March 17, 2006
NASA's long-lived Mars rovers demand lots of care as they age and
the Martian winter approaches.
Dr. John Callas, newly named project manager for NASA's Mars Exploration Rover mission, is coordinating the work to meet these challenges. He is a scientist at NASA's Jet Propulsion Laboratory in Pasadena, Calif. He was named project manager after earlier roles as science manager and deputy project manager for the Spirit and Opportunity rovers.
"It continues to be an exciting adventure with each day like a whole new mission," Callas said. "Even though the rovers are well past their original design life, they still have plenty of capability to conduct outstanding science on Mars. The JPL operations team and the remote science team working on the project are the best in the solar system at what they do. It is a pleasure and a privilege to lead such an outstanding team and great mission."
One of Spirit's six wheels has stopped working. Dragging that wheel, the solar-powered rover must reach a slope where it can catch enough sunshine to continue operating during the Martian winter. The period of minimum sunshine is more than 100 days away, but Spirit gets only enough power for about one hour per day of driving on flat ground. And the supply is dropping fast.
Spirit's right-front wheel became a concern once before, when it began drawing unusually high current five months after the January 2004 landing on Mars. Driving Spirit backwards redistributed lubricant and returned the wheel to normal operation. This week, during the 779th Martian day of what was originally planned as a 90-Martian-day mission, the motor that rotates that wheel stopped working.
"It is not drawing any current at all," said JPL's Jacob Matijevic, rover engineering team chief. One possibility engineers are considering is that the motor's brushes, contacts that deliver power to the rotating part of the motor, have lost contact. The motors that rotate Spirit's wheels have revolved more than 13 million times, far more than called for in the rovers' design.
Spirit's solar panels have been generating about 350 watt-hours of electricity daily for the past week. That is down about 15 percent since February and less than one-half of their output during the Martian summer.
The best spot for Spirit is the north-facing side of "McCool Hill," where it could spend the southern-hemisphere winter tilted toward the sun. Spirit finished studying a bright feature called "Home Plate" last week and is driving from there toward the hill. It has approximately 120 meters (about 390 feet) to go. Driving backwards with the right-front wheel dragging, the rover needs to stop and check frequently that the problem wheel has not snagged on anything and caused other wheels to slip excessively. Expected progress is around 12 meters (40 feet) per day under current conditions.
Opportunity is closer to the equator, so does not need to winter on a slope like Spirit. Opportunity spent most of the past four months at "Erebus Crater." It examined layered outcrops, while the rover team determined and tested a strategy for dealing with degraded performance by a motor in the shoulder of its robotic arm. Opportunity left Erebus this week and is on a 2 kilometer (1.2 mile) journey to a giant crater called "Victoria."
Callas has worked on the Mars rovers' mission since 2000 and five other Mars missions since joining JPL in 1987. He succeeds Jim Erickson, who switched to a leadership role with NASA's Mars Reconnaissance Orbiter. Callas grew up near Boston and graduated from Tufts University, Medford, Mass. He earned his doctorate in physics from Brown University, Providence, R.I.
JPL, a division of the California Institute of Technology, Pasadena, manages the Mars Exploration Rover and Mars Reconnaissance Orbiter projects for NASA's Science Mission Directorate.
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Guy Webster (818) 354-6278
Jet Propulsion Laboratory, Pasadena, Calif.
Dwayne Brown/Erica Hupp
NASA Headquarters, Washington