Mars Rover Team Diagnosing Unexpected Behavior

Guy Webster 818-354-6278
Jet Propulsion Laboratory, Pasadena, Calif. January 28, 2009
Guy.Webster@jpl.nasa.gov

Mars Exploration Rover Mission Status Report

Mars Rover Team Diagnosing Unexpected Behavior

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.

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