Cape Canaveral - Nasa plans to revive its planet-hunting Kepler space telescope for a new mission after a positioning system problem sidelined the observatory last year, officials said on Friday.
The telescope was launched in 2009 to search for Earth-sized planets suitably positioned around their parent stars for liquid water, a condition believed necessary for life.
Kepler scientists are still analysing data to find a true Earth analogue, but already have added 962 confirmations and 3 845 candidates to the list of 1 713 planets discovered beyond the solar system.
Kepler's steady gaze was broken last year when it lost the second of four positioning wheels. Three are needed for precision pointing.
"Good news from Nasa HQ," Kepler deputy project manager Charlie Sobeck wrote in a status report posted on the Kepler website. "The two-wheel operation mode of the Kepler spacecraft ... has been approved."
The first observations of the new campaign, called K2, are scheduled to begin on 30 May.
Kepler worked by monitoring about 150 000 target stars for slight but regular changes in brightness, a possible sign of a planet passing by, or transiting, relative to the telescope's line of sight.
An Earth-sized planet moving around its host star as close as Earth circles the sun would transit once every 365 days. Scientists want to see at least three transits to be sure any tell-tale light dips are caused by a passing and not a stellar flare or other phenomenon.
Engineers developed a plan to use pressure from sunlight to balance the telescope, though it no longer will be stable enough to catch the faint signs of small, transiting planets.
Nasa approved a two-year follow-on mission encompassing all types of stars, rather than just stars like the sun. The observations also will include star clusters, supernova and objects beyond the Milky Way.
Kepler currently costs Nasa about $18m a year.
The telescope flies in an orbit about 64 million kilometres from Earth.