"We are here to let you know officially that we will be moving the shuttle Discovery's return to flight launch window, or launch, from the May-to-early-June window to the mid-July window," Nasa Administrator Michael Griffin said on Friday.

Discovery, which was wheeled to its launch platform earlier this month at the Kennedy Space Centre in Cape Canaveral, Florida, had been scheduled to blast off on a mission to the orbiting International Space Station between 15 May and 3 June.

Safety measures

Griffin said Nasa had a number of small fixes it wanted to make before relaunching the space shuttle, including a review of what he described as debris issues.

"No one thing, but the sum of all those things together necessitates that we move out six or seven weeks into the July window," he said.

"This is consistent with our overall approach to return to flight, which is that we're ... not going to rush to flight," he said. "And we want it to be right."

By delaying the launch, an anonymous source told The New York Times, Nasa engineers will have more time to fix problems with fuel-tank sensors, which shut down the engines if the fuel level drops too low.

It will also allow for a closer review of the measures taken to prevent debris from the shuttle's external fuel tank from hitting the spacecraft on takeoff.

A stray piece of insulating foam cracked Columbia's outer layer on liftoff, leading to its disintegration and the death of all seven astronauts on board upon its re-entry into the atmosphere.