On Thursday, July 18, 2013 the team initiated exploratory recovery tests on the spacecraft's two failed wheels. The recovery tests are a series of steps to characterize the performance of Reaction Wheels (RW) 4 and 2, and to determine if either could be returned to operation.
The initial test began on Thursday, July 18, 2013, with RW4. In response to test commands, wheel 4 did not spin in the positive (or clockwise) direction but the wheel did spin in the negative (or counterclockwise) direction. Wheel 4 is thought to be the more seriously damaged of the two.
On Monday, July 22, 2013, the team proceeded with a test of RW2. Wheel 2 responded to test commands and spun in both directions.
Over the next two weeks, engineers will review the data from these tests and consider what steps to take next. Although both wheels have shown motion, the friction levels will be critical in future considerations. The details of the wheel friction are under analysis.
Kepler requires extremely precise pointing to detect the faint periodic dimming of distant starlight— the telltale sign of a planet transiting the face of its host star. Too much friction from the reaction wheels can cause vibration and impact the pointing precision of the telescope.