Just seen this on ceefax:
NASA REJECTS U.S. SHUTTLE DAMAGE THEORY
A piece of insulating foam is no longer thought to have caused the break-up of the Columbia space shuttle, Nasa says
The probe had focused on damage to tiles under the left wing, which it was thought could have caused by a chunk of foam insulation on take-off.
But Nasa said the foam debris was neither heavy enough nor traveling fast enough to cause the damage.
The probe will now focus on the automatic control system.
BBC News / In depth, shuttle disaster