Small Movement During Spirit's Latest Drive
Spirit attempted to turn all six wheels on Sol 2126 (Saturday, Dec. 26, 2009) to extricate itself from the sand trap known as "Troy," but stopped earlier than expected because of excessive sinkage. Telemetry indicates that the rover moved forward 3 millimeters (0.12 inch), left 2 millimeters (0.08 inch) and down (sinkage) 6 millimeters (0.24 inch). The right-front and right-rear wheels did not move.
This four-frame animation, which rover drivers use to aid evaluation of the drive , shows wide-angle views northward from Spirit's front hazard-avoidance camera. The most obvious change is in the position of shadows, a change unrelated to the wheel's movement during the drive. Changes in the soil in front of the left-front wheel can be seen as the sequence progresses, but there is very little net movement of the rover.
The rover team planned to command Spirit to rotate wheels in several steps covering about 50 meters (164 feet) if traction were perfect. Stall detection was modified for the right-front and right-rear wheels, so if they did not function, the drive would still proceed. The rotation speed of the rear wheels was reduced relative to the others in order to prevent "wheelies" from occurring with the rover's middle wheels.
The rover team began commanding extrication drives in November after months of testing and analysis on Earth to develop a strategy for attempting to drive Spirit out of Troy. The extrication drives are expected to make slow, if any, progress and the probability of success in escaping from Troy is uncertain.
Image credit: NASA/JPL-Caltech
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