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NASA to Ground Shuttles Again

But Discovery's mission is also a trial run for the safety measures and new procedures implemented during the 2 1/2 years the shuttle fleet was grounded after Columbia disintegrated during reentry. A chunk of foam from the external fuel tank pierced that shuttle's leading-edge heat shielding during launch, allowing superheated gases to penetrate the wing as it plunged back into the atmosphere.

Although Discovery apparently avoided a similar fate Tuesday, the crew spent its first full day in orbit using the shuttle's new 50-foot Canadian-built sensing boom for an inch-by-inch examination of the reinforced carbon-carbon on the wings and nose.

Mission specialist Andrew Thomas attached the shuttle's 50-foot grappling arm to the new boom and sensor system, a 50-foot extension with a television camera and two laser imagers mounted at the far end.

The 100-foot span allowed the shuttle crew to get close-up images of virtually every spot on the shuttle. Thomas, assisted by pilot James Kelly and mission specialist Charles Camarda, took six hours to compete the inspection. The sensors produced startling images that allowed viewers on Earth to see screw holes and creases in the heat shielding and even read serial numbers on thermal panels.

The survey went so well, as did the crew's other planned activities, that flight director Paul Hill sounded almost euphoric early Wednesday, suggesting that the chipped thermal protection tile "didn't look like it was going to be a significant problem."

But as the day progressed, the mood shifted drastically as details of the foam debris began to come into focus.

A flying piece of something was readily visible in the launch footage taken Tuesday by a camera attached to Discovery's external tank. It turned out that the debris was foam from a "protuberance air load ramp," a thick ridge of insulation running down the side of the tank to provide aerodynamic protection -- the rocketry equivalent of a wind break -- to protect the tank's cables and pressurization lines.

Engineers had examined the ramp after the Columbia accident, and while they were not altogether satisfied, they cleared it for launch.

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