CAIB Briefing Transcript 11 March 2003 (Part 2)

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QUESTION: Can you tell us whether any of the panels six, seven or eight that appear to have been hit in that film have been recovered? And what--if there's any tell-tale conditions on them?

(UNKNOWN): I would have to take that question to be specific. But in the left wing we have recovered a piece of almost every RCC. Now it may be a mounting bracket or something like that, but I believe that we're only missing two or three of the total number of RCCs from the left wing. I don't know if anybody wants to help me with that, but the guide--but to get to your specific question, we'll get back to you on that. But we have recovered some part of almost every RCC panel in the left wing. But so far we have nothing on the left wing--if we had something on the RCC on the left wing which related to this video, we would have told you that immediately. No, so we don't have anything exciting about that.

QUESTION: My question has to do I think for General Barry on the blips here you saw at 62 seconds (OFF-MIKE) How does this play in to what you're looking at? That's interesting as though it might be one of the series of events that happened on this particular mission that played into it. (OFF-MIKE)

BARRY: I've been doing the analysis and trying to figure what was different about this flight. We're trying to pick on anything and everything that stands out as different.

This particular incident had to do what they call the absolute angle. It has to do with the amount that the solid rocket motor moves to be able to (inaudible) either roll or turn the orbiter. This is a software program input that is done on the ground in order to counteract what they know to be a wind sheer up top. What's interesting is this one was the highest and the closest to the max dynamic pressure point that they had on flight.

Now, what does that mean to the mishap? We're looking at this as just another additional stress load on the orbiter on ascent. Now, does that mean that there are anything that contribute to the mishap or are our foam? But this is at 62 seconds. We know the foam that we think came off from the external tank--and we're still, you know, clarifying what exactly that material is--came off at 81 seconds. So we're looking for any of these abnormal--not abnormal--anomalies that might stand out as making this a different aspect. So stress load and stress factors and what we call high (ph) loads also are some of the things that we are looking into on this ascent.

So we're still digging. It's a defective story we take one piece at a time.

QUESTION: Could you just clarify that, when you said this is the most extreme or the second most or--do you mean in all sub launches or some other period of time?

BARRY: What we looked at is what is common. You know, all the shuttles do to different inclinations. They have different external tanks, in some cases lightweight, super lightweight. It turns out Columbia had the two that stand out.

And I can go over this in a little bit more detail with you on slides after we break up. But clearly the two that stand our are STS-90 and 107. And both of them were at 39 degree inclinations. Both of them had lightweight tanks. Both of them were Columbia. And we're just trying to see if there's any kind of a common thread there that might lead us down a path that could give us some kind of an insight into the stress on the orbiter.

QUESTION: I think this is for Dr. Widnall.

Earlier there was some discussion about the breach in the wing, plasma breaching the wing. Has there been any analysis done on the debris that gives an indication where the plasma may have initially--the location where it may have initially breached the wing?

WIDNALL: Well, I think examining the debris down at KSC, I think one sees several interesting things. One sees melted aluminum slag on some of the interior sections of the RCC panels. One sees some very suggestive patterns in some of the tiles and some of the metal around the wheel well. It really is a detective story. I'm not ready to, you know, make any final conclusions about it.

But the debris is really reflecting the heating and aerodynamic load that it saw. So I think there's a wealth of information in that.

QUESTION: But nothing definitive yet?

WIDNALL: I would say nothing definitive. Again, I don't think we want to leap to conclusions too early on this. There's going to be a chemical analysis and material properties analysis.

And, of course, the whole question is, how can you analyze that without destroying the piece? So there's a whole question of what sample size, you know, can we use to get the data without destroying the piece. So that's a really important question.

QUESTION: To follow up on that, Dr. Widnall, is what you're seeing giving you any further indications as to whether gas was escaping out or coming in at the left wheel well?

And also, is the new time line data giving you any further information?

WIDNALL: Well, you know, I'm sure everybody has their favorite scenario on that. The scenarios that are being examined are really a balance, you know, between damage to the leading edge, damage to tiles.

I guess when I think about everything that's being examined, I would say the bulk of those show hot gas going in upstream of the wheel well and exiting in the wheel well. But I don't want to be categorical. There may be some other scenarios that are being examined that have other features.

QUESTION: And the additions to the time line, are they helping you?

(UNKNOWN): Everything helps. I've been over the time line, kind of, line by line myself, and I didn't see anything in there that struck me as being very revealing. A lot of times the more data we get the more it confuses us rather than help us.

But I didn't see anything in the latest revision of the time line. And I'm fully aware of all the issues about the data element that seems to indicate that the stick had been moved.

And there's another one which we are also puzzling over. It's a few seconds before that. I think it's in the first five seconds. It shows a master alarm--a master warning light, which, of course, would have been seen in the cockpit. But the data is not able to attribute what caused the master alarm to go off. So that's interesting, too. Could have been any one of a thousand things by this time, because it's at loss of signal.

QUESTION: Back to the time line--and by the way (inaudible) it's a marvelous document for insight and for questions, especially the very first page, which talks about the earliest known off-nominal external event. It's event sequence number 21 and 21.5. The earliest known off-nominal external event having to do with, first, a left yaw followed a few seconds later by a right yaw, presumably stopping the left yaw motion.

I don't understand what this earliest known external event, off-nominal event is. Is it just the RCS firing or what caused the RCS firing? And do we have any idea why the RCS jets fired at that time?

(UNKNOWN): Actually we don't have any real conclusions on that, other than as we work through the whole time line it becomes apparent that the shuttle, working with the digital flight controls in auto, is compensating up until the very end for the yaw rates that are starting to come onto the shuttle.

QUESTION: And that's occurring with a Q-bar (ph) of under 10 PSF (ph)? How big of a drag, do we have any idea, would that be? Is it a one-or two-square-foot irregularity or is it bigger or smaller?

(UNKNOWN): I think that I might try to pass this off to Dr. Widnall...

(LAUGHTER)

But realistically, this is...

(CROSSTALK)

(UNKNOWN): This is part of the investigative process that's ongoing. You know, they'll actually working through the structural scenarios like this so they can have a full understanding about how much of a problem would have to be present to cause the shuttle to react down the path that's laid out in that chronology that you have there. And we're just not there yet.

(UNKNOWN): Yes. And let me jump in on there.

It's a very good question. And last week I mentioned that one of the things that the time line had demonstrated to us was the impression that things were happening earlier in the reentry than we previously had been given to understand, what you are looking at there.

To me, the question that I take away from that is, even though I understand that yours is a very good question, but to me what it gets to is the question of, which started first?

In other words, did the thermo event cause loss of tiles, and thereby these aerodynamic forces, or did we lose an aerodynamic surface, which then allowed the heat to start unzippering this aircraft? And every time I think I've got it figured out, I get a piece of data which changes my mind.

If the aerodynamic surface were disturbed long before re-entry, well, that then leads you to believe that there was some physical misarrangement on the wing that had nothing to do with entry.

On the other hand, all of our photographic evidence indicates that if there was a physical misarrangement on the wing it was so tiny that it's not visible to anybody else, which would lead you that it was some kind of a thermal event which was the triggering event which then started the unzippering process. And so, the fact that the orbiter was fighting an aerodynamic misarrangement earlier than we previously had thought, it makes my riddle very intriguing, OK?

QUESTION: (OFF-MIKE)

WIDNALL: I mean, I actually, you know, just returning from Cambridge. I haven't really had a chance to study the time line. But you know, it could be one of the situations where the commander leaned on the stick and it would go (inaudible).

QUESTION: Dr. Widnall, could you go into greater detail about what the wind tunnel tests have shown?

WIDNALL: Well, I mean, it's really quite straightforward, and I got a briefing on this.

NASA put a model of the shuttle with a little notch out of the leading edge and measured the moments--the aerodynamic moments. And then compared those with the basically guidance and control analysis that backed out of the flight data what aerodynamic forces must have been acting on the vehicle in order to produce the observed flight behavior, the reaction jets and all the things the vehicle was trying to do. And so out of that analysis is inferred the aerodynamic forces and moments that must have been acting on the vehicle during the last part of the data where the aerodynamic got really serious.

And so they tested the shuttle in the wind tunnel with a notch out of the leading edge. And they found that the--basically, the moment coefficients were--they had their sign right--but the magnitude was about four times smaller than it needed to be. So the obvious thing to do is to--and they will do this--to go back into the wind tunnel and remove more sections from the leading edge and see at what point do you get moments that are comparable to the calculated moments from the guidance and control solution.

QUESTION: Just to follow-up, do you have an idea of how big that notch was (OFF-MIKE)

WIDNALL: I believe it was equivalent to one panel. So roughly speaking, we'd be looking to take four or five panels out of the leading edge, roughly speaking, in order to reproduce the observed flight characteristics.

QUESTION: I'm sorry to keep going, but it went on a curve. What point on that curve are we looking at? At the maximum at the end, or...

WIDNALL: Yes, well, I mean, this was--basically they have data for the entire flight trajectory, up to the point where they had lost their signal. And so, they can back out the aerodynamic moments and relate them to--they know the vehicle attitudes. They can relate it to the vehicle attitude and they can calculate basically the moments that existed on the vehicle. So they can back out the effective vehicle trajectory.

QUESTION: For the admiral, you mentioned that the piece of debris we see in the video is not the only piece of debris that you've--you're aware of. Could you tell us what you're either photo documentation or other evidence has shown you about other pieces coming off during launch, where they might have come from and whether they hit the vehicle?

GEHMAN: From other camera angles with a little bit more sunlight, most photo analysts think that there were a total of three pieces of debris. This is the largest one. In this angle--and by the way, they're all clumped together and they all hit the wing at the same time. So you can't tell whether--you can't tell piece by piece how each one acted from the photography.

In this particular angle, it looks like one piece of debris, but it's all one event. In other words, they all come off at the same time, they all followed the same path, and in one or more of them hit the underside of the wing.

From other angles you can see what appears to be debris number two and debris number three. And they all fly the same path. So you can't discern anything out of it. Now whether or not two of those pieces is foam and one is ice or whether they're all foam with ice on it, I mean, we can't tell that.

But I mean, I just wanted to make sure that the record didn't seem to indicate we're changing our story about three pieces of debris. That's still a good, valid analysis.

QUESTION: For Dr. Widnall, I wonder if you could talk a little bit about this issue of boundary layer prohibitions.

WIDNALL: OK.

QUESTION: Do we know if Columbia was experiencing that transition at the time of the accident? And how big a factor might this be?

WIDNALL: OK, well, at the same briefing that we had on the--basically the aerodynamic affect and the size of the R moments (ph) and the wind tunnel tests that were done on the single panel missing, roughly speaking the--I'm going to get this wrong--asymmetric boundary layer transition--more boundary layer transition on one wing than on the other wing--produces a moment that is roughly comparable to one leading edge panel missing.

In other words, it is roughly a factor of four smaller than the observed asymmetry in the moments, due to whatever damage existed on the wing.

So even if you had a symmetric boundary layer transition, it appears to be a factor of four too small to explain the size of the moments that existed on the vehicle.

QUESTION: So you're saying that has been ruled out as a factor?

WIDNALL: Well, I don't want to rule anything out, but it does not seem to be of the magnitude that was measured in flight.

QUESTION: Maybe for Dr. Widnall: Just to clear up a little bit what the wind tunnel analyses, combined with the data from the flight show--I mean, is there some kind of convergency you're seeing in terms of you think that the debris hit in this, on a sense in this defined area of the RCC and it looks like you maybe need one or more RCCs to come out of the left side of the wing to produce the effects you saw on descent?

I know you haven't settled on one theory, but is there a convergence that you're seeing in these different pieces of evidence on pieces of the RCC on the left wing?

WIDNALL: Well, I'm not going to settle on a single theory, but I've looked at the data and I guess from my point of view what I see is a heating event followed by a very rapidly developing aerodynamic event. And I think the Guidance and Control Group has done a really good job at backing out those aerodynamic forces.

So, you know, the aerodynamic event, when it occurs, is pretty dramatic. And I mulled over that for a while and I looked at the flight profiles and I realized that the aerodynamic event occurs at the time when the dynamic pressure is undergoing a rapid increase of roughly 30 percent.

Now, that makes sense to me that the vehicle was, kind of, coasting along with heat damage, and then there was a sudden increase in dynamic pressure that came from the flight, and that was the onset of aerodynamic--the aerodynamic event. And that makes sense. But I'm not going to speculate.

QUESTION: Yes, just to follow up on that, can you say when in the time line that aerodynamic event was at its maximum?

WIDNALL: I'm having trouble hearing you, but, I mean, it--there is a point in time where the guidance and control analysis indicates the onset of a rapidly increasing, I hate to use the word yaw moment, because it's so technical, but that's--it's the twisting moment on the vehicle.

(UNKNOWN): But you refer to that as a knee in the curve.

WIDNALL: Knee in the curve.

(UNKNOWN): Right. In other words, as the vehicle reenters the Earth's atmosphere, there's a time when the aero forces start going up more rapidly than a straight line and, lo and behold, at that point the orbiter starts to exhibit non-aerodynamic tendencies; remarkably more.

QUESTION: Have you done any analysis, or are you having any analysis done, on the heating from the videotape of the crew to check and see what was burning on the outside, if it was just nitrogen, oxygen? Have you done any analysis in that area?

And also, in your theory of the leading edge, I understand that the first four panels were pretty well badly damaged, you only have the supports of those, and then if you have panel six, seven and eight, that's getting to the area, possibly, of where you have enough to give you this type of aerodynamics that you've been talking about.

WIDNALL: OK, well, those are really two separate questions. Let me take the first question.

My understanding from the crew video is that what was observed on the video was completely normal, completely expected. It is the normal flashing of plasmas that occurs--what?--some five minutes before reentry into the atmosphere?

(UNKNOWN): Six.

WIDNALL: So, again, I'm not discounting anything, but I think that is not connected to the later events.

Now, the aerodynamic--I've, sort of, lost the train of thought on your aerodynamics question.

QUESTION: Well, I was just saying, Doctor, that I understand that the first four RCC panels, that you only have small pieces of them but you have a lot of damage of the supports there.

WIDNALL: Yes, right.

QUESTION: Now, if you have those four opens, open on six, seven and eight, don't you have enough there to give you the aerodynamic drag that you were anticipating?

WIDNALL: I believe so.

But, again, I think one has to go through that scenario very carefully, look at which underlying support structures are severely heat damaged, look at the condition of the individual panels that we do have, and really sort that all out.

I don't want to leap to conclusions at this point.

(UNKNOWN): And we have to compare the left wing to the right wing. It may be that the right wing in-board support structure in RCC may show the same type of heating, in which case the deformations we see in the left wing would be break-up deformations, reentry deformations, rather than the accident cause deformations.

But you're--the underlying understanding in your question is correct. The left wing in general, the pieces of the left wing show more trauma than the pieces of the right wing.

But we aren't to the point where we can pinpoint things yet.

QUESTION: This question is for General Barry. Can you explain something to me just so I'm sure I can understand it, can you explain to me--you said as we followed--no, sorry, you said that the, yes, the ET-93, the external tank, was mated, demated and then remated, and you said there was a report on damage found, it was visually inspected, concluded there was no problem. Can you explain to me what you're talking about there and what time frame this was? What does that mean? Can you clarify?

BARRY: Right, in the fall time frame the external tank was mated to solid rocket boosters. It was subsequently decided that those solid rocket boosters needed to be moved to another mission, so what happened was the external tank was demated and then remated onto Columbia.

So this is something that has happened before, as I understand it, but clearly you have to follow the issue on the foam. A problem report was generated, as you mentioned and I stated earlier, which required a follow-on inspection.

The concern we've got right now is just to see that problem report which we've already investigated and see if there's any more follow-on information that can help us understand cryo-pumping, maybe some additional cracks that might have been in there, we're trying to look at after, or just before last inspections on launch to be able to make that determination.

So, again, as we follow the foam story here, we're trying to look at each one of the iterations, and this is one of those things that stands out as a little bit different, that may or may not be contributing to the mishap.

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