Shuttle launch to go ahead despite crack

Nasa's deputy space shuttle programme manager points to a model of the external fuel tank. Picture / Reuters

CAPE CANVERAL - Nasa has decided to go ahead with the launch of space shuttle Discovery despite finding a small crack in the foam insulation on the ship's fuel tank, officials have said.

Discovery is due to lift off from the Kennedy Space Centre in Florida at 2.38pm EDT on Tuesday (6.38am Wednesday NZT), after two weather-related delays during the weekend.

"We've laid out the data. We've looked at it calmly. We're ready to go fly," said Bill Gerstenmaier, Nasa's associate administrator for space flight.

The fuel tank's insulation has bedeviled Nasa since fallen foam caused the shuttle Columbia to break up, killing seven astronauts in 2003.

Discovery's flight is intended to prove the tank, which has been redesigned twice since the accident, no longer sheds hazardous chunks of foam during launch.

If it fails or if the shuttle sustains some other serious problem, the shuttle fleet could be grounded permanently, leaving the future of the half-built, US$100-billion (165bn) International Space Station in jeopardy.

Even before the latest foam problem, Nasa's top safety officer and chief engineer had argued for additional repairs on the tank's foam before Discovery's planned 12-day mission.

Nasa managers met to assess whether the crack in insulation foam near the top of the shuttle's fuel tank would pose a hazard during launch.

Inspectors using cameras and sensors found the crack on Monday morning local time, as well as a small foam wedge that apparently fell from the damaged area and landed on the launch platform.

The crack is believed to have been caused by condensation trailing down the shuttle's fuel line and solidifying into ice during the second launch attempt on Sunday.

When the fuel tank was emptied after the delay, the ice melted and the foam cracked as the line expanded in the warm air. The crack is about 12.7cm by 1cm.

Kennedy Space Centre technicians came up with a method to get detailed, close-up pictures of the area using a tiny camera encased in flexible plastic. The images showed the rest of the foam, which covers a metal bracket holding the shuttle's liquid oxygen hose, is in good shape, Gerstenmaier said.

"It became apparent that a repair was not necessary," he said.

An inspection team will scrutinise the cracked area carefully once the shuttle's tank is refilled for tomorrow's launch attempt. Engineers believe a small amount of ice will form in the crack, but not enough to pose a debris hazard to Discovery during its climb to orbit.

The foam that fell is less than half the size of what would damage the shuttle's heat shield, had it flown off during launch instead of on the ground.

Discovery's flight is just the second since the Columbia disaster. Nasa had hoped to resume regular shuttle missions last year but the foam problem that downed Columbia reoccurred during Discovery's launch in July 2005.

A major problem with Discovery on this mission could bring a premature end to the US space shuttle programme.

Nasa has spent US$1.3 billion in the past three years to attempt to fix the foam problem and to make safety upgrades to the shuttle, which is scheduled for retirement in 2010. Foam still is still expected to fall off during launch.

The mission is going ahead over objections of senior Nasa safety and technical officers, who wanted more time to work on the fuel tank's long-standing foam-shedding problem.

But the space agency says the crew is not at risk because of a plan to have them stay aboard the space station and await rescue if their ship was too damaged to safely return home.

- REUTERS