One of the reaction wheels required to keep the space telescope pointed in the right direction has failed, although mission engineers hope to find a way to save the craft, a NASA administrator said.
Kepler mission engineers were able to communicate with the observatory after it put itself into thruster-controlled safe mode Sunday, John Grunsfeld, Science Mission Directorate associate administrator told a conference call Wednesday.
Engineers attempted to communicate with wheel four, and although it was being commanded to speed up, it was not moving, Grunsfeld said.
Kepler has four reaction wheels, but one already failed last year after experiencing erratic friction. The craft needs three wheels to keep it pointed with the extreme precision required to view possible planets.
"Unfortunately, Kepler is not in a place where I can go up and rescue it," he said. "This is something we've been anticipating for a while."
Astronomers said the odds of fixing the wheel or finding another solution are 50-50.
Deputy project manager Charles Sobeck echoed Grunsfeld when he said he "wouldn't call Kepler down and out just yet."
"Our next step is to see what we can do to reduce fuel consumption," Sobek said, as the thrusters burn through fuel.
Sobek said the vehicle may be put into a "point-rest state," where the vehicle "nods back and forth" using the pressure of the sun.
In such as state, "we have years of fuel left" to either repair the wheel or figure out a new way to keep the telescope pointed.
Engineers first noticed trouble with the wheel in January, when it too began to experience excess friction. They put Kepler in "safe mode" in the hopes the problem would remedy itself by redistributing internal lubricant.
When they took it out of the protective mode, the problem remained, although observational capability had not been disrupted until now.
Launched in March 2009, Kepler's mission was to search for exoplanets in the "Goldilocks zone," where liquid water could make planets habitable. Potential planets are spotted by looking for decreases in starlight when the solid body passes in front of its sun.
To date, Kepler has identified 132 planets spotted more than 2,700 potential planets.
“It was one of those things that was a gift to humanity,” one astronomer told the Times. “We’re all going to lose for sure.”
But even if Kepler is down for the count, the information it has already gathered could prove to be enormously useful in the hunt for new Earth-like planets.
"Kepler has an enormous archive of data, and I believe we've only just begun to scratch the surface of that data," Grunsfeld said.