Sol 2151-2158 : Spirit is still embedded in the area called "Troy" on the west side of Home Plate. Energy levels for Spirit have been decreasing rapidly as winter approaches. To prepare for winter, the project is taking actions to improve northerly tilt of the rover to maximize solar illumination.
The best approach has been to drive Spirit backwards. The drives employ a wheel steering action "frog kick" with each drive step. To mitigate against wheel stalls associated with driving in this embedded terrain, an autonomous wheel diagnostics has been added.
If a wheel stall occurs, the diagnostic test is run on the stalled wheel. If the wheel passes the diagnostic, then driving resumes. This has been effective in permitting the driving to continue much further than otherwise.
Spirit continues to make several centimeters of backward progress with each drive without further sinkage. In some cases, the rover has gained in elevation.
However, northerly tilt has not improved due mainly to the counterclockwise yaw of the rover. Backward driving will continue with the aim to position the rover for the winter with the most favorable orientation achievable.
As of Sol 2158 (Jan. 28, 2010), the rover solar array energy production was down to 182 watt-hours with an atmospheric opacity (tau) of 0.379 and a dust factor of 0.522. Total odometry is 7,730.46 meters (4.80 miles).
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