Washington, D.C.
The Commission met, pursuant to recess, at 10:10 a.m.
CHAIRMAN ROGERS: I would like to call the Commission to order, please.
Yesterday we had a meeting in executive session, at which time the NASA officials and others produced documents at our request, and memoranda, dealing principally with the O-rings and seals on the booster rockets. They complied fully with the request that we made and were very forthcoming in discussing all aspects of it that we were able to discuss at the meeting.
This morning we will start the meeting with officials from NASA, particularly dealing with the matter of seals on the booster rockets. And I would like as much as possible to limit our discussions today to that one subject matter.
We will attempt to advise the press of our plans as they are formulated, so that you can plan your own schedules. We are contemplating at the moment tomorrow having a day off, hopefully to get a little better organized and getting our staff organized. On Thursday, we plan to go to Kennedy and probably stay over Friday in order to see the facilities, discuss with the NASA officials all aspects of the launch, and to be available to have presented to us any other matter that
NASA feels would be appropriate.
During that time we will have informal discussions with people. We expect those will not be open sessions, because physically it is impossible. We may divide into subcommittees or we may [328] have individual interviews, but we will keep you advised about that. We would hope at that time, keeping in mind that we are going to focus today on the seals of the booster rockets, we would hope at that time that NASA will be in a position to show us and to show the media more of the pictures of the flight itself.
And also, we hope that we will be able to get some more information about telemetry and measurements that are being studied now. We want to do this in a way that will not be intrusive as far as the investigations under way are concerned, but we want to get as much information as quickly as we possibly can.
Later on - and I'm not sure when, probably next week - we will have meetings, either in executive session or closed meetings, dealing with the problems involving the weather and all of the weather-related problems, and we will take testimony from the Thiokol people and from NASA officials and get information about meetings that were held prior to the launch, all aspects of the weather and how the weather might have related to
the launch.
So today we will start with NASA officials, and first I would like to ask Dr. Graham, the Acting Administrator of NASA, to take the stand and address the Commission.
DR. GRAHAM: Good morning, Mr. Chairman. Do you wish to swear me in or shall I proceed?
CHAIRMAN ROGERS: No, you have been sworn in. You may proceed.
DR. GRAHAM: Thank you.
Mr. Chairman, members of the Presidential Commission on the Challenger Accident: I would like to assure you that NASA is continuing to review the facts and circumstances surrounding the accident that occurred with the Challenger.
As NASA continues to analyze the system design and data, as I said at the meeting last Thursday, you can be certain that NASA will provide you with its complete cooperation. In keeping with that, we have implemented several procedures.
One of them is that all NASA testimony that is given to the Commission will be reviewed on a word by word basis by a knowledgeable NASA technical review team. Should any error, partial, or incomplete statement, or potentially misleading statement be found in the testimony, an amendment to the testimony will be filed in order to clarify the issue of concern. That will certainly be called to your attention.
In addition to that, the NASA policy concerning the release of material is that NASA is making available to the Commission and then to the press and the public all information related to the tests that we have in NASA reviewed and which we find to be reasonably factual and not grossly misleading. We will continue that policy and, while I am sure that there will be concerns on NASA's part and as well as elsewhere over the time it takes to review some of this mass of information, to pull it together, and to provide it in a form that can be distributed to the press, nevertheless we are making very, very substantial efforts to have that information available to you and then subsequently to the public as quickly as we possibly can.
[329] Do you have any questions, Mr. Chairman, concerning that, before I go on to introduce the next speaker?
CHAIRMAN ROGERS: Yes. I would like to have a discussion with you about that first. Are there many confidential or classified documents among the documents in your possession?
DR. GRAHAM: There are very few that we have found to date, Mr. Chairman, that are of a national security nature that are classified.
CHAIRMAN ROGERS: So you will be able to make
all the documents available, in the final analysis, to the public?
DR. GRAHAM: Within the constraints of the law, either constraints concerning national security issues or constraints concerning technical export or transfer, we may have to exercise some discretion on a very, very small set of the documents. But in general, and certainly the vast bulk of the information, the relevant material and the data will be released to the public. And of course, all data is accessible to the Commission.
CHAIRMAN ROGERS: Now, there is no feeling on the part of NASA that the work of the Commission is in any way interfering with the disclosure of information, I hope?
DR. GRAHAM: No, sir. In fact, the work of the Commission is very much in accord with the work that NASA is undertaking and conducting internally, and we find these to be in general complementary.
CHAIRMAN ROGERS: In fact, you asked me to have this public session today in order to make it clear that NASA was not trying to brush anything under the rug, isn't that right?
DR. GRAHAM: Yes, sir. I suggested to you that you consider having a public session today on
specific characteristics of the SRB's, the solid rocket boosters, and any other matters you saw fit to question the NASA officials concerning.
CHAIRMAN ROGERS: I assume that there are thousands and thousands of documents that you are now considering for purposes of the investigation and for purposes of this Commission, is that right?
DR. GRAHAM: Yes, sir, a large number of internal documents that we have in review and consideration. We plan to release to the press today at the conclusion of this discussion the material that will be presented to you or is being presented to you today. And then tomorrow NASA will have a press briefing, and at that time we plan to release the entire bulk of the material that was released and presented to the Commission yesterday.
The amount of that material alone is a stack probably close to three inches high, and that is just a small part of the total data that we are reviewing and preparing for transmission to you and to release.
CHAIRMAN ROGERS: In light of the memorandum which has appeared in the press, written by Mr. Cook to Mr. Davis - and incidentally, those gentlemen are here today and will appear and testify - I assume that there are a lot of other documents of that nature, which make
suggestions about how matters should proceed, pointing out risks that were involved in launches, et cetera, is that correct?
DR. GRAHAM: Yes, sir. In any highly sophisticated technical operation such as the operation of the space shuttle system, there has to be a continuing dialogue within the agency that is responsible for operating it concerning the performance of the system, the characteristics, how [330] well the design is behaving in comparison with the operational data and the design expectation of the system.
All that is being constantly cross-checked and reviewed and re-analyzed, and you will find that there is a substantial volume of information that documents that process inside NASA, and we will make that available to you as soon as we have a chance to accumulate it and put it together in a form that is comparable.
CHAIRMAN ROGERS: The point I'm making is it's not unusual in an agency like yours to have employees make critical comments, suggest dangers that might be involved in the program. That is the way the system works, isn't it?
DR. GRAHAM: Yes, sir. It is very, very important, in fact, for the system to work to be somewhat
self-critical, and in the process of operating these systems to constantly review the issues, the engineering decisions, the performance. That internal self-criticism is in fact one of the strongest characteristics of NASA and one of the things that makes it in my view such a high quality technical operation.
CHAIRMAN ROGERS: And it may very well be that there will be a lot of other memoranda that appear in the press that neither you nor we know about? That would not be unusual at all, would it?
DR. GRAHAM: I wouldn't be in the least bit surprised if other issues come forward as we proceed through this review process.
CHAIRMAN ROGERS: And if we focus today on, to some extent on seals and O-rings and memoranda that are written by Mr. Cook and others dealing with that subject, the fact that we focus on it doesn't mean that that is the only area of concern as far as you're concerned or as far as the Commission is concerned, is that right?
DR. GRAHAM: No, sir, it is not the only area where we will find memoranda expressing engineering issues and engineering concerns. And it certainly doesn't mean that the NASA internal analyses has singled out any one area at this point - the O-rings, the seals, the field joints, or any other specific area -
as a unique source of concern and analysis.
We are still looking across a broad range of issues to try to establish what actually occurred in the Challenger accident.
CHAIRMAN ROGERS: Very well. Then the Commission will try in an orderly way to consider each one of those aspects, so at the end of our deliberations we will have a complete record of all of the documents in your possession and a complete record of the pictures and telemetry and all other aspects of it, that will help us make a judgment.
And I thank you very much for this colloquy. Maybe other members of the Commission might want to ask some questions.
DR. FEYNMAN: I wanted to say that there's as aspect of trying to figure out exactly what happened, in that first something looks obvious. Then, it is the experience of Commissions who have looked into accidents that what looks obvious at first turns out later to have a little flaw, and, when you make a long list of things that are out of the ordinary, that are called anomalies, you discover that there is something that doesn't quite fit, and then the theory has to be completely changed.
So that kind of work we don't want to have to drag the public through. We're thinking of
possibility A, possibility B, possibility C, and as we go through all of these things all the newspapers are always saying, now they think it is this, now they think it is that.
We don't know what it is, and we would like to investigate that physical question, I should hope, if it is at all possible, without the public directly, and then we can give a complete report. But when we are discussing this particular matter, it doesn't imply that this is what was the cause of the accident, but as an example the kind of thing that we have to investigate.
I don't think you should conclude that we know that this is directly related or whether it is or it isn't directly related. Certainly it is information we have to have to the actual accident.
DR. GRAHAM: Yes, sir.
CHAIRMAN ROGERS: I think there is one other aspect that deserves some comment at this point. Usually in investigations of this kind, you find that the press is not very knowledgeable on the subject and therefore the reporting is not very accurate. It seems to me that in this case the reporting has been quite fair and accurate on the part of the press, partly because they know a lot about it and they have followed it very closely.
And so I hope that we don't develop any friction between the media and NASA and this Commission, because we are all working to the same end. And as far as I can tell up to date, it has been a very fair process on the part of the media, and I hope we can cooperate with them in all ways to deal with this very difficult and tragic accident, which is of such importance to the nation.
All right, Doctor, you may proceed.
DR. GRAHAM: Thank you. Mr. Chairman. And that is certainly our intention, to proceed in just that manner.
I would like to now introduce the Associate Administrator for Space Flight, Mr. Jesse Moore. Mr. Moore plans, directs, and executes the development, acquisition, testing, and operation of all elements of the space transportation system within NASA and, as I mentioned last week, he has also been named as the director, the new director of the Johnson Space Flight Center at Houston.
Mr. Moore.
MR. MOORE: Mr. Chairman and members of the Presidential Commission:
What I would propose to do today is to give you a short status report of what my task force is doing and the areas we are focusing in on, and then I would like to call on the project manager of the solid rocket booster from the Marshall Space Flight Center to discuss with you and members of the Commission the solid rocket booster aspects and to try to address some of the issues that have been raised before the public here and to let you, as well as the public, know what actions have been taken with the solid rocket booster and what its functions are and so forth.
So that is kind of the agenda that I plan to cover this morning.
(Viewgraph.) [Ref. 2/11-1]
[332] I would like to say at the outset that I think the discussion that you and Dr. Graham had lays a very good foundation for the type of work we're conducting in our task force. We plan to cooperate very fully with the Commission and provide the data to the Commission as required.
As you indicated and Dr. Graham indicated,
there is an enormous amount of data that is available on all aspects of the space shuttle, and we will pull and are pulling all relevant documents together related to the 51-L tragic accident.
On February 5th, Dr. Graham formed a data analysis design task force on the 51-L mission incident. I am chairing that task force.
(Viewgraph.) [Ref. 2/11-2]
This was a transition from an interim mishap board that I had been chairing previously, and we're in the process now of formally establishing our charter and our membership. We had our first organization meeting at the Kennedy Space Center yesterday. I was obviously unable to attend, but the group is meeting, and we are preparing a list of and setting up a group of panels to address specific areas associated with the space shuttle 51-L mission incident.
We are planning to include on our panels, as well as the overall task force, members not only from NASA, but members from the outside to address specific areas of expertise as far as this overall incident is concerned.
Where we are today is we are continuing our salvage operations to try to find as much physical evidence as we possibly can that would allow us to piece
together the set of circumstances that caused the 51-L tragedy
(Viewgraph.) [Ref. 2/11-3]
In the area of data analysis, which is one of the most complex areas to try to look at, our primary concentration is to try to reconstruct a mission events time line, and this time line will tell us in great detail the sequence of events that went on from launch until the incident happened, some 70-plus seconds later.
We are looking at photographic data, and you mentioned that earlier in your opening comments. We will share some of that data with you in Florida on Thursday, and we are also trying to understand what load effects might have been applied to Challenger's launch, meaning there are different forces that we don't understand that happened during the trajectory: Were there any unusual set of circumstances happening prior to launch that we need to know about?
And our efforts are aimed at trying to get what I'd call an integrated load picture of what the flight looked like during pre-launch as well as during its ascent.
And you mentioned weather. Weather is certainly an issue that we're going to be working very
hard and are working very hard to try to understand what effects, if any, the weather played. We will be looking at temperature effects. We will be looking at wind conditions, not only surface wind conditions but upper atmospheric wind conditions, as well as moisture conditions, rain content, and so forth.
All these will be looked at in very great detail, and we will be happy to discuss weather activities with you and the Commission at your discretion.
CHAIRMAN ROGERS: On that subject, in preparation for hearings it would be useful if we had a scenario worked out of conferences and meetings and discussions, so that we can have a narrative form of what happened, in addition to all of the weather data itself.
[333] MR. MOORE: I presented to you and the Commission, I guess last week when we had the public hearing, that there were a number of mission meetings held in the chronology of this launch. We will go back, and are doing it right now, expanding that chronology, so we will be able to talk to you and the Commission in great detail on the weather aspects associated with this launch.
CHAIRMAN ROGERS: Very good.
MR. MOORE: In addition to things like
weather, loads, and other kinds of effects, it is critical to understand the pedigree of the hardware, how the particular hardware was processed, who handled the hardware, what kind of safety inspections were performed, and how many times the hardware had been used, and so forth. So these areas are also being looked at in very, very great detail.
There is a very complex procedure set up to apply and reuse hardware from the various shuttle flights and, as you know, there are two major elements that are reuseable from the shuttle flights. The shuttle orbiter certainly is reuseable, as well as the two solid rocket boosters are reuseable. They are launched and deployed, and we bring those boosters back in, refurbish those boosters to a certain set of specifications, and then refly those boosters on subsequent missions.
You asked a question of us the other day that I would like to answer. A new set of solid rocket boosters, flight set, meaning two of them, costs about 65, $66 million, is what a brand new set costs. A refurbished set costs on the order of 22 to 23, $24 million.
So there is about a factor of three in terms of cost relative to buying new flight sets of SRB's for
each flight versus the reusing of these flight sets. And so I thought I would present that piece of data to you, to answer one of your questions that you talked about.
Another element that is very important in this particular launch is the launch pad. This was the first time we had launched a mission off pad B. Our previous 24 launches had been on launch pad A at the Cape, and we are clearly spending a lot of time looking at any differences there may be relative to the two launch pads that were used.
We were carrying some cargo on board this flight. We were carrying a Tracking and Data Relay Satellite system, as well as a Spartan-Halley. We had flown the Tracking and Data Relay Satellite system and the inertial upper stage before, but we are trying to find out, were there any unusual circumstances associated with that.
No STS element - and "STS" is "Space Transportation System" - will be left unturned. No stone will be left unturned. We are not exonerating any aspect of this particular mission as far as free from either being a cause or an effect from the tragic incident that happened on 51-L.
We are putting together, as has been
previously discussed, several of what I would call failure scenarios. These are things that could go wrong, and we are putting those together across all parts of the program. And our job in this task force is to try to go and prove each of these scenarios did not contribute to this accident, and we are doing that by analysis and by tests that are being conducted now.
(Viewgraph.) [Ref. 2/11-4]
And also by test data that has been previously run in the program. And so that will be a process we will be going through to discount and to say conclusively that this particular failure scenario was not a contributor in the 51-L mission incident.
[334] CHAIRMAN ROGERS: Jesse, based upon what you told us before, though, you have been doing that each time, haven't you? I mean, this analysis is not new to 51-L?
MR. MOORE: We have failure modes and effects analysis for all elements of the shuttle, and that has been done and documented, and we're using those failure modes and effects analyses that are in the program as starting points for the kind of analysis that we're doing right now, Mr. Chairman.
CHAIRMAN ROGERS: Good, because we wouldn't want to leave the impression that you're doing it just
because of this accident. Your records indicate you have been doing this on a regular basis.
MR. MOORE: Yes, sir. It has been done since the program, since the start of the program, as part of the normal analysis of a system like this where you do go through and do detailed failure modes and effects analysis and so forth.
And what we're trying to do is make sure that what has been documented and known and done in the program is consistent with the postulates that we're putting forward now, that may have been a cause relative to the 51-L mission.
We are also trying to be very careful and discriminating between cause and effect, and it is easy to say, here's a picture that shows a piece of information, but that piece of information may have been the result of some other cause. And so we are trying to be very careful and discriminating between cause and effect as far as where we are focusing in on the problems with respect to this accident.
The solid rocket booster is obviously one area that we are focusing very heavily on, and I will say a little bit more about that, and that is the purpose of our agenda here today, is to try to tell you and the Commission what we're doing in
the solid rocket booster area and some of the potential areas that are of concern relative to the solid rocket booster.
The external tank is also involved in one or more scenarios as far as potential failure modes in this whole program, as well as the other elements, as I said earlier. And I would like to emphasize to the Commission that we have not exonerated any aspect of the 51-L mission as of now.
Finally, with respect to the solid rocket booster, we are looking at things like design specifications, materials that are used, the manufacturing process that was used, how the system was stacked and how it was prepared for launch, who was involved, the safety aspects of it, the quality assurance aspects of it, any photography that we have which closes out the work prior to a launch, and we do that on a routine basis, take photographs -
(Viewgraph.) [Ref. 2/11-5]
- of the flight hardware at various stages during its preparation for launch. And we call those closeout photography. And that data has also been impounded and is being used in our process of trying to understand what happened.
We're also going to discuss seals. That has
been a very visible topic lately, and Mr. Mulloy of the Marshall Space Flight Center will go into a fair amount of detail on seals.
And we're looking at environmental effects. So there is a range of things that we're focusing on, Mr. Chairman, in our task force, that we will be working and interacting with you and your [335] Commission to make sure that all the data that is being generated by our task force is available to you and you understand that particular data.
And I think a point that was made earlier that I would like to just close on before I introduce Mr. Mulloy is that, you know, a lot of memos have been written about different concerns and issues in the program, and those memos, there are hundreds and thousands of those kinds of memos throughout the whole program.
Those concerns are looked at by the engineering and the technical analysts in the overall program. They are thoroughly reviewed as a part of our flight preparation process, which starts out at the contractor and then goes to the project office at a particular center that is responsible for this, and then goes up to the center management and then goes to what we call level two management at the Johnson Space
Center, which we described the other day, and then comes to my level.
So there has been a thorough look at all of those elements that are critical to the launch of a space shuttle. And I would just like to say that on the solid rocket motor we believe that has been done as well, and you will hear that from Mr. Mulloy.
And we're also going back and looking at the engines, the tank, and so forth with that same degree of thoroughness to assure that all of that has been done for those elements as well.
With that, Mr. Chairman, I would like to turn this over, if there are no questions.
CHAIRMAN ROGERS: Let's see. There may be some questions.
(No response.)
MR. MOORE: I would like to introduce Mr. Larry Mulloy, who is the project manager of the solid rocket booster at the Marshall Space Flight Center.
(Witness sworn.)
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[336] [Ref.
2/11-1] AGENDA. [Ref. 2/11-2] STS 51-L TASK FORCE.
[337] [Ref. 2/11-3] STS 51-L TASK FORCE.
[338] [Ref. 2/11-4] STS 51-L TASK FORCE.
[339] [Ref. 2/11-5] STS 51-L TASK FORCE.
MR. MULLOY: Mr. Chairman, members of the Commission:
As Mr. Moore has stated, I intend to give you a briefing on some aspects of the solid rocket booster assembly, the details of that solid rocket booster, and then concentrate with a bit of information on how the solid rocket motors are assembled, how they were refurbished, and particularly on the seals and the joint.
(Viewgraph.) [Ref. 2/11-6]
The solid rocket booster is made up of a number of assemblies. The forward assemblies here are manufactured and refurbished by the United Space Boosters booster production company, and the forward skirt and forward frustum and the nose cone. That assembly contains the electronic devices and also the recovery system for the solid rocket boosters. It has three main parachutes, a drogue parachute, a pilot parachute, in that assembly, which does return the booster to the ocean, where it is retrieved by retrieval ships, brought back to the Kennedy port for disassembly, and returned to the manufacturer for refurbishment.
The aft assembly, which is known as the aft skirt, which is the hold-down point for the total shuttle system, is also manufactured and refurbished by the United Space Boosters booster [341] production company, and then the center section here is the solid rocket motor, which is the primary area of interest that we have here today.
The solid rocket motor consists of four casting segments. Each of those casting segments is about 24 feet long. The booster is 146 inches in diameter. The casting segment itself is made up of two tank segments and joined by a factory joint.
When the motors are cast at Thiokol, they are then shipped by rail car to the Kennedy Space Center, where they are assembled into the shuttle stack. This center factory joint here is covered with the insulation that is inside the motor. There is an insulation, then a liner, and then the propellant.
The end joints or the field joints are metal joints with a tang and clevis that I will describe in more detail, and sealed with two Viton O-rings. When the boosters are recovered and returned to the Kennedy Space Center and disassembled, there is a very thorough inspection done of those assemblies immediately after retrieval.
Steps are taken to preserve the hardware, as you will see in this model or this section, out of flight hardware that I will show of an actual section of the joint. The D-6 steel material is very susceptible to corrosion, so immediate steps are taken to wash down that metal and apply grease to protect the joints particularly from any corrosion.
CHAIRMAN ROGERS: Mr. Mulloy, could you as much as possible relate what you are saying to 51-L?
MR. MULLOY: Yes, sir.
CHAIRMAN ROGERS: How many retrievals were made?
MR. MULLOY: The aft segment on 51-L, the right hand booster, the aft segment had been used twice, once in a test motor and once in a flight motor. The aft center segment had been used once. We have used segments up to four times.
CHAIRMAN ROGERS: And is there data on how each segment was handled, both in retrieval and in Utah?
MR. MULLOY: Yes, sir. There is a complete record of the inspection results immediately after retrieval. Then when the booster segments are returned by rail car to the Wasatch Division of Morton Thiokol, there is - the process that goes through is a washout, initial washout
of the remaining insulation material, then a grit blast, and the amount of material removed with that grit blast to take the paint and remaining insulation off is measured and recorded.
There is a detailed inspection then made for cracks, surface blemishes, and dimensional tolerances, and a structural analysis made to assure that that is acceptable. Then that segment is put back into what we call a hydroproof test, where we apply 112 percent of the maximum operating pressure that that segment has to sustain in the next flight.
Subsequent to that hydroproof test then there is what is called a magnetic particle inspection made of the case segment, to assure that there aren't any flaws that are not visible to the naked eye. And then that segment is put back through processing.
One of the critical things in the acceptance of that segment is a dimensional check to assure that particularly the mating joint, the tang on one end and the clevis on the other, is within the dimensional tolerances for new hardware. Reused hardware has no different tolerances than new hardware.
We do have a procedure whereas a hardware that doesn't precisely meet the drawing specification can be dispositioned by material review boards or a waiver can
be issued. One of the things that is being investigated, of course, for 51-L is if any of those things applied to any of the segments on the 51-L vehicle.
To my knowledge, all of the hardware in the solid rocket motor on 51-L met all of the requirements for new hardware.
DR. RIDE: Have you ever recovered any of the solid segments that didn't meet the criteria for reuse?
MR. MULLOY: I believe in STS-1, either 1 or 2 - and perhaps Bill Lucas may remember - there was one segment, due to the splashdown loads and cavity collapse loads - I would point out that there are stiffeners. These rings that you see back here on the aft segment are stiffener stubs; I believe my recollection is that we added an additional stiffener into the segment to preclude the loss of the aft segment.
And I do believe that in the early flights one or two segments had gotten outside of dimensional tolerances and could not be reused.
Since STS-5, which is when I took over the program, we have had no loss of segments due to flight loads or splashdown loads.
DR. RIDE: Do you X-ray any of those segments?
MR. MULLOY: Yes. The segments are X-rayed in
Utah. In the initial stages of the program, there was 100 percent X-ray, 100 percent to the extent that you can get to 100 percent X-ray of a large structure like this. The maximum possible X-ray was done on all of the development qualification motors, and through a period up through the first six flight sets, to assure that our process that we had in place was producing a repeatable product.
We never found any problems as a result of X-ray, and what we are doing right now is a periodic X-ray to assure that the process controls that we have in place for the propellant, liner, and insulation, that we're not getting outside our experience on that.
And so essentially, what we're doing right now is X-raying about one segment a month on a sampling basis.
VICE CHAIRMAN ARMSTRONG: Anything other than X-ray? Ultrasound or NMR or other approaches used?
MR. MULLOY: Yes, ultrasound is used, and visual inspections, particularly visual inspections of the end of the segments, where you can determine whether there is any de-bond of the insulation to the liner or the insulation to the case wall.
DR. RIDE: What percentage of the segments is
one segment per month?
MR. MULLOY: Well, of course, at the rate we've been going now, at a rate of 12 per year, we are casting eight segments per month, and so it is one of eight, essentially.
MR. WALKER: Have you X-rayed any recovered segments?
MR. MULLOY: No, there has been no X-ray of the recovered segments. There is nothing there but the steel. We do not do an X-ray of the steel. We do a surface dye penetrant inspection of that steel segment and a proof test.
CHAIRMAN ROGERS: So you will have a history, a full history of these two booster rockets that were on 51-L?
MR. MULLOY: Yes, sir.
[343] CHAIRMAN ROGERS: Has there been anything that's come to your attention that was unusual about the two boosters on 51-L?
MR. MULLOY: No, sir. In going through - and I will cover the readiness review process that we went through - there is nothing that is in any of the records that I have reviewed that is unique about the boosters on 51-L.
DR. RIDE: What kind of effect would you
expect from the corrosion on particularly the O-rings and the putty? I guess what I'm interested in is, if you recover the solids from 51-L do you expect to learn anything about the O-rings and the putty and the joint, or do you expect corrosion?
MR. MULLOY: What we are particularly interested in - and perhaps I should get into the details on the joint here. From a corrosion aspect, the primary concern for corrosion - and let me turn this in the flight direction here. The primary concern for corrosion is in the sealing surfaces of where the O-rings, which are these two black 280 thousandths diameter devices you see in these grooves here.
We are particularly concerned for pitting that may be inside of that sealing surface, because a pit obviously can provide a path for hot gas to get by the O-ring.
CHAIRMAN ROGERS: Could you describe what you're holding?
MR. MULLOY: Yes, sir. What we have here is a section from an actual solid rocket motor. The bottom section is the upper portion of one of the casting segments. The black on the inside is the propellant insulation.
The piece on the top is what is called the
tang end of a motor segment. This is the field joint. It also is the factory joint, case to case. As I mentioned, two of these 12-foot segments go together to make one casting segment, and that is what goes to Kennedy for assembly.
On the factory joint, there is no discontinuity in this insulation, because the insulation is applied after the joint is made. So you have insulation over this joint.
On the field joint, however, there is this discontinuity in the insulation, since you have to put it together at KSC, at the Kennedy Space Center. And this gap between the insulation is filled with a zinc chromate asbestos-filled putty. That putty is laid up in strips prior to assembly.
We use strips of putty that are eighth inch and quarter inch thick and an inch to an inch and a half wide, to lay that putty up in a precise drawing pattern such that we are sure that the putty, when laid into this joint, does not extrude outward, but you have a good fill of the putty between the insulation surfaces, but that it does not extrude down into the O-ring gap such that it would tend to unseat the O-ring.
These O-rings in here are Viton rubber, provided by Parker Seals, and they are, as I say, about
280 thousandths in diameter, and there are two of these at each one of the joints on the vehicle. The assembly is done in this position, with the tang end up and - excuse me, with the clevis end up and the tang end down.
Looking on this side, you see a pin that is a one-inch pin that is a high strength steel, that there are 177 of those pins in a joint. That provides the structural integrity of the joint.
You also see what looks like a little clip here on the outboard leg of the clevis. That is a 32 to 36 thousandths of an inch shim. The purpose of that shim is to assure that we have a [344] controlled dimension on the outer leg of the tang to - the outer leg of the clevis to the tang, to maximize the O-ring compression or the squeeze on these O-rings between this inboard tang, the inboard leg of the clevis and the tang.
MR. HOTZ: When do you get that squeeze?
MR. MULLOY: On assembly.
MR. HOTZ: You don't get it during launch?
MR. MULLOY: Sir?
MR. HOTZ: Do you get it during launch?
MR. MULLOY: Yes, sir. The design is to assure that you maintain launch, such that, the way these seals operate is it is a
that compression during pressure-actuated seal, that you want compression on the seal such that when the motor pressure is applied to the seal that the seal will extrude into the gap downstream of the pressure and provide the pressure seal.
MR. HOTZ: Is there any particular phase of launch when that pressure is the strongest?
MR. MULLOY: Yes, sir. We go from zero up to the maximum pressure in about 900 milliseconds, and so it is instantaneous. And then we hold that max pressure for 20 seconds. And I will show you a pressure profile later in the briefing.
And then that pressure drops down to about 600 psi, and then it ramps back up slightly, and then you go into the thrust tailoff at approximately two minutes into the flight. And I do have a profile of that in the briefing.
DR. RIDE: Could you describe the corrosion on the joint?
MR. MULLOY: Yes. You can see the corrosion. What it amounts to is pitting in the metal, and so you see the corrosion that is on the outside of this piece here, is what we don't want to have inside the O-ring groove. That is why we take extra precaution to assure that we immediately preserve that hardware, because when we get it back it has been in the sea water
for perhaps 30 hours longer with rough sea.
DR. RIDE: What about corrosion of the putty and O-ring? Is that a problem?
MR. MULLOY: Corrosion? Extrusion of the putty?
DR. RIDE: No, I think what I really want to know is how does the sea water affect the O-ring and the putty. "Corrosion" is the wrong word, but do you expect to find the O-ring intact when it has been in the sea water for a long time?
MR. MULLOY: Oh, yes. And we also find the putty intact. And as we have shown you in the data that we have presented to the Commission, where we have all of the data about our experience with this joint post-flight, you can clearly see the putty is still there in the joint. You can clearly see hot gas paths through the putty, and you can see very clearly any erosion that has occurred to the primary O-ring, and that is definitely attributed to the flight motor operation and not any effects of sea water.
DR. FEYNMAN: Can I ask a few questions in succession to help explain how this thing works?
MR. MULLOY: Yes, sir.
DR. FEYNMAN: This rubber thing that is put in, the so-called O-ring, that is supposed to expand to
make contact with the metal underneath so that it makes a seal, is that the idea?
[345] MR. MULLOY: Yes, sir. In the static condition it should be sealed to - it should be in direct contact with the tang and the clevis of the joint, and be squeezed 20 thousandths of an inch.
DR. FEYNMAN: And if it weren't there, if it weren't in contact at all and there was no seal at all, that would be a leak. Why don't we take the O-rings out?
MR. MULLOY: Because you would have hot gas expanding through the joint and destroy- -
DR. FEYNMAN: Pushing the putty through, and so on?
MR. MULLOY: Yes. You will always push the putty through, because the motor pressure is 900 psi nominally, 1,000 psi at max, and that putty will sustain about 200 psi.
DR. FEYNMAN: Now, we couldn't put instead of this some sort of material like lead, that when you squash it it stays? It has to be that it expands back, because there is a little bit of play in this joint and it has to be able to come back. I mean, it is a rubber material, so that it comes back when you move a little, and it stays in contact, is that right?
MR. MULLOY: Yes, sir, that is the purpose of the putty, as a thermal barrier, a thermal barrier. In the data that we have presented to the Commission, as you noted yesterday, we have looked at other alternatives, some of those alternatives are things like - -
DR. FEYNMAN: I'm talking about the rubber on the seal?
MR. MULLOY: I'm sorry?
DR. FEYNMAN: In the seal, in order to work correctly, it must be rubber, not something like lead?
MR. MULLOY: Yes, sir.
DR. FEYNMAN: Because when the seal moves a little bit when there is vibration and pressures, it would lift the lead away, which the rubber expands in place?
MR. MULLOY: Yes, sir.
DR. FEYNMAN: So it is important that it have this property of expansion and not be plastic, like lead. And I think you call that resilience, right?
MR. MULLOY: That is correct. It has to have resiliency, and that is why we use an elastomer.
DR. FEYNMAN: If this material weren't resilient for say a second or two, that would be enough to be a very dangerous situation.
MR. MULLOY: Yes, sir.
DR. FEYNMAN: Thank you.
MR. MULLOY: If it was rigid.
MR. HOTZ: Mr. Mulloy, could you tell us whether the shim that you have put in here to damp out some of the vibration is an original design consideration, or is that something you added as a result of experience?
MR. MULLOY: That was added. It has been on since the first flight vehicle. It was added as a result of experience during the early development testing on the motor. It is not for the purpose of damping vibration. It is for the purpose of assuring a uniform gap on the outside and maximum squeeze on the O-ring on the inside.
DR. COVERT: Mr. Mulloy, for purposes of my own understanding, I would like to have you go through the ignition process. And I find that I understand things best if I can feed them back to you so I want to ask a series of questions, and I will use this as an example.
This gap here is filled with the zinc chromate asbestos putty-like material.
MR. MULLOY: Yes, sir.
DR. COVERT: And it's designed to more or less be plastic?
[346] MR. MULLOY: Yes, sir.
DR. COVERT: Now, when you pressurize this side of it there is a little volume in here between the termination of the putty and where the O-ring lives, is that correct?
MR. MULLOY: Yes, sir.
DR. COVERT: And when you pressurize it, then, because the plastic is able to flow, it flows into this gap and compresses the air in that gap until the pressure is equal to the pressure in the combustion chamber, is that correct?
MR. MULLOY: That is one thing that could happen.
DR. COVERT: Don't confuse me with a lot of alternatives at this point.
[Laughter.]
DR. FEYNMAN: Why don't you put up the picture two from now, the one called "SRM No. 3."
MR. MULLOY: Would you put chart number three on, please.
(Viewgraph.) [Ref. 2/11-7]
DR. COVERT: Now, the point I want to get to at this point is that this O-ring then is subjected to the pressure that is caused by the plastic deforming and helping to fill this little cavity, and that in turn drives the O-ring into this crack in back of it. That
is called extrusion, I believe?
MR. MULLOY: Yes, sir.
DR. COVERT: And so that is the mechanical joint that carries the pressure seal, is that correct?
MR. MULLOY: That is correct.
DR. COVERT: Now, if there was a flaw of some kind, then what would happen would be, instead of the plastic deforming and coming into this, then there would be hot gas flowing in a narrow jet into that cavity, is that right?
MR. MULLOY: A flaw in the putty?
DR. COVERT: Yes, sir.
MR. MULLOY: Yes, sir, a flaw in the putty would cause a hot gas jet to impinge on the primary O-ring.
DR. COVERT: So that would in turn then, that hot gas, would be what would drive the O-ring and cause it to extrude and carry the pressure load?
MR. MULLOY: The hot gas jet erodes the O-ring, and the pressure rising in the cavity tends to seat the O-ring.
DR. COVERT: So you have sort of a redundant system, then. The way the design works out is that there is - if the putty holds, the gas compresses the O-ring and extrudes it into the gap; and if the putty
for one reason or another has a flaw in it and a little jet of gas comes in there, there is still a pressurization in there, and that causes this to be sealed?
MR. MULLOY: Yes, sir.
DR. COVERT: And the second O-ring then is a backup just for safety purposes?
MR. MULLOY: It was a backup to make the - to provide a redundant sealing capability.
DR. COVERT: Thank you very much.
MR. MULLOY: Yes, sir.
[347] MR. WALKER: I have a question about the O-ring. The manufacturer generally specifies the amount of compression on the O-ring by specifying the depth of the O-ring groove. Is the compression that you get here equal to the amount of compression recommended for O-rings of this diameter?
MR. MULLOY: Yes, sir. The minimum O-ring compression that we have here is 7.54 percent, and that is within the recommended levels.
MR. WALKER: What was the impact of adding the metal plates which you put at each place where you have a steel pin? Was that to increase the compression, or what was the exact purpose of that?
MR. MULLOY: The primary purpose is to assure
a uniformity of gap, and also then to assure that we would achieve the minimum compression by pre-shimming that to the 32 thousandths.
MR. WALKER: So are the shims placed on all 177 of the pin locations?
MR. MULLOY: Yes, sir.
MR. HOTZ: Mr. Mulloy, how are these materials, this putty and the rubber, affected by extremes of temperature, both hot and cold? Do they change their characteristics at all?
MR. MULLOY: Yes, sir, there is a change in the characteristic. As elastomers get colder, the resiliency decreases, and the ability to respond - -
MR. HOTZ: Now, the elastomers are what?
MR. MULLOY: That is the Viton O-ring.
MR. HOTZ: The rubber?
MR. MULLOY: Yes, sir.
Now, the putties are not as sensitive as the elastomers are to the temperature over the range of temperatures we operate. Of course, temperature - -
MR. HOTZ: How about moisture? Are the putties affected by moisture?
MR. MULLOY: Yes, sir. And in order to control that, we maintain the putty in a refrigerator and have limits on the time that it can be outside of
the refrigerator before the joint is mated. What we have found, especially at the Kennedy Space Center, with the putties, that they do tend to take on moisture, and as the putty gets more moisture it becomes extremely tacky and sticky, which makes it very difficult to lay into the joint and to work with.
And it can take on enough moisture such that the putty loses its ability to hold together. So we control the humidity that that putty sees prior to installation into the joint until we have the joint made up.
CHAIRMAN ROGERS: Was the putty on flight 51-L the same quality putty you used on other flights?
MR. MULLOY: Yes, sir, it is the same putty we have been using since STS-8. It is a Randolph type two putty, zinc chromate with an asbestos filler.
CHAIRMAN ROGERS: The same manufacturer?
MR. MULLOY: Yes, that is the manufacturer, Randolph. We did have a change of putty in the program because the original supplier of the putty, which was Fuller-O'Brien, went out of making this particular putty because of its asbestos content.
CHAIRMAN ROGERS: When was the change made?
MR. MULLOY: STS-8. And somebody could help me with the date on that.
CHAIRMAN ROGERS: How far back in terms of number of flights?
MR. MULLOY: This was the twenty-fourth, so 16 flights.
MR. HOTZ: Were you considering any further changes in the brand or the type of putty?
MR. MULLOY: Yes, sir, because asbestos products, of course, people are going out of the business of making asbestos every day. We were evaluating other putties. We were looking at a non-asbestos putty, as well as an Inmont Canada putty, which is asbestos-filled, and we have done some testing on that in some of our development motors that we have currently in test in the filament wound case program as an alternative to the Randolph putty.
But none of that has been implemented into the program yet.
CHAIRMAN ROGERS: Is there any reason why you were thinking of changing the putty, except for the asbestos problem?
MR. MULLOY: That's the only reason, sir, to have another source, not because of any concerns for the performance of the putty.
CHAIRMAN ROGERS: Then there is nothing unusual about the putty that was used in 51-L that you
want to call to the Commission's attention?
MR. MULLOY: No, sir, not that I'm aware of. As I say, we're looking at all of the records and the paper to assure that the handling of the putty was as it was supposed to be, that the joint was mated within 12 hours of the time that the putty was first removed from the storage.
MR. HOTZ: But you did have some very high moisture conditions on the pad just before launch.
MR. MULLOY: Yes, sir. But we haven't seen any indication that, with the exposure of the putty, as Sally mentioned, even to sea water, we don't see that kind of breakdown in the putty when we get the hardware back for evaluation, just even after 30 hours in the ocean.
VICE CHAIRMAN ARMSTRONG: When we go to Kennedy, will we be able to see how this putty is applied?
MR. MULLOY: Yes, sir.
DR. COVERT: Do you throw away the O-rings after each use and put new ones in?
MR. MULLOY: Yes, the O-rings are single use items. You fly new O-rings on each flight.
MR. WALKER: A fairly detailed question. On your diagram, there is a gap at the end of the inside
leg of the clevis - I mean, of the tang. The U-shaped device is - I mean at the other end, right there. Is that gap filled with putty or is that gap air, and the putty extrudes into that gap during launch, is that correct?
MR. MULLOY: That is air. And as I say, we take precautions to be sure that we hold the putty back off of here, such that during assembly the putty doesn't extrude down into the O-ring gap and unseat the O-ring. And yes, under pressure the putty tends to extrude into the gap.
It does not extrude totally into the gap, because, as I say, the putty won't sustain 1,000 psi, and in almost all instances, rather than the situation that Mr. Covert described, rather than a uniform decompression of putty, there is usually a breakthrough of the putty up at the 1,000 psi.
We don't see when we get it back. We see putty getting further down than it was on assembly, but we don't see it extruded all the way into the O-ring gap.
MR. ACHESON: Have you experimented with material as a substitute or alternative to putty which would tend to fill that groove under high pressure and temperature?
MR. MULLOY: Fill this groove?
MR. ACHESON: Yes, sir.
MR. MULLOY: No, sir, because that is not a desirable situation to have anything that would fill and get into the O-ring gap at all. We have experimented with materials that are alternatives to putty which is in the data that I presented to the Commission yesterday, looking at carbon mesh, wire mesh, and channels that would allow uniform pressurization of the cavity to eliminate the hot jet impingement that goes through the putty and other alternatives.
At this point, with the testing that we have done over the last year, we have concluded there is no better alternative than the putty that we are using based on the testing that we have done.
DR. RIDE: What methods do you have to verify that the putty has been laid properly? Do you have any
way of examining it after it has been laid to make sure that there are no air gaps?
MR. MULLOY: It is examined after it has been laid on, and I wish I had a diagram, but you will see it Thursday at Kennedy as to how that is laid up. But literally, what you do is you just lay these putty strips directly on the surface, and we use quarter inch strips here and then eighth inch strips, and they are laid up in a prescribed pattern. It is not an operator option to put enough putty on there to be sure you fill the gap. It is a drawing, it is controlled and it is inspected and signed off by quality inspection that the putty strips are installed in accordance with the procedure, and that procedure is to assure that the putty is laid in tightly onto the insulation and that you don't have air gaps in there.
And we have shown by tests that that provides the best thermal barrier. We have also shown when you deviate from that that the thermal barrier is compromised. So we are very, very careful about how that putty is laid up.
DR. RIDE: Have you had a chance to go back and look at the quality assurance records on 51-L and verify that those were signed off properly?
MR. MULLOY: That is in process now under Mr.
Moore's Design and Data Analysis Task Force, and that is in process, and hopefully Thursday at KSC you will be able to see some of the certification of the rereview of those records. All those records are at KSC where the assembly is made. All of them are under the control of the NASA investigative board, the interim board, and now the task force. But nothing during the assembly of 51-L where I get involved in that assembly process, if there is some requirement to deviate from the requirements that we have for the assembly, then I would get involved in that because it would require a waiver to deviate from that.
I have checked with my managers and with the contractor at Morton-Thiokol and the manager of the solid rocket motor project who works with me at NASA, and they assure me that they have no recollection of any deviations being worked in the assembly of 51-L.
GENERAL KUTYNA: Mr. Mulloy, we have had a history of some problems with these O-rings since about 1980.
[350] Could you summarize the history of the erosion problems and the blow-by and when they occurred, the conditions under which they occurred?
MR. MULLOY: Yes, I can. I think it would be useful, if I may, to proceed through the next diagram
and then move into what causes the erosion, and review - it is not in this presentation today, but to review with you the numbers of instances that we have had in a summary fashion that summarizes the detailed data that I presented to the Commission yesterday.
Next chart, please.
(Viewgraph.) [Ref. 2/11-8]
DR. WALKER: Before you leave that chart, I have one more question.
MR. MULLOY: Go back to Chart 3.
(Viewgraph.) [Ref. 2/11-7]
DR. WALKER: How wide is the gap between the insulation pieces of the two different sections where the putty goes?
MR. MULLOY: Let me get those dimensions out of the presentation from yesterday.
The gap size on the field joint varies from .01 down at this narrow section here up to .4 inches at the top, and the length of this channel right here is 3.3 inches.
DR. WALKER: So is the putty just laid into that gap, or is it worked into the gap?
MR. MULLOY: No, the putty is laid on before the joint is assembled. It is laid on to the surface here and then assembled in a very precise, precisely
controlled pattern to assure that we don't get any voids, or minimize the voids that we have in the putty.
DR. WALKER: And then it is visually inspected after the joint is made?
MR. MULLOY: Well, you can't inspect it after the joint is made. All you can see is that you have extruded the putty out of the joint which you would expect to do under the configuration that we have it in prior to the lay-up. You would expect to see this kind of a bead here. The inspection is, if you didn't see the putty coming up to here, obviously it wasn't laid up properly. But the inspection is made prior to pushing the joint together, and we have many, many tests that assure that if you lay the putty in that way and then assemble the joint, you will get a fill with minimum voids.
Let me back up one chart to talk more generally about joints.
Let me have Chart 2, please.
(Viewgraph.) [Ref. 2/11-8]
MR. MULLOY: The joint we have been talking about is represented here for these three field joints. These are the three joints where the four segments are tied together. As I mentioned, there is an identical joint in each one of these segments which is covered
with the rubber in the casting process at Thiokol. There is another joint which has erosion history on it that is not the case-to-case joint but it is the - where the nozzle is attached to the aft end of the solid rocket motor. That configuration is significantly different than the case-to-case joint.
And in the case joints we have two O-rings in series on the same bore, if you will. On the nozzle joint it has this right angle sealing surface here, and when the nozzle is inserted, and I will show you on a bigger diagram, there is an O-ring that is a face seal as well as a bore seal.
So let me go to Chart 5, please.
[351] (Viewgraph.) [Ref. 2/11-9]
MR. MULLOY: Chart 5 is a larger diagram of that nozzle-to-case joint where we have also experienced some O-ring erosion, and this shows the two O-rings, this being the face seal and this being the bore seal. Because the tolerances are somewhat tighter on this joint than we have on the case-to-case joint, this O-ring groove is somewhat wider than the O-ring groove on the case joint to assure that we can assemble this nozzle to the case without damaging that O-ring.
Now, let me move forward.
MR. ACHESON: Let me ask why the tolerances
are less tight on the field joints?
MR. MULLOY: Well, because the 146 inch diameter that has to be mated to assure that we don't have any gathering of the material when we mate the joint or puckering, there has to be somewhat more tolerance in that. This is 103 inch diameter versus 146 inch diameter.
Okay, let me go to the next chart, please, which would be Chart 5.
(Viewgraph.) [Ref. 2/11-10]
MR. MULLOY: Or 6.
CHAIRMAN ROGERS: Excuse me.
Would the television people, is it necessary to have the lights on so bright? It is really intolerably hot here.
Is there any way to turn them down a little bit?
MR. MULLOY: General Kutyna, I am going to get to your summary, if you will allow me. I would like to give a little precursor to that that I think leads in to how we dealt with those data relative to 51-L.
And as Mr. Moore has mentioned, we do have a very thorough preflight review process for the solid rocket booster. That preflight review process starts with the recovery of the hardware from the last flight,
because we are very sensitive to anything that we see on the last flight that might pose a consideration that we should have for the flight readiness of the next one. So we have had that opportunity to go back and do a detailed examination of the hardware from the previous flight prior to committing to the next one.
The key thing in our flight readiness review is that previous flight performance. We look at the ballistic performance of the motor, and then particularly any problems from the previous flight.
Now, we have not had in the solid rocket motor in terms of ascent performance, we have had no anomalies related to ascent performance in the motor. What we have seen on recovering the hardware are some things that would indicate that there are some improvements that could be made in the design to provide more margin, and the particular point of interest here is the case joints and the nozzle joints, and particularly the erosion of the O-ring seals. So we have dealt with that finding on all previous flights in the flight readiness for all subsequent flights, and 51-L was no different.
Sometimes as the flight frequency increases we are in a situation where we have something from two flights back, maybe, that is still under analysis that we, even though we were able to continue with the
previous flight, if that isn't closed out, we look at it even for the second flight downstream. There are several things in the SRB world that have fit in that category. One of them has been some damage that we have been getting to rate gyro assemblies just due to the splashdown and the tow back and the porpoising as we tow the boosters back. We have been trying to work that problem. That is a reuse issue.
The thing of interest here is what have we seen in the O-rings. Now, the fact is, before 51-L we hadn't seen any anomalous erosion for about a year. The O-rings had been performing very well. The last time we had seen any erosion on O-rings was the January launch the year before. But we were very sensitive to, mainly because of the activity that we've had going on in the last year to try and improve the margin in that joint, we had been very sensitive to how that was going on, and we were continuing to look very carefully at the previous flights to assure that nothing had changed in that area that would change our rationale that we had developed for continuing to fly in light of the erosion we were seeing on the O-rings.
We considered that in 51-L, and concluded, particularly since we had not seen any significant erosion in the last year, and we had no test data that
changed our rationale, the same rationale then applied for 51-L as it applied to the last year in the flight readiness review.
Then we looked very carefully at the flight performance requirements for our next flight. In the case of the solid rocket booster, those performance requirements are in terms of the ballistic performance of the motor. And we review the small motor testing that was done at Thiokol to characterize the ballistic performance of the propellant that is in this particular motor. That was done in this case.
And then we go through our complete certification and verification status, and this is where I gained my confidence that there wasn't any kind of a waiver or deviation in the assembly process of 51-L because we review all of those at that point in the flight readiness process, and none are in the record, and I am confident none were brought to my attention.
Next chart, please.
(Viewgraph.) [Ref. 2/11-11]
CHAIRMAN ROGERS: Could I say on that that the only thing you say that you have had a history of one year's success with the O-rings previous to flight 51-L.
MR. MULLOY: Yes, sir.
CHAIRMAN ROGERS: The only thing that might be different or that might affect the O-rings differently was the weather then?
MR. MULLOY: Yes, sir, and I am addressing at this point the flight readiness review process, and at that point the weather was not a factor, and I will get into the one day prior to launch consideration of the weather.
CHAIRMAN ROGERS: Okay. I think we prefer, and I don't want to disrupt your presentation, but I think we should have a full session just on weather so we can focus on it.
MR. MULLOY: Okay. There are no charts in here on that.
Okay. The levels of review. In the case of the SRB, we do require that our contractors have a flight readiness review process that covers all of that information, and that is documented. That is chaired by a Senior Vice President at Thiokol above the level of the program manager.
[353] And he uses other people at the Wasatch Division who are not on the SRM project to do that flight readiness review.
Then my element managers, I pointed out that I have essentially two contractors on this.
MR. HOTZ: Could we have his name, please?
MR. MULLOY: Yes. That would be Calvin Wiggins.
MR. HOTZ: How do you spell that?
MR. MULLOY: W-i-g-g-i-n-s. He is the Senior Vice President in charge of the Space Division at Thiokol. Thiokol is organized into three divisions, the Space Division, Tactical and Strategic. The SRM program manager works for Mr. Wiggins. The SRM program manager is Mr. Kilminster.
MR. HOTZ: How do you spell that?
MR. MULLOY: K-i-l-m-i-n-s-t-e-r.
MR. HOTZ: First name?
MR. MULLOY: Joseph.
Then my element managers then go through that same review process at a minute level of detail, and I think when the flight readiness review proceedings are presented to the Commission, you will find that there is a great deal of detail reviewed relative to the configuration and the performance predicted for the particular solid rocket motor that is going to fly.
And then I chair a review with senior managers at the Marshall Space Flight Center in the Science and Engineering Directorate there where my element managers and contractors present that to me. I am then required to review that with the manager of the Shuttle Projects
Office at Marshall, and then we have a center review with Dr. Lucas which includes all of the elements of the Marshall Space Flight Center, and that is a very thorough review. And then the level 2 National Space Transportation System manager reviews the flight readiness, still using the same agenda, the same agenda items in every one of these.
And then Mr. Moore, who is the Associate Administrator for Manned Space Flight has the level 1 review. And then one day before launch what we call now L minus 1, we used to do it L minus 2, but lately it is L minus 1, the level 1 has a review to assure launch readiness, and the purpose of that review is to assure that nothing has changed in the two weeks since they had - Mr. Moore had his level 1 flight readiness review. Any deltas that occur are then presented to that board.
I can give you one example of where nothing was presented relative to the solid rocket booster until we got to the L minus 2 day review, and that was because we were at a frequency of flight that we did not get a look at the joint between the nozzle and the case joint until after the level 1 review, and you will find in the record that at the L minus 2 day review I presented the details of our observation there and the rationale for
flight for that.
And then in the case of 51-L, up through the L minus 1 day review, no concerns regarding SRM joint O-ring erosion were expressed during any of that process.
Now, I would like to get into what the basis for that was at that time. If you will go to, ] guess it is Chart 7 - next chart, or Chart 8 - -
(Viewgraph.) [Ref. 2/11-12]
[354] MR. MULLOY: - our experience when we were looking at 51-L that we were looking at - and this is a summary of the detailed information that was provided to the Commission yesterday - our experience was that prior to 51-L we had eleven static test motors and 48 flight motors. The field and nozzle joints of those 57 motors had been examined which represent some 288 joints with 456 O-rings, and this is a summary again of the detailed data. Six of the 171 field joints exhibited some erosion of the primary O-ring.
Now, if I may, I would like to go to Chart 10 and then come back to this one.
(Viewgraph.) [Ref. 2/11-13]
MR. MULLOY: I think it is helpful when we say some erosion, what kind of mechanism we are talking about there. This is the nominal configuration I have
already shown you where we have zero pressure in the motor and we are ready for ignition. We have these two O-rings in here which are specified to have a 20/1000 inch minimum compression such that when they are called upon to do so, the primary O-ring can be extruded into this gap and form a seal.
If it did not have the compression on it, the gas - and I will show you a scenario there that does that - the gas can blow by the primary O-ring, and it will never seat. So you have to have that compression, and we are sure we have that from the dimensions of the clevis and the tang in the steel, and assuming a minimum O-ring with - and some compression set in that O-ring, to account for the resiliencies that it has to follow the metal as it expands.
Now, as the motor is pressurized, and if I may take that down for a moment and bring up Chart 9 - -
(Viewgraph.) [Ref. 2/11-14]
MR. MULLOY: - this is a typical pressure time trace. Full pressurization of the motor from time zero occurs in 600 milliseconds, .6 second. And then we are up here at the maximum pressure, operating pressure, nominally 900. It is qualified for 1004, but 900 is the nominal operating pressure, and we stay there for about 20 seconds, and then we have a thrust tail-off to limit the G forces on the Shuttle vehicle to 3 Gs, and this thrust profile is designed to do that in conjunction with the throttling of the engines to such that we don't exceed a 3 G load on the vehicle.
And then at about 50 to 60 seconds, we start ramping back up again, and that is what this bar indicates. And so there are two times in the motor operation when the motor is increasing in pressure, and that is in the first 600 milliseconds, and in the 50 to 75 second timeframe.
So what is going on in this first 600 milliseconds, if I may go back now to the previous chart, Chart 10 - -
(Viewgraph.) [Ref. 2/11-13]
MR. MULLOY: - the nominal situation, and I pointed out to you that only six of 171 have exhibited any erosion, and so the other 165 of them performed as you see in this diagram here, which is the intended function
of this joint.
Two things happen with that motor pressurization. The additional tension loads are put into the case due to the pressure. The 1000, getting up to that 1000 psi tends to want to pull this joint apart. That pulling on these pins then tends to rotate this clevis outward as you pull with tension load on the pins. The other thing that is happening is the outward pressure on the motor is tending to want to expand the motor more out here in the membrane area of the case than it is [355] in the stiffer joint section, which further tends to cause a rotation of this clevis upward, which tends to reduce the initial squeeze on the O-ring.
Well, what has happened in 165 of the 171 cases, when this O-ring was called upon to exercise itself, it did so by extruding into this primary groove. You see no erosion on the O-ring. You don't see any soot blow by the O-ring, and the secondary has not even been energized because the primary has done what it was designed to do.
Any questions about that?
MR. HOTZ: Could you describe the rotation again? I am not quite clear on that.
MR. MULLOY: Okay, sir. The motor is at zero
psi, zero pressure. We come up in 600 milliseconds to 900 psi. So there are two things that that case is wanting to do. It is wanting to expand outward due to that pressure, and it is also wanting to expand longitudinally. The longitudinal load pulling on that pin tends to want to rotate that clevis. In other words, if you can visualize, if you pulled on that long enough to fail it, the clevis would open up until the tang end pulled out of there.
The other thing that is happening is that that joint is much stiffer. It is like having a belly band, if you will, around a balloon, a belt around a balloon. Now you blow up the balloon, or say an elastic belt around the balloon. Now you blow up the balloon, the balloon will expand more where the elastic belt is than where it isn't. And so you get this exaggerated shape like that which further tends to rotate the joint.
VICE CHAIRMAN ARMSTRONG: What holds the pin in place?
MR. MULLOY: The pin is held in place by a metal strap. After all the pins are put in, there is a metal strap that is put around the pins and cinched down just like a container strap mechanism, and then that is closed out with cork. A quarter inch of cork is put around that just over, just over this section of the
clevis, and that cork is there to assure that during ascent, since the heat sink of that band is much less than the heat sink of this whole mass here, if we got any aerodynamics under that band, that band could heat up and fail, and we could lose the pins during ascent. So the cork is a thermal protection for the retaining band on the pins.
DR. WALKER: I have a couple of questions on the O-ring. There are some tolerances on the diameter of those O-rings.
Do you inspect each O-ring to see that it is within tolerance?
MR. MULLOY: Yes. The tolerance is plus 5 and minus 3, and the O-ring is inspected with a micrometer on receipt to assure that it is within tolerance.
DR. WALKER: Do you inspect it at many places along its length?
MR. MULLOY: Yes. I believe it is every two feet, and relative to 51-L, all of the O-rings that are in the inventory are being re-inspected to get a statistical data base to try and understand if possibly there could have been an undersized O-ring, for instance, in 51-L.
VICE CHAIRMAN ARMSTRONG: Is there a tolerance on this pin and these holes that isn't shown in that
diagram?
MR. MULLOY: I am sure there is, Mr. Armstrong. I am not sure exactly what that is. Il not an interference fit. There is a tolerance. I can get that for you.
[356] CHAIRMAN ROGERS: Mr. Mulloy, on your O-ring history, which is a very useful review, I think, for our purposes, would you mind taking each one of these observations and just making some comment on them? For example, you say that you examined 228 joints with 456 O-rings. The first observation is 6 out of 171 exhibit some erosion of the primary O-ring.
MR. MULLOY: Yes, sir.
CHAIRMAN ROGERS: That did not disturb you, I suppose? You would like to correct it, but it wasn't, in and of itself, it didn't disturb you too much?
MR. MULLOY: It wasn't disturbing from a standpoint of safety because the O-ring, even though it was eroded, had done what it was designed to do. It was disturbing from the standpoint that we were looking for ways to increase the margin such that we wouldn't even have that incidence of erosion.
CHAIRMAN ROGERS: Going to the second, you say that two of those joints, there was some soot behind the primary O-ring.
Was that a serious problem, and if so, what was the problem?
MR. MULLOY: That is more disturbing than just having the O-ring erosion and then the joints or the O-ring then seated, although this, too, is in the population of the six. The six with erosion, two of the six with erosion showed soot. The concern there is that there is some blow by the primary which says that we are concerned that we have adequate squeeze on that primary such that we won't get that blow-by, and it will energize and go into, extrude into the gap without blow-by.
And yes, that is where we started looking at things like how can we decrease the joint rotation.
CHAIRMAN ROGERS: And were those instances just prior to 51-L or a long while back?
MR. MULLOY: No, sir. As I said, there were no instances of that for a year before 51-L.
CHAIRMAN ROGERS: On the next one, 16 of the 57 nozzle joints exhibited some erosion of the primary O-rings. How did that relate in terms of concern to the other two? Was that more serious or less serious or about the same?
MR. MULLOY: It is about the same. There is
more concern for the case-to-case joints because of that rotation. In the case of or in the instance of the nozzle-to-case joint, we don't have that same rotation of the joint. So we deemed that fixing, improving the margin in the case joints by reducing the rotation to put it in the same population as the nozzle joint would be a desirable improvement.
CHAIRMAN ROGERS: The next one refers to soot in the nozzle joints, eight out of 57, and would the answer be the same?
MR. MULLOY: Yes, sir.
CHAIRMAN ROGERS: And then you have one nozzle joint secondary O-ring which has been eroded. Was that of particular significance?
MR. MULLOY: Yes, sir, it was because until we saw that, we were always assured that even though we were causing some initial damage to the primary O-ring, that the primary O-ring was functioning. In the instance of that nozzle joint, we were now seeing a violation of the secondary seal, and we did after that, and before we would commit to another flight, we went and did some extensive testing of the tolerance to that, and did an analysis that matched that testing so we could determine what the limiting mechanism was, in other words, how long, if you - since the size of that cavity behind the
primary O-ring is of limited volume and you are pressurizing that cavity with a very large volume of gas, which is inside the solid rocket motor, there is a limit of time that that gas can flow into that cavity.
Once the gas flows into that cavity and the pressure becomes the same as in the motor, flow stops. So our rationale was through testing, can we get enough damage to the secondary O-ring before the flow stops such that we would have a failure of the secondary O-ring? And our analysis and our tests which the analysis correlated very well with, said that we had a margin of three - we could take three times what the maximum amount of erosion that we had observed and have a margin of two on what was theoretically probable under the limited time that that flow could occur. And thus, we concluded that that was an acceptable situation.
We have not had any other secondary O-ring erosion on any joints since that instance.
CHAIRMAN ROGERS: So you were satisfied based on that experience that you did not have a problem with 51-L in that connection?
MR. MULLOY: In that connection, yes, sir.
MR. ACHESON: If soot blows by the primary seal, will it lodge between the secondary seal and the wall of the chamber to prevent a tight squeeze?
MR. MULLOY: No, sir. We haven't seen that. What we tend to see is that that soot is very, very fine. It is the products of grease, the pyrolysis of the grease and some pyrolysis probably of the O-ring itself, the primary O-ring, and it is a powder, and blowing - it would have to blow by the secondary before it could compromise that, and we have seen no evidence of that at all.
You see a kind of a fan-shaped sooty spot in the putty, if you will, impinging but not into the groove generally. You will see that in the primary groove, but you do not see it in the secondary groove.
DR. WALKER: A question on the six incidences of erosion of the primary O-ring in the field joints.
Was each of those associated with some channel or damage to the putty?
MR. MULLOY: Yes, sir. There is a track through the putty to that erosion.
DR. COVERT: Mr. Mulloy, on the six rings that exhibited some erosion, do you have numbers comparable with those on the nozzle joint erosion? In other words, you eroded half of those needed or what?
MR. MULLOY: Yes, sir. Theoretically we have a factor of two, based upon tests and analysis, over the maximum observed.
MR. FEYNMAN: Sir, you suggested that if the primary O-ring were to fail, it is still no big problem because the secondary O-ring might hold.
MR. MULLOY: Yes, sir, it should energize.
MR. FEYNMAN: But there is a way for the gas to come out, at least possibly, and that is the leak test port that you put in to make a pressure to test the O-rings, and I wonder how good we can expect - how was it sealed? How was it closed, and how good is it? Can we guarantee that that might not fail, that is, the gas come out through the hole that you used to put the pressure on to test the O-rings to see if they were okay earlier on?
MR. MULLOY: Yes, sir, that is installed to a torque requirement and inspected and signed off. It is installed to that torque requirement, and then there is extensive test data that indicate [358] with that test plug, and it has the O-ring sealing surface also at that torque, will not leak at 1000 psi.
But if a human error was made and the test port plug was left out, obviously - and you went by the primary seal, that would be a leak source, or if it wasn't properly torqued, there could be a leak source through there which could lead to failure of the secondary O-ring.
CHAIRMAN ROGERS: How many checks of human failures do you make? In other words, if one person - do you have to rely on the one person's activity, or does somebody supervise that one person? How many checks do you make to avoid that kind of human failure?
MR. MULLOY: Well, the first check is the technician who makes the installation. The second check is by the contractor, quality inspection, of whoever is making that installation, and then there is a government inspection check on that.
CHAIRMAN ROGERS: Who makes that? Who is the government?
MR. MULLOY: In the instance of the leak check port, for instance, that is Air Force Quality at KSC.
CHAIRMAN ROGERS: Yesterday we talked about the orientation of the leak ports on the two solid boosters. Since we have a model here, could you indicate where those were?
MR. MULLOY: Yes, sir. On 51-L, on the right hand booster, it is located on this axis, and on the left hand booster it is located on the other axis.
MR. HOTZ: Mr. Mulloy, while you are at the model, could you indicate and describe for us the pressures on the solid rocket boosters that are caused by the so-called Twang maneuver just before launch?
MR. MULLOY: Yes, sir.
The main engines ignite approximately 6 seconds before the solids ignite. That timing is set such that when the main engines ignite, and the Shuttle stack is bent over, the hold-down point for the whole stack is here on four points at the bottom of the aft skirt on the solid rocket booster. That is restrained. So there is a bending in this direction.
So the stresses that are put on are bent - it is a bending moment.
MR. HOTZ: They are bending forward in the same direction as the Shuttle?
MR. MULLOY: Yes, in this direction because the only thing that is applying force are the main engines over here, which is an eccentric kind of a load, which tends to rotate it this way. And then the timing of the ignition of the boosters is timed such that you are back in the vertical position at ignition.
MR. HOTZ: Have you any measurement of the quantity of the force that is put on the SRB?
MR. MULLOY: Yes, sir. That was done in the facility verification vehicle early. There was a stack made, and then there was what was called a Twang test and a deflection test that was run on the boosters where they were deflected for the maximum predicted amount and the strains measured, and that is accounted for in the
design.
In other words, they were actually pulled over from this forward - -
MR. HOTZ: What was that maximum predicted amount, do you recall?
MR. MULLOY: The deflection?
MR. HOTZ: Yes, sir.
[359] MR. MULLOY: No, sir, I don't recall what that is at the tip. It is very visible in watching launches.
MR. HOTZ: Thank you.
DR. RIDE: Have you - when you have gone back and inspected the O-rings that have experienced erosion, have you seen the erosion occur at the same point circumferentially on the different O-rings?
MR. MULLOY: No. In the data that I presented to you yesterday, you will see on the field joint that there is no preferred location on the case field joints, and those six occasions, you find that scattered over all 360 degrees of the circumference, and the same is true in the nozzle-to-case joint. There is no preferred location. It seems to be random in circumference, more related to the point, I think, where the pressure breaks through the putty as opposed to any loads or gap dimensions in the joint.
CHAIRMAN ROGERS: Mr. Mulloy, just to clarify for the record, the material you presented to us yesterday is not any different than the material you are presenting today, is it?
MR. MULLOY: No, sir. What I have done today is on that one chart that we are dealing with here is summarize the details of all of those detailed observations by flight number, degree of erosion, location of the soot around the azimuth, etc.
DR. WALKER: A couple of times you referred to the vacuum grease that you use on the O-ring.
Is that silicone grease, and could you explain the purpose?
MR. MULLOY: That is an HD-2 grease, and it is not silicone.
DR. WALKER: What is the purpose of putting grease on the O-ring?
MR. MULLOY: The purpose of putting grease on the O-ring is to ease the installation of the O-ring into the joint and assure that you don't damage it. The purpose of having the grease in the joint is to keep the D-6 from