The crew of Columbia may have known for up for to 90 seconds that something was drastically wrong with their shuttle before it disintegrated.

Eliezer Wolferman, the father of the Israeli astronaut Ilan Ramon, said yesterday that officials had told him they believed there would have been between 60 and 90 seconds during which the crew would have been aware of the steep rise in temperature in parts of the fuselage and of the drag on the left wing.

"These seconds are always spinning around in my head. It's very difficult ... I try to imagine what they went through," he said. "One second is like 20 years. I can't explain it. It's hell, hell in the sky."

Some of his son's remains and those of three other astronauts have been recovered and identified by crews collecting scattered wreckage from the shuttle, which disintegrated on return to Earth.

News of the possible warning period emerged as Nasa cast doubt on the theory that a piece of foam debris striking the shuttle during take-off was the root cause of the disaster.

Ron Dittemore, the space shuttle programme manager, said that, after a careful study of the damage possible from the loose chunk of foam insulation, investigators were looking at other causes. "It doesn't make sense to us that a piece of debris could be the root cause of the loss of Columbia and its crew," he said.

The programme manager said investigators were focusing more closely on the desperate effort of Columbia's automatic control system to hold the speed of the spacecraft stable despite an increasing amount of wind resistance from the left wing.

Mr Dittemore said his team was intensifying efforts to recover the final data from the spacecraft. Pieces of debris have been found in Arizona and California, indicating that disintegration began before the shuttle reached east Texas, where most of the wreckage fell. "Perhaps the [final] 32 seconds will help us understand," Mr Dittemore said.

* Authorities indicted a woman and a man from Texas yesterday on federal charges that they stole pieces of the Columbia wreckage.