A motor
glitch has resurfaced aboard NASA's Mars rover Opportunity and may hinder some
of the long-lived robot's ability to wield its mechanical arm.
The troublesome
motor powers the sideways movement of the shoulder joint on Opportunity's
instrument-tipped robotic arm and has suffered from intermittent
stalling problems since 2005.
But the
glitch appeared to have worsened last week, when the motor stalled much earlier
than in the past. Opportunity's robotic arm is currently deployed and NASA
engineers are determining whether an earlier fix can still be used to move the
motor as desired.
"Motion of
the stall-prone shoulder motor is necessary to unstow the arm," mission
managers said in a statement. "So if the motor were to become unusable with the
arm in the stowed position, the arm could not be deployed again."
The motor
stalled on April 14 just after it was unberthed from its stowage hook, mission managers
added.
If the
motor failed outright while the arm was extended, Opportunity could still
conduct science by compensating with other arm motors and some fancy wheelwork,
NASA officials said.
"Even
under the worst-case scenario for this motor, Opportunity still has the
capability to do some contact science with the arm," said John Callas,
project manager for Opportunity
and its robotic twin Spirit at NASA's Jet Propulsion Laboratory in
Pasadena, Calif. "The vehicle has quite a bit of versatility to continue
the high-priority investigations in Victoria Crater and back out on the
Meridiani plains after exiting the crater."
Like Spirit,
Opportunity wields a single, 3-foot (1-meter) long robotic
arm tipped with a turret containing four instruments to analyze the martian
surface. The 13-pound (6-kg) arm contains five motors that provide sideways and
vertical shoulder motion, as well as elbow and wrist movement.
The balky
shoulder motor on Opportunity's arm began acting up in 2005, when it first
stalled due to suspected degraded wiring.
By applying
higher voltages than normal to the motor, rover engineers were able to overcome
the stall and move the shoulder sideways. Since then, rover handlers have left
Opportunity's robotic arm deployed overnight - rather than folded up at the
front of the rover - after each day's drive to ensure it can be used for
science even if the motor fails permanently.
Engineers
are studying whether the same fix can be used for the renewed stall issue, and
are holding off on moving Opportunity out of a sandy patch of ground inside
Victoria Crater - a 2,625-foot (800-meter) wide depression on the martian
plains of Meridiani Planum.
"We'll
hold off backing out of the sand until after we've completed the diagnostic
tests on the motor," Callas said. "The rover is stable and safe in
its current situation, and not under any urgency. So we will take the time to
act cautiously."
The Spirit
and Opportunity rovers have
been exploring Mars since their January 2004 landing. The hardy rovers are
more than four years into what was initially planned to be a 90-day mission.
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