Air Force Test Pilot Charlie Duke became the tenth person to walk on the Moon when he was lunar module pilot of the Apollo 16 mission in April 1972. Duke and Commander John Young landed their lunar module "Orion" on the Cayley Plains near the crater Descartes six hours later than scheduled because of problems with the main rocket engine of their command module "Casper." Concern over the engine forced them to shorten their planned flight by a day, but Duke and Young nevertheless spent almost three days on the lunar surface, including nearly 21 hours outside Orion.
Apollo 16 was the second of the "J" Type missions, utilizing a modified version of the spacecraft used for the first three lunar landings. The J type spacecraft allowed crews to stay on the lunar surface for extended periods of time. The Portable Life Support Systems (PLSS) doubled the capacity of those first used by Aldrin and Armstrong during Apollo 11. Apollo 16 also had the distinction of being the second mission to feature the lunar rover, an electrically-powered vehicle that allowed the two astronauts to travel much greater distances than before on the lunar surface.
Charles Moss Duke, Jr., was born October 3, 1935, in Charlotte, North Carolina. He attended the U.S. Naval Academy, graduating in  1957 with a B.S. degree in Naval Sciences. In 1964, he earned an M.S. in aeronautics and astronautics from the Massachusetts Institute of Technology.
After pilot training, Duke spent three years with the 526th Interceptor Squadron at Ramstein, Germany. He attended the USAF Aerospace Research Pilot School at Edwards Air Force Base, California, in 1965, and was an instructor there when selected by NASA. As a pilot, Duke logged 4,200 hours of flying time, including 3,600 hours in jets.
Duke was one of 19 members of the fifth class (Group 5) of astronauts selected by NASA in April 1966. Calling themselves the "Original 19," this group of astronauts was eligible for Apollo missions, but were left out of the Gemini program rotation. Of the 17 that eventually flew, only three did not go into space on Apollo-related missions.
Duke entered the "official" mission rotation as a member of the support crew for Apollo 10. He also served as back-up lunar module pilot on Apollo 13 and 17. Duke was also Capcom on the White Team during the first lunar landing mission.
Following the Apollo program, Duke worked on Space Shuttle development for several years before resigning from NASA on January 1, 1976, and from Air Force active duty. Explaining that he worked 80 hours a week for the past few years to get to the Moon and that his work in Space Shuttle development was boring, Duke followed in the footsteps of his close friend and fellow astronaut Stuart Roosa and started a wholesale Coors beer distributorship. A self-described workaholic, Duke sold out of the business in March 1978 and went into a series of investing concerns and real estate development ventures. Duke also continued work with the Air Force as a brigadier general in the Reserves.
Duke's most profound experience after leaving NASA was a spiritual awakening as a born-again Christian. During his career as an astronaut, he and his wife Dorothy ("Dottie") had marital problems. Dottie turned to her religious faith for help and Duke followed in kind to become a Christian Lay Witness. After associating with fellow Apollo astronaut James B. Irwin's High Flight ministry, Duke started the Duke Ministry for Christ. His autobiography, Moonwalker, written with his wife, was published in 1990.
 Editor's Note: The following are edited excerpts from an original interview with Charles M. Duke, Jr., conducted by Doug Ward on March 12, 1999, as part of the NASA Johnson Space Center Oral History Project.
You were one of, I think it may have been more common at that time than it is now, the Naval Academy graduates who went into the Air Force . . . How does that work?
Back in those days there wasn't an Air Force Academy. Their first class was 1959, so they allowed ("they" being the Defense Department) 25 percent of West Point and Annapolis graduates to volunteer for the Air Force. So the Air Force was basically culling out their regular Officer Corps from West Point and Annapolis . . . So before we graduated, we said, "Well, we'd volunteer for the Air Force." And I'd fallen in love with airplanes at the Naval Academy rather than ships; and I knew that's what I wanted to do. The airplanes I thought were better. You could stay in the cockpit longer in those days.
How did you get hooked on airplanes?
My first recollection of flight was back in the early '50s. I was with a friend, and we'd just gotten our driver's license and were driving along. He had a little old convertible, and I looked up and there was a contrail going over. In the early days of jets, you didn't see many contrails back then. And I said, "Gosh, it'd be nice to make a contrail. I wonder what that'd be like?" And I started dreaming about flying airplanes then. I went on to the Naval Academy and they gave me a couple of rides in an open-cockpit, bi-wing seaplane called the N-3N Yellow Peril. I was hooked from that moment on.
Didn't get sick?
No. I got seasick, but I never got airsick. [Laughter] And maybe that's another reason that I decided to go [in the Air Force], because I really did get seasick. But I never did get airsick. [Laughter]
 Getting back to the astronaut selection process and after you'd applied, you started moving through the process, the physicals and all of that. You get down to the final interview . . . do you remember who participated in that?
Yes, I do. John Young, who I ended up on the Moon with, and Mike Collins, Deke Slayton, and Warren North were the four that I remember that were on that committee. I don't remember the nature of the interview. It was more a get-to-know-you kind of "What's your motivation?" interview because they had our backgrounds . . .
And we had gone through the physicals and nobody had any problem with the physical. And, you know, we'd taken some preliminary tests but with a master's degree and all I knew we were in the running . . . I was really getting pumped up by then. I really wanted to get picked.
Did you have the impression, at that point, the extent to which public relations would be a prerequisite for the job?
No, I didn't . . . I didn't perceive that would be part of my job. I perceived that they were certainly in the limelight-the original guys and the astronauts who'd been selected. Gemini was going on and I knew that they were in the limelight but I never realized that this was a big part of the job . . . It turned out I ended up liking that but, I didn't realize that was going to part of it when I started.
So they really weren't as up front as they might've been?
No. It was something that I'm not sure anybody would've turned it down because they had to go out and make a speech. But, you know, it just turned out some people are more comfortable doing that than others. And I love to meet people . . . when your heart's in something, you can really talk about it and be sincere.
Getting back to [Deke] Slayton and [Alan] Shepard. How did you perceive, at that time, the relationship between the two of them?
 I sense it was a close relationship. Of course, I was in awe when we got here, you know. Gosh, here's Alan Shepard, and Deke Slayton, you know, and Wally Schirra and all those famous astronauts who I just admired and looked up to for years. I sense that Shepard, Deke, and that whole group were real close; and their working relationship, which I didn't quite understand in those days, was very tight. I didn't see any competition.
Do you think that whatever criteria Deke and Al used in selecting crews was fair and effective and did you ever sort out what that criteria was?
I never sorted that out. [Laughs] I've been asked that many, many times. "How did you get picked?" I said, "I don't know." Even to this day, I'm not sure how the crews were selected. I got an inkling that Deke and Al sat down and said, "Okay, who's going to be the next commander?" And, "Okay, it's John Young." And John Young gets called in. And then Deke says to John, "Well, here are the guys that we think we ought to fly, what do you think?" So in some way, through that process, you got selected and then it went up to the directorate, from there to Washington . . . it is a mystery to me. There was no "check out the squares," you know, "fill this board of squares," "do this task," "do that run," "do this thing." And you get all these squares filled and you're going to get a flight. We didn't have any of that. It was just, "do your job."
When we first got here we started training. Everybody did geology. Then we did spacecraft systems for four or five months. And then everybody got assigned to some sort of little engineering oversight job. I remember Stu Roosa and I got assigned to Frank Borman, who was head of the Propulsion System for the side of the Astronaut Office. These things were all sort of unofficial, I think, as far as organization within the Office but that was where you concentrated your effort.
And so, on behalf of the Astronaut Office, you went to design reviews on the Saturn or the engines or the guidance system which took us to Marshall and to Kennedy. I remember we went to Ames a couple of times to try to "fly the Saturn V in orbit manually." Ames  had a program and some sort of simulator that Stu [Roosa] and I went out there and we could fly the Saturn V into orbit from the pad. There was a program in the guidance system in the Saturn in the Instrument Unit [IU] and it was connected through software to the controller in the command module. The commander could sit there and, with the eight ball, fly this thing into orbit like you do an instrument landing in an airplane. We showed that we could do that . . . We never had that capability, at least not in first stage but in second and third stages we had that ability. It was incorporated into the software.
What was your assignment on Apollo 12?
I wasn't really assigned to that flight. I was backup on 13 so I was not involved officially in Apollo 12. I had been support crew for Apollo 10 and helped develop the lunar module procedures during that time for activation and checkout. I was a Capcom and support crew during the training. Then for the flight I was Capcom for the lunar orbit activation, checkout, and rendezvous on Apollo 10. As a result of that, I probably had the most experience of any of the astronauts in the lunar module that was not on a crew. And so I ended up on Capcom and doing the same job on Apollo 11.
Did Armstrong have a vote in that?
Apparently he did. Neil had come by and said, "Charlie . . ." (I believe it was Neil and Buzz . . . maybe just Neil) " . . .we'd like you to do activation and checkout for us for the landing." And I said, "That'd be a great honor. I'd love to do it." And of course, that's what I did.
That really wasn't the normal rotation. You wouldn't normally go as a Capcom for one flight right into the next, would you?
No. Normally, you worked support crew, then you went into maybe a backup crew and then on into a flight crew. So about every three flights, you had some progression and that's what happened for me. From [Apollo] 10 to 13 to 16, was the prime way it went for me;  and it just turned out that I didn't get on the backup crew until after 11. I think they didn't announce that crew until after 11, and that's how I ended up Capcom for Neil and Buzz for the landing.
Prior to that, I had taken over the lunar module engine oversight. The descent stage engine was doing really well, but the ascent engine was in trouble. This was in early 1968. They were trying to qualify it and were having some instability in the engine. And that's a critical engine. If it didn't work, you were going to either crash on the Moon or be trapped on the Moon.
It was kind of like the service module engine in the command module. It just had to work.
It just had to work . . . and so, George Low, who was Apollo Program Manager at the time, organized this committee to decide what we were going to do. Would we get this thing qualified or should we have a parallel development?
We met for a couple of months and visited with various contractors. We listened to proposals from Bell [Aerosystems Company in Buffalo, New York] about how they were going to fix theirs, and we went to Rocketdyne and they said, "Well, we could do it." And it ended up, about six months later, we decided to have this big meeting with [George] Low. There was a vote. "What are we going to do?" I remember everybody sort of looked at me. "What does the crew want to do?" And the response was, "Well, I think we ought to go with a new contractor." We'd been parallel this time; Rocketdyne was selected and within a month they had their engine qualified. It turned out it was a great engine for . . .
You changed horses in midstream. Went from Bell to Rocketdyne . . .
Which was rare that close to a launch. It was beginning to impact the schedule because Kennedy said, "Land by the end of the decade," and now we're at late '68. It was a critical time, and that was a big decision because to change a contractor that close . . . We did it and I thought it was a bold move by Low.
Has the thought crossed your mind that you may be remembered as much in history for your role on Apollo 11 as for your own lunar landing?
You know, I was just pleased to have been part of that team. I loved the Mission Control team. I thought we had the greatest bunch of guys and gals in that Mission Control. They were dedicated, young, but experienced; and it was great working with them. All the flight directors that I worked with, we all hit it off really well. And [they were] very confident, very cool, in all of the problems that we experienced.
Now that's interesting, because it really wasn't always that way. If you go back and talk to some of the early groups, there were some battles between the astronaut representatives who were sent out to the remote sites, between Deke's [Slayton] guys and  Chris's [Kraft] guys, as to who was going to be in charge. And it's pretty clear that, through Mercury and Gemini, all that got sorted out; it really was a nicely functioning team by the time you guys got into Apollo.
Yeah, I'm sure it was, and I'd heard some of those stories but I never experienced that. By the time I got there, Apollo 10, I had done one of the trench jobs. I remember in Gemini, there was an astronaut and also a Capcom that was an astronaut in the booster position. And I did that in Gemini XI and XII. I really didn't know what I was doing there but even then, I felt smooth-running teamwork had evolved into the Mission Control, and there wasn't any of that "I'm in charge here" dynamics.
It certainly gave you a lot more confidence when you had to rely on the judgments of the ground and you were the one in flight.
Which we did. On Apollo 16, an hour before we were to land on the Moon, we were on the backside of the Moon and Ken [Mattingly], in the command module, had to burn the SPS [Service Module Propulsion System] to boost his orbit up . . .
And this was after the lunar module had separated?
We were separated. We were a mile or two apart and we were within an hour of landing. The next half revolution around, we were going to start our descent. And on the backside, he was to boost up to a 60-mile circular orbit so that we could have the right phasing for the rendezvous if we had to abort. Well, he reports a real problem in the engine. When he powered up the secondary control system, it wouldn't stabilize the engine and it was wiggling back there. And he thought that the thing was going to shake him apart. So John says, "Don't burn."
If your heart can sink to the bottom of your boots in zero gravity ours did, because there we were, two years of training, 240,000 miles away, an hour before the landing on an orbit when you can look down at your landing site eight miles beneath you, and they're  about to tell you to come home. And that's what we thought was going to happen, because it was, according to mission rules, an abort. So we came around, reported no circularization burn and they said, "Roger, stand by. Start getting back together." We started a slow rendezvous, thinking that was it, but they said, "We'll look at it."
I don't know all the dynamics which went on in Mission Control, but four hours later, after a couple of more revs, they kept briefing us and said, "Well, we think we're isolating the problem and think we can work around it." Later on, I saw a video that they'd taken at Mission Control, and I can remember Chris Kraft sitting there, scratching his head saying, "Let them have a go at it." And he said, "Go," and so Jim Irwin said, "We're go for this attempt," the second time around. We didn't know what was wrong but they figured it out. At that point in our flight to have management say, "Yes," to a landing I thought was really tremendous because it would have been a lot easier to say, "Well, come on home, you guys," "We don't want to risk it." You know, "We've done it before, and . . ." But to let us go ahead and land was really terrific. Almost every flight, you could see that the Mission Control team had a great hand in aiding in the rescue or continuation of the mission or overcoming some problem that we didn't have a clue of what it was in the cockpit.
There were a couple of problems on the Apollo 11 descent that, as I recall, were pretty unnerving. One was the continual communications dropouts and telemetry dropouts with the lunar module. Of course the other was the computer alarms. At the time, do you remember which of those or other problems were uppermost in your mind?
Communication dropouts were a nuisance more than a danger, but a computer problem was a showstopper. I vaguely remember reading something about a 1201 alarm. I didn't really know the consequences of those alarms and you didn't have time to break out your guidance and navigation [G&N] checklist to go to the emergency procedures and find out what that was. But fortunately, Steve [Bales] and those guys on G&N console knew.1
 Then later on, the most critical was, of course, the fuel state. We didn't quite have the tracking right in those days. We didn't understand what the gravity anomalies [mascons]2 were on the Moon, so we were a little off in position. And when they pitched over to look at the lunar surface, they didn't recognize anything and they were going into this big boulder field. Neil was flying a trajectory that we'd never flown in the simulator or in our integrated SIMs with Mission Control; it was something we'd never seen. We kept trying to figure out, "What's going on? He's just whizzing across the surface at about 400 feet," and all of a sudden the thing rears back and he slows it down and then comes down. And I'm sitting there, sweating out . . .
You could see all that from the telemetry . . .
Yeah, we could see all of that. I had that plot on my screen. We were getting critical fuel-wise. I remember I was giving them this running commentary. We were down to the last couple of minutes and Deke Slayton is sitting next to me. We were glued to that screen and I'm just talking and talking and telling them all this stuff. And Deke, I remember, punches me in the side and says, "Charlie, shut up and let them land." [laughs] "Yes, sir, boss." So I got real quiet, and the tension began to rise in Mission Control. We had a 60-second call and . . .
That was 60 seconds to abort?
That's right. When Mission Control said, "60 seconds," it meant you had 60 seconds to get on the ground. And the problem was fuel. We wanted enough fuel remaining in the descent engine that when he throttled up, he would get a positive rate of climb and start up before we had an abort stage because that was critical . . . And then the next call was "30 seconds." And so I called, "60," and they were still in the air. And I called, "30" and "Man, it's getting close." And then, of course, the dust was flying. And then I heard, "Contact. Engine stop," and I knew we were on the ground.
 This was after the 30-second call?
After the 30 seconds, right. Later on you look at the data and there was between 7 and 17 seconds of fuel remaining.
That was 17 seconds remaining before you would have had to make an abort?
Before I would've had to abort . . . Now whether Neil would actually have aborted or not, I don't know. Had I been the commander and I was within the dust and if somebody even called "Abort," you know, and you were 10 feet off the ground, what were you going to do? Well, I'd probably have landed.
Anyway, we landed before the 30 seconds were up and, of course, everybody erupted in Mission Control. Then we herad the [Neil Armstrong] famous lines about, "Houston . . . Tranquility Base here. The Eagle has landed." And so we made it and it was really a great release . . . Then Gene Kranz got us all back to work because, at that point, we had to make sure this thing was safe, that we didn't leak anything and if we had to, we could lift off again quickly in an emergency.
Your comment at that point was obviously very spontaneous.
It was. I was so excited. I couldn't get out "Tranquility Base." It came out sort of like "Twangquility." And so it was, "Roger, Houston. Twangquility Base here." Let's see, what did I say? No, it was, "Roger, Twangquility Base. We copy you, down. We've got a bunch of guys about to turn blue, we're breathing again. Thanks a lot." And I believe that was a true statement. It was spontaneous, but it was true. I was holding my breath, you know, because we were close.
Getting back to the simulators. One of the things that I've been told is that almost invariably the commanders in landing on the Moon and in landing the Lunar Landing Training Vehicle (LLTV) tended to use a lot more propellant and take it down a lot closer  to the wire than they did when they were in the lunar module simulator. I don't know if that was your experience . . .
Well, I didn't get to fly the LLTV out here at Ellington . . . After Neil Armstrong ejected from the one that went out of control, they only let the commanders fly that thing. So, I didn't get to fly it.3
I think that was generally viewed as probably one of the most dangerous parts of training.
Yes, it was. As I recall, the LLTV had a jet engine that took out five-sixths of the Earth's gravity and then used lunar module-like thrusters to give you the rest of the one-sixth gravity. We had something that was similar to that up at Langley, but it was on a wire and you slid down this wire at sort of one-sixth type gravity. I did fly that, but it wasn't very good.4 I thought the simulator was a lot better. The only thing with the simulator was that it was bolted to the floor so it didn't give you the motion cues that you had in actual flight. But other than that, the simulation was really, really good. And I believe you're right. In the simulations, you tended to be a little bit more cautious than in the real world.
For some reason, when we came down to land, John [Young] just continued right straight on down and we were basically in a constant descent of some rate throughout our landing. And I remember at about 25 feet, he did level off, and we just sort of stopped. And I remember saying, "Okay, John, you've leveled off. Let her on down." I was feeding him the information that he needed for the velocity and the control and the rate of descent. After a second or two of hovering, we began to sink down about one or two feet a second, and touched down with plenty of fuel left.
Of course, that's a function of experience. We were the fifth landing and while you'd never done it yourself before, everybody else had done it, and you just gleaned that experience from the briefings and the debriefings and talking to guys about it. And so we felt real confident, when we were there, that we were going to have plenty of gas for the trip.
 Of course by the second mission [Apollo 12], Pete Conrad was able to set down very close to the planned landing site. You must have surveyed it.
Yes. We'd figured out the gravity anomaly deal and so we were able to track and tell the computer accurately where it was and where it wanted to go. That guidance system would take you right down if you gave it the right information. It was a good system.
The mascons, as I recall, were present because of the fact that the Moon isn't made of one consistent mass. It has mass concentrations like raisins in a cookie that affect the gravitational pull on a vehicle.
That's right. As you go over one of these, it pulls you down. More gravity, and you sort of start going in an orbit like this and as you go down, it slows you down and so speeds you up. We ended up not being where we thought we were as we projected two to three revs later. So we had to figure that out . . .
One of the things that struck me, I don't know if you remember it as clearly, is the reaction at Mission Control during the simulations for the lunar landing, when they finally got all of the final guidance software in from MIT and had the actual program that was going to be used for landing on the Moon . . . On your mission, of course on all the lunar missions, one of the things in the lunar module simulator that people today would probably find a little incredulous is that you didn't use computers to generate the television views out the window. You had a big board adjacent to the simulator where the lunar surface itself was actually mocked up in all the detail that the scientists could give.
That's correct. Our landing site was selected by the site selection committee of scientists in various disciplines; and it had been selected from photographs taken on Apollo 14. Stu Roosa, as he orbited, had a mapping camera and their orbit took them over the Descartes highlands region. And so, it was decided that we would go land there. They took some of his photographs and made a....
....mockup of our landing site. It turned out that the photographs had a resolution of about fifteen meters. In other words, anything less than forty-five feet in diameter, you couldn't see in the photograph. But the major features, you could see. And so they built that into the model and they put this model on a big board. There was a TV camera that ran on a track above it so that was the view you had in your window . . .
And you were simulating a landing?
 Yes. Thousands of times John [Young] and I came in for landing and we'd pitch over and recognize features. One crater we called "Gator," and another one was called "Lone Star." I could look out the right window of the simulator, my right side, to the north and see North Ray Crater up there and John could look out his side and see Stone Mountain out to the left. These were names that we had given these prominent features in our landing site. When we really did it for the first time, I mean for real, in flight, as you recall, the lunar module trajectory was such that the first seven or eight minutes of the descent was with the window pointed out at space and you couldn't see the lunar surface.
So you kept the engine in front of you, slowing down . . .
Yes. So you were slowing down. Now you could've rolled over 180 degrees to put the windows down, but then you had a problem with communications. So we chose to land, or start down, with the windows pointed out to space and just depend on the LM to bring us in. At 7,000 feet, the guidance program maneuvered the vehicle to windows forward down, and for the very first time, at 7,000 feet, you saw the lunar surface. Well, I mean it looked exactly like the mockup. There we were. "John, there it is!" you know, "There's Gator. There's Lone Star." We'd had some debate about getting up to North Ray Crater during the training because, in the photographs, it looked really rough. I looked out the window and looked north, and said, "John, I can see North Ray. It's smooth up there. We're going to be able to make it." About that time, I'm just out the window, and John says, "Give me some information, Charlie." And so I get back in and start helping him land because we've got to pick out a landing spot.
About three months before the mission, I had this dream about John and me driving the rover up to the North Ray Crater and we came over one of the little ridges, and there's a set of tracks in front of us. It's rover tracks! Well, gosh, you know, this was all in the dream and we reported to Mission Control. We started following these tracks. Well that dream was so real that when I got to the Moon I wanted to look north to see if I could see that set of tracks . . .  Well of course there wasn't any set of tracks. I did figure out, as I looked north, that the surface wasn't as rough as we expected. So we ended up maneuvering, and we were like 300 feet above the surface, and John was fully in manual.
The lunar module had dual controls like an airplane. The commander was on the left side, like the captain of the airplane. I was on the right side, like the co-pilot. And I had my throttle and control stick.
Of course you're not seated. You're standing.
We're standing. We were anchored to the floor by a set of cables. As you stood there, in front of your position, there was a window here. I had a little abort guidance computer with some other switches. The main instrument panel was in between us in the center and the main computer was in this point. I'm standing and we have these cables that pull up, they're bungee-type things and you could hook on and anchor yourself on the floor. This was necessary because, if something went wrong and the thing started rolling rapidly, you wanted to be anchored . . .
I guess you couldn't afford the weight of seats.
No. There was no room, really, for seats. You really didn't need any in weightlessness or in one-sixth gravity. So anyway, we had trained that John would land and I would provide him all this information to help him down to land it. And if we had any emergencies during the final stages of descent, I would handle that because I could reach over behind him and pull circuit breakers. I could reach all the switches that were necessary to overcome any emergency. That was the way we had trained and if he had a problem with his control stick, or throttle, I'd take over and he'd perform the secondary role.
Well, it turned out everything worked right, and so I fed him the information he needed to make this landing and kept everything running right. And so he did the actual landing, and it was a great job . . . A great Navy landing! We hit solid and stable. We'd  picked out a great spot. The lunar module could land on a ten-degree slope; but if you did, it was tough because the experiments were around at the back of the lunar module and that meant they would have been above my reach because I was standing downhill trying to reach up. We couldn't have done some of the experiments. But it turned out we were within one degree of level, and so we were able to work around the lunar module.
Did you kick up the amount of dust that Neil and Buzz did on the first landing?
It's hard to say. We did have a lot of dust. In a comparative sense, I would imagine it was about the same, even though our landing site was considerably higher in elevation than theirs and in a different textural context of the Moon, as far as the geology went. The dust was probably the same. I remember we almost had the surface obscured at about 20 feet. When we leveled off at 20 feet, I remember looking out and you really couldn't see through the dust that was being blasted away.
We had selected what we thought was a good landing spot. No major craters, and so we landed. It turned out, though, that when we got out the next day for our first EVA [Extra-Vehicular Activity] and I went around to retrieve the Apollo Lunar Surface Experiments package, which was called the ALSEP, there was a big crater about two meters behind us that we hadn't even seen.
And if we'd have landed like three meters back to the east, we'd have had the back leg [of the LM] in that crater.
Was it deep enough to have tipped you [the LM] over?
Probably not. If you'd gone back another six meters, I mean, this was a pretty big crater and it tendered out maybe 15 feet deep. It would have been hard to work because I'd have been standing downhill in the crater trying to get this ALSEP out. It was amazing  how things like that were sort of camouflaged. Without the right lighting conditions, you could miss some of these subtle features.
The Moon's surface had some unusual reflectivity characteristics that I guess accounted for why you wanted to land with the Sun relatively low on the horizon.
The Sun low on the horizon gave us long shadows and generally that was very helpful. You realized if you were landing on a slope that was very bright, it meant it was tilted towards you. If it was very dark, it was tilted away from you because you were in the shadows getting into the shadow side. So we tried to pick a spot that was sort of an average brightness . . . without any major rocks, boulders there. Also, you use the shadow of the lunar module to judge altitude. For instance, if you lost the landing radar at the last 200 feet, as you got closer, the shadow came in and you could use the shadow to give you some sense of altitude. And so it was very important that we land with a very low Sun angle not only because of the temperature of the lunar surface, but also for the landing aids that we needed.
One of the things we haven't touched on in detail before we continue on with Apollo 16 (your mission) is your role on Apollo 13. One of my favorite political cartoons from that era (I think it was a Bill Mauldin cartoon) showed three very glum Apollo 13 astronauts sitting in their suits, getting ready for launch, with their helmets off, covered with the measles . . . And one of them looked at the others and said, "Well, at least none of us is pregnant." . . . And of course you had a pretty direct role in that episode.
Oh the infamous measles.
I'd like to get your recollections of how all that came to pass.
I was the lunar module backup to Fred Haise on Apollo 13. John Young and Jack Swigert and I were the backup crew. In those days, you had two crews [prime crew and backup crew] for each mission  and you trained in parallel so that the backup crew could take your place if something happened to the prime crew. The thought was that, you know, they [the prime crew] might have an accident or they could get sick or something like that, and then you'd have a replacement for them. You wouldn't have to abort the mission.
I guess about two to three weeks before flight, our son Tom was three, and he had a little friend named Paul Hause who was the son of some good friends of ours down in Houston. We were off for the weekend with the Hauses and sure enough, we came back a week later and Suzanne Hause called and said, "Paul has got the measles." I said, "Oh Lord" and I caught the measles from Paul, this little three-year old. And so I'm down there training all this time and I break out with the measles and go to the doctor because I'm pretty sick. And they get all excited, of course. (I forgot who the flight surgeon was down there.) But anyway, he gets all excited and starts testing everybody a couple of weeks before the flight. It turned out that everybody had had the measles except for Mattingly. So Lovell and Haise were immune, but Mattingly wasn't. So there was this big debate: "What are we going to do?" Finally the decision was made, "Take Mattingly off. Put in Jack Swigert." And they could launch if they thought they were able to do that.
This was only about a week before flight?
A week before launch. So I guess they had maybe two or three days of training. The movie Apollo 13 seemed to imply that Swigert wasn't ready, and that he was sort of a fill-in and really wasn't qualified. That wasn't true. Jack was a real good command module pilot. We were ready to go as a crew and it showed the beauty of the synergy of all of our training, that you could take somebody, a week before liftoff, stick him in, and everybody felt comfortable . . .
Lovell seemed to think that they were ready to go, and so they launched. By this time I think I'd gone back home. I was back in Houston (I think) for the launch, and when the explosion occurred, I was home in bed. John [Young] called and said, "Hey, they had this explosion and [there's] a real problem. Come into Mission Control." So, Ken and I, and John, showed up at Mission Control with some  of the other guys, and that started, if I recall, 35 hours of work either in Mission Control or the simulator-as John, myself and others were figuring out the procedures to power up the lunar module, to get them back on a free return trajectory and recover them.
Just to set the stage a little for that, the spacecraft-combined lunar module/command module were about two-thirds of the way to the Moon when that oxygen tank exploded.
It was 55 hours out.
And so, that disabled the command module. I know that one of the things that people were greatly concerned about at that time was that procedures and step-by-step checklists that had been worked out months and months in advance now suddenly were out the window.
And you guys had to then figure out, "All right, how do you run this new spacecraft arrangement to keep from getting in any more trouble?"
We had to not only figure out how to power up but to get them back on trajectory. We practiced and developed those procedures in the simulator. We felt like we had a good handle on it. But then the problem came: "How are you going to make this thing last for 99 hours?"
The lunar module . . . which was designed for three days?
It was designed for three days. It was designed for two people, not three people. And so we had electrical power; we had oxygen concerns; we had water. All the consumables that were necessary for life had to be shepherded, if you will, very carefully. And to be honest, for the first 25 hours, I didn't think we were going to make it. I thought that something was going to run out. But by the time  they did the burn to put them back on free return, which was, if I recall, something in the 70-hour timeframe, when we whipped them around the Moon and started back, it started looking better and better to me. And my thoughts changed to, "If we don't screw this up, either in Mission Control or onboard, we've got it made." And sure enough, everybody did a great job; and, I mean, the miraculous things that Dick Johnston's guys did to get the lithium hydroxide working . . . Thank God for gray tape. You know, every flight had two rolls of gray tape; and then the electrical guys figured out how to take power from the lunar module and go back into the command module and keep those batteries charged . . .
That's right. Because regardless of whether the lunar module got you back, you had to have the command module to reenter.
That's correct. And so, you know, it was a tense time during the whole procedure . . . 99 hours of drama, or thereabouts, till they separated and reentered . . . I remember we had figured out, in the simulator, that they had a series of maneuvers to do right before reentry because we had never separated this whole stack of the command module, service module, lunar module combined for reentry. It had never been designed for that.
They were going 25,000 miles an hour at that point.
Right. And accelerating . . . we were concerned about how they are going to be reentering. Could we crash them together? We had to figure out what was the best attitude and we'd done that, but it required a number of maneuvers to get it in the right position. And the more we thought about that, the more concerned I became, because we could still be maneuvering and reenter and not get it all done, or we get to gimbal lock if we have a problem with a jet. And so it was a real moment of decision, if you will. As I recall it, John and I went to (I think it was Gene Kranz) and said "Gene," you know, "why don't we just take what we got and just separate and let's just go?" And we did one or two little maneuvers, but we cut out some of them and that's what we agreed to do. And sure  enough, everything came back in; and we didn't have any problems at all with collisions.
Did Mattingly ever thank you?
When I caught the measles and he was off the mission, he was really, I think, sad . . . and especially after the explosion. You know, he had that sense of duty and that's where he should be . . . But after the recovery it was announced that we would go on into Apollo 16 together.
I don't ever remember us talking about it. It was never a moment of, "Charlie, how could you do that?" . . . you know, it was just one of those things that happened. By the way, after the measles, it turned out on Apollo 16, Fred Haise was the backup commander for us. We were climbing into the command module on the launch pad and Guenter Wendt and the team were up there. John gets in, and I'm the next in on the right side. As I start to climb in, I reach in and look over and taped to the back of my seat was a big tag that said, "Typhoid Mary." [laughs]
Getting back to Apollo 16, as you and Young prepared for your landing what kind of advice did you get from the prior crews, from Apollo 11 through 15?
On every mission after it was over, we had a day of debriefing that was basically just the Astronaut Office. Of course 11, 12, and 14 were in quarantine after the missions, and the whole Astronaut Office went over and spent a day just talking about procedures, attitudes, and feelings, all of the things that you want to know about after the flight's over. You sort of get more of a feeling of what it's like, rather than just the technical procedures of it.
A lot of suggestions came out of those debriefings. For instance, I remember that Apollo 15 was to be the first flight of the lunar rover, and John and I were scheduled to be the first crew with the rover. But they canceled Apollo 18 and 19 and moved what was the called the "J" missions from 16, 17, 18 up to 15, 16, and 17. So instead of being the first flight with the rover, we were the second.
 John and I had monitored the development of the rover and one of the concerns we had about the rover was the seatbelt. The seatbelt was very difficult to buckle and get cinched in on the lunar surface because in the suit, you can't see down into the part where it connects on a special bar down on the side of the rover. It was sort of a blind connection. It turned out, they had a real difficult time on Apollo 15. When they got back that's what we discussed; and as a result of that, we went into redesign for Apollo 16. So John and I didn't have any trouble. We just reached over and hooked it in and then flipped it over and locked ourselves into the seat. So the debriefings really were important, I thought . . .
The lunar rover was an incredible machine . . . it revolutionized lunar surface exploration. Instead of 400 yards, you could go four miles in any direction. Our objective, of course, was the Descartes highlands of the Moon. It was a valley eight to ten miles across, and the objective was to explore the south to a place we called Stone Mountain and then to the north, three or four miles, to a place called North Ray Crater, which was at the base of the Smoky Mountains, (these were names that we had selected). With a rover, you could do that.
You know, we took 40-50 minutes to drive south. We had trained, so I was the navigator; and John was the driver of the rover. The TV camera couldn't be on during our drive across the Moon (the antenna had to be pointed right at the Earth to get a TV picture), and so as we drove the antenna whipped around and would never stay pointed. It wasn't gyro-stabilized, so we never had TV back in Mission Control while we were under way. To cover that gap, which might be as much as two kilometers, I was taking pictures and describing the terrain we were going over. I was sort of the travel guide for Mission Control-the eyes of Mission Control during that time. I had a set of maps that would take us from lunar module to Point A, Stop One. And these maps were the same photographs that had been taken on Apollo 14 of our landing area, and so it was like you were looking down. Unfortunately, once you get on the surface, some of the features just disappear, it's not like looking down from altitude. You could see the major features, like Stone Mountain, but if you were looking for a small spot like Plum Crater,....
....which was 1.7 kilometers to the west of us, it was like you couldn't see the forest through the trees type deal. You were just too close. But the maps were really good. We landed within a couple of hundred meters of where we thought we were going to land . . .
The lunar rover had a little directional gyro. There was no magnetic field on the Moon, so a magnetic compass wouldn't work. We had a little gyroscope that was mounted in the instrument panel of the rover, and we pointed it down-Sun and it was the old Navy lubber's line: You had a bar come down across it, cast a shadow on the gyroscope compass card, and we assumed that shadow was west so we just turned the card until 270 was up underneath that shadow; and that was our direction. We had a little odometer on the wheel that counted out in kilometers and that was our distance.
Generally, our traverses were egg shaped, elliptical maneuvers. We'd start out in one direction and we'd make a big loop and  come back to the lunar module six to seven hours later. That was the plan. You never really worried about getting lost up there because everywhere you drove, you left tracks. If you really were unsure of your position, it was easy just to turn around and follow your tracks back.
Those tracks are probably still there?
I'm convinced they are, unless there was a meteorite impact nearby that, you know, created a big explosion.
The car was amazing. It was electric, four-wheel drive, and it would climb a 25-degree slope. Going up Stone Mountain, it felt like we were going out the back of the seat, because it was a pretty steep hill.
We got up to our objective, which was a place called Cinco Craters, and we turned around and sort of started back downhill and, golly! Then you really saw how steep it was, because it felt like you were going to fall out the front of the rover. Fortunately, we found a little bench, level area and we parked the car, and then we started our experiments. That was probably the most spectacular view that we had on the lunar surface.
We were three-quarters of a mile to the south and several hundred feet above the valley floor. From this advantage, you could look out all the way across the valley that we had landed in. You could see, in the distance, Stone Mountain and North Ray Crater. And there right out in the middle was our little lunar module. Looking off to the northwest as far as the eye could see, was just a rolling terrain of lunar surface, shades of gray. It was really an impressive sight. My only regret of the whole mission was that we didn't take enough pictures with people in them.
What scientifically were you looking for at Descartes?
The major objective, of course, was the geology and the photo-geology interpretation of our landing site. There were two major volcanic-type rocks: a very viscous rock that bulged up and caused the Stone Mountain topographical relief, and then down in the  Cayley Plain, the valley was another kind of less viscous rock that flowed out. We were looking at a contact between those two geologic features to see if there was any. It turned out that our landing site produced very little volcanic rock.
The major rock was breccias and igneous rock, so we had very little volcanic material. When we started describing this, I suspect that our geology team back in Mission Control were thinking "We wasted our time on these guys. They're not looking at what they're doing." But as we did more and more, they realized that this really was a unique landing site and was not like the Mauro, that it was really different. And so the rocks we collected were a unique suite of lunar materials.
The other objectives, of course involved the Apollo science package, which included a heat flow experiment which was to measure the heat coming out of the Moon. It included a magnetometer, which was to measure any residual magnetism of the Moon. It included a spectrometer, which was to measure the gases escaping from the lunar surface and two seismic experiments: one active, one passive. That was the basic science package.
Once we got the rover off the lunar module and put the TV on, I pulled out the science package. I fueled it with the RTG, which was a radioactive thermal generator (a little plutonium source). I put that into the cast that would generate the electrical power for the experiments. I hooked the packages onto the edge of a bar and remember throwing it up in the air and hooking it in my elbows. I started jogging out to the deployment site, which was a couple of hundred meters to the west of where we landed.
On the way out there (I'm jogging out), one of these packages falls off the bar and bounces across the Moon. "Oh my Lord," was my thought. I'd blown the whole deal and broken all the experiments. Well, it turned out that the package was pretty robust, and so I hooked it back up. I looked around real quick to make sure that nobody had seen that but unfortunately the TV camera was pointed right at me, and so everybody had seen this. But I recovered, and we went on out and deployed everything.
I was drilling some holes into the Moon for the heat-flow experiment while John was putting up the central station and the data  area. It was a "spaghetti bowl full of cables" around this thing, with all of the experiments attached. We said, "You know up on the Moon with one-sixth gravity, these things are going to coil up like spaghetti." And sure enough, that's what happened. Unfortunately, John got one [of the cables] wrapped around his foot. He ran off and pulled a cable loose. That [cable] was the data source collector and power source for the experiment. We lost the heat flow experiment, which was tragic because I had worked hard on it, and the principal investigator was a real great guy, and, you know, we wanted to do a good job. That was the only real major problem we had as far as experiments go. Everything else worked right.
House Rock was one of the features that you guys encountered. That was a very spectacular sight on television because it loomed on the horizon, it looked so big. What was your first sensation when you saw that?
My first sensation was that it wasn't very far away. And John's sensation was, "That's a big rock!" I said, "Oh no, John. Come on. It's just right out there, let's go down there." Well, there's a problem on the Moon. Your depth perception is thrown off because you're looking at objects you've never seen before, so a big object far away looks very similar to a smaller object close in. You don't have any telephone poles or houses or trees or cars to sit and judge scale like we have down here on Earth. In my mind this rock was sort of average size and was just out there and "Let's go do it." John was a little hesitant, but Mission Control said, "Well, have at it." So we started jogging, and then I realized, "This is a big rock!"
We kept jogging and jogging, and the rock kept getting bigger and bigger and bigger. We were going slightly down hill, so we didn't sense how big it was at first, and so we get down to this thing and we called it "House Rock." It must've been 90 feet across and 45 feet tall. We walked around to the front side or the east side, which was in the sunlight, and, you know, it was towering over us. And we had this little hammer in our hand, thinking, "What are we going to do with this rock?" When we got down there-this humongous rock towering over us-John and I hit it with a hammer  and a chunk came off. We were able to collect a piece of House Rock. Then we had a struggle hiking back, uphill.
We had some nuisance things that happened. Sample bags falling off and clips not working. But all and all, everything worked right.
Astronauts, even to this day, will talk about how difficult it is to work in a full pressure suit.
You didn't really sense a problem. I mean, you're so pumped up out there on the lunar surface. We had a good cooling system that kept us very comfortable. We had a bottle of water Velcro'd to the inside of the suit that we could drink out of. A little high-energy food bar was also Velcro'd inside the helmet that you could snack on to keep you nourished.
But you couldn't scratch your nose.
You couldn't scratch your nose. But you could reach over and hit the side of your helmet and things like that. Or if you had to, you could sort of rub your back against the suit. You couldn't bend over at the waist without great difficulty. You couldn't really bend at the knee so you had to learn how to operate the suit to make it work for you. It turned out that when we got back inside and took everything off, we were exhausted. I mean, it was hard work. You're squeezing that glove for 7-8 hours was like, if you can imagine squeezing a ball for 7-8 hours. And doing curls and stuff in the suit, and trying to make it work for you. It was real work.
I remember a couple of times the flight surgeon said, "Slow down. Your heartbeat's up to 140 a minute or so. We want you to rest." Generally, we rested in the car when we drove from point to point. But a couple of times they had to make me just slow down and rest. The suit was tough work.
I remember my arms were cramping and the end of the fingers, under the fingernails, were sort of black-and-blue from blood bruises that were a result of the Apollo pressure suit. It kept you alive, though. Only one time did I have a feeling that, "I'm in trouble" in the suit, and that was the final part of our stay on the Moon.
We were going to do the Moon Olympics, but John said, "Houston, we're going to do the Moon Olympics but we're running out of time, so we won't do that." And I said, "Yeah, Houston, I was going to bounce and set the high jump record." And I started just kidding around and bouncing, and when I jumped the last time, I went over backwards and disappeared behind the lunar rover, and the TV camera's pointed at me. That was a moment of panic . . .I was in trouble. You could watch me scrambling like that, trying to  get my balance. I ended up landing on my right side, and bouncing on to my back. And my heart was just pounding, you know.
What was your concern? That you'd damaged the suit?
That I'd have damaged the suit. You know, the backpack is very fragile. I thought the suit would hold, but the backpack, with the plumbing and connections and all, if that broke, it was just like having a puncture in the suit. And, you know, falling over backwards on the Moon. Hardly ever did we think about, "We're in a vacuum. This thing's got to work." I don't remember thinking or worrying about that. But this time, as I started over backwards, the thought occurred to me, "I'm in trouble." I was able to spin right before I hit, and my right foot and right hand hit, and I bounced on to my back. And John came over and helped me up. I got real quiet, and you could hear the pumps running in the backpack. And I checked my suit pressure. It was okay so this fear began to subside.
Then I realized the TV camera was pointed at me and then embarrassment came. You know, "The stupid stunt." I forgot what Mission Control said. I think Tony England was our Capcom, and he said, "That's enough of that, guys." Anyway, that ended our Moon Olympics. Other than that time, there was not another moment where we didn't feel secure in our suits.
Did you find that you adapted very quickly to moving in one-sixth G.
Yes, we did. I found that either the hop or the skip was the best for me. John was more of a jogger-type. I put my right foot out front and I just sort of skipped along. Then again, if the ground was level, you would start a little jog and it was sort of effortless as you went across. We fell down a lot, at least I did. I found when you did fall down on your front, then you could just do a series of push-ups and you'd sort of rock yourself back up and then eventually you'd pop up.
It was great fun. John and I really had a ball. We were joking and just having a tremendous sense of enjoyment and adventure.  It was a real adventure for me and John and it built a friendship that is real solid now, 27 years later.
If you had a chance to go back to Descartes, what do you think you'd find? Do you think your lunar module and the flag and all would still be there?
Without a nearby meteorite impact, I believe it'd still be there.
You don't think the flag blew down when you took off?
Well, it didn't look like it. I was running a camera out of the window and as we pitched over it [the flag] wiggled a lot, but I think it stayed upright.
One of the things that changed on your mission from the previous one was a reaction, I wonder if you think perhaps it was an overreaction, to the exhaustion and the irregular heart rate that Jim Irwin experienced on Apollo 15 because of the heavy workload. As a result, they really loaded you guys down with potassium.
I'm glad they did that. They changed our medical kit. They gave us some sort of injection that we could take if we did see heart problems developing. That was an experience that was (looking back), at the time, humorous. We were in flight medicine getting a briefing on this new medical kit with this thing that was heart medication. It wasn't oral, but it was an injection. One of the flight surgeons was telling us, "Well, you count down so many ribs" and this was going to be injected right into the heart muscle. And you'd press it. (It was like those battlefield syringes that would fire this needle in and inject the stuff.)
So he said, "Well, let me demonstrate this." And he took a Styrofoam ball about the size of a grapefruit and he pressed this thing. When it went off, the Styrofoam ball exploded and I almost passed out. I knew at that moment, "that thing is never going into my heart and I don't care how sick I am." We never had to use it, of course but they did put the potassium in to try to regulate the heartbeats.
 We also generated tools that would help us overcome the hard workload previously experienced on Apollo 15. For instance, the core that we had to drill (10 feet deep), [Apollo] 15 could hardly get the thing back out of the surface. Dave Scott and Jim Irwin (Dave Scott was strong as a gorilla) had a tough time so we developed this little jack. It was a collar that went around the stem of the drill that was sticking out of the surface. Like a car jack, I could just keep jacking it and this would slowly jack this thing out of the surface. It was easy to do. Those kinds of things came about in debriefing.
We found that potassium did work as a laxative and we had problems with, you know, our BMs5. At least I did and it turned out that it wasn't very pleasant. The Apollo system wasn't the most high-tech system in the world to use. While we didn't have any real serious accidents, it was just the frequency . . .
You mentioned that at the end of the day, you get back into the lunar module, get the suits off, and you're in an environment one-sixth gravity. You have no place to lie down. How were you able to sleep between EVAs?
You're tight, but I wouldn't call it "jammed in." Once we got off the suits, there was a place between us, behind us over the ascent engine cover, where we could drape the suits over and they were out of the way. For me, I could lean back and sort of semi-sit on the environmental control unit. We just felt it was comfortable, really, without having to sit down.
When we got ready for our rest period, we each had a little beta-cloth hammock. Mine attached across the LM. There were hooks on the left side, and two hooks on the right side. So I hooked up this little hammock, cinched it up, so it was about six inches off the floor, and I rolled up one of the liquid-cooling garments for a pillow. John's was up above the ascent engine cover. He hooked on to the sides of the instrument panel and the back bulkhead, so we were sort of in a cross. He would climb up and get in his hammock. Amazingly, he went right to sleep.
The first night, we had changed our flight plan due to this late landing that required us to go to sleep before we went outside for  the first time. I'm on the Moon and six hours after landing, "go to sleep." My mind's just racing like crazy and, even though we were tired, I couldn't get to sleep. So I asked Mission Control if I could take a sleeping pill, which I did, and then I drifted off to sleep. And the sleep was very comfortable in the little hammocks.
I remember that first sleep period. We had been warned that, some time during the night, a master caution alarm would go off due to a reaction control regulator problem that we had prior to descent. When we powered up the system, we lost the pressurization controller; both regulators failed and we were overpressurizing, but John quickly vented the pressure into the ascent engine tank to save the mission. As we rested, it began to heat up and overpressurize again. And we knew that when we got to a certain level, this warning would go off. Sure enough, I've just dozed off and "bong, bong, bong!" I have the headset on and this master alarm went off. I almost went through the top of the lunar module. I cycled whatever I had to cycle to vent the pressure and went back to sleep.
It was all right for the rest of the time?
It was all right the rest of the time. After that first night, I didn't need any sleeping pill. I was physically tired after working on the lunar surface and able to get right to sleep. I'd say we averaged, maybe, six hours sleep on the lunar surface. The best rest I got was on the way home. You started home and your attitude was, "Mission complete. We've done it. We're on our way back. Let Mattingly handle this thing from now on."
On the way home, I was being monitored, and the flight surgeon was watching me sleep. I think my heartbeat got down to, like, 28. I was dead to the world, and it was really refreshing. When I woke up, they said, "Man, we thought you were dying."
While you were on the Moon, Tony England, your Capcom at Mission Control, relayed the news to you that the House of Representatives passed the NASA budget with funding to go design and build the Space Shuttle.
That was exciting. In fact we had just saluted the flag. John had just saluted the flag and gave that little jump for joy and saluted. When we were changing positions, if I remember correctly, right after that Tony relayed that they had just received word of funding for the Space Shuttle. And John and I were excited. John made the comment, "Yeah, we really need that Shuttle."
Two other things that I thought were memorable while I was on the Moon. I was the only Air Force officer on the Moon during 1972. We had two missions, Apollo 16 and 17, and it was the 25th anniversary of the Air Force in 1972. They had some special medals  struck, like silver dollars, that had the Air Force seal on one side and Apollo on the other. I took two to the Moon with me, with the approval of NASA, and left one on the Moon (took a picture of it) and brought the other back. So I was able to say "Happy birthday, Air Force," while we were on the lunar surface. I also had an Air Force flag that I took and gave them a piece of Moon rock. These are in a museum now up at Wright-Patterson Air Force Base.
The other was: I took a picture of my family. Our kids were five and seven. I had a little picture that had been taken in my backyard by one of the NASA guys, Loudy Benjamin, and we had that shrink-wrapped. On the back of this photograph we wrote: "This is the family of Astronaut Duke from Planet Earth. Landed on the Moon, April 1972." And the kids signed it to get them involved with the flight. I left that on the Moon and took a picture of the picture, and that's one of our neatest possessions now.
1. One of the most serious threats to the landing came in the form of a "1201" alarm from the lunar module's (LM) computer. When it flashed those numbers, the LM was signaling that it had an overload of information and needed to sort through its tasks. A continuous alarm would have meant an aborted landing, but its intermittent nature in this instance led the LM computer expert Steve Bales to signal a "go" for landing.
2. "Mascons" were unexpected irregularities in the gravitational field of the Moon, discovered by the unmanned lunar orbiter mission in 1966-67.
3. In 1963, Bell Aerosystems Company in Buffalo, New York, was initially awarded a contract by NASA to design and develop two unique manned Lunar Landing Research Vehicles (LLRV). Bell based their design for the LLRV on the so-called "flying bedsteads" that were flown in the 1950s to study the potential of jet lift for vertical take-off and landing (VTOL) aircraft. On May 6, 1968, Neil Armstrong, while making his 21st flight in the LLRV, narrowly escaped disaster. After lifting off and flying to an altitude of 150 meters, he began a simulated lunar landing. Suddenly the LLRV began to pitch forward at about 70 meters while at the same time picking up speed. Armstrong attempted to make corrections but could not stop this motion and chose to eject. Seconds later, the LLRV crashed in a field while Armstrong parachuted to safety. After further initial tests of the first two vehicles at NASA's Flight Research Center (now the Hugh L. Dryden Flight Research Facility), three improved versions of the trainer, renamed the Lunar Landing  Training Vehicle (LLTV) were ordered by the Manned Spacecraft Center. Two of the LLTV's were used by astronauts at the Kennedy Space Center while one remained at Ellington Field in Houston. After a second near fatal mishap occurred when test pilot Joe Algranti punched out of LLTV No. 1 at Ellington Field, there was talk of ending the flights altogether. The program remained, however, after astronauts argued that the vehicles accurately forecast the LM's handling characteristics during the final critical moments of descent to the lunar surface. Ed Hengeveld, "Training for a Lunar Landing: The LLRV and LLTC," Quest, Vol. 6 No. 1, pp. 50-54.
4. NASA's Langley Research Center in Hampton, Virginia, developed a Lunar Landing Research Facility (LLRF) which was basically a tethered version of the LLRV, suspended from a giant support structure, that allowed an LM-type vehicle to practice the final 50 meters of lunar landing while hanging from moving cables. The LLRF was primarily used by Langley pilots to test instruments and software designed for the LM. The original helicopter-like cockpit was later modified to allow the pilot to stand upright, as he would during a real lunar landing, so he could get used to flying in that unusual position. The LLRVs and LLTVs did not allow a pilot to practice while standing up because they were equipped with ejection seats. Ed Hengeveld, "Training for a Lunar Landing: The LLRV and LLTC," Quest, Vol. 6 No. 1, p. 51.
5. The potassium that the crew received during their mission was in the form of enriched orange juice. The crew had some pretty strong words to say regarding this mixture. Prior to the first lunar EVA, and during their first meal on the Moon, Duke managed to accidentally release some orange juice from the siphon attached to their space suits. The juice eventually worked its way into his hair and helmet, causing him some distress. At one point he remarked, "I wouldn't give you two cents for that orange juice as a hair tonic." While the incident probably amused Duke's fellow moonwalker at the time, the orange juice would later come back to haunt John Young. As Duke and Young were debriefed after returning to the LM from the first EVA, Young left his microphone on voice activation, meaning that every time he spoke, it was relayed live to Houston. This resulted in an unusually vivid and colorful account of post debrief activities. Houston picked up quips from Young about how the potassium enriched orange juice was giving him gas, including a few colorful remarks about never eating oranges again. The Capcom on duty picked up on the conversation and politely informed the crew of the "hot" mike. Richard S. Lewis, The Voyages of Apollo: The Exploration of the Moon (New York: The New York Times Book Co., 1974), pp. 245-248; For a transcript of the infamous conversation, see Mission Elapsed Time 128:50:37 - 128:54:15, in Eric M. Jones, ed., "Apollo 16 EVA 1 - Debrief and Goodnight," [Apollo Lunar Surface Journal Home Page]. [Online]. Available: http://www.hq.nasa.gov/alsj/a16/a16.eva1debrief.html. [link no longer valid, Chris Gamble, html editor]