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Home , Exploration of Mars, LaRa, Life on Mars, Mariner 9, Outflow channels, Water on Mars

IAC-04-IAA.3.8.1.08

LARA: NEAR TERM RECONFIGURABLE CONCEPTS AND COMPONENTS FOR LUNAR EXPLORATION AND EXPLOITATION

P.E. Location: Code 695, NASA/GSFC, Greenbelt, MD 20771 USA Affiliation: L3 Communications, GSI., 3750 Centerview Drive, Chantilly, VA 20151 USA Pamela.Clark@gsfc..gov

M.L. Rilee L3 Communications, GSI, 3750 Centerview Drive, Chantilly, VA 20151 USA [email protected]

S.A. Curtis1, C.Y. Cheung1, G. Marr2, W. Truszkowski3, 1Code 695, 2Code 588, 3Code 595, NASA/GSFC, Greenbelt, MD 20771 USA [email protected]

M. Rudisill MS 328, NASA/LARC, Hampton, VA 23681 USA [email protected]

ABSTRACT

NASA’s Exploration Initiative requires tools to support of near term human activities on the or . ANTS Architecture is well suited to such applications using current ElectroMechanical Systems (EMS) for Addressable Reconfigurable Technology (ART). We have analyzed the and behaviors required of ANTS components for such an application designated LARA ( Amorphous Rover Antenna). Basic structures are highly modular, addressable arrays of robust nodes, from which highly reconfigurable struts, tethers, and fabric are autonomously and reversibly deployed for all functions. An ANTS craft is an appendageless multi-tetrahedral structure, harnessing the effective skeletal/ muscular system of the frame itself to enable more ‘natural’ movement, effectively allowing ‘flow’ across a surface or into a particular morphological form. Individual craft would be deployed, with or without a human crew, land, using a miniaturized version of high impulse thruster technology, transform into rovers, bowl-shaped antennas, hut-like human shelters, or more specialized service providers, as needed, and ultimately return to the point of deployment. We have developed conceptual and physical models of ANTS systems to determine design requirements and are currently working on an EMS-based prototype. ANTS structures could be thus used for exploration, reconnaissance, communication, transportation, and construction, , protecting human crews and facilitating their work.

1 CONTEXT OF THE ANTS APPROACH Table 1: Lunar Mission Strategy for the Exploration Initiative relevant to LARA The ANTS approach to exploration [1,2,3,4,5] discussed here is directly relevant • Lunar Exploration activities as ‘testbed’ to the NASA’s Exploration Initiative goals of enabling sustained human and robotic sustainable and affordable robotic exploration and more remote targets • Series of robotic missions begin in 2008 to of the [6,7]. The mission prepare for later human exploration of lunar application, Lander Amorphous Rover surface Antenna (LARA), is particularly in line with • First extended human exploration missions the new Initiative goals for the Moon and begin in 2015-2020 time frame Mars, where the focus is on establishing • Lunar exploration missions make scientific human crews with robotic assistance in bases discoveries, develop new technologies and on the Moon and Mars and exploring to approaches, identify resources to support search for evidence of resources, biological sustained activity in space. precursors, or itself [6,7]. Table 2: Mars Exploration Initiative relevant The LARA concept would result in to LARA further development of enabling technologies identified in the Initiative [6,7] as well: a) • Robotic exploration goals include searching sustainable autonomous systems and robotics, for evidence of life, understanding solar system b) advanced, reusable, transportation in space formation, and preparing for future human and on the ground, and c) reliable, durable, exploration; modular systems and structures. • Robotic exploration of other solar system In this paper, we will describe the bodies, such as , continues in parallel. conceptual framework, design, and models, • Develop key capabilities to support long duration combined human and robotic for LARA, based on ongoing work. We will exploration, including power generation, life identify requirements and essential features, support, transportation, communication. and assess capabilities the ANTS architecture • Human exploration of Mars begin after robotic to provide reconnaissance, transportation missions have completed full reconnaissance of (lander and rover), communication, and the and human presence on the Moon shelter, and other functions to support the becomes sustainable. establishment of a human presence on the flexibility for visits to multiple targets and Moon and Mars (Tables 1 and 2). cost effectiveness than the currently utilized What is the nature of the contribution approaches, where the major systems, to and Mars that the landing, surface transportation, and ANTS architecture can provide through the communication, require separate structures. use of the LARA concept [8a,8b] (Tables 3 Stowed LARA craft could be launched from and 4)? The LARA concept could be Crew Exploration Vehicles. Reconfigurable, implemented within the next decade using reshapable LARA craft could also be used to current technology, and be available to assist provide temporary shelters or to enclose the human return to the Moon in 2015-2020, natural formations, such as tubes, to prepare for human exploration of Mars. By providing permanent shelters, as tools to using the structures themselves as a skeletal search for and acquire natural resources, or, muscular frameworks, LARA craft use a collectively, as antenna arrays for dramatically new strategy of transforming communication on the ground or in space. themselves for the required activity enroute to On the Moon, starting in about a or on the surface, providing far higher decade, the use of the LARA concept would

2 Table 3: LARA Solution that can be reversibly and/or partially deployed or stowed to allow motion, forward • Robust, ‘form follows function’ craft transform on a surface, at a controllable scale or gait. 3D providing all key functions: transportation in networks are formed from interconnecting space and on the ground, communication, reconfigurable tetrahedra, making structures shelter, resource identification and capture. which are scalable, massively parallel • LARA systems deployable from /Earth systems. As more tetrahedra are , , or Moon/Lunar orbit and operate autonomously as robotic mission or interconnected, the degrees of freedom are through interface to support human exploration. increased and motions evolve from simple to • LARA rover capable of operating in terrains complex, and from stepped to continuous. with high and variable relief and roughness ANTS Addressable Reconfigurable inaccessible to appendaged vehicles through Technology (ART) can be constructed from capability to continuously change scale, motion, the available electromechanical systems and gait with many degrees of freedom. available. The prototype is being constructed thus enable the goal of performing a global from macroscopic electromechanical systems reconnaissance of resource potential, as (EMS)-ART, and LARA could be developed roving robotic explorers with or without at this level of technology. As Micro-EMS humans, and of providing a testbed for the (MEMS ART, Miniaturized ART or MART) human return to Mars. LARA systems would or nano-EMS (Super Miniaturized ART or allow the human/robotic interface to be fully SMART) become available, within the next optimized with less risk of failure. decade or two, such components could be On Mars, starting in about two incorporated to minimize and power decades, the LARA craft could be used for a requirements. The 3D network of actuators robotic mission capable of returning samples and structural elements is composed of nodes from the most desirable locations from the that are addressable as are pixels in an LCD standpoint of the search for life and : screen. The full functionality of such a system cracks, crevices, and caves. Mars terrain, requires fully autonomous operation, and will particularly the volcanic terrain of interest, is ultimately be realized through a neural basis highly fractal and thus so extremely function (NBF) possessing the capability for hazardous as to be inaccessible to actuator-level autonomic response and permanently appendaged (wheeled or legged) heuristic-level decision-making, which will be vehicles. discussed elsewhere (9a,9b,9c,9d). The ANTS architecture for LARA will be discussed here. THE ANTS CONCEPT LARA: APPLICATION OF ANTS TO ANTS SMART (Super Miniaturized EXPLORATION OF TERRESTRIAL Addressable Reconfigurable Technology) PLANETARY SURFACES architecture was initiated at Goddard Space Flight Center (GSFC) to develop a What have we learned from our revolutionary approach to space vehicles and attempts to explore the surface of the Moon systems epitomizing the ‘form follows (Table 4)? The campaign for human function’ approach. Such craft are capable exploration of the solar system was changing form to optimize function or to inaugurated with the Apollo Program. The adapt to environmental demands (4,5). The challenge of launching a human crew along basic unit of the structure is a tetrahedron with a large payload to support them into consisting of nodes interconnected with struts deep space, delivering them into orbit around

3 Table 4: Moon and Mars Exploration Lessons Although only limited portions of the lunar surface were sampled, the Apollo We can deliver a human crew to another body, Program was cancelled early. Some mission keep them on the surface for at least a short time, operations were automated, but not and return them safely. autonomous, with control resident on the ground, resulting in high demand for A human crew provides a more effective surface exploration tool than rovers alone. resources, time and expense despite the limited duration (days) of the missions. Many Exploration with humans is costly. questions, which demand the gathering of samples from the still largely unexplored We can deliver rovers to another body and keep lunar surface, remain unanswered. Clearly, them on the surface indefinitely. the development of autonomous systems and robotics was required to cut down on the use Rovers can move to, collect samples and send of resources. But, well trained and curious back analyses from relatively easy targets selected human explorers are extremely valuable in through human telepresence. guiding the discovery process, as witnessed by the extraordinary job done by the Rovers have limited coverage and limited flexibility for dealing with the range of astronauts in selecting and documenting the challenging terrains. sites they visited. The lesson here apparently is that, in order to make exploration How could we increase cost effectiveness of sustainable, additional support required for human crews and effectiveness of rovers? human activities should be utilized as an important enhancement to truly autonomous Table 5: LARA Characteristics robotic exploration, when the human presence is critical for leading the exploration. * Support, sustain robotic or human exploration What have we learned from our * Operate autonomously, singly or collectively, attempts to explore Mars (Table 4)? The with or without human partners * Key functions include lander, rover, antenna, exploration of Mars, largely driven by interest reconnaissance, shelter in the possibility of finding , has * Surface targets by preselection or been entirely remote, and, more recently, * Search for resources, evidence for life robotic. 9 was the first to * Cover many kilometers/day on ground. orbit Mars, but revealed nothing until the * Operation on any surface global dust cleared. Viking orbiters, * Propulsion in Space: Mini Chemical Thruster Mars Global, Surveyor, and Mars Odyssey * Propulsion on Ground: Node and Strut have revealed progressively more details of * Power: solar or nuclear batteries Mars complex terrane as instrument another body, landing them on that body, resolutions have improved: evidence for the returning them alive from another its surface, largest mountains (volcanoes) and and having them gather a scientifically useful observed in the solar system, and a past global payload from that surface was a remarkable [12]. These missions most achievement, one that was accomplished in striking revelation is that water has played a ten and then repeated successfully 6 major role in creating Mars landscape: times. As a result of the samples gathered cyclical climate changes have caused periodic from the surface and data gathered from orbit, ages [13] which have resulted in massive major advances were made in our , and loss of an earlier ocean understanding of planetary formation and [14]. Speculation and now substantial conditions for the origin of life [10,11].

4 evidence for the existence of liquid water on which are currently available, or MEMS Mars surface has resulted in renewed interest (MART) level system which will become in the search for life on Mars [15]. Rovers available over the next two decades, to have been deployed to look for this evidence address the two the greatest challenges in in samples. Viking Landers had indicated longer duration missions far more effectively Mars was covered with weathered iron-rich than existing vehicle designs. These derived from in a rugged terrain, a challenges are a) the need for far greater result confirmed by [16,17]. flexibility and autonomy in robotic Viking biological experiments had given operations, and b) the need for far more unexpected, but not convincing results, for the sustainable and efficient use of expendables presence of life [16]. Mars Exploration for autonomous operation and for crew Rovers and Opportunity have collected support and protection. many samples on their traverses within a The ANTS architecture creates a space small area, and, with the finding of filling material from addressable, deposits, given even more evidence for the reconfigurable, self-similar components presence of liquid water during formation of which provides a skeletal muscular these samples, but have not found water in the framework. The structural components present [18]. themselves are flexible, allowing adaptation, Of course, the limitations of robotic through their reversible rapid reconfiguration rovers prevent them from going to the more over seconds, for functions required at each rugged landscapes. Their permanent phase of a mission. ANTS reconfigurable appendages, wheels in this case or even the structure thus reduce mass, power, and ‘leg’s that are planned, make them relatively expendable requirements by eliminating the inflexible, optimize them permanently for need for specialized systems for key functions operation over a limited range of landscape such as space and ground transportation, scales. But it will be highly fractal landscape, communication, and shelter. with constantly varying scales of relief and We first considered the Autonomous roughness where the deep fissures buried in Nano-Technology Swarm (ANTS) chaotic outwash channels, where life would architecture for a future application, the PAM continue to exist on Mars. Because the risk of concept, which is discussed in detail injury to appendages is great even in the elsewhere [19,20,21] (See ANTS: The Movie typical desert pavement being traversed, at the official ANTS website [1]).. Here we extensive decision making must go into every consider the LARA application in detail step, placing tremendous demands for (Figure 1). (See LARA: The Movie at the autonomy that are difficult to meet. As a official ANTS website [1]). The LARA craft result, the cautious, slow (due to the roundtrip is transformed from lander to rover over light time to Mars) telepresence approach to rugged terrain, to various functions, all navigation will continue to be limit autonomy described in Table 6. These include antenna and coverage. The lesson here may be that we for transmitting or receiving information, need a dramatic breakthrough in our approach carrier for a payload such as a sample to robotic rover design in order to locate and collector/analyzer, to provider of crew shelter. reach areas most likely to contain evidence These functions could be performed for life with any degree of autonomy. autonomously, or through interface with crew The LARA application of ANTS either in situ or remote. architecture, summarized in Table 5, uses application of EMS (ART) level systems

5 Table 6: LARA Forms and Functions

Function Form

Lander Flattened with mini- Space Mobility thrusters at edges

Amorphous Rover Size for terrain scale Surface Mobility Shape for required movement, e.g., amoeboid for rough slither for uphill, cracks spheroid for smooth Gait for roughness

Payload Carrier Same as Rover Transportation

Antenna Beacon/Bowl shape Figure 1. LARA Mission Components, including Communication Single or arrayed landers on top, antennae in crater and astronaut shelter in foreground. Amorphous rover in various Shelter provider Cover over natural contortions stretching from back to front of scene. enclosure or hut-like in open, single or arrayed contracted by various mechanisms, including cables or springs, and b) double ‘tape Specialized Task Form stable platform for measure’ device which links or unlinks the Reconnaissance Measuring or collecting oppositely wound flexible rolled sheets. Rolls operation with opposite orientations develop great tensile strength when combined. Similar ANTS/LARA DESIGN FEATURES nodes could be used as attachment points for payloads, such as instruments. These LARA frame components are structures are discussed in more detail electromechanical structures forming a elsewhere [19,20,21]. continuous network of struts which are An outer covering for the LARA network of struts which are reversibly craft, also discussed in more detail elsewhere deployable/stowable from EMS or MEMS [19,20,21], could be provided by specially nodes equipped for wireless operation. designed nodes which would deploy Payload and subsystem components are fiber composite ‘memory’ sheets with attached ‘inside’ the tetrahedral network, relatively low aerial density using between layers of nodes, and thus protected. Polymer/Carbon Nanotube Composite (PNC) After manufacture, the frame could be springs and structural elements [22,23]. A reduced to a minimum strut extension size stack of ‘sheet’ roll devices could deploy for shipping to a launch or deployment size. multi-layered sheets for external covering of Nodes and Struts would be used for the desired thickness and reflectivity. all functions The greatest number would be The LARA Lander (Figures 1 and 2 structural nodes which deploy/stow flexible ) is formed by flattening the tetrahedral struts based on one of several design schemes, network so that mini chemical propulsion ranging from a) telescoping struts extended or thrusters are effectively attached around the periphery.

6 Figure 2: Evolution of Tetrahedral Walker. On left, single tetrahedral walker taking one step. A prototype of this model is currently being constructed. A 4Tetrahedral walker, with an interior node, which could contain payload, is currently being designed and proposed for field testing [19]. In the middle is a 12Tetrahedral Walker illustrating more complex, less punctuated, movements. On right, highly developed movement from multi-tetrahedral amorphous rover which become continuous including, from top, lander becoming amoeboid at landing, transforming to slithering, storing as sphere, and then becoming antenna. The LARA Amorphous Rover (on from side to side as it moves forward. Put an right in Figure 2 ) is created by additional strut at each node and divide that continuouscontraction and extension of struts tetrahedron into 4 tetrahedron (like the 4Tet in a way that optimizes the efficiency of we are proposing to field test), and an inner movement across a terrain, and thus depends space is created for attachment of a payload. on the variability and scale of the relief and In a 12Tet model (Figure 2), motion is far roughness in a given terrain. The ability to more continuous [19]. Ultimately, with control the timing and extent of strut interconnecting, space filling tetrahedral deployment allows control of the scale and material, very high degree of freedom gait of the rover. movement emerges, more ‘natural’ than A single tetrahedron (Figure 2), like wheels, effectively allowing ‘flow’ across a the prototype we are currently building, rocks

7 surface and into a particular morphological form. Table 7: LARA Requirements

Examples of morphological forms for Launch Date: 2010-1015 the continuous tetrahedral motion can be Duration: Months or even years observed in Figure 2. Clear amoeboid-like Location: 1.0-2.0 AU movement can be observed for very rough Spacecraft Mass: 10-50 kg surface, more ‘natural’ than wheels, Spacecraft Materials: 10-100 g/cm2 effectively allowing ‘flow’ across a surface or Power system: Solar Cells or Nuclear Batteries into a particular morphological form. For a Power system mass: 5 kg very smooth surface, or for ‘storage’ the Power requirement: 10-30 Watts minimum surface area spheroid, rolling across Torque at node: the ground, could be effective. Uphill climb Space Propulsion system: Chemical Mini-thruster or slipping through narrow openings could Ground Propulsion system: Node and Strut Operations: require a slithering snakelike morphology. Autonomous or through with crew When surmounting obstacles, the rover could Individual or collective operation either change its scale, growing in size, or use Cover tens of kilometers per day a climbing motion, pulling itself over using No single point failure facets on the obstacle itself as ‘toe holds’. Robust to minor faults and major failure LARA craft is transformed into an or terrains, to determine , Antenna (Figure 2) whenever significant morphology, age, would inevitable lead to the bandwidth communication is required. The identification of sites with important clues on tetrahedral network itself, bowl-shaped above the origin of , the solar system, or life with a broader base below, is equipped to itself. Whenever necessary, rovers could form receive and transmit data. antenna to transmit findings and receive The Payload could be placed within instructions. Such systems could also be used active or passive nodes on the ‘inside’ of the to provide shelter, by creating, seeking, and tetrahedral structure. (A continuous network enclosing natural semi-enclosed formations. could have an ‘inside’ and ‘outside’. LARA craft could also find, collect, or mine materials of use in exploration or LARA MISSION SCENARIOS construction. A network of LARA craft could be used to form a temporary or permanent A wide variety of mission scenarios communication, navigation, or observatory could be employed in using LARA systems. facilities. Deployment and use could be either entirely robotic and autonomous, or through a human REALIZING THE ANTS CONCEPT: interface. The human interface could be REQUIREMENTS AND ENABLING remote in near real time, through TECHNOLOGIES telepresence, or in situ, acting as extensions for a human crew active on the surface. As part of the ANTS/LARA study, we LARA craft could first land payloads are determining the major requirements for autonomously, then form roving ‘advance such mission (Table 7). We should be able to reconnaissance teams’, mapping, gathering meet all of these requirements with and analyzing samples and images of the anticipated, incremental technology terrain for use in site selection. Such analysis developments over the next two decades. of samples, to determine elemental, , Anticipated incremental improvements in water, biogenic material, or abundances, MEMS technology subsystems will be useful,

8 but are not essential. Improvements in the most lightweight, durable, and rigid materials efficiency of nuclear batteries and solar cells, that are currently available. Specially communication and tracking devices, would manufactured thin sheets of this carbon film also be useful in reducing weight and power on fiber material with shape memory have requirements. already been manufactured [22]. A particular The development of autonomous area of concern for our application would be navigation without appendages is an area the ability to ‘retain’ memory over potentially we are now actively engaged in developing. millions of deployments, and the power We have already developed of the expenditure requirement to hold the material movement of single, 4, 12, and continuous at partial deployment. tetrahedral structures (See still and movies at the official ANTS website [1]). The first ACKNOWLEDGEMENTS demonstration model of an EMS-level (ART) single ANTS tetrahedron, designed to be a We would like to acknowledge the walker (TET), will be completed in October important contributions to this work made by 2004 (TRL 3). Plans are underway to test the our students Jason Leggett, Richard Watson, TET in January 2005 in with Noah Desch, Tom Comberiate, and Jeff Lee. remote operation via the Internet using a 3-D We thank NASA/GSFC IR&D, GSFC Codes graphical user interface. We have completed a 695 and 588, and the RASC program for their preliminary conceptual design of a 4- support. tetrahedron system (4-TET) capable of carrying a scientific payload in a central node, REFERENCES and have proposed to build and test that system on a field campaign in Iceland (‘Mars [1] The Official ANTS website: on Earth’) (TRL 6). The next milestone will http://ants.gsfc.nasa.gov be to build the 12TET model. At this level, [2] Curtis, S.A. et al., 2000.: the ability for ‘continuous’ movement clearly Autonomous Nano-Technology Swarm. emerges. Proceedings of the 51st International LARA utilizes a totally new type of Aeronautical Congress, IAF-00-Q.5.08; space architecture based on an autonomous, [3] Clark, P.E., Iyengar, J., Rilee, addressable, reconfigurable components. The M.L., Truszkowski, W., Curtis, S.A., 2002. A potential flexibility and adaptability of such a conceptual framework for developing system demands a level of artificial intelligent software agents as space explorers intelligence we are in the process of PROCEEDINGS OF THE DECISION developing through our role in ST-8 COTS INSTITUTE (in press). High Performance Computing and Multi- [4] Rilee, M.L., Clark, P.E., and agent Simulations using Beowulf clusters here Curtis, S.A., 2002. IAU Proceedings, in press. at GSFC [1,9c]. [5] Curtis, S.A., Truszkowski,W.F., Another key technology driver is the Rilee, M.L., and Clark, P.E., 2003, ANTS for availability of carbon-based materials to the Human Exploration and Development of form surface structures in order to minimize Space. Proceedings of the 2003 IEEE deployment, mass, and power requirements. Aerospace Conference. Ultimately, to minimize the mass and power [6] The President’s Vision for Space requirements, ANTS structures will be built Exploration, February 2004. entirely on carbon-based materials. Currently available carbon fiber composites [23] are the

9 [7] Report of the President’s [16] Mars and 2 website: Commission on Implementation of United http://www.solarviews.com/eng/viking.htm States Policy, June 2004. [17] Mars Pathfinder website: [8a] Clark, P.E., Curtis, S.A., Rilee, http://www.solarviews.com/eng/path.htm M.L., Truszkowski, W.F., Marr, G., 2002, [18] Chan, M.A., Beitler, B., Parry, ANTS: exploring the solar system with an W.T., Ormo, J., Komatsu, G., 2004, A autonomous nanotechnology swarm, Lunar possible terrestrial analogue for haematite and 33, #1394. on Mars, NATURE 429 (6993): [8b] Clark, P.E., Curtis, S.A., Rilee. 731-734. M.L., Cheung, C.Y., 2003, From present [19] Clark, P.E., Rilee, M.L., Curtis, surveying to future prospecting of the S.A., Cheung, C.Y., Marr, G., Truszkowski, belt, Lunar and Planetary Science 35, #1099. W., Rudisill, M., 2004, PAM: Biologically [9a] Rilee, M.L., Curtis, S.A., Clark, inspired engineering and exploration mission P.E., Cheung, C.Y., Truszkowski, W., 2004, concept, components, and requirements for An implementable pathway to SMART matter asteroid population survey, IAC-04-Q5.07, for adaptive structures (this meeting). (this meeting). [9b] Rilee, M.L., Curtis, S.A., Clark, [20] Clark, P.E., Curtis, S.A., Rilee, P.E., Cheung, C.Y., Truszkowski, W.F., 2004, M.L., Truszkowski, W., Marr, G., Cheung, From buses to bodies: SMART matter for C.Y., and Rudisill, M., 2004, BEES for space systems applications (this meeting). ANTS: Space Mission Applications for the [9c] Cheung, C.Y., Curtis, S.A., Rilee, Autonomous NanoTechnology Swarm, AIAA M.L., Clark, P.E., Shaya, E., 2004, ANTS and Intelligent Systems Technical Conference, the distributed synthesis architecture (this Session 29-IS-13: ANTS, Chicago, Illinois. meeting). [21] Curtis, S., Clark, P.E., Cheung, [10] http://www.hq.nasa.gov/office/ C.Y., Rilee, M.L., Truszkowski, W., Marr, G., pao/History/apollo.html 2004, The ANTS Mission Architecture and its [11] Spudis, P.D., Nozette, S., Bussey, application to the PAM Mission, DRM (Final B., Robinson, M., 1999, Lunar Exploration, Report) for the RASC program. The next step, AEROSPACE AMERICA 37, [22] http://www.esli.com 2, 34. [23]http://www.meetingsmanagement. [12] Connerney, J.E.P., Acuna, M.H., com/pdf/PF_2004.pdf Ness, N.F., Spohn, T., Schubert, G., 2004, Mars crustal magnetism, SPACE SCIENCE REVIEWS 111 (1-2): 1-32. [13] Head, J.W., Mustard, J.F., Kreslavsky, M.A., Milliken, R.E., Marchant, D.R., 2003, Recent ice ages on Mars, NATURE 426 (6968): 797-802. [14] Jakosky, B.M., Mellon, M.T., 2004, , PHYSICS TODAY 57 (4): 71-76. [15] Hubbard, G.S., Naderi, F.M., Garvin, J.B., 2002, Following the water, the new program for Mars Exploration, ACTA ASTRONAUTICA 51 (1-9): 337-350.

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