NASA’s Opportunity Rover Flexes Robotic Arm
NASA's Mars rover Opportunity successfully unstowed its robotic arm on Dec. 13 for the first time since Nov. 25 after a shoulder joint motor glitch prevented deployment. The rover reaches toward a rock outcrop at Erebus Crater in this view from a front hazard camera.
Credit: NASA/JPL/Cornell.

NASA's Mars rover Opportunity has sucessfully reached out toward a Martian rock with its robotic arm, overcoming a motor glitch that prevented deployment last month.

Opportunity unstowed its instrument-laden robotic arm Tuesday, aiming the multi-jointed appendage straight ahead towards a rock outcrop jutting from a crater at its Meridiani Planum landing site, the mission's project manager said.

"It went fine...we successfully put an instrument on the rock," Jim Erickson, project manager for the Mars Exploration Rover mission at NASA's Jet Propulsion Laboratory (JPL), told "The team did a great job but we've got more work to do."

Stalled science

Opportunity's robotic arm - which carries four instruments designed to photograph, brush, grind and determine the composition of Martian rocks - stalled in its stowed position on Nov. 25, preventing active study of the nearby outcrop at its Erebus Crater location. A problematic shoulder joint motor, which swings the arm out from its stowed position tucked under the rover, appeared to be the cause.

"We were fearful for a time that the motor may have failed permanently," said Steve Squyres, principal investigator for the rover mission at Cornell University, during a Dec. 12 discussion at the American Museum of Natural History in New York City. "If that were the case, we'd never be able to use the arm again."

But on Dec. 8, rover engineers managed to move the arm slightly. The motor glitch appears to be the result of a broken wire in one of nine windings - or coils - inside the shoulder joint, Erickson said. By applying a higher voltage than normal to the windings, the joint moved, he added.

"We're developing a mode for keeping the arm out in front," Erickson said, adding that engineers are now studying various positions in which to stow the arm and ensure its continued use as a science tool. "We'll essentially stow it now by putting the instrument pack up over the rover's deck."

Erickson said more analysis and arm motor tests are planned in order to determine the best configuration for the arm during drives.

Martian year milestone

Like its robotic twin Spirit, which is currently descending Husband Hill in Mars' Gusev Crater and heading toward a target dubbed "Home Plate," Opportunity has spent more than one entire Martian year - about 687 Earth days, or 670 Martian sols - exploring the red planet. Opportunity's red planet anniversary occurred on Dec. 12 and set a new milestone for the Mars rover expedition, which had a primary mission that originally spanned just 90 Martian days.

"I used to think that dust on our solar arrays was going to be the limit for these rovers, I don't think that anymore," Squyres said. "I think, instead, that something is going to break. We have a lot of moving parts and electrical parts on these rovers."

Squyres added that the success of Spirit and Opportunity has changed the way he looks at Mars.

"[Before launch] it just seemed impossibly far away, it seemed unreachable," Squyres said of the red planet. "Tonight, I go out knowing our rovers have been there a whole Martian's a much more familiar planet. We know the place."