Shuttle Ready After Window Problem

NASA resolved the last few technical concerns about Discovery on Tuesday and pronounced it ready for launch on the first space shuttle flight since the Columbia disaster two and a half years ago.

"We're go for launch tomorrow, pending the weather," NASA Administrator Michael Griffin said Tuesday.

CBS News Correspondent Bob Orr reports that there was a last minute glitch. As crews were removing the lightweight panels that cover the cockpit windows, one of the panels was dropped and fell more than 60 feet before striking a bulge in the fuselage. NASA quickly fixed the problem and said it was still on track for launch Wednesday.

The mishap was an eerie reminder of the very thing that doomed Columbia — damage to the spaceship's fragile thermal shield.

Stephanie Stilson, NASA manager in charge of Discovery's launch preparations, said that two tiles on an aluminum panel were damaged and that a spare panel was installed in its place late Tuesday.

Discovery and its crew of seven were set to blast off Wednesday afternoon on a flight to the international space station. The biggest worry was thunderstorms in the forecast.

Discovery is scheduled for blastoff at 3:50:52 p.m. Wednesday and forecasters say they expect a 60 percent chance of good weather, reports CBS News Space Consultant Bill Harwood.

Griffin said that the remaining technical concerns "had been put to bed" and that NASA managers had engaged in a free and open exchange of ideas before giving the go-ahead.

He said that given the complexities of spaceflight, something unforeseen could come back and "bite us." But he added: "Everything we know about has been covered."

Investigators in the Columbia accident blamed the tragedy in part on the space agency's "broken safety culture," or a tendency to downplay risks and discourage engineers from speaking up. Since the disaster, NASA has worked to increase openness and respect dissenting opinions.

"Obviously, it is utterly crucial for NASA, for the nation, for our space program to fly a safe mission," said Griffith, who is overseeing his first launch as NASA chief. He added, "We have done everything that we know to do."

Wednesday's scheduled afternoon launch is the first since the Columbia disaster 2½ years ago.

Discovery is outfitted with dozens of motion and temperature sensors embedded in the wings to detect any blows from fuel-tank foam insulation or other debris. The spaceship also holds a brand-new laser-tipped 50-foot boom that will be used by the astronauts to survey the wings and nose cap for any cracks or holes.

More than 100 cameras on the ground and aboard two planes will focus on Discovery as it climbs toward orbit, and spy satellites as well as astronauts on both the shuttle and the international space station will take their own pictures.

Engineers this time should be able to see damage if it occurs, reports Orr. While they've experimented with different repair technique, they will not be able to repair any significant damage in flight.

But the greatest technical change since the Columbia accident is the redesigned fuel tank, reports CBS News Correspondent Peter King.

"Before STS-107, we had debris coming off the tank that could be as large as two pounds or so," said flight director Paul Hill. Now he expects miniscule pieces of debris from the new tank, "about two-hundredths of a pound of foam" — much smaller than the five-pound piece that punched a hole in Columbia's wing two and a half years ago.

Discovery's crew of seven is slated to visit the international space station and test out some of the fixes made since the last space shuttle visit. The shuttle will spend more than a week at the space station, replenishing its cupboards and repairing broken equipment both inside and out.

"It will be a very exciting time. People's hearts are beating, we're getting excited about the upcoming flight," said

NASA managers agreed they were exuberant in the final days before launch.

"It's like Christmas is coming," Hale said.