The announcement firms up plans for the resumption of space shuttle flights more than two years after the Columbia disaster.

"Nasa's Space Flight Leadership Council met today and refined the launch planning window for Discovery's Return to Flight mission to 15 May to 3 June 2005," the US space agency said on Friday.

"STS-114 will rendezvous with the International Space Station (ISS)", with seven crew members on board, according to a Nasa statement that described elaborate testing and system checks as almost completed.

Atlantis also has a mission to the ISS in the works, with a launch window of 12-31 July, the agency said.

NASA mothballed its shuttle programme after the Columbia tragedy and has since been working to modify the remaining three shuttles to avoid a recurrence.

Columbia disintegrated on re-entry on 1 February 2003, killing all seven astronauts on board.

An inquiry board found that a piece of insulating foam dislodged from a fuel tank during takeoff and hit the leftwing of the Columbia hard enough to damage the craft's protective thermal skin.

On re-entry, superheated gasses entered the wing and destroyed its internal structure, triggering the craft's destruction.