Cosmic Log

Alan Boyle, Science Editor NBC News

July 4, 2013 at 12:00 AM ET

NASA

An artist's conception shows the Kepler observatory in space.

The team behind NASA's planet-hunting Kepler observatory says it will start trying to revive the ailing probe in mid- to late July.

Two of the four reaction wheels in Kepler's fine-pointing guidance system are out of commission, which has left the 15-foot-long (4.7-meter-long) spacecraft in limbo since mid-May. Three wheels have to be working in order for Kepler to observe distant stars with the precision needed to detect planets.

Kepler identifies distant worlds by looking for the telltale dips in starlight that occur when a planet passes across its sun's disk. The spacecraft is designed to stare at 150,000 stars in a patch of sky that straddles the constellations Cygnus and Lyra. Since the telescope's launch in 2009, Kepler has identified 3,277 planet candidates and 134 confirmed planets and there's lots more archived data yet to be analyzed.

Roger Hunter, project manager for the $600 million mission, laid out the rescue plan in an update issued Wednesday. "The engineering team has devised initial tests for the recovery attempt and is checking them on the spacecraft test bed at the Ball Aerospace facility in Boulder, Colo.," he wrote. "The team anticipates that exploratory commanding of Kepler's reaction wheels will commence mid- to late July."

The spacecraft is currently in an energy-conserving mode known as Point Rest State, and will remain in that mode during the tests, Hunter said. He said other adjustments have been made to improve the spacecraft's fuel efficiency and reduce the possibility that it would retreat into safe mode. Both those steps should improve the chances that Kepler can be nudged back into service.

Read more:

NASA readies its rescue plan for planet-hunting Kepler probe