Columbia Accident Investigation Board Public Hearing Monday, March 17, 2003 1:00 p.m. Hilton Houston - Clear Lake 3000 NASA Road One Houston, Texas Board Members Present: Admiral Hal Gehman Rear Admiral Stephen Turcotte Brigadier General Duane Deal Mr. Roger E. Tetrault Dr. Sheila Widnall Mr. G. Scott Hubbard Mr. Steven Wallace Witnesses Testifying: Dr. William Ailor Mr. Paul Hill Mr. Robert "Doug" White ADM. GEHMAN: Good afternoon, ladies and gentlemen. Welcome to our second public hearing. The subject of this afternoon's hearing is going to be a discussion of the reentry of the Shuttle Columbia, and we'll hear from several witnesses this afternoon. The first one is Dr. William Ailor. Dr. Ailor is the director of the Center for Orbital Reentry Debris Studies from Aerospace Corporation. We are very thankful, Dr. Ailor, for you for taking time to come down here and help us walk through this. What the board is interested is, first of all, a non-NASA view of how things reenter the atmosphere, which will help us form our questions for later this afternoon when we get the detailed analysis of how the Columbia entered the atmosphere, and your presentation will help us understand to a much greater degree what we'll hear later. Dr. Ailor, I would offer to ask you to give us a short bio or short background, if you please; and then if you're prepared to start, we are prepared to listen. WILLIAM AILOR testified as follows: DR. AILOR: Okay. Thank you very much. Just by way of background, I joined Aerospace in 1974 and have been basically working reentries ever since that time. I'll go over in my presentation a little bit more detail on some of the ones we've worked on before, but Aerospace established the Center for Orbital Reentry Debris Studies back in 1997 in recognition of the kinds of issues that we expected to see from both space debris and the hazards posed by reentry and in recognition that there needed to be a fair amount of work done to understand the reentry breakup process. I'll go over some of that in my presentation. So a little bit more background, I did work on the external tank reentry a number of years ago, one of the issues where it was associated with what altitude did that break up. We worked very closely with NASA in resolving those issues. Then I've also been in various capacities on the Interagency Nuclear Safety Review Panel, which reports to the White House on space missions which carry radioactive materials – so Cassini, Mars Pathfinder, Mars Exploration Rover. We've worked on all of those. So if I could have the first chart. Okay. Go back one. No, that's good, I'm sorry. What I'm going to talk about is what we can learn from reentry debris. This is really based on the experience that we've had over the last 25 years in this area, actually longer than that. Aerospace has been working in this area for a long time, and our desire has been really to understand the breakup process. Again, these things coming down through the atmosphere can present a hazard to people and property on the ground. One of our objectives has been to understand what that hazard is and to be able to model it and perhaps minimize it as time goes on. So what I've got here is an overview of the reentry breakup process. This is just for a standard reentry; and as I'll show you in a minute, we see a number of these a year. For a typical satellite reentering, it slowly comes down through the atmosphere, slowly works its way down out of orbit in an orbit decay fashion or, in fact, you can actually drive something into the atmosphere – and I'll talk about that in a bit, as well. Basically for unprotected space hardware, the heating and loads will gradually tear it apart. I'll talk more about that in minute. The kinds of things that we've seen that survive reentry are things that you would probably guess might, things like steel sometimes – I'll talk about that – glass, titanium, and then parts that are sheltered by other parts. One of the things about the reentry breakup process is that the heating is like, in a sense, cooking an onion. You basically start from the outside; and then as you heat the pieces up to a point where the materials will fail, that will expose some new materials. They'll go through the same process and the object can be broken apart. We do have objects that are melted and shedded away, things like aluminum, solar panels. Things like that come off pretty early. Mylar sheets. Some satellites are wrapped in Mylar sheets. Once this debris comes off from the parent body, it follows its own trajectory at that point. So it will go on about its business, basically, based on its own properties. If it's a very dense, heavy piece, for example, it may go further. If it's a very lightweight piece like a solar panel or something like that, it will fall early in the trajectory. Then the debris pieces impact on a footprint on the ground. I've got an illustration there that just shows that typically what we see is initial breakup or shedding of some things like solar panels that come pretty quickly. And we have catastrophic breakup. I'll talk more about that but typically it can be quite a substantial event. There can be secondary breakups that happen when those pieces come apart. Then you see a footprint where you get low-mass debris that comes in early; and typically longer, heavier pieces go late. We'll talk more about that, as well. Next chart. Okay. So just some characteristics of reentry breakup. It's characterized by intense heating and major fragmentation; and as I mentioned, fragments are shed as the structure heats and fails. Typically we see instantaneous high loads. For example, when an object comes off of a parent body it now experiences the air stream that exists there; and it will respond based on its own characteristics. For example, if you've got a very lightweight piece that comes off of a heavier object that's coming through the atmosphere, it's like throwing a piece of paper out of a car. That will decelerate very quickly, and the same things happens even at Mach 20. So when you do that, you see very high loads; and you can also see very high heating. That can be important if you're trying to understand what actually happened in the process, because now you've got an object that's been separated from a parent body that, just because of its own interaction with the atmosphere, will have seen a fairly severe environment. You can have some events with a moderate velocity increment. What I mean by that is if you've got a fuel tank or something like that that explodes, it's like a balloon. Some of those fragments will pick up some velocity increment from that. We've measured as high as a thousand feet per second. And the initial breakup can be energetic. Basically a typical way for things to break up when they reenter is that they'll come down through the atmosphere for a certain amount of time, they look absolutely fine, we've seen videos of these things where they just like spacecraft coming down, and all of sudden they come apart. When they come apart, they just disintegrate. That altitude typically is about 42 nautical miles, plus or minus a few nautical miles; but that's a pretty good guess. So just as a rule of thumb, it seems like a critical point for space vehicle reentry and breakup is around 42 miles. We have never had any measurements internal to a spacecraft during this breakup process and that's something that we would like to see. It would really help us understand the process better. Next chart. Survivability depends on a numbers of factors. The material. For example, the melting point of the material, the heat capacity. Just by example, it's very rare to find aluminum on the ground from a standard spacecraft reentry; and finding aluminum on the ground would basically mean that that aluminum was somehow protected as it came down. Steel can survive. It doesn't have to, though. We have cases – for example, there was a Russian satellite that came down in Canada, had steel, a reactor case. That reactor case basically disintegrated during the reentry, but also I'll show you some pictures of steel that did. Size, shape, and weight. An empty fuel tank, in a sense it's a lightweight object relative to its size. That will affect its survivability, and that can be very important. For example, fuel tanks survive. Things as dense as battery? We've never found a battery on the ground. Release conditions. If an object comes out late in the reentry, after being shielded for a portion of the reentry, that means a lot of the energy has been taken out of that trajectory prior to that object's release; and that object is more likely to survive. And shielding. Again, objects that have been shielded for partial reentry can survive; and that's one reason, by the way, that, for example, you can find circuit boards on the ground from satellite reentries. What that means is typically when a satellite is being constructed, circuit boards are built internal to other boxes which are internal to other structures and so forth. Again, if you think about this heating process where you're removing the outer layers as you come in, every time you do that, you're removing energy and then finally these things will be released. Next chart. When these things come down, there's a typically generated debris footprint. Now, this is a notional footprint here. I've got several breakup conditions separated by about 30 seconds in trajectory time. This shows things like the types of dispersions that we typically see. This has got dispersions in winds. So winds will affect things as they fall, even a big, heavy object, as I'll show you in a minute. Ballistic coefficient is a measure of, in a sense, how dense an object is; and that will affect where things go. Typically on these footprints at least, for example in the red swatch you see up there, things that have gone longest downrange, farthest to your right, would be heavier objects. The lighter objects would hit towards the up-range portion. Then atmospheric density. We don't quite know what density is in most trajectories. So in that case we have to build a factor in to allow for that. Then also, as I mentioned, it's possible to get some velocity increment as things come down. So we put in a delta feed for that. So basically what you can see here is these ellipsoids were generated at each of these time intervals, and you can see how they overlay each other. If you look carefully at Breakup 4 down there, that's the one where the trajectory is now healed over a bit and you can see that even though the same types of debris are there, the footprint is inside of the one just prior to that. This indicates that trying to figure out where debris came from on a reentering spacecraft and where it happened is a very difficult process, indeed. These are four specific time steps. What you have to recognize is this is basically happening continuously as the spacecraft reenters. So the footprint is not even as nice as what you see here. Next chart, please. Noteworthy reentries. Just to give you a little background, it was mentioned earlier that someone said this is not a data-rich area; and I have to agree with that. What you see here are some of the primary data sources for doing this type of work. Cosmos 954 came down in 1978. That was a reactor-powered satellite and there was radioactive debris that came down in Canada. Since it was radioactive, you could find it pretty easily and a lot of that debris was recovered and was examined and documented. That's probably exceptional on these kinds of things. Typically the effort is simply not put forward to find debris on the ground, and so we simply don't have as much. Skylab occurred in 1979. Some of the debris fell in Australia. There was some debris found, but again there was really no detailed analysis of the footprint itself, as far as I'm aware. I'll show you some pictures of some Delta 2nd stages in a minute. We do have large debris pieces surviving from that. We did reconstruct the trajectories and try to understand the breakup of those. And there were two targeted reentries. The ones above that were all basically, in a sense, brought down just by the atmosphere itself. In other words, the atmosphere drags things out of orbit slowly. The last two were actually targeted into ocean areas because of potential hazards they posed. The Compton Gamma Ray Observatory, that was targeted to an ocean area. There was no debris found from that one. And then the Mir space station was also targeted to an ocean area. The only debris I'm aware that was found was reported by a guy who was beachcombing down in Fiji, a job I'd like to have. He did have one piece. It's not been substantiated that it actually came from Mir, but likely Mir had debris surviving and it may float up on a beach somewhere. Next chart. The type of work you can do with a reentry as far as reconstructing what actually happened to it, there are a number of things you need to do. There's maybe tracking data – for example, radar data. Video data, for example, the type of thing that people would take. If people have seen it from aircraft, any of that data can be very useful in rebuilding what's happened in a reentry break. Public sightings of witnesses. On most of the reentries we've got here, the public actually has seen some of these things coming down. That information has been very useful in rebuilding what happened in the reentry. Debris on the ground. Knowing where things are, what they look like, how much they weigh – all that information can be critical to rebuilding what happened. That's one of the reasons why the work that's going on now, both from the public and other agencies looking for debris, is really critical to this investigation. Data on the original vehicle. It's one thing to have debris on the ground, but you need to know what the original configuration was like. Sometimes we simply don't have good information on that. If it's a foreign satellite or something like that, we may not know exactly what was coming through the atmosphere. So we don't have a good feel for taking the debris back up. The next thing you try to do is fuse all that information and basically rebuild the reentry trajectory, try to match the impact locations to possible release points and take any existing weather data, any of that sort of thing in, and then finally conduct metallurgical analyses on the debris to estimate temperatures, really look at what went on, those kinds of things. Next chart. This is an example of a reentry. This one came down over Canada. This was in 1997. You can see that on that chart we show a breakup altitude at the magic 42 nautical mile number. And there are some fragments. We'll talk more about those, but this is one. This again, the public was out. This was about 3:00 o'clock in the morning. There were reports to news stations and so forth, and we actually used that information. Next chart. This is some pictures of the debris recovered from that one; and this is one of the larger debris fields, I guess, that we've actually had a chance to see. As I say, typically unless it lands next to a farmer's house as you see in that chart there, people don't find these things unless they happen to be out and about. So what you see in the upper-left corner, this is the original configuration as it was being loaded onto the launch vehicle up there. There actually was a satellite on top of that. This stage was released in orbit and was in orbit for about nine months and then gradually the atmosphere dragged it down. The big brown tank you see over there is about a 575-pound stainless steel tank. It landed about 50 yards from a farmer's house here in Texas. He was not pleased. The woman you see on the top right actually was brushed on the shoulder by a piece of the debris. Again, she was very lucky; but it's a very lightweight piece. The sphere you see down here was one of four on that vehicle. That was the only one found, although we believe they all survived. So they're still on the ground somewhere. The bottom one just shows that these things can survive in pretty good condition. Those are screws that you actually could unscrew. They held an aluminum plate onto the tank itself. The aluminum is gone, but the screws were still there and just fine. Next chart. This again gives you a little detail on that one. Again 550-pound tanks. 67-pound titanium sphere. 100-pound thrust chamber. Footprint length was about 400 nautical miles on this one. Next chart. This is a detail of the trajectory reconstruction. The trajectory comes in from the top and each of those little black dots is about two seconds apart. So you can see just by the spread of those dots that it's moving at a pretty good clip originally. That's up and around 18 nautical miles up. When you get down to around 10 nautical miles, it looks like it does a little dogleg there and that is due to wind. So basically where an object of this type comes into the atmosphere, typically all the orbital and all that motion is gone, the atmosphere has basically taken that energy out, and it will fall from, say, 50,000 feet straight down. That's one reason why when you see debris on the ground, even on the pictures of the farmer's house with the debris there, you'll notice there's really no crater. Most people don't realize these things just fall straight down and they just land. That's just a characteristic of this. That little dogleg is again caused by winds. It hit the jet stream, and it blew it over. This, again, was a 575-pound tank. So you can see that even that can be moved. One of the things that we did was we were able to get a portion of this fragment that brushed Lottie Williams on the shoulder and we actually wanted to find out if, in fact, it did come from the launch vehicle or from that vehicle. We analyzed that and found that – if you take the next page – that it did. The trajectory time was consistent. She was out walking at around 3:30 in the morning and actually saw the reentry and then this thing came down and brushed her on the shoulder and she recovered that. We did get a piece. We brought it into our labs and did an energy dispersive X-ray analysis of it. There are actually two on this little red chart you see here. There are actually two lines there. One is the original material, and the second is what was recovered. So we are very confident that this material actually came from that vehicle. Next chart. The second thing we did is take samples from the large tank itself, put it through a metallurgical analysis. We found, for example, that in portions the aluminum actually combined with the stainless steel and that we were able to use that to pin down the maximum temperature on the tank between 1200 and 1280 degrees centigrade. The other interesting thing, and I'll show you another example of this, is that it appears that this aluminum splashing back – again, aluminum is there on other parts of the structure – that the aluminum splashing back on the tank can actually oxidize or burn and the heat released by that can melt holes. We believe that's why the hole was actually melted in this tank. Next chart. Just to show you, this is not all that unusual an event. This is some pictures of basically the same debris objects. These came down near Capetown, South Africa, in April of 2000. So basically the same objects. Next chart. This is another one we have. This is a solid rocket motor stage that came down in Saudi Arabia. This one is made of titanium, which makes it a little unusual. The ones you saw before were typically out of steel. This is titanium. It would be expected to survive very nicely. We have evidence again that the hole you see here was actually burned, in a sense, in the casing as the aluminum oxidized on it. Next chart. So just learning a little bit from the debris and limitations there, we typically model reentry breakup at the macro level. We simply don't have a good understanding of what happens at the micro level with these kinds of things simply because we don't have a lot of data to base our models on at that level. We do have a few reentries where significant debris is found; but, just by way of information, of the stages that down in Texas and South Africa – we have about ten of those that come down a year – those are the only two we've found, only two where debris was found. So most of these are laying in water or in places where not discovered. We also see about a hundred reentries of major objects a year. So finding debris on the ground is very unusual, although we do get hits on our website. People E-mail with things they have found and ask us if that potentially is of that type. Just by rule of thumb, we would estimate that about anywhere from 10 to 40 percent of an object will actually survive reentry and that depends on what it's made of. If it's got some big, heavy, empty fuel tanks, that can really be a factor there. There has been relatively little work on reconstructing reentry breakup events. The ones I've mentioned are about all there are. Again, one of the most important features is there's really been no systematic retrieval effort except in a couple of cases. I guess the Cosmos 954 would an exception and, again, the objective there was to recover the radioactive material. Next chart. Some observations. As I mentioned, the heating to an object can really be exacerbated by burning of other material. For example, this phenomenon of aluminum melting and splashing back and the heat of oxidation actually increasing the temperature and burning holes, we believe that's a real situation. There are large aerodynamic deceleration loads, and also you've got an object that's already been fairly well heated as the reentry progresses. So that can lead to structural failure and actually can mask other information about what happened during the breakup. Combing data from multiple sources can be critical for reconstructing a reentry event. Finally, the distribution of debris on the footprint may actually be very useful in providing clues on the breakup sequence itself. So things like if you find objects early in a trajectory, that can be really very critical to seeing how that reentry progressed. Next chart. So, in summary, reentry breakup is not well characterized at the micro level. That breakup and subsequent disintegration can and does destroy clues of critical events. The debris field may be very useful in helping to track down what ultimately happened. Data fusing is really a critical part of this. You really must take everything that you can learn, all the data you can get, and try to reconstruct what the event was. Then a final piece of that is laboratory analysis of the debris pieces themselves to look for things that can be shown to have occurred earlier or have been protected by other objects as the event progressed. I think that's my briefing. ADM. GEHMAN: Thank you very much, Dr. Ailor. All right panel. Let me know if you've got some questions. MR. HUBBARD: Dr. Ailor, thanks for being here with us. We appreciate someone of your expertise speaking to us. I have two questions that are follow-downs on some statements that you made. One is about the percentage of material that's been recovered in your previous data base. Where we are today with the Columbia is something on the order, by weight, of 15 to 20 percent. So I would like your assessment, based on what you know, of whether you think this is a low or a high or what we might expect in the future. DR. AILOR: Well, as I mentioned for typical reentries we see between, say, 10 and 40 percent. It really can depend on what materials the object is made of. There may be significant debris pieces that have yet to be discovered, I don't know, but I would say that's certainly in the range of the experience in the past. The other part of this is that we've never had the detailed look or the energetic search for debris that we're seeing now. So it's possible that you may get a higher percentage as time goes on. MR. HUBBARD: Thank you. The other question was related to your statement about aluminum rarely being found on the ground. We're finding some aluminum, although mixed with other debris or attached to other debris. Can you give us a brief explanation of why that might be the case? DR. AILOR: Yes. Our experience has been that unprotected aluminum will not survive a reentry. The heating is just too high. It typically comes off very early in the trajectory. We do find aluminum, say, bits of aluminum that has been flowed back on to tanks and been protected, say, by a titanium sphere or something like. It will flow onto the lee side and be protected back there. But we typically don't find that. For debris that you're finding now, most likely aluminum on the ground was protected for a significant part of the reentry and probably was released late, when there was sufficient heating to cause it to melt. ADM. GEHMAN: Thank you. MR. TETRAULT: Dr. Ailor, one of your charts talked to the five satellites that had broken up in the atmosphere. To put this in perspective, could you tell me how many total pieces of history have we had compared to the 30,000 pieces that we are now left with on the shuttle. DR. AILOR: Well, the history, we actually have examined probably five or six, just to give you an example, the several big tanks and so forth. There was a number of debris pieces that were picked up from the Cosmos 954. I would say in history we're probably talking about in the order of maybe 250 or so that have actually been noticed by humans on the ground and reported. MR. TETRAULT: One follow-up question. You talked about the ballistic coefficient. For everybody's edification, could you kind of distinguish the difference in the ballistic coefficient between something like a tile, a tank, and maybe a landing gear strut. DR. AILOR: Absolutely. Ballistic coefficient is a measure of how significantly the atmosphere is going to affect the flight of an object. The way to think about it is a very low ballistic coefficient object would be like a feather. Extremely low ballistic coefficient. A shuttle tile, for example, released by itself, very light object, would have a very low ballistic coefficient, as well. Something with a medium ballistic coefficient would be something like a tank, an empty fuel tank. That big tank I just showed you here has a ballistic coefficient on the order of 15 to 20. Then something like you were mentioning, a landing gear strut, I probably would imagine that would be up to 40 or 50, something on that order. A ball bearing would be something that would have a high ballistic coefficient. So it would be something where the aerodynamic properties really would make it less susceptible to the atmosphere and also its mass properties would give it a lot of inertia. MR. TETRAULT: Thank you. ADM. TURCOTTE: In the examples that you gave of the different reentries that you had, they were obviously at different inclinations and they were at different reentry profiles. Would you kind of explain the difference in what you know of the shuttle's reentry profile at that inclination and some of the data that you've had in the past from the other satellite reentries. DR. AILOR: Yes. The other satellites that I spoke of either were deorbited or basically were orbit decayed down, had very shallow path angles typically. They flew what we call ballistic trajectories, which mean there really wasn't much lift involved with them. Of course, the orbiter is a lifting object and lift did play a big role in its trajectory – for a good portion of it, anyway. That trajectory will affect the heating rates and so forth and will affect how the object responds to the atmosphere. MR. WALLACE: This is the first time we've had a breakup of a vehicle designed for reentry. Is that a fair statement? DR. AILOR: Of this type, yes. MR. WALLACE: This ballpark, your 42-mile estimate, was pretty close, given the situation of the Columbia. Does the fact that this was a vehicle designed for a safe reentry change some of your estimates about percentage we're likely to find and any other sort of effect on the breakup sequence? DR. AILOR: Well, it certainly could. As a matter of fact, the fact that there is a heat shielding on at least a portion of all the body for a portion of the time and then some of the body parts after that will affect what survived. That's certainly true. I should mention that the shuttle external tank also is a reentering vehicle after it's released from the orbiter during launch. That typically breaks up at a slightly lower altitude, maybe around 40 nautical miles plus or minus a little bit. What happens there is there is some amount of heat shielding and it does protect it for a little bit. So there are objects where there is a shielding existing and I think the fact that the breakup sequence that can be shown that there was a material loss at a very high altitude for the orbiter may indicate that the heat shield may have had a problem. DR. WIDNALL: You mentioned earlier that aluminum rarely survives, certainly in its bare state. Could you sort of go over all of the possible things that you could think of happening to aluminum in reentry both for, say, an individual panel that suddenly found itself all by itself in the atmosphere and also maybe a panel, say, on the leading edge, like leading edge spar of the shuttle wing, that was attached to the shuttle but was bare? What are the different range of things that could happen to such aluminum? DR. AILOR: I'll give you an example. Some of the work we've done has been looking at a large spacecraft that reentered with solar panels and we believe and have data to indicate that the solar panel came off early in that reentry. Some of data we have makes us believe that that solar panel, even with an aluminum structure, actually survived. So that's a case where again you have a big – DR. WIDNALL: Now, that's ballistic coefficient. DR. AILOR: That's exactly right. it's a big, flat, plate. It spreads out, stops quickly, and then essentially just falls to the ground. So something like that could survive. So in that case aluminum could be expected to survive. If aluminum is being carried along by a heavy object – for example, you saw the tanks we have here – these were big, solid pieces of material. The aluminum on it is a piece of structure. As it's being carried by that heavier object, it's really governed by the aerodynamic and heating and so forth that's characteristic of that object. That could be much higher than the aluminum itself can stand; and when that aluminum gets weak, it will come apart. DR. WIDNALL: I'd like to go beyond that. So you're saying melting? DR. AILOR: Melting. Absolutely. DR. WIDNALL: Vaporization? DR. AILOR: Melting, yes. Turn into droplets. DR. WIDNALL: Well, droplets? How about individual atoms, vaporization? DR. AILOR: I would assume. You'd have to ask somebody more qualified in that area than I am. DR. WIDNALL: Oxidation? DR. AILOR: Oxidation for sure. We've seen evidence of that. DR. WIDNALL: Of course, another word for oxidation is burning. DR. AILOR: Exactly. DR. WIDNALL: The example you gave was aluminum deposited on another tank which essentially burned and created – but I suppose it could also burn all by itself. DR. AILOR: It could, although aluminum released by itself probably would stay in a droplet form and be sorry pretty quickly. So aluminum that would be carried along by something I think would really be more likely to see that. MR. TETRAULT: In the hole that was created that you talked about, was that created by the aluminum burning or the alloying effect? DR. AILOR: It was, we believe, by the oxidation of the aluminum itself; and that raised the temperature up where you could actually see the alloying occurring. ADM. GEHMAN: I was very interested in your comment about the ball of paper being thrown out the window of the car – not just because that's my level of understanding. What you suggested was that in an entry scenario like we're investigating here, there is a heating and an aerodynamic force, one of which is extraordinarily fast, and then when the object then becomes free and floats down to earth, it's still got heat but it's no longer of this extraordinarily short-period high intensity. My question is: When we go looking through debris, should we be able to detect those two phenomena – that is, a piece of metal which has been flash heated versus a piece of metal that's been subjected to prolonged – by prolonged I means tens of seconds or maybe even more? Can you see the difference, in your experience? DR. AILOR: For aluminum to actually see, as you say, the flash heating, the way that will work is that when an object is actually kicked off, if it's has got material attached to it – for example, it's tile material with some substructure attached to it – if it comes out in a way where the tile material is forward and actually protects the material behind it, then that might be likely to survive. The problem is going to be with, No. 1, the breakup process is going to continue on about anything, about any object that's put out into the stream that's going to continue to see heating for a short period of time. If there is much material there and it's a very low ballistic coefficient item like a big, flat plate with some material behind it, structural material, that will heat up very quickly, as you say. The aerodynamic loads will also be quite high as soon as it hits the air stream. That can have a tendency to fracture it further. So this breakup process is going to continue as it comes down. Secondly the dynamics may actually get into the process. So this object is tumbling. Then the different sides will see the air stream. So it will be a difficult process, I think, to try to see a piece on the ground and make sense out of it from that perspective. ADM. GEHMAN: I take it in one of your viewgraphs, for example, of a sphere that came from one of the Deltas or something like that in which all of the burn marks all around the sphere look approximately the same, would it be, in your experience, safe to conclude that that sphere had been tumbling and all of the sides had been subjected to the same amount of heat, whereas the one that had the hole burned in it it's safe to analyze that that was another event of some kind? That's kind of what I was getting at. DR. AILOR: That certainly can be. You're right about that. As a matter of fact, on one of the Delta tanks, one of the spheres, about a 2-foot diameter sphere, one side actually does have droplets of aluminum that are clearly visible on it. The other side is absolutely clean. So you can say that during the heating phase that one side was facing the oncoming air stream and saw more heating than the other side did. Exactly. ADM. GEHMAN: Another question. Certainly in the case of those spheres – and by the way, in the case of Columbia, I'd ask, Mr. Tetrault, we have found essentially 20 out of 25? MR. TETRAULT: We found at least 25, not counting fragments, out of approximately 30. I don't know what the exact count is from construction. ADM. GEHMAN: (To Mr. Ailor) As you predicted, the spheres all survived. But in the debris field, not discounting the spheres, your suggestion is that in the terminal velocity, in the terminal vectors, even when you start off going 10,000 miles an hour, by the time you reach the thick part of the atmosphere, you're essentially dropping vertically. DR. AILOR: Correct. ADM. GEHMAN: Therefore, how would you characterize whether or not we should find buried debris or not? Would you expect most of the debris to be on or near the surface? DR. AILOR: I would expect most of the debris would be on or near the surface. Buried debris would not be typical for a spacecraft reentry. That would require a very dense material and would also require it to have some aerodynamic properties which you're not going to find on a reentry object. GEN. DEAL: Dr. Ailor, I've got a few questions for you. You're probably aware that from the to the fourth day on orbit this piece of debris that was separated from the shuttle and that went on to reenter, we have some extensive analysis going through testing at Wright Patterson Air Force Base right now, trying to determine the radar characteristics of it. Are there any type of predictive methods that you know of that might tell us, by the characteristics of its reentry, what type of material it was? DR. AILOR: Certainly if we had information on the reentry itself, yes. On the rate of decay, the rate of decay from orbit would be indicative of the overall aerodynamic properties of the object and its weight. So that would be some useful information to have. If there's tracking data, for example, on the reentry itself, that could be useful. GEN. DEAL: Then a second question. I looked at your slide that said from a Saudi Arabia reentry back in 2001, analysis is still ongoing, which doesn't bode well for us to get back to our day jobs anytime soon – two years later. Can you tell us what we can expect to find through laboratory analysis of the debris in the short term? DR. AILOR: In the short term, the critical thing, I think, is going to be to try to center the analysis on certain debris pieces that there's some reason to believe have high value. What I mean by that is if there's debris that can be determined by analysis to have come from a particular part of the vehicle itself, that's of interest. Then you should really focus on that. I think the initiating event is probably what is of interest here. So a lot of the final debris that is in the debris field will have happened well after the initiating event. So the search that's going on for early debris is really very intelligent and the right thing to do. The other thing would be to look for the debris itself and see again if there's characteristics of the field that would indicate that debris in this area, for example, came from a portion of the orbiter of interest. So I would really try to focus on that. Laboratory analysis? There's too much debris here to be doing that extensively. So it's going to have to be focused. DR. WIDNALL: Why do things tumble in the atmosphere, and is there a possible diagnostic use of measurements that appear to show something tumbling? DR. AILOR: Well, even in orbit, things can tumble. For example, as you come down from orbit, you know, there's still a little bit of atmosphere up there and so as you get into the portion where there's enough to actually affect the dynamics of an object and have that become a more principled player, it will gradually overpower the gravity gradient forces which are there and try to stabilize the spacecraft. That interaction then will cause an object to tumble. As you come down through the atmosphere, the mass properties and aerodynamic properties of an object will also cause it to tumble. We certainly see that. As to whether or not things like tumble rate could be a factor? It certainly could be, but you'd have to know a fair amount about the aerodynamic properties, about the geometry and other properties of the object to be able to determine that, I think. MR. HUBBARD: I'd like to pursue a little bit more the question of how we might be able to determine the initiating event and distinguish that from the process as it may have happened post breakup. In your experience, would you say that from directionality of, let's say, a deposition of molten materials or the way the surface had been worn away by heat, we could begin to separate the two? Would that be fair characterization? DR. AILOR: Certainly could be. For example, the orbiter was controlled for a good period of time and if evidence is found that could have occurred during that period and it indicates that a particular flow pattern or something like that, I think that could be very useful. Absolutely. I think the early debris would be really critical to an analysis like that. MR. HUBBARD: Even from debris on the ground, following the discussion of ballistic entry of a steel strut, if it's worn away sort of equivalently versus something that shows that's there's more deposition or thermal damage on one side or another, it might be a distinguishing characteristic? DR. AILOR: It certainly could be. ADM. GEHMAN: Sir, based on your analysis of previous satellite reentries – I don't want to put words in your mouth, but let me make sure I understand it – your suggestion there on kind of your first viewgraph was that the typical reentry, the process starts rather slowly and little things come off but then it reaches some catastrophic point where everything flies apart. I have got that right? DR. AILOR: That's basically correct. ADM. GEHMAN: And that is not an unusual scenario, doesn't indicate a design flaw or anything like, it's just that aerodynamics and heating of the things reach a point where it can't tolerate it? DR. AILOR: Exactly. And basically when the disintegration process starts, it is typified by not a violent event exactly but you can call it a catastrophic event where the spacecraft really comes apart into a number of portions and then from that point on, an observer on the ground would essentially see a number of objects proceeding through the sky. MR. TETRAULT: We've struggled, like everyone, with how do you separate out reentry heating from the event itself; and our plan is to really look hard at the differences between the right wing and the left wing. I would assume that you would agree that that's probably a good approach in trying to look at the differences between the two? DR. AILOR: Yes, indeed, I would. MR. WALLACE: In the civil aviation field where I usually work, we often have the challenge of differentiating damage that may have precipitated a failure event in the sky or damage that was sort of part of the failure sequence versus what was impact damage on the ground, often very critical distinctions to be made; and, of course, here we add in the thermal effects. What are your sort of thoughts on the basic methods you can use to sort those things out? DR. AILOR: Well, as you say, the challenge here is going to be that the heating itself is going to have the potential of masking the heating and loads during the breakup process; and as an object comes down and continues to break up as it enters atmosphere, it's going to have this tendency to mask the initiating event. That's going to be really the challenge here. That's why I think that the effort really needs to be focusing on the early debris and on, as you say, the differences. If there are scenarios that would cause differences in some of the debris, that would be very useful to know about. Thirdly, to focus on surviving objects which can be traced back to areas of interest by one fashion or another. MR. WALLACE: Has there been anything generally in your observation of the Columbia debris distribution and recovery process that has sort of surprised you? DR. AILOR: Well, I've been pleasantly surprised by the efforts that's been made to really recover the debris pieces and get specific information on those things – the weights, the latitude and longitudes of those. The amount of effort that's being put into it, I think, is not really characteristic of these kinds of events and may be useful. So I would say I've been very pleasantly surprised by that. ADM. GEHMAN: Dr. Ailor, the two most western pieces of debris that we've found both have been tiles, either a fragment of a tile or an individual tile, not connected to a metal or any structure. My understanding is you are suggesting, then, that a tile would have a relatively low ballistic coefficient – DR. AILOR: Right. ADM. GEHMAN: – and therefore the flight path is nearly vertical? DR. AILOR: Well, certainly ultimately will be vertical, yes. ADM. GEHMAN: What I mean is compared to something with a high ballistic coefficient. DR. AILOR: Yes. ADM. GEHMAN: Backtracking into space, then, it would be safe to assume that these things, these tiles came off relatively close to where they were found on the ground, compared to a dense object? DR. AILOR: Yes. That's exactly right. ADM. GEHMAN: The fact that all the dense objects that we've found we've found a couple of hundred miles down range, what I'm trying to do is rationalize in my find the dichotomy between something with a low ballistic coefficient that comes off late versus something with a high ballistic coefficient that comes off early, because you could have them found in reverse places on the ground. DR. AILOR: Well, a lot of that will depend on the timing of the release, too. If you've got something that's released at a very high altitude early in the reentry and it has a very low ballistic coefficient, as you said, that object will, in essence, stop very quickly and flutter to the ground. It's complicated by the fact that if it was simply a tile that came off, that's one thing; but if it was actually bringing something else with it, then there may be more going on there. That other piece of material would have probably increased the ballistic coefficient a little bit, which would make it blow a little further down. As you saw from the footprint chart that I gave where it had the multiple footprints there, the altitude and what the trajectory looks like as it begins to heal over there will really affect how things fly; but there can be low ballistic coefficient pieces that are released all through that process. So some will be carried further because they're attached to heavier debris. Some will be released and then flutter to the ground. So as you move forward in time, the footprint becomes much more complicated. ADM. GEHMAN: Another question. You mentioned the inability of aluminum to survive reentry for one reason or another. It either burns up, melts, oxidizes, vaporizes. What is your experience with rubber? We have found five of the six tires, and maybe a fraction of the sixth. We have found five of the six tires, two or three of which actually look like tires. DR. AILOR: Well, in the first place, I've never seen a spacecraft come down with rubber on it before. ADM. GEHMAN: You've probably never seen one with wheels either? DR. AILOR: No, never. ADM. GEHMAN: You've never seen rubber in the debris? DR. AILOR: I haven't. I'm sure someone could take a look and basically say if rubber experienced heating of this type, how would it be expected to respond. Some materials can be protected by the fact that they actually shed away external layers, for example, ablative materials that are used on the spacecraft reentries typically. So it may have properties that would enable it to survive of that type. ADM. GEHMAN: Very good. This debris field that we have here I think you're familiar with. We're talking about just west of Dallas to just over the Louisiana border, which is about 375 miles or something like that. Are you surprised it's that small or that big, considering that, I guess, the first shedding event that we know about was at about 225,000 feet – actually we're going to find that out here in another 20 minutes or so. Right. You had a viewgraph up there that indicated in one of these reentry things it was spread over 400 miles. What do you conclude for this one? DR. AILOR: That footprint I was talking about was from the little piece that actually brushed the lady on the shoulder. Very low ballistic coefficient piece, probably less than 1 – so it was something that, in fact, did flutter down – to the fairly large objects which were ballistic coefficients up to around 50, 60, something like that. So those are a reasonable range of ballistic coefficients. The size of the footprint here is about what you would expect to see, I think. MR. WALLACE: You were very complimentary of the amount of shoe leather that's gone into this recovery. Do you expect that any further major breakthroughs or strokes of luck are more a matter of shoe leather, or are there calculation methods you think might be further explored, backtracking pieces you have found? DR. AILOR: Well, there's a couple of things. First, I think the work that's going on relative to finding the debris is really an important part; and that has to be emphasized. That's going to be key to solving this puzzle, I believe. The second part would be to look at the debris field itself, but you have to have collected debris in that field. So this idea of going out and finding these things, I imagine that pieces will continue to be found over a period of time and they need to be cataloged and brought in and examined just as they are being now. But to really look for anything that's relate to, as I've mentioned before, possible scenarios – for example, the right-wing-versus-left-wing scenario and those kinds of things. So I think that's the way it should go. MR. HUBBARD: One last question for me at least. Looking at your observations and summary, you bring up the concept of data fusion here. I wonder if you could elaborate on that a little bit. What do you really mean there? DR. AILOR: Well, basically the data fusion means that, for example, where we have videos that have been taken by private citizens, taking those videos, processing those things, we know the orbiter's trajectory very well during portions of reentry, in a sense, fusing that data so you take the video data, you marry it with the trajectory data so you know exactly what you're looking at. You can use that information to help derive information about, when objects are shed, where are these objects, what the timing is, what are the characteristics of those objects, things like that. We talked about ballistic coefficient; but you can estimate, based on how fast something separates from the orbiter in a video, what the characteristics of that object are. So that's what I mean by fusion, just taking all of the existing data and bringing it all together so that you actually have a complete picture, as good as you can do with the data you've got, of what actually happened. MR. HUBBARD: Would you include thermodynamic analysis, you know, reentry heating in addition to these actual empirical observations? DR. AILOR: Yes, I think that's true; but the fusing I'm talking about really is more of a trajectory level, if you see what I mean. There's certainly other data. The data on the ground, for example, needs to be brought into this, as well, and should be. So it's really a question of fusing the various data. I come out of the trajectory side of the house. So looking at data from where things happened in the trajectory, tracking them down, trying to derive information on the ground, and then really developing a best estimate of what actually happened is what I'm speaking of. ADM. GEHMAN: That leads to my last question – that is, if you would, make a value judgment for us on the accuracy and efficacy of this reverse trajectory analysis. In other words, if you find something on the ground, how much effort and what value should be placed on trying to predict the point in the sky that this thing became an independent object? If you would, take a shot at that. DR. AILOR: That is going to be a real tough problem, quite frankly. ADM. GEHMAN: You mean because it's just not an accurate process? DR. AILOR: It's not an accurate process. As I mentioned in my opening remarks, we don't have internal information from a spacecraft that's breaking up as to what exactly is happening with it. So modeling it down and doing computer models of the reentry and breakup of a spacecraft, we recognize that there's uncertainty in there. The problem with taking debris on the ground and transferring it back up is you don't really know how it got here. There will be debris on the ground that will be surprising, very lightweight things, things that in a sense could burn very easily but may have actually survived and impacted the ground. Those objects we know were shielded, because they wouldn't have gotten there otherwise; but where it was originally in the vehicle and then the scenario that it followed for shedding the various layers of material and the changes in the aerodynamic and mass properties of that post object as it came through the atmosphere is going to be a very tough thing to derive. That's why I think that really a key here is to look at the early debris as closely as you can to really try to determine what really happened prior to a lot of that breakup process going on. ADM. GEHMAN: Of course, it's probably a variable – once again, I don't want to put words in your mouth. For example, if you were to tell me the ballistic coefficient of a sphere, a fuel sphere, I bet you could pin that ballistic coefficient pretty well; but if it was a piece of debris or a jagged-edged thing that was part tile, part metal, part strut, part bar, the ballistic coefficient might be a pretty big estimate? DR. AILOR: Yes. In fact, again, the ballistic coefficient of what you actually find on the ground was different at say, 75,000 feet or 100,000 feet or 120,000 feet. So the higher up you get, the bigger the changes, if you're talking about going backwards in time. So what you find on the ground is one thing, but trying to translate that back up and say, okay, well, we know it fractured off of something, what was that? We don't quite know what that was. DR. WIDNALL: From a forensic point of view, what are some of the most interesting observations that you can imagine making on the debris? The second part of that is does Aerospace Corporation have any metallurgic capabilities to help us analyze some of the observations we make on this debris? DR. AILOR: We do have, and we have analyzed some of the debris in the past. So we have some experience of doing this work. The kinds of things that, again, will be important to look for here are opportunities, if you want to call them that, for preserving some of the original events. That could be where material is found, either heat shield material or something like that is found from areas where it likely came off and protected some evidence of the original events, that would be really critical. So I think it's going to be a question of looking for objects on the ground where it's likely that some of the original evidence from the original burning or fragmentation would be preserved, perhaps behind the wing leading edge or behind tiles, those kinds of things. ADM. GEHMAN: Thank you very much. Would you like to have the last word? Any advice for us on how to solve this riddle? DR. AILOR: No. It's certainly a tough problem, but I think the advantage here is that there's been so much interest by the public in actually helping to gather debris pieces. I think that's really to be complimented. We typically don't see that kind of interest, and those debris pieces can really be essential in helping solve this puzzle. So I think that's really been valuable. ADM. GEHMAN: Thank you. On behalf of the board, we thank you for your appearance here today and for summarizing what I know is a deeper and more exhaustive study of the reentry physics and aerodynamics. We appreciate your effort and want you to know that we've learned from you and we'll see if we can't solve this riddle with your help. Thank you very much. The board will take about a five-minute break. (Recess taken) ADM. GEHMAN: All right. Board, we're privileged to have two people who have been studying this tragedy since the first day and know more about it than most other people. Paul Hill and Mr. Doug White. Gentlemen, before we start, we don't swear witnesses in but we do ask them to affirm that they're going to tell the truth and the whole truth. So I will read a statement of affirmation to you and ask you, if you agree with it, just say you will. So before we begin, let me ask you to affirm that the information you provide to this board will be accurate and complete to the best of your knowledge and belief. MR. HILL: I will. MR. WHITE: Yes, I will. ADM. GEHMAN: Gentlemen, we know you, but for the record we would like you to introduce yourself and say a few words about where you work and what your background is and then we would be delighted to listen to as much of an opening statement as you want to make. PAUL HILL and DOUG WHITE testified as follows: MR. HILL: My name is Paul Hill, and I'm a missions operations director here on the space shuttle. I'm a space station flight director. I've been a flight director for about seven years. ADM. GEHMAN: And you are currently – what are you doing for the MRT? MR. HILL: For the MRT I run a team that's called the video sightings assessment team. After Doug talks about the time line, I'll go into great detail about what we do and how we do it. The short answer is we're trying to make some sense out of the public imagery and any external sensor data that we can get our hands on to tell us what was happening to us as early in reentry as possible and maybe shed as much engineering information as possible on what was going on with the vehicle before we knew what was happening on the ground. MR. WHITE: My name is Doug White. I'm a director of operations requirements for United Space Alliance. In my job I'm responsible for turnaround test requirements at the Cape. I'm also responsible for anomaly resolution. I'm also responsible for the engineering support during missions. I do have the time line to talk about today. As far as what I'm doing on the mission response team, I am on the team which we call technical integration team. Basically our job is, from a management perspective, to try to pull together all the different efforts of the different teams, the aero, the thermal, the scenario teams, and try to make sense out of all the data from all the teams and then try to bring a coherent story together. ADM. GEHMAN: Thank you very much. Which one of you is going to go first? MR. WHITE: I think I'll go first. I plan to walk everyone through the time line. If you go to page 3 of my briefing, please. On page 3, this is a graphic showing the sensors that we're most interested in in the left wing. This particular chart shows the sensors in the left wing. There are a number of sensors in the wheel well that we are interested in that we got data from that behaved in an off-nominal way. There are also temperature sensors out in the wing, some of which went off line, which was off-nominal, and some of which did stay on line, which also tells us things that were not affected. The different colored wires that you see represent the wiring runs for those particular sensors. The pink one is for sensors that were aft in the wing and runs forward past the wheel well and then ultimately into the mid body where some sidewall temperature sensors, one of which has a yellow line coming from it, that indicates the wire run for that sensor which was inside the mid body. There's also a green and a gray wire run you see in the back there that goes through a connector box and into the aft. The green wire run is for sensor data from those particular sensors indicated by green dots. Then the gray wire run is for a power cable. It's a little bit different than the sensor wires. This provided power to the actuators and came from a box there which is labeled ASSA4. That stands for air surface servo amplifier. That basically provides electrical power and commanding to the actuators for the elevons on the back of the wing. ADM. GEHMAN: Doug, before we leave that, pardon me for interrupting. To what degree is that a cartoon and to what degree is that a fairly accurate representation of where the cables actually run? MR. WHITE: It's kind of in between a cartoon and fairly accurate. For example, the pink wire does run exactly alongside the wheel well and does turn and go in front of the wheel well and does run to a connector right forward of the wheel well, as is indicated there. So those are approximate locations of where those wire runs. Now, in the back there we see the green and gray and pink all together. Those wires may actually be separated in space by 1 or 2 or 3 feet. This is looking down on the wing, and so you can't see the actual vertical separation between these wire runs. Just because they happen to show up on top of each other in the picture doesn't necessarily mean that they're bundled together within the vehicle. ADM. GEHMAN: What's the little insert box? MR. WHITE: I'm sorry, I forgot to mention that. That little insert is for some sensors that were forward on the orbiter. These are temperature sensors on a supply water dump nozzle, which is a nozzle used to dump excess water overboard. Right below that is a temperature sensors for the waste water dump nozzle, again used to dump waster water overboard. Then there's another one forward which is called the vacuum vent dump nozzle. Those sensors also gave us some off-nominal readings. Since they were too far forward to show in this scale, we just put them in as a little inset. MR. WALLACE: Just to follow on Admiral Gehman's first question, are the orbiters different? Are there variances in the actual location of the wires in the orbiters? DR. AILOR: There maybe slight differences between 102 since it was the first one built. 102 had a lot of wiring which was called development flight instrumentation, a lot of wiring for that. During its most major modification period, we removed a lot of that wiring. Some of it we just left in place. So the wiring on 102 was substantially different in the DFI aspect. But for the sensor wiring, it was pretty much the same – ADM. GEHMAN: DFI? Developmental flight instrumentation? MR. WHITE: Yes. DFI, developmental flight instrumentation. ADM. GEHMAN: I'm the acronym authority here. MR. TETRAULT: Let me continue with the wire questioning. We do know that there were actually four cable runs running back aft that went around the wheel well compartment, one on top of the other. Are all of those sensors that you show going off in one those runs or in all of those runs or some portion in each of those runs? DR. AILOR: All of the ones in the pink are all within one particular cable. We don't have the specifics about whether or not, for a particular part of run, any one of the wires was like at the back of that bundle or on the top of that bundle. There are also more – MR. TETRAULT: The question is: As I look inside the shuttle wheel well door and look up, there were four wire bundles that run aft? MR. WHITE: Right. All of the ones in the pink wire are in a single bundle. MR. TETRAULT: Okay. Are the red ones in that same bundle, the ones that went off in the aft end? MR. WHITE: Yes, all of the ones that went off in the aft. MR. TETRAULT: So everything that went off are in one single bundle? MR. WHITE: Yes. There are also many other wires, though, in that bundle for which we do not have data. MR. TETRAULT: Understood. Do we know if that's the top bundle or the middle bundle or the lower bundle? MR. WHITE: If I remember the picture right, it's the upper one. ADM. GEHMAN: But we'll find that out. MR. WHITE: Yeah. And I can give you the more exact answer. I'm just trying to remember it off the top of my head now. ADM. GEHMAN: We'll go back to the blueprints. Okay. Please continue. Thank you. DR. AILOR: All right. Next slide, please. This particular time is about 7 1/2 minutes before loss of signal, at a GMT of 13:52, and all of our sensors appeared nominal. Next slide, please. Now, this slide we didn't show any sensors going off line but we put this in the time line. This particular time 13:52:05 is the first indication that we had some off nominal from an aerodynamic standpoint. We were able to derive aerodynamic coefficients in yaw and roll which showed us that we were flying differently than we expected to. You're going to hear a lot more about that tomorrow, but basically the way we have done that is to look at the way we should have been flying, look at the way we actually were flying, and take the difference between the two and come out with some moments on the vehicle both in the yaw and the roll. This particular off-nominal event, it started first in the yaw component. We are seeing a different yaw at this point in time than we expected to see. Next slide, please. This is our first sensor that we saw with a small rise, and I want to stress that this was a very small – ADM. GEHMAN: Excuse me for interrupting again. If it's okay with you, we'll talk about these things while you have them up. MR. WHITE: All right. That's fine. ADM. GEHMAN: This off-nominal measurement we will talk about tomorrow when we talk about aerodynamics. I want to get to the level of detail that and your team have been going through. You didn't realize this until about Rev 12 or Rev 10. Can you tell me when this became apparent? DR. AILOR: Well, fairly early on, the aerodynamic guys knew that we had differences in the flight control from what we would have normally seen. They looked at the aileron, and the aileron was behaving differently and continued to behave differently throughout the entry. It took a while before we could back out that particular moment in time that we just went through there was the very first indication that this derived yaw delta was first affecting us at that point in time, but fairly early on we were able to see some of the larger flight control responses that were off nominal to us. ADM. GEHMAN: I could look it up here, but you may be able to tell me. We are approximately what altitude and what speed here? MR. WHITE: I don't have those numbers. There are versions of this that do have all those numbers on there. I guess I could look it up, too. I have some notes here. ADM. GEHMAN: But we're approximately 235,000 feet. MR. WHITE: That's about right. ADM. GEHMAN: Okay. Please go forward. MR. WHITE: All right. This is the first sensor that went off line. This is a left main gear brake line, Temperature D. It began a very slow rise. We call it a bit flip, which is essentially one bit in the data stream showed that it was rising. And we believe this is the first indication that there was an off-nominal event and something was going on with the orbiter inside that was causing that measurement to rise. Going on to the next page, these are the supply water dump nozzles A and B that I talked about. There are three nozzles to the forward there – the supply water dump; the vacuum vent dump, which is the very forward one; and the waste water dump, which is actually below the supply water dump. These nozzle temperatures A and B both began an off-nominal rise rate. If you look at the graphs, you'll see a very small knee in the graph where the two sensors are rising at a particular rate and then there's a bend where they start rising at a faster rate. This continues for about 15 seconds or so and then it bends back over and starts rising at the same rate that it had been before, at the nominal rate. MR. WALLACE: This picture doesn't tell you where that is, does it? MR. WHITE: Well, again, that's why it was an inset. They're very far forward on the orbiter, just right at the beginning of the wing. That little diagonal you see there is the very beginning of the wing chine, and they're just aft of the crew module portion of the vehicle. They're on the side wall. We're just showing them on the top for visibility. They're actually both on the side wall, just above the wing. MR. HUBBARD: Now, this anomaly is in a completely different place – as you say, well forward. Is there anything that would lead you to believe that this is, in fact, a sensor malfunction, you know, something wrong with the box, the electronics box? MR. WHITE: It does not appear to be. We don't know of failure scenario that would explain this as a sensor malfunction. We think it is real data showing us there was a change. Now, whether or not the change that caused these temperatures to rise is related to what ultimately caused our tragedy, we don't know. They may be detected. So we're including this in our data, and we'll continue to look at it until we can explain it. MR. HUBBARD: So you're including that this is really data, from everything that you know? MR. WHITE: Yes. DR. WIDNALL: How anomalous was this anomaly? Have you looked at early shuttle flights to see if you had similar events? MR. WHITE: For this particular measurement, we did look at every single mission; and every single mission, these vent nozzle temperatures rise at a very straight, steady rate. So this is an anomaly in that the rate changed; but it was a very short duration, about 15 seconds or so. They were rising at a higher rate; and after that, they went back to their same nominal rate. So whatever caused them to rise at this higher rate was a transient, at least locally transient event. ADM. GEHMAN: I'm just stating the obvious here. Obviously this is pre-video here. We're out over the ocean? MR. WHITE: Right. There is out over the ocean. If you notice in the lower left, there's a ground track trying to show approximately where we were with regards to the ground tracking. We're still well off the coast. ADM. GEHMAN: So if something was going on, we have no video of it. MR. WHITE: Right. MR. HILL: We are within a few minutes of having our first video when we see this. MR. WHITE: All right. If you go on to the next slide. This is the vacuum vent, just a few seconds later. It began its rise as well. Next slide. Now we're back into the wheel well. This is the left main gear brake line temperature A. This is down on the strut for the landing gear, and it began a very slow rise. Again, all of temperatures in the wheel well first exhibit a very slow rise rate. It wasn't until about two minutes from now in the time line that they began a much more rapid rise rate. ADM. GEHMAN: We're both trying to do the same thing here. We're trying to characterize the heat in the wheel well. MR. WHITE: Yes. ADM. GEHMAN: Can you describe to me exactly where the sensor is? Is it inside a block that's measuring the hydraulic fluid temperature, or is it up against the block where the sensor is out? MR. WHITE: This particular one is on the hydraulic line that's on the strut. So it does have some exposure, fairly good exposure to the atmosphere in the wheel well. ADM. GEHMAN: So it's not buried inside a great big block or something? MR. WHITE: That particular one is not; but, you know, there is a heat sink of the actual strut itself. That provides some heat sink. Some of the temp sensors down in the wheel, you have the heat sink of the wheel itself. Many of the temp sensors that you see lined up four in a row that are on the side wall, some of those are actually under epoxy covers and so would not have a good exposure to radiation or convected heating. ADM. GEHMAN: But this particular one? MR. WHITE: This particular one would have a fairly good exposure. ADM. GEHMAN: Thank you. MR. WHITE: Next slide, please. This is back on the side wall. Again, this is the left main gear brake line temp C. Again, beginning a very slow rise. Next slide, please. All right. Now we start to see things going on in the wing and we believe this is directly related to some sort of burning or disintegration of that pink wire run that's affecting these sensors. The reason we believe that is because some of the other sensors nearby them don't show any effects and these sensor do start to show effects. So we think it's happening away from where those sensors are. It's showing that completely colored in. It's off line. These sensors, we've done some testing that when you burn through the wire, you end up with a variable shorting, a variable resistance in the wire and you start to see the same kind of trail-off in time. It doesn't immediately just go off to its off-scale low reading. So this particular sensor at this time began to trend down. Next slide, please. Then a few seconds later that sensor was completely off line. Next slide, please. All right. Here's another indication that we put in the time line of another off-nominal aero event. This is the first clear indication. We mentioned before that we had the derived yaw moment showing us we're off nominal. At this point we began to have an off-nominal roll component to the aerodynamics. Next slide, please. Again, this is another sensor in the wing which began to trend down. This is the hydraulic System 1 left inboard elevon actuator return line temperature, and it began its movement downwards. Next slide, please. Hydraulic System 3 for the left outboard elevon – MR. HUBBARD: Just clarification as we go here. The ones that you feel fairly certain are showing the actual wire damage, have you been able to back up and reconstruct in the wire bundle what was where? MR. WHITE: No, that's one of the things that we don't know. The drawings are not specific enough to allow you to reconstruct which wire might have been on the outside of the bundle, if you will, and which wire might have been farther back in the bundle, which wire might have been right in the center. We don't have that level of detail to know what the placement of each single wire was within its larger bundle. MR. HUBBARD: Is there a hope of reconstructing that from closeout photos or as-built drawings or anything or is that pretty much – MR. WHITE: No, we will not be able to reconstruct that. ADM. GEHMAN: Are the wire bundles themselves encapsulated or covered other than the individual wires being covered? MR. WHITE: Individual wires, sometimes you have like twisted shielded pairs and you have shielding around those; but then once you make a larger wire bundle, no, the wires themselves are not covered with any kind of insulation. We do, for a lot of our wire runs, put convoluted tubing around, that black crenelated tubing that provides some impact resistance for people working around the wire. That's made out of a Teflon-like material and provides some impact resistance, but it wasn't designed to provide any kind of a thermal barrier or anything like that. ADM. TURCOTTE: As you're talking about all the wire here, all of this wire that you are talking about is all Kapton wire. Is that correct? DR. AILOR: Yes. This is all Kapton-covered wire. Yes. All right. We'll go to the next slide. This is the hydraulic System 3 left outboard elevon actuator and return line temp that actually finally went off line. As I said, it had begun its little – it takes a few seconds for these things to go down. Some of the ones that I'll show you a little bit later actually took quite a while to go off line, which indicates to us that maybe they were shorting or that part of the wire was burning through more slowly at that point. Next slide, please. This is back to the system 1 on the inboard. That one has now gone off line. Next one. This is hydraulic System 1 on the left outboard. That particular sensor is now gone off line. Again, as I said before, the reason we believe that the damage is occurring away from the actually location of the sensor is because you see that green dot right next to it and that particular sensor was not reading anything off nominal at that particular time. So whatever was causing the damage was happening somewhere else. Next slide, please. This is back to Hydraulic System 2 left inboard elevon actuator. Return line temperature again started its slow change to going off line. Next slide, please. Now we'll go back forward, and you notice that our supply water dump nozzles have now come back to their nominal rise rates. So whatever effect was going up front is now not there anymore and the supply water dump temperatures are back to their – they're still increasing. That's nominal, the way they've been for every other flight. Next slide, please. Then also the vacuum vent nozzle also at the same time went back to nominal. You can see at this point we're just now crossing the California coast and just about to pick up video, which Paul will talk to you about in a moment. ADM. GEHMAN: Doug, the sensors back by the elevons, all of them back there – I've got the same thing in front of me that you have. For the people in the audience, there's a time line, this little sliding scale across the top of the viewgraph. MR. WHITE: Right. ADM. GEHMAN: The first sensor. I'm talking about just the sensors that dropped off scale. The first one is 52:56, and then the one just before this you've said was 53:35. So essentially that scenario that you just went through with these five sensors, that happened in 40 seconds. By my arithmetic it took about 40 seconds, that little scenario you just went through. If we assume that you're right that the insulation of the wires were melted and they shorted to each other or shorted to ground or opened – and by the way you should be able to tell us that, right? MR. WHITE: Well, again, we haven't done testing so far to where we took – we're planning on doing more tests to get a more representative case, but we took a wire bundle, we attached sensors to the end of it, we put a torch on it, and we looked at the characteristics of the sensors going off line, and they do look similar to what we saw in the vehicle. We do see them begin to do a slow decline, and then they eventually go off scale low. ADM. GEHMAN: So just for my mental picture, then this little scenario of whatever happened in that wire bundle took about 40 seconds, according to my arithmetic. MR. WHITE: Yes. ADM. TURCOTTE: Before we continue, could you explain the physical – I guess the void that is the wing, is it possible, for example, for air to flow freely in there? Is it a sealed compartment? Could you explain that as you're looking at the sensors – in particular, the relationship? MR. WHITE: Let me see if I can explain a little bit. If you see the panels all along the edge there of the wing, those are the reinforced carbon-carbon panels or RCC panels. Behind them is an aluminum spar that runs all the way down the length of the wing. You see the vertical lines. Those are solid aluminum spars with some cutouts through them that would allow a vent passage, if you will. There's one main vent passage pretty much where the pink wire runs, which is how you get through those spars. The horizontal lines are representative of rows of boron aluminum rib struts which are basically tubes that are there for reinforcing the structure of the wing. So that area from up and down on the slide here would be all open; but in each one of the spars, which are those vertical lines, you're closed out except for some small openings. ADM. GEHMAN: And the wheel well? DR. AILOR: The wheel well is completely enclosed from the rest of the wing. There is a hole in the very front of the wheel well that's about 5 inches in diameter which would allow some flow into there. There are some other drain holes and some small openings around some of the hinge covers which would allow a very small amount of flow out. The square area of the hole into the wheel well in the front is about 19 square inches. The remaining holes altogether total less than 1 square inch. ADM. GEHMAN: So the forward bulkhead of the wheel well, there's a hole with a screen – MR. WHITE: Yes, it does have a screen on it. ADM. GEHMAN: – which allows kind of free communication into this what we call the glove area. MR. WHITE: Yes. ADM. TURCOTTE: So it's safe to say that an air molecule, once inside the wing, is pretty much free to flow around the inside of the wing? MR. WHITE: Through the vent passages. Right. Also there's another hole between the wing glove area and the mid body that's forward, about where that yellow arrow is. There's another hole in the mid body there which is rather large. That particular hole is about 146 square inches. DR. WIDNALL: What is the material that the wheel well structure is made out of? DR. AILOR: It's made out of aluminum honeycomb. DR. WIDNALL: How thick is it? DR. AILOR: I do not know that thickness. We can get that for you. DR. WIDNALL: Okay. But it's basically a thin piece of the honeycomb and another piece? MR. WHITE: Right. A thin face sheet, some honeycomb material, and another face sheet. Next slide, please. All right. We've annotated the debris events. We are over California now and we'll see in the videos from the public that we were starting to see debris being shed from the orbiter. This is the first one that we've seen in any of the videos that have been provided to us. So we call it Debris No. 1. The timing on that is plus or minus 2 seconds, which is about the best we can resolve from the video. Next slide, please. Debris No. 2. Next slide. Debris No. 3. Coming off relatively rapidly. Next slide, please. You notice with the little time hack up at the top there, we're starting to put triangles below the line for the debris events. The diamonds along the line there are for the off-nominal sensor readings, and then the two triangles on the top of the line are for the aerodynamic readings. That's how you read that little graph up at the top. Next slide. This is the fifth debris. Next slide. Okay. Now, we start to see another temperature rise in the wheel well. This is again also on the strut. Also should have some fairly good communication with the flow of whatever is happening in there. This is left main gear brake line Temperature B. MR. TETRAULT: Can I ask a question about that? This one is probably the most confusing sensor for me personally. Line Temperature A went off – and I notice that you appear to have changed the timing on this a little bit – went off at about a minute to two minutes. Line Temperature A and B are about – the sensors are about 2 inches apart. MR. WHITE: That's correct. MR. TETRAULT: At the same time, you have D and C gone, which have significantly gone off already early, significantly separated both in the X, Y, and Z dimensions, which would tend to suggest that the entire wheel well compartment is warm. Why do you see this big, huge time lapse between A and B, which are separated by 2 inches? Is there any explanation that you all have come up with, or at least theory on why there is this big separation in time? MR. WHITE: Right now we do not know of a good theory that holds together that says why one would show the rise and not the other. At about this time now, the rises are starting to become significant. So we don't have a good theory. It may be the amount of heat sink, the way it was attached to the strut itself that provided some more resistance to temperature rise. We really don't have a good theory right now for why one 2 inches away would rise earlier than another one. MR. TETRAULT: It's significant in terms of the time. A minute in this entire frame is a virtual eternity. MR. WHITE: Yes. One possible explanation that we've been kicking around is the fact that whatever the event is that is causing heating in the wheel well might not be constant in the sense that it's continuing to direct flow into the wheel well. Perhaps we were directing flow in at one point in time and through the dynamics of the vehicle through the evolving change in the damage to the vehicle that the flow was redirected to some other part of the wing for a time and then came back. MR. TETRAULT: You're talking about the equivalent of a run-away fire hose kind of thing. MR. WHITE: Something like that. I wouldn't describe it quite that way; but, yeah, something like that where if you had some sort of a plume heating into the wing that maybe it was pointing one direction first and then another and then back again. DR. WIDNALL: Given the extensive damage that has already occurred to the vehicle at this early time, I guess I'd question the use of the word "early debris." I guess from my point of view I would call them mid debris. I mean it's clear to me from the time line that things must have fallen off in the ocean well before California. And we don't know obviously. MR. WHITE: Right. We don't have any evidence of that. These are the first debris events that we see. So we just started at 1. DR. WIDNALL: But at this point you've already got some kind of hole in the vehicle, you've got a wire bundle that's either completely burned through or burning through, you've started to pick up what I call flow inside the wing. So clearly some structural damage has already taken place, by whatever mechanism. MR. WHITE: Right. We do believe that we had structural damage somehow at this point in time that was allowing flow into the wing. Whether or not we had shed any debris out over the ocean earlier, we can't say one way or the other. It would be speculation. MR. HILL: We call them early debris to distinguish them from the actual spacecraft breakup over Texas. DR. WIDNALL: I understand that. ADM. GEHMAN: Doug, in your machine here, you don't have the sister viewgraph? DR. AILOR: I do, but they told me they could only project one at once. If you want to see the other one – you're talking about for the vertical elevations between these? ADM. GEHMAN: Right. If you could do one of them. I don't know if you could do the companion to this one or not. MR. WHITE: Well, if they want to go ahead and bring it up, it's called Part 2. ADM. GEHMAN: Well, okay. Let's not do that. MR. WHITE: Okay. We could do that. I think they only have the capability to show one at once, though. All right. Let's go on to the next slide. All right. You asked about how early we were able to see things. The start of the slow aileron trim change – again, I put the triangle up on top of the line there – this was one of the early aerodynamic things that we noticed. The two events that we talked about earlier took some time for us to back out or reconstruct. From examining the data shortly after the accident, this was one of the things that we noted pretty early in the data. So this is another aerodynamic event that's off nominal. We started to see a slow trim change in the aileron. In the orbiter there is no real physical aileron like you might have in an airplane. The aileron is a theoretical difference between the elevon position on one side of the vehicle and the elevon position on the other side of the vehicle. So by adjusting the relative different positions between those, you can create the aileron effect. So that aileron effect was keeping the vehicle flying the way we wanted it to. So as the forces began to change on the vehicle, the trim changed; and we saw that in the data. MR. HUBBARD: Doug, I just want to check and see that we're working from the same time line here. What I've got is what's called Rev 15. MR. WHITE: Yes. This should be Rev 15. MR. HUBBARD: Now, you skipped past what are labeled "Unexpected Com Dropouts." Is that because they are not part of the temperature sensor story? MR. WHITE: When I was coming here today and preparing for this, it was a question to myself whether I should brief from the time line that has every single event in it or I should brief from this more graphical presentation which did leave some of the events out. This particular graphical presentation does not have every single event like some of the com dropouts. To this point we've already had numerous com dropouts that we consider anomalous. We just did not model those in this particular graphical presentation. MR. HUBBARD: So I guess the follow-up question to that is: Where are the avionics boxes or the antennas or whatever associated with those and can you make any connection between this set of anomalies and the com dropouts? MR. WHITE: Well, we are trying to do that. We are trying to create an entire picture where we can explain events that would affect everything that we see. So com dropouts would be one of the things that we would try to explain. As for the location of the actual avionics boxes, they're in the avionics bays which are forward in the crew module; and the antennas are in the crew module region, on the top and the bottom of the vehicle both. MR. HUBBARD: So this is work in process. MR. WHITE: So they're well forward of this area where we're seeing the heating, but that's not to say whether or not some disturbance in the hot gas flow around the vehicle may or may not create a situation that would cause the com to drop out. We were at fairly good look angles between us and the satellite. So we should have had good communication in this region. We have looked at past flights. So we did have good communication in these regions. So again, that's why we consider some of these com dropouts as anomalous events. MR. TETRAULT: Have you seen any relationship to the com dropout and the debris event? MR. WHITE: I'd have to look at the timing that says how close one was to the other, but I don't believe we have been able to link any of those very closely. MR. HILL: There are debris events that are within seconds of some of the com dropouts. That doesn't necessarily tell you they're related, but there are debris shedding events in this same time frame. MR. HUBBARD: Okay. So the set of charts here, Rev 15, just looking quickly through those since you're not going to cover these, I see up through Com Event 14. How many of those are there? MR. WHITE: Well, let's see here. Let me get my other version of the time line. We had at 13:52:09 through 13:52 – well, let's back up. 13:50:00 through 13:50:43, we had five periods of com dropout from one to six seconds each. 13:52:09 through 13:52:55, there were four periods – again from one to six seconds each. That would cover Events 6 through 9. Then again, 13:53:32 through 13:54:22, which would be right in this period here, there were two more periods. One was two seconds. One was 8 seconds. Those would be Com Events 10 and 11. There are some more events, 12 and 13, that are down in the 55, 56 time frame; and Com Event 14 was down at 13:56:55. MR. HUBBARD: Okay. So can we expect to see some point in the near future a composite plot or a plot like this that shows the antenna wire, the antenna, where the avionics is and so forth and kind of be able to put it together? MR. WHITE: Well, the scale – we could probably do on a separate page just because of the scale. Yes, we could go ahead and do some kind of a graphical representation of that. Again, we don't see anything anomalous in the behavior of the com system other than com wasn't getting through to the ground. So there may not have been anything physical going on within the orbiter itself at that location on the vehicle itself. MR. HUBBARD: It could have been some interference between the orbiter and receiving stations? MR. WHITE: Yes, it could have been, again, as I said, some kind of disturbance in the hot gas around the vehicle at that time possibly. MR. HUBBARD: Okay. Thank you. We'll, I'm sure, be pursuing this further. GEN. DEAL: I'd like to bring up a question about Dr. Widnall's statement about perhaps earlier debris that was not witnessed. Can you kind of put it in context, where we saw heat onset and also the beginning of peak heating? MR. WHITE: Let's see here. Let me look at my really detailed time line and the event times for that. The beginning of entry interface, which is about 400,000 feet, is 13:44:09. The start of peak heating is at – DR. WIDNALL: 50. MR. WHITE: 50. Okay. Thank you. GEN. DEAL: The reason I ask that is to underscore her statement. There could have been things that weren't witnessed because you aren't starting to experience heat before – MR. WHITE: Right. There could have been. DR. WIDNALL: About the com. I'm very interested in the com. Is that anomalous for the whole range of shuttle missions, this loss of com? MR. WHITE: Yes. For this particular period, we have called these losses of com "anomalous events." We've compared them to other flights of Columbia on similar trajectories and we believe we should – again, because of the look angles and where we were, we believe we should have had good com. DR. WIDNALL: So it wasn't just a simple matter of shielding by the vehicle of some antenna? You've already dismissed that possibility? MR. WHITE: Yes. We've looked at that