Extreme Environment Robots: Mars Exploration Rovers

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Extreme Environment Robots Mars Exploration
Rovers

• Maria G. Bualat
• March 15, 2005

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My Background

• B.S.E.E., Stanford University, 1987
• Started working for NASA on graduation
• M.S.E.E. Emphasis Controls, Santa Clara
  University, 1992
• Have been working in robotics since 1995
• Project manager for the K9 rover project since
  1999
• Areas of interest rover navigation, computer
  vision, human/robot interfaces

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Mars is an Extreme Environment

• Extreme temperature changes (20C to -120C)
• Rough, rocky terrain
• No global positioning system
• Communications time delay
• Narrow communications bandwidth
• Dust

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Why is Mars interesting?

• Most Earth-like planet
• Once had/may still have liquid water and thus
  life
• NASAs Mars exploration strategy
• Follow the water
• Water is key because almost everywhere we find
  water on Earth, we find life.

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Mars Rovers Past, Present, Future
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Sojourner Specs

• 13 cm (5 in) wheel diameter
• Rocker-bogey chassis
• Top speed .6 m/min (.02 mph)
• .22 m2 solar panel providing peak of 16 W
• With batteries, peak available power of 30 W
• Normal driving power requirement is 10 W
• 80C85 CPU, at 100 KIPS
• 176K of PROM and 576K of RAM

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Sojourner Instruments

• Navigational
• Front viewing stereo pair of cameras
• Laser striping system
• Gyro
• Corrections made using lander imager
• Scientific
• Alpha Proton X-Ray Spectrometer (APXS)

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Pathfinder Mission Highlights

• Launched December 4, 1996
• 7-month cruise to Mars with 4 trajectory-correctio
  n maneuvers
• Landed 957 a.m. PDT July 4, 1997
• Bounced at least 15 times up to 12 m high
• Sojourner driven down the ramp on Sol 2
• Primary mission 8 sols
• Total mission 83 sols
• Sojourner traversed 100m around the lander
• Pathfinder returned over 16,000 lander images and
  550 rover images
• Sojourner performed 16 chemical analyses of rocks
  and soil

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Spirit Opportunity Specs

• Brains
• CPU PowerPC RAD6000 (200 MIPS)
• 128 MB DRAM, 256 MB Flash
• Brawn
• 1.2 meters high
• 180 kilograms
• Top speed 5 cm/s (.1 mph)
• Capable of 100 m/sol
• Lifetime
• Primary mission 90 sols
• Spirit is currently on Sol 167
• Other
• Solar panels 140W (4 hrs) on Sol 1
• 2 batteries
• 100W required to drive
• Communication via orbiter and direct-to-earth
  (DTE)

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MER Science Instruments

• Pancam
• High resolution imagery
• Mini-Thermal Emission Spectrometer (Mini-TES)
• Mineralogical and temperature information
• Rock Abrasion Tool (RAT)
• Remove surface dust and weathering
• Microscopic Imager
• APXS
• Moessbauer Spectrometer
• Determine the properties of iron bearing materials

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MER Navigational Instruments

• Mast-mounted Navcam
• Front and Rear Hazcam
• Sun sensor
• Used to determine global bearing (no compasses on
  Mars!)
• Sun filter on pancam
• Inertial Measurement Unit (IMU)

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MER Landing System

• EDL an adaptation of the Mars Pathfinder method
• Aeroshell and parachute decelerate lander through
  the Martian atmosphere
• Retro-rockets fired to slow landers speed of
  descent, airbags inflated to cushion lander at
  surface impact
• Lander bounces along Martian surface until it
  rolls to a stop
• Airbags deflated and retracted, and lander petals
  and rover egress aids are deployed
• Rover deploys its solar arrays, and places system
  in a safe state

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MER Mission Highlights

• Spirit landed in Gusev Crater on January 3, 2004,
  835 p.m. PST
• Opportunity landed on Meridiani Planum on January
  24, 2004, 905 p.m. PST
• Opportunity discovered evidence of past standing
  water on Mars
• Spirit and Opportunity successfully completed
  their prime missions in April and are continuing
  exploration on an extended mission
• Spirit has traversed over 2 miles and is starting
  its exploration of the Columbia Hills
• Opportunity has entered Endurance crater

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Next Rover Mission MSL

• MSL Mars Science Laboratory
• 2009 launch
• Study habitablility
• 687 sol primary mission (1 Mars year)
• 1 metric ton robot
• 10x MER payload
• Nuclear powered
• 6 km range
• Powered skycrane landing

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MSL Skycrane Landing System

• Rocket system hovers 5 m above the surface
• Rover lowers down on a bridle
• Once the wheels touch the ground, bridle is cut
• Rockets fly off and crash elsewhere

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Human Exploration

• Robots will act as aides for humans exploring
  other planets
• Rover roles for exploration with humans
• Scouts
• Videographers
• Assistants (scientific, construction, site
  survey)
• Pack mules
• Rescuers

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Mars Rover Prototypes (K9)

• Prototype of Mars rovers
• Used as a testbed for software and autonomy
• Size
• Scicam height 1.6m
• 70 kg
• Computing
• 1.2 GHz Pentium M laptop
• Linux operating system
• Software written in C
• Power
• Li-Ion batteries
• Subsystems can be powered on/off

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K9 Instrumentation (Science)

• High resolution color cameras
• Same resolution as human fovea
• 5 degree-of-freedom (DOF) arm
• Waist, shoulder, elbow, twist, and wrist
• Near-Infrared spectrometer
• Enables detection of carbonates
• Camera HAnd lens MicroscoPe (CHAMP)
• Zooms from 7mm to infinity

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K9 Instrumentation (Navigation)

• Mast-mounted navigation cameras (navcams)
• Body-mounted hazard avoidance cameras (hazcams),
  front and rear
• Inertial Measurement Unit
• Compass/Inclinometer
• Encoders on motors
• Potentiometers on joints

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K9 Software

• CLARAty Rover Software Architecture
• Jointly developed with Jet Propulsion Laboratory
  (JPL), Carnegie Mellon University (CMU),
  University of Minnesota
• Modular with many generic parts
• Two layers Functional Decision
• Functional device controllers, lower-level
  autonomy and behaviors
• Decision higher level reasoning (AI, planning
  scheduling)

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Mission Scenario

• Placement from a distance on MER takes up to 3
  sols
• Single Cycle Instrument Placement
• Increased autonomy makes science more efficient
  and more robust
• Provides safer and more accurate target approach
• Provides options in case of non-optimal
  performance (contingencies)

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Navigation Obstacle Avoidance

• Morphin Navigator
• Developed by CMU
• Performs traversablility analysis
• Generates a 2D traversability array
• Stereo point mapped to cells
• Points within cells are fit to a plane
• Traversability calculated based on slope, quality
  of the plane fit (roughness), and step height

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Navigation Path Planning, Mapping

• D Global Cost Function
• Integrates traversability analysis data into a
  global map
• Calculates optimal paths
• Visual Odometry
• uses motion of objects between successive images
  to determine the rovers position
• Simultaneous Localization and Mapping (SLAM)
• Maps landmarks around the robot
• Uses landmarks to determine the rovers position

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Tracking Mesh Registration

• Uses stereo vision to create 3D models of the
  target (meshes)
• Initial estimate of alignment is given by rover
  odometry
• Meshes are register to each other to recover the
  target location relative to the new rover
  position
• From up to 10m away, system uses mast-mounted
  cameras to allow pointing
• As rover nears target, target is handed off the
  hazcams
• Mesh registration is used for target handoff
  between stereo pairs

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Instrument Placement

• Build 3D model of target
• uses stereo vision
• Register model using mesh registration
• tells the rover where the target is w.r.t. itself
• Find goal point
• Find closest safe point
• looks at the surface of the rock to avoid sharp
  points
• Plan arm motion
• uses 3D models and kinematics to detect possible
  collisions
• Place instrument

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Contingency Planning

• Seed plan generated with maximum expected
  utility
• Plan evaluated to determine where it might fail
  given uncertainties
• Branch point chosen
• Alternative (contingency) plan constructed for
  the branch and incorporated into primary plan
• Plan is reevaluated and additional branches added
  as needed

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Robust Execution

• CRL - Contingent Rover Language
• CX - Conditional Executive
• Flexible, condition-based execution
• temporal conditions (absolute, relative)
• resource conditions
• state-based conditions
• conditions on any node (high- or low-level)
• Hierarchical structure
• task executable action
• block sequence of nodes
• branch choice point

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Fault Diagnosis

• Expect the unexpected
• Natural terrains create uncertainty
• Systems break
• Fault Diagnosis
• The system and the environment are modeled
• Measured results compared to predicted (expected)
  results
• Model used to reason about what caused the fault
• Must distinguish between faults and interaction
  with environment

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Field Testing

• Rover testing in Mars analogs
• Test technologies in realistic environments
• Demonstrate and validate new technologies
• Simulate operational conditions on Mars
• Rugged terrain
• Geographically interesting
• Communications delay
• Lessens the likelihood of tuning an algorithm to
  home conditions

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Scorpion Robot

• Biologically-inspired robotics
• Excellent mobility in rocky terrain
• Small, light-weight
• Could be carried by a larger robot

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Antarctic Traverse

• Robotically traverse the Antarctic continent
• Completely autonomous system
• Looks out for hazards such as crevasses
• Performs science along the way
• Meteorites
• Microscopic life

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Questions?