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Astronaut Repairs Heat Shield on Spacewalk


This is MORNING EDITION from NPR News. I'm Linda Wertheimer, in for Renee Montagne. She's on vacation.

Astronauts Stephen Robinson and Soichi Noguchi are back in the airlock. They've returned from this morning's space walk. While they were outside the spacecraft, Robinson plucked two small pieces of ceramic fabric that were protruding from the space shuttle's delicate heat shield.

(Soundbite of Discovery communication)

Unidentified Man: The brakes are on. You're a go.

Mr. STEPHEN ROBINSON (Discovery Crew Member): OK, I'm grasping it and I'm pulling; it's coming out very easily.

Unidentified Man: Beautiful.

WERTHEIMER: Those pieces of fabric have been worrying NASA engineers because anything sticking out of the heat shield could disturb the airflow around the shuttle when it tries to return to Earth. It's scheduled to land on Monday. NPR's science correspondent David Kestenbaum joins us now to update us on the space walk.

First of all, can you tell us what they are doing now?


Well, they've finished pulling both pieces, and so now they're heading back to stow the tools. But it took--the whole thing took sort of a long time to set up. Stephen Robinson had to put himself in these portable foot holders on the end of the robotic arm, and they had to be very careful to tie up all his tethers so there was nothing swinging around, and they took off all the extra tools that he'd been carrying so that he wouldn't bang anything when he was underneath the space shuttle.

No one has ever gone under a space shuttle on a space walk before, and they really like to keep people away from there because the tiles are delicate and they're really important for being able to do a safe landing. So once they had him strapped in, they moved the arm out around and underneath the space shuttle, and they read him some warnings, basically saying, `Please try not to hit anything,' and then when he was getting close they asked Robinson if he could see it.

(Soundbite of Discovery communication)

Mr. ROBINSON: Yeah, I can see it pretty well.

Unidentified Man: How far are you from it, by the way?

Mr. ROBINSON: I'm about eight feet from it--maybe seven feet, the--looking just about straight down on it. It's up to my right by just six or seven inches. It looks to be about close to three inches on one side and about an inch and a half on the other side. The corner looks like it has been bent over and then flipped back up in the vacuum. I guess I'm ready to go in and get it when you are.

KESTENBAUM: So he could see the strip really clearly there. The camera images were coming back from the top of his helmet, and they were sort of intermittent because he was blocked; some of the transmission line was blocked because he was underneath the shuttle. But he said that the bottom of the shuttle looked stunning; it was like a work of art. And then he pulled on the strip and he said it--he estimated it was a pound and a half of force he applied, and it came right out, and they moved over and he pulled the second piece out.

WERTHEIMER: Well, let's just--remind us why these pieces of fabric were a problem.

KESTENBAUM: Well, the concern is that--there actually was an example in 1995 when the shuttle Columbia was coming back in, and it experienced some extra heat, and after it landed they looked and they saw there was a teeny little piece of this fabric that was sticking out. And the reason it causes trouble is because when the space shuttle's coming in at the upper edges of the atmosphere, the air is flowing really smoothly over the wings, and that creates what's called laminar flow, and it creates sort of an insulating layer, which helps protect the belly of the shuttle. And then turbulent flow sets in at some point and it gets warmer. And so they're worried that the piece of fabric there would cause the turbulent flow to start earlier, so you'd get greater heating. And in that case in 1995, the heat temperature rose by several hundred degrees in some places.

WERTHEIMER: Now this space walk takes a while. Everything seems to operate fairly slowly, even though they got--they seemed to get those pieces of fabric more quickly than they had planned on doing it. What else are they doing out there?

KESTENBAUM: Yeah, actually, this was sort of the second or third thing they actually did. It's what everyone on Earth seems to be paying most attention to. But first they attached this platform that has some spare parts and tools for future missions, and then they actually put a science experiment up. It's a material science experiment and it's going to be radioing back information about some materials that are in it that are exposed to the vacuum of space, down to Earth to some naval researchers.

WERTHEIMER: Now how do you think the crew feels at this point about the shuttle's safety? This is the first time a repair like this has ever even been attempted.

KESTENBAUM: I think they have to feel really good, especially that it went so well, but also--you know, it used to be they'd sort of cross their fingers and assume the bottom of the shuttle was OK, and now they've really gone over every inch of it. So I think the managers on the ground and the astronauts will feel, in some ways, more confident than ever before that they're heading back to Earth with a shuttle that's in really solid shape.

WERTHEIMER: Thanks very much.

KESTENBAUM: You're welcome.

WERTHEIMER: NPR's David Kestenbaum. Transcript provided by NPR, Copyright NPR.

David Kestenbaum is a correspondent for NPR, covering science, energy issues and, most recently, the global economy for NPR's multimedia project Planet Money. David has been a science correspondent for NPR since 1999. He came to journalism the usual way — by getting a Ph.D. in physics first.