Following the failure of Reaction Wheel No 2 (out of four available) in July 2012, NASA’s Kepler “planet finder” spacecraft has been suspended from normal operations after another reaction wheel began showing signs of increased friction during January 2013. As a precaution, NASA has now decided to put the Kepler spacecraft into a 10 day safe mode, resting the remaing reaction wheels and relying on thrusters for control. All observations were suspended during this period. Three working reaction wheels are needed for scientific operations.
Kepler spacecraft. Courtesy: NASA