On July 19, 1969, a pair of lunar orbit insertion burns put Apollo 11 into orbit around the moon after three-day coast from Earth. On the 11th revolution, the White Team assumed the consoles in Mission Control in preparation for descent. Here, the knuckle-biting story of the first lunar landing, replete with computer alarms and a low-fuel indicator, as the astronauts drop toward the cratered surface where they will open the hatch and take their first steps.
JULY 20, 1969 — LANDING DAY
* Gene Kranz, flight director (FLIGHT), White Team, Mission Control: I remember very clearly when I left the house. I had my fresh haircut, and my wife had packed me a sack lunch that was enough for three shifts of people. As I arrived at my parking spot at [the Manned Space Flight Center], I realized I didn't remember driving through Clear Lake, or anything else. I was so preoccupied I was on autopilot.
* Steve Bales, guidance officer (GUIDO), White Team, Mission Control: When we came in that morning, the lunar module was dead. We had to power it up, get the thing aligned and checked out. In the simulations, that's where we'd always had the biggest difficulty, really. We had never completed without some major problem--and I don't know if we ever completed successfully in training--what we called a power-up and initialization of everything, and then gone ahead and done a landing.
* Sy Liebergot, electrical, environmental and communications officer (EECOM), Black Team, Mission Control: We had both the descent team and the ascent team in the Control Center at the same time. If we had to abort and get off the lunar surface, the descent guys would move off the console and we ascent guys would move into position to perform the part of the mission we were specially trained for.
* Chuck Deiterich, retrofire officer (RETRO), Black Team, Mission Control: Coming from an abort there are many places you could start from, so that made it more complicated. But the abort target tries to get you to a point that simplifies the rendezvous.
* Llewellyn: I used to go into the Control Center at night by myself and bring up the computer; I'd work with Collins in the simulation building. He'd simulate aborts and I'd tell him what kind of orbits he got into and talk about how we handled it. That really kept me on edge.
* Kranz: I had a talk with the controllers prior to the time we entered into the landing phase of the mission. I indicated that whatever decisions they'd make that day, I'd stand behind them--that we came into the room as a team, and we'd leave as a team.
* Jack Garman, group leader, program support group, Apollo Guidance Software Section: It got very, very real as [the spacecraft] went around the moon and got ready to undock. In fact, I remember vividly them locking down the Control Center. The guards were not to let anybody in or anybody out.
Buzz Aldrin, lunar module pilot, Apollo 11: At that point we're maneuvering to go backwards, engine first and facedown, in the attitude where we're going to start the powered descent.
* Joe Gavin, director, Lunar Module Program, Grumman Aerospace Corporation: The whole thing was tense, because we were basically aircraft designers. In the aircraft business you always flight tested something before you delivered it. In the case of the lunar module, you couldn't flight test it. Every launch was a brand-new vehicle.
* Doug Ward, NASA public affairs officer: All the way down we kept losing communications and it would come back and we'd lose it again. I was right on the edge of my seat thinking, "You know, we're gonna abort for that."
* Kranz: I had one Mission Rule that I was sole interpreter of. That was: Did we have enough information to continue—both voice and telemetry.
* Glynn Lunney, flight director (FLIGHT), Black Team, Mission Control: Mission Rules were sort of like what it would take for us to stop trying to land on the moon. They became like a set of commandments, or a set of ethics for helping to figure out how much risk we were willing to take, and for how much reward.
* Kranz: The first thing [my team] did was use Mike Collins as a relay--we had done that in training a couple times.
* Ward: In fact, the people responsible for communications weren't overly concerned because they realized why it was [cutting out]. The lunar module was getting in an attitude where it was blocking the high-gain antennas. They knew that as it maneuvered going down to the lunar surface that would correct itself.
* Aldrin: It finally locked on and was in good shape, just the way it was supposed to be.
* Don Eyles, software engineer, lunar module guidance computer, MIT Instrumentation Laboratory: The landing maneuver started with the spacecraft in its low point in a lunar orbit of about 9 miles.
* Bob Carlton, lunar module control officer (CONTROL), White Team, Mission Control: When we first kicked it off, the flight director would go around the room and take a status. He wanted to hear your voice. When Gene got to [Steve Bales], he just exploded "GO!" And I heard Gene snicker a bit, and we all did, but it sort of relieved the tension. I said to myself, "Now you don't do that." So when I gave my go, Gene said, "Control," and I said, "I'm go, Flight." He later commented on how cool and calm I was, but he didn't know I was putting on an act.
* Kranz: We gave 'em the go for the start of powered descent and, doggone it, right at the time the engines started we lost data again. We picked it up momentarily thereafter, and very shortly after that a guidance officer indicated we had some trajectory perturbation. In fact, he said, "We're halfway to our abort limit." Well, that is sort of sporty before you even start down to the surface.
"Neil says to me, and the Earth, 'I think we're gonna be a little long.'"
* Aldrin: We're about a minute, maybe 2 minutes, into powered descent, facedown, and Neil says to me, and the Earth, "I think we're gonna be a little long." I said to myself, how in the world can he really, at this point, tell that we're gonna be a little long? But sure enough, we were.
* Neil Armstrong, commander, Apollo 11: Prior to igniting the lunar module's descent engine to initiate the trajectory toward the lunar surface, I had been timing our angular rate over the craters on the surface below to calculate our altitude. I noted that, at ignition, we were somewhat west of our intended starting location. I inferred that our entire trajectory and landing point would be somewhat west of our planned landing spot.
* Aldrin: I've learned that whenever Neil says anything, you'd better pay attention because there's good meaning to it.
* Bales: The lunar module could do a lot of things independently, but it had to rely on people on the ground to tell the computer where it was starting on its landing position. On the backside of the moon there had been some venting--some perturbations unknown to us. The time we gave them to light the engine was about 4 or 5 seconds late.
* Aldrin: There comes a point in the checklist where we yaw around so that we're faceup, then pitch forward a bit before we throttle down. The purpose of doing that is to get the landing radar to lock onto the surface at about 30,000 feet.
* Bales: As the lunar vehicle pitched over, the landing radar had to change positions. We'd always said that if that switch didn't happen at 10,000 feet, we were going to abort. The day before we landed, I was in a meeting with 30 or 40 people who built the radar, who built the computer, who knew the landing trajectories, arguing about what we were going to do if the radar gets hung up in the primary position.
* Kranz: We had given the spacecraft the best knowledge we had of its altitude above the lunar surface prior to powered descent, but we had to update it based on actual data from the radar.
"At the time, I thought our worst problem was over. Our worst problem was just about to start."
* Bales: As soon as it locked on, the radar saw that we were going a little bit fast in radial velocity and corrected the computer. At the time, I thought our worst problem was over. It turned out our worst problem was just about to start.
* Aldrin: We got the first 1202 alarm. So we look at each other, and we know it's in the guidance and navigation dictionary, but rather than try and get it out while the module is making a powered descent, Neil asked them what's the reading on the 1202 alarm. Then we got a 1201.
* Charlie Duke, astronaut, capsule communicator (CAPCOM), White Team, Mission Control: I was shocked. Actually, "stunned" is a better word. I started reaching for my guidance and navigation checklist to see what a 1201 and a 1202 was. And, of course, Steve Bales knew immediately and didn't hesitate very long to say, "We're go on those alarms, Flight."
* Bales: I barely heard him. If you listen to the [voice] loops, there's a lot going on. And then finally the data comes in and we see the 1201, and Jack [Garman] is yelling--I mean, almost literally yelling, "It's okay! It's okay, as long as it doesn't keep going on!"
Garman: There was a team of flight controllers whose duty it was to come up with simulation profiles that train the flight controllers and astronauts together to survive and fix things. At one point, they had asked me to come up with a failure that was totally software-related. I did that months earlier, and they stuck that in during one of the simulations.
* Liebergot: There was usually a pretty adversarial relationship between the simulation-training guys and us flight controllers because they were trying to see if they could outfox us. But they were pretty important. They trained us to respond to most of the problems we would ever see.
* Kranz: Dick Koos, our simulation supervisor, gave us the 1201 and 1202 alarms. Steve [Bales] had never seen this before. During the simulation, they had an abort, which was his call.
* Bales: There's a general rule in flight control: If you don't know what to do, don't do anything. The problem is, in the middle of a lunar landing, not doing anything is not an option.
* Garman: Gene Kranz sat us all down and said, "I want you to figure out every possible alarm code that can happen in flight so that we're prepared." In those days, there was no such thing as desktop computers. So I wrote down all the alarm codes on a sheet of grid paper, with crib notes on what they meant and what our response should be. And I stuck it under the plexiglass of the console I was to sit at. And, lo and behold, one of them--well, a couple of them--popped up during the actual landing.
* Eyles: What led to [the alarms] was an obscure mismatch deep in the electronics--two signals that should have been locked together in phase were only locked together in frequency. That hardware glitch involved the rendezvous radar, which really wasn't needed during the descent to the moon.
* Aldrin: I left it on. That turned out to be the main cause, and maybe the cause, of the program alarms.
* Eyles: Based on a random-phase relationship between those two signals, the rendezvous radar electronics were sending pulses to the computer at a very high rate.
"There's a general rule in flight control: If you don't know what to do, don't do anything."
* Ward: The computer was simply saying, "Hey, I've got more than I can handle, but I'm gonna do the important things, so don't worry about it."
* Eyles: Under the software control, it did a software restart. Five times during the landing, the whole software was flushed and reconstructed in terms of what was being executed. And that load shedding was what allowed us to complete the landing without any appreciable glitches in the way the guidance system worked. Without quite knowing it, we had built a fault-tolerant computer.
* Garman: The problem is that those program alarms set off what is called the "master caution and warning," which is red lights and very large klaxon sounds--if you've seen submarine movies, kind of like the klaxon that goes off when they say, "Dive! Dive!" And as I gathered from after-flight readings, the heart rates for Neil Armstrong and Buzz Aldrin went up just a bit.
* Armstrong: The powered descent was the most challenging segment of the flight. The systems were heavily loaded, the margins were slim, and this would be the first time that the entire descent strategy would be fully tested. A decade earlier, while I was flying in the X-15 program, we learned, surprisingly, that all the pilots, while flying the X-15, had heart rates between 145 and 185. It reflected the mental intensity appropriate for a challenging situation. The Apollo data seemed to correlate well with our prior experience.
* Duke: I didn't notice anything panicky, any tension at all in them. We just kept feeding them the information, trying to be as professional about it as possible. I don't think I was relaying any anxiousness in my voice--I tried not to, anyway--but tension was building.
* Aldrin: As long as you've got communication, Houston knows what [the problem] is, and they have more information, so they're going to be the ones that call the shots.
* Liebergot: We weren't exhaling, but very businesslike. And that's not to say the job was just ho-hum; it was not. It's that we, with hearts racing, did our job.
* Eyles: The first two [landing] phases were very much under the computer's control using different targets. The final landing phase was the point where the astronauts took over semimanually to maneuver the spacecraft like a helicopter. When I say semimanually, I mean that the automatic system was controlling the throttle to maintain a commanded descent rate while the astronaut commanded the attitude of the spacecraft in order to scoot along the surface in whatever direction he needed to go.
* Bruce McCandless, astronaut (CAPCOM), Green Team, Mission Control: Neil was flying, looking for a boulder-free spot. It's fair to say people were holding their breath. But Neil had a considerable amount of experience in the lunar module simulator and in the lunar-landing research training vehicle.
* Armstrong: Every flying machine has its own unique characteristics, some good, some not so good. Pilots naturally fly the craft in such a manner as to take advantage of its good characteristics and avoid the areas where it is not so good. In the case of the lunar module, surprisingly, it flew much more smoothly than I had expected based on all the simulator work we had done. It was a welcome surprise.
* Gavin: The lunar module had the first really throttle-able descent engine. When it first fired, it had to operate at about 10,000 pounds of thrust. But as they approached the lunar surface, the vehicle became much lighter, having burned up a lot of fuel, and they had to get the thrust down to maybe 2000 pounds. So it was quite a development to get a rocket engine that would not only do this, but would operate smoothly in either range.
* Bales: There wasn't a lot being said, but we had a lot of data. I was thinking, "What in the bloody heck is going on?" Normally, in the simulations, once [Armstrong] got on a path to come down, he killed all the velocities but altitude rate and pretty much just came straight down. But he wasn't. He had a forward velocity of 20 feet per second. And, of course, that was eating up fuel.
* Gavin: In an airplane you usually have, oh, at least an hour's extra fuel in case the airport is closed where you're going. But in the case of the lunar module, we had about 120 seconds of margin.
* Kranz: We got what we call "low level" in the propellant tank. Once we got that indication, we knew we'd have roughly 120 seconds of propellant remaining at a hover throttle setting.
* Carlton: We had never seen that light, never expected to see it. In all of the sims, we had so much margin, that wasn't normally a factor.
* Garman: At that point there was nothing the ground could do except watch. It became a spectator activity. The tension went up noticeably. Very noticeably.
* Duke: When we got down to the last minute or so, it was real quiet. Everybody was glued to his monitor.
* Carlton: I had a stopwatch. I'm looking at it, and at the same time I'm looking at the altitude, and I can see it's still a long way down. I didn't know it, but the guys were flying over a crater. We call up 30 seconds. I'm thinking there's no way we're going to make it.
* Kranz: I'm a Catholic, and in the flight director business, you want all the help you can get.
* Carlton: When the engine shut down, I had 18 seconds to the point where we would have aborted.
"I'm a Catholic, and in the flight director business, you want all the help you can get."
* McCandless: I was in the control center as a spectator, sitting right next to Charlie Duke, who was the CAPCOM. Once Neil came back with his transmission, "Tranquility Base here. The Eagle has landed," in spite of the earlier admonitions to maintain decorum, we burst into spontaneous cheers and applause.
* Duke: That's the first time he'd used that. The call sign was Eagle, so we'd just been using, "Eagle, this is Houston," "Houston, Eagle." As you can hear in the transcript, I was so excited, "tranquility" came out, "twank." I caught myself before I finished the word, "Twank--I mean, Tranquility. Roger, Tranquility, we copy you down."
* Ward: Kranz immediately got on the loop and said, "Everybody settle down. Settle down. We've got some critical calls to make, and we've got to focus on what's coming up here."
* Kranz: We had a job to do, because in the next 2 minutes, we had to make the first of our stay/no-stay decisions.
* Ward: But in the meantime we could hear this roar from the viewing room behind us. All of the politicians and top managers and astronaut families and so on were back there behind the glass.
* Aldrin: It was certainly momentous, but there were no trumpets blowing or cymbals crashing. We're there, we're two guys, and we're not the yippee type. We see something, absorb it, think about it and that's it, accept the way it is.