Mars Rover Team Diagnosing Unexpected Behavior

artist concept of the Mars Exploration Rover Artist's concept of Mars Exploration Rover. Image credit: NASA/JPL-Caltech/Cornell University.
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January 28, 2009

UPDATED on Jan. 29: Spirit Working Well While Diagnostics Continue

Diagnostic activities performed by Spirit on Thursday, Jan. 29 narrowed the range of factors that may have contributed to its unexpected behavior earlier in the week. No clear explanation has been established yet. Spirit is healthy and responding to commands. It recorded and returned images of nearby scientific targets. The rover team plans further diagnostics on Friday of Spirit's inertial measurement unit -- a combined gyroscope-and-accelerometer device that measures rover movements and attitude. Spirit may resume driving over the weekend.

CORRECTION on Jan. 28: In paragraph 3--Early Tuesday, Spirit reported that it had followed the commands, and in fact had located the sun, but not in its expected location.

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 followed the commands, and in fact had located the sun, but not in its expected location.

"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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