Opportunity’s Robotic Arm Stalls

NASA engineers say Opportunity’s robotic arm, which has been intermittently problematic since 2005, has worsened recently. A small motor in the shoulder joint of the Mars Exploration Rover’s arm stalled on April 14, and engineers are diagnosing the problem and assessing whether the motor can possibly be used again. They are also trying to determine the impact on Opportunity’s work if the motor were no longer usable.

The motor is one of five in the robotic arm and it controls sideways motion of the shoulder joint. The stall last week occurred after being used briefly, and after much less motion than earlier stalls. Engineers believe the problem is electrical rather than mechanical, and additional tests are being performed to determine whether the is trouble is intermittent or a permanent failure.

The arm is used to place a microscopic imager and spectrometer in contact with rocks and soils to study their composition and texture.

“Even under the worst-case scenario for this motor, Opportunity still has the capability to do some contact science with the arm,” said JPL’s John Callas, project manager for the twin rovers Opportunity and Spirit. “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.”

The two Mars rovers, Opportunity and Spirit, have been studying the Red Planet since January 2004, and each have shown some signs of aging.

When Opportunity’s shoulder motor began stalling occasionally in November 2005, engineers increased the voltage to the motor, and that allowed the motor to still be operational. Additionally, the engineering changed the standard procedure by unstowing the arm at the end of each day’s drive rather than leaving it stowed overnight. This keeps the arm available for use even if the motor then stops working.

This spring, Opportunity began crossing an inner slope of Victoria Crater to reach the base of a cliff portion of the crater rim, a promontory called “Cape Verde.” On April 14, Opportunity was backing out of a sandy patch encountered on the path toward Cape Verde from the area where the rover descended into the crater. As usual, the commands included unstowing the arm at the end of the day’s short drive. The shoulder motor barely got the arm unstowed before stalling.

“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.”

Original News Source: JPL Press Release