Trouble strikes planet-finder Kepler

This artist rendition provided by NASA shows the Kepler space telescope. The spacecraft lost the second of four wheels that control the telescopes orientation in space, NASA said. Source: NASA

NASA'S space-based Kepler telescope is in trouble with the failure of a key maneuvering device.

The exploration satellite is in "safe mode" as has lost altitude and is in an slow, uncontrolled spin.

A NASA statement says communications with the satellite are also unstable, as the datalink comes and goes as Kepler spins.

The future of the telescope, which has so far found 115 planets and compiled a list of 2740 possible contenders, remains uncertain.

The problem has been linked with the probable failure of the second of four "reaction wheels". The first failed in January.

The spacecraft needs three of these wheels to enable it to make the precise movements it needs to stare at a point in the sky long enough and stable enough for accurate readings.

Attempts to halt the spin have so far failed.

This illustration provided by the Harvard-Smithsonian Center for Astrophysics shows artist's renderings of planets Kepler-20e and Kepler-20f compared with Venus and the Earth. Scientists have found the two Earth-sized planets orbiting a distant star, an encouraging sign for prospects of finding life elsewhere.

"This is a clear indication that there has been an internal failure within the reaction wheel, likely a structural failure of the wheel bearing," a NASA statement says.

Ground control teams continue to examine exactly what can be done to alleviate the problem, and what science can continue to be done.

"Kepler is safe and in no danger. We will evaluate what it's future mission will be," a NASA spokesman said.

Kepler can continue to be pointed by traditional thrusters, but these are not as accurate or as stable as the reaction wheels.

"With the failure of a second reaction wheel, it's unlikely that the spacecraft will be able to return to the high pointing accuracy that enables its high-precision photometry. However, no decision has been made to end data collection," the NASA statement reads.

Kepler was launched in March 2009. The planet finder completed its expected three-and-a-half year mission life in November 2012. It has since been in an "extended mission phase".

A concept image for the Kepler planet-finding mission.

"Kepler has truly worked wonderfully. It's achieved all our requirements," spokesman Bill Borucki said.

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