NASA warned nine years ago over danger of lift-off routine

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.

After receiving the warning, NASA made changes in materials and flight rules to lessen the risk of debris breaking loose, Paul Fischbeck, an engineering professor at Carnegie Mellon University who conducted the 1994 analysis, said yesterday.

"There are very important tiles under there. If you lose the tiles on those stretches it can cause the shuttle to be lost," he said.

The underside of the left wing is where NASA is focusing its investigation into Saturday's disaster, which killed seven astronauts.

A spokesman at NASA's Johnson Space Centre, David Drachlis, said last night no one was available to comment on the report.

Also yesterday, the space agency sent teams to check out reports of shuttle debris found as far west as California and Arizona material that could shed light on the earliest stages of Columbia's break-up.

And investigators are also getting new military images of the spacecraft's fiery, dying streak across the country from an Apache helicopter.

Mr Fischbeck and a colleague at Stanford University studied the damage caused by debris during the first 50 shuttle launches and concluded that on average, 25 thermal tiles per flight sustained damage of at least 1in.

He said his risk analysis showed that the most vulnerable spots on the shuttle were the undersides of both wings close to the fuselage, and right under the crew compartment.

To reach that conclusion, he weighed three factors: which tiles were most likely to be hit by debris, which tiles endured a lot of heat on atmospheric re-entry, and which tiles had critical systems underneath them.

It is not clear exactly where under the wing Columbia was hit, but just before the shuttle break up, temperature spikes were detected around the left wheel well, which is close to the fuselage, and on the left side of the fuselage itself.

Mr Fischbeck said NASA took a lot of his advice on board and made improvements.

The investigation into the Columbia disaster is focusing on the possibility that a 2.5lb, 20in chunk of foam insulation from the shuttle's external fuel tank fell off during lift-off and hit the left underside of the wing, causing damage to the thermal tiles that doomed the ship.