The report by the Columbia Accident Investigation Board was to have been sent to Congress before the end of July.

But the board chairman, Admiral Harold Gehman, said the document "sometime in August, middle or third week."

"It's more important that we get it right than we get it quick," Gehman told a Washington press conference.

Columbia disintegrated as it returned to Earth on February 1 killing all seven crew on board.

Investigators are convinced that a foam panel that came off during takeoff on January 16 pierced the heat insulating skin around the shuttle, letting in boiling gases.

The report is to set out the sequence of events between takeoff and the disaster as Columbia re-entered the Earth's atmosphere, before its landing at Cape Canaveral base in Florida.

It should also set out the errors of appreciation by National Aeronautics and Space Administration (NASA) officials during the mission and the impact of budget cuts at the agency on safety.

It is expected to recommend technical and organisation changes but no date for a resumption of shuttle flights.

"There will be no return to flight recommendation to Congress," Gehman said.

The inquiry is expected to cost between 15 million and 20 million dollars. The Columbia debris recovery operation has already cost 300 million dollars.

SPACE.WIRE