After four years of service, NASA’s planet-hunting Kepler telescope has suffered a second serious malfunction — one that threatens to permanently end the mission. Controllers on the ground can no longer control its orientation. It looks bad, but NASA isn’t giving up hope.


This story actually began last July when one of Kepler’s four reaction wheels broke down. The spacecraft requires at least three functional wheels, so NASA was nervous about any further failures.

But on May 14th, as the Kepler Team went about its usual business of making contact with the space telescope, they found it in safe mode, slowing spinning about the sun-line.


And to their horror, they could not regain control of the spacecraft.

Further analysis revealed that yet another reaction wheel had failed. NASA thinks it’s an internal malfunction within the wheel, likely a structural failure of the wheel bearing.

Kepler has been returned to Thruster-Controlled Safe Mode as the Kepler team tries to figure out what to do. It can function in this state for several months, but given the seriousness of the situation, it’ll likely be put it into a deeper fuel-preserving stasis, called Point Rest State, which would extend its life to several years.

“We will take the next several days and weeks to assess our options and develop new command products,” noted the Kepler team through an official release. “These options are likely to include steps to attempt to recover wheel functionality and to investigate the utility of a hybrid mode, using both wheels and thrusters.”


But with the failure of the second wheel, Kepler will likely never return to the high pointing accuracy that enables its high-precision photometry.

Repairing Kepler in orbit is considered impossible.

While it’s heartbreaking, the $600 million Kepler space telescope had already completed its three-and-a-half year mission. Everything since November 2012 is a bonus. And indeed, the mission should be considered nothing less than a spectacular success. To date, it’s helped astronomers identify 132 exoplanets, including another 2,700 candidates. Owing to Kepler, astronomers now estimate that there may be as many as 17 billion Earth-sized planets in the Milky Way.


Image: NASA/Kepler Mission.