The vaunted Kepler Spacecraft, responsible for the discovery of hundreds of exoplanets, has experienced the failure of it’s final reaction wheel. The spacecraft has four reaction wheels and needs at least three to function properly. The reaction wheels are used to point the spacecraft without using thrusters. This is so that the fuel can be conserved as the reaction wheels use only electricity where as the thrusters use the finite fuel on board.
Reaction wheel number 2 had failed a few years ago, leaving the minimum number of three available. Recently reaction wheel number 4 had shown signs of failure. There were current spikes indicating a problem with the wheel bearings. Controllers took some proactive measures, trying to redistribute some of the lubricant in the hopes of prolonging the life of this wheel.
Unfortunately on May 14th the spacecraft had placed itself in thruster-Controlled Safe Mode, the second time this month. While recovering the spacecraft reaction wheel 4 remained at full torque while the spin rate dropped to zero. A clear indication that there has been an internal failure within the reaction wheel, likely a structural failure of the wheel bearing. The spacecraft was then transitioned back to Thruster-Controlled Safe Mode. NASA is in the process of placing Kepler in point rest state which will minimize the amount of fuel needed to maintain communications while in thruster control. In this mode the fuel could last for years, but no science data could be collected.
This could indeed end the mission. It would slow the discovery of exoplanets and be significant loss in the search for other habitable planets like earth. NASA will explore other options to return the mission to science mode, such as possible reactivation of damaged reaction wheel number two, but the outlook is not good at this time.
Kepler had completed it’s primary mission duration and goals. It was in an extended mission operations phase at this time. There are currently 10 planets discovered that could possible support life, including the discovery of a planet in a solar system virtually next door to us.. Let us hope they find some way to recovery this spacecraft and begin once again searching for exoplanets.