During a routine call up of NASA’s planet-hunting Kepler mission on 14 May, the spacecraft was found to have fallen into a safe mode with an attitude error. During an attempt to return to reaction wheel control as the spacecraft rotated into communication, and commanded a stop rotation, it appeared that all three wheels responded and that rotation had been successfully stopped. However reaction wheel 4 remained at full torque while the spin rate dropped to zero. According to NASA, this is a clear indication that there has been an internal failure within the reaction wheel, likely a structural failure of the wheel bearing. The spacecraft was then transitioned back to Thruster-Controlled Safe Mode. NASA may now elect to retire the spacecraft which has exceeded its three year old design life by over a year. During its service the spacecraft has discovered hundreds of planets orbiting distant stars.
Reaction wheel failure means only two left on Kepler and it may be the end for the mission
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