The crew of the doomed Columbia space shuttle would have known something was wrong with the spacecraft for more than a minute before it began to break apart, relatives of one of the astronauts have said.

We apparently will never know if they suffered Gadi Ramon, brother of Israeli astronaut Ilan Ramon

"It's very difficult, as if I'm with them and I try to imagine what they went through," Eliezer Wolferman, father of Israel astronaut Ilan Ramon said.

"One second is like 20 years."

News of the astronauts' probable final moments comes amid reports that the US space agency (Nasa) was warned at least nine years ago that a space shuttle flight could end in disaster if tiles protecting critical wing parts were damaged by debris.

Footage examined

Nasa, which has expanded its search for debris, said it hopes to review footage taken by a US military helicopter above Texas. This may include pictures of the shuttle's re-entry into the Earth's atmosphere.

Nasa officials also want to examine amateur video footage taken of the shuttle over California which is said to show the craft breaking up.

Ilan Ramon's brother, Gadi, said he had been told by Nasa officials that the astronauts most likely perished as soon as the shuttle began to disintegrate.

"We apparently will never know if they suffered," he told an Israeli newspaper.

Prior warning?

As investigations continue, damage to the heat-resistant tiles is emerging as a leading theory for Columbia's catastrophic end.

SHUTTLE BREAK-UP

Re-entered atmosphere at 12,500 mph (20,000 km/h) Disintegrated 40 miles (65 kilometres) above the Earth Debris scattered over Texas and Louisiana - reports now being checked of sightings in California and Arizona

Click here for a step-by-step guide to the disaster

Paul Fischbeck, engineering professor at Carnegie Mellon University, said he had warned about the tiles in a 1994 study for Nasa.

The most vulnerable spots on the shuttle were the undersides of both wings close to the fuselage and right under the crew compartment, he said.

"There are very important tiles under there; if you lose the tiles on those stretches... it can cause the shuttle to be lost," Professor Fischbeck told the Associated Press news agency.

Nasa shuttle programme manager Ron Dittemore has confirmed that Nasa engineers are still focusing on the possibility that a piece of insulating foam - which fell off and struck the shuttle during lift-off - damaged the shuttle's heat-resistant tiles near a wheel well.

However, Mr Fischbeck stressed that it was still not certain if debris had been the cause of the disaster.

Several Nasa employees and former astronauts who worked on previous missions have said that almost all shuttles return to Earth with tiles damaged by space debris.

SHUTTLE CREW

Commander Rick Husband, US Pilot William McCool, US Michael Anderson, US David Brown, US Kalpana Chawla, US Laurel Clark, US Ilan Ramon, Israel

Click here for profiles

Nasa teams are now also in California and Arizona to investigate reports of debris landing there.

Authorities said that material found in the two western states could be from the wings. This could lend weight to the possibility that the shuttle was experiencing problems sooner than originally thought.

"Early debris early in the flight path would be critical because that material would obviously be near the start of the events," said a senior Nasa official, Michael Kostelnik.

"It would clearly be very important to see the material earliest in the sequence."

Remains recovered

Ilan Ramon's remains have now been identified using DNA and dental records, Israeli reports say.

His body will be flown to Israel in the coming days after a service in Texas.

"This is a relief to all of us, especially the family," Brigadier General Rani Falk, an Israeli air force attache in Washington, told the Associated Press.

Nasa has reportedly recovered some remains of at least three other crew members but has not yet released their names.

During a memorial service for Ramon and his six colleagues on Tuesday, President George W Bush led the tributes and vowed that the "cause of discovery" would go on.