US President George W. Bush vowed this evening that "America's journey into space will go on" despite the deaths of seven astronauts killed when the space shuttle Columbia disintegrated.
"The seven brave men and women from the Columbia will be remembered for their achievements, their heroism and their sense of wonder," Mr Bush said in a speech at the National Institutes of Health.
"Their 16-day mission held the promise of answering scientific problems that elude us here on Earth," he said. "While we grieve the loss of these astronauts, the cause of which they died will continue."
"America's journey into space will go on," said Mr Bush, who was to attend a memorial for the Columbia's crew in his home state of Texas tomorrow.
The space craft disintegrated on Saturday, just minutes before its scheduled landing in Florida.
As investigations as to how the tragedy occurred NASA scientists focused on a sudden temperature rise and a sharp corrective manoeuvre by the automatic pilot.
Shuttle programme manager Mr Ron Dittemore said it was much too early to speculate on what caused the disaster - the second loss of a shuttle since the Challenger exploded 17 years ago, almost to the day.
But the latest analysis of data beamed down from the Columbia - which first flew 22 years ago - showed that the temperature on part of the left-hand-side fuselage rose 32 degrees in five minutes as the space craft was re-entering the atmosphere.
Four minutes later, "we had an increase in drag on the left side of the vehicle," Mr Dittemore said.
"The flight control system was countering that drag by trying to command the vehicle to roll to the right-hand side. . . . Soon after, we had loss of signal," he said.
"What's a little bit unusual . . . is that, even though it was within the capability of the flight control system to respond to this increased drag, the degree of which the elevons were trying to correct is outside our family of experience," Mr Dittemore said.
Mr Dittemore said NASA had received a flood of calls from the public - 600 on Saturday alone - offering witness accounts and amateur video of the shuttle breaking up.
Hundreds of police and soldiers fanned out across Texas and Louisiana to search for clues to the disaster on Saturday that killed all seven astronauts just 16 minutes before the shuttle's scheduled landing in Florida.
Body parts and components of the shuttle were strewn across an area 100 miles long and 10 miles wide. In rugged rural areas, horses and four-wheel drive vehicles were used in the search and by midday more than 500 pieces of the shuttle had been recovered in Nacogdoches County, Texas.
NASA officials said the three remaining shuttles are grounded until the cause of the disaster is found and corrected.