Developing Technologies and Techniques for

Robot-Augmented Human Surface Science

David L. Akin,� Mary L. Bowdeny

Space Systems Laboratory, University Of Maryland, College Park, MD, 20742, USA

Srikanth Saripalli,z Kip Hodgesx

School of Earth and Space Exploration, Arizona State University, Tempe, AZ, 85287, USA

The University of Maryland (UMd) and Arizona State University (ASU) are collabora-tively developing and testing robotic technologies and operating protocols to increase theability of humans to perform extended science missions on the Moon and Mars. In pastyears, the UMd Space Systems Laboratory (SSL) has developed fully functional pressuresuits for Earth-based simulations, along with space-quali�ed dexterous robotic systems. Inparallel, ASU has developed a number of instruments for in situ geological sampling andexamination which would dramatically increase the scienti�c yield of future human explo-ration missions. These technologies are being integrated for the lunar exploration scenarioby the joint development of a �eld assistant robot for EVA exploration: the Robotic AssistVehicle for Extravehicular Navigation, or RAVEN.

RAVEN is a minimally-sized robotic rover to assist in the human science mission. Con-ceptually, this robot is similar in size and functionality to the Modular Equipment Trans-porter (MET) used on Apollo 14, but is self-propelled to eliminate the considerable impacton crew physiological workload induced by the requirement to manually pull the METthrough the regolith. The rover is used to carry tools and instruments for the astronauts,as well as collected samples. A UMd manipulator arm has been provided to add dexterouscapabilities to the robot, and to expand the range of potential human/robot task allocationsduring the exploration mission.

This paper details the design and development of RAVEN, leading to its initial �eldtrials in the Arizona desert near ASU in September, 2010. During these trials, RAVENwill perform three separate exploration functions: surveying the exploration site prior tothe human EVA; accompanying and assisting the humans during their geological sortie;and performing directed activities at the �eld site after the humans have returned to theirlander, rover, or habitat. Metrics have been established to measure the scienti�c produc-tivity of the overall system, and to test various approaches to human/robot interaction tomaximize science data return.

In the basic design scenario, the RAVEN rover would be deployed early in an Apollo-likesurface stay, and would be capable of self-tended recharging from the landing vehicle and acombination of autonomous, locally controlled, and ground-controlled activities. The roverwould be capable of independently performing an extended traverse to survey the comingEVA route, categorizing the exploration sites geographically and aiding in detailed EVAplanning. Following a quick recharge, RAVEN will be ready to accompany the crew on thehuman exploration phase, autonomously staying close to the humans while transportingmaterials needed for the EVA operations and science data collection. One of the critical de-sign requirements is that the rover must be capable of meeting or exceeding human traversevelocities, while being able to navigate on the same terrains chosen for human ambulation.During the EVA, RAVEN will support the crew by providing data relay, video monitoring,and a variety of viewpoints (e.g., telephoto, microscopic, and data visualization) not avail-able during the Apollo era, fed directly into head-mounted and suit-mounted displays built

�Director, Space Systems Laboratory. Associate Professor, Department of Aerospace Engineering. Senior Member, AIAAyVisiting Assistant Professor, Department of Aerospace Engineering, University of Maryland. Member, AIAAzAssociate Research Professor, School of Earth and Space ExplorationxDirector and Foundation Professor, School of Earth and Space Exploration

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AIAA SPACE 2010 Conference & Exposition 30 August - 2 September 2010, Anaheim, California

AIAA 2010-8801

Copyright © 2010 by Space Systems Laboratory, University of Maryland. Published by the American Institute of Aeronautics and Astronautics, Inc., with permission.

into the UMd MX-� pressure suit. Conceptually, RAVEN could augment crew safety bycarrying life support consumables for replenishment, or even directly supply life supportconsumables to the EVA suit via robotically-tended umbilicals. Following the completionof the human EVA, RAVEN will then return to the exploration site and perform directedtasks, which might include photographic documentation and controlled sample collection,core drilling, or other complex tasks which are not good uses of limited crew EVA time.It is the goal of the UMd/ASU team to develop the technologies to support extensivenew science capabilities for both the robot and the human crew, and to explore throughperiodic extended �eld testing the optimal use of this expanded exploration capability.

Acronyms

AHP Analytical Hierarchy ProcessAMCM Advanced Mission Cost ModelASU Arizona State UniversityATV All Terrain VehicleEVA ExtraVehicular ActivityFMEA Failure Modes and E�ects AnalysisFPGA Field Programmable Gate ArrayGFE Government Furnished EquipmentGPS Global Positioning SystemHD High De�nitionHMD Head Mounted DisplayIMU Inertial Measurement UnitLASER Lunar Advanced Science and Exploration ResearchLRS Lunar Relay SatellitesLRV Lunar Roving VehicleLuHRI Lunar Hand Lens ImagerMET Modular Equipment TransporterMIPS Million Instructions Per SecondMLI Multi Layer InsulationNIMS Near Infrared Mapping SpectrometerPLSS Primary Life Support SystemPRA Probabilistic Risk AnalysisPWM Pulse Width ModulationRAVEN Robotic Assist Vehicle for Extravehicular NavigationRDF Radio Direction FindingRF Radio FrequencyRPN Risk Priority NumberRRC Remote Rover ControllerRWC Rover Wrist ControllerSAM Simple Aurora MonitorSSL Space Systems LaboratorySVLCM Spacecraft/Vehicle Level Cost ModelTLX Task Load IndexUHF Ultra-High FrequencyUMd University of Maryland

I. Introduction

At some point, humans will return to the Moon and explore Mars. While a working knowledge of thehuman capability to perform surface science is available from Apollo experience, this data base is sparse.There were only six successful missions to the Moon, none lasting longer than 72 hours. The suits had littlecapacity for data transfer other than voice communications and limited biomedical telemetry. Aside fromthe added mobility of the lunar roving vehicle (LRV) in the last three missions, almost all exploration tasks

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were performed manually by the astronauts while overcoming the restrictions and workload impacts of theirpressure suits.

Although concepts for the Constellation program envisioned a focus on infrastructure development, lead-ing to the completion of an extensive outpost near the lunar south pole, it seems probable given recent eventsthat any potential near-term lunar exploration activities may follow the Apollo sortie paradigm, where in-dividual missions are targets to speci�c sites of high scienti�c interest for a single exploration experience.Tight payload limits driven by budget constraints may preclude even the provision of an astronaut transportsuch as the Apollo LRV. Given this scenario, what technologies could be brought to bear to keep the missionfrom simply returning to the early Apollo pattern of daily (walking) extravehicular activities (EVAs) withmanual instrument placement and sample collection? How might we increase the scienti�c return of EVAs,or retire some of the risk associated with EVAs, through the use of mobile robotics?

The goal of a lunar sortie mission is to land in a remote location away from permanent infrastructure,and to conduct as many scienti�c experiments as possible in a only few days of human presence. Astronautsalready have trouble walking in their space suits; in order to gather samples and conduct experimentsastronauts must carry awkward hardware and sample bags. There is Apollo video footage of multipleastronauts dropping tools and samples, then falling as they try to retrieve their equipment. It takes greate�ort for the astronaut to re-situate their center of mass over their feet in order to recover. In the process,they may contaminate their samples, or break valuable science hardware. This wastes astronaut strengthand extravehicular activity (EVA) time.

During the �rst two Apollo missions, an average of 42 kg of samples were collected per trip, and weremoved on foot by suited astronauts. The distance traveled was around 1km per EVA, and took almost 4hours. During Apollo 14, astronauts used the Modular Equipment Transporter (MET), a small cart designedto carry their tools (Figure 1). The MET took 10 minutes to set up and was not capable of traveling throughthe EVA traverses. At one point Edgar Mitchell radioed, \Al’s got the back of the MET now and we arecarrying it up. I think it seems easier." On later missions, the 210kg LRV was deployed from a volume ofnearly 8 m3, and designed to carry astronauts rather than provide logistic support during EVA.

Based on the assumption of a highly cost-constrained lunar sortie model, it is our objective to provideastronauts with a small, easy to assemble fully supportive assistance vehicle while on EVA, as conceptuallyillustrated in Figure 2. These support systems include cargo and mission equipment transport and access,robotic mechanisms to assist with science objectives, the ability to follow and keep up with a loping astronautat speed without direct input, the identi�cation of hazardous terrain to avoid obstacles, and continuedoperation via remote control after the astronauts depart. This vehicle will also be required to carry anastronaut in an emergency situation. Some of the project Level One requirements include a stowed massunder 150 kg, a stowed volume of less than 3 m3, the ability to traverse 20� slopes, clear 30 cm obstacles,utilization of a dexterous manipulator, recharge autonomously to support an eight hour EVA, and keep pacewith loping astronauts on the lunar surface while following them autonomously.

Figure 1. Modular Equipment Transporter (MET) inuse during Apollo 14 EVA

Figure 2. Artist’s concept of astronaut support rover(art by Paul Hudson)

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II. Mission Pro�le

The duration of each EVA with the astronauts will be 6 to 8 hours. The science objectives of the sortiemissions are to take high resolution images of the lunar terrain, to collect lunar samples, and to searchfor signs of water-ice. As a reference mission for RAVEN, the area around Shackleton crater will be themain focus of exploration during the EVAs. The total distance that RAVEN and the astronauts will traveltogether during one EVA is between 1 and 2 km. A maximum speed of 3 m/s will be achieved during theEVA to enable the rover to travel at astronaut surface locomotion speeds.

III. Project Structure

The two senior capstone classes from the University of Maryland’s Department of Aerospace Engineeringand the Arizona State University School of Earth and Space Exploration, designed RAVEN to meet LevelOne requirements established by the faculty. Lunar and Earth analog rovers were designed concurrently,as shown in Figures 3 and 4. The goal was for the Earth rover to mimic the lunar rover’s capabilities andspeci�cations in order to test vehicle con�gurations and design features. Due to the concurrent design andtime constraints, the two vehicles diverged slightly, as will be discussed later in this report. This paperwill cover the lunar rover design process, and then continue into the design and testing of the Earth analogvehicle.

Figure 3. Lunar con�guration of RAVEN Figure 4. Earth analog version of RAVEN

It should be emphasized that this report is a summary of the work of 30 seniors in capstone designcourses for an entire academic year. The comprehensive �nal report is 370 pages long, and can be obtainedby contacting the authors.

IV. Lunar Vehicle Design

A. Con�guration

Several trade studies were conducted to determine the optimal wheel con�guration that would minimize thevehicle’s overall mass while providing adequate stability. The conclusion of these trade studies was that athree wheeled system o�ered a 10 percent mass reduction as compared to a four wheeled vehicle. Use of apassive swiveling rear wheel allowed a di�erential wheel drive for steering, which further eliminated the massof dedicated steering actuators. The front two wheels, which are mounted on the same axis, act as the drivewheels; steering is achieved by varying the speed of each individual wheel. Static stability analysis showeda 50% increase in minimum turning radius for the three-wheeled rover as compared to a more traditionalfour-wheel system, which equates to a requirement for a 20% velocity reduction to achieve equivalent turning

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radius to the four-wheel vehicle. The lower mass and signi�cantly enhanced simplicity of the three-wheelsystem with two drive motors led to its selection, and to a major objective of validating the three-wheeleddesign in Earth analog testing.

B. Concept of Operations

For operations on the the lunar surface, RAVEN was required to have the capability to scale a 20o slopeand a 30-cm obstacle. The vehicle’s tires were sized by ensuring the tire dimensions produced a net positiveforward force (drawbar pull). The wheel diameter was chosen to be 60cm in order to minimize mass whilebeing able to scale a 30cm obstacle with a passive suspension system. A terramechanics analysis producedan optimal drive wheel width of 10 cm and a caster wheel width of 5 cm. Grousers, protrusions from the tirethat dig into the regolith to increase tractive force, were also required in order to achieve positive drawbarpull up the maximum slope. Twelve grousers with a height of 3mm were selected. The tire chosen forRAVEN was an aluminum wire mesh tire, the same tire chosen for the LRV.

When selecting and sizing the motors, two driving scenarios were considered: a standard mission and acontingency situation in which an astronaut would be carried. The astronaut-carrying contingency drovethe motor requirements, with each motor required to provide 55 N-m torque and 112 W.

C. Structures

1. Loads Analysis

During the chassis optimization process, the beam elements on the left and right side of the vehicle wereassumed to be symmetric. The selected cross sections are hollow square tubes with outer dimensions of 20,30 and 40 mm and wall thicknesses of 1 and 2 mm. The primary requirement for the chassis was that itwithstand the forces experienced during launch and operations, while having a mass less than 12 kg. Thematerial chosen for the lunar chassis is 2024 aluminum. A safety factor of 2 was chosen, and the marginof safety minimized during the optimization process. All loading conditions were approximated using pointforces. The overall result is that the chassis is able to support expected loads with approximately 11 kg ofstructural mass.

2. Suspension System

RAVEN’s suspension was designed to optimize the range of motion of the suspension, minimize force trans-mission, and quickly damp oscillations. The suspension was approximated as a two-degree-of-freedom mass-spring-damper system. The worst-case loading scenario was found to be a 30-cm drop during the astronautcarrying contingency. Figure 5 plots the maximum displacement under this load for di�erent spring anddamping constants. Analysis of the graph, along with the forces acting on the suspension system led to thedetermination that the suspension should have a 35,000 N/m spring constant and a 2,500 N-s/m dampingconstant.

The two front wheels employ a Chapman strut design, which consists of a spring/damper and lowerA-arm that are both mounted to the chassis. A traditional viscous damper was deemed unsuitable for themission due to the range of temperature extremes that RAVEN will experience during its life on the moon.A magnetic damper was chosen because magnets are able to maintain their magnetic properties over muchwider temperature ranges.

The rear wheel system utilizes a trailing-arm suspension, which is modeled in Figure 6. The rear wheelis connected to the chassis at the chassis pin (blue piece in model) and it is allowed to rotate 360o at thisposition.

D. Avionics

1. Navigation Overview

RAVEN is equipped with a sensor suite that allows it to track and follow an astronaut, autonomously avoidobstacles, and determine its own position, velocity, and acceleration. The con�guration for the vehicle isshown in Figure 7. The rover tracks the astronaut using a laser range scanner and a radio direction �nder.The radio direction �nder provides the bearing to the astronaut of interest and the laser range scanner (beamshown in orange) provides the distance. The rover is equipped with a second laser range scanner (beam shown

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Figure 5. Wheel suspension dynamics parameters Figure 6. Solid model of rear wheel suspension

in red) dedicated to obstacle detection. A set of stereo science and navigation cameras are mounted to thefront sensor arch, and two hazard cameras are mounted to each side to aid in obstacle detection. RAVEN isequipped with wheel encoders on each of the front driven wheels, and an inertial measurement unit (IMU)placed at the rover center of mass for dead reckoning navigation. Ranging from the Lunar Relay Satellites(if available) provide the absolute position of the rover on the lunar surface.

Figure 7. Navigation sensor overview

2. Radio Direction Finder

In order to follow the astronaut, the rover must know the distance to the astronaut and the astronaut’sbearing. The laser scanner gives the distance to any object at a height above most obstacles (1.4 m) andthat objects’ bearing. The radio direction �nding (RDF) system gives the bearing of a radio frequency (RF)source on the astronaut’s suit, allowing the rover to di�erentiate between an obstacle and an astronaut. Eachastronaut will transmit at a di�erent frequency so if more than one is in the �eld, the astronauts can selectwhom the rover follows.

The RDF antenna consists of two sets of Adcock aerial pairs and one omni-directional antenna to resolvea 180 ambiguity. The primary constraint on the design of the antenna is the aerial spacing (aperture). In

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Adcock antennas, as the spacing becomes wider, the lobes begin to lose their circularity which causes bearingerrors. On the other hand, if the spacing is too narrow, sensitivity is reduced. Therefore, the spacing waschosen to be no more than 1/3 wavelength and no less than 1/10 wavelength. For an operational frequencyof 440 MHz, the antennas were designed with a 10 cm aperture.

Besides spacing, the main source of error is multipath and re ections of the signal; however, there arenot as many possible sources of interference on the Moon (no large buildings or terrain features), and sincethe RDF system is being used to verify the direction information provided by the laser scanner (not totriangulate), the errors will not signi�cantly a�ect the performance of the astronaut following system.

3. Laser Scanners

There are two scanning laser range �nders on RAVEN, which provide two-dimensional range and bearinginformation to targets or obstacles. The distance to an object can be extracted from the light pulse re ectiontime. A rotating mirror spreads the pulses out over a 180o arc and gives the corresponding bearings. Laserscanners are ideal for a mobile navigation platform like RAVEN because they are fast (30 Hz), preciseand have a relatively long range. Their typical range is 30 meters, with a resolution of 1 cm or better.The detection capability of the laser scanner is dependent on the re ectivity of the obstacle surface for theoperational wavelength of laser light.

The �rst laser scanner is dedicated to astronaut tracking, and is placed on the front sensor arch at 1.4mabove the ground, where it will clear most obstacles. This scanner is mounted so that the scanning plane isparallel to the ground. The second laser scanner, dedicated to obstacle detection, is angled down 12o from thehorizontal. The laser scanners also provide a \follow astronaut’s path" ability, where the navigation systemrecords astronauts position over time to calculate a path versus calculating a direct path to the astronaut.

4. Obstacle Detection and Avoidance

The rover is designed to clear obstacles 30 cm or smaller with a worst case stopping distance of approximately4 m. The placement of the second laser scanner was chosen so that it can detect an obstacle larger than 30cm at a distance of 5 m in front of the rover. The 5 m distance was chosen to incorporate a minimum 1 m(0.33 second, 10 laser scans) margin to give the system time to react. The laser scanner was placed justbelow the �rst laser scanner at a height of 1.4 m and tilted down 12 from the horizontal to give the shortestdistance to the ground and the largest e�ective �eld of view.

RAVEN is limited to travel on a 20o slope, so it must be able to detect the grade of a slope that it isapproaching as shown in Figure 9. Since the tilt angle is 12o (the largest possible based on obstacle detectionrequirements), the scanner needs to be articulated so that the angle can be adjusted when a down-slope ofgreater than 12o is encountered. Additionally, as the rover passes over uneven terrain, the IMU will be usedto correct for the tilt of the vehicle plane.

5. Stereo Camera System

Stereo cameras will be used as part of the navigation system for medium to long range sensing. Since thestereo camera system will have a slower response time than the laser scanners (4 Hz versus 30 Hz), they willbe used as a preliminary obstacle detection system only. While the laser scanner alone will provide enoughcoverage for the rover to safely maneuver its maximum turn radius (3.7 m up slope, max speed), the hazardcameras allow for a zero radius turn and aid in teleoperation. The rover will be equipped with high intensityLEDs providing a 45 lighting �eld illuminating 30 m forward. They will be mounted with the cameras toprovide light for the regions in the �eld of view.

For navigation purposes, the stereo cameras will detect objects at 30 m with a resolution of 10 cm andthe images will be down sampled to 256 x 256 pixels in order to speed up the processing algorithms. Even atthis reduced resolution, stereo image processing is computationally demanding and thus will be implementedon its own FPGA (Field Programmable Gate Array) with an estimated update rate of approximately 4 Hz.

6. Odometry System

A two-level odometry system will be implemented on RAVEN. The primary system is based on an IMUand wheel encoders, where the IMU gives rotational information and the encoders give 2D translationalinformation. This system is expected to maintain a 10% position error for nominal driving conditions.

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A secondary visual odometry system (using the stereo cameras) will be running in the background and acomparison between the two systems will be used to detect wheel slippage. Once slip has been detected, therover will favor the visual odometry system information until it resumes normal driving conditions.

7. Computer System

RAVEN’s computer is based on the SpaceCube developed by Goddard Space Flight Center. This computerhas two Xilinx Virtex 4 Field Programmable Gate Arrays each with two embedded PowerPC hard cores.FPGA’s excel at signal processing and other math-intensive applications, so algorithms for laser scanningand stereo image processing will be implemented in the FPGA logic. In addition to the resources of theFPGA, RAVEN’s general purpose processors must provide an estimated 680 MIPS. The current ight testedSpaceCube provides 700 MIPS, which satis�es this requirement. The computer communicates with the restof the hardware on RAVEN via a Spacewire bus. Spacewire can handle a data rate of 200Mbps, which meetsRAVEN’s requirement for providing HD video. It also provides a standard mechanism for packets, simplifyinginterface de�nitions between components, and saving engineering cost and e�ort. Other advantages includelow voltage data signaling, which leads to power consumption 1/2 to 1/3 that of legacy buses such as RS-422and MIL-STD-1553B.

E. Crew Systems

1. Rover Controls

During an EVA, the astronaut will constantly need to be fed information about suit health, mission checklists,status of RAVEN, warnings, etc. A Head Mounted Display (HMD) o�ers the astronaut the ability to havea customizable display that can show them information they deem important to the task at hand. By beingworn on their head, the display follows their line of sight, not forcing them to look away from the task beingperformed.

As the primary means of interaction with the rover, voice commands are top-level orders which directthe rover’s functions other than driving. These include a kill command to halt all driving and robotic armfunctionality, a lights on/o� ability, and the astronaut following or follow my path commands. Besidesproviding functional commands to the rover itself, voice commands will control the display viewed by theastronaut on the HMD by verbally navigating menus and selecting di�erent options.

To complement the HMD and voice commands, the astronaut will also have an array of buttons directlyintegrated into their suit known as the Rover Wrist Controller (RWC). It will serve as a functioning systemwhile providing redundancy for controlling the rover, and consists of four command buttons (activate, lights,follow me, follow my path) and a covered kill switch. The kill switch is a mechanical switch, while the otherbuttons are pressure sensitive and electrically conductive electronic textiles. In order to prevent accidentalinitiation of commands, the activate command is used in sequence with the command desired. For example,to initiate astronaut following, the command would be as follows: Activate!Follow Me!Activate. The killswitch however, is designed for fast activation as a covered mechanical switch with no need for the activatecommand.

2. Remote Rover Controller (RRC)

While in normal operation, the astronaut will have the ability to control the rover remotely using the RRC.It will be a joystick that can be mounted to the torso section of the astronaut suit, with accelerometersinside the mount that will detect irregular operation (e.g. the astronaut falling onto the controller).

The decision to make the RRC a joystick interface was based on the results of a in-house experimenttesting three input interfaces joystick, game-type controller pad, and head tracking in combination with twotypes of displays monitor and HMD. Using the Terrabuilder MoonTM add-on for Microsoft Flight Simulator2004TM, a simulated lunar environment course was created to navigate the rover through. The goal was tonavigate the course in the shortest time while avoiding all obstacles.

Each test recorded the times it took to navigate through each gate, the number of crashes per run, andthe number of ips per successful run. After each timed trial, test subjects were asked to rate the controlsusing the NASA Task Load Index (TLX) and the Cooper-Harper System. The Analytic Hierarchy Processes(AHP) pair-wise comparison was used in the post-test questionnaire to compare each system to each other.

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Analysis of the results indicated that a monitor controller pad/joystick control scheme performs thebest using the rating and testing protocols mentioned. In order to more accurately simulate astronautcapabilities with handling controllers, another round of experiments was conducted using a glovebox, whichis a depressurized cylinder sealed at a negative 4.3 psi pressure di�erential. It has two ports for insertingshuttle suit arms to simulate a pressurized suit. With the glovebox, the test subjects preferred the joystickover the controller pad. Between the results of the original and the glovebox experiments, the joystick waschosen as the most e�ective controller for rover driving purposes.

3. Astronaut Carrying Capability

In the case of an emergency where an astronaut is incapacitated, RAVEN will have the ability to carry anastronaut. The healthy astronaut will be able to secure the injured crew member to the rover and driveRAVEN back to the lander remotely.

To accommodate an incapacitated astronaut, mass will need to be removed from the rover in order tomaintain stability. Removable mass such as the science instruments and the robotic arm will be discarded,removing 25kg of mass and leaving only the components necessary to drive RAVEN back to the lander. Toremove the robotic arm, there are quick releases that allow the arm to fall o� when disengaged. Once themass is removed, the front arch on the rover will be folded down, and there will be a soft seat that willunfold and stretch between the stanchions of the folded down front arch. As the laser scanners are mountedon the front arch, this con�guration of RAVEN will not be able to use the astronaut following ability, soonce the incapacitated astronaut is seated and restrained, the healthy astronaut must remotely drive therover back to the lander. In order to restrain the astronaut in place, the injured astronaut’s Primary LifeSupport System (PLSS) will use a latch system to connect and lock to the rear arch, which will hold theastronaut’s upper body in place, along with supporting most of their weight as shown in Figure 8. Thelatches will be able to withstand 7400N of force, based on crash load requirements. If the seated astronautneeds to unlatch from the rover on their own, there are quick releases easily accessible to release their PLSSfrom the rover. To keep the astronaut’s lower body in place, an adjustable belt strap will be used to restrainthe waist. The astronaut is placed such that their center of mass is situated over the center of mass of therover, minimizing the destabilizing e�ects of adding the mass of the astronaut. However, since adding themass of the astronaut raises the center of mass of the rover by 0.8m, the static stability is reduced such thatRAVEN must operate at a reduced maximum speed of 1.5m/s.

Figure 8. Contingency crew accommodations

F. Communications

The rover communications platform serves two main purposes: transmitting science data collected duringthe mission, and aiding in teleoperation of the rover. Additionally, the rover can serve as a voice and datarelay platform for the astronauts while on EVA. The rover is equipped with three antennas: a high gainKa-band antenna for data transmission to Earth, an S-band hemispherical antenna for local lunar surfacecommunications and for contact with the Lunar Relay Satellites (LRS), and an omni-directional UHF antennafor receiving astronaut voice commands and voice relay. An overall diagram of the system is displayed inFigure 9.

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Figure 9. Communications architecture

The S-band hemispherical antenna transmits at 2.29 GHz with a 4 dBi gain and a 135o half-power beamwidth. While on EVA, the astronauts’ suits transmit images from their helmet cameras to the rover alongwith suit telemetry. If the LRS are available, the S-band antennas may also be used to get ranging informationfor absolute position determination and to relay data through the LRS back to Earth. In addition to theS-band data relay, an Ultra High Frequency (UHF) omni-directional antenna transmitting at 279 MHz isused for voice command and voice relay.

For direct to Earth communications, a Ka-band parabolic dish antenna transmitting at 32 GHz is mountedon a motorized pan and tilt mechanism so that it can be pointed at Earth when the rover is stationary totransmit high resolution images, video, and science data. At 8 watts power, the system has a 150 Mbpsdata rate, which means up to 67.5 GB/hr data transfer is possible. Using MPEG-2 High 1440 level videocompression, HD video (1440 x 1080 px) can be encoded and transmitted at 60 Mbps, for a maximum of twopossible channels of streaming HD video. If the parabolic dish fails, direct to Earth (DTE) communicationswill not be lost. If the LRS are in orbit, the S-band antenna can transmit data to the LRS, relaying it backto Earth. If the LRS and Ka systems are not available, a low bandwidth DTE link can be established usingS-band.

G. Science Experiments

The science experiments include a camera experiment that will survey the landscape and take panoramicviews, a microscopic imager connected to a robotic dexterous manipulator that will take images of rocksamples, a seismometer experiment that will be performed to locate the presence of water-ice, and a magne-tometer experiment that will measure the magnetic anomalies on the lunar surface in order to map a magnetic�eld near the lunar South Pole. The dexterous manipulator will be attached to the front of RAVEN and willbe used to help support the science objectives. It is important to note that the design of the dexterous ma-nipulator was not part of the design task for RAVEN. The dexterous manipulator is Government FurnishedEquipment (GFE) and will integrate with the systems on RAVEN. It will ful�ll tasks that astronauts arenot capable to do themselves due to the restrictions of their pressure suits. The dexterous manipulator willbe controlled by the astronauts from RAVEN, and also teleoperated by ground control and the astronautsat the lunar lander. The robotic arm will serve interchangeably for the use of the microscopic imager andas a tool to place seismic units on the lunar surface when used on EVAs with the astronauts.

Before the lunar lander departs the Moon’s surface, a series of con�guration changes will be performedto RAVEN. The dexterous manipulator will be teleoperated once the astronauts leave the Moon, and itwill be dedicated to the microscopic imager. Solar panels will be mounted onto the lunar rover in order toobtain power. Once the astronauts depart the Moon, RAVEN will be teleoperated from the ground stationon Earth. The scienti�c missions that RAVEN will perform after the astronauts depart include imaging thelunar surface, collecting magnetometer data, and utilizing the microscopic imager attached to the dexterousmanipulator.

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1. Camera Experiment

Stereo cameras were chosen to help identify geologic structures and rock compositions of the lunar regolith.These cameras will act as navigation and extra-vehicular activity performance tools. Separated with abaseline of 10cm, the cameras have the ability to identify an object 10cm in diameter from a distance of 3m.

A near infrared mapping spectrometer will be used for identifying a mineral resource known as water-ice. Water-ice can be identi�ed at the near infrared wavelengths using the characteristic peak at 1.8umsurrounded by a trough at 1.5 and 2.0 micrometers. The spectrometer will be based on a larger version ofthe NIMS that ew on the Galileo spacecraft.

A Lunar Hand Lens Imager (LuHLI) will capture images of samples of interest to identify �ne scaleminerals. The ability to look at minerals up close can tell a scientist the environment in which they wereformed as well as which minerals formed �rst. LuHLI will have white LEDs to illuminate the sample of interestto allow for imaging in poor lighting conditions. LuHLI can be attached to the dexterous manipulator forteleoperated control.

2. Seismometer Experiment

ASGARD seismometers will �rst be calibrated using lunar simulant, lunar simulant on top of ice sheets,and lunar simulant mixed with water-ice to determine the seismic velocities we would expect to �nd ifwater is present in the lunar subsurface. Once these velocities are determined, di�erent materials will betested for their seismic velocities to see if their seismic velocities can be distinguished from that of water.Examples include CO2 ice and other volatiles, metal alloys, basalt, and K-poor plagioclase. Once theseseismic velocities have been determined, lunar experimentation can be successfully conducted.

The Apollo experiments were conducted in the low- to mid-latitudes of the Moon. By conducting a similarexperiment at a pole, it will be possible to determine if the subsurface of the Moon is homogenous at alllatitudes and if water-ice may be present. The active seismic experiments conducted by the Apollo astronautscreated their own seismic events by using a thumper, which set o� explosive charges. Water is known tohave a strong e�ect on seismic velocities on Earth. Seismic velocities of regolith range from 92 to 114 m/s,while Earth sediments have measured about 1650 m/s unfrozen and over 2400 m/s frozen. Regolith seismicvelocities may be di�erent when ice is present, so Earth-based experiments will be conducted to determinewhich seismic velocities our seismometer should look for. Most lunar rocks are basalts, so crushed basalticrock will be placed in a basin, and a weight will be dropped onto the basalts. The seismic velocity will berecorded by the seismometer, and this will be done with and without frozen water.

3. Magnetometer Experiment

The objective of the magnetometer sensor package for lunar exploration is to measure magnetic �elds onthe surface of the Moon in order to understand the thermal history of the lunar crust, and to determinethe evolution of a theorized core/dynamo. The magnetometer will also study the physics of basin formingimpacts on surface magnetization. Determining the remnant crustal magnetic �eld is important in piecingtogether the Moon’s magnetic history. The magnetic history of the Moon is largely unknown at present,but the data obtained from high resolution mapping of lunar surface samples will help us begin answeringquestions about the evolution of the Moon’s interior and surface.

The magnetometer is a combination of three separate triaxial magnetometers. Two magnetometers willbe mounted to the rover. In order to measure all aspects of the local magnetic �eld, one magnetometerwill be situated near the base of the rover close to the ground in order to measure the regolith magneticin uence. The second magnetometer will be mounted high up on the rover to measure the ambient magnetic�eld of the area. The third magnetometer will be portable sitting atop a tripod and will be used to measurespeci�c areas of interest determined by vehicle traverses. Mapping traverses will be made by traveling ina grid pattern. Data will be logged continuously at a sample rate of 10 Hz and downloaded at the endof each traverse for analysis. The uxgate sensors used in this system will have a range of �400 nT andresolution of 0.1 nT. Anomalies will be detected and recorded both by the rover magnetometers and theportable magnetometer.

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H. Power

The critical power requirement is the ability to support an eight hour EVA. This naturally translates into therequired ability to also maintain power throughout the remainder of a lunar day, as well as the extended lunarnight. The rover is intended to operate until failure and as such its power source needs to be rechargeable.Table 1 divides the rover operations into six separate modes of power consumption. This is broken downinto less ambiguous power usage groups. The constraining energy requirements are the 8 hour EVA andthe approximately 15 day lunar night. The computed values for these situations are shown in Table 2 alongwith the total energy that would be used in the course of a typical lunar day. The lunar night has the largerrequirement because even though the night power mode only consumes a small amount of power, the roverdoes not have the opportunity to recharge like it does during the lunar day after an EVA.

Table 1. Scenario-speci�c power budgets (all values in W)

Driving Science Stopped Stopped Manipulator Science

(Day) (Day, Stopped) (Night) (Day) Operations (Day, Driving)

Avionics 165 141 12 162 97 195

Propulsion 372 372

Science 20 16 16

Manipulator 480

Crew Systems 4 4 4 4 4

Heating 3

Totals 541 165 15 166 597 587

w/ 15% margin 622 190 17 191 687 675

Table 2. Composite energy requirements (values in Whrs)

Typical Mission 2084

Full Lunar Day with Mission 3751

Full Lunar Night (quiescent) 4320

Lithium ion batteries were chosen as the battery type because they have no charge memory, a high energydensity, and a high open circuit voltage. The Saft VES 180 was chosen as the battery because even though ithas a lower volumetric energy density than some of the other options, it was superior in its nominal capacity(50 Ah), weight (1.11kg), and gravimetric energy density (175Wh/kg). Arranging three strings in parallelof eight cells of VES 180 batteries in series provides a total 4662 Wh of energy. This arrangement will weigh27kg, will occupy a volume of 0.03 m3, and will also provide approximately 225 Ah at 24 volts, or 5.4 kWhrsof energy.

In order to maintain teleoperation after the astronauts depart from the lunar surface, the rover will needa power source to recharge its batteries. Without a base station to recharge from or an onboard energysource, the implementation of a solar panel is the most viable choice because solar energy is abundant anddirectly accessible.

NASA’s Space Technology 8 mission produced a lightweight deployable solar array called the UltraFlex-175 as a part of the New Millennium Program. It uses triple junction gallium arsenide solar cells that are28% e�cient. This highly e�cient type of solar cell coupled with the superb stowed packing e�ciency of 40kW/m3 and beginning of life speci�c power of 175-220 W/kg made this array ideal for the rover.This arrayself deploys by actuating a motor driven lanyard that retracts pulling the outer gore almost 360o until itlatches into place without requiring any astronaut involvement. The UltraFlex-175 is a completely scalabletechnology that has achieved a TRL of 5 on a 5.5 m diameter array. RAVEN requires an array scaled downto a 1.5 m diameter.

The rover will recharge from the lander as necessary until the lander departs from the lunar surface.In order to extend the battery life as long as possible, the rover will recharge immediately after sorties in

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order to avoid ever discharging more than 80% of the batteries charge. The batteries will be charged viaconstant current constant voltage with a 4.1V maximum cell voltage at a 0.2C rate from the lander, takingapproximately 5 hours to charge. When recharging from the UltraFlex-175 solar array, the batteries will becharged at a 0.1C rate and require 10 hours to fully charge. However, in order to maximize battery life andmission e�ciency, the batteries will be continuously supplied power from the solar array as practical duringa sortie in an e�ort to minimize each depth of discharge.

I. Thermal

Heat is radiated from the Sun, the Moon, and re ected o� the Moon from the Sun. The avionics equipmentand batteries are encased in a thermally isolated electronics box that is 45x28x15 cm. The electronics boxis coated in Aeroglaze A276 paint, known for its high emissivity and low absorptivity, and insulated usingmulti-layer insulation (MLI). To maintain a safe operating temperature (0oC to 40oC), the worst case hotand cold lunar scenarios were considered. The worst case hot scenario is during day time operation whenthe temperatures can reach as high as 127oC. With a maximum of 200W being generated by the avionicsequipment and batteries, a radiator will be necessary to dissipate the additional heat. By considering exible silvered Te on optical solar re ectors and aluminum radiator coated in Aeroglaze A276, the silveredTe on optical solar re ectors result in a smaller radiator of 0.4 m2 because they re ect solar radiation moree�ciently. A solar louver will be placed on top of the radiator to regulate the heat ow. A louver is athermal shutter that opens up when the internal temperature is too high and closes when the temperatureis too low. It will require no power and when closed will protect the radiator from regolith.

The worst case cold scenario is during the 14-day lunar nights when temperatures are as low as -169oC,and only the processors are running and the antenna is transmitting. To survive thermally, the quantity ofMLI is important. An emissivity (ability to emit energy by radiation) of 0.11 or lower is needed to maintainthe lower limit of the safe operating temperature. This can be achieved with a minimum of 5 layers of MLI.Additionally, electrical resistance heaters will provide heat if necessary.

V. Lunar Vehicle Feasibility Assessment

A. Probabilistic Risk Analysis

In order to get a complete picture of the strength of the design for RAVEN, a failure mode and e�ectsanalysis (FMEA) was completed to get an idea of the weak points in the design. At the end of the FMEAprocess, numbers quantifying the severity, occurrence and ability of detection for each cause of each failurewere calculated, after which each failure was ranked by a risk priority number (RPN). This number givesan early approximation of which systems have the greatest risk, and thus identi�es what further designdecisions should be made in order to increase the reliability of the system. A chart displaying the top causesof RAVEN mission failure and their risk priority numbers is shown in Figure 10. This chart displays thatfurther design iterations should be made on the pivot point for the third wheel, and on the axle stresses inorder to lower the overall risk of the RAVEN system.

B. Costing Analysis

Two common NASA cost estimators are the Spacecraft/Vehicle Level Cost Model (SVLCM)estimator andthe Advanced Mission Cost Model (AMCM). The SVLCM estimator is solely based on power-law heuristicsrelating mass to cost. Since RAVEN is a design in between a manned spacecraft and a scienti�c instrument,both of those mass relationships were considered. Assuming RAVEN weighs 149 kg (rover mass plus roboticarm mass), then SVLCM predicts RAVEN to cost around $360 million in developmental costs and about $20million for the �rst unit production cost if RAVEN is considered to be most similar to manned spacecraft; thecosts drop signi�cantly to about $28 million in developmental costs and $11 million for �rst unit productioncosts if the vehicle is considered a scienti�c instrument. As a general note, all cost analysis numbers mentionedin this paper are in 2010 dollars, in ated from their original prediction year value using the NASA New StartIndex In ation Calculator.

The range of values above are too broad even for initial cost estimation, so an additional cost model wasused, the Advanced Mission Cost Model. The AMCM bases its cost estimates on of the quantity needed,dry weight, mission type, year of the initial operating capability, the block number, and the di�culty level

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Figure 10. Top risk sources from FMEA

of programmatic and technical features of the design. This cost model is useful because it considers morefactors than just mass and has a more compatible mission type option, lunar rover, but it only produces apredicted total program cost instead of splitting developmental and production costs. This makes it di�cultto determine the reasonability of the results. If the system is given the parameters of RAVEN, assumingoperating capability by 2020, and a high di�culty value, then it produces a total program cost for producingone vehicle at $223 million. This total value falls almost exactly in between the Spacecraft/Vehicle LevelCost estimator predictions for the manned spacecraft and scienti�c instrument, and thus appears to be ofa reasonable order of magnitude. Pending a �ner level of design to re�ne the cost estimate, the AMCMprogram cost of $223M will be used, with a marginal cost for producing additional RAVEN vehicles in therange of $11M-$20M from the SVLCM cost estimation approach.

VI. Earth Analog Vehicle Design

In parallel with the lunar design development described above, an Earth analog version of RAVEN wasdesigned, built and tested to assess the e�ectiveness of the astronaut-assistance rover concept, and to supportfuture joint UMd/ASU research in planetary surface exploration.To the extent possible, the Earth analogRAVEN was designed to the same Level One requirements as the lunar vehicle. Due to the structuraldemands of operations at full Earth gravity, there was no attempt to hold to the 150 kg mass target of thelunar case. In addition, the Earth analog RAVEN was a highly cost- and time-constrained system, with atotal development budget for parts and materials of $6000, and a functional development period (within theoverall class schedule) of six weeks. This drove the design team to use simple and quick solutions; for example,the vehicle was constructed primarily out of 80/20TM T-slot extrusions and other commercial-o�-the-shelfcomponents, which allowed the fabrication process to essentially consist of cutting structural extrusions tolength and bolting them together. The following sections detail design speci�cations and decisions.

A. Con�guration

As shown in Figure 11, the con�guration of the Earth analog vehicle maintained the three-wheel arrangementand physical dimensions of the lunar design. For the Earth analog rover, a dry sand terrain model was chosenas a conservative terramechanics analysis. A 60-cm pneumatic ATV tire was used for all three wheels, anda terramechanics analysis carried out to determine the motor torques necessary for operation. The drivemotor for each front wheel was found to require 350 N-m of torque and 140 Watts of power. The motorselected was a high-torque motor with a 24:1 gear ratio that came standard as part of the motor system.This step-up in torque was not quite enough, however, so an additional 3.75:1 gear ratio was necessary.

The purpose of the drive system is to transfer torque to the rover’s two powered wheels, while preventing

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Figure 11. RAVEN Earth analog rover in UMd Moonyard test facility

loads from being carried directly by the electric motors. To accomplish this, a wheel hub was manufacturedthat attached the wheel’s 110 mm 4 bolt pattern to a 1-in diameter, keyed driveshaft. The driveshaftwas supported by two ange-mounted ball bearing units produced by SKF USA Inc. The ange-mountedbearings were attached to the 80/20 chassis using 1/4-in aluminum plates. All radial loads from the tire aretransmitted though the bearings, and plates into the chassis. The ange-mounted bearings allow the shaftand wheel to rotate. In order to drive the system, a 5.92-in diameter, keyed roller sprocket is attached to a2.09-in diameter sprocket on the shaft of the electric drive motors using an ANSI #50H roller chain ratedfor a maximum load of 1400 lbs. The 2.8:1 gear ratio (adequate for current testing) can be increased 3.75:1by replacing the sprocket mounted to the driveshaft.

The rear caster wheel was designed similarly to the drive wheels. A 1-in diameter axle was secured to acustom-manufactured wheel hub and allowed to spin freely on two SKF USA Inc. ange-mounted bearings.The additional caster degree-of-freedom was provided by mounting a steel turntable between the main roverchassis and the rear wheel assembly. The turntable allowed the caster wheel to rotate passively.

B. Concept of Operations

The intent behind the Earth analog rover was to replicate the planned operations of RAVEN on the lunarsurface for extended �eld trials. Field operations would be performed using space suits analogs developedat the University of Maryland, and incorporating advanced displays and controls to directly interface withRAVEN’s control system. The rover was to be fabricated, assembled, and functionally tested at the Universityof Maryland, then transported to Arizona State University for actual �eld trials at geological sites used bythe School of Earth and Space Exploration for geological �eld training. ASU and UMd students in space suitanalogs would act as scientist- and engineering-astronauts performing extended simulated lunar geologicalexploration assisted by the RAVEN Earth analog rover, with control runs where the simulated astronautswould repeat the same extravehicular activity (EVA) without the rover for comparison purposes.

C. Structures

As stated previously, the Earth analog rover was constructed from commercially available aluminum slottedextrustions, and bolted together for speed and simplicity of construction. In parallel with this, a detailedstructural analysis was performed on the Earth analog rover. This analysis was a critical aspect in the Earthanalog design, because the need for an articulated suspension was brought into question due to the expenseand complexity of its implementation. A loads analysis was performed, which indicated that the rover couldwithstand the driving and obstacle impact loads based strictly on pneumatic tire compliance, without the

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aid of a suspension. Loading was analyzed for collisions at the rover’s maximum Earth operating speed of 1m/s and for a drop from a 30 cm obstacle.

D. Avionics

1. Navigation

Similar to the lunar design, the Earth analog vehicle will be equipped with two laser range scanners. They arethe Hokuyo UTM-30LX and the Hokuyo URG-04LX-UG01, which have 30 m and 5.6 m ranges respectively.Both laser scanners transmit data over USB to the main computer. The laser scanners will be used inobstacle detection during semi-autonomous operation. They will be placed in a similar con�guration as onthe lunar vehicle, with the 30 m laser scanner scanning parallel to the ground and the 5.6 m angled downtowards the ground. The pointing angle of the second laser scanner will be optimized through testing basedon the response time of the electronics and the stopping distance for the Earth rover. Initial testing with theURG-04LX showed obstacle detection resolution of approximately 50 cm. Higher data sampling rates notcurrently implemented on the rover computer are expected to reduce the minimum detectible obstacle size.

The Earth analog vehicle is also equipped with four webcams which can stream real-time video. Oneon the front, two on the sides (to simulate the hazard cameras), and a fourth mounted on the rear so thecaster wheel behavior can be observed. These cameras will be used to simulate both EVA supervision androver teleoperation from a ground control center and are currently being used as an aid to the driver in theopen-loop control of the vehicle.

To determine its position, the analog vehicle uses a Garmin GPS 18x model GPS unit. This is analogousto the lunar relay satellite ranging for the lunar design. The GPS data is paired with heading informationfrom an HMC6352 compass module to allow the rover to determine the heading and distance required tomove to another GPS point. A scheme is currently in development to follow a moving target, such as anastronaut in a mock EVA. GPS data will be transmitted from another GPS unit on the astronaut’s suit andthe rover will continuously determine the direction it must travel to follow the astronaut.

Odometry information will be provided by Hall e�ect sensors mounted in the wheel box assemblies. Thehall sensors will be mounted next to the magnets on the motor sprocket, and each time a magnet passes, apulse will be generated. From this, the rotation rate of the wheel can be calculated, and therefore the roverspeed can be determined. The analog vehicle will also be equipped with an accelerometer to determine itsorientation.

2. Control and Data Handling System

The main computer was selected to be a Mobile Computing Solution Mini-ITX Carputer. It features a 1.6GHz dual core Atom processor, 1 GB RAM, and a 32 GB solid state hard drive. A solid state hard drive wasselected due to the shocks expected from driving over rough terrain. Mechanical hard drives are prone todamage and failure in high vibrational environments. The robotic arm’s is a similar model, and the sciencecomputer is a Mac Mini.

The main computer alone does not have the necessary interfaces to communicate with and control someof the analog’s avionics hardware. These interfaces include an I2C databus and analog to digital conver-sion for some of our sensors, as well as general pin input-output to control power distribution, and pulsewidth modulation (PWM) to control the motor controllers. These interfaces are provided by an ArduinoDuemilanove development board.

Figure 16 shows the overall Earth analog avionics block diagram, with data interfaces for each of thesensors and other hardware. The main computer communicates with Arduino via USB. Each of the computersis connected to the router via wired Ethernet, and can be accessed individually over the wireless network.For example, commands for arm motion would be sent to the robotic arm computer, commands to drivewould be sent to the main computer, and a command to conduct an experiment or transmit science datawould be sent to the science computer.

Commands to move the rover are sent to the main computer and forwarded to the Arduino, which thengenerates a PWM signal to control the motor controllers. The motor controllers are IFI Victor 883’s, andare capable of providing 60 amps at 24 volts to the motors. The main computer also has the ability to turnselected components of the rover o� and on, using a set of relays toggled by the Arduino. The robotic arm’scomputer, motor controllers and actuators, as well as the main drive motors for the rover, are all powered

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Figure 12. Avionics block diagram with internal networks

by a relay, and can be toggled o� and on with software. The relay board provides 6 relay channels, and eachchannel is toggled with a GPIO line from the Arduino.

A kill switch was implemented by placing a push-button locking switch in series with the power to therelay driver board. Cutting power to this board results in loss of power to the relays’ coils. The relays arenormally-open, so when power is cut, the contacts open and power is cut o�. Since all of the actuators relyon power passing through relays, all powered movement of the rover and arm is stopped.

3. Software

Software’s role in the Earth analog is to support and lead operations of the rover throughout its missionpro�le. The rover must operate at the astronaut loping speed (1 m/s), so the control scheme had to beable to operate at that speed. The rover must also have the ability to be controlled by someone who is notphysically with the rover. Finally, control of the robotic arm also needs to be supported. The arm and itscomputer were provided by the Space Systems Lab to be integrated onto our analog vehicle.

One onboard computer runs the main rover control software, a second computer controls the roboticarm, while a third computer is provided for data collection for the science experiments. They communicatevia a wireless local area connection provided by the onboard router. Any number of outside computers canconnect to the network to command the rover and request data.

The software is divided into two sections, the client software and the main software. The main softwareruns on the main rover computer itself, while the client software works on separate client computers. Thesoftware has been designed and also implemented in a current Earth analog rover. The software on the roverand the software on the computer communicate using UDP data packets. The Arduino microcontroller onboard speaks with the main rover computer through data placed in the serial bu�er to read. Feedback isthen given from the Arduino to the main computer on the motor outputs. To control the rover, a joystickconnected to the client computer provides driving inputs.

The rover is driven using a standard gamepad controller, where the right and left joysticks control theindividual motor speeds. Testing has been done to ensure safety and for joystick calibration. Software alsoprovides protection from either network connection failures, or joystick input failures. Both pieces of softwarehave failsafe measures that shut down the power relays that run the rover if a failure occurs.

Continued testing will be done with sensors to sense obstacles and provide autonomy to the softwareand in the control scheme of the rover. A basic path planning algorithm will be further implemented todemonstrate lunar rover astronaut following. Also, a separate client computer is installed control to therobotic arm.

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E. Crew Systems

Operation of the Earth analog rover is based on collaborative activities with a human subject wearing theUMd MX-� space suit simulator, as shown in Figure 13. This suit replicates the bulk and joint restrictionsof a pressurized space suit, without requiring the support infrastructure and test subject training of anactual pressure suit. In addition, MX-� was designed from the outset to accommodate advanced controlsand displays for wearer interaction with robots and external data sources. Direct RAVEN control can beaccomplished by voice or gestural controls, or by direct control via a wireless control pad. A keypad on thesuit wrist allows discrete commands, including an emergency kill switch for the rover.

Figure 13. UMd MX-� space suit simulator with RAVEN Earth analog vehicle

In addition to operation by the suit subject, a remote control station is used in �eld trials to performthe function of ground control for lunar missions. This is currently a fairly straightforward control stationconsisting of a laptop computer with a dedicated hardwire interface to two three-degree-of-freedom handcontrollers for vehicle command inputs. The test personnel in the remote control station can communicatewith the suited subject via two-way radios, and can monitor video from both the rover and the suit via alocal area digital network.

F. Communications

For simplicity, the Earth analog rover communicates with the outside world via a wireless 802.11g router.This is used for command links from the local suit subjects and the "remote" control site simulating MissionControl on Earth. The same system carries compressed video from multiple cameras on the RAVEN analogrover. The communications system block diagram is shown in Figure 14.

G. Science Experiments

1. Camera Experiment

Two 1.3MP color CCD Point Grey cameras were selected for the Stereo/Navigation experiment. Attached toan adjustable baseline and pan/tilt mechanism the cameras are able to perform 360 panoramas with varying+/- 70 dip angle. All images are processed with a MATLAB calibration tool to reduce warping from lens.Using a photo-stitcher called Hugin and a point cloud maker such as Microsoft Photosynth, a multitude ofphotometric analyses can be executed.

A 1.3MP monochrome CCD Point Grey camera was selected to act as an infrared camera. Attached toan Orion �lterwheel, the camera will image behind a 1.5, 1.8 and 2.0 m �lter to allow for water detection.The infrared camera is placed at a similar viewing point as the stereo cameras for image referencing.

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Figure 14. Earth analog rover external communications system block diagram

A color CMOS Dino-Lite microscopic camera will operate as our hand lens imager. Attached to themanipulator arm with a camera retraction mechanism, the camera will image �ne-scale minerals. Theresulting image will be referenced with images captured by the stereo cameras. An interpretation of rockcomposition will be made from stereo camera observations and then compared to the observations andinterpretations made from the following microscopic image capture. All subsystems of this camera experimentare operated through a wireless controlled Mac Mini as a science computer powered by a Carnetix powerregulator.

2. Seismic Experiment

The seismometer consists of a geophone, accelerometer, data logger, XBee radio transmitter and receiver,and Arduino microcontroller. The speci�cations require four identical seismometers whose data must becollected, stored, and sent wirelessly to the rover’s onboard computer at a minimum distance of 0.805 km.The seismometer must have a minimum battery life of six hours in the �eld and store 30 minutes worth ofdata onboard. The seismometer must also be held within a casing, with a large spike connected directly tothe geophone. The geophone’s range is from 10 to 240 Hz, and it has a three-axis accelerometer as a backupseismic wave detector that detects orientation to determine that the seismometer is level. The uLog datalogger can hold one hour of seismic data. The XBee radio can transmit the data a mile, start and stop datacollection remotely, and enable wireless reprogramming. The electrical components run o� 9-volt batteries,and the schematic was designed using Eagle CAD software.

The communication for the seismic experiment is based on DigiKey Xbee Pro radios, organized in a starnetwork with a radio attached to the science computer at the center. The science computer will be able tocontact all nodes at once, while each node will contact only the science computer. Like the lunar design,the Earth analog seismic experiment software has two main sections: the data recording and transmissionsoftware, which runs on the Arduino microcontroller in each node, and the coordinator software, which runson the science computer in the rover. The only signi�cant di�erence between seismic experiments for theLunar and Earth analog designs is that the Earth analog does not have live transmission of experiment data,due to hardware and programming time constraints.

The software on the node waits for the rover to send a global "start" signal, which will allow all nodesto start logging data simultaneously. Once started, each node logs data from all sensors to the uLog at 100Hz. They continue logging data until the rover sends a global "stop" signal, at which point they wait forindividual commands to send data back to the rover. The science computer software is a Python script thatwill be run by mission control. It sends a signal for all nodes to start recording, and then waits for missioncontrol to tell it when the experiment has ended. Once this occurs, it sends the global "stop" signal, andstarts querying each individual node for its data. As data comes in, it is saved to text �les on the rover.

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3. Magnetometer Experiment

An initial prototype has been constructed in order to test the implementation of the magnetometer. Thedesign and speci�cations for the magnetometer were modi�ed to function in Earth’s much stronger magnetic�eld. The signal processing unit for the Earth analog system is the Simple Aurora Monitor (SAM) kit whichis capable of measuring the output of two single axis magnetometer sensors and consists of an LCD screenand attached keyboard with four buttons used for basic commands. The two sensors, which can measure arange of 50,000 nT with resolution of 1.2 nT and have a sample rate of 10 Hz, are mounted at the end oftwo separate PVC pipes which are connected orthogonally to one another using a simple T-connector. Asmall circuit board is mounted inside the T-connecter providing a connection to both sensors and the outputcable to the SAM kit. The SAM kit is located on the rover near the Mac Mini computer, connected to it viaserial (RS-232) to USB. The Mac Mini is responsible for running all data logging software during testing. AGPS unit logs position coordinates during testing which are correlated with magnetic readings. Data loggingis performed by software supplied with the SAM kit. Once a traverse has been completed, data from themagnetometer as well as position data from the GPS unit is imported into MATLAB and analyzed to createmagnetic intensity maps.

Some initial testing of the prototype system has been performed with moderate success. Three separateexperiments have been completed to verify that all components of the system are functional. The �rstexperiment was conducted in order to verify the sensors were working correctly. This was achieved byplacing several small samples of various minerals next to the PVC mount for a period of 30 seconds and thenremoved. As expected, the only mineral to register a change in the magnetic �eld was magnetite, thus theexperiment was determined to be successful. The second experiment tested the a�ect of a running motornear the sensors. A running drill was placed next to the sensors and once data was logged with the drillrunning, a sample of magnetite was placed next to the drill. Both the drill and magnetite were then pulledaway simultaneously. The running drill was placed next to the sensors after 60 seconds. At 120 seconds themagnetite was placed next to the drill and at 160 seconds both the drill and magnetite were pulled away.This experiment was also determined to be successful as expected spikes were observed for both the drill andmagnetite sample. For the third test, a mock traverse of the Student Recreational Complex �eld at ArizonaState University was performed. All systems were placed on a mobile cart and pushed around the �eld ina grid pattern. This experiment was also successful considering the GPS and magnetometer system loggeddata successfully for the entire traverse.

H. Power

Powering the earth analog vehicle are two Ritar RA12-150 deep cycle 12V sealed lead acid batteries. Hookedin series to create a 24 VDC bus, they provide 150 Amp-hours at a 10 hr-rate, and weigh roughly 80 lbs.each. The power distribution system for the RAVEN Earth analog is shown in Figure 15.

I. Thermal

Thermal control of avionics systems on the Earth analog rover are via traditional air cooling approaches.Two fans circulate ambient air through the electronics box containing all computers and interface electronics,with �lters to minimize dust in�ltration. Thermal sensors internal to each avionics component allow themonitoring of board temperatures, and permit the establishment of test termination criteria to preventpermanent damage to systems from external or internal heating.

VII. Earth Vehicle Development and Testing

Initial testing was performed on the Earth analog rover to determine vehicle performance on variousterrains. Although desert-type terrains are not readily available in the Washington DC area, an averagetop speed of 1.1 m/s was recorded on both pavement and grass-covered areas. Slopes of over 30o were alsosuccessfully traversed in all directions. A number of minor structural issues were identi�ed and addressed.The most serious early testing failure was of the swivel bearing for the freely-castoring rear wheel, whichbroke free from its attachment �ttings at the end of a long day of test operations. The system was redesignedand modi�ed with the creation of a custom 360o swiveling bearing for the rear wheel. In the initial series oftests, RAVEN met or exceeded all Level One requirements for the Earth analog rover.

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Figure 15. Earth analog vehicle power distribution block diagram

VIII. Future Work

Currently, RAVEN is undergoing modi�cations and upgrades in preparation for a series of �eld testsat ASU in September, 2010. On the same trip, it will be demonstrated at the NASA Desert RATS �eldtests near Meteor Crater, Arizona. The current development focus is on improving the robustness of theRAVEN control system, by upgrading electrical connectors and replacing some poorly manufactured wiringharnesses.

The Arizona �eld trials in September represent the �rst integrated simulations using the RAVEN rover.ASU students wearing the MX-� space suit simulator will serve as scientist-astronauts performing lunargeological explorations assisted by RAVEN. Test sorties will be repeated on the same experimental sitesfeaturing the suited subject alone, RAVEN alone, and the combination of EVA human plus RAVEN. Testingprotocols are aimed at identifying the roles of human/robot cooperation in planetary surface activities, andattempting to quantify the performance impact of human/robot cooperation in lunar exploration.

As an additional outcome of the UMd/ASU collaboration started on the student RAVEN project, thetwo organizations were recently informed that their joint proposal under the NASA Lunar Advanced Scienceand Exploration Research (LASER) program was selected for funding. Under this program, the RAVENEarth analog vehicle will evolve for use in a series of annual �eld tests near ASU of increasing scienti�c andoperational complexity. The goal for this four-year research e�ort will be to demonstrate a Earth analogastronaut assistance rover which is fully capable of improving human performance in planetary geologicalexploration, and which is also increasingly capable of extensive autonomous operations on the Moon andMars.

IX. Conclusions

The RAVEN initial development program was highly successful on a number of fronts. As an educationalendeavor, it provided senior engineering and science students with a realistic �rst look at the science-directedengineering environment in which most of their technical careers will take place. The year-long course resultedin a highly detailed design of a lunar rover, and in the development and early testing of an integrated rover

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system for Earth analog studies. The quality of the team’s output was validated by �rst-place awards in boththe NASA Revolutionary Aerospace Systems Concept - Academic Linkage (RASC-AL) and NASA ESMDMoontasks 2010 student design competitions. Although it did not happen within the 2009-2010 academicyear, the original goal of an integrated �eld test at ASU will be accomplished by the end of September,2010, including an opportunity to demonstrate the rover/space suit system at the NASA Desert RATS�eld site. And, �nally, the teaming relationship between UMd and ASU has resulted in long-term researchcollaboration between the two schools. The success of RAVEN highlights what can be accomplished forridiculously small sums of money in the academic environment, and is a testimony to the bene�ts of seniorcapstone design courses and the value of innovative engineering design competitions to motivate students.

Acknowledgements

The authors would like to thank the students of the UMd ENAE 483/484 Senior capstone design course inSpacecraft Design (Elaine Petro, Jennifer Donaldson, Kevin Davis, Wayne Yu, Albert Zhou, Kevin Buckley,Brandon Hall, James Doggett, Jayne Breitwieser, Justin Hill, Samantha Lustig, Chistopher Mak, GregHolste, Marissa Intelisano, Brandon Litt, Laura Meyer, and Zach Gonnsen), and of the ASU SES 410/411Senior capstone course in Space Exploration (Robert Wagner, Rodric Richenberg, Ji-hyoung Woo, LeonManifredi, Ricardo Gutierrez, Timothy White, Tut Gatyiel, Andrew Britton, Lauren Puglisi, MatthewSmith, Sean Marshall, and Kyle Montgomery). We would also like to thank the graduate students in theUMd Space Systems Laboratory who served as mentors during the fabrication and testing phase, as well assupplying the EVA suit systems for RAVEN operations.

We would like to express our appreciation to the Maryland Space Grant Consortium for �nancial supportin the development of RAVEN, and to the NASA Revolutionary Aerospace Systems Concept AcademicLinkage (RASC-AL) and ESMD Moontasks programs for their support of engineering design competitionsin space systems design.

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