US mourns astronauts as search for clues goes on

Thousands of people, led by President Bush, gathered at Nasa's Mission Control yesterday for a memorial service to the seven astronauts who died in the Columbia space shuttle disaster.

The President was visibly moved and the first lady Laura Bush wiped away a tear as Mr Bush declared: "America's space programme will go on."

Paying tribute to the victims, Mr Bush said: "Their mission was almost complete and we lost them so close to home. Each of these astronauts had the daring and discipline required of their calling. Each knew great endeavours are inseparable from great risk, and each accepted those risks willingly, even joyfully, in the cause of discovery."

Earlier, the President was accompanied on Air Force One by Neil Armstrong, the first man on the moon. The former astronaut John Glenn was also on board with Sean O'Keefe, a Nasa administrator, and many congressional figures. The service was attended by between 10,000 and 15,000 people.

Meanwhile, the search for missing pieces of Columbia spread out across a tract of the country. Recovery teams started digging up the nose cone, found in thick forest on the Texas-Louisiana border, and investigators said the answer to the disaster might lie as far west as Arizona or California.

The nose cone, weighing about 500lb (230kg), was found almost intact by a farmer near his property in Sabine County, Texas. It was embedded deep in the ground where it fell, with pieces of fabric, insulation and square grey plates strewn several feet around. One piece was wedged into a nearby pine tree, and a piece of a spacesuit had landed in the farmer's back yard.

The cone was the most significant single piece to have been discovered so far, with pieces of the cockpit recovered in nearby Nacogdoches County. However, as investigators become increasingly convinced the destruction of the shuttle was caused by heat rather than navigational problems, attention is slowly moving westwards to the area directly beneath the first phase of Columbia's break-up.

The first protection tiles from the shuttle's exterior might have fallen over desert areas in California, Arizona or New Mexico. If these can be recovered, they would offer clues as to which part of the shuttle overheated first. Ron Dittemore, the head of shuttle operations, told reporters: "There have been unconfirmed reports that debris has been found as far west as Phoenix. If that exists, that is extremely important to us."

At the weekend, one man in eastern California reported seeing streaks of light in the early morning sky that may have been the first sign of trouble aboard the shuttle. One theory suggests the body of the shuttle was crucially damaged about 80 seconds after take-off on 16 January, when a piece of fuel tank insulation became detached and hit the left wing. Establishing a "burn pattern"of heat protection tiles would go a long way to corroborating or disproving that theory.

Four days after the disaster, debris collection has continued apace, with about 12,000 pieces recovered so far. The "debris field" has become wider than first anticipated, with collection centres set up as far apart as Forth Worth, near Dallas, and Shreveport, Louisiana.