http://www.jpl.nasa.gov/news/news.cfm?release=2009-011

Mars Rover Team Diagnosing Unexpected Behavior
Jet Propuslion Laboratory
January 28, 2009

Mars Exploration Rover Mission Status Report

PASADENA, Calif. - The team operating NASA's Mars Exploration Rover
Spirit
plans diagnostic tests this week after Spirit did not report some of
its
weekend activities, including a request to determine its orientation
after an incomplete drive.

On Sunday, during the 1,800th Martian day, or sol, of what was
initially
planned as a 90-sol mission on Mars, information radioed from Spirit
indicated the rover had received its driving commands for the day but
had
not moved. That can happen for many reasons, including the rover
properly
sensing that it is not ready to drive. However, other behavior on Sol
1800
was even more unusual: Spirit apparently did not record the day's
main
activities into the non-volatile memory, the part of its memory that
persists even when power is off.

On Monday, Spirit's controllers at NASA's Jet Propulsion Laboratory in
Pasadena, Calif., chose to command the rover on Tuesday, Sol 1802, to
find
the sun with its camera in order to precisely determine its
orientation.
Not knowing its orientation could have been one possible explanation
for
Spirit not doing its weekend drive.  Early Tuesday, Spirit reported
that
it had tried to follow the commands, but had not located the sun.

"We don't have a good explanation yet for the way Spirit has been
acting
for the past few days," said JPL's Sharon Laubach, chief of the team
that
writes and checks commands for the rovers. "Our next steps will be
diagnostic activities."

Among other possible causes, the team is considering a hypothesis of
transitory effects from cosmic rays hitting electronics. On Tuesday,
Spirit apparently used its non-volatile memory properly.

Despite the rover's unexplained behavior, Mars Exploration Rovers'
Project Manager John Callas of JPL said Wednesday, "Right now, Spirit
is
under normal sequence control, reporting good health and responsive
to
commands from the ground."

JPL, a division of the California Institute of Technology, Pasadena,
manages the Mars Exploration Rover project for the NASA Science
Mission
Directorate, Washington. Spirit and its twin, Opportunity, landed on
Mars in January 2004 and have operated 20 times longer than their
original prime missions.

Guy Webster (818) 354-6278
Jet Propulsion Laboratory, Pasadena, Calif.

2009-011
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