Systems Failure on NASA’s Kepler Probe – Halting Its Search for Alien Planets

NASA’s planet-hunting Kepler space telescope suffered a second failure in its reaction-wheel control system, forcing a suspension of its search for alien planets while the space agency determines whether the four-year mission is truly finished.

“It’s certainly not good news,” Charles Sobeck, deputy project manager for the $600 million mission at NASA’s Ames Research Center, told reporters Wednesday.

But Sobeck and other mission managers emphasized that there was still a chance that the probe could be revived. “I wouldn’t call Kepler down and out just yet,” said John Grunsfeld, associate administrator for science at NASA Headquarters.

The problem has to do with the reaction wheels that are part of Kepler’s fine-pointing system. The space telescope identifies worlds in far-off solar systems by watching for the telltale dips in starlight when the planet’s disk passes over its parent sun. But in order to make those observations, Kepler has to hold itself in a precise position with the aid of four gyroscopic reaction wheels. One of the wheels failed last July, but Kepler could still do the job with the other three.

On Sunday, however, the spacecraft put itself into safe mode when it couldn’t stay in its proper orbit around the sun, 40 million miles (640 million kilometers) from Earth. When the mission team did its regular check-up with Kepler on Tuesday, they found that a second reaction wheel wasn’t working. In a mission update, NASA said the problem was probably caused by “a structural failure of the wheel bearing.”

That forced an end to Kepler’s planet quest. “We need three wheels in service to give us the pointing precision to make this work,” the mission’s principal investigator, William Borucki of NASA Ames.

Sobeck said the spacecraft itself could remain stable as long as it had fuel for its thrusters, but the thrusters aren’t capable of providing the precise pointing that Borucki and his colleagues need. Over the next several months, members of the Kepler team will assess their technical options, and gauge what kind of science could be accomplished using those options, said Paul Hertz, astrophysics director at NASA Headquarters.