Mars Exploration Rover Mission Status Updated
After three days of completing Earth-commanded activities
without incident last week, NASA's Mars Exploration Rover Spirit
had a bout of temporary amnesia Friday, April 17, and rebooted its
computer Saturday, April 18, behavior similar to events about a
week earlier.
Engineers operating Spirit are investigating the reboots and the
possibly unrelated amnesia events, in which Spirit unexpectedly
fails to record data into the type of memory, called flash, where
information is preserved even when power is off. Spirit has had
three of these amnesia events in the past 10 days, plus one on Jan.
25. No causal link has been determined between the amnesia events
and the reboots.
The most recent reboot put Spirit back into an autonomous
operations mode in which the rover keeps itself healthy. Spirit
experienced no problems in this autonomous mode on Sunday. The
rover team at NASA's Jet Propulsion Laboratory, Pasadena, Calif.,
revised plans today for regaining Earth control of Spirit's
operations and resuming diagnostic and recovery activities by the
rover.
"We are proceeding cautiously, but we are encouraged by knowing
that Spirit is stable in terms of power and thermal conditions and
has been responding to all communication sessions for more than a
week now," said JPL's Sharon Laubach, chief of the rover sequencing
team, which develops and checks each day's set of commands. During
the past week of diagnostic activities, the rover has successfully
moved its high-gain dish antenna and its camera mast, part of
checking whether any mechanical issues with those components may be
related to the reboots, the amnesia events, or the failure to wake
up for three consecutive communication sessions two weeks ago.
Spirit and its twin rover, Opportunity, completed their original
three-month prime missions on Mars in April 2004 and have continued
their scientific investigations on opposite sides of the planet
through multiple mission extensions. Engineers have found ways to
cope with various symptoms of aging on both rovers.
The current diagnostic efforts with
Spirit are aimed at either recovering undiminished use of the rover
or, if some capabilities have been diminished, to determine the
best way to keep using the rover.
Laubach said, "For example, if we do determine that we can no
longer use the flash memory reliably, we could design operations
around using the random-access memory." Spirit has 128 megabytes of
random-access memory, or RAM, which can store data as long as the
rover is kept awake before its next downlink communications
session.