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Columbia Accident Investigation Board Roundtable
Thursday, June 12, 2003

2:30 p.m.
National Transportation Safety Board
Conference Center
429 L' Enfant Plaza, SW
Washington, D.C.




MS. LAURA BROWN: Okay. I think we still have a few stragglers outside, but I'm gonna get started here.

My apologies to the people on the phone bridge. We're gonna try to get questions in from you before we loose the bridge at 3 o'clock, but I'm gonna get Scott started here. He is gonna give you an update on where we are with the foam testing.

MR. SCOTT HUBBARD: Okay, thank you very much.

As we've done a few times before, I'm happy to give you a briefing this afternoon on the latest tests against foam hitting the reinforced carbon panel six. We're gonna go to the first set of slides, please?

Right, let's go to the first – there we are. I think everybody knows that we conducted the tests at Southwest Research Institute in San Antonio. Several of you were there as we conducted the tests and you know that we have a large outdoor facility – it's a nitrogen powered gas gun that fire a piece of foam through a 30 foot barrel and that that impact occurs against a mock-up of the wing leading edge and it's built as close to flight specification as possible, including in key areas actual flight hardware.

Let's go to the next slide. The projectile that we used is the same foam that was used for the bipod ramp, the so-called BX-250, and I've got the dimensions and the velocities and the masses, both the planned and the actual. We have, thanks to a lot of people and a lot of analysis, settled in on a 1.67 pound foam piece traveling at 775 feet per second as the projectile that is most representative of what happened during the accident. So, the planned mass was 1.67, the weighed actual projectile in this test, 1.68. Dimensions, as you see there, about five-and-a-half by eleven-and-a-half by twenty-one inches in this case. The actual dimension length will change slightly, that length and width are determined by the – or the width and the height are determined by the barrel and the length is adjusted in order to get the mass.

The mass is the constraint that we work to, the 1.67 pounds. We planned for velocity of 775 feet per second. We got 768, so within a percent or so, the angle of the impact relative to the wing leading edge, 20.6 degrees. And the angle of the gun barrel, that is to say whether it was vertical or slanted was straight up and down and we call that a clocking angle of zero degrees. So, that was the set-up and the projectile.

Next picture. The test occurred at Southwest Research June the 6th and we hit within a quarter inch of the planned target so that accuracy of this gun seems to be quite reproducible and quite good. The foam, as you'll see in the high speed video in a minute and for those of you who were there, you know it broke into small and large pieces, resembling to a large extent, what we've seen in the actual video of the accident.

I will point out that in the video that most all of you have seen of the strike in the accident, it appears that there were more smaller pieces than in what was observed at San Antonio and the tests that were done at Glenn Research Center prior to this investigate – or prior to this experiment showed that in a vacuum, it looks like the foam breaks up into smaller pieces, so that accounts for the difference. However, when we measured the actual loads, we found that there was no difference. So, that's why even though the appearance is slightly different, we are confident that we're reproducing the actual event itself.

You see the post test. Many of you saw this for yourselves. The projectile had been inked so as to leave streaks and outlying the area of the impact and it started at the impact area in T-seal 6 and then went on to cross the T-seal – started in panel six, went across the T-seal and then on to the fiberglass panel seven. And you can see little dips of foam that were caught in the area between panel six and the T-seal.

Next slide. Okay, here is the first of two high speed videos that show the impact, show the piece breaking up and if you look closely, you can see the deflection of the panel. I'm going to show in a little bit, another view from the inside of the wing leading edge that shows the violence of this impact much more directly. The deflection of the panel is less in RCC than in fiberglass and that is directly attributable to the material. The material itself reinforced carbon is a much stiffer material, although it does not have the strength of fiberglass. Fiberglass is more flexible.

So, as you can see the break-up, the impact, the streaks and what we'll do now is go to some of the analyses after the tests of what happened. Initially, we measured about a three inch crack. We've gone and made a much more careful measurement and the total length measured along the entire length of the crack is about five-and-a-half inches. It goes all the way through the thickness of the reinforced carbon panel. It is located on what is called the lock side. I have the model here and just to remind everyone or perhaps explain it if you haven't seen this before that a reinforced carbon panel and the T-seal have two sides. One is called the flip side and that's the side where it – this element, the T-seal could actually slide back and forth a little bit and take up minor differences.

And then there's the lock side. There's a groove – there's a groove here where the T-seal locks any two. So, this is the slip side, this is the lock side, this T-seal has on it a corresponding groove and then a smooth edge. And so, this is the lock side here of the T-seal, this is the lift – slip side of the T-seal, so the damage that was observed was on the lock side, between panel six and panel seven.

It – the damage wrapped around the entire rib and showed up eventually as a three-quarter inch crack observable on the surface. Most of the length of the observable damage is seen from the inside. Next slide.

This is – some additional pictures showing the crack from different vantage points. I think the one thing to note here is although the shuttle program largely deals in English units, the people who have made these measurements have put up centimeter scales. So, just be careful. Having had Tom Young on the panel earlier, we know that it's important to distinguish between English units and metric units. So, these rulers here in centimeters, so if you download these from the Web site, be sure that you recognize that the dimensions in the briefing are all in English units.

MS. LAURA BROWN: Is there a Martian in there?

MR. HUBBARD: Not that I know of.

So, that was the first damage that was visible. We reported that right after the test. A little bit later that same day, a more careful inspection, closer inspection, showed that the T-seal was cracked. This is an actual piece of T-seal here and what's cracked is not the surface here, but rather what's called the “web” – and that is this piece down here. It's the chunk that goes in-between the leading edge and the next panel, it's this unit right here, not the outer surface, but this piece, that's where the crack is, about two-and-a-half inches long.

And an x-ray that was done at Southwest Research the next day show that this crack extends all the way into what they call the fillets (sp), that is the material at the bottom here. So, there is damage that is not apparent to the naked eye and that's one of the issues that we'll continue to look at with this particular panel is how much damage is there that is, in fact, hidden from simple visual inspection.

Next slide. There is an additional crack that was found on the flange of the panel six. Out here, you have a way to attach these panels to the rest of the structure. You have to have a mechanical attachment with bolts and what are called spanner beams and so forth. There is a panel – I mean a crack there right around this fitting a so-called sheer fitting. It's part of what attaches this to the rest of the structure, about three-eights of an inch long. This is a point where stresses get transferred from this unit into the rest of the structure that holds it to the orbiter. It doesn't appear to go all the way through, but it is evidence of more damage and damage that gets down to the structure of the orbiter.

Next chart. This is something that we noticed right on the site at the time which was about a one inch square divot, a piece of material knocked out of the carrier panel. It looks like this was a repaired area. And this is, of course, makes you think about all the repairs that have occurred to the orbiter over the years and I think this will be an element of what needs to be examined in the future is whether or not the repaired areas, in fact, are as strong as they need to be. This particular piece of damage was relatively small.

Next chart. Now, here are some displacements. When you look at what is called the step in the gap. The step refers to how smooth the panel is. When you put it all together, it's supposed to be a very, very small difference across the surface. Perhaps, I think, the specification is 40 thousandths or less difference, and then you look at the gap. That's how closely do these pieces fit together. Is there a significant seam here or not? That is also supposed to be in the tens of thousands per specification. Well, we found that the step and gap showed a change of about twice the flight spec post-test, compared to pre-test. This may be due to the fact that the foam got lodged in here and spread the T-seal relative to the panel. There was also a change in – on the other side of the T-seal and the slip side is down here of about 30 thousandths. So, they were significant in the sense of being a factor to more than what you would set as a flight specification, although small in the absolute number.

Next thing I want to show is a very interesting video from inside the wing leading edge. And I'm just gonna let it play first and then I'm gonna come back and describe in a little more detail what you're seeing. You can see the violence of the shot, the shaking, and then if you'll watch briefly at the end, you will see, well, I see it's looped here. Okay.

Let's go to the next slide and come back to this. These are three stills taken from this high speed video. We were lucky in having six cameras in there. One of them pointed at the exact area where the crack appeared. So you can, in fact, if you look a the video carefully on your monitor, see before the impact, you can see the crack beginning to appear right here, you can see the crack growing, and then you can see – see this difference in space in here? You can see this actually pulling apart to a maximum deformation then snapping back together again.

So, why don't we go back and repeat this and watch, oops. Watch right up in here.

Yes, so you see some foam puffing through there at the end. You know, this looks like a long time period, but remember you're looking at millis – you know, tenths of milliseconds here. And you can see if you look over here the deflection and the shaking of the RCC panel. I the longer version of this video, you see very briefly at the end the flash of light, which is actually daylight coming through. The force of the impact was sufficient to actually spread the panels apart briefly, let the daylight in and then it closed back up again. It says we opened it up to the atmosphere, the external part of the wing-leading edge.

So, I think the importance of this is to show that this is not a static event. This is a dynamic event and that this crack, depending on what was happening, what kind of force it was under, could be much larger and then close up again.

All right. Let's go on then to the comparison of predictions. Overall, the impact loads were pretty close to what was predicted. We measured 2,600 pounds. It was predicted was 3,500. The stresses in the various areas, the rib, and again, the thing that was cracked was a so-called rib area. That and out here in the surface in this were about as predicted. However, the panel response that was further away from the impact was lower than anticipated and that's probably because this didn't deflect as much as the analysts thought it would.

Next? Now, an interesting fact that appeared when we looked at the sensor data is that this failure occurred very early – almost as soon as the foam hit the panel, and we have the scale model piece of foam here, almost as soon as it impacted, this crack occurred. And the foam was still diving into and compressing against the wing leading edge well after that happened. Now, it could be that we simply have very simplified models and we don't understand yet all of the complex interactions, and that we're actually looking at a system response, not just a simple piece of reinforced carbon.

The other thing that was surprising and I'll show you some numbers in a minute, was the fact that even though we greatly exceeded the predicted design limits, the shell here itself did not break. The break again was over here at the edge. And we don't know quite what that means yet. Partially, it's that we have a very limited information on the dynamic properties of this material and the whole leading edge structure.

So, let me show you a little bit – next slide. This is where the various sensors were. This material is rated at around 4,500 PSI, pounds per square inch. It failed at 4,940. So, just over the load limit. That's a little unusual because ordinarily these load limits are not a sharp cliff that you just fall off. Usually there's some margin in there.

On the other hand, we have a gauge out here at the face sheet that recorded three times the allowable limits and it didn't fail. Now, that may be because edges are more sensitive than the properties of the big face sheet here. Maybe there was some little spot, a little crack or something that was invisible over here that served as a propagation point. We don't know that yet and we may never know it. The T-seal crack, though, occurred over here at – very near this impact point at a measured value at about three times the breaking point.

The next slide shows the predicted stress levels. The group at Sandia did some pretest prediction for us and where they showed the stresses building up out in here in the center of the sheet, in the center of the shell and over here at the edge are very close to what was actually measured. So, I feel like we've got a good handle on that part of it, even though some things occurred much earlier, like the break on the rib, much earlier than expected, and some other areas didn't fail at all when, you know, a factor of three greater says you might expect that.

So, after the test was done, after we made these observations checked the comparisons, we went and did some non-destructive evaluation. Let me show you in this next little piece of video something called thermography. Watch right here. What you're seeing is a flash of heat, a flash of infrared radiation, heat radiation, against this material. It heats up and then it cools off and you watch this with an infrared camera basically and then what you see in doing this kind of test is that the crack appears right here.

So, if you look at the next slide, this is a snapshot of that and it shows how the thermography can identify the crack through the panel. In fact, it goes beyond what you can see with your naked eye and this was part of the recommendation that we've made, which is that the whole fleet have non-destructive evaluation techniques, perhaps like this one used to detect cracks and flaws and other things that might be a problem down the road.

So, the next slide shows the conclusions thus far. I think we've established the failure mechanism. We've established that you can, in fact, crack reinforced carbon by using the foam under the conditions observed in the accident. Saw two types of damage to the panel. We saw damage to the T-seal, carrier panel and we saw a shift in the positioning of the entire structure. But, I want to caution that this is just a single data point. We don't know yet what the potential would be for this crack growing and for hot gas penetrating into the rest of the leading edge.

This panel sticks out, it's gonna be sent off to Kennedy Space Center for a very detailed examination, basically a CAT scan, a x-ray scan – computer-aided tomography is what that stands for – and that it's a detailed x-ray of the entire 3D structure of the material that may tell us more.

My conclusion is it's too early to extrapolate to the complete foam impact story for this single data point and we need to do more, which is the point of the next slide.

All right. What do we do next? Our objective all along has been to look at this place on the fault tree to see whether or not the foam can create a breach that would be sufficient to simulate the observed damage in the accident. See if the tests match the sensor evidence, the debris evidence, and so forth.

So, before we begin the tests on the reinforced carbon in the panel eight through ten area, which other evidence is saying was the most likely breach, we need to know four things, maybe more. First of all, we need to improve the models a little bit. Secondly, we need to know that by picking that particular spot right there, which is based on analysis, that we had, in fact, loaded the panel in a representative way. We need to know whether or not the angle of the gun and, therefore, whether or not the angle in which this strikes a so-called clocking angle makes a difference. And we need to also understand whether or not having this RCC panel next to an RCC T-seal, next to a piece of fiberglass makes a difference. It may be that we end up saying that we want to use multiple RCC pieces. That would be taking resources away from the inventory, but it may be required in order to establish in a much more direct way, the types of damage that can be created by the foam.

So, what we're going to do is the following: we're gonna go back and do some fiberglass tests on panels five through seven. We use the same mass and velocity and so forth. But, we're going to instrument panel eight. Panel eight is a very unusual panel. It's the one where some of the debris evidence is saying the breach occurred. Most of the rest of these panels are basically – basically rectangles. I mean if you look at the footprint of this, it is essentially rectangular.

The footprint of panel eight is more like what's called, if you remember your geometry, a trapezoid. It is spread apart. The two sides aren't parallel to each other. They go off in an angle. Panel eight is the largest panel. It has some of the most unusual structure in the whole leading edge. And we want to know how this impact propagates down the system and, therefore, whether or not we ought to have reinforced carbon at least at two panels before we do the next set of RCC tests.

So again, we're gonna do a couple of things. One is, we're going to aim about three inches below the first shot to see how we load up the panel. We're going to rotate to the thirty degree clocking angle and see if the analysts are right. If that ends up damaging the fiberglass, it doesn't matter because we'll be done and we'll be moving on to the panel eight, nine, ten area. And then, we'll apply all of that to the tests in the eight, nine and ten region. And I think I've got one more slide which is the schedule for this.

We'll resume the fiberglass test I just described on Monday, June the 16th. Second fiberglass test will be on Wednesday the 18th, and then the dates for the reinforced – first fiberglass and then reinforced carbon for the panels eight through 10 will be at the end of June.

So, I'm – that concludes my briefing. I'd be happy to take questions. I think we've got about a minute and a half for the phone bridge.

MS. LAURA BROWN: Let me just check and see if anybody's left on the phone bridge first. Cindy (sp), are you on the bridge? Okay.

MS. IRENE BROWN: Hello, this is Irene Brown, if I could ask a quick question?

MS. LAURA BROWN: Okay, quick and you may get cut off and – .

MS. IRENE BROWN: Okay.

MS. LAURA BROWN: – I apologize if you do, but go ahead.

MS. IRENE BROWN: Scott, my understanding in your last briefing, these – there are not replacements for these panels and I'm just wondering what is available to be installed back on the shuttle for flight?

MR. HUBBARD: It varies. There are several RCC panel nine – panels nine. There is one spare panel eight and so forth. It varies by panel what's available and what is and is a spare. We're very cognizant of the fact that there's a single spare panel eight and if we decide to make that the impact point, it will be with all due consideration. But, given the system effects I described, the fact that it may be necessary to have the RCC next to each other to really have the representative test, it may be required that we do that. It takes about eight months to build a new one. I understand that NASA Shuttle Program has already put in an order for a complete replacement set.

MS. IRENE BROWN: And it's not your intention that these objects are to be flown on the shuttle, these test objects?

MR. HUBBARD: Oh, no, no.

MS. IRENE BROWN: Okay, thank you.

MR. HUBBARD: These are – .

MR. PHIL CHEN: This is Phil Chen.

MS. LAURA BROWN: Phil, one question.

MR. CHEN: Okay, Scott, when you are talking about a zero degree clocking angle, you're talking about you can use it on slate on at the panel? No side angle whatsoever?

MR. HUBBARD: No, zero degree clocking angle has only to do with the – whether the gun barrel is straight up and down or turned at an angle so that the straight up and down gun barrel is zero degrees as it was for the tests. On June the 6th, we intend to rotate the gun barrel by one notch and that will cause the foam to hit with the full edge, the full leading edge, striking the RCC panel. That's what we mean by clocking angle.

MS. LAURA BROWN: Okay. Anybody else from the phone bridge?

Okay, I think we're gonna leave you guys, so thanks for being with us and we'll go on to the folks here. Matt, go ahead.

MR. MATTHEW WALD: Scott, Matt Wald, New York Times.

What is the potential relevance of the damage you saw to the ability to lose a mystery Day Two object? Yesterday, O'Keefe said the damage that you inflicted couldn't possibly be seen by an astronaut, unless you got two inches from it, implied you couldn't see it with a national security asset – but didn't go into the idea that with this kind of damage trigger with thermal conditioning on orbit, losing a bigger piece later?

MR. HUBBARD: That – you make a good point and I've thought a lot about this, along with the rest of the team. What we saw was a snapshot in time. We did a single test and then very carefully preserved the panel and the T-seals and so forth, so as to not let anything grow or change.

On orbit, we were at 81, 82 seconds, so we're only at a fraction of the time of the – of the entire mission. I just looked up a few facts on this. We are 66,000 feet. The SRB separation is 126 seconds. An engine cutoff is 502 seconds. So, we're only at about 18 percent of the altitude that you get at MECO.

Talking to our astronaut colleagues, these are events that you feel – the SRB separation, MECO and so forth. So there's – even though we're past the so-called Max Q, past the maximum pressure on the orbiter as it ascends, the dynamic with aerodynamic loads, there's still a lot of other events that go on. In addition, of course, you go through thermal expansion and contraction as you go from seeing the sun and being several hundred degrees positive Fahrenheit to several hundred degrees negative Fahrenheit, so there's a big temperature swing.

How this could affect the panel is unknown at this time. That's a part of going and taking the x-rays. There are various analytical techniques you can use to test this or to simulate this. But, that's gonna take a while. So, all I can say at the moment is that what we had there was a snapshot in time of one test. It's conceivable those cracks could have grown and propagated and changed throughout the life of the mission.

MS. LAURA BROWN: Okay, Bill?

MR. BILL HARWOOD: Bill Harwood, CBS.

Just to look ahead at the test schedule, just the course of the geometry are great versus seven and nine, which I've thought about a lot. I mean, I realize there's no spare for eight, but I guess what I'm trying to figure out is just the geometry alone is going to give you a different system response. It's a strike on eight versus nine. I'm just wondering the relevance of these tests and maybe extrapolate to, you know, what you get if you actually hit a real eight?

MR. HUBBARD: You mean the relevance of what we just did?

MR. HARWOOD: Well, yeah. In the context, maybe the exact same hit on eight because of geometry would give you a different response or a more violent or less or whatever, how do you extrapolate from one of these flat panels to this one that has got the weird geometry to convince yourself that the test is valid and representative.

MR. HUBBARD: Right, that's exactly that – the point I was hoping to make which is that the system response and the different shapes of these panels tends to drive you toward firing a shot at panel eight, even though it's the only spare in the fleet. We don't – we wanted to do that deliberately and thoughtfully though. And we're using our best analytic tools to figure out if we can extrapolate or not.

I think that what you're seeing here is physics in action. I mean we're doing the type of research and development work necessary and parallel with an accident investigation to understand the impact and part of that is weighing doing on one hand a simulation versus on the other hand an experiment. And given what's happened thus far, I'm leaning in the direction of doing an experiment, but we're going to do some more work next week and then make the final decision.

MS. LAURA BROWN: Okay. Mike?

MR. MICHAEL CABBAGE: Mike Cabbage with the Orlando Sentinel.

What sort of analytic work have you done to see whether the cracks that you've seen in the testing so far on panel six could propagate into the type of damage that eventually caused Columbia to break up? I can't – from what you know, can cracks of small and displacement of the type you've seen, lead to the kind of break-up that we saw?

MR. HUBBARD: The only thing that I've got at the moment is, you know, gut feelings from engineers that helped design this. There is no analytic work done to date. There is a program called “FLAGRO” – F-L-A-G-R-O – which was used on the shuttle liner crack and it took a million hours of super computing time to get that one so it duplicated what was seen. I have no doubt that people will be running these kinds of programs, but they take a while. So, we don't have any analytic evidence right now.

And as I said at the time, this is why you do the experiment. We're learning as we go.

MR. CABBAGE: Well, if I could just follow-up to that. So, there is – you really have no evidence at all at this point then, that those cracks could have propagated into the sort of damage that we saw go through the left wing on the sensor data and the remnants and what's your gut feeling on that?

MR. HUBBARD: We don't have any analysis done. Materials scientists know that cracks propagate – stresses cause cracks to propagate. You know, that could be temperature effects, it can be mechanical effects. I gave you a little list of the sort of things that this crack might have been – may have experienced.

On the other hand, the – you know, some gut intuition of people says, well, that probably would be fairly stable. The answer to that question is unknown and that's why we're continuing to do the work to prepare for the panel eight, nine, ten shot which is much more representative of the – before the breach occurred, at least that's where we think it occurred from all the other evidence and that's why we're collecting some more data.

MS. LAURA BROWN: Okay. Todd?

MR. TODD HALVORSON: Todd Halvorson of Florida Today.

I was wondering what your thoughts are on the differences between the two materials you are using: fiberglass and reinforced carbon-carbon. The pretest predictions on each of those materials and then what you've actually seen in the two tests to date.

MR. HUBBARD: Let's talk about the most recent tests and there what we observed was that pretest predictions on RCC and what actually happened were pretty good in terms of total load and total stress. The surprise was that we didn't get a break in an area with very high stress – three times the supposed limit. We did get a break in a place that was just, you know, barely above the limit. Now, what does this tell you? I think one of the earlier conclusions is this is not a simple tension or compression event. It may have elements of torsion. It may have, you know, where something is bending and twisting at the same time and that is kind of the feeling that the structural engineers are thinking about. And so, they're going to try to take the simple models that they started with and put in this torsional element. You know, the fact that it may not just be a bending, but maybe a bending and a twisting simultaneously. That could account for what we've seen.

The fiberglass, we know that it is a different material. It was chosen years ago as being a fairly good surrogate for RCC. I mean the panels we got, we didn't manufacture. They came off of Enterprise. And we thus far have done reasonably well in extrapolating from one to the other. As long as we stick to kind of a qualitative story, I think we'll be fine.

MS. LAURA BROWN: Okay. Gina?

MS. GINA TREADGOLD: Gina Treadgold with ABC News.

Is there anything more on the Day Two Object? Since that crack was sort of halfway down the T-seal and the speculation is that half T-seal is what floated back in, can you tie this together at all? That blew a crack halfway down the object that came back?

MR. HUBBARD: Well, not anymore than you just did, I think! The float away object on Day Two seems to match its radar peripheral file seems to match two possibilities. One: a piece was one of these panels about this big, about a hundred square inches. Or, you know, a chunk of T-seal, three-quarters or five-eights or something on the T-seal.

I emphasize that we hit, you know, at a chosen angle and force and so forth. If there were 30 percent more, you know, or you had more force to it, could this have cracked across? That's what we're gonna attempt to find out as we do these tests.

And then, seeing what the experiment tells us, then we can go and try to better match that to the Day Two object.

MS. LAURA BROWN: Tracy?

MS. TRACI WATSON: Traci Watson, USA Today.

Dr. Osheroff went into a little bit of detail about what kind of hole you need to get the thermal effects that you saw. Can you elaborate on that a little bit? He said it was bigger than one inch, and then he wasn't quite clear on whether it was smaller than six inches. If you could go into some detail.

MR. HUBBARD: What he's talking about are the thermal dynamic, or so-called aerothermal. It's a combination of aerodynamics and thermal dynamics, calculations being done at different hole sizes to see if the heat then that got in could burn through the wires and create the kind of damage that matches the sensor data. And I don't think that analysis is quite complete yet. I know that they've done some six inch holes.

One of the things that they – and the match with the timeline seems to be pretty good. But, one of the other things that not completed yet is a gap, a slit. It's much harder to do, the analysis is tougher, but they're going to do an analysis to see what would happen if the T-seal were missing. And that was the path for entry. And that result should be available in a – in maybe a week or two.

MS. LAURA BROWN: Earl?

MR. EARL LANE: Earl Lane with Newsday.

Are there any plans to do any arc jet testing on these cracks, either after all the other testing is done, to see what kind of thermal propagation might get through a crack like that?

MR. HUBBARD: There's not a plan at the moment, but it is an idea that has been kicked around. What is in the works is a test of the edge of a piece of RCC, to see if it sharpens up to a knife edge the way some of the debris looks.

There have been a few tests of round holes. It was thought, based on one flight that showed a very small hole in RCC, which appeared to come from micro-meteorite damage. As a result of that, they did an arc jet test with a – started with a small hole and then heated it in an arc jet, and it does expand in a more or less circular fashion, and it forms a very sharp knife edge.

To my knowledge, no one has done a test yet on a crack like we saw, but I can imagine that that would be something people would be interested in. But, that type of test may well go beyond the life of this Board. Those things take time.

MS. LAURA BROWN: Kathy?

MS. KATHY SAWYER: Kathy Sawyer, the Washington Post.

Hi. If you can't make a hole big enough to satisfy yourselves by all of these methods you've just been outlining, is there any likelihood you'll start working things into the scenario such as the windshear during launch, the bolt – the flying bolts from the bolt catcher scenario and so forth? In other words, a combination scenario, or what will you – if not that, what will you do if you cannot figure out how the hole got big enough?

MR. HUBBARD: Well, let's examine just the foam test. It is – you know, I think that we have established the potential failure mechanism. Whether or not we hit it just right is open to speculation. But, getting the crack that we got established that this failure mechanism is at least plausible.

Whether we go from plausible to highly likely, I think, will be determined somewhat by how the rest of these tests turn out, and what kind of analysis you could do to move it around. That's part of the reason they collect this extra data.

For example, if the next test says, well, we get a crack now all the way across, the fact that we have a better analytic tool says, okay, if the actual event were a little bit higher or lower or something, then it would have done this. If we have confidence in that, then we can go from plausible failure mechanism to highly likely. And I think that's the range that we're working in. So that's the answer – part one answer.

Part two answer is, as Admiral Gehman and some of the other board members have said, there are probably some fault tree elements we can never exclude. You can never be absolutely sure that you didn't have a micro-meteorite hit. You can't be absolutely sure that some other debris didn't come off. And those will just remain out there as items that the return to flight people need to consider for future missions.

MS. LAURA BROWN: I'm going to be more liberal about the one question per organization rule here. So, if you guys both want to ask questions, go ahead.

Mark?

MR. MARK CARREAU: I'm Mark Carreau from the Houston Chronicle.

I just kind of want to back up to a basic question on where the testing goes at this point, as you move fiberglass and RCC. What is it that you're attempting to demonstrate at this point? More cracking? Something more dramatic?

MR. HUBBARD: If this was a perfect world, which it isn't, we would be able to establish that we have a very, very probable failure scenario. And that in turn leads to, I mean, knowing what you need to do for a return to flight and knowing, you know, what the origin of this problem was and so forth.

Since it isn't a perfect world, in the sense of being able to absolutely for sure simulate what happened, the best we can do, I think, is to try to bracket the event, demonstrate failure mechanisms, and then understand through analysis what else might have happened.

We've got limited resources in terms of the reinforced carbon panels, and we have, you know, a certain capability to try all these things out. So, that's been out approach, is to try to bracket the event, get some good analysis that compares with the experimental data, and establish where on the line from plausible to highly likely this foam event, as an initiating event, sits.

MS. LAURA BROWN: Alan, do you have a question?

MR. ALAN LEVIN: Alan Levin, USA Today. Sort of follow up on what Matt asked earlier. This at least raises the possibility that you could have relatively minor and difficult to see damage on an RCC panel, but that you'd nevertheless want to know existed while you were in space. What sort of questions does this raise about what kind of tests might be necessary in space and all to determine that the RCC is acceptable?

MR. HUBBARD: The – I think ultimately, it raises the question of, you know, how much vehicle health monitoring do you need to do for a, you know, vehicle that is – still has a lot of developmental characteristics.

This crack was – that we saw and the state that it was produced was visible. It's certainly – the hole crack during the standard investigation, or standard inspection that is done before flight, would've been easily detected, both visually as well as from what they call the tap test. In addition to which they look at all sides of this before – between flights. The interior cracks would've been easily seen. So, in terms – as far as an event, or as far as a defect before a flight, this would've been easily seen.

If it occurred as it did in the accident, on launch, then I think that the unknown yet – we know that there was a breach of sufficient size, which may have been on the order of, you know, inches, that let in enough heat to cause the damage that we saw. So, that size of a thing one would think would be visible from an EVA or some other type of inspection.

The dots – we haven't connected the dots yet from this initial test to the kind of breach that almost surely was present to cause the accident. And that's why I'm saying don't extrapolate too far from the single data point, and come along with us on the, the next few weeks of this R&D activity to see what might have happened.

MS. LAURA BROWN: That doesn't amount to a direct invitation, right?

MR. HUBBARD: Well, I mean, I don't think I've got enough room for all of you, but you can bring your blankets and bedrolls and, you know, whatever else you need.

MS. LAURA BROWN: Bill? Oh, sorry. Wait, wait. I'm sorry. I got the wrong end of the boom mike here. Is there someone over there who wants to ask a question now?

Oh, go ahead.

MS. GWYNETH SHAW: Gwyneth Shaw with the Orlando Sentinel.

I realize this probably sounds like a stupid question, but how did the crack go from being three inches on Friday to being five and a half inches now? Did you take two measurements? Is it the mix up with the centimeters? Is there a possibility that it grew after the first time you looked at it? I mean, I'm just curious.

MR. HUBBARD: No, first of all, there are no stupid questions.

What you got on Friday was my quick, you know, minutes long, you know, 30 minutes or so, investigation of a very complex test reported to you as rapidly as possible so that you'd get some feel for what happened.

I hope I was clear at the time that this was a very preliminary result, based on a quick inspection and promised what we're doing today, which was to come back after we had had time to look at it much more carefully and go and look at all the sensor data and take actual measurements, as opposed to, you know, holding a little pocket ruler up to what you can see inside this thing. I mean, they actually took this whole thing apart, the T-seal, the panel and everything, took it into the shop and were able to make very careful measurements.

So, you know, it's just the difference between, you know, going into your, you know, kitchen quickly and looking for your car keys or something and – or you know, trying to find the right utensil and you do what you can in a few minutes versus taking the time to go and do it carefully. And that's the only difference.

MS. LAURA BROWN: Okay. Bill?

UNIDENTIFIED MAN: So I just want to be clear. We have two new cracks since last Friday.

MR. HUBBARD: We have – what I reported Friday during the press conference was the crack that is now, by careful measurement, five and a half inches long. It appears as a three-quarter inch crack on the surface.

Later that day we found the crack on the T-seal and we put that in the press release, and that was about two and a half inches long in this area here. And then, after even more careful investigation – and I also at the time reported that this panel had been shifted a little bit, gave some approximate numbers, and we found that there was a chip on the carrier panel.

What we've added since then is the crack up here near the flange area, where the bolts attach this to the structure. So I believe, if I've counted that up right, we only have actually added one new piece of damage.

UNIDENTIFIED MAN: So given then the scope of the damage, can you characterize just generally how the panel sustained or didn't sustain the damage from the impact?

MR. HUBBARD: I'm sorry. I didn't follow you on that one.

UNIDENTIFIED MAN: Did it hold up better than expected or worse than expected?

MR. HUBBARD: The pretest predictions were all over the map, from a simple crack, which is what we observed, to breaking into pieces. And it's because nobody has ever done this kind of testing before that we are in this, you know, research development type of activity.

The – what we saw is more at the lower end of the predictions. But, as we peel the onion and look deeper into it, we see that some things match up very well and other things are somewhat of a mystery. Like, how could we have a force out here three times the breaking strength and nothing happens? So, that's why we're conducting more data.

So, in general, I think we got a pretty good match with one set of models, but there are still some question marks.

UNIDENTIFIED MAN: I'm gonna ask you a question unrelated to the immediate subject at hand, which is – that I assume you know the answer to. The explosive bolts and the bolt catchers we were talking about earlier, can you just explain in a very simply way how that mechanism works? I mean, if the bolts get split, is there a thing that blocks it? If it gets moved out of the way mechanically?

MR. HUBBARD: What – you have a bolt holding the solid rocket booster onto the external tank. And when the bolt, explosive bolt explodes, it separates, and one piece goes with the external tank, one piece goes with the solid rocket booster. But, it's just a mechanism of cutting it, you know, so that – .

UNIDENTIFIED MAN: – So the bolt actually gets cut.

MR. HUBBARD: Yeah. Just cut it. These things are often called “bolt cutters” in the technical parlance.

MS. LAURA BROWN: Ricardo?

MR. RICARDO ALONSO-ZALDIVAR: Yeah, Ricardo Alonso-Zaldivar with The L.A. Times.

Okay, this is kind of like an arcane question, but I was just wondering. That tiny little three-quarter inch crack on the surface, right? I just wondered, did you calculate what the space is, like how many square inches that would be, the opening, to give us an idea? You see what I'm saying? The gap?

MS. LAURA BROWN: You mean how wide is the crack?

MR. ALONSO-ZALDIVAR: Yeah.

MR. HUBBARD: Oh, no. Haven't calculated that yet. And if you remember in the video there it actually, depending on how this thing flexes, it opens and closes, you know, the crack itself is the sort of thing you'd slip a piece of paper into and it's not very wide. But I don't have a number for you, off the top of my head.

MR. ALONSO-ZALDIVAR: (Inaudible).

MR. HUBBARD: Ah, interesting point. The – when it's closed, a quick look didn't show any light shining through it. Somewhere – and we didn't – you didn't get to see the full video – somewhere in that impact, something opened up enough to let light into the channel here, the inside of the leading edge. Whether it was the crack or not, I don't know. It could've been as simple as the T-seal moving aside and then going back together again.

But, the point is, the point is not whether you can see light through it, and it's not how – it's not how wide it is. It's the fact that you have penetrated the thermal protection barrier. This crack goes all the way through the rib. The thermal protection of this material is provided by the silicon carbide, which is a part of this material. This material is made in a very complex process and, essentially what happens is, they really convert the carbon on the outside into silicon carbide, which is the actual protecting material. And we have a crack that wraps all the way around, that goes – that penetrates the thermal protective material.

MS. LAURA BROWN: Okay, do we have other questions?

Bill?

UNIDENTIFIED MAN: Just a scheduling question. Scott, you said you're leaning toward maybe using a real panel eight. The schedule you gave for shooting this panel eight through ten, would that support – if you're using a real one or if you decide to use the real one, would that test slip into July?

MR. HUBBARD: The three or four options that we're looking at all support a panel eight through ten test by the end of June.

UNIDENTIFIED MAN: Is that something we'd be able – be able to come to if we wanted to?

MS. LAURA BROWN: I guess we'd have to work that out. I mean, it depends on a lot of different factors at that point. But I think we would – .

MR. HUBBARD: – We'd lean in the direction of doing what we did before for the real RCC test. I don't think you're – you know, you need to spend your time on the fiberglass run-ups and all that. But, for the real test, you know – .

UNIDENTIFIED MAN: (Inaudible).

MR. HUBBARD: Yeah. We'd try to do it if we could work it out, like we did before.

MS. LAURA BROWN: Okay, other questions? Okay, we've exhausted you! Finally!

So, all right. Thanks everybody for your patience and – .

UNIDENTIFIED MAN: (Inaudible).

MS. LAURA BROWN: That's the last hearing that we have – currently have scheduled.

UNIDENTIFIED MAN: (Inaudible).

MS. LAURA BROWN: We are considering a press briefing in two weeks. We have a schedule with the Board right now where, since several members of the Board are on the West Coast, we're getting the full Board together for several days together, every other week. And so we would probably not do a briefing next week. But there's a possibility we would do one two weeks from now.

UNIDENTIFIED MAN: Here?

MS. LAURA BROWN: I don't know if it's gonna be here or not. We have – if the room is available, we may be doing it in one of the – in this area. We have several other facility options, too. But, it would probably be in this part of town.

UNIDENTIFIED MAN: (Inaudible).

MS. LAURA BROWN: Yeah, exactly.

Thank you.


END




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