Kepler glitch suspends NASA's search for new planets
Sen—NASA's phenomenally successful planet hunter, the Kepler space telescope, has temporarily shut down operations after problems with part of the system that orientates it to keep it pointed at its stellar targets.
The spacecraft, currently more than 72 million km (45 million miles) away in its orbit around the Sun, has been put into a safe mode for ten days to allow one of its manoeuvring wheels to recover.
Kepler's discoveries have boosted the number of confirmed exoplanets discovered transiting other stars to more than 850. But there are many more candidates awaiting confirmation. Another 461 were announced on January 7, at a gathering of the American Astronomical Society in California, bringing the total of those to 2,740.
Kepler has made all its finds in one relatively small area of the sky. Following launch in March 2009, it has been staring constantly at around 160,000 stars in one small region of the Milky Way in the constellations of Cygnus and Lyra. As it does so, it watches for fades in any star's light that may indicate planets passing in front of it.
A diagram of the Kepler spacecraft. Credit: NASA
The spacecraft was launched with four so-called reaction wheels that spin to help keep the telescope pointing at its target fields of stars. One of these, reaction wheel No 2, failed in July 2012, leaving three to do the manoeuvres, including a quarterly roll to a new orientation.
Now reaction wheel No 4 has shown early indications that it might fail, prompting its NASA controllers to attempt some long-distance maintenance. They hope that by resting the wheels, their lubricant will spread to ease increased friction.
Kepler mission manager Roger Hunter reported on Thursday: "Earlier this month during a semi-weekly contact with the spacecraft, the team detected an increase in the amount of torque required to spin one of the three remaining reaction wheels.
"This increase in friction occurred before the January 11, 2013 quarterly roll, and persisted after the spacecraft roll and several momentum desaturations of the reaction wheels. Increased friction over a prolonged period can lead to accumulated wear on the reaction wheel, and possible wheel failure.
The region of sky being watched by Kepler. Credit: NASA/Carter Roberts
"To minimize wheel friction, the team implemented several mitigations including increased operating temperatures, higher spin rates, and bi-directional operation following the failure of reaction wheel No 2 in July 2012."
He added: "Given the persistence of this recent event in reaction wheel No 4, the project team will place the Kepler spacecraft in a 'wheel rest' safe mode for a period of ten days beginning today. Science data collection will be stopped during this period and the spacecraft solar panel orientation will be aligned with the sun to maintain positive power for Kepler.
"This is similar to a normal safe mode configuration, but with thrusters maintaining attitude instead of reaction wheels. Resting the wheels provides an opportunity to redistribute internal lubricant, potentially returning the friction to normal levels."
All being well, Kepler will take around three days to return to science operations after its ten-day rest so that it can begin again to harvest many more new alien worlds in a mission that is scheduled to last until 2016.