In the midst of its extended mission on Mars, NASA's Spirit rover ran into a software glitch over the weekend and rebooted itself, mission managers said Monday. The anomaly represented the first software reset since Spirit froze up early in its mission. This time, however, the consequences were not nearly as serious.
Spirit mission manager Mark Adler told MSNBC.com that the problem was not caused by faulty hardware or old age, and that the rover appeared to be "perfectly healthy" after the reboot.
"It was just bad luck, just a weird off chance," he said from NASA's Jet Propulsion Laboratory in Pasadena, Calif.
The rover's computer is programmed to "write-protect" its software unless a specific command is given to lift that protection to make a change, Adler explained. On Sunday, such a command was given as part of one software routine — but before the change could be written to the rover's memory, a different routine apparently put the write protection back in place.
"It caused the system to say, 'I can't write to that area, so this is a software problem I can't do anything about, so therefore I have to reboot,'" Adler explained. The reset canceled all the work sequences that had been stored on the computer, leaving Spirit idle for the rest of the day, he said.
No big problem
The mission team at JPL learned of the problem after Spirit's working day was finished, later Sunday. The next Martian day, or sol, was devoted to diagnosing the problem and uploading the sequences again, Adler said.
"The net effect was actually not that much of a problem. ... The only problem was that we lost about a sol or two of productivity," Adler said. He noted that "our original mission plan allowed for a lot more nonproductive sols than we've been having."
Both Spirit and its twin, the Opportunity rover, have exceeded their hoped-for life expectancy of 90 days. Monday marked Spirit's 132nd day of operation on Mars. In January, two weeks after Spirit landed, a memory overload put the rover's computer into a troublesome cycle of repeated reboots. This time, one reboot did the trick, Adler said.
The mission team will study the problem further and determine whether the software should be revised to keep the glitch from recurring, Adler said. "This is a very low probability event, so it's just random chance that we happened to hit it at the wrong time," he said.
Spirit was expected to resume its trek through Mars' Gusev Crater, heading east toward a set of slopes dubbed the Columbia Hills. Adler said Spirit should reach the hills in mid-June.
Opportunity rolls along
Meanwhile, on the other side of the planet, Opportunity is sampling rocks blasted out when the 430-foot-wide (130-meter-wide) Endurance Crater was created. The rover is skirting the crater's rim and sending back data that should help mission managers decide whether it's worth risking a trip inside. So far, Opportunity has traveled around about a third of the rim's circumference.
"As we were proceeding from our first viewpoint toward our second viewpoint, we saw a rock that looked like nothing we'd ever seen before," Cornell University's Steve Squyres, head of the rover science team, said in a status report issued Monday. The rock, dubbed Lion Stone, was apparently thrown up by the impact that created Endurance Crater.
Squyres said Lion Stone had a composition similar to, but not exactly the same as, the rocks analyzed earlier in Opportunity's mission at Eagle Crater, where the rover bounced to a stop.
"It may give us the first hint of what the environment was like before the conditions that produced the Eagle Crater rocks," Squyres said.
The evidence found at Eagle Crater led scientists to conclude that the area was once covered with salty water. Squyres and his colleagues hope that Endurance Crater, which is much wider and deeper, could provide much more information about Mars' geologic past, and particularly about how long liquid water existed on the now-barren planet.
Squyres and another member of the science team, Phil Christensen of Arizona State University, discussed their latest findings in Montreal at a joint meeting of the American Geophysical Union and the Canadian Geophysical Union. Christensen noted that the bedrock layers exposed at Endurance Crater represented only a small fraction of the 650-foot-thick (200-meter-thick) stack of rock seen from orbit at some other locations in the surrounding Meridiani Planum region.
"It's possible that the whole stack was deposited in water — some particles washed in by flowing water, and others chemically precipitated out of the water," he was quoted as saying in the NASA status report. "An alternative is that wind blew sand in."
The main aim of the $835 million twin-rover mission is to analyze the geologic traces of ancient water and determine whether past conditions on Mars were conducive for the development of life.