Nasa inquiry chief takes control

He and his team of investigators spent the day at Nasa's Johnson Space Center being briefed on how the investigation is going so far.

" We continue to investigate the foam as a possible root cause "
Ron Dittemore, space shuttle programme manager

Admiral Gehman, who co-chaired the independent commission that investigated the attack on the USS Cole in Aden, Yemen, in 2000, has already visited the area of eastern Texas where much of the shuttle debris landed.

The search for wreckage, which Nasa experts hope will yield vital clues as to why the shuttle broke up on re-entry into Earth's atmosphere, continued throughout Thursday, although heavy rain and sleet made the task more difficult.

'Looters' arrested

The recovery effort has already been hampered by members of the public trying to keep parts of the shuttle, reportedly as souvenirs.

Two Texans were charged on Thursday with stealing pieces of debris - they could each face up to 10 years in prison and a $250,000 fine.

But police reported that an amnesty offered for anyone handing over looted shuttle parts had resulted in a number of pieces being turned in.

Members of the public have until 1800 EST (2300 GMT) on Friday to hand over debris without facing a penalty, US attorneys said.

Foam theory

Nasa is particularly interested in finding parts of the shuttle's left wing which had recorded a rise in temperature and increase in drag just minutes prior to the disaster.

The agency has moved away from the theory that insulation foam seen to peel away from Columbia's external tank on launch and hit the vehicle's left wing was responsible for the accident.

But at the latest technical press briefing Ron Dittemore, Nasa's space shuttle programme manager, said that this did not mean the possibility had been discounted.

" They were soldiers and scientists and doctors and pilots, but above all they were explorers "
Vice-President Cheney

He said that a number of tests would be carried out, checking the damage that such an impact could have incurred.

"We continue to investigate the foam as a possible root cause," Mr Dittemore said.

"Although I said before that we thought it unlikely that this was the cause it is not being discounted. No possibility is being discounted," he added.

Top secret device

Reuters news agency reported that around the town of Bronson, near the Texas-Louisiana border, hundreds of national guardsmen joined federal agents and volunteers to search for what was believed to be a top-secret device from the shuttle.

People involved in the search said they were given written instructions on what the device looked like as well as a picture of a plate attached to it which read "Secret Government Property".

SHUTTLE BREAK-UP

A report in a Texas newspaper on Thursday said searchers were looking for a communications device that relayed encrypted messages between the shuttle and the ground.

More than 12,000 remnants, many as small as coins, have so far been recovered.

Much of the debris landed in heavily wooded areas and pastures, making the search difficult.

Mr Kerss said driving rain meant that it was difficult for heavy vehicles and equipment to cross the terrain to collect the debris.

The cold conditions meant the horses being used in the search were becoming more easily tired and hundreds of people scouring the countryside had to be sent out in shorter shifts.

Nonetheless several significant pieces of wreckage were found near the town of Hemphill, including parts of the fuselage, nose cone and computer circuits, said Marq Webb, a spokesman for the US Forest Service.

Meanwhile on Thursday US Vice-President Dick Cheney presided over a service at the country's National Cathedral in Washington, where a stained glass window holds a piece of Moon rock, to honour the crew of Columbia.

"They were soldiers and scientists and doctors and pilots, but above all they were explorers," Mr Cheney said.

Later on Friday a memorial service will be held on the runway where the ill-fated Columbia was supposed to land at the Kennedy Space Center.