The Report of the Presidential Commission on the Space Shuttle Challenger Accident - The Tragedy of Mission 51-L in 1986 - Volume 5 Hearings Part One
National Aeronautics and Space Administration (NASA), World Spaceflight News, Presidential Commission on the Space Shuttle Challenger Accident, Rogers Commission
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Report of the Presidential Commission on the Space Shuttle Challenger Accident
June 6th, 1986
Washington, D.C.
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IN MEMORIAM
"The future is not free: the story of all human progress is one of a struggle against all odds. We learned again that this America, which Abraham Lincoln called the last, best hope of man on Earth, was built on heroism and noble sacrifice. It was built by men and women like our seven star voyagers, who answered a call beyond duty, who gave more than was expected or required and who gave it little thought of worldly reward."
President Ronald Reagan * January 31, 1986
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Francis R. (Dick) Scobee - Commander
Michael John Smith - Pilot
Ellison S. Onizuka - Mission Specialist One
Judith Arlene Resnik - Mission Specialist Two
Ronald Erwin McNair - Mission Specialist Three
S. Christa McAuliffe - Payload Specialist One
Gregory Bruce Jarvis - Payload Specialist Two
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Report of the Presidential Commission on the Space Shuttle Challenger Accident - Volume 5 - Hearings of the Presidential Commission on the Space Shuttle Challenger Accident: February 6, 1986 to February 25, 1986
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SECTION 1 * FEBRUARY 26, 1986 SESSION (part 1 of 2)
SECTION 2 * FEBRUARY 26, 1986 SESSION (part 2 of 2)
SECTION 3 * FEBRUARY 27, 1986 SESSION
SECTION 4 * MARCH 7, 1986 SESSION (part 1 of 2)
SECTION 5 * MARCH 7, 1986 SESSION (part 2 of 2)
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FEBRUARY 26, 1986 SESSION (part 1 of 2)
Lawrence B. Mulloy and George Hardy
Stanley Reinartz and Judson A. Lovingood
Charles Stevenson, B. K. Davis and E. F. Kolczynski
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PRESIDENTIAL COMMISSION ON THE SPACE SHUTTLE CHALLENGER ACCIDENT
WEDNESDAY, FEBRUARY 26,1986
Dean Acheson Auditorium * Department of State * Washington, D.C.
The Commission met, pursuant to recess, at 9:35 a.m.
PRESENT:
WILLIAM P. ROGERS, Chairman, Presiding
NEIL A. ARMSTRONG, Vice Chairman
DR. SALLY RIDE
DR. ARTHUR WALKER
DAVID C. ACHESON
MAJOR GENERAL DONALD KUTYNA
ROBERT HOTZ
DR. EUGENE COVERT
JOSEPH SUTTER
ROBERT RUMMEL
ALSO PRESENT:
AL KEEL, Commission Executive Director
PROCEEDINGS
CHAIRMAN ROGERS: I will call the Commission to order, please.
The first witnesses this morning will be Mr. Mulloy and Mr. Hardy. Will they please come forward.
(Witnesses sworn.)
TESTIMONY OF LARRY MULLOY, MANAGER, SPACE SHUTTLE SOLID ROCKET BOOSTER PROGRAM, MARSHALL SPACE FLIGHT CENTER; AND GEORGE HARDY, DEPUTY DIRECTOR, SCIENCE AND ENGINEERING, MARSHALL SPACE FLIGHT CENTER
CHAIRMAN ROGERS: Welcome, gentlemen. Will you begin by identifying yourselves and giving a little background of the experience that you have had with NASA and your present assignment? I assume that you have some information you want to start with this morning.
Which order do you want to go in?
MR. HARDY: I believe Mr. Mulloy will go first.
CHAIRMAN ROGERS: Thank you. Proceed.
MR. MULLOY: Mr. Chairman and members of the Commission:
I am Larry Mulloy. I am currently the manager of the space shuttle solid rocket booster program at the Marshall Space Flight Center. I joined NASA in 1960. 1 worked as a loads and dynamics analyst, and then in the Apollo program I worked in the structural subsystem area of the second stage of the Apollo program.
Subsequent to that, I was on a leave of absence for a year for some postgraduate work, doing doctoral studies in public administration; and subsequent to that I was assigned as the chief engineer of the external tank project at the inception of the space shuttle program. I held that position until approximately 1979, and then I was the chief engineer for NASA on the inertial upper stake in conjunction with the Air Force until 1982.
In November of 1982, I was assigned as the project manager for the solid rocket booster program. I have a B.S. in engineering from Louisiana State University, a master's in administration from the University of Oklahoma, and, as I previously stated, some postgraduate work in administration at the University of California.
CHAIRMAN ROGERS: Mr. Hardy.
MR. HARDY: Mr. Chairman, members of the Commission: My name is George Hardy, and I am currently the deputy director of science and engineering at the Marshall Space Flight Center.
I joined Marshall in 1960. I served for a number of years as project engineer on the Saturn 1B booster. I later served as an assistant program manager on that program.
From about 1967 to 1974, I was in charge of program engineering and integration on the Skylab program. In 1974 1 became project manager of the solid rocket booster and served in that position until 1982. Subsequent to that, I served in the position as associate director for engineering in the science and engineering directorate.
I graduated from Georgia Institute of Technology. After approximately six years service in the Navy, I was employed by the Army Rocket and Missile Center.
CHAIRMAN ROGERS: Thank you.
May I ask the still cameras now to take your pictures, and then during the testimony I would ask you to refrain from making shots. It is distracting to the witnesses to have so many shutters clicking each time. And so if you want a period now of taking stills, go ahead, and then I would ask you not to do it during the testimony.
(Pause.)
CHAIRMAN ROGERS: It's not that we object to you taking pictures. We want this to be an open hearing. But with all of the clutter and all of the shutters clicking at one time, it's awfully distracting and unfair to the witnesses.
Okay. Mr. Mulloy, will you proceed?
MR. MULLOY: Yes. Mr. Chairman and members of the Commission, yesterday in the testimony that was given before this Commission, and before that I think in more dramatic statements that have been attributed to Thiokol personnel by the media, a picture has been painted of the events of January 27th that I think at best may be misleading.
Mr. Chairman, with your permission, I would like to state the facts of the events of January 27th, beginning with the 8:45 telecon. I believe there has been a great deal of testimony as to the events leading up to the 8:45 telecon and, with your permission, I would like to begin at that point.
CHAIRMAN ROGERS: Yes, you may, Mr. Mulloy. We want you to feel free to present any evidence that you would like to and as long as you would like to. We will hear anything you want to say.
MR. MULLOY: Thank you, sir.
I previously testified to the flight readiness review process leading up to the launch minus one day review at Kennedy Space Center on January 26th, '86. I have stated how this continuing concern for joint O-ring erosion had been treated in flight readiness review process and all of the events leading up to the decision on the 51-L launch.
I would like to now begin with the 8:45 telecon. After being notified of that and arriving at the resident office at the Kennedy Space Center and halving the data that had been telefaxed in from the Utah plant
CHAIRMAN ROGERS: Was that the first time you considered the weather aspects of it?
MR. MULLOY: Oh, no, sir. We-after we stood down from the launch on the 27th at 1:00, I and Mr. Reinartz, Mr. Reinartz polled all elements of the shuttle system for which he is responsible, the SRB, the external tank, and the space shuttle main engines. And I had a discussion on my SRB loop with the SRB people dealing with the question of a 24-hour turnaround to attempt to launch again at 9:38 on the 28th and the effect that the predicted cold temperatures for the night of the 27th might have on that.
The input was received back both to Mr. Reinartz and myself that we were looking at the Launch Commit Criteria relative to temperatures. It was felt there was a need to look at the recovery battery temperatures that are in the forward skirt of the SRB and the fuel service module temperatures that are in the fuel service modules for the thrust vector control system in the aft skirt of the solid rocket booster.
The input received back by me was that they did not feel that would be of any concern. They were going to continue to look at it, and if any concern arose they would let me know.
I went to the 2:00 Mission Management Team and reported that there were no constraints to the solid rocket booster for a 24-hour turnaround, that we had taken a look at the recovery battery temperatures and the fuel service module. We did not feel at this time that there would be any Launch Commit Criteria for the low temperature limits that were established for those systems, but that we were continuing to assess that; should anything change in that regard, I would so report that.
CHAIRMAN ROGERS: You referred to the Launch Commit Criteria. What were they as far as you knew in terms of weather conditions? Any?
MR. MULLOY: In terms of weather conditions, yes, sir, I'm aware that there is a Launch Commit Criteria for the system for weather. There are a number of factors in that Launch Commit Criteria. One of them is the ambient temperature, which is established at 31 degrees.
Another is the sea state and winds in the SRB recovery area. Another is the cross-winds at the return to landing site runway at Kennedy Space Center. Another is the trans-Atlantic landing site weather, and another is severe weather, which is related to lightning and thunderstorms in the area.
CHAIRMAN ROGERS: And when you say there were no constraints in the 2:00 meeting, does that mean that as far as you could see there were no problems in those areas?
MR. MULLOY: No, sir, I did not evaluate those areas of the Launch Commit Criteria. What I was looking at was the specific Launch Commit Criteria items that are on the solid rocket booster and the effect that the low temperatures would have on that.
I would expect Mr. Aldrich would normally make the judgments on, and his people at Johnson Space Center, would make the judgments on crosswinds and trans-Atlantic weather and the general ambient environment for launch.
CHAIRMAN ROGERS: Just so the Commission has a little better idea, at least I have a better idea, of what you would discuss at the 2 o'clock meeting, would you say, well, we don't know what the weather's going to be like tomorrow, we will have to look at it as we go along, or would you say, we're not sure what the seas are going to be and whether we can recover?
What type of discussion was it? I have a little problem following when you say no constraints, and it is the language that I don't quite follow.
MR. MULLOY: Yes, sir. The discussion centered around the conditions that the launch pad would be exposed to during the night, particular attention to freezing of the water system on the pad, freezing of the water in the sound suppression devices that are filled with water at the base of the pad, concern for the formation of ice on the pad, which could cause potential damage to the shuttle vehicle, with primary concern for the orbiter tiles in that case, and I believe for the insulation on the external tank.
Some other discussion, I believe, about the predicted weather for the landing sites, trans-Atlantic landing sites, and the predicted weather for the local weather for KSC.
None of those discussions or the considerations of those discussions posed any constraint to the solid rocket booster.
CHAIRMAN ROGERS: "Constraint" meaning that at that point you thought it would be okay to launch the next day, but you couldn't be sure because those things might change?
MR. MULLOY: Yes, sir. Based upon the weather conditions that were being looked at the time and based upon the concerns that were being addressed at that time, I saw - and with the commitment that we were going to continue to look at the weather through the night and then assess that in real time in the morning, which is actually what was done, and the launch was delayed because of the ice on the pad and getting some ice out of the sound suppression blankets.
CHAIRMAN ROGERS: Okay, will you proceed? So at the 2:00 meeting you felt that, although there were problems that might exist the next day, that you felt that those problems probably could be overcome and you could be able to launch?
MR. MULLOY: Yes, sir, I was confident that the only thing that would violate Launch Commit Criteria on the solid rocket booster at that time were a potential violation of the recovery battery low temperature and the fuel service module low temperature.
And as further analysis was done in the afternoon, the initial assessment of that was upheld and we did predict no violation of those Launch Commit Criteria.
CHAIRMAN ROGERS: And at that point the O-rings and the seams and so forth were not discussed?
MR. MULLOY: No, sir, they were not.
I subsequently learned that my- and it was testified to yesterday, I believe, by some of the Thiokol people. I subsequently learned that my solid rocket motor element manager, who was at the Huntsville operations support center supporting the launch, did communicate to Mr. Boyd Brinton, who is the project chief engineer for the solid rocket motor for Morton-Thiokol, that the query had come, did we have any constraints for a turnaround.
That had been relayed to Mr. Brinton, who then called, I believe, Mr. Ebeling, it was testified to, at Thiokol in Utah, to begin to look into that. And that led into the events.
CHAIRMAN ROGERS: And what was the man's name you referred to? You said your man?
MR. MULLOY: Mr. Larry Wear. He is my solid rocket motor element manager. I have a solid rocket motor element manager and I have a booster assembly element manager for the other aspects of the solid rocket booster other than the motor.
CHAIRMAN ROGERS: Okay, proceed. I'm sorry to interrupt you.
MR. MULLOY: Okay, sir. When we got the charts containing the Thiokol engineering data and the conclusion that Thiokol was drawing from those data arrived at KSC and Marshall- began arriving at about 8:45, when the conference began.
We went ahead and began the conference, but the, conclusion and recommendation charts that Mr. Lund subsequently testified to yesterday did not come in until somewhat later. I don't know exactly when they were there, but when we started into the telecon and began discussing the data we did not have those conclusions and recommendations.
We were simply looking at the engineering data and reviewing those engineering data. The concern, of course, that was being expressed was for the low ambient temperatures that were predicted for the night and the effect those low ambient temperatures would have on the propellant mean bulk temperature and on the joint particularly.
If I could have chart SRB-6, please, on the screen, I would like to clarify. When we talk about temperatures -we have a number of them. These specific temperatures don't represent any particular condition on STS 51-L. What we are showing there is the ambient temperature at pad B is at ground level, and it is about 50 feet away from the pad. For example, that temperature, as an example, might be 36 degrees at ground level.
Then there is a local ambient temperature- and we will provide hard copies of this, sir, for you later. The local ambient temperature is referred to as in the vicinity of the solid rocket booster, that local ambient temperature will be in a tank condition. It will be below the general ambient because of the effects of the cryogens in the external tank and the heat short that exists through the to the attachments SRB and the wind blowing the cold air around the SRB.
That, for example, might be 30 degrees, while you have a ground ambient of 36 degrees.
CHAIRMAN ROGERS: "Ambient" means outside?
MR. MULLOY: Yes, sir.
CHAIRMAN ROGERS: Outside temperatures?
MR. MULLOY: Yes, sir. The ambient temperature at a point here in this room will be slightly different than the ambient temperature at a point back there by those lights.
But the ambient temperature, it doesn't have to be outside. It could be the ambient temperature of the body of this room or a body of air in this room. Then the local ambient is affected by the proximity of heat sinks that are around the solid rocket booster and the wind blowing around that. At that same time, you might have a joint temperature or a temperature right at the field joint that is lower than the local ambient, and that will occur because the local ambient and the ambient temperature has been lower possibly three or four hours earlier, possibly say 18 or 20 degrees. And due to the lag, the local ambient and the ambient may be coming up, but the steel parts are still cold, and so you may have a joint temperature of 27 degrees.
And then when we speak of the propellant mean bulk temperature, that is the average temperature of all the particles of the propellant in the motor taken- it is an average of from the outside, inside. There is a slight gradient through that. That may be 57 degrees, because that is a large heat sink, and if it was 60 or 70 degrees three or four days before, or say 70 degrees, the temperature can get very low and that propellant mean bulk temperature doesn't track that.
And so I just submit that for some clarification. The concern that we were talking about was for the effect of the overnight low on the propellant mean bulk temperature and the effect that it would have on the joint and the seals and the performance of those joints and seals.
The Thiokol engineers were stating that they believed the effect of that lower temperature on the O-rings would be to slow the time for the primary O-ring to seal, resulting in greater hot gas past the primary seal and possibly erosion of the secondary seal. The data that they showed included the previous coldest launch, which was STS 51-C, which they stated at least qualitatively had the worst blow-by of any previously observed.
Considerable discussion between Marshall and Thiokol on the significance of those data then ensued. There was at that time- we still didn't have conclusion and recommendation charts. All we were trying to do was understand what the data were telling us.
The major focus of that discussion was the effect low temperatures could have on blow-by of the primary O-ring seal.
Now, if you bring up chart SRB-3, I think at this point it might be helpful to graphically show again the configuration of the joint. When we were assessing- and if you could scale that down and focus on the left side first, if you would, please, and get the title in.
Okay. We will go from the upper left corner, down the column, and then back up to the right. In the initial condition, the joint is assembled and it has squeeze on the O-rings. What we have been talking to is the O-ring is actually compressed into that joint.
In the specific conditions of STS 51-L, that compression far exceeded the minimum compression required. The compression on the particular joint that has been of interest to us has been 38-thousandths to 40-thousandths, where the minimum requirement is 20-thousandths.
In that initial condition, you have redundant seals, the primary on your left and the secondary on your right.
If you would move down in the left column now.
MR. HOTZ: Mr. Mulloy, may I interrupt you for just a moment. Now, what is the time element there in making that leak check?
MR. MULLOY: That leak check, sir
MR. HOTZ: What day and what calendar day was it made?
MR. MULLOY: I believe it has been reported that it was about 28 days before the attempted launch. It was about the 1st. But when it is made is when the joint is assembled.
MR. HOTZ: Before it goes out to the pad?
MR. MULLOY: Oh, yes, air. As we assemble each SRM joint, before we put the next SRM segment on we leak check the previous one. In the event that you don't pass the leak check, you have to de-mate and do it over again. So we don't run up the whole stack and then leak check all the joints.
We build it up from the bottom and check each joint as it is assembled.
MR. HOTZ: So it would have been at least 28 days before the launch?
MR. MULLOY: Yes, sir.
DR. COVERT: Mr. Mulloy, may I ask a question, please? You said that there was plenty of squeeze in the O-ring. What temperature would you say that that squeeze referred to?
MR. MULLOY: Okay, sir. In that initial condition, that referred to an ambient condition of 75 degrees. The consideration that was given during the course of the discussion is how much would that squeeze be reduced as the temperature was reduced to 20 degrees?
That was calculated and it was 3-thousandths of an inch. That occurs for two reason: the diametrical shrinking, as well as the stretching of the O-ring as it is chilled.
DR. COVERT: Your 38- to 40-thousandths then would go 35 to 37?
MR. MULLOY: Yes, sir, that is correct.
DR. COVERT: At 20 degrees.
MR. MULLOY: At 20 degrees, I believe is the temperature that was calculated at.
DR. COVERT: Thank you, sir.
MR. MULLOY: Okay. Then when we do the leak check, the O-rings are then displaced as shown in the second diagram down in the left column. It pushes that primary O-ring back toward the motor pressure side. It pushes the secondary O-ring back against the surface against which it will subsequently seal, if called upon to do so, by any pressure from motor operation impinging on it.
If you will go to the third one in the left column, please. Then, after you take the pressure off- this pressurization is 200 psi initially, to be sure that the O-ring is pushed up against that gap, and then that pressure is reduced. That is with an open source, just turning, opening the valve and letting it flow as much as it will, because you will get some blow-by initially in moving that in the pressure check. Then that is reduced to 50 psi and held, and the spec ion that is one psi allowable leakage in 15 minutes. That is with a closed source. It has to hold the pressure between the regulator, the valve on the pressure source, and flow by the seal.
Now, when that pressure is taken off there is some relaxation. Those O-rings don't stay smashed up against that gap, as they were shown when you had the 200 psi.
If you will go to the center column in the top, please.
Now, during motor operation there are two things that can occur. The first is where the primary seal is actuated. Initially in the initial pressurization, as was testified to yesterday, from zero to about 170 milliseconds, which equates to about 200 psi, there is no significant joint rotation.
We have test data, and I believe the engineers stated yesterday, there is a knee in there and it is not linear. It is not linear with pressure. You don't get one-third of the rotation at 200 psi. You get less than one-third, and then it tends to ramp up due to the stiffness of that joint.
So when the motor is pressurized at about 30 psi, which is 50 to 60 milliseconds, that primary O-ring is translated across from the forward face of the groove to the face that it wants to seal against. We have shown in tests that an O-ring will seal or seat and begin to extrude into the gap at 30 to 50 psi.
Go to the center on that center column, please.
Now, what happens at about 200 psi, again joint rotation is not a significant factor here. You may got 2- to 3-thousandths of joint rotation at a in maximum in this kind of a condition. The pressure is impinging there and beginning to extrude the primary seal into the gap.
Go to the bottom of that center column, please.
Now we get the joint rotation. Tests have shown that a good O-ring with a durometer of 90 even- and our spec on the O-ring is 75. This is the sponge. and brick analogy that was used by one of the engineers yesterday. I think that is a little dramatic in describing the change in that O-ring stiffness in going from 75 to 90.
But it has been shown that the O-ring will extrude into that gap and seal.
Now, if you will go to the top on the right, please. Another condition that can happen, the reason we have redundant seals, here at the moment of motor ignition the system is redundant. If for any reason the primary seal does not seat-it is damaged, it has a twist in it, it has a void in it or whatever- the primary seal does not seat, the pressure actuation is now taking place on the secondary seal. That is where the redundancy is, in zero to 170 milliseconds.
Go to the center, please.
Now, that continues, and what happens to the secondary seal is exactly what happens to the primary seal. The primary seal has failed to function, the redundant seal is performing its function at 200 psi.
DR. WALKER: Mr. Mulloy, can I ask a question about that? Would you in your discussion also include your understanding of the waiver and what that meant in regards to how you could consider whether or not the secondary seal was really going to operate?
MR. MULLOY: Yes, air, I had planned to do that later, but I will just answer that now. My understanding of the waiver is the design goal on the shuttle was to have redundant systems. That design goal is not met in all systems. There are some 829 Crit 1s waivers on the shuttle system. There are 213 Crit 1 waivers on the SRB.
This particular waiver is one of IS on the solid rocket motor. Now, my understanding of that waiver, it is required because we have defined a condition under which the secondary seal may not form a seal, and I emphasize "may not."
MR. SUTTER: Could I ask a question, please? Are all of these waivers of equal importance, or of all of these waivers which do you think is the most important?
MR. MULLOY: We are assessing that now, because we're going back and looking at all of the Crit 1s. At the time that the Crit 1s were established, they were all considered to be loss of life and loss of vehicle should that system fall.
I think the question you're asking me is, what is the probability of failure and what is the experience with the system that would say, well, this one is more likely to fail than the next one and the next one, and put a priority order on those. I am not at this point prepared to say that, of the 18 critical systems on the SRM, that an igniter, for instance, is more or less critical than a seal.
But we are assessing that, and the way you have to do that is look at our experience with that.
DR. WALKER: But you did have a task team working on this particular problem?
MR. MULLOY: Yes, air.
DR. WALKER: Did you have task teams on any of the other problems?
MR. MULLOY: Yes, air. Yes, air, we did. As a matter of fact, on the nozzle we had, as has been related, on STS-8 we found that we were getting some very unusual nozzle erosion. We applied a task team to that to solve the problem, and that is a Crit 1 item. Burn-through of the insulation on the liner of the nozzle is loss of mission and crew.
And yes, we had a task team working on that. And really, on the SRM, those are the two that had very equal importance, really, because the criticality- in answering your question, air, those two, they would be a real foot race as to which one we would have considered more critical, depending upon the particular time that you looked at your experience with that.
If you'd asked me that question a year and a half ago, I would have definitely said the nozzle.
CHAIRMAN ROGERS: It sees to me, though, that based upon the testimony yesterday, and what I think you're leading up to here, is that the argument is being made that this should have been Criticality 1R. You're arguing there was a redundancy in the item and the item itself says there isn't a redundancy, that you have to operate on the basis of Criticality 1; if there is a single failure, it is a loss of life and loss of crew.
MR. MULLOY: Yes, sir, but if you read that total document, which perhaps you have, what it says is under worst case conditions it can be Criticality 1.
CHAIRMAN ROGERS: Wasn't this a pretty bad case, with the weather and all of the alarms that you had, and the recommendations from the engineers at Thiokol? Wasn't this what seemed like a pretty dangerous situation?
MR. MULLOY: It did not seem that way to me then, sir.
Now, if I may continue and answer the question about what the CIL applies to, it says under certain conditions you may have a single point failure. It very carefully says "under certain conditions."
Mr. McDonald testified yesterday- and I cannot assert to the factualness of what he stated, but what he said was, in reality we have never had that worst case condition where we actually flew Crit 1, except on one motor, which was one joint on STS-4. Now, we're looking at that.
I think that certainly is closer to the case than we have had Crit 1 on everything except one motor, and the reason it is is because you look at the squeeze that you actually have, given the dimensions that you actually have, and you look at the worst case rotation that can occur under that condition, and that worst case rotation does not result in a secondary seal unseating such that if the primary seal fails the secondary seal will work. Therefore, it is redundant.
DR. RIDE: Does that calculation take into account the out-of-roundness of the segments, the calculation on the squeeze?
MR. HARDY: Yes, it does. If I could make
DR. RIDE: I would just like to ask whether when you did this calculation for 51-L, which it looks like you did on the 27th, to find out how much squeeze you had on the O-rings, whether you actually did take into account the out-of-roundness on the segments, calculating the squeeze?
MR. HARDY: Yes. Those calculations, Dr. Ride, were made prior to the 27th meeting, but the out-of-roundness is taken into account. The rounding of the three cylinders, if I could describe it that way, you've get inner leg and the outer leg of the clevis, and then the tang itself. The rounding of those cylinders, which occurs at relatively low pressures, is also taken into account.
I would like to mention one thing, if I could read from one place in the critical items list regarding this waiver, I think it clearly describes my interpretation of the waiver, and I don't choose to get into a discussion with somebody else's interpretation. But there is a note that says leakage of the primary O-ring seal is classified as a single failure point due to the possibility of loss of sealing at the secondary O-ring because of joint rotation after motor pressurization.
And I am personally aware of the facts that drove the submission of this waiver, and it was clearly associated with the fact that after motor pressurization, after it's been through the ignition transient, you can have a stackup of tolerances on the metal parts and the O-ring which indeed would not- under which case you would indeed not have a redundant seal.
CHAIRMAN ROGERS: Let's stick with that language, because it seems to me that goes right to the heart of it. Read it again. And as I read it, it means that if the primary seal fails that the mission will fail. Am I wrong?
MR. HARDY: That is not my interpretation.
CHAIRMAN ROGERS: Well, let's read it. "Loss of mission" - this is actual loss. "Failure effects summary. Actual loss. Loss of mission, vehicle and crew due to metal erosion, burn-through, and probable case burst, resulting in fire and deflagration." Now "Note, leakage of the primary" -and this is the part that I want to refer to.
"Leakage of the primary O-ring seal is classified as a single failure point "-" as a single failure point "-" due to possibility of loss of sealing at the secondary O-ring because of joint rotation after motor pressurization."
Now, that suggests to me that the critical items list says that if the primary O-ring seal fails, that you have got a good probability that the mission will be a catastrophe. Am I wrong about that?
MR. HARDY: You are not wrong, if I might put my clarification into that, if the primary O-ring fails after motor pressurization, after joint rotation.
CHAIRMAN ROGERS: I guess what I'm saying is, isn't that a possibility of exactly what happened in this launch?
MR. HARDY: I don't believe so.
CHAIRMAN ROGERS: Why?
MR. HARDY: Well, I will elaborate on that a little bit later here. But in the considerations, at least in the considerations of the subjects at hand, relative to the discussion on the 27th, the discussion on the 27th had to do with the possibility of the cold temperature delaying the complete actuation of the primary seal, thereby extending the duration of blow-by.
Now, when we talk about blow-by of the primary seal, blow-by has to go somewhere, and where it goes to is the secondary seal. If blow-by occurs as soon as the pressure gets to the primary seal, early in the ignition, and that seal doesn't sustain that pressure, it goes immediately to the secondary seal, prior to the time that the joint is rotated.
CHAIRMAN ROGERS: This says "possibility of the loss of the sealing of the secondary O-ring."
MR. MULLOY: After the joint has rotated, sir. The condition that is on the screen now is before joint rotation.
DR. WALKER: But I think a critical and a literal interpretation of that waiver has to be that the primary seal is a single point failure. Now, the wording goes on to explain why this is so, but the wording does not make an exception. It merely explains why the single point failure mode refers to the primary seal.
But a strict interpretation of that wording to my mind is that the primary O-ring is a single point failure.
MR. HARDY: I wouldn't deny that. I am relating to what many of us knew about the performance of that joint, its rotation, when we lost-when we could lose, because of the stackup of tolerances, when in the ignition transient prior to full motor pressurization or after full motor pressurization when we could lose that secondary seal.
Our interpretation or my interpretation of the waiver was not to remove the secondary seal from the hardware.
DR. RIDE: It seems to me that really crucial to all of this is the timing function and how quickly you think that the primary will seal, whether it's in that first 160 milliseconds or whether it's not. And if it is not, then you run the risk of getting into the period where joint rotation is more likely.
I guess what I wonder about is the data that you've got to show how the timing function changes at low temperature, because it is certainly going to be a function of the temperature, just because the O-ring is different and it is behaving differently. It is deformed in some way.
And it is not clear to me that you've got the data to say that, to discriminate at the level of milliseconds, which is what you are really doing, and to apply engineering judgment based upon really not very much data, and applying that engineering judgment to a Criticality 1 case.