Instrument Host Overview
  ========================
    The Microrover Flight Experiment (MFEX), also known as the 'Mars
    Pathfinder Rover' and 'Sojourner', is a NASA Office of Advanced
    Concepts and Technology (OACT) flight experiment for autonomous
    mobile vehicle technologies.  Its primary mission was to
    determine microrover performance in the poorly understood
    planetary terrain of Mars.  The microrover was delivered,
    integrated with the Mars Pathfinder (MPF) Lander, to Mars on July
    4, 1997.  After landing, the microrover was deployed from the
    lander and began a nominal 7 sol mission, which was later
    extended, to conduct technology experiments such as determining
    wheel-soil interactions, autonomous navigation and hazard
    avoidance capabilities, and engineering characterizations
    (thermal control, power generation performance, etc.).  In
    addition, the microrover carried an Alpha Proton X-ray
    Spectrometer (APXS) which when deployed on rocks and soil
    provided element composition.  Lastly, the microrover imaged the
    lander to assist in status and damage assessment.
 
 
    Mechanical, Thermal, and Mobility Subsystem
    -------------------------------------------
      The microrover is a 6-wheeled vehicle of a rocker bogie design
      which allows the traverse of obstacles a wheel diameter (13 cm)
      in size.  Each wheel is independently actuated and geared
      (2000:1) providing superior climbing capability in soft sand.
      The front and rear wheels are independently steerable,
      providing the capability for the vehicle to turn in place.  The
      vehicle has a top speed of 0.4 m/min.
 
      Microrover components not designed to survive ambient Mars
      temperatures (-110 degrees Celsius during a Martian night) are
      contained in the warm electronics box (WEB).  The WEB is
      insulated, coated with high and low emissivity paints, and
      heated with a combination of 3, 1W RHUs, resistive heating
      under computer control during the day and waste heat produced
      by the electronics.  This design allows the WEB to maintain
      components between -40 and +40 degrees Celsius during a Martian
      day.
 
 
      Control and Navigation Subsystem
      --------------------------------- Control is provided by an
      integrated set of computing and power distribution electronics.
      The computer is an 80C85 rated at 100 Kips which uses, in a 16
      Kbyte page swapping fashion, 176 Kbytes of PROM and 576 Kbytes
      of RAM.  The computer performs I/O to some 70 sensor channels
      and services such devices as the cameras, modem, motors and
      experiment electronics.
 
      Vehicle motion control is accomplished through the on/off
      switching of the drive or steering motors.  An average of motor
      encoder (drive) or potentiometer (steering) readings determines
      when to switch off the motors.  When motors are off, the
      computer conducts a proximity and hazard detection function,
      using its laser striping and camera system to determine the
      presence of obstacles in its path.  The vehicle is steered
      autonomously to avoid obstacles but continues to achieve the
      commanded goal location.  While stopped, the computer also
      updates its measurement of distance traveled and heading using
      the averaged odometry and on-board gyro.  This provides an
      estimate of progress to the goal location.
 
 
    Power Generation and Distribution
    ---------------------------------
      The microrover is powered by a 0.22 sqare meter solar panel
      comprised of 13 strings of 18, 5.5 mil GaAs cells each.  The
      solar panel is backed up by 9 LiSOCL2 D-cell sized primary
      batteries, providing up to 150 W-hr.  This combined
      panel/batteries system allows microrover power users to draw up
      to 30W of peak power (mid-sol) while the peak panel production
      is 16 W.  The normal driving power requirement for the
      microrover is 10 W.
 
 
    Radio Communications
    --------------------
      Command and telemetry is provided by modems on the microrover
      and lander.  The microrover is the link commander of this 1/2
      duplex, UHF system.  During the day, the microrover regularly
      requests transmission of any commands sent from Earth and
      stored on the lander.  When commands are not available, the
      microrover transmits any telemetry collected during the last
      interval between communication sessions.  The telemetry
      received by the lander from the microrover is stored and
      forwarded to the earth the same as any lander telemetry.  In
      addition, this communication system is used to provide a
      'heartbeat' signal during vehicle driving.  While stopped, the
      microrover sends a signal to the lander.  Once acknowledged by
      the lander, the microrover proceeds to the next stopping point
      along its traverse.
 
      Commands for the microrover are generated and analysis of
      telemetry is performed at the microrover control station, a
      Silicon Graphics workstation which is a part of the MPF ground
      control operation.  At the end of each sol of microrover
      traverse, the camera system on the lander takes a stereo image
      of the vehicle in the terrain.  Those images, portions of a
      terrain panorama and supporting images from the microrover
      cameras, are displayed at the control station.  The operator is
      able to designate on the display points in the terrain which
      will serve as goal locations for the microrover traverse.  The
      coordinates of these points are transferred into a file
      containing the commands for execution by the microrover on the
      next sol.  In addition, the operator can use a model which,
      when overlayed on the image of the vehicle, measures the
      location and heading of the vehicle.  This information is also
      transfered into the command file to be sent to the microrover
      on the next sol to correct any navigation errors.  This command
      file is incorporated into the lander command stream and is sent
      by the MPF ground control to the lander, earmarked for
      transmission to the microrover upon request.
 
      For more information on the Microrover Flight Experiment, see
      the papers [MATIJEVIC1994] and [MATIJEVICETAL1997A].
 
      Copyright 1996, Jet Propulsion Laboratory, California Institute
      of Technology and the National Aeronautics and Space
      Administration.