Fwd = Mars rover recovering from memory problems
- Mars rover recovering from memory problems
13:35 28 January 04
NewScientist.com news service
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.
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
David L Chandler
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