Astronauts today gave the space shuttle a four-and-a-half hour inspection using cameras on the orbiter’s robotic arm early to see if its heat shield was damaged by a mysterious object that apparently floated off the spacecraft.

NASA was warned nine years ago that the space shuttle could fail catastrophically if debris hit the vulnerable underside of its wings during lift-off the very scenario that may have brought down Columbia.

A small meteorite or piece of man-made space junk may have struck the Columbia shuttle while it was still in orbit causing it to crash on its return to earth, Nasa said today.