NASA investigators were today due to continue their search to find the reason for the Columbia tragedy.They were believed to be focussing their attention on the craft's left wing which was damaged when it was hit by a piece of insulating foam which fell off the external fuel tank during launch on January 16.

NASA investigators were today due to continue their search to find the reason for the Columbia tragedy.

They were believed to be focussing their attention on the craft's left wing which was damaged when it was hit by a piece of insulating foam which fell off the external fuel tank during launch on January 16.

Terrorism has been discounted because Columbia was flying too high and too fast to be shot down – and it would have been impossible to plant a time-bomb on board.

Human error by the crew has also been discounted as a cause of the tragedy.

Debris, including human remains, has been found across a wide area of northern Texas, Oklahoma, and Louisiana.

The loss of the space shuttle, and the likely suspension of the entire programme, causes a major problem for the work to create the International Space Station currently taking shape in orbit.

There are three astronauts on board there who are expecting to remain there for several months before being replaced by a new crew flown up on a space shuttle.

However they do have a Russian Soyuz "lifeboat" attached to the station which they can use to return to earth if no relief crew can be sent.

That would put the whole future of the space station, being built by 20 nations, in doubt as it needs astronauts to carry out routine maintenance.