Mon, Aug 24, 2009
How To 'Unstick' A Rover
A second, lighter-weight test rover
has entered the testing setup at JPL where rover team members are
assessing strategy for getting Spirit out of soft soil where it is
embedded on Mars.
The rover team has begun using a test rover that does not carry
a science payload or robotic arm, as do Spirit and Opportunity on
Mars, and the primary engineering test rover at JPL. While the
primary test rover's weight on Earth is greater than Spirit's
weight on Mars, the second rover is even lighter on Earth and
closer to the weight of Spirit on Mars.
Making comparisons between motions of the two test rovers in
duplicated drives will aid the rover team in interpreting effects
of differing gravity on rover mobility. The testing team plans to
run such comparisons both in the soft, fluffy material being used
to simulate the soil at Spirit's current location and also on
coarser, crushed rock that offers better traction.
"There is no perfect Earth analog for Spirit's current
situation," said JPL's John Callas, project manager for the twin
Mars Exploration Rovers. "
There's less gravity on Mars, little atmosphere, and no moisture
in the soil where Spirit is. It is not anything like being stuck in
sand or snow or mud on Earth. Plus, since the rover moves only
about as fast as a tortoise, you cannot use momentum to help. No
rocking back and forth as you might do on Earth."
The comparison experiments with the two test-rover siblings to
Spirit and Opportunity precede a planned "dress rehearsal"
long-duration test of driving as far in the test setup as the
distance that Spirit would need to achieve on Mars to escape its
predicament at the site called "Troy."
The team has also made further assessments of the position of a
rock underneath Spirit relative to the rover's center of
gravity. Part of the strategy for getting Spirit free will be
to avoid getting in a position with the center of gravity directly
over a rock touching the rover.
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