Remains found among shuttle debris

All seven astronauts on board were killed when the craft broke up after re-entering the Earth's atmosphere on Saturday.

Two technical inquiries are opening into the disaster - the American space agency Nasa will conduct an investigation, and so will an independent board.

US President George W Bush led the mourning for the crew, killed almost exactly 17 years after the Challenger shuttle exploded on lift-off.

Shock and grief 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.

Mr Bush ordered flags to fly at half-mast on government buildings around the US. But in a televised address he pledged that the "journey into space will go on".

The future of the shuttle programme - and of Nasa's manned space exploration - remains unclear.

But Russia said a planned launch of a cargo vessel to serve the International Space Station will go ahead on Sunday.

Sensor malfunction

Nasa said it did not yet know what caused the break-up of the shuttle 40 miles (65 kilometres) above the Earth.

" We can't rush to judgement "
Ron Dittemore,
Nasa shuttle manager

Problems were first noticed when sensors on the left wing malfunctioned 23 minutes before the scheduled touchdown and six minutes before the shuttle disintegrated.

That 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 but Nasa said there was no reason to be concerned about the tiles which cover the shuttle to protect it from the extreme heat of re-entry.

Hours after the disaster, Nasa shuttle manager Ron Dittemore said: "As we look at that now in hindsight... we can't discount that there might be a connection.

"But... we can't rush to judgement on it because there are a lot of things in this business that look like the smoking gun but turn out not even to be close."

SHUTTLE CREW

Experts have suggested that the problems are likely to have been mechanical or structural.

A key part of the investigation - which will likely take months to complete - 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 along with a helmet and uniform badges.

The remains have been removed for DNA testing.

" The Columbia is lost; there are no survivors "
President Bush

Mr Bush praised the astronauts for their "high and noble purpose in life".

Large parts of the shuttle have been found about 30 miles (50km) away in Nacogdoches but the debris is spread over a huge area.

Debris injuries

At least eight people in Hemphill needed hospital treatment for burns and breathing problems after getting too close to pieces of the wreckage.

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

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 about 200,000 feet up and travelling at 12,500 mph (20,000 km/h) at the time.

Television pictures showed a vapour trail from the craft as it flew over Dallas.

It then appeared to disintegrate into several separate vapour trails, and witnesses in the area said they heard "big bangs" which also shook their homes.

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.