Mars Pathfinder Rover Description

Table of Contents

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 square 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 overlaid on the image of the vehicle, measures the location and heading of the vehicle. This information is also transferred 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.

Related Information

The following links provide some additional information about topics related to the Mars Pathfinder mission. You must be connected to the Internet for most of these links to work, since they are located at the Central Node of the Planetary Data System.


Mars Pathfinder


Alpha Proton X-ray Spectrometer
Rover Cameras


PDS Welcome to the Planets: Mars
PDS High Level Catalog: Mars