Uh-oh: Kepler has been shut down for ten days to save the mission.
The spacecraft was launched with four so-called reaction wheels that spin to help keep the telescope pointing at its target fields of stars. One of these, reaction wheel No 2, failed in July 2012, leaving three to do the maneuvers, including a quarterly roll to a new orientation. Now reaction wheel No 4 has shown early indications that it might fail, prompting its NASA controllers to attempt some long-distance maintenance. They hope that by resting the wheels, their lubricant will spread to ease increased friction.
If this wheel fails permanently, the Kepler mission would be over, as it would be impossible to orient the spacecraft with enough precision with only two wheels.