Shuttle returns to orbit

The Independence Day launch - a quirk of weather rather than a July 4 celebration - is the first in a series of make-or-break missions for the US manned spaceflight program. Over the next four years, NASA is scheduled to launch 16 additional missions in a bid to finish building the International Space Station before the agency ends the shuttle program in 2010.

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This mission aims to resupply the station, as well as round out a program of tests for surveying and repairing the craft's protective heat-shielding tiles. It also is putting a redesigned external fuel tank through its paces.

For now, however, the crew and controllers are just happy to be off the ground.

"I can't think of a better place to be - here on the Fourth of July," said shuttle commander Steven Lindsey, just before yesterday's liftoff into the blue Florida sky.

Between now and the scheduled docking with the space station on Thursday, the astronauts are focusing on the foam-debris issue, as well as preparing to dock with the space station. Digital photos they take of the external tank as it falls away, plus images taken by cameras at various positions along the orbiter, tank, and solid-fuel boosters will help mission managers determine the size and amount of debris the system sheds during launch.

Combined with sensors on the shuttle's robotic arm, which the astronauts will use to inspect the tiles on the belly and under the wings of the orbiter, mission managers say they expect to have plenty of information early in the mission to gauge whether the orbiter's thermal protection system is up to the rigors of reentry. A large chunk of foam struck the shuttle Columbia in 2003. The damage it inflicted on the tiles under one wing led to the orbiter's destruction during reentry, killing its crew.

Indeed, on Monday, foam damage again took center stage. After bad weather forced mission controllers to scrub the second launch attempt on Sunday and technicians returned to the pad to perform inspections, they spotted a crack in foam insulation covering a bracket on the external tank. Within hours, a triangular piece of foam two to three inches on a side had fallen to the launch platform.

The crack appeared after the tank had undergone two refueling cycles in 48 hours - expanding and contracting as technicians filled, then emptied the external tank of its superchilled liquid hydrogen and liquid oxygen. The foam fragment that fell, however, "was way below the mass we'd be worried about" during launch, explained John Chapman, the external-tank project manager. Still, launch managers said they wanted to ensure that the remaining foam would provide the insulation necessary at that spot, that any ice that might form wouldn't cancel the mission, and that the rest of the foam covering the fixture was free of cracks.

By Monday evening, technicians had taken high resolution snapshots of the rest of the fixture, which appeared to be free of additional defects. And engineers calculated that the remaining insulation was more than sufficient to fulfill its role.