Mars rover
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Spirit, one of the two NASA rovers that have been roaming Mars's surface during the past five years, has encountered some memory glitches, but will be back on track as soon as this weekend. The Spirit, the first rover NASA sent on Mars (on 3 January, 2004), surprised engineers when it lost memory and aborted a drive last Sunday.

NASA engineers still wonder what could have caused the memory loss, but there's no need to worry about Spirit, which is doing "pretty good," as William Nelson, chief of the engineering team for NASA's Mars rovers, said. Although the two rovers (Spirit and Opportunity) were not expected to last more than three months on the unfavorable surface of the Red Planet and after five years the two complex machines are still in activity, the engineers at NASA are still wondering what could have caused the memory loss.

Spirit didn't follow instructions to move and did not keep recording its actions. NASA engineers said the rover probably did not record the data using its flash memory and instead used the so-called random access memory. The data then disappeared when Spirit went back to sleep after trying to execute the instructions. However, it's "very mysterious," Mr. Nelson said, how the rover programmed itself to go into "cripple more" (the term used to describe the decision to record data on random access memory instead of flash memory - the part that persists even when power is off).

NASA said it plans to run diagnostic tests to find out what caused Spirit to go into "cripple mode." The rover also lost track of its orientation after the glitch and its controllers at NASA's Jet Propulsion Laboratory in Pasadena, California, commanded Spirit to point its camera at the sun in order to determine its orientation. The rover located the sun with its camera, but it was not in its expected location when it did it.

"Our next steps will be diagnostic activities," said JPL's Sharon Laubach.

One of the theories to explain what caused the glitch holds that a cosmic ray could have affected Spirit's electronics.

The two Mars rovers have surprised the NASA community by remaining active and operative after five years on Mars, although they were expected to malfunction after about three months. During the five years on Mars, Spirit and Opportunity made more than 13 miles of tracks on the planet's dusty surface and sent more than 250.000 images to Earth. The rovers helped NASA uncover evidence that the climate on Mars was very different in the past. The evidence helped experts discover that there was once water on Mars and it also was warmer than it is today.

"Right now, Spirit is under normal sequence control, reporting good health and responsive to commands from the ground," said Mars Rovers project director John Callas.

However, after five years on Mars, NASA experts expect the two rovers to crash at any time without any warning.

"We realize that a major rover component on either vehicle could fail at any time and end a mission with no advance notice," said Mr. Callas.