NASA’s Kepler Spacecraft May Be Finished

A critical failure in Kepler's alignment may spell the end for the storied planet hunter.
Kepler is designed to look for Earth-like planets orbiting Sun-like stars in a temperate "Goldilocks zone," where temperatures are right for liquid water. It stares at a patch of around 156,000 stars in the constellations Cygnus and Lyra and notes teeny blips in their brightness, which could indicate planets passing in front of the stars' faces. NASA

The diversity of the phenomena of nature is so great, and the treasures hidden in the heavens so rich, precisely in order that the human mind shall never be lacking in fresh nourishment.
–Johannes Kepler

The storied Kepler space telescope, finder of scorched baby Mercuries, a real Tatooine, gigantic Jupiters and possible other Earths, might be on its last planet-hunting breath. The telescope put itself into safe mode yesterday and its control wheels may have failed, meaning it cannot properly point at the stars. NASA says the telescope is not dead, but they are not sure they can keep it going, either.

“I think the most interesting, exciting discoveries are coming in the next two years. The mission is not over,” said William Borucki, Kepler’s chief scientist and the man who conceived it decades ago. “But the mission is not taking data. There is a reasonable possibility that we will be able to mitigate that problem. I don’t think I’d be a pessimist, here.”

Kepler, which orbits the sun trailing 40 million miles behind the Earth, is controlled by four gyroscopic reaction wheels, which keep it parked in the right direction. It stares at a patch of 150,000 stars between the constellations Cygnus and Lyra, looking for blips in brightness that indicate a planet passing in front of them. This type of search requires incredible pointing precision, and that’s where the wheels come in. The reaction wheels keep Kepler in place despite the pressure of the solar wind.

Launched in 2009 on a $600 million mission that’s already been extended through 2016, the telescope has been experiencing issues with one of the wheels for some time. Wheel No. 2 has been turned off for a while, and earlier this year, managers on Earth noticed another stuck wheel, so they put Kepler in park and hoped the kink would work itself out. On May 12, Kepler put itself into safe mode when it noticed it was drifting out of position. When NASA woke it up Tuesday, May 14, telemetry indicated wheel No. 4 wasn’t moving, despite commands for it to spin.


Scientists need at least three working wheels to keep Kepler pointed with extreme precision, as carefully as the Hubble Space Telescope. Without them, it might be able to hang out in a “point rest state” and do other types of astronomy, but that’s not clear yet. NASA managers said they were trying to think of ways to fix it–maybe ordering the wheels to wiggle around, or spin like you might spin a stuck car tire–but they’re not sure it will work.

“I wouldn’t call Kepler down and out just yet,” said John Grunsfeld, NASA’s associate administrator for science and a former astronaut.

Kepler has been phenomenally successful, finding more than 2,700 planet candidates and 130 definite planets. In some respects, Kepler bridged the emotional void between the end of the space shuttle and the landing of the Mars rover Curiosity. During that gap, NASA still had an awe-inspiring, romantic explorer to share with the public–and with scientists.

“When we started out, we didn’t know virtually every star in the sky had planets around them,” said Paul Hertz, NASA’s astrophysics director. “Now we know that.”

Even if it can’t be fixed, Kepler’s discoveries will continue rolling in. It has a list of 2,740 planet candidates, which can be verified with ground telescopes or with Kepler’s own data. Granted, those self-checks would be better if the telescope had another couple years to stare at the same stars. But it has an enormous archive of data, so no matter what happens to it now, Kepler findings will not cease for some time.

Borucki said he has at least two years of work to do with the data he already has.

Though NASA managers and scientists said they are not counting Kepler out, their words Wednesday were certainly fitting of a eulogy.

“For me, it goes back to sitting on my porch, looking at the stars and wondering what’s out there. And now we know, because of Kepler,” Grunsfeld said.

Go here to check out some of Kepler’s current highlights.