Nasa officials decided a crack in Discovery‘s fuel tank insulating foam was not enough of a threat to stop the countdown on Tuesday to their first Independence Day holiday shuttle launch and ”a nice fireworks display” for the United States.
Inspectors spotted the crack on Monday. A 7,6cm piece of foam also popped out of the area, which covers an expandable bracket holding a liquid-oxygen feed line against the huge external fuel tank.
After several hours of inspections and meetings, officials decided to continue with the launch as planned. Nasa administrator Michael Griffin said on Tuesday that the crack is not a major concern and that cameras are trained on the area, so if ice builds up after the super-cold fuel was added, the launch can be delayed.
”We establish days, weeks, months in advance the criteria that we have to meet in order to be able to launch. If we don’t meet them, we stand down,” meaning the shuttle does not launch, Griffin told NBC’s Today show.
”If we get through the list without a problem, we’ll see a nice fireworks display,” he said.
Another technical problem sprung up on Tuesday morning when inspectors discovered they lost back-up circuit breakers that control heaters on both solid rocket boosters. Crews were being sent to repair the problem, though Nasa said the shuttle remains fully functional and can fly without the fix.
If Discovery gets off the ground on Tuesday, it will be the first manned launch by the US on the nation’s birthday, the first launch in almost a year, and only the second launch since the Columbia disaster killed seven astronauts in 2003.
Columbia‘s wing had been hit by a chunk of flyaway foam during lift-off. That damage caused the shuttle to break apart over Texas on re-entry on February 1 2003.
Nasa managers decided to go ahead with the attempt on Tuesday for three reasons: they are confident enough that the foam is still on the bracket to prevent a large piece of ice from forming; they do not believe the area will be exposed to extreme heat during ascent; and the area of foam where the piece dropped is still intact.
”They fully have shown that the foam is acceptable and ready to fly,” said Bill Gerstenmaier, a Nasa associate administrator. ”There were no dissenters when we went around the room … no concerns raised.”
Early inspections on Tuesday were promising, with no ice build-up overnight in the area where the piece fell off. Discovery‘s fuelling was completed in just under three hours, and the forecast improved to an 80% chance that weather conditions would be favourable for launch — the best odds so far. Nasa had scrubbed launch plans on Saturday and Sunday as electrically charged clouds loomed over the area.
The 7,6cm triangular piece of foam that dropped from the tank is far smaller than the 0,5kg foam chunk that brought down Columbia. Gerstenmaier showed reporters the piece of foam, which looked like a wedge of toast.
Nasa has spent millions of dollars trying to prevent foam from breaking off at lift-off. Engineers were startled when it broke off Discovery during last year’s mission — the first shuttle flight after the Columbia disaster — but it did not harm the shuttle.
The external tank expanded when the super-cold fuel was drained after Sunday’s launch was cancelled because of the weather. The ice that formed ”pinched” some of that foam, causing the crack and the piece of foam to drop off, officials said.
Griffin decided two weeks ago that the shuttle should go into orbit as planned, despite the concerns of two top agency managers — the top safety officer and chief engineer — who wanted additional repairs to the foam insulation.
But the two agency officials said the foam loss will not threaten the crew because Nasa has a plan for the astronauts to move into the international space station if in-orbit inspections find serious damage to the spacecraft. The crew would then await rescue 81 days later by a second space shuttle.
The mission for Discovery‘s crew this time is to test shuttle-inspection techniques, deliver supplies to the international space station and drop off European Space Agency astronaut Thomas Reiter for a six-month stay. — Sapa-AP
On the net
Spaceflight.nasa.gov