of thesewater resources from the sub-surfaces. This will re-quire sub-surface penetration and the acquisition ofthe water ice. The aluminium silicate mineral zeo-lite is a porous ceramic which can absorb water orcarbon dioxide. Zeolite crystals comprise alternatingarrays of SiO2 and Al2O3 of which there are some

50 different types. Their variable ratio of silicate toalumina and impregnation of impurities generates vari-ations in crystalline geometry characterised by a 3Dnetwork of interconnected tubes and cages which canstore molecules at low temperature and release themolecules at higher temperature to act as selectivemolecular sponges, sieves and storage tanks. They aremost commonly used as catalysts for a wide rangeof chemical processes. In fact, the use of zeolites hasbeen suggested for the storage of hydrogen feedstockfrom Earth without the need for cryogenic cooling.Zeolite will absorb up to 40% of its own weight ofCO2 during the cold Martian night but release it dur-ing the warmer day. Zirconium oxide (zirconia) maybe employed as an electrolytic cell which can split COinto CO2 and O2 which may be used as propellant:CO2 → CO + (1/2)O2. This also opens up the possi-bility of using CO and O2 as input to the Sabatier reac-tor: 4CO+12H2 → 4CH4+4H2O (methane recycled)and 4H2O → 4H2 + 2O2. Zeolite will also absorbwater [27]—the zeolite of choice is UOP MolecularSieve 3A which has an aperture size of 3 A slightlylarger than a water molecule thereby excluding car-bon dioxide, nitrogen and argon contaminants fromthe Martian atmosphere. The zeolite may be mountedas a cap to the rear of each mole. As the mole de-scends, the zeolite cap is left sealing the top of theborehole. As the mole descends, it exposes any waterice deposits to ambient Martian atmospheric pressurecausing them to sublime. The zeolite caps absorb thereleased water vapour. Cross-correlating the infraredspectrometer’s water signature with the absorbed wa-ter vapour captured by the zeolite cap would provide ameasure of efficiency of water mining. A critical issuewould be the lateral thickness into the borehole wallsof the sublimed water ice. If indeed liquid water doesexist in the sub-surface at such shallow depths (thoughthis is not expected above depths of ∼ 100 m), hydro-static pressure would provide the means to mine wa-ter efficiently with a wide catchment area around theborehole. Regeneration of the zeolite would requireheating to 130 ◦C to release 5% zeolite mass of the ad-sorbed vapour leaving a residual fraction ∼ 20% of thezeolite mass of water vapour—this could be achievedin conjunction with the Sabatier reaction though thiswould not be required as part of the Vanguard missionwhich is concerned demonstrating the water miningprinciple.

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5. Conclusions

Vanguard represents a versatile planetary explo-ration architecture that can provide a platform for thedemonstration of a number of a number of differenttechnologies that need to be developed for the Auroraprogramme. In terms of robotics, these include surfacetraverse across a hostile terrain, sub-surface drilling,and ISRU through water mining. As a byproduct ofthese goals, valuable scientific information can beobtained including a number of local physical, miner-alogical, chemical and biological sub-surface profilesto a depth of 5 m, augmented by contextual GPRsub-surface surveys.

We therefore recommend Vanguard as an ideal can-didate for an Aurora Arrow mission.

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