NASA Mars rover wheels bedevil latest extrication effort

Work continues in NASA's effort to get Spirit moving again after 8 months in slippery sand

One step forward, two steps back may be the best way to describe NASA’s latest attempts to save its stuck Mars rover Spirit.

On the positive side, Spirit's right-front wheel, which had stopped operating in March 2006, showed signs of life this week by spinning slightly during one of the attempts to move the rover. The wheel however stopped later in another test.

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Still, NASA scientists said movement of the right-front wheel for about 3.5 minutes was a surprise. It is not clear whether the wheel will work again, since it stopped during the final drive segment and it’s not clear whether extrication from the sand trap would be possible even with an operable right-front wheel, NASA said.

NASA said Spirit’s other four wheels all drove forward in the most recent attempt to extricate Spirit from the sand trap but that positive note was tempered by the fact that while Sprit moved forward, it also dug in a little further. According to NASA, the rover moved 2 millimeters (0.08 inch) forward and 4 millimeters (0.16 inch) downward. That ratio of forward to downward movement is well below what would be necessary over longer distance for extrication, NASA noted.

NASA said the most immediate plan was to perform another set of low-voltage tests on the three right-side wheels and then command another four-step forward drive. This drive would not use the right-front wheel in conjunction with the others, but that wheel would be driven briefly by itself after each step to gain more information about its possible usefulness, NASA stated.

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Spirit has been stuck in a place NASA calls "Troy" since April 23 when the rover's wheels broke through a crust on the surface that was covering brightly-toned, slippery sand underneath. After a few drive attempts to get Spirit out in the subsequent days, it began sinking deeper in the sand trap.

Being stuck in the sand hasn’t stopped Spirit from working but that could change should it be stuck in place as winter approaches. Because of the current rover tilt, the environmental conditions and dust accumulation on the solar arrays, Spirit is at risk of inadequate power for surviving through the next southern Mars winter. Even if extrication is not possible, some limited rover motion may be able to improve rover tilt and increase the chance of winter survival.

Even in the best of conditions, moving the stuck rover could take weeks.

Spirit faced the prospect of not surviving Martian winter in 2006 when it was having trouble moving into what NASA called a “suitably north-facing slope. The rover must face its solar panels northward to collect enough solar energy as the sun sinks low above the horizon,” NASA said.

In the meantime, NASA said the rover has been mapping its Martian surroundings with tools on its robotic arm and its camera mast. The rover's work at Troy has augmented earlier discoveries it made indicating ancient Mars had hot springs or steam vents, possible habitats for life. If escape attempts fail, the rover's stationary location has resulted in new science findings, NASA stated.

This latest problem is one of many the venerable probe has had in the past year. Recently NASA said Spirit was “suffering from the inability to access the on-board, flash memory file system. However, the operations team has developed a strategy to allow science activities to continue.” In January, the rover failed to respond to instructions. NASA engineers fixed that problem within a few days. Then in April the rover rebooted itself without direction from its engineers.

While there have been those occasional glitches, Spirit and its twin rover Opportunity have been wildly successful. Since landing on the red planet in January 2004 they have explored Mars for five years, far surpassing their original 90-day mission, NASA said.

NASA has had more luck with its Mars Odyssey spacecraft which is orbiting the planet. Last week Opportunity shut itself down due to what NASA called a response to a memory error onboard the craft’s computer. To clear the memory error, the team commanded Odyssey today to perform a cold reboot of the orbiter's onboard computer. The spacecraft reported that the reboot had been completed successfully, NASA stated.

This story, "NASA Mars rover wheels bedevil latest extrication effort" was originally published by Network World.

Copyright © 2009 IDG Communications, Inc.

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