Mars Exploration Rover Mission Status
Engineers on NASA's Mars Exploration Rover team are
investigating possible causes and remedies for a problem
affecting the steering on Spirit.
The relay for steering actuators on Spirit's right-front and
left-rear wheels did not operate as commanded on Oct. 1. Each of
the front and rear wheels on the rover has a steering actuator,
or motor, that adjusts the direction in which the wheels are
headed independently from the motor that makes the wheels roll.
When the actuators are not in use, electric relays are closed
and the motor acts as a brake to prevent unintended changes in
Engineers received results from Spirit today from a first set of
diagnostic tests on the relay. "We are interpreting the data and
planning additional tests," said Rick Welch, rover mission
manager at NASA's Jet Propulsion Laboratory, Pasadena, Calif.
"We hope to determine the best work-around if the problem does
Spirit and its twin, Opportunity, successfully completed their
three-month primary missions in April and five-month mission
extensions in September. They began second extensions of their
missions on Oct. 1. Spirit has driven more than 3.6 kilometers
(2.2 miles), six times the distance set as a goal for mission
success. It is climbing into uplands called the "Columbia
JPL's Jim Erickson, rover project manager, said, "If we do not
identify other remedies, the brakes could be released by a
command to blow the fuse controlling the relay, though that
would make those two brakes unavailable for the rest of the
mission." Without the steering-actuator brakes, small bumps or
dips that a wheel hits during a drive might twist the wheel away
from the intended drive direction.
"If we do need to disable the brakes, errors in drive direction
could increase. However, the errors might be minimized by
continuing to use the brakes on the left-front and right-rear
wheels, by driving in smaller segments, and by adding a software
patch to reset the direction periodically during a drive,"
Erickson said. Engineers believe the steering-brake issue is not
related to excessive friction detected during the summer in the
drive motor for Spirit's right-front wheel, because the steering
actuator is a different motor.
Meanwhile, the team continues to use Spirit's robotic arm and
camera mast to study rocks and soils around the rover, without
moving the vehicle until the cause of the anomaly is understood
and corrective measures can be implemented.
information about the project is available from JPL at
and from Cornell
University, Ithaca, N.Y., at http://athena.cornell.edu
Guy Webster (818) 354-6278
NASA's Jet Propulsion Laboratory
Don Savage (202) 358-1727
NASA Headquarters, Washington, D.C.