NASA managers hoped to make Discovery the most inspiring sight in the US skies as the space agency prepared for the first Fourth of July launch in history.

The launch attempt came after meetings Monday where NASA managers pondered whether a 5-inch long crack in the external fuel tank's foam, which caused a 3-inch piece of foam to pop out on the launch pad, posed a threat to the shuttle during liftoff.

A graphic from NASA shows the external fuel tank, close-up of the lock speedline bracket showing an area of missing foam and a photo of the missing chunk of foam from space shuttle Discovery's external fuel tank in Cape Canaveral July 3, 2006. [Reuters]

The patch of foam fell off an area that covers an expandable bracket holding a liquid oxygen feed line against the huge external tank. NASA engineers believe ice built up in that area from condensation caused by rain Sunday.

If Discovery gets off the ground Tuesday, it would be the first manned launch by the United States 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.

NASA scrubbed launch plans Saturday and Sunday because of weather.

NASA managers decided to go ahead with the attempt Tuesday because of three criteria: They are confident enough foam still is on the bracket to prevent a large piece of ice from forming; they don't believe the area will be exposed to extreme heat during ascent; and the area of foam where the piece dropped was 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."

The 3-inch triangular piece of foam that dropped from the tank is far smaller than the foam chunk that brought down Columbia. Gerstenmaier showed reporters the piece of foam, which looked like a wedge of toast.

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