Shuttle launch to go ahead despite risk of 'catastrophe'

NASA managers have rejected last-ditch pleas from their top safety officer and chief engineer to scrap next month's shuttle launch, saying that they will press ahead despite potentially catastrophic risks.

The head of the US space agency, Dr Michael Griffin, overruled warnings that there was a "relatively high" chance the shuttle's external fuel tank could shed some of its solid foam coating when it launches on 1 July, carrying seven crew including Briton Piers Sellers, an Edinburgh University graduate.

In 2003, falling foam knocked a hole in Columbia's wing, causing the craft to break up as it returned to Earth, resulting in the deaths of seven astronauts. Last year, Discovery came within inches of disaster when a chunk rattled loose from the tank and nearly struck the orbiter seconds after lift-off.

During a weekend meeting at NASA's Kennedy Space Centre at Cape Canaveral, Florida, Dr Griffin gave the final nod for next month's mission, despite what he called an "intensive and spirited exchange" with senior colleagues who recommended a "no-go". "We have elected to take the risk," he said.

If the mission ends in disaster, NASA's multi-billion dollar shuttle programme will be scrapped, leaving construction of the International Space Station unfinished and marking the end of an era in human spaceflight.

"If we were to lose another vehicle ... I would be moving to figure out a way to shut the programme down," Dr Griffin admitted.

Engineers have addressed the foam-shedding problem suffered during last year's mission by removing a stretch of insulating material from the shuttle's external fuel tank.

But smaller pieces could be shed from 34 aerodynamic structures known as ice-frost ramps, which protect the tank's fuel lines from ice build-up.

If a big enough slab hit a certain part of the shuttle, "the results would be catastrophic," said John Chapman, project manager for the external tank.

Former astronaut Bryan O'Connor, now NASA's safety chief, and chief engineer Christopher Scolese have recommended that the next mission should be postponed until the ice-frost ramps can be redesigned.

Dr Griffin said that if the shuttle's thermal tiles are damaged by debris during launch, the vehicle would still make it safely into space. The danger, he said, would come during re-entry.

The astronauts could make minor repairs before coming down or take refuge in the International Space Station and await a rescue mission by a second shuttle, Atlantis.

Dr Griffin said: "I do not see the situation we're in as being a crew-loss situation. If we are unlucky and we have a debris event on ascent, it will not impede the ascent. The crew will arrive safely in orbit, and then we will begin to look at our options."

The Columbia Accident Investigation Board, which was set up to probe the reasons for the 2003 disaster, condemned NASA in its final report for a "culture of complacency" in which engineers' concerns were slapped down and debate stifled.