* It helped hunt Earth-like planets beyond the solar system
* Telescope's pointing system broke in May
* Alternative missions are under consideration
By Irene Klotz
CAPE CANAVERAL, Fla., Aug 15 The Kepler space
telescope's planet-hunting days are over because its broken
positioning system cannot be fixed, NASA officials said on
The observatory was launched in 2009 to hunt for Earth-sized
worlds suitably positioned around their parent stars for liquid
water, a condition believed to be necessary for life.
The telescope was sidelined in May when it lost use of
equipment needed to keep its gaze steady on about 100,000 target
stars. Kepler worked by finding slight dips in the amount of
light coming from a star, a telltale sign of a planet passing
by, relative to the telescope's line of sight.
The technique requires precise pointing, which was
accomplished by three spinning wheels to control the telescope's
motion up and down, left and right and side to side. Kepler also
had a fourth spare wheel, but that was put into service after a
previous wheel failure in July 2012.
Engineers began tests last month to see if either jammed
wheel could be recovered, but the efforts ultimately proved
fruitless, the U.S. space agency said.
"The wheels are sufficiently damaged that they cannot
sustain spacecraft pointing control for any extended period of
time," Charles Sobeck, Kepler deputy project manager at NASA's
Ames Research Center in Moffett Field, California, told
reporters during a conference call on Thursday.
Scientists may be able to use the telescope for projects
that do not require such precise positioning, such as looking
for asteroids, comets and other celestial objects.
NASA is soliciting proposals for alternative Kepler missions
and expects to make a decision early next year on whether to
continue funding the telescope's operation. The Kepler project's
budget currently is about $18 million a year.
So far, the telescope has found 135 planets beyond the solar
system and another 3,500 possible planets that are awaiting
confirmation, according to scientists. While some planets are
even smaller than Earth and others have been found in
potentially life-friendly orbits, so far a perfect Earth analog
has yet to be identified.
An Earth-sized planet orbiting a star about the same
distance that Earth is from the sun would take a year to pass
under Kepler's gaze. Scientists want three or four years' worth
of data to be sure a change in the amount of light coming from a
target star is due to a passing planet and not an eclipsing
neighbor star, a stellar flare or some other phenomena.
Scientists have about two years of archived Kepler data yet
"I'm confident that we are going to find what we expected
... but we're going to have to work hard for the next couple of
years," said Kepler lead scientist William Borucki, also with
Ames, referring to an Earth-sized planet hospitable to life.
Kepler flies about 40 million miles (64 million km) from
Earth, too far away for a robotic or astronaut-led repair
(Reporting by Irene Klotz; Editing by Jane Sutton and Will