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WASHINGTON– NASA said it had again postponed the launch of the space shuttle Discovery, already pushed back to February, to an undetermined date to allow more time for repairs.

"The decision was made today to allow the teams additional time and delay the next launch opportunity out of the early February launch window," the space agency said in a statement on its website on Thursday.

Discovery has been plagued by setbacks since its initial launch attempt in November and was moved from its launch pad at the Kennedy Space Center in Florida to an assembly building on December 22 for evaluation and repairs.

NASA had initially been forced to delay the launch on November 5 when hydrogen was discovered leaking from the external fuel tank.

During repairs, engineers went on to find small cracks on the metal supports of the tank, with the aging shuttle undergoing X-ray testing before its final space mission.

NASA has said that if, as has happened, the February 3-10 window became impossible, the next available window would be from February 27 to March 3.

Another shuttle, Endeavor, is set to take off in April in what will be the last shuttle launch scheduled for the US program.

One more as yet unscheduled launch could take place in the summer before the entire fleet is retired for good.