Severe increase in temperature may provide crucial clues

Nasa scientists said last night that the space shuttle Columbia underwent a severe and unexpected rise in temperature and experienced unprecedented drag just minutes before it disintegrated. Investigators believe these could be crucial clues as to what caused the shuttle's demise.

As teams continued to gather thousands of pieces of debris scattered across east Texas and Louisiana, investigators said an initial review of flight data appeared to confirm speculation that Columbia had suffered a lethal rise in temperature ­ possibly as the result of losing one or more of its 20,000 thermal shields.

"We are gathering some confidence that it was a thermal problem rather than structural," Ron Dittemore, Nasa's shuttle programme manager, said. Data revealed that as the shuttle was travelling over California, the mid-section of its fuselage underwent an increase in temperature of about 15C about seven minutes before mission control lost contact with the spacecraft, he said.

The sharp rise was followed by increased drag on the spacecraft that caused its automated flight system to adjust its path. Though the information was preliminary, it could suggest that the thermal tiles designed to protect the shuttle from burning up during re-entry into Earth's atmosphere were damaged or missing, possibly from an episode earlier in the shuttle's flight, he said.

Nasa engineers are still trying to recover 32 seconds worth of additional data from the flight computers. "We've got some more detective work. But we're making progress inch by inch," Mr Dittemore said.

The left side of the spacecraft has been the focus of suspicion almost from the start. Investigators are looking at whether a piece of insulation from the big external fuel tank that broke off during lift-off on 16 January caused damage to the shuttle's left wing.

In addition to Nasa's inquiries, and those of the House Science Committee, which oversees Nasa, an independent investigation will be carried out under a retired admiral who led the inquiry into the October 2000 terrorist attack on the destroyer USS Cole at Aden.

Harold Gehman, with 35 years of active duty in the navy, is seen as one of the Pentagon's wisest and most experienced investigators.

He has a career of high-ranking military appointments behind him ­ the most recent as Nato's supreme allied commander for the Atlantic.

The tragedy of Columbia, though less deadly than the attack on the Cole, in which 17 sailors died, promises to be far tougher to investigate. Though severely damaged, the Cole was taken back to America for repairs and examination. The oldest shuttle in the US space programme disintegrated into thousands, perhaps tens of thousands, of fragments.

The Gehman investigation will review all of the information Nasa collected as the spaceship began its descent, then started breaking up more than 200,000 feet over Texas. This includes transmissions from the crew, records from the shuttle's sensors, analysis of the debris and data from government and commercial satellites.