NASA's Mars
Exploration Rover Spirit is back on track. The robotic rover drove on Thursday
for the first time since April 8 after its recent bout of amnesia.
Spirit was
acting on commands from engineers who are still investigating the cause behind Spirit's
recent glitches.
The drive
took Spirit about 5.6 feet (1.7 meters) toward destinations about(about 500
feet (150 meters) away. The rover has already operated more than 20 times
longer than its original prime mission on Mars. Spirit and its twin Opportunity landed on Mars more
than five years ago.
This week,
rover engineers at NASA's Jet Propulsion Laboratory in Pasadena, Calif., judged that it would be safe to send Spirit
commands for Thursday's drive. They also anticipated that, if the rover did
have another amnesia event, the day's outcome could be helpful in diagnosing
those events.
Three times
in the past two weeks, Spirit has failed to record data from a day's activity
period into non-volatile flash memory. That is a type of computer memory where
information is preserved even when power is off, such as when the rover naps to
conserve power.
"We
expect we will see more of the amnesia events, and we want to learn more about
them when we do," said JPL's Sharon Laubach, chief of the rover sequencing
team, which develops and checks each day's set of commands.
The team is
also investigating two other types of problems Spirit has experienced recently:
failing to wake up for three consecutive communication sessions about two weeks
ago and rebooting its computer on April 11, 12 and 18. Engineers have not found
any causal links among these three types of events.
After
checking last week whether moving the rover's high-gain antenna could trigger
problems, routine communication via that dish antenna resumed Monday.
Spirit has
maintained stable power and thermal conditions throughout the problem events
this month, although power output by its solar panels has been significantly
reduced since mid-2007 by dust covering the panels.
"We
decided not to wait until finishing the investigations before trying to drive
again," Laubach said. "Given Spirit's limited power and the desire to
make progress toward destinations to the south, there would be risks associated
with not driving."
The team
has made a change in Spirit's daily routine in order to aid the diagnostic work
if the rover experiences another failure to record data into flash memory.
To conserve
energy, Spirit's daily schedule since 2004 has typically included a nap between
the rover's main activities for the day and the day's main downlink
transmission of data to Earth. Data stored only in the rover's random-access
memory (RAM), instead of in flash memory, is lost during the nap, so when
Spirit has a flash amnesia event on that schedule, the team gets no data from
the activity period. The new schedule puts the nap before the activity period.
This way, even if there is a flash amnesia event, data from the activity period
would likely be available from RAM during the downlink.
One the
other side of Mars, Opportunity
completed drives of 315 feet (96 meters) Tuesday, 449 feet (137 meters)
Wednesday and 95 meters 312 feet (95 meters) Thursday in its long-term trek
toward a crater more than 20 times larger than the biggest it has visited so
far.
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