Clues sought for shuttle disaster

People across the US mourned the death of the astronauts

Nasa has vowed to leave "no stone unturned" in its investigation into why the space shuttle Columbia disintegrated upon re-entry into the Earth's atmosphere.

As Americans mourned the deaths of the shuttle's seven astronauts, police teams scoured large areas in Texas for shuttle fragments, and found some human remains.

She was proud to be representing her country

Astronaut Laurel Clark's aunt

Families remember loved ones

Already accusations are being levelled that Nasa chiefs ignored a series of safety warnings.

But these were rejected by Nasa administrator Sean O'Keefe, who said every safety concern was tackled before a shuttle launch.

The disaster has raised questions about the future of the 16-nation International Space Station (ISS).

However, Russia on Sunday went ahead with the launch of an unmanned cargo vessel to serve the ISS.

After the dramatic and tragic end to Columbia's 28th flight on Saturday, the painstaking work is under way to establish what went wrong.

Nasa experts are analysing a mass of data transmitted back from the shuttle in the last minutes of its flight.

	:	Shuttle disaster
How Columbia broke up over Texas

On the ground, FBI agents joined local police officers combing through thousands of square kilometres of Texas in a search that could go on for weeks.

Families' pride

Shock and grief at the disaster has been expressed around the world - not just in the US but in India, where one of the crew was born, and in Israel, which had hoped to celebrate the return of the first Israeli astronaut.

President Bush led the US in prayers as the astronauts were remembered at church services nationwide.

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

The crew's relatives have been speaking of their grief, but also pride.

Laurel Clark's family said she had sent them e-mails on Friday speaking of her love of space.

"She was proud to be representing her country and dealing with advanced scientific projects from all over the world," her aunt Betty Havilan told local television in Wisconsin.

Inquiry's focus

The shuttle broke up 40 miles (65 kilometres) above the Earth.

The Columbia is lost; there are no survivors

President Bush

Full text of speech

A focus of the immediate inquiry is possible damage to Columbia's protective thermal tiles on its left wing.

The wing was hit by a piece of insulating foam which peeled away from the external fuel tank a little more than a minute into Columbia's launch on 16 January.

The incident was spotted and checked at the time.

On Saturday, Nasa officials acknowledged that they could not now rule out a connection.

Click here to watch reports on the disaster

Another key part of the investigation will be analysing the pieces of the shuttle which rained down from a clear blue sky over the southern US.

Body parts believed to be from the astronauts have been recovered near Hemphill, in eastern Texas, near the state's border with Louisiana.

Safety warnings

Around three dozen people needed hospital treatment for burns and breathing problems after handling pieces of the wreckage.

Nasa warned that any debris found should be avoided as it could be hazardous.

Although the investigations could take months, concern has already been raised that Nasa ignored repeated warnings that such a disaster was waiting to happen.

Former Nasa technician Jose Garcia said he voiced worries that budget cutbacks were compromising safety in the 1990s.

Don Nelson, who also worked as a technician with Nasa, told the Observer newspaper in London that he had asked President Bush to intervene because of safety fears.

First flight: 1981

Orbiting speed:
17,500 mph

Landing weight: 105 tonnes

Crew (for this mission):7

Columbia: Space pioneer

But Nasa administrator Sean O'Keefe, who has promised an exhaustive inquiry into the disaster, denied that budget cuts had affected safety standards.

"Each and every time is an effort to ensure that ...flight and conduct of mission is done safely, all the way through," Mr O'Keefe told US television.

Columbia, had been due to land at 0916 EST (1416 GMT) at the end of a 16-day mission. Contact was lost at about 0900 EST.

Nasa said the shuttle was travelling at 12,500 mph (20,000 km/h) at the time.

Never before in 42 years of human spaceflight, has Nasa lost a space crew during landing.

In 1986, the space shuttle Challenger exploded shortly after lift-off with the loss of all seven crew on board.