http://www.nytimes.com/2009/01/30/science/space/30rover.html?_r=1&ref=science
Mars Rover Doing Well After Memory Glitch By KENNETH CHANG Published: January 29, 2009 NASAs Mars Spirit rover may be rolling again as soon as this weekend, although engineers remain perplexed as to what caused it to lose memory and abort an attempted drive last Sunday. Spirit is doing pretty good, as a matter of fact, said R. William Nelson, the chief of the engineering team for the two Mars rovers, Spirit and Opportunity. On Sunday, Spirit did not move as instructed and, oddly, did not keep the data recording what it had done. The data files are usually written to a part of the rovers memory known as flash memory, which retains information even after power is turned off. The best guess for what happened is that Spirit somehow slipped into what NASA engineers call the cripple mode, in which the rover avoids using flash memory and instead writes to so-called random access memory. The data may have disappeared when the rover went back to sleep after trying to execute the instructions. This cripple mode proved invaluable during Spirits early days on Mars, when a software glitch caused the flash memory to overflow and Spirit was caught in a cycle of continually rebooting itself. By avoiding flash memory, engineers were able to troubleshoot the problem and send a software fix to the rover. The hypothesis would explain Spirits amnesia, but it is not at all clear how the rover could have instructed itself to go into the cripple mode. Its all very mysterious at this point, and we may never find out what happened, Mr. Nelson said. The engineers are also investigating a second, apparently unrelated glitch: the rover thinks the Suns position in the sky is four degrees off the actual position. Analysis on Thursday ruled out a problem with the camera, and the prime suspect for the error is a problem with the rovers gyroscopes. Mr. Nelson said that the team could work around any problems with the gyroscopes and that the rover otherwise appears to be in good health. http://www.sfgate.com/cgi-bin/article.cgi?f=/c/a/2009/01/29/MNN915JL6B.DTL Mars rover may be feeling its age - finally David Perlman, Chronicle Science Editor Friday, January 30, 2009 Spirit, the aged and somewhat creaky Mars rover, is stalled on the Red Planet with a touch of bewilderment, but earthbound engineers are confident they'll get the mobile explorer up and running smoothly soon. The Spirit and its sister rover, Opportunity, landed on Mars five years ago for what was designed as a 90-day mission, but have far exceeded all expectations, exploring successfully on opposite sides of the planet ever since. The only signs of age have been a little wear on the wheels and problems with some of their onboard instruments. Lately, though, the Spirit apparently is disoriented. The robot vehicle has failed to obey radio commands from Earth to start driving, and has been unable to find the sun, NASA scientists say. "We may never know what went wrong up there, or what caused the problem," Bill Nelson, a leading engineer at the Jet Propulsion Laboratory in Pasadena where Spirit and Opportunity are controlled, said Thursday. "But we're quite optimistic that it won't stop the vehicle." Scientists and mission control engineers calculate that a Mars day, or "sol," is 39 minutes and 35 seconds longer than a day on Earth. It was during Spirit's 1,800th sol on the planet Sunday that it failed to start driving. Two sols later, it was told to find the sun with its camera, but the rover was disoriented and reported the sun's location in the wrong place. Communication between Earth and the rovers is relayed by the Mars Odyssey spacecraft, which has been orbiting Mars for almost nine years, and on Thursday Nelson and mission controllers were awaiting a new downlink carrying a fresh report from Spirit via Odyssey to help efforts at diagnosing the problems. One possible cause of the communication problem, Nelson said, might be an errant cosmic ray from distant space that somehow sparked a glitch in Spirit's computer and prevented it from storing the proper commands from Earth and responding correctly to them. The inability of Spirit's camera to locate the sun, he said, could have been a case of mistaken identity when it instead picked up a bright glint caused by the sun's reflection on one of the rover's metal body parts. Spirit was supposed to start trundling 20 to 25 feet this week from its present location in a spot on the Martian surface known as Home Plate. And that would precede a journey of about 900 feet to a new location called Goddard-von Braun, named for rocket pioneers Robert Goddard and Wernher von Braun. Both Spirit and Opportunity are powered by solar arrays, and dust storms now and then have left dusty films on their solar panels, Nelson said. This has cut power for both rovers, he said, but hasn't immobilized them, and once Spirit's health is restored, its stalled drive will start again. Since January 2004, when they landed, Spirit has roamed across the Martian surface for a total of about 4.7 miles, and Opportunity has journeyed 8.5 miles - not much for a human hiker, but a lot for a Mars rover. E-mail David Perlman at <mailto:dperl...@sfchronicle.com>
