Glitch may cut telescope's working life

NASA's exoplanet-hunting Kepler space telescope has experienced an equipment glitch that could limit its useful scientific lifetime, astronomers say. Data from Kepler on July 16 alerted ground controllers that one of its four reaction wheels, whose spin controls the probe's orientation and aiming, had stopped turning, NewScientist.com reported. Accurate aim is critical to Kepler's operation as it monitors thousands of stars for changes in the intensity of light caused by orbiting planets passing between the star and the telescope. To detect transits of planets, Kepler must keep a given star centered in its light detectors for months on end. When controllers shut down the malfunctioning wheel Kepler briefly stopped gathering usable exoplanet data. Kepler only needs three wheels to function, using one to control the probe's motion along each axis, and the probe resumed its observations on July 20, but if the glitch can't be fixed Kepler will be left without a backup wheel. "This is reducing the odds of making the mission go as long as we can," Kepler chief scientist William Borucki said. It's doubtful Kepler could point accurately enough to look for transiting planets if reduced to two reaction wheels, he said. "It was a disappointing surprise to find this wheel stopped so early."