Mars rover recovering from memory problems

31 2004

Mars rover recovering from memory problems

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A full revival of the Mars rover Spirit from its electronic ailments now seems highly likely. Engineers now think there is no real hardware or software problems, but something much easier to fix - a simple overload of files in its onboard memory.

If further testing confirms this diagnosis, that will be very good news for Spirit's twin, Opportunity. Any software bug or hardware weakness would probably be present in both rovers and might require weeks of analysis and repair.

But if, as it appears, the problem is a previously unrecognised limit on the number of files that can be stored in the craft's flash memory, then Opportunity's data collection and file management can be planned to prevent the problem.

This would avoid the bleak situation faced by engineers when Spirit fell silent for more than a day and failed to respond to commands. Having initially described the Spirit's troubles as "critical", mission manager Jennifer Trosper says "the patient is now in rehab".

However, Opportunity has developed a problem of its own, according to another mission manager Jim Erickson. The rover is losing power, apparently due to a heating unit that is switching itself on when it should not. What this will mean for the rover's mission and whether it can be fixed are not yet known.

Coaxed communication
Spirit's controllers have been coaxing the rover back into communication since it ended its silence on Thursday with a single bleep. The engineering data returned has allowed them to piece what had happened.

The rover first failed halfway through a test of a moving mirror that directs light to the mini-TES instrument. The high-gain antenna was also being used at the time, and the spacecraft entered a "safe mode" associated with antenna problems

Later data returns showed the craft had entered a repeating cycle of resetting its computer system, preventing it from carrying out anything but the simplest commands. At last count, it had rebooted itself more than 120 times. This constant resetting prevented it from entering its night sleep cycle, needed to conserve its batteries.

But detailed analysis of the start of each reset cycle eventually led to the apparent answer to the mystery. The problem was clearly associated with the handling of files being written to one of its three types of internal memory: a non-volatile 256 megabyte flash memory.

Testing on Monday and Tuesday suggests that it is not the flash memory itself that is at fault, but the software's file-handling system. Unbeknownst to the engineers, there seems to be a limit on the number of files that can be simultaneously stored in the flash memory, even though the overall memory capacity is not full.

The solution is likely to be simply deleting unneeded files, many of which were accumulated during the eight-month journey to Mars. It will require some skillful programming to get the computer to do this without falling back into its resetting cycle, but Trosper says a full recovery is now expected.

David L Chandler


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