CAPE CANAVERAL, Fla. (AP) - NASA signed off Monday night on a Fourth of July shuttle liftoff despite worries about a piece of foam that popped off Discovery's external fuel tank while the spacecraft sat on the launch pad. "We're go to continue with the launch countdown," said Bill Gerstenmaier, NASA associate administrator, at a nighttime briefing. The decision for the 2:38 p.m. EDT Tuesday liftoff was sure to stir more debate about whether the space agency was putting its flight schedule ahead of safety even though Gerstenmaier said "there were no dissenters ... no concerns raised" at a meeting of managers.
He said the astronauts and NASA administrator Michael Griffin were in on the discussion. Griffin "didn't raise any question or comments but he listened intently," Gerstenmaier said.
The 3-inch triangular piece of foam that appeared to come from a 5- inch-long crack late Sunday or early Monday is far smaller than the foam chunk that brought down Columbia, killing seven astronauts in Gerstenmaier showed reporters the piece of foam, which looked like a wedge of toast.
"I don't think we're taking any additional risk than we did in our original assessment" in going ahead with a launch, he said.
Managers had spent most of Monday pondering the problem. NASA has spent millions of dollars trying to prevent foam from breaking off at liftoff, threatening the kind of damage it did to Columbia. Engineers were startled when it broke off Discovery during last year's mission, but it didn't harm the shuttle.
The loss of foam from that area of the tank while on the launch pad is a rare occurrence, happening only once before, Gerstenmaier said.
Some outside experts familiar with shuttle foam loss problems were concerned about plans to launch Tuesday.
Carnegie Mellon University engineering and risk analysis professor Paul Fischbeck, who had been worried earlier in the day by the falling chunk of foam, said NASA's rationale in going ahead made sense and he is slightly more comfortable with a launch try Tuesday.
Fischbeck, who has consulted with NASA on the shuttle's delicate heat protection system, wondered why foam had broken off on the launch pad. "It's something you might want to understand before you launch," he said.
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.
The tank expanded when the super-cold fuel was drained after Sunday's launch was canceled because of the weather. The ice that formed "pinched" some of that foam, causing the quarter-inch-wide crack and the piece of foam to drop off, officials said.
The size of the fallen foam was less than half the size of one that could cause damage, NASA officials said.
NASA managers decided to go ahead with the launch attempt because of three criteria: They are confident enough foam still is on the bracket to prevent a large piece of ice from forming; that the area of foam where the piece dropped was still intact; and they don't believe the area will be exposed to extreme heat during ascent.
Inspectors spotted the crack in the foam insulation during an overnight check of the shuttle. NASA had scrubbed launch plans Saturday and Sunday because of weather problems.
The forecast for a Tuesday liftoff was better than previous days, with just a 40 percent chance that storm clouds would prevent liftoff.
Griffin decided last week that the shuttle should go into orbit as planned, despite the concerns of two top agency managers—including the top safety officer—who wanted additional repairs to the foam insulation.
But the two agency officials said the foam loss will not threaten the crew because NASA has a plan for the astronauts to move into the international space station if in-orbit inspections find is serious damage to the spacecraft. The crew would await rescue 81 days later by second space shuttle.
The mission for Discovery's crew this time is to test shuttle- inspection techniques, deliver supplies to the international space station and drop off European Space Agency astronaut Thomas Reiter for a six-month stay.
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AP Science Writer Seth Borenstein in Washington contributed to this story.
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