[meteorite-list] Mars Rover Opportunity Has Wheel Trouble

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Tue Apr 19 15:55:34 2005
Message-ID: <200504191955.j3JJt4T10651_at_zagami.jpl.nasa.gov>

http://www.newscientist.com/article.ns?id=dn7284

Mars rover Opportunity has wheel trouble
Kelly Young
New Scientist
April 19, 2005

The Mars rover Opportunity has lost the ability to steer one of its
wheels. While the vehicle can still move, the failure may make it harder
to study rocks up close.

The rover has six wheels aligned in two rows and each of the four corner
wheels has its own steering mechanism. The problem is with the front
right wheel, which can still roll but is now stuck at a 7? inward angle.
NASA rover project manager Jim Erickson says it is like a car losing its
power steering.

"At this point, with this one actuator failed, it's an inconvenience,
nothing more," says rover chief scientist Steven Squyres. But he adds
that the failure is a reminder that the rovers will not run forever and
that "we should continue to get every bit of science out of these that
we can".

On 13 April, the rover was travelling south from the Voyager crater
when, at the end of one manoeuvre, the front right wheel stopped.
Sometimes this happens when the wheel hits a rock, so ground controllers
reversed the rover and tried again to turn the wheel, but the same
problem occurred.

At that point, engineers decided it was a problem with the wheel's
steering motor and not a physical obstacle. Ground controllers have now
disabled the wheel's ability to steer.

A consequence of the failure is that Opportunity's ability to make very
precise manoeuvres to touch a target sample with its instrument arm will
be reduced. Erickson says Opportunity is likely to stop to sample rock
and soil with the arm before it reaches its current target - a crater
named Erebus.

Software saviour

But the rover should be able to travel without too much trouble. In
February 2005, NASA transmitted a software package to the rovers giving
them the ability to determine how well they are staying on course and to
correct their steering for themselves if they did lose the function of a
wheel.

If the steering on the wheel has permanently failed, the rover could
drive with just three other wheels directing the vehicle. In addition,
the team may opt to steer the rover like a tank, with the three left
wheels turning one way while the three right wheels turn the other.

"I have always said my goal is to wear these things out," Erickson says.
But NASA managers still hope to get a lot more from the rovers before
they roll to a final halt. Opportunity and Spirit landed on Mars in
January 2004. The pair were given a further 18-month mission extension
on 5 April 2005.

Spirit is now heading toward an outcrop of bedrock, named Methuselah,
spotted this weekend in photos taken by one of its cameras. "We found
the biggest and most spectacular outcrop of bedrock that Spirit has ever
seen in those images," Squyres says.

He says there are fine layers visible in the bedrock, with "hints of
interesting structuring". Spirit should arrive at the rock later this week.
Received on Tue 19 Apr 2005 03:55:03 PM PDT