(CNN) -- Stargazers crossed their fingers Thursday as NASA attempted to revive the planet-hunting Kepler probe, idled since a piece of critical equipment gave out in orbit two months ago.
Kepler has been sidelined since mid-May, when a reaction wheel that helps aim the spacecraft's telescope failed. Controllers launched a series of tests that will determine whether that device can be restarted, or whether another reaction wheel that quit in July 2012 can be reactivated.
Controllers have remained in communication with the craft, which is about 45 million miles from Earth. It takes about four minutes for a radio signal to traverse that gap.
In the first round of tests, telemetry from the craft indicated the wheel that shut down in May spun counterclockwise, but didn't respond to commands to turn clockwise, NASA reported. Controllers will go ahead with tests scheduled for next week on the other wheel while they study the results of Thursday's effort.
Kepler project manager Roger Hunter called Thursday's findings "an interesting development."
"While this is a positive start, it is very early in the multi-stepped process to characterize the performance of the reaction wheels and to determine if one could return to operation," Hunter said in a written statement. "The team will remain focused on the upcoming tests and report the cumulative test results at the end of the month."
The 15-foot, 2,300-pound spacecraft was launched in 2009 to search for Earth-size planets circling stars like our sun. The roughly $600 million mission has so far confirmed 134 planets and identified nearly 3,300 possible planets beyond our solar system.
Kepler was built with four reaction wheels and needs three to keep the spacecraft aimed precisely at its targets -- one to fine-tune the spacecraft's position on each axis. After May's failure, only two remained in service and the probe went into a low-powered state to preserve fuel.
"We're kind of hoping for the best, but planning for the worst," said Sara Seager, an astrophysicist at the Massachusetts Institute of Technology.
Kepler's observations have focused on a sliver of the cosmos around the Northern Hemisphere constellations Cygnus and Lyra. They have led scientists to believe that most stars in our galaxy have planets circling them.
The craft's light-recording photometer has shown that the intensities of as many as two-thirds of stars are more variable than our sun.
And in April, researchers reported that they had identified three planets that could potentially host life. Two of those -- Kepler 62e and 62f, located about 1,200 light-years away -- are considered the best candidates so far.
"We really want Kepler to be able to return to be able to operation in the same way that it was before the wheel failed," said Seager, a former member of the Kepler science team. "That's the ultimate hope."
But the probe has already surpassed its three-and-a-half-year minimum expected lifespan, and it has collected enough data to keep scientists busy for up to two years. And even if Kepler can't regain the kind of steady precision required for its observations to date, NASA may be able to use the spacecraft for other purposes, Seager said.