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Kepler, a prolific hunter for other Earths, is suddenly in trouble (+video)

Kepler's quest for an Earth-like planet orbiting a sun-like star has been put on hold, NASA said, after the spacecraft sensed it was facing in the wrong direction and put itself in 'safe mode.'

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The discoveries the additional data would have yielded "would have been in some sense frosting on the cake," he acknowledged. "But we have an excellent cake."

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If Kepler can't be revived, analyzing the 2,700 planet-candidates in the queue so far will keep the team busy for at least two more years, he noted.

But engineers have some tricks up their sleeves they want to try before they give up and NASA declares the mission finished.

Reaction wheels spin constantly at high rates of speed, so engineers anticipate that they will fail at some point.

One approach would be to command the balky wheel to rotate back and forth to see if whatever is preventing it from operating can be dislodged. If the reaction wheel can't be revived, the team could try to reactivate the wheel they took out of service last year.

If that doesn't work, the team will examine other science missions the craft might be able to perform that don't require the level of precision pointing that planet-hunting does. That means relying on the thrusters more frequently to orient the craft, so remaining fuel supplies become a limiting factor.

If the requisite number of reaction wheels can't return to service, and even if researchers can cobble together other astronomical observations the craft could undertake, that does not guarantee that NASA would extend Kepler’s activities. Any new science plan for Kepler would still have to compete for funding with  other NASA missions being proposed.

Should Wednesday’s announcement truly herald Kepler's imminent demise, the mission's impact will be felt for a long time, researchers say. The mission has been nothing if not an object lesson that if you give smart people the right tools, they can wield those tools in ways few imagined when the tools were first built.

For instance, the craft has measured light from the individual stars in its target patch of sky with enough sensitivity to track the smallest variations in starlight.

Indeed, the craft has delivered such high-quality data on the stars themselves that the mission has been a gold mine for astrophysicists studying star structure and behavior.

Apart from its own discoveries, Kepler data and the operating experience gained in running it for four years can inform future planet-hunting missions.

In 2017, NASA plans to launch another planet-hunting craft, called TESS, that will focus its gaze on the 500,000 stars nearest the sun. These are close enough to allow space-based telescopes such as the James Webb Telescope, currently planned for launch in 2018, to study the atmospheres of planets TESS discovers.

"Kepler's been such a wonderful story," said John Grunsfeld, associate administrator for NASA's Science Mission Directorate and a former shuttle astronaut who helped perform the last set of repairs to the Hubble Space Telescope before the space-shuttle program ended.

"I wouldn't call Kepler down and out just yet," he said.



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