NASA will go ahead with Tuesday's scheduled launch of the space shuttle Discovery after examining a pencil-sized crack in the foam insulation around the shuttle's fuel tank, the space agency announced.
"It all looks fine, and the structure is in good shape," Associate Administrator William Gerstenmaier told reporters.
Discovery is scheduled to lift off from Cape Canaveral at 2:37 p.m. Tuesday. That would mark the first time a shuttle has taken off on the Fourth of July.
The launch, already scrubbed twice due to bad weather, was threatened a third time Monday after an inspection found a four- to five-inch crack in the external fuel tank's foam insulation.
The cracked insulation covered a bracket that connects the liquid oxygen feed line to shuttle Discovery's external fuel tank.
Engineers believe the problem stemmed from a buildup of frozen condensation that crushed a small piece of foam, Deputy Program Manager John Shannon told reporters earlier Monday.
When engineers went to inspect it, they found a .0057-pound, 3- inch piece of foam had "pinched off."
Even so, Shannon said, had that piece fallen off during launch, it wouldn't have damaged the orbiter.
"It turns out there is more foam on this strut than is really needed for its intended purposes," Gerstenmaier said.
Investigators blamed a 1.6-pound piece of foam insulation falling off the external fuel tank for the damage that caused the loss of Discovery's sister ship Columbia. All seven astronauts aboard the shuttle died when it broke up on re-entry over Texas in February 2003.
NASA managers huddled well into Monday evening after discovering the problem.
"I think it would not have gotten as much attention prior to Columbia as it is getting now," Shannon said. "I think it's a very good thing that we have this sensitivity and that we're looking this closely at the vehicle."
Tuesday's planned launch would be the second shuttle flight since the Columbia disaster.
The crack was discovered during an inspection Sunday evening, and is an eighth- to a quarter-inch wide, NASA said.
The Mission Management Team met Monday morning and again in the evening to go over possible scenarios -- including a possible fix.
For a repair, NASA would have to build a platform that would reach out to the bracket, which would allow engineers to make the fix, according to NASA spokesman Bruce Buckingham.
That would have taken more than a day and delayed Tuesday's launch.
But Buckingham said that still wouldn't have pushed the launch beyond a window of time that closes July 19.
There are two concerns with the cracked foam. First, it could fall off during launch, and the piece is close to the belly of the orbiter. The second concern is that ice could form in the crack, causing it to expand or the ice chunk to fall.
NASA postponed the launch of the shuttle Discovery on Saturday and Sunday because of bad weather.
Weather conditions for Tuesday give NASA a 60 percent chance of launching. Those odds drop to 40 percent on Wednesday, according to U.S. Air Force 1st Lt. Kaleb Nordgren.
No launch attempt was scheduled for Monday because the weather forecast was even worse, and because NASA needed time to top off the fuel cells that provide power while the shuttle is in orbit.
If the launch hasn't happened by July 19, the next window for the mission will open in late August.
Those windows of opportunity are determined by the path of the orbiting international space station, the shuttle's destination.
With each passing day, the time for a launch gets earlier by 22-1/2 minutes. That could be good news for NASA because summer thunderstorms are less likely to be a problem earlier in the day.
Plans call for a 12-day mission to deliver supplies to the space station and drop off European Space Agency astronaut Thomas Reiter, who will join the Expedition 13 crew members already there.
Two astronauts, Piers Sellers and Mike Fossum, will conduct two spacewalks, to test a new shuttle robotic arm and to repair a damaged piece of equipment outside the space station.
They might also do a third spacewalk to test repair techniques on the shuttle's thermal protection system.
NASA's decision to resume shuttle flights this summer is not without controversy.
In the weeks leading up to the launch, two NASA officials, chief engineer Chris Scolese and chief safety officer Bryan O'Connor, gave a "no go" for the launch.
Program manager Wayne Hale said NASA engineers have learned a lot about foam dynamics in the past year, but there is no way to stop the foam from flying off the tank.
NASA Administrator Michael Griffin called the disagreements with the repairs a good sign that the culture at NASA has changed. The agency was faulted by the Columbia investigation board with having a conformity of opinion.
"I personally want every engineer to express the best opinion that they can give us," Griffin said.
He and top senior officials took into consideration O'Connor and Scolese's concerns but concluded that if falling foam damages Discovery, engineers will know about it, and the crew can take refuge on the space station and wait for a rescue mission.