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Written by Derek Kessler on
Wednesday, 30 April 2008
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 Since 2005, the Mars rover Opportunity has had a problem: arthritis. Starting a few years ago the motor that controls the sideway’s movement of the rover’s robotic arm has suffered from intermittent stalling, and now the glitch has grown worse. On April 14th, Opportunity started to extend its arm and the motor froze. With the arm stuck where it is, the important instruments on its tip cannot be used.
Opportunity has been studying Mars for over four years, seventeen times longer than its original 90-day mission. While the motor glitch has occasionally hampered Earth-bound scientist’s efforts, engineers have usually been able to let the arm sit out overnight and wiggle it loose with some higher voltages. The stalling is believed to be caused by corroded wiring, and the higher voltages successfully pushed through to allow the shoulder motor to operate without normal impediment.
When the motor has stalled in the past, the arm has been extended, allowing the science team to continue using the arm’s tools. Even though the arm could not move side to side, it was still able to move up and down and the with some fancy wheelwork the rover could maneuver into place to allow most of the desired science to be completed. This time, the arm is stuck barely moved from its berthing hook. Engineers are going to again try to up the voltage again to see if they can get the motor to work again.
Even if the motor cannot be unstalled, NASA will still be able to perform valuable ground reconnaissance with Opportunity’s stereo cameras, as well as a thermal spectrometer that is used to identify minerals in rocks that are promising for further study. Of course, without the arm able to extend, those promising rocks will remain just that, promising. For now, while engineers attempt to wriggle the arm free, Opportunity will stay put where it is, a sandy patch inside Victoria crater.
Opportunity’s twin, Spirit, is still busy on the other side of Mars. Like Opportunity, Spirit is also suffering from the effects of old age. It’s front right wheel has failed and now the rover has to be driven backwards and the grinding rock-abrasion tool has been worn down to the point that it can only be used to brush off dust.
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"It's like I said: the more things change, the more they stay the same."
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