- Associated Press - Friday, December 17, 2010

CAPE CANAVERAL, FLA. (AP) - NASA fueled space shuttle Discovery at the launch pad Friday, not for flight but rather for testing to understand the mysterious cracking that occurred last month.

Discovery is grounded until at least the beginning of February because of potentially dangerous cracks that popped up in the fuel tank during an actual launch attempt. The cracks have been fixed, but engineers still do not understand why they happened.

So in a countdown test that began at sunrise, the launch team pumped more than 500,000 gallons of liquid hydrogen and oxygen into Discovery’s external fuel tank. The tank was rigged with sensors and other equipment.

Whenever Discovery does fly, it will be its last trip into orbit and one of the final two or three shuttle missions remaining. It’s loaded with supplies for the International Space Station as well as an experimental humanoid robot.

“We’re not committing to flying anytime soon. We’ve got to wait until we know we have a good answer to go fly,” launch manager Mike Moses said as Discovery’s 15-story tank filled up. “We want to make sure we know the risk we have in front of us.”

The concern is that any cracks in the brackets could cause chunks of foam to pop off and, in the worst case, slam into the Discovery at liftoff. A large slab of foam doomed space shuttle Columbia in 2003.

Back on Nov. 5, NASA halted the countdown for Discovery because of leaking hydrogen gas. An unrelated problem _ cracking _ later was discovered in the insulating foam of the fuel tank, in the ribbed central portion that holds instruments. When the foam was removed, cracks were found in two of the more than 100 aluminum ribs, or brackets, making up that area. The two damaged ribs _ 21 feet long apiece _ were next to each other.

Both the leak and cracks were fixed, and NASA aimed for a possible December flight. But engineers were stumped as to what caused the cracks. They now believe there may have been a buildup of stress in the brackets during assembly, which caused them to crack when the super-cold fuel was loaded into the tank, Moses said.

Besides stringing cables with gauges and sensors on the suspect portion of the tank, technicians also painted small black dots _ 10,000 to 12,000 of them _ on the exposed white foam over the repaired area. Moses called it finger-painting and it was; technicians worked in freezing temperatures, dipping their gloved fingers in paint and then pressing them gently onto the foam.

The dots were part of an optics test. A pair of cameras provided stereoscopic views of the dots, recording the motions of the tank in that area and hopefully providing additional clues to the cracking.

There was no leakage and no immediate signs of cracking as of late Friday morning.

Discovery will be taken back to the Vehicle Assembly Building next week so engineers can X-ray the brackets on the back of the fuel tank.

The goal is to launch Discovery as early as Feb. 3 or at least by month’s end, Moses said.

NASA’s shuttle program is set to retire next year after 30 years of flight. Space shuttle Endeavour is due to fly in April, and Atlantis may follow in the summer if funding is forthcoming.

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