expert summary

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Expert Summaries of ChassisTechnologies

Michigan Mars Rover Team

May 2005

The purpose of this document is to provide details relating to the following

core technologies: fuel cells, fuel storage, drive by wire, modular

interfaces, in-hub electric motors, and software. For each technology this

paper will discuss why it is necessary for the universal chassis concept,

the current level of technology development, the necessary level of

technology development, and how to bridge the gap in the technology.


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University of Michigan Mars Rover Project Expert Summaries

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INDEX

Computing..pg 3

Drive Control.pg 8

Interfacespg 13Hub Motorspg 21

Mobility..pg 27Fuel Cells / Fuel Storage...pg 32

Summary of Current Level of Development...pg 38

Cost of Universal Chassis Development..pg 39


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COMPUTING

Introduction

There are two important features that the software in the chassis must implement, namelymodularity of software and autonomous functionality. Due to the modular structure of the chassis

hardware it is crucial for the software on board to be able to adapt to new vehicle configurationseasily. As modules are changed to allow for different functionality of the vehicle, the software

should not have to be rewritten from scratch (as it was done for past missions to the Mars andMoon), but should recognize the capabilities of the module and preserve the controllability of thevehicle.

Additionally, for many functions the vehicles on the planetary surface must operate semi-

autonomously. The Earth-based controllers give high-level descriptions of the tasks remotely andthe vehicles perform the required operations to achieve the goal. For the small chassis class this

functionality is extremely useful in scouting and EVA support, while the large chassis will find ituseful for initial habitat construction and reactor deployment.

Current Level of Development

Software

There are two approaches to providing modularity of software. First, similar to Universal Plug

and Play devices in todays computers, it requires the core to have information aboutfunctionality of all possible modules. The modules are required to have a common interface withthe core. When a new device is plugged in, it is automatically detected and the correct interface

(driver) is used to access it. The second approach (similar in principal to USB flash drives)makes use of modules own memory to keep a copy of the driver. In this case the core loads the

driver from the module itself.

Coupled Layer Architecture for Robotic Autonomy (CLARAty), developed at JPL, is an

autonomous software structure being developed specifically for Mars rovers. The frameworkallows development of robotic software with high-precision navigation and control and

communication with human operators or other robots. The advantage of CLARAty is that it canbe applied to a number of different vehicles with various capabilities and hardware architectures.Today this framework is tested on the Rocky 7 and 8, and FIDO experimental robotic vehicles.

IDEA (Intelligent Distributed Execution Architecture) is another advanced autonomous software

currently being developed by NASA. Similar to CLARAty, it contains an applicationindependent engine that can be used on different types of rovers and for different missions. Webelieve, however, that this type of autonomy is exceeding the requirements for the class of

chassis discussed here and is more applicable to smaller robots. However, the framework used inboth CLARAty and IDEAS is promising for usage on the larger chassis described in this paper.


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Hardware

Today the most powerful space qualified computer is the RAD750 build by BAE Systems thatruns at 133MHz (5.8 SPECint95 3.5 SPECfp95). The computers on the Mars Exploration Rovers

are a previous generation RAD6000 that runs at about 33 MHz. The computers used on todays

experimental rovers, on Earth, are based on Motorola and Intel processors, which are not spacequalified but run at much higher speeds (~ 300 MHz) and higher efficiencies. It is obvious that

todays space-qualified components have insufficient processing power to provide the level ofcomputing required for larger planetary vehicles.

Most autonomous navigation done today is through image processing. Compact and lightweightcameras (like NavCams and HazCams on MERs) monitor the environment the rover operates in

and recognize obstacles, or direct the rover towards interesting objects. The Jet Propulsion Labhas several decades of experience with miniature cameras and sun tracking devices. Each of the

navigation cameras on MERs are 320 by 180 by 180 mm in size, weigh about 2.8 kg, have aresolution of 1024 by 1024 pixels, and an effective field depth from 0.5m to infinity. Moreover,the cameras are able to operate at the extreme temperatures of space and planetary surfaces.

There are several other types of sensors used on the Mars Exploration Rovers as well as Earthexperimental vehicles. They include gyros, accelerometers, and wheel odometers.

Current Level of Development Computing

Company Level (TRL) Products

JPL 9 MAPGEN software

JPL 4-5 CLARAty architecture

NASA 4-5 IDEA architecture

BAE System 9 RAD750 processor

Motorola 4 68060, PowerPC and other processors

Intel 4 Pentium processors

JPL9 MER Navigation, Hazard and Sun

tracking cameras, internal sensors

Required Level of Development

Although CLARAty and IDEAS offer a much higher level of autonomy than the Mars

Exploration Rovers that use MAPGEN software, the MER type semi-autonomy is applicable forthe chassis described in this report. Our estimations, based on JPLs research using the FIDOrobot and Mars Exploration Rovers, show that for the small chassis class, computing capabilities

roughly equal to Pentium II 266 MHz processor are sufficient to provide the required level ofautonomy. For larger vehicles, the computing hardware capabilities should be at or above

Pentium 4 3.0 GHz level. Today, there are no space-qualified components possessing thisamount of computing capability. It is crucial that computing hardware is developed on time forsystem level testing (2013 for medium chassis and 2017 for large class).


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The current level of development of navigation and hazard avoidance cameras (used on MERand experimental Earth rovers) is adequate for the functionality of the small chassis class. For

larger vehicles, smaller and more efficient cameras and internal sensors will be needed. We donot foresee the need for radically newer sensors than the ones used on the MERs.

Required Level of Development ComputingSmall Medium Large

Sensors needed

Navcams (2),

Hazcams (4),Sun tracker,Wheel odometers,

Gyros & accels

Navcams (4),

Hazcams (5),Sun tracker,Wheel odometers,

Gyros & accels,GPS

Navcams (4),

Hazcams(5),Equipmentmonitoring sensors

(cams, gyros),Sun tracker,

Wheel odometers,Gyros & accels,GPS

Computing capability~ Pentium II 266Mhz

~ Pentium 41.0 Ghz

~ Pentium 43.0 Ghz

Power for computingand sensors (w/o

externally mountedcams)

30W 45W 65W

Size and mass ofcomputing and sensor

block (w/o externallymounted cams)

200x250x400mm5kg

200x250x4507kg

200x250x4507kg

Size, mass and powerper cam

320x180x180mm,2.8kg, 5W

280x150x150mm,2.5kg, 5W

250x120x120mm,2kg, 5W

Size, mass and powerof equipment

monitoring block

300x200x200mm,5kg, 10W

Need for distributed(USB-like) software

High Avg. Avg.

Development Timeline

We believe that the cost of software development for each chassis will be around $5M, since

with introduction of a modular software architecture each subsequent software version can reuseprevious code. For the first version, the development framework needs to be standardized, which

might incur additional costs of up to $5M.


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Hardware costs will increase from the small chassis (est. $10M) to the medium (est. $30M) to

the large ($60M) due to the need for developing much more powerful, space-qualifiedprocessors.

2006 2007 2008 2009 2010

Small Class

Standardizationof the software

interface

Modularinfrastructure

developmentfrom CLARAtyand IDEAS

research

Softwaredevelopment

and testing(modular)

Softwaredevelopment

and testing(system level)

Testing

Medium Class

Standardizationof the softwareinterface

System levelsoftware design,research on

computinghardware

Large ClassStandardizationof the software

interface

2011 2012 2013 2014 2015

Small ClassVehicle ready

Medium Class

Softwarecomponentsdesign and

testing,hardwaremanufacturing

Software andhardwarecomponents

design andtesting

Softwareprototype readyto undergo trials

Testing Vehicle ready

Large Class

Research oncomputinghardware

Research oncomputinghardware

Softwarecomponentsdevelopment

Softwarecomponentsdevelopment

Hardwaremanufacturing,softwaredevelopment

2016 2017 2018 2019 2020

Small Class

Medium Class

Large Class

Hardware

manufacturingsoftware systemlevel testing

Hardware and

softwareintegrationtesting

System

integration withdeterministicelectronic drive

control



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References

CLARAty: Coupled Layer Architecture for Robotic Autonomy,JPL [online] 2003, URL:http://robotics.jpl.nasa.gov/tasks/claraty/overview/objectives/index.html [cited 23 February

2005]

IDEA: Reusable Autonomy, NASA :: Intelligent Systems [online] URL:

http://ic.arc.nasa.gov/story.php?id=244 [cited 23 February 2005]

Simmonds J. California Institute of Technology/JPL, Imaging Instruments for Engineering andScience: Systems, Technology, and Applications,ENG450 lecture notes, 8 January 2004.

Burcin L., Rad750 Experience: The Challenge of SEE Hardening a High PerformanceCommercial Processor,Microelectronics Reliability & Qualification Workshop (MRQW2002)

[online] URL:http://www.aero.org/conferences/mrqw/2002-papers/A_Burcin.pdf [cited 17 March 2005]

A. Trebi-Ollennu, Terry Huntsberger, Yang Cheng, E. T. Baumgartner, and Brett Kennedy(2001). "Design and Analysis of a Sun Sensor for Planetary Rover Absolute Heading Detection",

National Aeronautics and Space Administration (NASA), Jet Propulsion Laboratory, CaliforniaInstitute of Technology, NASA CR-2001-210800:pp.1-30.http://robotics.jpl.nasa.gov/tasks/scirover/factsheet/homepage.html

Other references:

http://telerobotics.jpl.nasa.gov/people/volpe/papers/aerospace01.pdfhttp://marstech.jpl.nasa.gov/content/detail.cfm?Sect=MTP&Cat=focused&subCat=MSL&subSubCat=RT&TaskID=791

https://claraty.jpl.nasa.gov/new_site/overview/objectives/index.htmlhttp://www.microsoft.com/technet/prodtechnol/winxppro/evaluate/upnpxp.mspx#EBAA

http://www.rad750.com/http://www.iews.na.baesystems.com/business/pdfs/04_c11.pdfhttp://www.iews.na.baesystems.com/space/pdf/rad6000_sbsc.pdf

http://www.spec.org/benchmarks.html


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DRIVE CONTROL

Introduction

Drive control consists of sensors, actuators, computing units, and interconnects. The purpose of

the electronic drive control is to replace all mechanical linkages between the vehicles controlsand actuators (i.e. motor, transmission, steering). The main advantage of this approach is the

elimination of heavy and bulky hydraulics, pneumatics, or mechanical linkages by smaller andlighter electronic equipment. This allows for increased redundancy, safety, and better overall

performance of the vehicle.

The technology behind electronic drive control is very similar to drive-by-wire technology,

which is starting to emerge in commercial vehicles on Earth. Since by-wire technologysignificantly reduces the weight of the vehicle, it will decrease the launch and overall mission

cost. It will also allow the chassis to have a multiple-redundant drive system, boosting missionsafety and flexibility.

Electronic drive control technology provides solutions for three major problems that planetaryvehicles would face: dust contamination, temperature variations, and need for autonomous

navigation. Fine dust and extreme temperature variations on both the Moon and Mars make theuse of complex mechanical and hydraulics systems extremely difficult. An electronic controlsystem eliminates most mechanical and moving parts, and requires less energy to be kept warm

due to a smaller volume. Moreover, given computer controlled vehicle actuators, it is mucheasier to make the chassis tele-operated or even autonomous. As reported by Embedded.com,

current prototypes of autonomous vehicles rely heavily on by-wire control. Also note that theMars Exploration Rovers (MERs) are drive-by-wire machines, where drivers commands fromEarth are interpreted by on-board computers and translated to motor commands. Another benefit

that electronic drive control brings to the chassis design is an ability to control the vehicle fromvirtually any point by using a wireless drive unit.


Most of the necessary technology is already available for the small universal chassis, althoughsome components would need to be implemented in rad-hard FPGAs. Due to small size of these

vehicles, the electronic control can be grouped together making the in-vehicle network relativelysimple. For the large chassis the main challenge would be a sufficient communications protocol,since the sensors and actuators would be placed physically far apart. A successful protocol for

such an application must have high dependability, availability, flexibility, and a high data

transmission rate. Several high data-rate deterministic in-vehicle networking protocols for Earthby-wire vehicles are currently in development.

Hardware

Radiation hardened hardware, for implementing the drive control, is partially available today

since it would be similar to Space Shuttle/MER systems. For example, multiple RAD6000


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computers from BAE systems with MIL-STD-1553 bus and rad-hard FPGAs could be used inthe small chassis with few modifications.

Current Level of Development Drive Control (Hardware)


BAE Systems/Actel8 and 9 RAD6000, RAD750, Rad-hard FPGAs,

ASICs

Aeroflex8 and 9 Rad-hard microcontrollers, motor drives,

FPGAs

Protocols

In the small chassis, most of the control electronics can potentially be brought together in oneblock. In addition to easier heating of all electronics, this approach makes using high-

performance microprocessors, instead of simpler distributed controllers, possible. Taking intoconsideration the slow speed of the small class vehicles, it is evident that they would not require

sophisticated bus protocols with determinism and guaranteed latencies. A high data-rate issufficient for safety. The MIL-STD-1553B bus standard for military aircraft utilizing a 1 Mbpsdata rate would be sufficient for this application.

In the medium and large chassis, where control is more distributed, a deterministic protocol and

higher data rates are desirable. Two of todays in-vehicle protocols (byteFlight and FlexRay)satisfy these requirements, guarantee message latency, and provide a 10 Mbps data-rate.However, both of them are currently at early stages of development, and it is unlikely that

qualified hardware will be available in time for the medium chassis. Therefore, protocols like

CANAerospace/AGATE or CAN-SU could be used in the medium chassis.

CANAerospace is similar to CAN used in todays Earth vehicles, and is used in NASAs SATS(Small Aircraft Transportation System) in Langley Research Center. CAN-SU was used in

several small satellites as an on-board telemetry bus. One advantage of this protocol is that it iscompliable with byteflight. Thus, in later more advanced medium class vehicles, byteflight (with

its higher data rate) can be used instead of CANAerospace with no need to replace the legacydevices. For the large chassis, byteflight and FlexRay protocols would be needed to provide real-time dependable performance.

Current Level of Development Drive Control (Protocols)


Aeroflex 9 MIL-STD-1553B hardware

Philips 9 PCA82C250 and other space-qual. COTS

Aurelia Microelettronica 8 and 9 CASA series CAN controllers

ByteFlight group 4 Hardware, software and development tools

FlexRay group 4 Hardware, software, development tools


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Required Level of Development Drive Control

Small Medium Large

Redundancy Double Quadruple Quadruple

Data rate Below 1 Mbps Up to 1Mbps Up to 5 Mbps

Deterministic protocol No No Yes

Number of ASICs Low Medium High


Since most of the hardware for the small class is available on the market right now, the cost ofdevelopment and design for this chassis is minimal. Judging from past JPL experiences and costof RAD6000 processors we estimate the cost of the drive control system for the small chassis to

be around $5M. The medium chassis requires some development since it uses less common CANrather than widely used MIL-STD-1533B bus. Due to distributed control, the need for new

hardware, and a higher degree of redundancy, the cost would be around $10M. The large chassiswill require re-designing significant portions of rad-hard parts from commercial designs, andmuch higher computing capabilities. We estimate the cost of developing and testing the drive

control system of the large chassis to be up to $50M.

2006 2007 2008 2009 2010

Small Class

Feasibilitystudy, proof of

concept,research onASICs in FPGA

Initial design ofhw and sw

Testing Testing Integration

Medium ClassSystem level

design

Large Class

2011 2012 2013 2014 2015


Medium ClassProof of conceptwith non rad-

hard hardware

HW testing andsystem level

testing

HW testing andsystem level

testing


Large Class

Preliminarysystem levelstudy

(Identifyingsystemparameters)

Preliminarysystem levelstudy

Initial designResearchreliability of the

hardware

Initial design Prototype ready(non rad-hard)


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2016 2017 2018 2019 2020

Small Class

Medium Class

Large Class

Hwmanufacturing

and testing

Hw testing andsystem level

testing

Hw testing andsystem level

testing,prototype formissionplanning

System leveltesting

Integration

Vehicle ready

References

Avionics Databus Tutorial,Ballard Technology Inc. [online], URL:

http://www.ballardtech.com/tutorial.asp [cited 11 April 2005].

Murray C. Auto experts see self-navigation coming,Embedded[online], October 26, 2004URL: http://embedded.com/showArticle.jhtml?articleID=51200614 [cited 10 February 2005].

Hanaway J.F, Moorehead R.W., Space Shuttle Avionics System,NASA Office of Logic Design[online book], 1989, URL: http://klabs.org/DEI/Processor/shuttle/sp-504/sp-504.htm [cited 01

March 2005]

Zimmerman W.F., JPL/NASA ,personal communication, [8 April 2005]

Rutkowski, B., Ford Inc,personal communication, [27 April 2005]

Anderson, T., Bose Corporation,personal communication [11 April 2005]

Other references

http://www.gm.com/company/gmability/adv_tech/100_news/sequel_011005.htmlhttp://www.gm.com/company/gmability/adv_tech/600_tt/650_future/hy-wire_overview_050103.html

http://www.gm.com/company/gmability/adv_tech/600_tt/650_future/autonomy_050103.htmlhttp://www.delphi.com/pdf/techpapers/safety_bywire.pdf

http://powerelectronics.com/mag/power_powering_connectivity_todays/http://www.flexray-group.org/http://www.byteflight.com/

http://marsrovers.jpl.nasa.gov/technology/is_autonomous_mobility.htmlhttp://marsrovers.jpl.nasa.gov/technology/bb_software_engineering.html

http://www.can-cia.org/can/ttcan/http://www.evaluationengineering.com/archive/articles/0305/0305flexray.asphttp://www.can-cia.org/applications/passengercars/

http://www.xilinx.com/publications/xcellonline/xcell_48/xc_pdf/xc_autobus48.pdfhttp://spacecom.grc.nasa.gov/newscenter/archive/mc-1999-14.asp


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http://www.interfacebus.com/Design_Connector_Avionics.htmlhttp://www.itsforum.gr.jp/Public/E4Meetings/P01/schaffnit0903.pdf

http://www.aber.ac.uk/compsci/Research/mbsg/fmeaprojects/SoftFMEAtechreports/systems/protocols.pdf

http://www.interfacebus.com/Design_Connector_1553.html

http://ams.aeroflex.com/ProductPages/RH_dbuses.cfmhttp://www.ddc-web.com/products/Components/1553.asp

http://www.spacer.com/news/radiation-00b.htmlhttp://www.aero.org/conferences/mrqw/2002-papers/A_Burcin.pdf

http://www.byteflight.com/presentations/avidyne_databus_technology_selection.pdfhttp://www.stockflightsystems.com/html/canaerospace.htmlhttp://klabs.org/mapld04/papers/p/p106_woodroffe_p.pdf

http://www.caen.it/micro/syproduct.php?mod=CASA2


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INTERFACES

Introduction

The concept of modular design for a planetary vehicle chassis is only beneficial if a wide variety

of modules can be used and/or interchanged on the chassis. Modules allow the chassis toperform the large range of tasks that will be required by planetary vehicles. The interface

between module and chassis must provide all the resources the modules need. Larger or morecomplicated modules require more resources, and thus the capabilities of the interface must be

greater.

From the list of hypothetical required vehicles, it was shown that three vehicle chassis sizes

(dubbed small, medium, and large) combined with different modules will be sufficient to providethe necessary functions for planetary exploration. The chassis function is to transport the

module where it needs to go and supply the module with the resources it requires. Thecombination of chassis and modules will create the vehicles described earlier.

Each module will have specific inputs/outputs that it needs in order to work properly. The majorrequirements that must be considered for each module are power, communication of information

between chassis and module, structural support, and heat dissipation.

Challenges in Interface Design

Power Ability to supply sufficient power to all possible modules

Communications Must be radiation hardened with high data transfer rate

Structural SupportPhysical link needs to be robust and easy to

connect/disconnect modulesHeat Dissipation

Heat transfer between chassis and modules keeps

modules below heat threshold

This report discusses the current technologies available for the module interface and givesexamples of current modular vehicles. Following that, the resource requirements of theequipment needed for rover functions are discussed and some estimated interface specifications

are laid out. Finally, a development timeline is estimated based on the relationship betweenwhere current technology is and where it needs to be.


Power delivery from generator to appliance has not changed much throughout the years. Voltageregulators are common in many applications, and circuits can readily be developed to deliver the

correct amount (voltage) and type (AC or DC) of power to each module. There is a large varietyof standard power supplies that can be used for the interface [1].

Many different types of buses exist for data communication [2]. Todays popular connections,


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such as Fire wire or USB, can achieve data transfer rates of over 400 Mbps. However, thesehigh performance protocols have not yet been fully developed for use in space applications.

Modern structural materials (such as carbon fiber [5]) that are strong and lightweight will play a

factor in the load carrying capacity of any chassis. Furthermore, the mechanisms which attach

the module to the chassis port may vary depending on the size and weight of the module. Thecommon traditional method for securing removable parts is to use threaded fasteners. However,

this may be overkill for smaller modules, and other methods of providing secure physicalconnections could provide quicker and easier module installation. An example is snap fit

connections [10], which are found in many plastic devices.

Current Modular Vehicles

A modular vehicle that exists today is GM's Hy-Wire concept car [7]. These cars are powered

by fuel cells and employ several innovative modular concepts. Each wheel is poweredindividually by hub motors. The cars chassis contains the control system of the car, whichconnects to other devices through a universal docking port. The steering system is electric,

allowing the driver interface to be placed on either side of the car. Many of the technologiesdeveloped by GM for these vehicles can be used as a starting point for future modular vehicles.

GM H2 Chassis [6]

Another modular vehicle that exists today is the Boxer MRAV [8]. This is an armored vehicledeveloped by the British and German armies that allows for the rear cabin of the vehicle to be

interchanged. Different modules have different specific functions, such as medical or tactical

command, and each module can be replaced by crane in less than one hour. The modulesoperate independent of the rest of the vehicle. Each module is connected to the chassis using

four mounting bolts. All cable connections are by plugs and sockets on flying leads. TheTimoney Terrex AV81 [9] is another modular armored vehicle, with a top deck that can be

interchanged to support different weapons.


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Boxer MRAV[8]

The Aerospace Corporation, with their Standard Interface Vehicle (SIV) program, is currentlydeveloping a modular satellite. These small satellites will have a standard interface between the

spacecraft and payload. The spacecraft bus is meant to support 3 separate instruments, which arebolted to a mounting plate containing evenly spaced holes. Any instrument manufacturers that

choose to use the SIV satellite need to ensure that their instruments conform to specific mass,volume, power, and thermal standards.

Resources Supplied by Spacecraft to Payload in SIV Satellites

Total Mass Less than 60 kg

Total Power Consumption Less than 100 W

Total Heat Dissipation Less than 100 W

Maximum Dimensions 71 cm x 60 cm x 27 cm

Voltage 28 V +/- 6 V

Operational Temperature Range 9 39 Celsius

Data Transfer Rate 200 Kbps

Data Transfer Bus RS-422 Serial connection


Each of the modules in the universal chassis design will consist of equipment that will be used to

perform the vehicles functions. The equipment necessary is dependent on the vehicles intendedfunction. Some estimated requirements for possible equipment that may be needed are shown inthe following table. It should be noted that these are just estimates based on commercially

available products. The actual equipment requirements will vary depending on the specificintended uses, and any technology changes that improve the efficiencies or capabilities of the

equipment. Also, specific design decisions (such as lowering video signal quality) could bemade that would significantly reduce resource requirements.


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Estimated Equipment Resource Requirements

RequirementsModule

Power Communication Structural Support

CamerasDigital Storage and

Transfer (0.6 kW)

Video Signal

(0.5-5 Mb/s)

Camera weight (0.5 2.5 kg)

Robotic ArmActuator (50-75 W) Actuator Control

(10 Kb/s)Weight of arm + sample(25 kg)

Storage Area None None Payload weight (25 kg)

Toolbox None None Tool weights (10 kg)

Seat(s) None None Crew + Seat weight (90 kg)

Tow and Truck

Bed

None None Tow bed + Cargo (650 kg)

Pressurized

Volume

Life support,science

experiments, etc.

(30 kW)

Video Signal,Audio Signal,

Actuator

Control, DriveControl, etc. (1-7Mb/s)

Large (2000 kg)

WinchMotor (4 kW) Actuator Control

(10 Kb/s)Winch and Heavy Duty Cable(100 kg)

Small

ConstructionEquipment

Small Crane

(13 kW)

Actuator Control

(10 Kb/s)

Large (1000 kg)

Large

ConstructionEquipment

Backhoe engine

(60-100 kW)

Actuator Control

(10 Kb/s)

Large (2000 kg)

Remote drive

control

Minimal Drive ControlSignal (1-20Kb/s)

Minimal

On Board drivecontrol

Minimal Drive ControlSignal

(1-20 Kb/s)

Crew + Seat weight plus drivecontroller (90 kg)

This table can be used to obtain a rough estimate for the minimum amount of resources delivered

by each chassis. For example, the ATV will contain on-board drive control, a storage area, and aseat. Thus, the chassis port must supply a minimal amount of power for the drive controller; it

must have a data transfer rate that will allow the chassis to be controlled from the drivecontroller; and it must support the weight of a crewmember, seat, the actual drive controller, andany cargo. The same chassis will be used for the Scout rover, which will require more power

and a higher data transfer rate for its cameras but less structural support than the ATV. The finalspecifications of the interface for each chassis will depend on the minimum resource

requirements of all the modules it is expected to support. These values are summed up in thefollowing table.


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Supplied Resource Requirements for Different Chassis Sizes

Resource Small Chassis

Requirement

Medium Chassis

Requirement

Large Chassis

Requirement

Power 1 kW 10 kW 80 kW

Data Transfer Rate 4 Mb/s 4 Mb/s 8 Mb/sStructural Support 150 kg 500 kg 2000 kg

Not mentioned here are the thermal considerations that should be laid out for the individual

chassis. Each module, and the chassis, will generate heat and be exposed to radiation. The heatdissipation of the chassis should be such that both the module and chassis remain within a

temperature range that ensures functionality.

The physical connections of the interface will be spaced evenly on the chassis so that larger

modules will have more connection points and therefore additional resources supplied to it.

Each connection will supply a given amount of power, bandwidth, and support to the module.

Layout of Connection Points at Module-Chassis Interface (Top View)

Individual Connection Resource Requirements

Resource Small ChassisInterface Port Medium ChassisInterface Port Large ChassisInterface Port

# of Connections 4 6 12

Power 250 W 1.67 kW 6.67 kW

Data Transfer Rate 1 Mbps 2.0 Mbps 5.0 Mbps

Structural Support 37.5 kg 83.3 kg 166.7 kg


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The power taken from the interface connection can be modified within the modules to deliver thecorrect amount of power to the equipment the module contains. A hard power and

communication connection (as opposed to one with wires) that slides right into the chassis portswould make module connection easier. However, this could only be used if enough structural

support exists around the connection to ensure minimal stress on the power and data link.


The technology improvements necessary for the chassis module interface are not far out of

reach. The limitations on the power requirements of the modules are not set by whether theinterface can transfer the power, but rather by whether the chassis can actually produce it. Thecabling and connectors for power transfer are already available qualified for space use.

Data transfer rates required by the modules already exist today, but are not designed for use in

space applications. For instance, todays USB 2.0 ports can handle data transfer rates of 480Mbps, which would be enough to handle any of the estimated communication needs. Acommunication bus similar to todays Firewire, called Spacewire [11], is currently being

developed for space applications and should be ready within the next 5 years. Spacewire datatransfer rates will also be on the order of 100 Mbps, which is enough to handle all estimated

communication requirements. Spacewire cabling and connectors are already available qualifiedfor space use. We estimate it to cost an additional $3 M to complete development of Spacewire.

The physical connection between module and chassis is the aspect of the modular design thatrequires the most development. Most physical connections that are used today require tools and

are time consuming for connection/disconnection. The physical links required for the modularchassis should be as simple as possible and be quick and easy to connect without sacrificingstrength. Also, dust contamination and radiation exposure on Mars could be a serious issue, and

the connections should have long lifetimes even when exposed to that environment. A goodfuture study would be to determine the most efficient way (threaded fasteners, snap on joints,

new methods, etc) of connecting the modules based on the estimated module weights and thelevel of interchangeability desired for the chassis. Development of a universal connector couldrange from $1-5 M depending on the complexity of the chosen design.


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2006 2007 2008 2009 2010

Small Class

Trade Study todetermine

requirments ofinterfaces.Development of

Spacewire.

Development ofSpacewire, and

mechanical interface

Development ofSpacewire, and

mechanicalinterface

Testing andIntegration

Integration

Medium Class

Trade Study todetermine

requirments ofinterfaces

Research to increasecapabilities of

mechanical interface

Large Class

Trade Study to

determinerequirments ofinterfaces

2011 2012 2013 2014 2015

Small Class Vehicle ready

Medium Class Research toincrease

capabilities ofmechanicalinterface

Testing Integration Vehicle ready

Large Class Research to increasecapabilities ofmechanical interface

Research to increasecapabilities ofmechanical interface

2016 2017 2018 2019 2020

Small Class

Medium ClassLarge Class Testing Integration Vehicle ready

References

Tables

Robotic Arm: http://www.activrobots.com/ACCESSORIES/arm.htmlConstruction Equipment: http://www.cat.com/cda/layout?m=37840&x=7

Cameras: http://www.lowcostbatteries.com/drillframe.htm

Tow and Truck Bed: http://trucks.about.com/cs/usedadvice/a/load_capacity.htmWheels: http://www.greencarcongress.com/fuel_cells/Data Transfer Rates: http://www.mlesat.com/Article7.htmlLIN Bus:

http://www.freescale.com/webapp/sps/site/prod_summary.jsp?code=MC33689&nodeId=01435957958445Audio Signal: http://www.mwrf.com/Articles/Print.cfm?Ad=1&ArticleID=5525

Video Signal: http://www.neptune.washington.edu/pub/documents/p_and_c_req.html


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Robotic Arm: http://www.gurpsmaster.de/10edison.htmRobotic Arm: http://www.sjgames.com/gurps/characters/Racial/SexaroidBoomerStats.html

Winch: http://www.tjmproducts.com.au/winches.html

Other References

[1] - http://kropla.com/electric2.htm

[2] - http://www.interfacebus.com/Interface_Bus_Types.html[3] -

http://zone.ni.com/devzone/conceptd.nsf/webmain/0D17AEEAED870FE486256F3C00407B73[4] - http://www.upnp.org/about/default.asp[5] - http://www.zoltek.com/panex_products/index.shtml

[6] - http://www.greencarcongress.com/fuel_cells/[7] - http://auto.howstuffworks.com/hy-wire3.htm

[8] - http://www.army-technology.com/projects/mrav/index.html#mrav2[9] - http://www.army-technology.com/contractors/armoured/timoney/[10] - http://www.aesolutions.net/cost_saving_designs.htm

[11] - http://www.estec.esa.nl/tech/spacewire/faq/index.htm#_applications[12] - Mark Barrera, The Aerospace Corporation, Personal Correspondence

[13] - Paul Berry, ARTEC in Mnchen, Personal Correspondence[14] - http://www.estec.esa.nl/tech/spacewire/overview/


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HUB MOTORS

Introduction

How they work

- Power and movement commands sent to a traction control box- Traction control box sends modulated signals to motors- Interior of motors connected to suspension.- Interior can include electronics, gears, and electromechanical breaks

- The stator and winding remain fixed while the rotor and permanent magnets spin.- The rotor is attached to the actual wheel diameter creating rotational motion

Advantages- Higher efficiency than full mechanical connection- Independent motors create redundancy

- Regenerative breaking can restore some energy- Removal of mechanical linkages benefits dust protection and reliability- Full torque supplied at 0 rpm (as much as 60% increase over conventional)

- Much better off-road performance because of increase in traction control

Disadvantages

- Increases unsprung mass. Must try to keep motors as light as possible.


Company: UQM Technologies

Website: www.uqm.comContact: Telephone# 303-278-2002, [email protected]

Specs:


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SpecData (INETS

system)Spec Data (APM12)

Length (m) 0.38 Length (m) 0.11

Diameter (m) 0.29 Diameter (m) 0.17

Mass (kg) 74 Mass (kg) 9

Efficiency 91% Efficiency 95%

kW 30 (cont) 75 (peak) kW 12 (cont) 17 (peak)

Torque (Nm) 1700 Torque (Nm) 14.3

RPM 1400 RPM 11000

Voltage (V) 250 DC Voltage (V) 300

Lifetime 97,000 km Lifetime

*These systems are not actual hub motor systems but are electric motorsfor vehicle applications.

Notes:

- UQM machines can be operated in either a forward or reverse direction of rotationand either in motor or generator mode and can dynamically change from one mode of operationto another in millisecond response time.

- Developed Phase Advance Control which allows UQM motors to deliver high outputtorque at low operating speeds and low torque at high operating speeds from the same machine.

- We have also developed and successfully tested a permanent magnet electronic motorsystem that achieves a 10 to 1 top speed to base speed ratio

Company: FUPEX Corp

Website: http://www.fupex.com/page8.htmlContact: 408-262-8668, Mike Chen at [email protected].

Specs:

Spec Data (Fupex)

Length (m)

Diameter (m)

Mass (kg)

Efficiency 85%

kW 28

Torque (Nm) 65

RPM 4000

Voltage (V) 120

Lifetime


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Company: Lucchi R. Elettromeccanica

Website: http://www.lucchirimini.com/eng_index.htmContact: [email protected]

Specs:

.

Company: Tech M4

Website: http://www.tech-m4.com/

Contact: [email protected] - Transport, Telephone: (450) 645-1444Specs:

Spec Data (Tech M4)

Length (m) 0.161

Diameter (m) 0.313Mass (kg) 25

Efficiency 95%

kW 3

Torque (Nm) 29 (nominal) 100 (max)

RPM 1000

Voltage (V) 200 VDC

Lifetime

Spec Data (Lucchi)

Length (m)

Diameter (m)

Mass (kg) 15

Efficiency

kW 25

Torque (Nm)

RPM

Voltage (V) 120

Lifetime


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Vehicle: MER RoversSpecs:

REO-20 Maxon motor

The HD Systems SHF 50:1 gear ratio harmonic drive hasthe following specifications:

Rated torque at 2000 RPM: 5.4 N-m or 0.55 kgf-m

Repeated peak torque at start/stop: 18 N-m or 1.8kgf-m

Maximum average load torque: 6.9 N-m or 0.70kgf-m

Maximum momentary torque: 35 N-m or 3.6 kgf-m


All motors should contain the following features:- Operate in forward or reverse direction

- Operate in motor or generator mode- Millisecond response time

- Something similar to UQM's Advance Phase Control- Dust Sealed- Brushless

Required Level of Development Hub Motors

Spec Small Chassis Medium Chassis Large Chassis

Length (m) 0.15 0.2 0.35

Diameter (m) 0.3 0.3 0.4

Mass (kg) 5 8 25

Efficiency 95% 98% 98%kW (cont) 2 4 25

Torque (Nm) 50 (nominal) 100 (max) 100 (nominal) 150 (max) 1000 (nominal) 1500 (max)

RPM 150 150 125

Voltage (V) 120 VDC 120 VDC 120 VDC

Lifetime (km) 30,000 50,000 80,000


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The technology is well developed. The main challenge is going to be taking the terrestrial designand modifying it for use on the Moon and Mars surfaces.

Currently TRL 5 - Technology has been demonstrated fully here on Earth.

Research that needs to be performed:- Better sealing mechanism to eliminate dust

- Increased efficiency- Lifetime testing- Redesign to fit specific specifications

- Modify liquid cooling system for Martian (Moon) temperatures- Integration into suspension and wheel subsystems

We estimate that developing and testing each of the in-hub motors will cost around $30 M. Thesmall chassis motors are available here on Earth, however the research money will go into

creating space-worthy versions. For the medium and large chassis the research money will gointo increasing the efficiency and capabilities of the motors.

2006 2007 2008 2009 2010

Small Class

Research and

Developmenton dust sealing,cooling system,

low temperatureoperation.

Research and

Development ondust sealing, coolingsystem, low

temperatureoperation.

Detailed Design

and testing ofmotors.

Testing Integration

Medium Class

Research andDevelopment to

increase efficienciesand capabilities.

Large Class

2011 2012 2013 2014 2015

Small Class Vehicle ready

Medium Class

Research andDevelopment toincrease

efficiencies andcapabilities.

Detailed design andtesting of motors.

Detailed designand testing ofmotors.

Integration. Vehicle ready

Large Class

Research and

Development toincreaseefficiencies and

capabilities.

Research and

Development toincrease efficienciesand capabilities.


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References

www.uqm.comhttp://www.fupex.com/page8.html

http://www.lucchirimini.com/eng_index.htm

http://www.tech-m4.com/http://www.greenspeed.us/wavecrest_electric_motor.htm

http://www.muskegonareafirst.org/News/Articles/AGeneralDynamics.htmhttp://hobbiton.thisside.net/rovermanual/

2016 2017 2018 2019 2020

Small Class

Medium Class

Large Class

Research andDevelopment toincrease

efficiencies andcapabilities.

Detailed design andtesting of motors. Detailed designand testing ofmotors.

Integration. Vehicle ready


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MOBILITY

Introduction

The mobility system is one of the most crucial aspects of the chassis. Even a vehicle with a

tremendously strong power source can fail to accomplish simple tasks, and more importantly canrisk the safety of the crew, if the right mobility system is not applied.

There are many considerations associated with mobility. Due to the inconsistency in the

structure and the geometry of the terrain, the off road capacity of the chassis is extremelyimportant. This will include several challenges such as keeping appropriate posture and motionin the low gravity, and providing enough traction in the Martian soil. We will consider handling

and maneuvering capabilities, and ways to reduce the harsh environmental effects of the RedPlanet.

In this paper we will provide information regarding the current level of technology in use today,

the required level of technology for future tasks, and a timeline for the transition between thesetwo stages.


Below is a chart showing the current level of mobility technology. The chart includes previously

launched planetary vehicles, future planetary vehicles, and terrestrial off-road vehicles.

Current Level of Development - Mobility

Vehicle CompanySuspension

TypeSteering

Wheel

InformationSpecs

Lunar Rover NASA

Doublehorizontalwishbone

4 Wheels Good road-holdingcapabilitiesand it takesup very littleroom underthe vehicle

Hummer GM

IndependentFront SuspensionWith Torsion Barand Gas Charged

Shock AbsorbersLive Multi-LinkRear SuspensionWith VariableRate Coil Springsand Gas ChargedShock Absorbers

PowerRecirculatingBall VariableAssisted

Steering

4 WheelsWith CastAluminumWheels, 17-In.

X 8.5-In.


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ATV(Quark fuel-cell four-wheeled

motorcycle)

Peugeot

Triangularwishbones

4 Wheels(17'' diameter)

Limitedmobilitysince theastronaut isunprotected,no sound,

efficientenergyusage

MSL JPL Rocker-Boogie 6 Wheels

R-GatorJohn Deereand iRobot

4 Wheels

Light truck McPherson struts 4 Wheels

Constructionvehicle

McPherson struts 4 6 Wheels


Small & Medium Chassis

We determined that trailing arms would be the best suspension system for the rear of the chassis.

Even though this is one of the older types of suspension systems available, it is still one of themost reliable and compact systems. It is composed of links connected directly perpendicular to

the chassis, allowing the rear to swing up and down. In addition, the links of the suspensionsystem travel along the chassis rather than sticking out from it, thus providing great compatibilitywith the shape of the modular chassis.

We have also determined to use McPherson struts in the front in order to increase the handling

properties of the chassis and to provide better steering. The small chassis will require 0.8mdiameter wheels and the medium chassis will require 1.0m diameter wheels. A larger than usualwheel size will assist the vehicle with getting over obstacles easily, in return of a small steer

angle reduction.

Large Chassis

The large chassis ranges from 3000 to 5000 pounds and the mobility system will require many

improvements over the smaller chassis. Since the vehicles of this chassis type will play a majorrole in the missions (such as carrying the nuclear reactor or construction) we believe it is the one

that deserves the most attention.

Our research determined that coiled and stiff suspensions provide low traction at even mild off-

road situations and cause wheels to lift off the ground in uneven terrain. Therefore, we decided toincorporate an independent soft air suspension design where increase in the ground contact force

and traction is provided, and ride quality is kept stable even under harsh and uneven terrainconditions.


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We decided to make use of the suspension system of the LRV (Double Wishbone Suspension)for the rear of the large chassis to improve ride and steering control over bumpy terrain. Anti-

roll bars attached to the lower arm are used to provide ground clearance and articulation.

Being the most widely used type of suspension for vehicles with similar properties, we suggest

McPherson Struts for the front of the vehicle. This suspension incorporates the shocks ordampers, and the air springs (instead of coils) in the vehicle design. With the adoption of anti-roll

bars attached to McPherson struts, full travel of the suspension is provided, resulting in furtherarticulation increase. Two-meter diameter wheels can be used for optimal performance.

Required Level of Development - Mobility

ClassSoft/Hard

SuspensionSuspension

TypeWheel

InformationMajor Mobility

Strengths

Small &

Medium

Class

Soft suspension

Trailing arms at

rear andMcPherson

struts at thefront

4 wheels

(0.8 and 1meter

diameterrespectively)

Reliable, compact and

compatible, goodhandling

LargeClass

Independent airsuspension(soft)

Doublewishbone at the

rear andMcPhersonstruts at the

front

4 wheels,(further

research for6), 2 meterdiameter

Significantly reducedterrain effects, good

handling andmaneuverability greattraction

To improve the functionality and compatibility of these suspension systems, additional

technological developments could also be adapted. Currently Bose is developing a suspensionsystem that uses a linear electromagnetic motor to increase the smoothness of the ride by

reducing the overall body motion and jarring vibrations. This system eliminates body rollsignificantly. An electrical actuator could be integrated into the McPherson struts, reducing thespace they occupy (making them more compatible with the modular chassis) and increasing

robustness under extreme temperature variations.

Trailing Arms McPherson Struts Double Wishbone


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We have decided to use 4-wheel, as opposed to 6-wheel, designs. 6-wheel designs haveadvantages such as better weight distribution, handling, and offer greater safety to the crew.

However, they also may add unnecessary complexity and weight to the chassis. We feel that adetailed trade study will need to be performed to determine the optimal number of wheels for

each chassis.


The main challenge is to develop chassis that are robust and durable enough to accomplish their

purpose successfully regardless of the conditions. More information regarding the terrain andsoil characteristics of the Moon and Mars should be gained to help successfully develop mobilitysystems for the chassis. When these tasks are accomplished and sufficient knowledge and

technical expertise is acquired from them, estimating the development of timeline would be a loteasier and more accurate.

The mobility systems for the small and medium class vehicles are mostly commerciallyavailable. The additional cost will come from making the mobility system more robust and

durable for the Martian terrain and environment. We estimated the cost of this process to bearound $10M. The large class requires significantly more development due to high relative

importance in the mission. It will integrate more complex suspension systems than the previousclass. As a result we estimated cost of this process to be around $100M.

2006 2007 2008 2009 2010

Small Class

Robustness

and Durabilityresearch

Initial design Testing Integration

MediumClass

Robustness

and Durabilityresearch

Large Class

Further studyof 4 vs. 6 and

single vs.double wheels

2011 2012 2013 2014 2015


Small ClassInitial design Testing Integration Vehicle ready

Large Class Study of activevs. passivesuspensions

Preliminarysystem levelstudy, testing

Initial design Initial design Incorporatingelectric motors

2016 2017 2018 2019 2020

Small &

Medium Class

Large ClassPrototypeready

Testing Testing Integration Vehicle ready


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References

The suspension bible URL: http://www.chris-longhurst.com/carbibles/index.html?menu.html&suspension_bible.html

Neon suspension design URL: http://www.allpar.com/neon/suspension.html

Jacob Isaac-Lowry, Suspension Design: Types of Suspensions 2, Oct 25, 2004, 00:37http://www.automotivearticles.com/Suspension_Design_2.shtml

Scott Memmer, Suspension III: Active Suspension Systems, Tech Center URL:http://www.edmunds.com/ownership/techcenter/articles/43853/article.html

LLC, - Air Suspension Kits 2004, Strutmasters URL:http://www.strutmasters.com/help/air-suspension.htm

John Brabyn, Range Rovers, URL:http://www.rangerovers.net

Kevin Schappell, How Your Cars Suspension Works,December 23, 2004 URL:http://www.articlecity.com/articles/auto_and_trucks/article_136.shtml

Matt Gartner, Design and strategy tips, 1999URL: http://www.gmecca.com/byorc/dtipssuspension.html

Alan McCaa, Sandcar Technology, Suspension & Handling, April 2004, URL: http://www.off-

road.com/dunes/features/suspension/

A Close Look At The Rover, MMIV, CBS Broadcasting Inc, Jan. 15, 2004, URL:

http://www.cbsnews.com/stories/2004/01/15/earlyshow/living/main593395.shtml


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FUEL CELLS AND FUEL STORAGE

Introduction

Fuel cells are the best option for power generation in Mars rovers. With no moving parts, fuel

cells offer a robust power system that has been proven in manned space applications and will beable to withstand extreme Martian conditions with few instances of mechanical failure. A fuel

cell system would be more efficient than internal combustion engines and safer for astronautsthan radioisotope thermoelectric generators (RTG), but the most compelling reason to use fuel

cells for the modular universal chassis concept lies in their adaptability and scalability.

A range of electrical outputs could be achieved with fuel cells and applied to the various-sized

rovers required on Mars by simply changing the number of membrane layers in the fuel cellstack1. The size and amount of power generated could be tailored to meet the requirements of

each type of rover. This is an advantage over other forms of power generation because it wouldallow the use of a single type of fuel cell for all rovers versus having different power systems for

each vehicle. Fuel cells could also be arranged in parallel to ensure redundancy and to meet loaddemands. Because they are entirely chemical rather than mechanical, there are very fewconstraints on the configuration of fuel cell power systems. The size of a system is dictated

simply by the power needs, and fuel cell stacks could easily be arranged to fit the variousplatforms of the modular universal chassis concept.2


The two types of fuel cells best suited for vehicle applications are proton exchange membrane(PEM) fuel cells and solid oxide fuel cells (SOFC). The ideal fuel for these fuel cells is purehydrogen. However, because of its low energy density by volume, an immense amount of

hydrogen would have to be carried to satisfy the energy requirements of the chassis. Instead, ahydrocarbon fuel would be used. Methane, which could be produced by the Sabatier reaction

with carbon dioxide from the Martian atmosphere and hydrogen brought from Earth3, is asuitable choice.

SOFC have a major advantage over PEM fuel cells in that they can use methane directly, withoutthe need to extract hydrogen by reforming the fuel. SOFC are also 45-50% efficient with a

methane fuel source4 compared to 40-47% for a PEM fuel cell5. However, SOFC operatebetween 650 and 1000C4, temperatures that would be difficult to dissipate in the sparseMartian atmosphere. SOFC also use brittle ceramics for an electrolyte. These sensitive

materials would require substantial protection for use on rugged Martian terrain and would

significantly reduce the durability of the rover power systems

6

.

PEM fuel cells operate at a more reasonable temperature of 80C and are the more advanced ofthe two types for vehicle applications5. Although they require the added mass of a reformer,

PEM fuel cells are smaller than SOFC, offsetting the mass difference. Finally, PEM fuel cellscan achieve lifetimes greater than 10,000 hours and can be shutdown and restarted multiple

times. SOFC have comparable running lifetimes, but are not intended for repeated shutdown andrestart. 7


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Due to volume concerns, methane and oxygen used by the fuel cell systems would be stored on

the rovers as liquid. Liquid natural gas (LNG) vehicles, which utilize liquid methane, have beenin use for many years. LNG is typically used for large vehicles, which have need for dense fuel

storage. A double-walled tank with a vacuum insulator allows these vehicles to remain fueled

for several days

2

. Because each class of chassis in the universal chassis concept must support atleast one unpressurized vehicle, the liquid oxygen tanks for the fuel cell system must be separate

from breathable oxygen tanks on the pressurized rover bodies. To keep oxygen a liquid, it mustbe cooled to -183C. However, on Mars, methane would need to be pressurized, as well as

cooled, to be stored as a liquid. This is because its boiling point is sensitive to pressure. At 1atm, methanes boiling temperature is -160C, but with lower pressure on Mars, the boiling pointwould be even lower. On Earth, high-pressure tanks store liquid methane at around 8,000 psi at

25C. The lower ambient temperature on Mars, however, would not require methane to bepressurized to such an extreme.

Pressurized storage tanks for liquid methane and oxygen are commercially available and havebeen used for years in space. Table 1 describes the specifications of the different tanks that can

be used to store methane and oxygen for each of the Mars rovers. The titanium tanks for thesmall and medium chassis are spherical while the tanks for the large chassis are cylindrical

composite over wrapped pressure vessels (COPV).

Methane and Oxygen Tank Specifications8

Small Medium Large

Methane Oxygen Methane Oxygen Methane Oxygen

Volume (m3) 0.0065 0.0039 0.0065 0.0157 0.0814 0.0814

Dimension (m)0.24

diameter

0.19

diameter

0.24

diameter

0.31

diameter

0.42 diameter

x 0.75 long

0.42 diameter

x 0.75 long

Mass (kg) 3.36 1.53 3.36 5.38 12.7 12.7OperatingPressure (psi)

4,500 3,600 4,500 3,600 4,800 4,800

Tank Material Titanium Titanium Titanium Titanium COPV COPV

Current Development: General Motors

While every major automotive manufacturer is developing fuel cell technology for Earth-basedvehicles, the research of General Motors is most applicable to the universal chassis concept. In

their concept vehicles AUTOnomy, Hy-wire and Sequel, GM has used PEM fuel cell technology

in a skateboard chassis intended to support multiple vehicle bodies. The fuel cell stack in theHy-wire is able to produce a peak power output of 129 kW9, which would cover the maximum

power requirements of each class of chassis. At 100 kg and 0.06 m3 9, the Hy-wire stack is also areasonable size for our applications.

GM has shown that using PEM fuel cells in a universal chassis is feasible and has manufacturedworking concept vehicles. In these concept vehicles, the fuel cell power systems are integrated

with electric motors for the wheels and x-by-wire controls. According to NASAs technology


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readiness guidelines, most components of a fuel cell power generation system for modularuniversal chassis are TRL 6.

Hy-wire Fuel Cell Specifications

Fuel Cell Type PEM

Fuel Type Compressed HydrogenEfficiency 40%

Continuous Power Output 94 kW

Peak Power Output 129 kW

Mass 100 kg

Volume 0.06 m3

Operating Temperature 80C

Current Development: Honda

Honda has focused its research on improving the range of temperatures at which its fuel cellvehicles can operate. Its latest FCX vehicle uses a PEM fuel cell and can operate at ambienttemperatures between -20C and 95C. This is achieved with the use of a new aromaticelectrolytic membrane that enables the vehicle to operate in a wider range of temperatures than

other fuel cells that use traditional fluorine electrolytic membranes. The FCX fuel cell stack hasa maximum power output of 80kW.10

Required Technology Level

Based on their current development level, it is clear that PEM fuel cells are the appropriatechoice for the universal chassis concept. However, advances still need to be made before a PEM

fuel cell system is ready for use in planetary vehicles. To be a viable option for long-termexploration of Mars, progress must be made in improving fuel cell restart from coldtemperatures. For use on Mars, fuel cells will need to start at ambient temperatures as low as -

89C.

Advances will need to be made in methane reforming technology as well. Steam reforming,where fuel is combined with steam and heat, is the most common method of reforming methane.This process adds complexity to the fuel cell system and significantly reduces efficiency. Also,

reformers tend to be massive and difficult to implement into a vehicle. Thus, more research willbe required to reduce the mass and volume of reformers. Research must be done on how

radiation affects PEM fuel cell performance and advances must be made in radiation shielding

for fuel cells.

Finally, due to the energy needs, the large-chassis requires considerable amounts of fuel. Toreduce the amount of methane and oxygen needed and, thus, maintain vehicle mobility, the fuel

cells used for the large chassis will need to be more efficient than those for the small andmedium chassis.


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Based on power and energy requirements, we estimated the size of each of the fuel cell systemsand the amount of methane and oxygen required for each class of chassis. These values are

listed in Table 3.

Fuel Cell System Size and Fuel Requirements

Chassis Class Small Medium LargeEnergy (kW-hr) 6 24 2000

Peak Power (kW) 8 16 120

Efficiency (%) 40 40 60

Lifetime (hours) 4400 4400 8400

Fuel Cell Mass (kg) 8.51 17.02 127.66

Fuel Cell Volume (m3) 0.005 0.01 0.075

Methane Mass (kg) 1.12 4.46 248.02

Methane Volume (m3) 0.0041 0.016 0.8532

Oxygen Mass (kg) 4.46 17.86 992.06

Oxygen Volume (m3) 0.0103 0.036 1.72

Methane Fuel Tank Mass (kg) 3.36 6.72 139.7

Oxygen Fuel Tank Mass (kg) 4.60 10.75 279.41

Reformer Mass (kg) 7 10 100

Reformer Volume (m3) 0.0041 0.0059 0.059

Total Mass (kg) 29.05 66.81 1886.85

Percentage of Vehicle Mass 11.62 16.70 62.90


Initial research for small-chassis rovers will include improving the range of startup temperaturesfor PEM fuel cells. Since this research is already taking place in the automotive industry, the

only need is for continued development and funding. We estimate the cost to be around $3M.Also at this phase the effect of radiation on PEM performance will be studied. This research and

advances in radiation shielding will cost approximately $5M.

The medium-chassis class will require research into fuel handling, specifically how fuel

impurities affect performance and how they can be eliminated. This phase of research will costaround $5M.

Beyond the small and medium chassis, the large class of rovers will require significant researchand development. Fuel cell efficiency must be raised to approximately 60%. Reformer mass

and complexity must also be reduced. The development for large rovers will cost approximately$40M.


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2006 2007 2008 2009 2010

SmallClass

Feasibility study,Proof of concept

Initial design withimproved fuel cell

startuptemperatures,Radiation study

Testing Testing Integration

MediumClass

Study of handlingfuel impurities

LargeClass

2011 2012 2013 2014 2015

SmallClass

Vehicle ready

Medium

Class

Reformer

manufacturingand testing

Reformer testing

and systems leveltesting


Large

Class

Research intoimproving

efficiency,lifetime, mass

Research onreformer and fuel

cell reliability

Initial design,Research on

reformer and fuelcell reliability

Initial design Proof of concept

2016 2017 2018 2019 2020

Small

Class

MediumClass

LargeClass

Reformer and fuelcellmanufacturing

and testing

Systems leveltesting ofreformer and fuel

cell


References

1National Fuel Cell Research Center, FUEL CELL POWER PLANT: MAJOR SYSTEM

COMPONENTS - Fuel Cell Stack, URL:

http://www.nfcrc.uci.edu/fcresources/FCexplained/FC_Comp_Stack.htm [cited 9 January 2005].

2Vanderwyst A., Beyer J., Passow C., Paulson A., and Rowland C., "Power Generation andEnergy Usage in a Pressurized Mars Rover," Martian Expedition Planning, edited by Charles S.Cockell, Vol. 107, Univelt, Inc., San Diego, 2004, pp. 327-340.

3Zubrin R., Baker D., and Gwynne O., Mars Direct: A Simple, Robust, and Cost EffectiveArchitecture for the Space Exploration Initiative, AIAA Paper 91-0328, 1991.

4National Fuel Cell Research Center, NFCRC Tutorial - Solid Oxide Fuel Cell (SOFC), URL:

http://www.nfcrc.uci.edu/EnergyTutorial/sofcindex.html [cited 9 January 2005].


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- 37 -

5National Fuel Cell Research Center, NFCRC Tutorial Proton Exchange Membrane Fuel Cell(PEMFC), URL: http://www.nfcrc.uci.edu/EnergyTutorial/pemfcindex.html [cited 9 January

2005].

6Thompson, L., University of Michigan Department of Chemical Engineering, Personal

Communication, March 2005.7Tamor, M., Ford Motor Company, Personal Communication, 2 May 2005.

8ATK Alliant Techsystems, URL: http://www.psi-pci.com [cited 17 April 2005].

9General Motors, Hy-wire Specifications, URL:

http://www.gm.com/company/gmability/adv_tech/images/fact_sheets/hywire_specs.html [cited25 February 2005].

10Honda, Honda Fuel Cell Power FCX, URL:http://world.honda.com/FuelCell/FCX/FCXPK.pdf [cited 25 February 2005].


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SUMMARY OF CURRENT LEVEL OF DEVELOPMENT

CHASSIS TECHNOLOGIES (current level)

Company TRL Products Company TRL Products Company TRL Products

Computing Drive Control Mobility

JPL 9 MER Navigation,Hazard and Suntracking cameras,internal sensors

Aeroflex 8-9 Rad-hardmicrocontrollers,motor drives,FPGAs, MIL-STD-1553B hardware

GM 4 Hummer (Front:Torsion bar & gasshocks, Rear: Multi-Link w/ var. rate coils& gas shocks/ 4 17"by 8.5" wheels)

JPL 9 MAPGENsoftware

BAESystems/

Actel

8-9 RAD6000,RAD750, Rad-hard FPGAs,

ASICs

Boeing 9 Lunar Rover (doublehorizontal wishbone/4wheels)

JPL 4-5 CLARAtyarchitecture

Philips 9 PCA82C250 andother space-qual.COTS

Peugeot 4 Quark ATV (triangularwishbone/4 17"wheels)

NASA 4-5 IDEA architecture AureliaMicro-elettronica

8-9 CASA series CANcontrollers

JPL 9 MER/MSL (Rocker-Bogie, 6 wheels)

BAESystems

9 RAD750processor

ByteFlightgroup

4 Hardware,software and dev-mnt tools

John Deereand iRobot

4 R-Gator (4 wheels)

Motorola 4 68060, PowerPCprocessors

FlexRaygroup

4 Hardware,software and dev-mnt tools

Intel 4 Pentiumprocessors In-hub electric motors

Interfaces UQM Tech. 4-5 In-hub electric motors

Fuel Cells and Fuel Storage

SingaporeTechnologiesKinetics

4 Timoney TerrexAV81

FUPEXCorp

4-5 In-hub electric motors

GM 6 PEM Fuel Cells(129 kW/100 kg)

GM 4 Hy-wire (modularconcept w/universal dockingport)

Lucchi R.Elettro-meccanica

4-5 In-hub electric motors

Honda 4 FCX Fuel Cells(80kW)

EuropeanArmamentsAgency

4 Boxer MRV Tech M4 4-5 In-hub electric motors

Maxon

Motor USA

9 REO-20 maxon motor

(MER)


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COST OF UNIVERSAL CHASSIS DEVELOPMENT

The following are rough order of magnitude cost estimates for the total design, development andproduction of each rover class in the universal chassis concept. The values were calculated using

NASAs Advanced Missions Cost Model and adjusted to reflect constant-year 2005 dollar

values.

Chassis Class CostSmall $559M

Medium $393MLarge $1342M

The total cost of design, development and production for a fleet of planetary rovers wasestimated to be $2.3 billion.

expert summary

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