The US space shuttle fleet is to remain grounded until November at the earliest, Nasa officials have said.

The US space agency has admitted it still does not know the cause of a recurring problem at lift-off - a piece of foam flying off the fuel tank.

The space shuttle Columbia was damaged this way in 2003, which led it to burn up on re-entering the atmosphere.

Nasa had hoped a successful Discovery space shuttle mission would help get its programme back on track.

But the mystery of the insulating foam and the fuel tank is causing its engineers a lot of problems.

In 2003 a chunk of foam came off the tank on lift-off and struck Columbia's wing.

Two-and-a-half years and $1bn (£553m) of modifications later and the same thing happened again.

But this time the foam did not hit Discovery and the mission was a success.

More modifications

Future shuttle flights have been suspended until the foam problem is resolved.

The man leading Nasa's investigation admitted there is no immediate answer or problem that jumps out, but he said modifications would have to be made.

That rules out a September launch, when the next mission was due to blast off from Cape Canaveral.

Nasa hoped to send Atlantis up next as a second test mission, and to continue work on the international space station.

There is only one more chance to send the shuttle into orbit this year, in November, and it is not yet known if the problem will be fixed by then.



from http://news.bbc.co.uk/1/hi/sci/tech/4144168.stm