NASA outlines ingenious plan to resurrect the Kepler planet hunter

A graphical representation of the K2 mission. I'd recommend reading below before trying to interpret this image.

NASA

Back in August, NASA formally threw in the towel on attempts to get its Kepler planet-hunting probe working again. With the probe down to just two fine-pointing devices, there was just no way to keep the telescope consistently pointed at the right field of stars. Apart from the pointing issue, however, the remaining hardware was all fine, so NASA said it would consider proposals for alternate uses of the probe. Now, the agency has announced that it has settled on one proposal and will consider putting it into its 2014 budget.

The failed hardware is called a reaction wheel, and its job is to exert a small force that can turn the telescope over time. At least three of these wheels are required to keep the telescope staring at a specific spot long enough to gather useful data. The new proposal would effectively turn the probe's solar panels into a third reaction wheel—though an extremely limited one.

As photons are absorbed and emitted, they generate a small force on the object doing the absorbing (it's the same force that causes some asteroids to spin). Kepler is powered by solar panels that are arranged symmetrically across the probe's long axis. If the probe can be oriented so that the sunlight strikes these panels evenly, the photons will exert a constant and symmetric force against the probe. Kepler's two remaining reaction wheels can then push against that force and keep the telescope gazing steadily at one point in the sky, just as it was designed to do.