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Astronaut to make first in-flight repairNASA decides protruding fillers should be removed
 This NASA image shows a protruding gap filler and tile damage on the underside of Discovery. RELATED
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YOUR E-MAIL ALERTSJOHNSON SPACE CENTER, Texas (CNN) -- NASA will send an astronaut on an unprecedented in-flight shuttle repair mission to remove filler material protruding from heat-resistant tiles on Discovery's underbelly. Analysis showed that protrusions in two areas could produce excessive heat during re-entry and threaten the spacecraft. "It was prudent to take action so that we wouldn't have to worry about some of the worst consequences," said Wayne Hale, NASA's deputy shuttle program manager, at a news conference Monday evening. During Wednesday's planned spacewalk, astronaut Steve Robinson will be dangled from a robotic arm on the international space station and maneuvered to the bottom of Discovery to remove what NASA calls "gap fillers." Gap fillers are thin fabric stiffened with a ceramic material and used to plug gaps between the shuttle's tiles. One keeps tiles from vibrating against each other during liftoff and has no purpose for re-entry. The other is designed to prevent repeated overheating of a gap between two tiles. However, not having it in place during a single re-entry would still be "well within our safety margins," Hale said. If he cannot pull the gap fillers loose, Robinson will use a tool to cut them flush, or nearly flush, with the tiles, so they don't interfere with the shuttle's aerodynamic flow during re-entry to Earth's atmosphere, Hale said. Discovery can return safely without either of the gap fillers in place, Hale said. While the protrusions might not pose any threat to Discovery, NASA acknowledges that "large uncertainty" concerning their potential effect prompted the agency to take action. "Given that large degree of uncertainty, life could be normal during entry, or some bad things could happen," Hale said. The in-flight repair would be a first for the program and is also considered risky, given the potential to damage the craft, said Cindy Begley, the mission's spacewalk manager. The crew is given the option of delaying the spacewalk until Thursday if they need more time to prepare, Hale said. He noted that NASA managers are satisfied that appropriate safeguards are in place to prevent Robinson from damaging the tiles during the operation. During the procedure, scheduled to last 90 minutes, Robinson will only be visible to the other members of Discovery via a camera on the space shuttle's boom. A second astronaut, Soichi Noguchi, will be spacewalking at the same time, but he will be working on other tasks -- among them, installation of an external storage platform on the space station. Earlier Monday, the pair completed their second spacewalk of the mission, replacing a faulty gyroscope on the space station. The protruding gap fillers were discovered during an extensive inspection of Discovery's exterior, carried out by cameras and lasers on the space shuttle's new boom. The international space station crew also photographed the shuttle's underbelly before it docked last Thursday, part of a new inspection procedure put in place after the Columbia disaster. Calculations by NASA experts showed that the protrusions could increase the re-entry temperature by 10 to 30 percent. Such an increase could exceed NASA's safety guidelines for how much heat the shuttle's thermal protection system should be allowed to endure, Hale said. Such protrusions have been found on shuttles after previous flights. But this marked the first time engineers have discovered the anomalies during flight, Hale said Sunday. And it is the first time they have had an opportunity to consider doing something about it, he said. "Our [spacewalk] team, they love a challenge like this," he said. "That's their bread and butter." Copyright 2005 CNN. All rights reserved.This material may not be published, broadcast, rewritten, or redistributed. Associated Press contributed to this report. 
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