HOUSTON – NASA may have to send astronauts on a special spacewalking mission to mend a 3 1/2 -inch gouge on Shuttle Endeavor’s belly that appears to penetrate all the way through two heat shield tiles that protect the orbiter.
Images gathered by lasers and cameras on an extension to the shuttle’s robotic arm confirmed Sunday that the divot went through the 1.12-inch-thick tile, exposing some of the heat-resistant felt-like material below. That material, as well as the tile itself, is designed to protect the orbiter from burning up during re-entry into the Earth’s atmosphere.
“It’s a fairly deep gouge,” John Shannon, chairman of the mission management team, said Sunday. That team will decide either today or Tuesday whether a repair spacewalk is needed, he said.
NASA developed new procedures after foam damaged Shuttle Columbia’s heat shield in 2003, causing the orbiter to disintegrate. On Sunday, Shannon said the agency has the necessary tools and know-how to fix Endeavour’s problem.
“This is exactly what we prepared to do,” Shannon said. “We are in great shape to go and address this exact problem.”
Using data gathered Sunday, engineers will calculate how the divot would react to temperatures reaching 2,300 degrees Fahrenheit on re-entry.
Ice buildup behind a bracket on the external fuel tank popped off a chunk of foam that ricocheted into Endeavour’s belly 58 seconds after launch, shuttle managers said.
The baseball-size chunk bounced off a strut connecting Endeavour to the tank.
There are three repair options if NASA decides a fix is necessary. An astronaut could paint over the gouge with a black wash that would give some heat protection. Two astronauts could screw a heat-resistant plate over the damaged area. Or an astronaut could use a thick, epoxy-like heat-resistant goo to fill the gap.
The black wash has been tested in the shuttle cargo bay on damaged tiles taken to space for that purpose. The other two have been extensively tested on the ground but not in space, Shannon said.
NASA will use computer models of the divot and actual heat tiles under simulated re-entry conditions to help decide whether a repair is necessary.
Sunday’s close inspection with lasers and a camera targeted four additional areas, all in the vicinity of the main landing gear door under the right wing.
Three are smaller divots behind the initial impact, and the other is a less-than-1-inch piece of thermal barrier peeking out of the landing gear door. All were deemed to be acceptable Sunday.
Endeavour astronauts Tracy Caldwell and Barbara Morgan used the shuttle’s robotic arm to sweep the laser extension over the area for about three hours.
Foam-damaged heat shield tiles have been part of shuttle flights from the beginning, but Columbia’s accident brought them into sharp focus.
Columbia’s damage occurred at the lead edge of the left wing, an area that endures temperatures exceeding 3,000 degrees Fahrenheit on re-entry.
The laser inspection Sunday and the slow backflip the shuttle performs before docking to allow high-resolution photography of its underside are two of the procedures put in place after Columbia.
Bracket foam is not a new issue, either. An almost identical piece came off during Atlantis’ launch last September but did not hit the shuttle.
A fix is being made to future tanks. Brackets on the 17-inch fuel line will be titanium, which will not be covered in foam and more resistant to icing. The tanks scheduled for the next three shuttle missions, however, will not have the modification.
Shannon said there will be thorough analysis after Endeavour returns before the next shuttle flights would be cleared.
“We have a lot of discussion to have before we fly the next tank,” Shannon said.
Shuttle managers were encouraged Saturday to find that the gouge is directly over a rib in the wing’s aluminum skeleton, providing more heat resistance.
On Sunday, managers decided to extend the mission to 14 days from 11 days to allow more work on the international space station. That extension will push back Endeavour’s landing to Aug. 21.
A new system on Endeavour allowing it to draw power from the International Space Station has worked well, permitting the shuttle to prolong its stay.
The extension also permits a planned fourth spacewalk on Friday, when astronauts also would carry out the repair mission if it’s deemed necessary.