Steve Johnson Interviews – Apollo/Saturn Program

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NASA MSFC Oral History Interview

Steve Johnson Interviews – Apollo/Saturn Program

Royce Mitchell

Interviewed by Steve Johnson

Huntsville, Alabama – Unknown, Circa 2012

Steve Johnson: I am talking with Royce Mitchell, who worked at Marshall Space Flight 

Center most of the time between 1963 and 1993. He retired in 1993. Royce, would you 

talk about your education that prepared you to be in the aerospace program?

Royce Mitchell: My degree from Auburn [University] is in aeronautical engineering.

That got me into the aerospace business, but my career caused quite a few branch outs 

of discipline, primarily having to do with entire systems. I got into the missile and space 

business out of college with the Boeing Company. I went to Seattle [Washington], 

worked on a ramjet-powered pilotless interceptor, and part of my job was in the test 

world to see how this high-speed interceptor reacted with its control system on the 

ground. That leads you to a lot of disciplines that I did not necessarily specialize in in 

college. I quickly learned that integrated systems are highly complex, very interesting,

and more and more, I got into the integration of large complex systems.
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I left Boeing mainly because of the Seattle climate. I moved down to Sunnyvale, 

California where it never rained and went to work on the Polaris submarine missile 

system. That was extremely interesting. I got into the systems part of Polaris, control 

systems, command distribution of functions, and the packaging of these systems within 

a very limited space. I got into a specialized area also called exploding bridgewire 

ignition. An exploding bridgewire is a tiny filament, about as big as a course hair, that 

you passed a lot of electrical energy through suddenly, and it caused that wire to 

vaporize and explode. This led to, downstream, pyrotechnics that would be touched off 

by this exploding bridgewire. The units that fired this, put out this high-voltage, high 

capacitates, were little black boxes connected by cable to these detonators. They were 

fairly complex, but they were also supposed to be very, very safe. 

The opportunity came for an interview with NASA [National Aeronautics and Space 

Administration] on-site while I was working for Lockheed. It turns out the people who 

interviewed me happened to be working on exploding bridgewire firing units for the 

Saturn Program as well as other aspects similar to what I was doing on Polaris. Having 

grown up as a native of Florence, Alabama, having an opportunity of moving to 

Huntsville [Alabama] was too good to be true. I was married by then, we came to 

Huntsville, and we have never regretted it. I enjoyed coming to Huntsville and getting 

in on the Lunar Landing Program and thinking how lucky I was to have the kind of 
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degree I had, which I was not sure would ever let me be back close to home. It did and 

that was a good thing.

Johnson: You came to Marshall to work on the ignition system for the Saturn V.

Mitchell: Partially, that was my job. It branched out into such things as the range safety 

system. I am one of the few people who are extremely proud that the system they 

worked on so hard never had to be used, and that was the range safety system. The 

Saturns were so unbelievably good and so reliable that they never had to exercise the 

destruct system. I worked hard on it, but I was so glad it never had to be used.

Johnson: The ignition system, many people probably think how hard could it be to start 

a rocket. Was that a problem? Was that a real challenge to figure out the right way to 

start the rockets?

Mitchell: You put it in a good question. One of the biggest problems in starting a rocket 

is that you do not want it to start too soon. You want it to start when the time comes,

but not start ahead of time, and certainly not late. These exploding bridgewire units, the 

little black boxes that generated and stored all this high energy just before they were to 

be used meant that the electrical connection to the detonator was inert. In other words, 
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there was no chance of an early detonation, no chance of a little, simple stray voltage. 

We even had an air gap within the detonator pins and you had to have enough voltage 

to jump that air gap, which took many hundreds of volts. The detonators were 

protected and the exploding bridgewires made it a very safe system so you fired when 

you needed to and did not fire when you should not fire. That was the critical aspect.

With liquid engines, we did not use these detonators. These detonators were used for 

the little rocket engines that settle the propellants in orbit, that fired retro motors to 

slow down, say the first stage after it had been spent. We fired little solid rockets to 

back that thing away from the rest of the vehicle. The linear shape charges between 

stages, these detonators were used in a lot of applications. The big liquid engines had 

what is the equivalent of spark plugs. Of course, there the premature firing is not as 

important because until you have liquids in there and mixed, you are not going to get 

any catastrophic problems. The spark plugs inside a liquid engine are another matter. I 

will talk about that later. 

Johnson: Talk about the testing you had to do. Was there a lot of testing?

Mitchell: [There was] a lot of testing for reliability. There is a phenomenon in the 

electronics world, especially electronics that use high voltage, called the Paschen curve. 
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Paschen became knowledgeable of the fact that if you get into a rarified atmosphere 

with high voltage, the air itself becomes a conductor, if the voltage is high enough and 

the air is at the right, critical density. We spent a lot of time making sure this 

phenomenon, because we used our systems all up through the atmosphere. We had to 

do a lot of testing to make sure this effect did not cause stray discharges and stray 

ignition at the wrong time, in the wrong direction. We did a lot of that testing.

Reliability, when you use a one-tie use like a detonator, becomes a matter of statistics. I 

will talk a little about solid rockets later. You are so dependent on processes and skill 

and inspections because there is no way to test. It is like testing a flashbulb. You tested 

it, but you do not know whether the next one is going to work or not. Numerically, 

statistically, it was a tricky business to make sure of the reliability of these. The 

consequences of unreliability, as you can expect, could be catastrophic. We spent a lot of 

time on the reliability of these very critical items.

Johnson: With many projects in the Saturn V days, there was somewhat of a time 

element. Were you under any time constraints? Were they wanting these systems to be 

readied quickly? Was there some pressure to proceed?
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Mitchell: [There was] a lot of pressure. I want to talk about NASA’s approach to this 

timeliness. 

Johnson: We are talking during the Saturn years?

Mitchell: During the Saturn. We all know the mandate, or the need, for this country to 

go to the Moon and return safely to the Earth by the end of this decade. We also knew 

we were under pressure because of the Russian influence. The Russian influence put as 

much pressure on Congress as it did on us because they needed to fund us. We went 

first class. We used to jokingly say we had the big inch pipeline to the Bureau of 

Engraving and Printing plus the mint. We did not stave for resources, we could take 

parallel approaches in trying to get these jobs done. 

There were some management approaches to getting this job done on time that were 

remarkable, George Mueller, who was the associate administrator under James Webb, 

and Deputy Administrator [Robert] Bob Seamans. George Mueller said we were going 

to go all-up. That was unheard of. It meant that when the first Saturn V, for instance, 

was launched, it was a complete first stage, it was a complete second stage, it was a 

complete third stage, the propulsion systems, the engines. That was unprecedented. I 

know in my experience, if you have a thing like this ramjet booster, it required a rocket 
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motor to get you going fast enough for those ramjets to work. They only work at 

extremely high dynamic pressures through the atmosphere. You had a booster. You did 

not put ramjets on the first thing, you shot this booster to see if it would work. After 

you were satisfied it worked, then you add the rest of the vehicle. Then later you add 

these kinds of controls. You went at it incrementally. Mueller said, “No, we are going at 

it full-up, everything, the whole shebang from the first launch.” Just about every 

engineer who had had any kind of experience in this game, their eyes got big. 

It did two things. Obviously, if things worked, it cut short verification of a lot of good 

flight systems. It also changed people’s attitudes. Their approach became so focused, so 

tied to success that there was not going to be any “if this blows up, we will have learned 

something.” No, you wanted everything to work. That was a remarkable stance for 

Mueller to take. 

Johnson: Everything had been tested though. I have heard other people say that this 

was not really the way the Germans liked to work. They liked to test each thing as you 

go. This was a change for them too, to speed things up, we did this.

Mitchell: Right. The many unknowns that normally you uncover doing a test program, 

an incremental test program, you had to do the tests as best you could. The flight 
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dynamic simulations, what happens when you have something over three hundred feet 

long that starts bending due to dynamic pressure, what kind of interaction between the

control system and the vehicle structure, bending and flexing, many, many dynamic 

things that cannot be fully tested on the ground you had to focus your best, do your 

damndest, and make sure when you went all-up that everything was ready to go. 

Johnson: Was the feeling at Marshall during those years that things were ready to go? 

Were there some systems where there was some doubt?

Mitchell: There was concern. We had some fine engineers. We did not have the current 

simulation capability current systems have. We did not model so much of it as current 

systems do. We did not have computational fluid dynamics that current systems do. 

There was so much, but no question there was exhaustive testing on every conceivable 

aspect that you could imagine, sometimes with backups to backups and on and on, 

trying to make things redundant and trying to make things complete. This all-up idea, 

again, caused so much focus on so many things and put tremendous pressure on the 

first article being correct, functioning correctly, and meeting the requirements. It was a 

remarkable experience. 

Johnson: It called for some long work hours, did it not?
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Mitchell: (Laughs) It called for unbelievably long hours. Another thing, the Marshall 

leadership, since we at this juncture just celebrated [Wernher] von Braun’s 100th

birthday, his leadership, I have never seen anything like it before or since. I have been 

around some very erudite, smart, and educated people, but von Braun was 

unbelievable, charismatic, fair. You could tell that one layer down from von Braun, they 

did not know whether their way would prevail or not, but they knew they would get 

heard, they knew they would get proper attention. They knew they would not be 

dismissed. He carefully considered all stories he heard, all facets of a problem he heard. 

There was no question that once he came to the decision, everyone would abide by it. 

Everyone felt good that if they had a concern, if they had an approach, if they had an 

idea, they knew it would get attention, it would get its day. That was important. It was 

extremely important to the workforce. Morale was wonderful, primarily due to that 

kind of leadership.

Johnson: Everyone felt like they were part of it.

Mitchell: We are in good hands. We are all in this together. We are a team. We cannot 

fail. He just had that aura to cause you to think this was going to be successful, we are 
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going to do it, and we are all going to get through this and it is going to be wonderful. 

And it was. 

Von Braun had to be convinced on a couple of things. One was how do we get to the 

Moon. James Webb, the administrator, did a wonderful job of keeping Congress on his 

side, keeping the funding coming, doing all the right political things as well as technical 

things. James Webb, and for a while von Braun, wanted to go directly to the Moon, it 

was called direct ascent. It meant the rocket would take off from the Moon, land with 

enough fuel to come back. If you think about that, that is a heck of a thing. The resulting 

vehicle is monstrous. A direct ascent, even though it was studied and even though 

James Webb at first thought that was it, and von Braun supported it, he had another 

approach. He wanted to do Earth orbit rendezvous. He wanted to take Saturns that 

would have been smaller than the Saturn V but still fairly large, and launch pieces of 

this lunar trip vehicle and assemble it all in Earth orbit. That reduced the size and 

complexity of the launch vehicles from Earth but still required quite a vehicle to go on 

to the Moon, again, carrying enough to come back to Earth. 

There was a guy up at Langley [Research Center] named [John] Houbolt, and he was 

kind of a voice in the wilderness. He kept petitioning NASA Headquarters and 

Seamans Committee and the people who were trying to make this configuration 
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decision. They had ground ruled out what he was interested in. What he was interested 

in was what eventually became implemented, the lunar orbit option. You landed on the 

Moon with the least amount to bring back. It required another vehicle with another life 

support system to land on the Moon, then come back, and then do the lunar orbit to get 

ready to come home. It was not planned for that purpose, but having a second life 

support system, I am sure, was welcome by [James] Jim Lovell and the people on 

Apollo 13 when they were able to use the Lunar Module to survive when the Service 

Module blew on the way to the Moon. 

The direct ascent was too big, too hard to do, too huge a vehicle. Earth orbit was better 

but still required a large vehicle to go to the Moon and back. Lunar orbit meant going to 

the vicinity of the Moon with a fairly small vehicle and going down to the surface of the 

Moon with an even smaller vehicle, a subset of that, and then coming home with the 

absolute minimum of hardware and, therefore, propulsion requirements. Some of the 

people began to see some of the advantages of the lunar even though it was more 

complicated and probably, from a reliability of so many more parts having to work, 

more risky. If we were going to get to the Moon reasonably and within the schedule the 

nation had committed to, the lunar orbit rendezvous of Houbolt was the best way to go. 

Once von Braun recognized that, he jumped on it fully and said that is the way we 
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ought to go. It took him a while to come around, but he was the second guy to 

recognize that. He brought along, eventually, the rest of the agency.

There was another aspect he was a little resistant about. General [Samuel C.] Sam 

Phillips, he was a major general in the Air Force that had impressed George Mueller. 

George Mueller, again, is the guy who dictated we will go all-up on every flight. 

Mueller had been impressed by Sam Phillips on the Minuteman Program and how he 

was able to orchestrate all the elements of the Minuteman Program and bring it along 

with rigor, with discipline, with good management. Mueller put Sam Phillips in charge 

of the Apollo Program from Washington [District of Columbia] and Sam Phillips started 

implementing his management systems on the centers. He got some pushback form 

Marshall, but after they saw the light, they embraced it. The management system at 

Marshall was probably superior once they embraced the idea of having this kind of 

interaction. 

Instead of having everybody working on tweezers, valves, springs, and rockets, to work 

on program requirements and schedules and making sure things got done. Otherwise, 

you do not make it, no matter how good your technology is. You have to have good 

management. Von Braun saw that and embraced it. That is the way he was. If he did not 
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think of it, he tested the idea. Once he was convinced, you had better get out of his way 

because things were going to be good.

Johnson: When all these things were happening, let us talk more about what you were 

doing. These things were happening, you were working at Marshall, you obviously 

loved the atmosphere, even the long work hours. During these times, you started out 

working on ignition systems, but you later went into the Integration Group.

Mitchell: The ignition system was part of the Integration Group because getting things 

ready to move and then making them move was part of it. Part of Sam Phillips’

management requirements was there would be well-disciplined project offices. We 

formed project offices within the laboratories that could integrate the activities of the 

laboratories and have everything function in a well-oiled management structure. I 

became a project engineer on the Instrument Unit for the Saturns. IBM [International 

Business Machines] was brought in to produce, test, and manufacture these Instrument 

Units. They are a ring the full size of the Saturn where they sat. They were only a little 

over three feet in length like a donut sitting at the top of the big Saturn V and issuing all 

these commands. The stable platform that kept up with where you are in space, the 

flight control computer that took the commands and converted them into things the 

Saturn needed to do to follow its flight program, all this was part of the Instrument Unit 
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Project Office, where I was. That became even more a part of my job, the integration of 

guidance, flight control, commands, power distributions, ignitions, timing, all the many 

things it took to make the Saturn work became part of the Instrument unit, which I 

worked on. [It was] a very satisfying job to work on the brains of the Saturn V.

Johnson: Knowing that it was going to have to work.

Mitchell: Knowing it was going to have to work.

Johnson: Were you able to test all the parts enough to feel comfortable that it would 

work?

Mitchell: Yes, we built up Instrument Units. We had one that was fully stocked with all 

the flight-type hardware connected to monitoring computers, monitoring consoles. We

could put the Instrument Unit through its paces, check all the timing, all the dynamics, 

all the flight control commands, all that. We felt very confident that the Instrument Unit 

would work.
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Johnson: How did you feel when we got to the point where the first Saturn V flew? 

Were you standing there wondering if enough testing had been done to go all-up? How 

did you feel?

Mitchell: It was awesome. I went to the Cape [Canaveral, Florida] for the first Saturn V 

launch. If you have ever been out to the Davidson Center here in Huntsville and seen 

that Saturn V, the immensity of it, my thought was how is that thing going to get up to 

4,000 miles an hour on the first stage alone. Then it is going to have to hold together, be 

at the right attitude, be at the right altitude. When that Saturn first stage, the S-IC stage 

with those five monstrous engines, separates at 4,000 miles an hour, will there be 

anything left after that event. I could not get that idea out of my mind. Here is 

something thirty stories tall that is going to be going through the air at over 4,000 miles 

an hour. Of course, that is just the start as far as velocity is concerned. Other stages were 

going to take over and do the higher velocities. 

Johnson: You were not convinced, it sounds like. There was some doubt that things 

would work like they were supposed to.

Mitchell: There are always the unknown unknowns. You hope you have covered 

everything, you hope you have tested everything and put in design margins to take care 
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of the unknowns. Until you fly it, until you make it happen, there is that queasy “what 

did it not do.” 

Johnson: But it flew, it worked.

Mitchell: It flew, it worked. People think of the Saturn as being “perfect.” Not quite. 

The second Saturn V launch, Apollo 6, I believe, was the nomenclature. We used the 

Saturn Is and IBs for Apollo jobs in between the Saturn Vs. The second Saturn V we 

launched developed what is called pogo. If you think of a pogo stick jumping up and 

down with a kid on it, the Saturn began to pulsate, its propulsion system pulsated. 

What happens when that develops, or what causes it, is that you have a vibration start 

in the vehicle and the lines and tubes feeding propellant to the engines pick up this 

vibration and they start shaking. Within those pipes, the propellant surges with each 

vibration. In other words, you get a chug, chug, chug effect and it runs away. 

When you have propellant entering the engine in pulses, the engine chug, chug, chugs 

and makes bigger vibrations. The second Saturn V called 502 almost shook itself to 

pieces. Fortunately, it held together for those F-1s even though they had developed the 

pogo. There was a successful separation, a successful second stage aft skirt separation, 

another use for the exploding bridgewires. When you see the old TV [Television] 
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images of a kind of circular ring falling away, you are looking back and that ring falls 

away, that is the skirt of the second stage falling away. If you look at it, you can see as it 

tumbles, it looks like it is trying to burst into flame. What it has done, it is being 

bombarded by the superheated steam of those hydrogen, oxygen engines of the second 

stage, there were five of them, each one about 200,000 pounds of thrust. You have 

1,000,000 pounds of thrust hitting that skirt.

We get through that and then the second stage, we later learned, had suffered some 

damage due to the first stage pogo and it began to develop pogo. An auxiliary 

propellant line had been damaged, which caused instable combustion in the engine and 

began to shake and have problems. The engine had a monitor on itself that if you got 

into really rough combustion, it would shut itself down. There were also accelerometers 

that sent signals up to the brains that said we have an engine acting up and you need to 

shut that engine down. The engine that was acting up shut itself down. The brains up 

front said I will send a signal to shut it down. It did except there had been a wiring 

mistake, and that signal shut a second engine down. On the second Saturn V, it almost 

shook itself to pieces and then it violated a flight rule when two engines shut down on 

the second stage.
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The guy sitting at the console was a friend of mine at Marshall, his name was Bob Wolf. 

He was on the console at flight control as the booster representative. In other words, the 

rocket representative. The flight controller said it is your call, booster. Bob started 

looking at his data because he had had some sporadic data and was not sure if two 

engines had really shut down. The flight rules say if you lose two engines on the second 

stage, it is an abort. You destruct the vehicle and it will not fly. By the time he had 

satisfied himself that we really had lost two engines, the simulations had said by that 

time the vehicle should be doing figure eights over Cuba or some wild maneuver and 

was going to crash anyway. You aborted. It had righted itself, it was humming on down 

the road.

We had the capability if you lost an engine, the other engines burned longer. It did not 

have a whole lot of effect on the mission. He said to let her go. Do not destruct. The 

flight controller took his lead. The vehicle went on and made it safely into orbit. There 

were some people who said that action made it possible for us to make it to the Moon in 

1969, which was the target year. Otherwise, with an abort, with a destruction of a stage, 

we would have stood down, we would have had failure investigations. It is interesting 

how things.

Johnson: How long did it take to fix these things, the problems you had?
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Mitchell: That is part of the story. What do you do? On the S-IC stage, the big, huge F-1, 

million and half pounds each, five of them on there, in the propellant lines, they added 

accumulators, kind of like shock absorbers. They were little chambers filled with 

helium. If you started getting the propellant surging, it would hit these pockets of 

helium and would damp out. In other works, the helium would allow the propellant to 

smooth out, it was a smoothing effect. It was an anti-pogo fix. They tested it on the 

ground. Likewise, they made sure the S-II engines, the problem there, had really been 

associated with the first stage’s pogo. 

This is a tribute to our management, to our forceful, competent, and aggressive 

management, after the second Saturn V almost shook itself to death, the third Saturn V, 

the next launch, took [Frank] Borman, [Jim] Lovell, and [William] Anders around the 

Moon. 

Johnson: We did not have a bunch of test flights?

Mitchell: We did not have test flights. We went from that near catastrophe to putting 

men all the way around and in orbit around the Moon. Of course, they did not land, but 

that shows you the tremendous capability, the tremendous spirit of can-do. The things 

that were done were done a t Marshall and it is awesome to think about.
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Johnson: When you look back at that, it almost seems like they what?

Mitchell: Right. Who would have thought. Every generation has their own arrogance. I 

think people today would not do or could not do that kind of step. They would be so 

cautious. That is probably not true. Today’s generation, when you put them on the spot, 

they produce. There was no question. That group of engineers at Marshall, I was glad to 

be a part of that whole shebang. Something like that is incredible.

This was more of a design remarkable thing that came up early in the program. We at 

Marshall, von Braun, of course, was instrumental, had an agreement with the Houston 

[Texas] people. It was not called Johnson Space Center at that time. It was called the 

Manned Spacecraft Center. It was later named for President [Lyndon Baines] Johnson. 

The people at Houston, we had an agreement with them. Marshall would produce 

60,000 pounds of payload to Earth orbit and then they would take over, living within 

that constraint, and do the Command and Service Module and the Lunar Excursion 

Module. That was the interface agreement, if you will. 

Early in the program, Houston realized they were not going to be able to make it on 

60,000 pounds. There was a big get-together and von Braun, the sly dog, said how about 

90,000 pounds? How about a fifty percent increase that you can use for your spacecraft 
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to the Moon. He had foreseen something like this probably happening. He had put in 

the margins and his whole staff knew that capability was there. It was hardly a bump in 

the road. Everybody thought maybe that would be the end of things for a long time. We 

were able to offer Houston 90,000 pounds instead of 60,000 pounds. It was all because 

of von Braun. 

Johnson: Because he had anticipated.

Mitchell: He had it up his sleeve. 

Johnson: Did you know during these times that you were making history?

Mitchell: You know, I did. I appreciate it more now than I did then. It was almost like 

every historic thing was just another day at work, but we were conscious. We had a 

leader, his name escapes me right now, but we were in a meeting that was breaking up 

and we were talking about how great this is, how wonderful that test went, and how 

wonderful this structure is. He said, “And to think we are just in the T [Test] model 

stage. It is historic, but we are just in the T model stage. There is more history to come. 

Make no question about it, we are doing some groundbreaking work here.” Of course, 

the press, they would underscore some of these events, some of these accomplishments, 
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some of these breakthroughs. We all knew, we all had this sense of this is great. We are 

really doing something unbelievable here.

Johnson: Let us jump ahead. The Apollo Program is over, or is ending. We are still 

doing some Saturn applications, but we are trying to decide what a space shuttle will 

be. Talk about figuring out what a space shuttle will be. You were involved with the 

conceptual design of the shuttle.

Mitchell: Yes, I was on what was called the Space Shuttle Task Team. There was an 

Electra commuter plane that flew between Marshall and Houston virtually every day. 

The Marshall people went to Houston, Houston people would come to Marshall. We 

would spend a lot of time arguing over what a shuttle should look like. The politics and 

the budget, that honeymoon was over. Washington was looking at how much money 

the space program needed. The [Richard] Nixon Administration was struggling with 

that. The Apollo Program had cost, in those years, not in today’s dollars, back in the 

1960s and 1970s, on the order of $24,000,000,000. It was really a large funding 

phenomenon. That was not going to happen again. We were going to keep funding at 

what we thought were unbelievably low rates. 
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We went from having a fully reusable shuttle that people really wanted. The booster 

was to fly back and land like an airplane. The orbiter was to be totally self-contained 

and go into orbit on its own fuel and propulsion system. You had two stages to orbit

and you were supposed to have this huge payload bay. The results in development 

costs were astronomical. People began to scratch their heads thinking what can we do 

to reduce costs. Little by little, by trying various configurations within the fiscal 

constraints, the guidelines had been given, we eventually came up with what was first 

called the rocket-assisted takeoff shuttle. When you think about it, that is really what 

we eventually had evolve. 

It was a spaceship with these solid rockets attached to it. The spaceship would light up 

with its engines and the rockets would boost for the first couple of minutes to get it up 

and going. To keep the size of the orbiter, the shuttle craft, from being unbelievably 

large, it was decided that the tank would become external and would be discarded 

every flight. It was a sacrifice of operational costs to stay within the development 

ceilings. That is where the term External Tank came from.

Johnson: I want to stop you here. When we were first talking shuttle, that huge tank 

would be inside the orbiter?
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Mitchell: Inside the orbiter. You can imagine what kind of booster it would take to put 

that up. Then the orbiter engines would not necessarily be burning at that time. You 

had the booster doing all the work, the orbiter propelling itself into orbit, and carrying 

its tank with it. It was a big vehicle, big booster, big orbiter. Making the tank disposable 

moved it outside the orbiter. That is where the name External Tank comes from. I am 

surprised I do not get asked more often why do you call it an External Tank. Because at 

one time, it was going to be internal. It was going to be part of the orbiter. That was 

how we eventually settled on it. That was how the shuttle came to be. 

Johnson: Looking back on how the shuttle was finally conceived, it seems awfully 

complicated. I have had one NASA veteran say to me before that he thought it was 

needlessly complicated. That was just one guy. The Saturn V, although it was incredibly 

complex, seemed almost simple compared to the shuttle.

Mitchell: The shuttle had to do things the Saturn V did not. You have this large delta 

wing craft up there. It had to have a life support system for a larger crew than Apollo 

had. It had to have systems to support whatever is in the payload bay, fuel cells. The 

orbiter is an unbelievably complex vehicle. Getting it to orbit is not all that complicated 

an idea. The Solid Rocket Motors, they were scaled up Titan solids. As a matter of fact, 

the Titan vehicle was begun when I was still a college student. I remember thinking 
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they are going to put a giant rocket together in pieces, a solid rocket motor joined with 

joints. I said that sounds dangerous to me. Little did I know that some years later the 

shuttle would suffer because of that business of stacking pieces of solid rocket together. 

Be that as it may, solid rockets are inherently simple. You pour them full of propellant 

in the proper shape and consistency and you ignite them. There is no whirling 

turbomachinery. There are no vents, explosive atmospheres generated in pockets and 

inner stages. Solid rockets are pretty simple. The Space Shuttle Main Engine, because of 

its extremely high performance is complicated, but when you consider Saturn V with 

the many, many engines it had, it had five engines on the first stage, five engines on the 

second stage, a restartable engine on the third stage. It was complicated, more 

complicated than you might imagine. What we asked the shuttle to do, and with it

cantilevered off the side of the stack the way it is, it is complicated. It had to be 

complicated for what we were asking it to do.

Johnson: Did you have the same feeling when the shuttle flew successfully as you did 

when the Saturn V flew successfully?

Mitchell: Yes, I was close enough to the Houston people. I remember being in Houston, 

working hard on the orbiter contract proposal evaluation phase the day George Wallace 
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was shot. I was concerned. I was not concerned about the Space Shuttle Main Engines, 

although I thought if we had a failure it would come from the Space Shuttle Main 

Engines. I was concerned about the orbiter reentering. When we launched the first 

shuttle, it got into orbit and everybody thought that was wonderful. All I could think 

about was they had to come back. They had to reenter with a system that has been 

tested, but they had to maneuver, a lot of the Houston simulations had the orbiter 

running out of its attitude control fuel before it touched down. It was a really tricky 

thing to have to have that orbiter survive reentry and everything work. 

I was a lot more relieved when the shuttle came back, after they went through the 

reentry phase that causes the plasma when you cannot talk to them. When they came 

out of that plasma reentry area and we could hear them talking and see the data, I was 

really relieved. [I was] a lot more concerned about the shuttle reentering than I was 

about getting it into orbit. Bob Crippen and John Young have to be two of the bravest 

astronauts, bravest people, that have ever lived. It is astounding what it was like on that 

first shuttle launch.

Johnson: Let us skip ahead to something you have already alluded to, and that was the 

Challenger disaster when there was a problem with the solid rocket motor. After the 
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disaster, you were put in charge of the Solid Rocket Motor, to bring it and the entire 

Shuttle Program back to flight. What was the chief challenge for you in doing that?

Mitchell: It was convincing the world that we knew what we were doing. Technically, 

there was not an element of the Solid Rocket Motor that we did not change. We 

changed the nozzle seals. We changed the ignitor up front, its seals. We changed 

everything. Of course, the focus was on the joints between those segments. We did two 

major things to those joints. We put a metal lip that kept the joints more stable. I really 

need to talk about the failure of the Challenger.

Everybody talks about how the O-rings failed. It might come as a surprise to people to 

know that the same O-rings were kept. God knows we tested every other possible 

material for the O-rings. And we kept the same type of O-ring that was on Challenger for 

the rest of the shuttle flights. It was not the O-rings themselves that failed, it was the 

fact that that joint flexed and tried to pry itself open when in that high pressure. That 

over 1,000 psi [Pounds per Square Inch] pressure inside that motor tried to flex and 

move and move relative to each other. On that cold day that we tried to launch 

Challenger, the O-rings got stiff and could not keep up with that flexure, that movement 

of those sealing surfaces. That was what caused the problem. You can say O-ring 
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failure, but inherently, those O-rings could not do what they had been asked to do. The 

blame was on the fact that that joint flexed.

To return to flight, we put a third metal lip in that joint that cut that flexure down 

significantly to near zero. We also added heaters to the joints, all the way around each 

joint of all the boosters. That heat would keep the O-rings more flexible, just having a 

belt and suspenders on this safety problem. That was what we did. People might be 

surprised to know that we had boosters on the pad out at Vandenberg Air Force Base 

that had that extra lip. The boosters at Vandenberg were not steel cases. They were 

composite, filament wound cases for lightness. The Vandenberg launches were going to 

go into polar orbit, and we needed payload out of Vandenberg because we did not get 

the benefit of the Earth’s rotation. We launch out of the Cape because the Earth is 

moving in the direction we want to go and it helps us get into orbit. Out of Vandenberg, 

we were going to launch spy satellites over polar orbits, over the poles, and therefore 

over Russia, with each revolution, so we needed more payload. 

Those boosters out at Vandenberg had joints that had that lip to keep them from flexing 

as much. We knew what we needed to do. You asked me the problem of bringing the 

program back online. We knew what we needed to do, but we had to convince the 

oversight committee, the Rogers Commission, rules and recommendations had been 
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sent down. Guyford Stever, who was Nixon’s scientific advisor, he had been put in 

charge of a committee to oversee what we were doing. We made presentations to the 

Rogers Commission enforcement people, the National Research Council, that yes we 

know what we are doing and here is where we are going to test it. We had oversight 

committees from the Astronaut Corps and we had to convince them we knew what we 

were doing. We had Congressional oversight committees. We had visiting congressmen 

and we had to convince them we knew what we were doing. Technically, the job was, 

relatively speaking, a lot more simple than convincing people we knew what we were 

doing. We had one congressman who stood up at the plant out at Thiokol and said, 

“Guys, you have to realize that I am here to posture. I am here to show that I am 

keeping on top of things. That is why I am here.” He said that off record, but everybody 

knew that is what was going on. 

Johnson: Was there any pressure that you had best not screw up, you had better get it 

right the first time?

Mitchell: We thought it would be the end of the space program if not the end of the 

agency. If we do not get this right, the consequences are unacceptable, unbelievable. It 

will be a national disaster. We have to get it right.
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Johnson: Did that make you proceed with a lot of caution?

Mitchell: Yes, but mainly a lot of testing, a lot of verification. The Thiokol people, there 

was a guy out there by the name of [Allan] Al McDonald. He had been in on the night 

before the Challenger launch. He estimated that our test program for the rocket motor 

was six times more extensive than the first time through. I had written a paper some 

time before that said I thought it was about five times more extensive than the test 

program. The main thing we realized was that because the solid rockets had originally 

been modeled after scaling up a Titan solid rocket, we did not have to characterize it so 

much, same propellants, same D-6 AC steel cases. We did add the second O-ring. The 

Titan, believe it or not, only had one O-ring at each joint. We added another one for 

“redundancy.” It turns out that solid rockets were not characterized as much as they 

perhaps should have been. That was another reason they were chosen, to save costs. 

Here is an existing technology. We do not have to spend all that money on some far out, 

high performance program.

Johnson: When you say characterization, what do you mean?

Mitchell: Understanding the behavior, characterizing that joint, its flexure, the 

structural integrity of it, the bonds of the nearby items such as the insulation that 
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protects the case from propellant. On and on and on. Do we fully understand where 

there is circumferential flow inside that motor? That is hard to model and hard to test 

for.

Johnson: Should some of this have been done before the shuttle ever flew?

Mitchell: Yes. It is easy to say that after a disaster. You look back and ask what were we 

thinking.

Johnson: Was there a little previous success?

Mitchell: There may have been some arrogance there. I recall the awful Apollo 1 fire 

when Gus Grissom and [Roger] Chaffee and those guys were killed. The feeling was 

that was another center, that was Houston, that was their problem. Could Marshall ever 

allow something like that to happen? Even on Apollo when we had Apollo 13, that was 

Houston’s problem, even though, a lot of people do not realize this, but that pogo thing 

I talked about at some length earlier, there was pogo in the Saturn V when Apollo 13 

went up. All it did was shut down one engine on the second stage and it went on into 

orbit with no effect on the mission to speak of. The Apollo 1 fire and the Apollo 13 
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explosion, that was another center. I think there was an arrogance that may have crept 

in. 

Johnson: That Marshall would not let anything like this happen.

Mitchell: While we are on this track, I find it incredible to think that it was the two 

simplest propulsion elements that caused both disasters. The Solid Rocket Motor, some 

people kiddingly called them those giant firecrackers. We had one of those fail and kill 

the crew. Then we had the External Tank shed the foam, hit the orbiter, and kill the 

crew. 

Johnson: You are talking about the Columbia disaster.

Mitchell: Here at the Marshall Space Flight Center, we had three major elements. We 

had the External Tank, we had the Rocket Motor, and we had the Space Shuttle Main 

Engines. It was not the unbelievably complicated, high performance, high pressure, 

high efficiency, high rotating machinery Main Engines that caused the problem. 

Everybody said if we ever have a problem it will be those unbelievably high 

performance Main Engines. They worked fine. The External Tank may have a valve or 

two, virtually no moving part, yet it killed the crew. The dark days at Marshall, it is 
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hard to think back to the Apollo days and think how did this happen. The second one, 

Columbia, the shedding of foam, here again we have a problem that has been seen 

before, it has repeated. Has the problem been bounded? How do we know how much 

foam can come off? How do we know what bad effects it may have? Yet, we continued 

to fly and we had another disaster. 

The O-rings, we had seen O-ring damage before Challenger and we lulled ourselves into 

thinking this was the norm, we can accept this, it has been seen before. It is “within 

family.” We had not bounded the problem. We had not said what is the worst that it 

can become. We had not analyzed and then anchored those analyses with hard 

empirical testing to say we know we have bounded the problem, we know the problem 

is not going to lead to catastrophic failure. In both cases, we repeated with the External 

Tank. I find that hard to take on reflection, that my center, the Marshall Center, 

somehow allowed that to happen.

Johnson: Let us go back to the Solid Rocket Motor.

Mitchell: I have not told you about something else. I said we did two major things to 

the joints. The second thing was a concept promoted by Dr. Joseph Pelham. He was 

originally from New York. He attended the University of Alabama. I think maybe he 
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was down here as a soldier and fell in love with a Southern belle. He went to the 

University of Alabama. He was at Thiokol out in Utah and he was very instrumental. 

He came up with great testing systems and ways to test this joint, part of that five, six 

times testing. We characterized the joint. We actually reproduced the Challenger failure 

with one of his test rigs.

The second major thing he did, he invented a sealed insulation. In other words, when 

you brought these booster segments together, the insulation met and sealed. We had a 

non-curing adhesive. If you struggle with the idea of what is an adhesive that does not 

cure up, think about at Post-It note. You have an adhesive on the back of a Post-It note 

that stays gummy through its life. We put some non-curing adhesive on the insulation 

parts. He conceptualized having this insulation that would meet from segment to 

segment at the joint and the flames would never even approach the O-rings. The Orings were there, but this sealed insulation did the job. The astronauts, they loved that.

Johnson: That was a redundancy they could handle.

Mitchell: Like most good things, it was elegant, simple, classic, just a magnificent 

design. I was later made manager of what was to be an Advanced Solid Rocket Motor. 

We were going to build it in an abandoned nuclear reactor site over in Iuka, Mississippi, 
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Yellow Creek was the name of the site. We were going to put a rocket motor plant there 

and we were going to build this advance Solid Rocket Motor. It was going to have a 

different type of joint, a joint that actually, due to its geometry and fashioning 

configuration, would close under pressure. I thought that was great. I presented to the 

astronauts and said we had a joint that will close. The sealing surfaces over the O-rings 

will actually get tighter. They asked if it was going to have that sealed insulation. We

said yes and they said that was all they wanted to hear. 

Johnson: I want to get your feeling after you have done the work on the Solid Rocket 

Motor after Challenger. It is time to fly again. You talked about your fear all the way 

back to Saturn that there was concern with the first shuttle flight. What was it like 

returning to flight? You have done the redesign. You have tested. You feel good about 

it, but I have to believe that was a good day for anxiety.

Mitchell: It was, anxiety was very high, but I had an ace in the hole. We had done 

something unprecedented in the test program, back to characterizing everything, 

testing the hell out of it. We had done something that had never been done before. After 

we redesigned the joint and had run the static test as the last thing we did, we said we 

were going to take a motor and deliberately ding it up. We were going to put surface 

blemishes on the sealing surfaces. We were going to cut holes through this wonderful 
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new sealing insulation. We were going to damage virtually every joint on that motor 

and test it on the stand. And we did. People told us we were crazy. Dr. [James] Fletcher, 

the NASA administrator at the time, said we could test it that way, but we were not to 

take that motor apart until after we fly the shuttle again. Somebody will find something 

and we will spend two years analyzing that. Test it. If it holds together, fine. Let us go 

fly. 

That test, that one test was kind of the culmination of all the other testing, all the other 

measurements, all the other process verification, all the work we did around the clock. 

That one test did more to let me feel confident. The intensity was there. The concern 

was there. The acknowledgement of what failure would mean was there. That one test 

successfully done, where we damaged those rocket motor joints and they still worked 

fine, what a relief that was. I cannot tell you how much that took a lot of the load off all 

those concerns. Again, there is always the unknown unknowns, the who would have 

thought of that. That is always there. That one test probably generated more hours of 

sleep for me than any other thing we did.

Johnson: We return to flight, have a successful flight, you had your ace in the hole, the 

test. Looking back, working on the Saturn V, the work you did there, helping come up 

with the conception for the shuttle, getting the shuttle back into space after a terrible 
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disaster, when you look back at your career, which one of those do you remember 

most?

Mitchell: That is easy. As we left the firing room after STS-26, the first flight after 

Challenger, I turned to a colleague and said, “It is a hell of a note to realize that 

everything in the future is going to be downhill from this one evening.” We launched 

that thing, everything was great. That launch, the STS-26 launch, was the highlight by 

far of my whole career.

Johnson: Coming back from disaster.

Mitchell: I had plenty of exhilarating successes before and after, but nothing compares 

with walking out of that firing room at the Cape with that satisfied feeling. As I said, it 

is tough to think that everything else will pale in my career in the future.