The most prolific planet hunter in history recently suffered a serious blow when the second of four reaction wheels failed and it could no longer steer itself and take science observations. A minimum of three reaction wheels are needed in order to continue the mission. In both failures the current needed to drive the reaction wheels increased indicating that the bearings were failing. When the current reaches an unsafe level the wheel is shut down and the spacecraft put into safe mode. Kepler has been responsible for discoveries of Earth sized planets near us, Moon sized worlds and even planets within the habitable zone. Currently Kepler is in a fuel saving safe mode as it undergoes testing to see if the wheels can be brought back to life. When the original failures occurred there were attempts made to condition the wheels in such a way to redistribute the lubrication, without apparent success,
On July 18, 2013 exploratory recovery tests on the spacecraft’s two failed wheels were conducted. 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. 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 which 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.
Although engineers are making heroic efforts to return the mission to operations there is no guarantee of success and this well could be the end if Kepler. There are more planets to be found lets hope for the best.