A steering
problem that plagued NASA's Spirit Mars rover driving abilities has resurfaced almost
two weeks after it first appeared.
Rover
engineers are still working to comprehend the malfunction, but believe a relay
used to turn Spirit's steering actuators - small motors controlling the robot's
wheels - on and off is the likely culprit.
"We are
continuing tests on Spirit and our testbed here at JPL," said Jim Erickson,
Mars Exploration Rover project manager at NASA's Jet Propulsion Laboratory
(JPL) in Pasadena, California.
The
steering glitch
first appeared on Oct. 1 and stopped Spirit in its tracks for about five days. JPL
engineers had devised a potential solution to the problem - such as
deliberately blowing out a fuse to disable the robot's brakes - but the
malfunction apparently cleared up on its own. On Oct. 7, Spirit drove a few feet
toward a new rock target dubbed "Tetl."
But on Oct.
13, the steering malfunction popped up again and occurred intermittently during
tests last week, NASA officials said.
JPL
engineers are still considering their initial plan to disable Spirit's brakes. Blowing
out the fuse would cut off the braking action of the rover's steering
actuators, but Spirit should still be able to operate without it.
"The only
change might be driving in shorter steps when the rover is in rugged terrain,"
Erickson said.
The
steering actuators aboard the six-wheeled Spirit and its robotic twin
Opportunity - also exploring Mars - keep their target wheels pointed in the
proper direction during any given drive. Each of the rover's front and rear
wheels has a steering actuator, which is different from the motor that actually
make the wheels roll.
Opportunity gets a boost
Rover
engineers did get a pleasant surprise from Opportunity, some bonus power after
months of declining energy production from its solar panels.
When
Opportunity first landed at Meridiani Planum on Mars in January, its solar
panels produced a steady 900 watt-hours of power each day, about enough to run
a 100-watt light bulb for nine hours, researchers said.
But the
buildup of dust on the panels and the onset of Martian winter bit into the
rover's power production abilities - as expected by Opportunity's engineers -
until the robot hit a plateau of about 500 to 600 watt-hours per day during the
summer months.
Since
September, however, Opportunity has managed to generate more than 700 watt-hours
each day, power levels it hasn't seen its first 10 weeks on Mars.
"We've been
surprised but pleased to see this increase," Erickson said. "The team is
evaluating ways to determine which of the few different theories is the best
explanation.
Opportunity
sits closer to the Mars equator and Spirit and enjoys a sunward-facing tilt while
it explored "Endurance Crater" in recent months. Researchers theorize that wind
may have removed some of the dust collected on the solar panels, or it may have
clumped due to frost.
"We seem to
have had several substantial cleanings of the solar panels," Erickson said.
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