CHAIRMAN ROGERS: Mr. Moser, will you go ahead and identify each of you and your present assignments.
MR. MOSER: Okay, Mr. Chairman, members of the Commission.
I'm Tom Moser. I'm reporting today in the capacity as the head of the failure scenario team from the Johnson Space Center. I have held that position until just recently at the same time I was director of engineering at JSC.
I began my experience with the space shuttle in 1969, and most of that time I served in capacities related to strength integrity of the orbiter and as deputy project manager of the orbiter itself.
DR. LITTLES: Mr. Chairman and members of the Commission:
My name is Wayne Littles. I am associate director of engineering at Marshall Space Flight Center, and I've been at Marshall for 18 years, and I've held my
current position for two years. And prior to that, I was deputy to the same position, and prior to that, I served as the chief of the engineering analysis division in S and E.
My education is in mechanical engineering, and I have a bachelor's degree from Georgia Tech, a master's degree from the University of Southern California, and a Ph.D. from the University of Texas.
MR. LEE: Mr. Chairman, members of the Commission:
I'm Jack Lee, deputy director of the Marshall Space Flight Center. I have held that position since 1980. I have been with the Marshall Center since 1958, and since the date of the incident I have directed the analysis of failure evaluation effort for the Marshall elements for those elements for which we're responsible. That includes the external tank, the solid rocket booster, the shuttle main engine, and the inertial upper stage.
MR. MOSER: Mr. Chairman, if it pleases the Commission, the next five speakers will proceed through a failure scenario beginning at the top level with the evidence as we see from the accident, and then into the top level fault trees, and then down into the detailed failure scenarios of each one of the possible causes.
And so I will begin that.
[1125] And to facilitate this, I will present an abbreviated time line this morning. I will provide to the Commission, if you so desire, a detailed four-page time line. But for the sake of presentation and clarity, I have abbreviated that for your presentation today.
CHAIRMAN ROGERS: I was going to ask, could you just as a preliminary matter explain the terms first? What is a failure scenario? What do you mean by failure scenario? I think I know, but it would be helpful.
MR. MOSER: And you will see that in one of our presentations here. Basically, the fault tree that you will see on the presentation
CHAIRMAN ROGERS: First you used the term "failure scenario." What is that?
MR. MOSER: Failure scenario is a detailed analyses of a fault tree as to why the various elements of the failure events could have taken place. It is using a model of a failure, a theory for a failure, and then the analysis to substantiate or to deny that each element of the failure model is in fact correct.
CHAIRMAN ROGERS: Am I correct that a failure scenario is a hypothesis of something that might have
happened, and then you consider each aspect of that to see whether it in fact did happen?
MR. MOSER: Yes, sir.
CHAIRMAN ROGERS: And then you draw conclusions from that?
MR. MOSER: Yes, sir, and we verify or deny or disprove each one of the steps of that. And today as we proceed through this, we will show you that some of the steps in the failure scenarios indicate that it is not a viable cause, and I think that will become very clear as we proceed through.
CHAIRMAN ROGERS: When you get to a fault tree, would you explain what that is, too, so the listeners understand what it is?
MR. MOSER: Okay, sir.
If I could have the first chart, please, M-1.
(Viewgraph M-1.) [Ref. 3/7-30]
This is-what I've shown here on M-1 is an outline of the investigation process, beginning with the incident. The description of the incident is captured by the evidence from the flight data, the physical data, and the photographic data. It is factual as best we know it, and I will present that to you today, along with the time line. That is the given for the problem, if you will.
The next level is what could have caused this accident, and that is the-please leave M-1 up, please, on the screen. If you could go back to M-1, please.
The second block per se is the fault tree development. It is what could have gone wrong and caused the accident. It could have been the orbiter, it could have been the external tank, it could have been any number of things which caused that failure. It could have been the weather conditions.
Those, it is the anomaly and the vehicle for the failures which constitute the fault tree. From those possible fault tree elements, we then establish and gather data to either substantiate or deny any one of the branches for that fault tree, and we will have a detailed fault tree for you for each one of these things by the other presenters.
To support that, in the middle of that investigation process, the incident data bases are derived, both from the evidence which has been measured, which we document as given up in the first block, and also there is data which is derived by test and analysis, looking at records, the [1126] type of things which you gentlemen-the gentleman just spoke to you on processing the hardware and the checkout. This is what
is then used to verify or deny parts of the failure process and analysis.
All of that then, with the details of the failure analysis which postulates the sequences, the causes, and the special tests and analysis which is conducted, which we will talk to you about in detail, are then fed back and the entire loop is iterated back and forth until we finally decide on those events which are still possible or probable and work those until we can either prove or disprove them, hoping to come out with conclusions as to what the causes were or findings.
And today what we're going to present to you are some findings, and I think. some of these elements, we are going to show that there is a very, very low probability that they contributed, in all probability they did not, they are not probable causes.
Others, we're going to report to you on the status of our analysis and investigation.
If I could have the next chart, please.
(Viewgraph M-2.) [Ref.3/7-31]
This is the beginning of the abbreviated. If you can scan in on the left-hand side of that chart if you will, please.
The time line that I have shown here begins
before T-zero. It begins with the SSME start command. As I stated earlier, I have abbreviated the time lines and the events just for the sake of clarity, and the start of this event in this time line is for the launch itself.
As we develop possible failures which were caused by any one of the elements that require that the time line begin earlier than this, during the checkout and processing of any one of the elements, that is shown with those particular scenarios.
I will now present to you evidence as we know today to be factual-it is not derived data that I am going to show-that goes with each one of the events of the time line. And so this is a given to any one of the detailed failure scenarios that you will see.
Starting with the SSME startup, that is the main engine startup, that begins at approximately 6.6 seconds before T-zero, which is the ignition signal to the solid rocket booster motor. Subsequent to that, at about one-half a second, .531, we saw-and if I could have chart M-8, please.
(Photograph M-3.) [Ref. 3/7-32]
We saw a puff of smoke at the aft field joint of the solid rocket booster motor. We have deduced from photographic evidence from multiple camera positions that
the puff of smoke is coming, originating from between the solid rocket booster and the external tank. It is in the quadrant that is to the right of the picture as you see it there and on the far side of the solid rocket booster.
That smoke was evident from .5 seconds up until a little less than four seconds. There are some photographic observations that indicate that that smoke and gases can be seen as late as 12 seconds. That is still under investigation by enhanced photography.
CHAIRMAN ROGERS: At what point in the time line do you think the smoke occurred?
MR. MOSER: It occurred at .531 seconds after ignition signal to the solid rocket booster.
CHAIRMAN ROGERS: About a half a second after liftoff?
MR. MOSER: Yes, sir.
[1127] CHAIRMAN ROGERS: And how closely have you identified the source of the smoke?
MR. MOSER: What we have done is we have identified it to be originating in the quadrant of the solid rocket booster, to the right-hand side of the solid SRM as you see it there, and between the SRM and the external tank.
We have not pinpointed from our enhanced
photography the exact location of the source of the smoke yet, sir.
CHAIRMAN ROGERS: How close are you to doing that?
MR. MOSER: I can't answer that right now. We thought we were about there about ten days ago, and that photography enhancement has not panned out and proven that yet, sir.
One of the cameras that had a better view of that was non-functional at the time of launch. So we are having to use some other techniques, and I don't know that we will be able to, with the data that we have, to pinpoint exactly what the source is.
We have concluded, however, from the photographic data that it is not coming from the extreme, in this photograph, from the extreme right-hand side of the solid rocket booster, which is where the check port, the test port, is located.
DR. RIDE: Can you put limits on the circumferential arc?
MR. MOSER: No, only to say that it is within that quadrant, Sally.
DR. RIDE: Between about 300 degrees and 210, is that the quadrant?
MR. MOSER: From this photograph, we can't get
it very close. From one of the other photographs that we have during the ascent we can get closer, and I will show you that here in a moment. But that is a different event.
CHAIRMAN ROGERS: It must have been an earlier photograph, though, than this, because the smoke is pretty far up on this photograph.
MR. MOSER: There could have been one, yes, sir. I have chosen the sequence of photographs to best describe it. There is one-we have some photographs that are earlier than this and that are later than this, but this is just indicative of that.
We can provide you with all of the photographs of every frame of this.
CHAIRMAN ROGERS: I think Mr. Stevenson gave us photographs in Washington which were prior to this one, which showed with a little more delineation exactly where the smoke initially came from. Am I correct in that?
MR. MOSER: The photographs that I remember seeing were about from this same angle, the same camera, as a matter of fact, I was just advised. Yes, sir, the same camera.
DR. COVERT: Mr. Moser, where vertically does the smoke first come out? You talked about the angular
position. How about the longitudinal position?
MR. MOSER: It comes out from, in the proximity of the aft field joint.
DR. COVERT: And that's close also to that ring there that we can see there?
MR. MOSER: Pardon me?
DR. COVERT: We can see a strap going around with some cork insulation or something under it, and that is reasonably close?
MR. MOSER: Yes, sir.
DR. COVERT: And that is also reasonably close to where the external tank attaches to the solid rocket motor.
[1128] MR. MOSER: That is correct, sir.
DR. COVERT: Thank you.
DR. FEYNMAN: Isn't it, so is this the black smoke you're talking about at. 5 seconds? Isn't it true that in even the first few frames immediately after the ignition that you can see some white smoke earlier?
MR. MOSER: From comparing the color of that smoke to this smoke, it appears to be a lighter color, yes, sir. I think there is some disagreement as to what the color actually is, whether it is less dense or whether it is the reflections.
DR. FEYNMAN: I'm not worried about the color,
but the time. It seemed to me that it was an extremely early incident in the pictures that could see that.
MR. MOSER: I don't believe it would be before a half a second, though, sir. That is the first visible evidence that we see.
CHAIRMAN ROGERS: Which is the first visible evidence? How would you describe, based on the first photograph that you've seen, the first visible evidence was what? Was it white smoke or black smoke?
MR. MOSER: It was a lighter colored smoke, and I don't want to say it's white. It was not white like the SRB is white, but a greyish colored smoke. That is the way it appears in the photograph.
CHAIRMAN ROGERS: And that preceded what appears to be blacker smoke?
MR. MOSER: Yes, sir, that is correct. It appeared to be-it appeared to be continuous from, certainly from a half a second to about 3.375 seconds it was continuous. After that, it is very difficult to interpret the photographs as to whether or not there is a continuous stream of anything coming out there. In some viewers' eyes and based upon the photographs that we have today, it appears to last as long as 12 seconds. But that is not conclusive at this time.
What I'm trying to do to set the stage here for some of the other detailed work is to tell you what we know to date with a lot of confidence.
CHAIRMAN ROGERS: Well, just to conclude the thought as far as I'm concerned, would you say that in your observation of the photographs the first thing you noticed was smoke that appeared to be white, and right about the same time some black smoke?
MR. MOSER: After that-first of all, it is a light colored smoke, and then it gets darker, as you see it here, and then it begins to dissipate and leave, especially as the flow around the vehicle begins and the vehicle begins moving. And so it begins light and then it gets darker.
CHAIRMAN ROGERS: But would you conclude it all came from the same area?
MR. MOSER: Yes, sir. It appears to all come from the same area.
CHAIRMAN ROGERS: Okay. Thanks.
MR. WALKER: Mr. Moser, have you verified that this phenomenon was not observed on any previous launch?
MR. MOSER: I'm sorry?
MR. WALKER: Have you verified that this phenomenon was not observed on any previous launch?
MR. MOSER: We have-I have, to my knowledge, we have not seen that event on any previous launch. There was a report at one time that they thought that an anomaly was seen after an [1129] SRB separation, but there has not been any signs of black smoke or any type of anomalous venting of the SRB's on previous launches.
MR. WALKER: Thank you.
MR. MOSER: Proceeding on in the time line, at about 20 seconds is where the solid rocket booster begins to decrease its thrust in getting ready for maximum dynamic pressure during ascent.
If I could have chart M-5, please.
(Viewgraph M-5.) [Ref. 3/7-33]
What I have shown here is some data we have acquired from telemetry, which is a presentation of the pressure, chamber pressure of the right-hand solid rocket booster motor versus time. Everything appears to be nominal at the right-hand solid rocket booster as at about 20 something seconds, 21 seconds, when it begins to decrease the chamber pressure. As it goes into the maximum dynamic pressure, everything is nominal essentially during that time.
If I could have chart M-6, please.
(Viewgraph M-6.) [Ref. 3/7-34]
This is again going back to the time line. Everything is proceeding well in the time line. It goes through the end of the thrust bucket, where it experiences minimum chamber pressure in both left and right-hand solid rocket boosters, and then the pressure begins to increase again, as was shown on the previous chart.
Shortly after that, about four seconds, we see our first evidence of the hot gases of the plume coming from the right-hand solid rocket booster. If I could have chart M-7, please.
(Slide M-7.) [Ref. 3/7-35]
In this photograph you can see t he bright spot on the right-hand solid rocket booster, and what we have done to try and enhance our understanding of where things are occurring on the vehicle, we have generated computer-aided graphics of the entire launch vehicle and overlaid them on the photograph so they are to the same scale.
This has enabled us to pinpoint as accurately as we can, with the accuracy of the photographs and the fidelity of the photographs, what the source is from this photograph.
And if I could have M-8 up now, please
(Slide M-8.) [Ref. 3/7-36]
which is a computer-drawn version of that same view. We have isolated that bright spot to be again in the quadrant, as shown right here, on the right-hand solid rocket booster. And that is the first indication of a visual plume coming out of that booster.
This we have been able to-Dr. Ride asked if we could identify it specifically, and this we have isolated to be at 45 degrees on the circumference, plus or minus ten degrees; and in the longitudinal direction we have isolated it to be at the field joint, within plus or minus one foot.
And the reason we cannot get any closer than that is just because of the granularity of the photographs, and also because of the angle of the vehicle to the camera.
DR. RIDE: Where are you taking zero degrees?
MR. MOSER: Zero degrees is on the bottom of the solid rocket booster, so it would be just about where that arrow is on the Z axis.
DR. RIDE: Say again what the foot measurement was, what you were referring to? You've isolated it within the area of one foot square?
MR. MOSER: In the longitudinal direction, we have isolated the plume which you see in the previous
photograph to be in the plus or minus one foot of the aft field joint. We cannot tell any more accurately than that from our photographic data; and circumferentially around the solid rocket booster motor, to be 45 degrees from the Z axis or, in this view, the bottom of the solid rocket booster motor.
We then proceeded into maximum dynamic pressure, and if I could have chart M-9 up, please.
(Viewgraph M-9.) [Ref. 317-37]
At 59 seconds we experienced maximum dynamic pressure on the vehicle, which was about 720 pounds per square foot of aerodynamic load. In comparison to other flights, this is less than some of our previous experience. It is well within the design nominal value of maximum dynamic pressure expected.
And the reason-I should point out also on the scale of time line, below the time in seconds shows the throttle profile for the main engines. At this time we had just gotten back up to 104 percent of our maximum thrust out of the main engines. We had been down as low as 65 percent, and that is to keep this maximum dynamic pressure to the levels that I just reported.
Within about a second after that, at a little over 60 seconds, we experienced a divergence in the solid rocket booster chamber pressure. And if you would
display chart M-10, please.
(Viewgraph M-10.) [Ref. 3/7-38]
If you can zoom in just to the lower right-hand part of that. That's good. Thank you very much.
Here you can see a deviation in the chamber pressure, and that is the internal pressure of the solid rocket booster, to that of the left hand. This is-before this time they had been tracking well within our experience base of comparing pressures between these two motors.
So we are beginning to see evidence here that that plume is consistent with a decrease in the measured pressure.
The next thing that we see is evidence of the plume deflecting. And if I could have chart M11, please.
(Photograph M-11.) [Ref.3/7-19]
The plume has grown in size. It is now being deflected because it is impinging on the external tank or because it is being deflected by the aerodynamics. It appears to us now to be deflecting because of impingement of the external tank.
CHAIRMAN ROGERS: I couldn't quite hear the last part of your sentence. What did you say at the
end?
MR. MOSER: It is impinging on the external tank.
Then at 64.6 seconds, there is, we see with the next chart, which would be-no, I'm sorry. Let me just tell you verbally what we do.
We see a change in the possible LH-2 tank leak at that time, because the pressure-the pressure is decreasing. And that is on chart M-13.
(Photograph M-13.) [Ref. 3/7-40]
DR. COVERT: Did you say, Mr. Moser, that that time corresponded with the pressure dropped in the hydrogen part of the external tank?
[1131] MR. MOSER: I'm sorry? Repeat, please?
DR. COVERT: You said at the same time the plume changed character you had evidence that suggested that the pressure drop in the hydrogen tank or the pressure in the hydrogen tank was dropping; is my understanding correct?
MR. MOSER: Yes, sir. And I will show that to you. I'm sorry I got out of sequence here. I wanted to show you the visual evidence that we are seeing of change in the plume characteristic, which is thought to be from the leak, which is thought to be a leak from the hydrogen tank.
On chart-in viewgraph M-13 is-what you see there, that is a plume characteristic. If you will go to M-15, please, and look at the top part of that plume, you'll see a change in character.
(Slide M-15.) [Ref. 3/7-41]
So that it is deflected more down, or appears to have more of a definite node at the top, as opposed to a rounded condition. That is occurring at the same time as M-17, which is the pressure profile. If you would put M-17 up, please.
(Viewgraph M-17.) [ Ref. 3/7-42]
This is the pressure profile of the liquid hydrogen tank. This is where we see that the decrease in the rise rate of the ullage pressure, that is the gaseous pressure in the liquid hydrogen tank is changing over what it had been.
It had been cycling up to that time as the demand required, and the characteristics of those cycles had been consistent within our experience base. Here we see a change in that pressure rise rate which is indicating that something anomalous is going on, like a leak.
And so when I coupled this with the change in the characteristic of the plume coming from the right-hand solid rocket booster, that is two strong
pieces of evidence that we do have a leak at that time in the liquid hydrogen tank. And I will show you some other supporting evidence to substantial that.
CHAIRMAN ROGERS: At what time was that conclusion that there was a leak in the external tank?
MR. MOSER: That was at 64.64, and that is on chart M-16, at the lower right-hand side, Mr. Chairman.
(Viewgraph M-16.) [Ref. 3/7-43]
That is when we see the change in the plume characteristic, at 64.64. And about three-tenths of a second after that is when we can determine from the measured pressure data that we are seeing a change in the pressure rate.
The data rate of the pressure is about five samples per second.
CHAIRMAN ROGERS: If you can conclude at that time that there was a leak in the external tank, can you also conclude that up to that point there had not been a leak in the external tank?
MR. MOSER: With some degree of rough granularity. There could be a small leak, I think like eight-tenths of an inch in diameter.
DR. LITTLES: About four pounds per second of liquid hydrogen could have been leaking without detection.
CHAIRMAN ROGERS: During the whole 60 seconds?
DR. LITTLES: Yes, air.
CHAIRMAN ROGERS: And what would be the size of that leak?
[1132] DR. LITTLES: It would be about a .8 inch diameter hole. I will discuss that in some of these scenarios that I will present.
CHAIRMAN ROGERS: Fine. Thank you.
MR. MOSER: I would like to add-or to tell the Commission that we will provide them with color photographs of all of the copies that you have in there today. Logistics kept us from doing that, so that will be provided to you today.
DR. FEYNMAN: I got confused in interpreting your charts and in what you said. You saw the changes in plume shape at 64.7 or so, and you see the pressure decrease in the rate of rise at 66.7. So it must be about two seconds between, is that right?
MR. MOSER: Yes, sir. I'm sorry, I did state that incorrectly, yes, sir. Thank you.
The next chart is M-18, please.
(Viewgraph M-18.) [Ref. 3/7-44]
Then at a little greater than 72 seconds into the flight is where we see motion of the right-hand solid rocket booster to the rest of the launch vehicle,
and that is shown on chart M-19, where here I display the rotation-
(Viewgraph M-19.) [Ref. 3/7-45]
-of the pitch of the right-hand solid rocket booster to that of the left-hand.
Not shown on this data is the fact that the left-hand solid rocket booster rate gyro is tracking exactly with that of the orbiter, and that is the way all three of the elements or all four elements-the orbiter, the external tank, and the two SRB's-have been tracking up until this point.
It is 72.201 seconds, we see a deviation from the right-hand solid rocket booster. It is our indication that something has failed in the aft attachment of the solid rocket booster to the external tank, and I will show you more of why we have concluded that.
If I could have chart M-20, please.
(Viewgraph M-20.) [Ref. 3/7-46]
This is a computer-drawn picture of the launch vehicle looking down on top with the solid rocket booster released from its lower link. The evidence that we have is that we have lost the load pad at that link. If that results, then the right-hand solid rocket booster then is free to pivot about its forward
attachment point and one of the remaining aft attachment points.
This is consistent with maintaining a data source from the solid rocket boosters, because the integrity of everything going on in the solid rocket boosters, the data flows through the top aft link. What is hypothesized here, and is supported by the analysis, is that the lower left-hand or the lower link has failed, the solid rocket booster has both rolled about that new hinge line so it has a new pitch and yaw attitude.
That is what we measure from the flight data. When it does that, it impacts the inner tank region, as shown here on this drawing, between the LOX tank and the hydrogen tank, there. It impacts it just at the lower portion of the frustum of the right-hand cone of the solid rocket booster.
If I could have the next chart, please.
(Viewgraph M-21.) [Ref. 3/7-47]
In a different view, we see that the SRB has moved up toward the orbiter at the aft end. And the next view, please.
(Viewgraph M-22.) [Ref. 3/7-48]
[1133] This is a view which looks at that same configuration from the forward end, and here you can get
a better feel for how it has rotated about its new hinge line. This impacts the tank, as I said, causing the tank to load up, rupturing the forward L0X tank, the hydrogen tank, and at the same time probably causing the aft bulkhead of the hydrogen tank to rupture.
DR. FEYNMAN: In order to determine the motion of this thing, of the right-hand booster, you have gyros that determine its orientation?
MR. MOSER: Yes, sir.
DR. FEYNMAN: Do you also have inertia measurement to tell whether it moves forward or back?
MR. MOSER: No, sir, just the rate gyro, sir.
DR. FEYNMAN: You don't have any inertia measurement?
MR. MOSER: No, sir.
DR. FEYNMAN: So there's no way to determine the absolute position except to guess that the upper support hadn't slipped yet, is that right? That is how you did that?
MR. MOSER: That is correct, sir, yes. And then that is part of the continuing photo analysis, too, is to verify that it is in fact still attached there. We did not see any other motion, and I don't know that it is a sufficient solution to look at the rate of change of both pitch and yaw, given that the
fixed geometry, okay, of rotating about those points, all of that data supports itself.
And then looking at the times at which the SRB rotating would have bottomed out and induced high loads in the tanks, is when we see changes in the pressure and also see physical evidence, visual evidence I might add, from the tanks, where they are beginning to lose liquid hydrogen and liquid oxygen.
And so we have about three pieces of data which supports that.
MR. RUMMEL: The aft rupture in the ET is after the explosion, due to explosive force? On what do you postulate the cause to be?
MR. MOSER: I'm sorry, Mr. Rummel. Could you repeat that, please?
MR. RUMMEL: I think you mentioned that after the LOX tank and the hydrogen tank and the inter-tank area had been damaged, that was followed by a separation in the aft end of the hydrogen tank. Did I understand that correctly?
MR. MOSER: Yes, sir. Let me verify that. We first see that, the spillage of the aft dome of the liquid hydrogen tank, at 73.137 seconds. We see-that is visually, and I think I'm going to show you a picture of that in just a moment.
MR. RUMMEL: Well, my question-perhaps you're coming to it-is the cause of the aft rupture. It appears that the SRB didn't hit the tank in that area. Was this due to overstressing from the rupture forward?
MR. MOSER: Yes, sir. The aft attachment is connected, the remaining aft attachment about which it is rotating, is connected right at the seam of the aft bulkhead to the cylindrical portion of the tank. And as soon as it rotates over and interferes with that region, then it loads it up in an out-of-plane load for the tank, and so it should rip the tank right in that region.
[1134] Plus, the solid rocket booster is rotating about 40 degrees per second at that time, and so it fits with the analysis that we have done that says that, it should have in fact tore the tank in that region.
MR. RUMMEL: So you're postulating the failing of that part of the attach fitting that is attached to the ET at that point in time?
MR. MOSER: That is correct, sir.
MR. RUMMEL: Thank you.
CHAIRMAN ROGERS: Mr. Moser, yesterday we looked at the debris and the right frustum is badly damaged. The left one looks as though it's not damaged at all. The right one seems totally consistent with
this photograph.
Have you seen that debris? In other words, the right frustum has damage which would be almost totally consistent with that photograph.
MR. MOSER: It was reported to me. I have not physically seen it myself, but it was reported to me what it appeared, and it does appear to be consistent with our failure model here, yes, sir.
DR. RIDE: Do you think that the contact between the SRB and the upper portion of the tank, the LO2 tank, is what caused the LO2 tank to rupture?
MR. MOSER: Yes.
If we could proceed on to the next chart, please, which would be M-23.
(Viewgraph M-23.) [Ref. 3/7-49]
Here, I have already described the time of events of when we see the ullage pressure drop. Go to M-24, please.
(Viewgraph M-24.) [Ref. 3/7-50]
It is-and I'm going to repeat myself somewhat here. At 72.564 seconds is the point you see here on the ullage pressure of the liquid hydrogen tank. It can now not keep up with the demands, with two flow control valves open.
Up until that time, the pressure had been
decreasing, but it had been maintaining its pressure. Now it can no longer do that. And Dr. Ride, that is when we think that the forward-we have lost the integrity of the forward end of the hydrogen tank.
DR. FEYNMAN: Sir, I hate to interrupt you. While we have the chart up, I notice that the decrease coming down earlier-and we're talking about something earlier and so I'm interrupting-from 64 seconds, the decrease is slower than the previous decreases.
Can we interpret that in some way?
MR. MOSER: I don't think I can give you an adequate discussion of that. We had seen, I think if we go all the way back in the pressure profiles, that that was not uncharacteristic. But I will verify that for you.
DR. FEYNMAN: Thank you. I'm sorry to interrupt you.
MR. MOSER: No, that's quite all right.
If you would go to chart M-25.
(Viewgraph M-25.) [Ref. 3/7-51]
Here we see the actuator motion from the right-hand. SRB, and that is very simply the flight control system trying to respond to what the rate gyro from the SRB is telling it to do. And so that tells us our flight control system is still behaving properly at
that time.
It is-
VICE CHAIRMAN ARMSTRONG: Is the rate gyro package a two-gyro package or three?
MR. MOSER: It is a three-gyro package-excuse me. Two axes, two gyros.
On chart M-26-
(Viewgraph M-26.) [Ref.3/7-52]
-now that both the LOX and the hydrogen tanks have lost their pressure, we see the inlet pressure to the SSME's dropping, and that will be discussed more by Mr. Hopson on what that event means to the main engines.
(Viewgraph M-27.) [Ref. 3/7-53]
M-27 is the same type of data for the LOX pump.
If you would go to M-28, please, back to the time line.
(Viewgraph M-28.) [Ref. 3/7-54]
This is where I pick up, at 73.137 seconds, the vapors near the inner tank region, and that is shown on chart M-29.
(Slide M-29.) [Ref. 3/7-55]
It's going to be very difficult for you to see the vapors in the inner tank region. If you can scan up
just a little bit on that, you can barely detect it. This photograph in the display here is not adequate, but that is our first indication that we can see vapors coming from the forward.
Also, at this same time there is spillage from the aft region beginning to initiate. Then in M-30
(Slide M-30.) [Ref. 3/7-56]
-we can see the increase in the vapors coming from forward, and here you can see it along the side of the external tank, just a few tenths of a second later. And then M-31, please.
(Viewgraph M-31.) [Ref.3/7-57]
Again, with the overlay from our computer-aided drawings, that is about the characteristic of the vapor coming from up forward.
M-32, please.
(Slide M-32.) [Ref. 3/7-5581
We now see a bright flash between the orbiter and the external tank, and what that is an apparent-and we can't prove this conclusively, but it appears to be now that that is a reaction or a burning of the liquid hydrogen and liquid oxygen. They have now mixed sufficiently in that region as they flow back to flash. Up until that point, it had just been vapors.
And then the next chart, please, M-33.
(Slide M-33.) [Ref. 3/7-59]
And that same type of thing propagates forward, and continuing to bum.
The next chart, please.
(Viewgraph M-34.) [Ref. 3/7-60]
That is just a highlight of where this rupture initiated with the LOX tank.
M-35, please.
(Viewgraph M-35.) [Ref. 3/7-61]
[1136] What I have done with the time line, as best I can, is to sort out anything-we try to have it as factual and true to feed into the other failure model analyses. We have categorized or
GENERAL KUTYNA: Mr. Moser, before you start on that, I wonder if I could pursue one point on the winds and air turbulence. We saw down at Marshall that the flame appeared on the side of the solid rocket at 58 seconds, and we had our max aerodynamic pressure at 60 seconds, so that was after the flame.
However, I think it is important, as you told us before, that it was quite a bumpy ride prior to that time. There were air currents or wind changes that caused the flight controls to react considerably more than we had seen in the past. While it was not out of limits, there was more activity than you had seen.
Could you characterize that for us?
MR. MOSER: Yes, I will do that. I do not have a detailed discussion for you today, but as the plume emanated from the solid rocket booster we have gone back through simulations and analysis to try and correlate the vehicle response.
GENERAL KUTYNA: No, prior to the plume, as you're going through.
MR. MOSER: Prior to the plume?
GENERAL KUTYNA: Yes. Could you characterize that? You said the nozzles were working harder than they had before.
MR. MOSER: That region, we have reconstructed all of the loads and the dynamic response of the vehicle from liftoff up until that point. The max dynamic pressure region we have not completed yet. I will give you my view of where it is at this time.
Everything appears to be okay, but we have not recreated all of the trajectory parameters.
GENERAL KUTYNA: Jack, do you know what I'm driving at?
MR. LEE: Yes, General, I believe I do. I believe we reported at that time that, even though-well, you characterized it as a rough ride, with game wind shears. They were within our flight data base.
Now, what Mr. Moser is referring to is the Max Q region. We do not have that completely reconstructed yet to be able to relate all the vehicle activities to that.
I would like to point out, General, that even though you mention Max Q at 60 seconds, Max Q really is kind of a region, say from 58 or so. It is not specifically a point. So we do relate the first evidence of hot gas emanating from the solid rocket motor as being in the region of Max Q for our analytical purposes.
GENERAL KUTYNA: But the point I was trying to make, and see if you agree with me, there was quite some load, although not out of limits, but there was some load on that vehicle prior to Max Q, from 40 to 50 seconds, that might have given it some stresses. Not out of limits again, but it could have given it some stresses that could have caused something.
MR. LEE: Yes, sir. At about 40 seconds we did see some wind shears that gave us about a two degree rate, which is not out of our data base again, but it is not exactly nominal.
VICE CHAIRMAN ARMSTRONG: Would you like to comment on the TVC limit cycle in that time?
MR. LEE: As it relates to that, the 40
seconds?
VICE CHAIRMAN ARMSTRONG: Yes, where the limit cycle reached.
[1137] MR. LEE: Can I refer that to Dr. Littles? Do you know that?
DR. LITTLES: I don't believe that the limit cycling at that point in time was really anomalous. I have heard it referred to as we were working them hard and that kind of thing, but I think that is a qualitative assessment.
I think the data we were getting was within the experience base. It is true that at Max Q we were seeing the loads that those may have had an impact, for instance, on the joint if we had something anomalous in the joint already, is what we believe.
The loads don't look to be near design limits at any point in time during there. We do still have some work to do, but the work we have done to date doesn't indicate that the loads are anomalous. We do, however, have more work to do looking at the 51-L loads, specifically as they apply to the joint for 51-L and as they might relate to some potential anomaly in the joint. So we do have some work to do there.
MR. MOSER: Thank you.
I think it is important for this, too, it
really appears now that everything is within the design limits, but what we're trying to do is reconstruct from the actual data and the best estimated winds and trajectories and everything else what the load is. And even if it is 30 percent of the design load, we want to know exactly what it is, to see if it is in fact contributing to already weakened joint.
And so it will be-I think that that analysis will be completed, perhaps this week-I'm sorry, next week is I think the schedule we are on for that.
DR. FEYNMAN: We ought to say what "Q" is. It is the resistance, the force of resistance for moving through the air, or the combination of the density of the air and the speed squared, I think, that you move through?
MR. MOSER: Yes, sir.
DR. FEYNMAN: As it goes faster, it is increasing, but as you go higher the density is decreasing. So it reached a maximum and then falls off as we go into the vacuum of space further UP.
MR. MOSER: Yes, sir, right.
DR. FEYNMAN: It's just worth explaining.
CHAIRMAN ROGERS: Does that complete your presentation?
MR. MOSER: No, sir. On chart M-35, what I have done is I have categorized the anomalies as we know them, and that is our category A, and those are the events that I have just gone through associated with the time line.
There are other possible anomalies, conditions, that we also know of that can be contributors to this accident. For instance, the temperature or the water in the joints, the dimensions at stacking, and on and on.
Now, all of those things then are picked up by the specific element which that can effect its failure and whether it could have caused it, and so that is our category for possibles. And we will have another list of anomalous conditions, those which we have derived, and so we hope to put those in the appropriate basket.
On chart M-36
(Viewgraph M-36.) [Ref. 3/7-62]
-this chart will serve to introduce the very top level of the failure analysis, starting with the explosion and then the external tank breakup, which we know, and then we want to get into unknowns of the causes.
[1138] The color code that you see here is green, a green indication along the analysis path, indicates that
it is improbable.
Today we will talk to you about-if you will move that, your camera, over to the right, please-we will talk about the orbiter, the main engine, and the cargo, the IUS, as being improbable to have caused the accident.
To the left, the things which are still possible are the external tank; and probable is the solid rocket booster.
And I would now introduce Dr. Littles, who will talk about the failure analysis associated with the external tank.
CHAIRMAN ROGERS: Mr. Moser, before you do that, may I have the pictures that we are referring to? I think we referred to them as 35. Can we show that first?
And the reason I want to do this is because there is so much discussion about a white flame first, or white smoke before the black smoke, and there's been all kinds of articles written about it, and so forth. And the photographs really don't show it.
Can you see this?
(Slide.) [Ref. 3/7-62]
MR. MOSER: Yes, sir. That in contrast-the lighting changes here, too, I think, with the
reflections and the intensity of the engines, and so that is one possible explanation for that.
CHAIRMAN ROGERS: But we're all talking about the same smoke?
MR. MOSER: Yes, we're all talking about exactly the same thing.
CHAIRMAN ROGERS: That is what I wanted to got straight for the record, because there has been a lot of discussion about the white smoke and black smoke, as if there were two different accidents or incidents. This suggests there's just one.
DR. LITTLES: I think it is just one instance, but I think if you look at different cameras and with different shadings you can get different impressions, of the color. There is a black and white camera that we have some photographs of, and if you look at that-or when I look at it, and I'm not a photographic expert, but when I look at it the first smoke that I see does look more white, and then later it gets dark.
So I think you get different impressions from different films.
CHAIRMAN ROGERS: Does everyone agree it's all the same smoke?
DR. LITTLES: I believe everyone agrees it is all the same smoke, yes.
CHAIRMAN ROGERS: Thank you very much.
DR. LITTLES: Could I have L-1, please.
(Viewgraph L-l.) [Ref. 3/7-63]
This chart continues where Tom left off, and in his chart he had the external tank and the SRB in a circle, and so I am picking up at that point and carrying to the right a little more detail at this point the items that we have been investigating and some that we are continuing to investigate.
There are some things which we have categorized as improbable and shaded green, both on the external tank and the solid rocket booster. Would you come a little closer to the right top so I can see the blocks a little more clearly. Thank you very much. That's good.
[1139] Okay, coming down from the top, the damage at liftoff and going over to the right, the pad debris. Those we have shaded yellow at this point and I will discuss those later within other scenarios. I won't go any further with that at this point.
Now, premature detonation of the linear shaped charge has been ruled as being improbable. That is based upon physical data, the hardware that has been recovered. We have recovered portions of the linear shaped charge and they weren't detonated, and so we know
that wasn't the cause of the explosion of the external tank.
A structural flaw, I will discuss also later that line, so I will leave that one for now.
Now, structural overload, we have touched on that in the last few minutes. We have looked at the loads. We have a complete reconstruction now of the liftoff loads, and we see nothing anomalous there. The loads are well below design.
We have done a lot of work already on the Max Q and the other phases of flight and, as Mr. Moser said, we haven't completed that, but the data that we already have indicates that that is not a probable cause. We are going to continue to do that reconstruction, and we should finish that within the next I think week or ten days and rule that one out.
DR. COVERT: Dr. Littles, when you say you have ruled it out or potentially ruled it out, do you mean as a single cause in and of itself, but initially there could be other events that took place so that that combined with these loads could in fact be a potential cause? Do I understand you correctly?
DR. LITTLES: Yes, air, that's absolutely correct. As I mentioned a minute ago, we are still particularly interested in these specific loads for
51-L, for instance as applied to the 51-L joint. And so there is continuing work in that area and will be even after we look at the final reconstruction of the loads. I will discuss that as I go through some of these other scenarios.
But we are doing some work in that area and we will continue to do that for awhile.
DR. COVERT: Thank you.
DR. LITTLES: We have lost our screen. I will continue from the chart, then.
All right, then. To the right of structural overload, the block is the thermal protection system on the external tank. We think that to be an improbable cause for initiating the failure. We have done analysis assuming that we have lost TPS in various places on the tank and through the flight regime that we had progressed before we had the problem and the failure beginning at 59 seconds.
We didn't see any areas that would be overheated to the point of having a failure. We also have photographic evidence and don't see anything there, and so we don't believe a loss of any part of the thermal protection system on the tank initiated the failure.
Coming down then to the solid rocket booster,
the same comments that I made relative to the external tank apply to the structural overload and to the liftoff and flight loads. But again, as Dr. Covert points out, we are still interested in those loads relative to other potential failure modes.
Relative to the item on the bottom, the premature linear shaped charge detonation, we know of course that the range safety system operated properly when we gave-when the range gave the boosters destruct at roughly 109 seconds. And so we've ruled that out, or we think that is an improbable cause of failure.
[1140] Now, case membrane anomaly, to the bottom right, that is covered in one of the scenarios that I will address, and so I will cover that one later. And also, the SRM pressure integrity and the joint seal, those are the primary items in the scenarios that I will present, and so I'll cover those in the next few charts.
Going then to L-2 -
(Viewgraph 1,2.) [ Ref. 3/7-64]
What I have on this chart is all of the scenarios that we are pursuing for the hot gas leak. I will step through these one at a time. The line that I will be pursuing is highlighted in red, so you can
follow it through.
What I will do is describe for you the failure mechanism which is hypothesized for each one of these lines. I will mention to you the work that we are doing, the analysis and the tests that we have going on to assess that hypothesis, and then I will give you a summary of our findings to date. And if we think we can say it is not probable, I will indicate why.
Okay. The first one, then, as you see in this chart is the solid rocket motor inhibitor flaw. Could I have chart L-3, please.
(Viewgraph L-3.) [Ref.3/7-65]
Okay. This is a schematic representation of the joint. I think you have seen this before. The failure which is hypothesized in this particular scenario is that we could have possibly had a flaw in the inhibitor. I Come in a little closer, please, just at the top. Move it up to the right, please.
Okay, you see the indication there of the molded inhibitor. If we had a flaw in that inhibitor-and it would have to be fairly large, something like an inch in diameter. If you had a flaw there and you started burning, getting hot gas through that flaw and igniting the propellant and had the propellant started
burning back toward the case membrane, then you could create a situation where in the time frame near 60 seconds you could get a burn-through of the membrane.
In this particular scenario, as you see, it is nut dealing with the joint itself on this leg. It is dealing with the potential of a case membrane burn-through someplace other than the joint.
We have done a number of things in looking at this. We have reviewed the build records and process papers for 51-L, the right aft segment inhibitor. We have reviewed our experience base with these inhibitors, and we have done some analysis to determine whether by analysis that failure mechanism is possible.
One thing that we know is that the molded inhibitor is laid up, it is eight plies of rubber which are vulcanized together. Now, having eight plies of rubber vulcanized together, it is not likely that you would have a flaw in eight pieces. So that is against having this particular scenario be true.
We have had no previous problem with this inhibitor. The problems in this area are not in our data base. The analysis of that, as I mentioned, indicates that in order to get the burnthrough or the burn-back of the propellant and the burn to the insulation and burn through that insulation and do that
in the time frame of 59 seconds would require about two and a half times as much heat transfer as you would expect to get at a maximum there.
[1141] So that doesn't make it look likely.
There are a couple of things that are positive. It could-as Tom mentioned, we saw a pressure change at 59 seconds in the motor. In order to have a failure somewhere inside the motor with anomalous propellant burning, you have to get it at a place where it won't allow the pressure to change in that motor. Normally, if you had a crack in the propellant which came from the middle down, you get a higher burn rate. You would see a higher pressure.
In this particular area, since you're burning back and beneath the propellant, you wouldn't see an increase in pressure. It would be very slight. It would be less than the bit change on pressure, and so that would support it.
But all of these things taken together-oh, another thing, too, of course, is that this would not be consistent with the smoke puff that we see initially. This would happen some time later in flight. And so, taking all of these things together, we don't think this is a probable scenario, and we have listed it as not probable.
Could I have L-4, please.
(Viewgraph L-4.) [Ref. 3/7-66]
On this particular one, I'm going to discuss two routes of a scenario together because they are very similar. This one hypothesizes what was mentioned a minute ago, the small hydrogen leak which you could have and not detect it with instrumentation, and that, as we mentioned a minute ago, is four pounds per second.
If you had a leak of four pounds per second and it leaked and the hydrogen burned and impinged either on the area of the joint, the aft field joint, or on an area of the membrane and heated it up enough, you might generate a failure, and that is what this hypothesis is.
Okay. The failure mechanism again is you have to have either an undetected flaw in the structure of the tank or you would have to have debris or some foreign object strike the tank at or near liftoff and cause the hole to create the leak. And then, as I said, the hydrogen bums and impinges on some location of the solid rocket motor and overheats either the joint or the membrane to cause the failure.
I have mentioned that we have established the size of that hole that is within the limitations of the instrumentation. We have reviewed all of the tank build
records and we are reviewing any potential for pad debris.
We have done analysis to determine what kind of heating we would get if we had burning hydrogen impinging either on the joint or the membrane. And we are also conducting tests to characterize hydrogen burning against the foam thermal protection system on the tank.
DR. FEYNMAN: Is this to explain also the black smoke?
DR. LITTLES: It could explain the black smoke, yes, because if you had the hydrogen ignite and bum on the TPS, you can get black smoke from smoldering TPS. So it could explain that if you had the hydrogen at ignition.
What you have to hypothesize is that actually, of course, the ice team went out, as has been reported, previously to the mission, about 20 minutes prior to launch and they didn't see anything that would indicate a leak. And I believe if there had been a leak there at that point in time, they would have seen some indication of it.
And so the leak somehow has to occur between that point in time and a half a second after ignition to be synonymous with the black smoke. So you're talking
about debris or either some overload during the ignition transient. And as I will tell you in a minute, we've already talked about the load thing and we don't think that the load is it.
So it really boils down to a debris or something else causing the hole in the tank.
DR. FEYNMAN: Burning hydrogen making the smoke would not be visible as a flame or a light in the photographs?
DR. LITTLES: Well, it depends upon where it is. You know, there is a considerable area that we can't see between the external tank and the SRB, and so it could be burning in an area where we don't have photographic coverage, possibly.
The smoke that we see initially, it is indicated to be somewhere between zero degrees around toward the tank. It could be burning in an area where those cameras even can't see it, and it could be emanating from the back and coming around. It is hard to say.
CHAIRMAN ROGERS: On the hypothesis, though, don't you have to conclude that debris hit the external tank and caused the leak, and that then caused the-what, it would cause some damage to the right booster, and all of this within a half a second?
DR. LITTLES: No, sir, not all of that within a half a second. If you have the hydrogen burning from the tank
CHAIRMAN ROGERS: On that hypothesis, though, what would cause that? What do you think would cause the leak in the external tank at that point?
DR. LITTLES: Well, it would have to be debris. You would have to have debris or something from the outside, we think. It could of course be a flaw in the structure which is overloaded and leaks.
CHAIRMAN ROGERS: And you've looked at that and excluded it?
DR. LITTLES: We haven't completely excluded it, but it is becoming remote. We are going back through all X-rays and all build records. We have had at least three different people review all of the X-rays, and so far we've found nothing in that area that is anomalous.
We haven't quite completed that yet, but it is
CHAIRMAN ROGERS: Continuing with the hypothesis, though, about the debris, suppose there is debris there. When would that have hit the external tank and caused the leak?
DR. LITTLES: Well, in order to be consistent
with the puff of smoke initially, it would have had to have been at that time or slightly before, some time before that time, to be consistent with the puff of smoke.
CHAIRMAN ROGERS: Okay. Is there any evidence at all of any debris that might have caused that?
DR. LITTLES: We haven't found anything yet. That is still being looked into, but we have no indications of anything anomalous there. That is still something
CHAIRMAN ROGERS: But it is at least a possibility?
DR. LITTLES: It is a possibility, yes, sir. But it is not something that we have seen on photographs or the movies that we can point to. I wouldn't say personally that it is a strong possibility.
VICE CHAIRMAN ARMSTRONG: Dr. Littles, if there were a hydrogen leak that you had at T-zero or approximately and it was ignited immediately, how long do you think it would take for it to heat up some area, to make black smoke?
[1143] DR. LITTLES: We have done that analysis and I'm going to discuss that now. We started this analysis is an iterative process. We started assuming that we had hydrogen burning with complete combustion
somewhere on the tank and flowing down by the tank within the boundary layer and heating up the joint.
That type of heating on the joint did not give us enough heating of either the joint or the membrane to cause a problem. We then went to the assumption that we had a jet of hydrogen coming out of the tank and impinging directly on, over the distances there, impinging directly on the joint or the membrane.
DR. FEYNMAN: By "the membrane," do you mean: the metal surface of the rocket?
DR. LITTLES: Yes, sir. It is a little thinner than the joint. If you move down just a few inches, it is a thinner cross-section.
DR. FEYNMAN: About how thick is it?
DR. LITTLES: I have that on a chart here. I never can remember the numbers. It is .479 inches, the membrane itself.
If you make that assumption, if you assume that the hydrogen is leaking from the tank and impinging directly on the surface, and if you assume that you have complete combustion-that is, you have all of that hydrogen mixing well with air-you get a stoichiometric mixture and it burns.
You can get temperatures under those conditions that would create some problems, for
instance, on the joint. You could have a temperature of approximately 900 degrees. If that happened for roughly 60 seconds, a 900 degree temperature on the joint would open the gap enough to unseat the O-ring, and you could get leakage coming out of there.
During that same period of time, with the same assumptions, you might heat the membrane up to 1300 degrees. Now, those numbers, however, let me quickly add, are unreasonable from the standpoint that we assumed complete mixing to get that. We did that as a test case, to see if we could just put it to bed and forget it. These numbers say that we have to do more work, so what we're doing now is we're going back and doing some jet mixing, get a more reasonable combustion in there, and see what more reasonable numbers will do.
Now, we are also going to do a test. In fact, we have already started some testing where we take a hydrogen tank with a hole in its side, ignite the hydrogen as it flows out, impinge it on a surface with a thermocouple, and get some physical evidence. And so we are doing both of those things to try to put this one to bed, and that is the direction we are going at this point in time.
Okay, could I go to L-5, please.
(Viewgraph L-5.) [Ref. 3/7-67]
The next six scenarios-I'm sorry. Five out of the next six scenarios all deal with the joint itself. Before I move into those, we have been looking very carefully at both the left and righthand boosters for 51-L. We of course have three joints on each vehicle, and we have looked very carefully at similarities and differences between those joints, because of course we had one anomaly on one joint, we had none with the other five as far as we know.
And if you look at the temperatures on all those joints, you find that there really is not a lot of difference in the type of ranges that we're talking about.
[1144] Could you come a little closer to the center so that we can see the temperatures, please. What you see there is, on the right-hand booster the aft field joint, the temperatures around the booster circumferentially range from 28 degrees to 52, and that is about the same temperature that you had at the top.
Now, I'm quoting nominal numbers and these are-we have been through the reconstruction that was discussed earlier with the IR sensor and those have been played into the analysis, and these are nominal numbers that I'm quoting in both cases just for comparison purposes.
On the left-hand boosters, you see roughly the same kind of temperatures, and so the temperatures were roughly the same for all of the joints.
In terms of the loads, the on-pad liftoff loads, where we saw the puff of smoke, the maximum load is not at the aft field joint. The maximum load is at the center joint. The maximum load, however, at Max Q is at the aft field joint, but at the liftoff case, we first saw the puff of smoke, the maximum load would be on the second joint.
If you will move to the right, please. There's a note on the right relative to joint rotation which we will discuss in some following scenarios, and the subject of a lot of discussion.
If you look at the joint rotation that you get on the various joints, the lowest joint rotation that you get is on the aft field joint, because the rotation is a strong function of pressure. As a matter of fact, the pressure is the major driver in that, and you have a lower pressure in the aft field joint than you do at the forward two.
The pressure at the aft field joint is about 760 psi. By the time you get to the forward field joint it's about 900 psi. So the rotation is lower at the aft field joint.
Would you scan to the bottom and pick up the two notes. There are two things that we have discovered that are unique relative to this aft field joint: on the right. One of them is, in a scenario that has been discussed somewhat this morning, we did have to use the rounding fixture which was described earlier to mate those segments.
And the note here that I have says this was the maximum reshaping to date. There is some new data which was mentioned to you this morning, which we just found out yesterday. When we made this note what we were referring to was the data that we had looked at that point in time.
The first thing we did when we started looking at this data base-and we are continuing to do that-we picked all of the segments which had been subjected to this rounding tool, thinking those were probably the population of the worst data and this is the worst one out of that group where the rounding tool has been used.
And there are some others that we will have to look at, but it was anomalous in that data base, in that
if you took the six where the rounding tool had been used, this one would have been at something like a three sigma extreme relative to the amount of rounding that had to be done on it. So it stood out from that standpoint.
We also have another thing that I will discuss, in that on this particular mating, the aft field joint, we have a photograph which indicates a suspect O-ring in the aft field joint, and I will discuss that later.
And so there are some similarities between the joints, the things like rotation going in the wrong direction, temperature is about the same.
[1145] Oh, one thing that I omitted to mention is that if -you look at squeeze on the O-ring-and those numbers are on the chart. The squeeze on the O-rings on the right, on the joints on the right booster, are roughly the same, and they are a little lower on the left-hand booster, and so there is nothing there that stands out.
DR. FEYNMAN: Excuse me. About the squeeze, this is a single number, but as you go around the circumference I presume the squeeze must vary. The two pieces don't fit absolutely perfectly. There are stresses and strains.
So the question is what was the maximum squeeze or the minimum squeeze? How does it vary as you go around? Can we say anything?
DR. LITTLES: Well, you are right. You're absolutely right. What we are quoting here is the minimum squeeze, and you get that minimum squeeze by assuming the maximum eccentricity of the joints and considering the actual dimensions, the measured dimensions of the tang and the clevis for this joint.
Now, you can have cases, I believe, where you can have probably metal to metal on one side, with almost complete squeeze of the O-ring, and then the other side it depends upon what those dimensions are. And so you're right, you're absolutely right, you could have a large variation around the circumference.
DR. FEYNMAN: And that can have an effect, because the thing is cold and it is squeezed very hard, and then due to stresses or with the pressure it changes the dimensions and leaves a little gap because it doesn't have the resilience on account of the lower temperature.
That is an interesting possibility, so that it is important to think about the variation of squeeze around the circumference.
DR. LITTLES: Yes, sir, that is correct. As a
matter of fact, relative to resiliency, the maximum squeeze I'm sure is worst case. That is absolutely true.
So you have to consider both. But on the other hand, if you look at these numbers you can see that the maximum-the minimum is about the same, so the maximum is probably about the same as well. But you are correct.
Okay, could we move on now to L-6.
(Viewgraph L-6.) [Ref. 3/7-68]
Okay. L-6 is the scenario that deals with the topic that was discussed this morning and which was one of the notes on the prior chart, and that is the potential damage to the primary and/or the secondary O-ring at assembly.
Due to the out of round condition, the mating process has been well discussed this morning and so I won't go into that at all. And I've already mentioned that we've made the comparison with some other data and we find this one to be a little anomalous.
We are doing some additional things to evaluate this condition. We are going to do some tests to simulate the conditions, which I will discuss in a moment, that we had on this particular joint. We have a partial segment that we are going to simulate the right
conditions and mate and de-mate with O-rings in there, and see if we can induce some damage. We are also going to simulate defects in some O-rings to see if we can get past the leak check, because if you damage an O-ring during assembly-and this one did pass the leak test [1146] you have to have it in a position some way where you can pass the leak test and still get performance.
We are also requesting, and I understand that it is going to be done, that we de-stack STS 61-G. STS 61-G is one of those which has had the rounding fixture used in mating that joint. It is not as bad as this one was, but it is, I believe, the next worse that we have seen in use of the rounding tool.
And so we're going to request that one be carefully de-stacked, using very careful procedures, to see if we can see any damage there.
MR. SUTTER: Can I ask a question or maybe make a suggestion? I am still interested in the fact that you put a load on that one joint, and you make the note that that is one thing you're going to study, but that load is put on there and the pressure check is made in the assembly hall and then the unit is taken out and put onto the launching pad and it sits there for 28 days.
And I know the metal isn't up to yield, but you've got the insulation and you've got the charge, and maybe it wants to go back to where it was, and what happens in those 28 days? And shouldn't this analysis be expanded to maybe look at the effects of what happens while it's sitting there in the weather for 28 days?
DR. LITTLES: Yes, sir. We have that exact thing going on. We are going to take-start with mating, with stacking the segments, and carrying it all the way through the flow and doing that total analysis. We have that in process.
CHAIRMAN ROGERS: Somewhere along the line I guess we should take a recess for lunch. Is this a good place to stop, or would you rather continue?
DR. LITTLES: It's your pleasure.
CHAIRMAN ROGERS: How much time do you have?
DR. LITTLES: It might be good to stop now. It might take another 10 or 15 minutes to finish this one.
CHAIRMAN ROGERS: Well, maybe we should have a recess.
And are you going to talk about the possibility of ice in the joints?
DR. LITTLES: Yes, sir. That is one of the scenarios I will discuss, yes, sir.
MR. MOSER: Mr. Rogers, I think I didn't give you a crisp answer between the difference in a fault tree and a failure scenario. Let me see if I can do that just a little bit better.
As you continue, these fault trees are the things which could have gone wrong, and the failure scenario then is the process to determine if they did or didn't, what did or didn't, or why that did or didn't go wrong.
CHAIRMAN ROGERS: But then you gradually exclude different aspects of it?
MR. MOSER: Yes.
CHAIRMAN ROGERS: And I gather from reading this that you have, without being totally conclusive, you have generally eliminated the orbiter, the space shuttle main engine, and the cargo inertial upper stage?
MR. MOSER: We will present those facts to you and then present those to the task force, but that is about where we are, yes, sir.
CHAIRMAN ROGERS: Okay. Thank you.
We will come back at 2:00 o'clock.
(Whereupon, at 1:05 p.m., the Commission was recessed, to reconvene at 2:00 p.m. the same day.)
CHAIRMAN ROGERS: The Commission will come to order.
All right, Mr. Littles, would you proceed, please.
DR. LITTLES: We will proceed with chart L-7.
(Viewgraph L-7.) [Ref.3/7-69]
We were beginning to discuss the out of roundness situation relative to a potential O-ring damage, and again the mating situation was discussed this morning so I won't go into that.
The chart on the screen depicts a number of things, but among those things the dimensions that we actually had on the 51-L right field joint, the first column of numbers. Could you-zoom in on the bottom left, please, se we can read the numbers.
And these were discussed to some extent this morning. The column on the left indicates the initial measurements prior to the beginning of the rounding, and the column on the right the final measurements.
I talked to Bob a few minutes ago and I want to make sure that we are all together. I want to make a correction. He indicated that the dimension was .094 inches, I believe, at the end of rounding, and it was
.094, but that was the dimension before the rounding tool was removed.
The dimension I have on the chart here, .216, is the dimension when the mating was actually made, and so they are both real numbers. It is just at different time frames.
As was discussed this morning, the critical dimension here is the maximum negative dimension, which is in the 120 to 300 degree area of .393 inches. If you will go now to chart L-8.
(Viewgraph L-8.) [Ref.3/7-70]
We have tried to do, Dr. Feynman, something along the lines that you mentioned this morning, to get a feel for what these dimensions mean to us. This is a graphic illustration and it is, of course, not to scale, and what we have done is assume that the clevis is completely round and then take the dimensions that were recorded and move the tang to the outboard leg of the clevis and look at the resulting negative dimension.
And the negative dimension, again, is a potential interference between the surface where the O-rings are and the outboard leg of the tang. And what you see in doing that is that there is a maximum interference potentially of .209 inches.
Now, that is the worst case, of course,
because what that assumes is that you have metal on metal on the outside, and there is a tolerance between the inboard leg of the tang and the adjacent clevis dimension of .184.
So if you subtract those two, you have the other side of that tolerance, which is .025. So depending upon how the tang and the clevis are centered you can have an interference between .025 and .209. So that is of some concern to us.
There unfortunately is no requirement specified on that negative dimension. There is the guideline of the .25 on the positive dimension, but there really should be a tolerance on that side. But that does lead to the potential of having an O-ring damaged as you are mating it, and of course we are concerned about that and that is an active scenario.
I have mentioned that we are going to de-mate STS 6l-G and look at that, and that we are also doing some work at Marshall with some clevis and tang segments, looking at interference [1148] mating and looking at what kind of O-ring damage we might get that might affect the seal and those kind of things.
So we are continuing with that.
DR. FEYNMAN: There's a small trivial point that is confusing me. I don't know how accurate these
drawings are.
DR. LITTLES: They're not accurate at all.
DR. FEYNMAN: Because on the inside where the O-rings are the piece of metal in this drawing has a 90 degree corner, which does cutting much better than if it had a cut on it. And in the previous drawing you had a little cut off of there, and I just don't know.
Does anybody know whether that is a 90 degree piece of metal that comes in?
DR. LITTLES: You're talking about the top of the outboard leg of the clevis?
DR. FEYNMAN: Yes, because on the previous drawing it was indicated that it wasn't so sharp, the one that was on some other speaker earlier on. And I'm just curious.
DR. LITTLES: There is no chamfer there.
DR. FEYNMAN: That is why I mentioned that, because I was told that, by the people who work on it, they've seen this 90 degree sharp piece rubbing up against the curved part as it comes up. You see, as it goes down there is a ramp, so to speak, and they look at it and it worries them. But they haven't communicated it very well up into the system.
DR. LITTLES: Okay. Can we go to chart L-9, please.
(Viewgraph 14.) [Ref. 3/7-71]
We are now going into a leg of the scenario which has four branches, the beginning point for each one of those being a blow-by or leakage of the primary O-ring, and then we will address the four branches individually.
The first one is the secondary O-ring defect. That defect could come from a number of sources: some damage to the O-ring in manufacture, not caught in inspection, or something else. We have been looking at closeout photos from this stacking. We have been reviewing O-ring records. We have been doing special inspections on O-rings.
I will tell you what that has produced, and we are going to do tests to evaluate the performance of a simulated O-ring defect and how it might pass a leak test.
Could we go to chart 10, please.
(Slide L-10.) [Ref.-3/7-72]
There is a closeout photo which I think you've probably seen before for this aft field joint, which has an indication of a potential O-ring anomaly.
Could you go on to chart L-10, please, which is a closeup view of this.
(Slide L-11.) [Ref. 3/7-73]
We have been analyzing this photograph in-house and we have had some experts from outside doing some work
CHAIRMAN ROGERS: Before you do that, could you just explain, identify the photograph, when was it taken and how was it taken and so forth?
DR. LITTLES: It was taken prior to mating, after the O-ring was installed on the aft field joint for 51-L.
CHAIRMAN ROGERS: Do we know the date?
[1149] DR. LITTLES: No, sir, I don't know the date. I have heard it, but I don't have it. I can get that date for you. I don't have it in my mind.
CHAIRMAN ROGERS: But it was some time before the launch, though?
DR. LITTLES: Yes, sir. It was during the stacking.
CHAIRMAN ROGERS: Okay. Go ahead.
DR. LITTLES: This is a closeup view of the same area, and the feature of interest is the apparent increase in the distance between the edge of the O-ring and the top of the O-ring groove. If you look at that, it looks as though there may be an anomaly in the O-ring and some change in the dimension at that point.
The work is still proceeding and it hasn't
been completed, but there have been two estimates of that made and they have both come out in the neighborhood of 15 mils. But we are still working on that.
CHAIRMAN ROGERS: What does that mean?
DR. LITTLES: 15 thousandths of an inch.
CHAIRMAN ROGERS: Is there a deficiency in it? Is it smaller?
DR. LITTLES: Yes, sir, a smaller dimension than it should be. The nominal dimension of the O-ring is .280 inches, and this would be-indicates a 15 thousandths reduction in that.
CHAIRMAN ROGERS: Because the last time we looked at this we were told, I think, that you were uncertain about whether it showed an anomaly or whether this was putty that was put on, that would make it meaningless, or grease, I guess it was.
DR. LITTLES: Grease has been one of the primary concerns in trying to interpret this data, because of shadows it produces and because of the apparent changes in thickness due to the grease.
CHAIRMAN ROGERS: Well, have you decided now it was not grease that made the photograph look like this?
DR. LITTLES: I don't think we can say it is
not grease that makes the photograph look the way it does relative to the streaks. That may be. The thing we are concentrating on is the gap distance between the edge of the groove and the O-ring.
CHAIRMAN ROGERS: In other words, you think there is an anomaly now. At that time you weren't sure; you didn't think there was.
DR. LITTLES: The experts at this point think there is, yes, sir. And it looks anomalous to me, but there is still work going on there and we're not ready to conclude yet. This is an interim report.
GENERAL KUTYNA: Have you looked at the other closeout photos of that ring?
DR. LITTLES: The other closeout photos, as I understand it, have been looked at and they don't see anything.
GENERAL KUTYNA: You might take a look at them. We looked at them a lot the other day and there were a lot of areas of darkness and separation, so that it is tough to tell.
DR. LITTLES: We will look at those again.
VICE CHAIRMAN ARMSTRONG: Have you definitely identified the location of this spot in the clock?
DR. LITTLES: Yes. This is located-the quadrant of interest relative to the puff and the plume
is between zero and 270, zero being the Z axis and coming back toward the tank to 270. This indication is not in that quadrant. It is in the quadrant right above it.
It is still in a quadrant that would be hidden and be between the SRB and the tank. So it is in a location where you could have initiated a puff or a leak at that point and have it propagate around.
VICE CHAIRMAN ARMSTRONG: Between zero and 90?
DR. LITTLES: Between 270 and 180.
MR. ACHESON: For the record, does any such slight variation in the gap appear anywhere else on the circumference from the photograph?
DR. LITTLES: Well, we haven't seen it in the photographs we have looked at, General Kutyna indicates that he may have seen something that we should look further at, but we haven't seen it in the things we have looked at.
MR. ACHESON: What I'm getting at is, can you compare this with the remainder of the circumference to see whether-for example, if three or four more such seeming anomalies appeared in the photographs, you would wonder whether this is illusory or significant or what.
DR. LITTLES: Yes, sir, and we have not seen
that. But we will go again and look at those photographs again.
And Jack has pointed out, in this joint we have looked all around it and we haven't seen it.
MR. LEE: In this particular photograph, we have gone as far as we can see on each side of both O-rings and we see no other such anomaly.
CHAIRMAN ROGERS: I'm not quite clear. If this is an anomaly, would it be related to the puff of smoke or is it another area?
DR. LITTLES: It could be related to the puff of smoke. As we've discussed, the exact origin of that puff of smoke is not pinned down. We believe it is somewhere between the plus Z axis or the minus Z axis, excuse me, and around toward the tank, around the SRB.
And we can't see have the two camera locations: D-63, if this is the SRB, pointing in this direction; E-60 pointing in this direction. And if the tank is over here, we can't really see back in this area.
So it could possibly be that, the puff of smoke coming out somewhere in this area and coming around with time. It is possible.
CHAIRMAN ROGERS: When you say it is possible,
but is it realistic to think it is? I mean, is there another area?
DR. Littles: Yes, sir, I think it is realistic to think that it could be. We're only talking now about being 90 degrees away. I will discuss later some results that we've gotten from some small subscale motor tests, where we see with simulated anomalies and O-rings and sealing surfaces, we see leaks starting at one place, stopping at that place, and then starting another place.
And so it is conceivable that you could have had a puff of smoke in a quadrant or in a location that would be 90 degrees around from where you finally had the burn-through. The small motor tests say that that is possible.
Also along the lines of potential O-ring defects, we have been inspecting O-rings and doing some special X-ray on O-rings. X-ray of O-rings is not something that is normally done in inspection. We found two things.
[1151] One is that in reviewing the records of the inspection for the O-rings which were on all of the joints on 51-L, on both right-hand and left-hand SRB, we found that there were seven out of the twelve O-rings which were not subjected to the same level of inspection
as prior O-rings had been.
The situation that occurred was that there was an engineering change order made to transfer some inspection notes from a drawing to an inspection document. It was properly approved, but in the process of making the change to the document there were two steps that were inadvertently left off and not caught.
Now, whether those are significant or not we are not making a judgment at this time. But the two things that were omitted was that: one, there was a requirement for only having five joints in an O-ring, and that was omitted and that inspection was not made at Morton Thiokol by the Air Force.
And the other is-and this one is more interesting to me relative to that photograph-there is a requirement that you can only have a ten mil or ten thousandths of an inch offset where the scarf joint is made, and that inspection was omitted.
Now, that applies to seven of the twelve O-rings. The secondary O-ring in this aft field joint was one of those. Like I say, we don't know what to make of that at this time, but it is something we have learned.
GENERAL KUTYNA: We have been looking at that for about a week now and are closing out that particular
item. I think there were three inspections that were dropped, as a matter of fact.
DR. LITTLES: I'm sorry?
GENERAL KUTYNA: There were three inspections that were dropped when that engineering drawing was changed by Morton Thiokol. And I guess our teams have been looking at that for about a week now.
The one thing we found last night, that those O-rings were inspected by someone at some time, either Thiokol or a sub at least once, and what was missing was the backup inspection by the government.
DR. LITTLES: It wasn't done by Thiokol, but it was done by a vendor.