expert summary
TRANSCRIPT
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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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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
Testing Vehicle ready
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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.
Current Level of Development
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)
Company Level (TRL) Products
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)
Company Level (TRL) Products
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
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
Development Timeline
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
Small ClassVehicle ready
Medium ClassProof of conceptwith non rad-
hard hardware
HW testing andsystem level
testing
HW testing andsystem level
testing
Testing Vehicle ready
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.
Current Level of Development
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
Required Level of Development
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.
Development Timeline
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.
Current Level of Development
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
Required Level of Development
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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Development Timeline
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.
Current Level of Development
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
Required Level of Development
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.
Development Timeline
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 ClassVehicle ready
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
Current Level of Development
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
Development Timeline
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
Testing Integration Vehicle ready
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
Testing Integration Vehicle ready
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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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.