About the size of a suitcase, "the foam is the most probable cause of the accident," Admiral Harold Gehman, who led the probe into the catastrophe, told a news conference.

It was the most definitive statement yet on the cause of the disaster that claimed the lives of seven astronauts.

Investigators previously had considered the foam, which separates from the central fuel tank minutes after launch, a possible cause.

Gehman said US shuttles could be back in flight in nine months or sooner.

"I dont speculate on the date of return to flight," he said.

"I would say that having read every word of the draft report and having gone over what might be possible recommendations I don't see any recommendations which are so difficult to accomplish that they shouldn't be able to return to flight in six to nine months."

SPACE.WIRE