The Kepler orbital observatory is back to planet hunting after taking ten days off to give one of its reaction wheels, which had been showing signs of abnormal friction, some days off (see earlier post here) : Kepler resumes data collection after safe mode – Spaceflight Now
Managers put Kepler into safe mode Jan. 17 when reaction wheel no. 4, one of the spacecraft’s three remaining reaction wheels, showed rising friction. The reaction wheels were spun down and the observatory switched to chemical rocket thrusters to control its attitude for a 10-day “wheel rest” period.
The wheel rest period was designed to allow the wheel bearings to cool and lubricant to redistribute inside the wheel housings, hopefully resolving the friction issue.
Engineers will review the performance of wheel no. 4 over the next month to evaluate the effectiveness of the wheel rest scheme, NASA said in an update. More wheel rest periods may be needed in the future if the procedure proves effective, according to Sobeck.