Spirit Resumes Driving While Analysis of Problem Behaviors Continues

MEDIA RELATIONS OFFICE
JET PROPULSION LABORATORY
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http://www.jpl.nasa.gov

Guy Webster 818-354-6278
Jet Propulsion Laboratory, Pasadena, Calif. April 24, 2009
Guy.Webster@jpl.nasa.gov

Spirit Resumes Driving While Analysis of Problem Behaviors Continues

Mars Exploration Rover Mission Status Report

PASADENA, Calif. -- NASA's Mars Exploration Rover Spirit drove on Thursday for the first
time since April 8, acting on commands from engineers who are still investigating bouts of amnesia
and other unusual behavior exhibited by Spirit in the past two weeks.

The drive took Spirit about 1.7 meters (5.6 feet) toward destinations about 150 meters (about
500 feet) away. The rover has already operated more than 20 times longer than its original prime
mission on Mars.

This week, rover engineers at NASA's Jet Propulsion Laboratory, 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.

Spirit and its twin, 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.

This week, Opportunity completed drives of 96 meters (315 feet) Tuesday, 137 meters (449
feet) Wednesday and 95 meters (312 feet) Thursday in its long-term trek toward a crater more
than 20 times larger than the biggest it has visited so far.

JPL, a division of the California Institute of Technology in Pasadena, manages the Mars
Exploration Rover project for NASA's Science Mission Directorate, Washington.

# 2009-074

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