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NASA readies its rescue plan for planet-hunting Kepler probe 

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.

When members of the Kepler team announced in May that the spacecraft was out of commission, they said they would probably try spinning one of the two unresponsive wheels backward or forward to get it unstuck.

Kepler is among several aging space probes that are going through transitions:

  • Jason-1, a U.S.-French satellite that tracked rising sea levels for more than 11 years, was decommissioned this week, NASA announced. John Grunsfeld, NASA's associate administrator for science, noted in a statement that since its launch, Jason-1 "charted nearly 1.6 inches (4 centimeters) of rise in global sea levels, a critical measure of climate change and a direct result of global warming." NASA said a non-recoverable failure in Jason-1's last working transmitter caused the spacecraft to go out of contact on June 21. The spacecraft is expected to remain in orbit for at least 1,000 years.
  • France's space agency, CNES, said the COROT planet-hunting spacecraft was being retired from service. The probe stopped sending data last November, and efforts to restart observations have been unsuccessful. "A series of operations will now be performed to lower COROT's orbit and conduct some technology experiments before passivating the satellite," CNES said in a statement. "Its journey will end as it burns up on re-entry in Earth's atmosphere."
  • NASA turned off the decade-old Galaxy Evolution Explorer, or GALEX, after lending it to Caltech for a year of privately funded operation. The $150 million GALEX satellite surveyed hundreds of millions of galaxies to help scientists study stellar evolution. The craft will stay in orbit for at least 65 years before burning up in Earth's atmosphere.

Alan Boyle is's science editor. Connect with the Cosmic Log community by "liking" the NBC News Science Facebook page, following @b0yle on Twitter and adding +Alan Boyle to your Google+ presence. To keep up with Cosmic Log as well as's other stories about science and space, sign up for the Tech & Science newsletter, delivered to your email in-box every weekday. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for new worlds.