Callas Takes Over As Martian Winter Approaches,
Spirit Loses A Wheel
NASA's incredibly long-lived Mars rovers demand lots of care, as
they age and the Martian winter approaches.
John Callas, newly named project manager for NASA's Mars
Exploration Rover missions, is coordinating the work to meet these
challenges. He is a scientist at NASA's Jet Propulsion Laboratory
(JPL) in Pasadena, CA. 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 Callas' first challenges will be working around the
latest malady to hit the Spirit rover. One of the rover's six
wheels has stopped working, meaning Spirit is now dragging that
wheel. That hinders the solar-powered rover as it travels to 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 that supply is
dropping fast.
Spirit's right-front wheel became a concern 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 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 its 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 toward the hill. It has
approximately 120 meters (about 390 feet) to go. Expected progress
is approximately 12 meters (40 feet) per day.
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' operation since 2000 and
five other Martian 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, MS. He earned his doctorate in
physics from Brown University, Providence, RI.
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.