One of Kepler’s reaction wheels — used to orient the space telescope — has failed.


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Bad news: One of Kepler’s four reaction wheels — used to orient the space telescope — has failed.

Kepler only needs three wheels to function – one to control the probe’s motion along each axis – and the probe resumed its observations on 20 July. “Kepler is functioning very well on three reaction wheels,” says mission manager Roger Hunter of NASA’s Ames Research Center in Moffett Field, California. If the glitch can’t be fixed, though, Kepler will be left without a backup wheel. “This is reducing the odds of making the mission go as long as we can,” says Kepler chief scientist William Borucki of NASA Ames, who doubts that Kepler could point accurately enough to look for transiting planets if reduced to two reaction wheels. “It was a disappointing surprise to find this wheel stopped so early.”

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