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Space Shuttle Astronaut Performs Heat Shield Repair


To the great relief of the U.S. space agency NASA, a spacewalking astronaut has solved a problem with the shuttle Discovery's exterior heat shield. But mission controllers say another irregularity might require an additional spacewalk.

Shuttle managers admitted they were apprehensive about sending astronaut Steve Robinson out to Discovery's fragile underside, where some ceramic tiles had already been chipped by launch debris falling from Discovery's external fuel tank.

But NASA officials felt they had no choice. Two pieces of heat-resistant fabric wedged between the tiles had popped out a few centimeters, threatening to make the searingly-hot, but normally smooth airflow beneath the shuttle even hotter by creating pockets of air turbulence during Monday's re-entry.

So astronaut Robinson was moved cautiously to the area on the end the robot arm mounted to the International Space Station, where Discovery is docked for a maintenance visit. He carried only the tools needed for the job, forceps and a hacksaw, for use if he could not pull the fabric out with his fingers.

Inside Discovery, astronaut Andy Thomas warned him to move very carefully.

"I think it goes without saying that we don't want to see inadvertent contact with tile or the belly of the orbiter," he says. "If by any chance you do need to contact the tile with your hand, we require only gentle hand reaction loads and we want you to distribute the load over several fingers or use the back of the fingers."

The job turned out to be easy. Mr. Robinson simply plucked the first piece out with his glove, then did the same to the other one a few meters away.

"Here we go. Okay, that came out very easily, probably even less force. It looks like this big patient is cured," Mr. Robinson says.

On the ground, NASA relaxed a little. The lead shuttle flight director is Paul Hill.

"I was absolutely relieved, and I think you could probably hear the sigh of relief throughout the building over there," he says. "When he pulled the second one out, it was a huge relief, and it definitely felt like the rest is downhill from here."

But one more problem is worrying mission control. A small piece of insulating blanket beneath the shuttle commander's window ripped during launch, perhaps torn by the falling debris. Deputy shuttle program manager Wayne Hale says there is concern it might tear away during the high-speed re-entry and threaten the shuttle.

"Worst case, we could do some structural damage, and that's obviously not something that we want to incur," Mr. Hale says.

NASA engineers are working overtime in a wind tunnel to analyze the force with which the blanket strip, weighing just 22 grams, could hit the shuttle. Mr. Hale says that this work, combined with the recent late night analyses of the loose tile gap filler fabric and the tile damage caused by the launch debris, has put unusual stress on Discovery's ground support team.

"The team is getting tired, quite frankly. This has been quite a workload to try to solve these problems on the ground," Mr. Hale says.

If engineering analysis shows the torn blanket to be a re-entry threat to Discovery, NASA is considering another spacewalk to remove it as one possible solution.