JIM LEHRER: Finally tonight, Ray Suarez looks at the shuttle's troubles.
SPOKESMAN: Top of Discovery about 20 seconds to photo start --
RAY SUAREZ: The underbelly of a space shuttle is a place no astronaut has ever been while in orbit. But today NASA scientists pondered whether or not Discovery's astronauts should be the first to venture there and remove material known as gap filler that is dangling from between the shuttle's protective thermal tiles. NASA officials have been studying whether the gap fillers in question could disrupt the airflow of the shuttle on reentry and lead to dangerous overheating. Today, NASA officials were asked if they spent a lot of time planning for a problem like this.
PHIL ENGELAUF, NASA Mission Operations: I won't say it didn't cross anybody's mind, certainly of the areas that the ops community has worked with, things that we're trying to respond to, this was not one of the big- ticket items. We have had gap fillers again. We've returned with them on the vehicle protruding in the past, again, without detriment but also somewhat in ignorance because we've never had the opportunity to observe the way we have now. (Clears throat) Excuse me. And this was not frankly one of the things we had spent a lot of time working on over the last two years
RAY SUAREZ: On today's seven-hour space walk, astronauts replaced a broken gyroscope used for steering on the international space station. While outside Discovery, they also removed a pry bar and forceps from an outdoor toolbox they might use for their next big repair job on the gap fillers.
Here to walk us through the decision NASA faces today is Keith Cowing, editor of NASA Watch, an online space publication. Welcome back. What is the material sticking off the bottom? What is gap filler?
KEITH COWING: Well, gap filler is a material that's sort of a silica fabric that when they put the tiles underneath the space shuttle orbiter there's a little crack, like with any other tile. You put this material in between it. And what it does is when the orbiter goes through some of the dynamic temperature changes it prevents the tiles from abrading each other, possibly damaging each other. Normally you rarely have this problem but occasionally a piece will pop up like this, and as was shown in your graphic, the air flow can be changed as they're coming back into the Earth's atmosphere, which can cause undesired heating in the under parts of the underside of the orbiter.
RAY SUAREZ: So that spot where it's sticking out, if I follow you, gets hotter than the rest of the surface that's heating up.
KEITH COWING: Actually, it's not that spot, but it's downstream. It changes the air flow such that the temperature -- there's a boundary layer that when the orbiter comes into the Earth's atmosphere as it slams in at 10,000 miles an hour, this layer of gases insulates to a great extent the orbiter from the even hotter gases outside. When you disrupt that current, an eddy forms and somewhat downstream, so to speak, it could get hotter.
RAY SUAREZ: If this gap filler sticking out -- and it is a matter of just like an inch and a half was sticking out somewhere else on the ship -- would it be viewed as less critical and less of a problem?
KEITH COWING: Well, like anything, it would be an issue, but it's right sort of near the gear doors and I know they're concerned about it because they've never really had the chance to look at the stuff in flight before. So they never really have been faced with having to deal with it. So it's automatically a concern especially in the post- Columbia environment.
RAY SUAREZ: Now, today as we showed in the earlier taped report, the astronauts were doing what's called an extra-vehicular activity, a spacewalk. They had some jobs to do. Why is it considered such a big thing to get them along the underside of the craft to do another extravehicular activity?
KEITH COWING: Well first of all it's never been done. So it has the advantage of being the first time you've actually attempted to go underneath. And second of all the geometry: You have the robot arm and the wires and so forth that the astronauts are connected to but to get underneath the orbiter is quite a bit of geometry even with the extension on the robot arm. And the real concern is that in so reaching underneath and around the orbiter you might actually bang into something and cause more damage. So it's like a ballet.
RAY SUAREZ: So in making a decision to fix the problem along the underside, you also have to take into account the risk of breaking it even worse.
KEITH COWING: Absolutely.
RAY SUAREZ: Wow. Are there tools? Are there trainings that someone does before they even go into space to understand this material and how it functions when it's in zero gravity and orbiting the Earth?
KEITH COWING: Well luckily they didn't spend a lot of time worrying about this. Quite frankly what it is, is it's a flexible material sticking up between the tiles. And either they're going to try and push it back in. If they can't do that, they may try to snip it off or they may just pull it right out. And they have tools, pliers and so forth, with which they can do that. So it should be straightforward.
RAY SUAREZ: Earlier today, every time they were asked during the news conference whether this is a big risk or a small one, engineers kept responding "we just don't know." Why don't they know whether it's a big risk or a small one?
KEITH COWING: They're learning as they go. And this is the first time again that they've been able to actually diagnose this issue on orbit during a mission and actually have the capability and the willingness to go out and actually try and fix it. So this is, to a certain extent, unknown territory for them. I think what you're seeing also is the rethinking of how safety is done at NASA now. And you're seeing played out in public a process that normally would have happened behind closed doors and you're seeing NASA being confronted with something that is not unexpected but wasn't in the high list of probabilities. Now suddenly they have to deal with it. And you're seeing in real time how they're going through the process of evaluating the risk, seeing if it's worth incurring other risks to go fix it or not. So I think it's a very healthy process that you're seeing them admit that they don't know something and that they're dealing with it.
RAY SUAREZ: Is it also because it's just hard to make a simulation to figure out what it is that you have to be worried about?
KEITH COWING: It's kind of like if you worried about absolutely everything that could ever go wrong you'd never launch the shuttle. At some point -- and you'd have an endless army of people figuring out every conceivable thing that could go wrong. They're very smart people at NASA so I'm sure they could come up with a lot of things to worry about. At some point you have to fly the shuttle. You have to say, all right, "We know this could happen, and we have to be prepared to deal with it if it does happen."
RAY SUAREZ: Are we watching in effect the new world, the post Columbia world and the post Columbia investigation world where things that they might have blown off in the past and indeed there have been landings with gap filler sticking out in the past, they just aren't so sure they're going to rush right into it.
KEITH COWING: Absolutely. I think you are seeing a NASA safety system that was, you know, clearly they've had two shuttle accidents now but this most recent one really got to the core of how they do business. You see people like Wayne Hale explaining this in great detail. I think you're really getting an insight into how NASA has really sort of re-looked at how they do everything as it comes to safety. Just because they've seen something before they no longer say, "Well, we've seen it before and it didn't come back to bite us." Now they're thinking, "Well, maybe there's something to that." So I think it's a healthy change.
RAY SUAREZ: If NASA confirms tonight that it's going to launch another extravehicular activity and astronauts are going to head out and go to the underside of this craft and take a close look at it, is there an upside? Are there things they'll learn from the act of doing that?
KEITH COWING: Yeah. They'll have done that. It will no longer be unknown territory. It's one more thing that you need to do if you're going to fly the space shuttle and you're going to want to have the ability to detect and fix things in orbit. The next time there could be a tile on the underneath of the shuttle that needs to be repaired, that could be a much more complex activity. And having done this once, you'll now know what to expect next time. That reduces the risk of doing it on subsequent missions.
RAY SUAREZ: We've just gotten word from mission control that they are going to go ahead with that repair mission and fix the two patches there that are sticking out. What should they be keeping in mind and what do they have to do between now and Wednesday?
KEITH COWING: Well, it's going to be, like I said, an intricate ballet with one astronaut-- I don't know which one it'll be -- actually inspecting and doing the repair while the other is likely going to be spotting him. Clearly they'll want to be able to see everything that's going on to be certain that the arm doesn't bump into anything and that the crewman himself doesn't put himself in harm's way. I think they're also going to want to document this to the greatest extent possible again for the reason that if they ever have to go back to do this again they'll have a very good record of what it took to do it the first time.
RAY SUAREZ: And this is not something where you just, "oh, hold on a minute. I'm going to run out and fix something." This is probably something that takes several hours, no?
KEITH COWING: The actual repair may take probably a few minutes. It's getting there, being certain you're not going to hit anything, assessing the situation. And then it's either again they're going to push it in, pull it out or snip it. That should take a very short period of time. It's the preparation that's the difficult part.
RAY SUAREZ: So what are we looking at as an envelope getting out there, coming back?
KEITH COWING: Oh, you know, they may do some other things. While they're there they may just look around and again use the time while they're underneath the orbiter to get some camera views, to see what it's like to work there and so forth. They're going to take advantage of the situation to learn more. I'm sure just the process of coming back will also take them to some other parts of the orbiter they may not be inspecting but have been seen before from that angle during flight.
RAY SUAREZ: Keith Cowing, thanks for being with us.