Then it set about to determine how tightly it could tie the foam strike, known to be in that region, to the breach.

Mr. Rocha said that when he learned of the foam strike in a phone call on Friday afternoon, he gasped.

During Columbia's fatal flight, the foam strike was studied and then dismissed by managers as a maintenance issue that was not a threat to the orbiter.

NASA noted in the press conference that launch-time video confirmed a foam strike.

Initial post-landing inspection of the orbiter showed very little additional damage to the thermal tiles affected by the foam strike during launch.

The engineers had said a "catastrophic" foam strike was "probable" at some point over 100 shuttle missions.

The majority of shuttle launches recorded such foam strikes and thermal tile scarring.

The investigation focused on the foam strike from the very beginning.

With Columbia, the foam strike was observed the day after the launch, and a group of engineers was tasked with accessing what damage could result.

Nasa officials said they could barely make out the foam strike in the photographs because of the poor quality of the images they had.