First Man

by James R. Hansen

  The technique devised by Armstrong during training to determine the PDI point (Neil did this in association with Floyd Bennett, a talented engineer in MSC’s guidance section) was a relatively simple one. It involved a direct, naked-eye check of the lunar surface combined with what Armstrong calls some “barnyard math.”

  “We used the equation v=r Ω,” Neil explains, “where r was the altitude that you wanted to know, Ω was the LM’s angular rate, and v was the LM’s velocity. We knew very well what our velocity was based on radar tracking from Earth and from our own navigation system, so to figure out altitude all we needed was our angular rate. Going into the mission, we knew we could determine that by watching a point on the ground.” Early in the descent phase, the LM flew with its windows facing down (and the LM’s back end forward), which made it easy for Armstrong to spot major landmarks on their way down. The facedown attitude was also useful for solving the altitude equation. On the double-paned window on Neil’s side of the LM there was a vertical line with horizontal marks on it. As the LM flew facedown, Neil used a stopwatch to time the number of seconds it took to move from mark A to mark B on the window line. By that he calculated the spacecraft’s angular rate. With him in the cabin Neil had a chart that he used to compare tracking rates with expected values at various positions along the orbit. Differences between his visual observations and the expected values allowed him to estimate both the altitude of the LM’s perilune and the time at which they would reach it. “It was a simple technique and easy to do,” Neil relates. “It was a valuable exercise to confirm that we were in fact at a good altitude to start the powered descent.”

  A minute and half later, Houston told Eagle, “You’re Go for powered descent.” Before Mission Control gave them the green light, as Neil explains, “all the guys in the trenches at Mission Control who were looking at all the various systems and subsystems made sure that the pressures, temperatures, valves, and so forth were all checking out okay.” Mission rules allowed the descent to continue even if some minor instrumentation was not functioning with 100 percent efficiency, but generally the flight directors required everything to be working very well before PDI commenced. “They looked at most everything in somewhat more detail, or at least with more time, than we could,” Armstrong reflects. “They had more eyes looking at the information.” What ground control could not know very precisely, however, was the LM’s altitude. “The barnyard math was something I came up with myself and did on my own. I’m not sure if any of the other astronauts even used it. I’m sure I told them about it.”

  Collins relayed the “Go for PDI” to his mates because Eagle was still incommunicado. Then even after swinging back around to the front side of the Moon, communications unexpectedly remained broken. “We had a small dish antenna mounted on top of the LM, which was a good antenna,” Armstrong notes. “It was steerable, but it had to be pointed very close to Earth to get much signal. We also had an omnidirectional antenna. The omni was just a blade antenna like a person has on his automobile; it was not very accurate or very powerful. It was important to get the dish antenna pointed directly at Earth, but it was not particularly easy to do when you were lying horizontal. If you were off in yaw angle just a little bit, you could easily lose the signal.”

  It took almost five minutes for Neil and Buzz to make final preparations for powered descent. “We had to get the computer into the right program,” Neil explains, “and make sure that all the switches and circuit breakers and everything else was ready to make the systems work and make the engines run for the powered descent.” Buzz’s focus was exclusively on readouts from the navigational computers, while Neil’s was on assuring that everything from engine performance to attitude control was working the way it was supposed to. As Eagle started down, the duo activated the sixteen-millimeter film camera that was mounted above the right-hand window next to Buzz; pointing forward and downward, the camera was to film every foot of the historic descent.

  Back on planet Earth, tension began to crescendo as network television coverage prepared for PDI and counting down the minutes to touchdown. On air with CBS, Cronkite said to sidekick Wally Schirra, “One minute to ignition, and thirteen minutes to landing. I don’t know whether we could take the tension if they decided to go around again.”

  In Wapakoneta Viola Armstrong, watching Cronkite while clutching a sofa pillow to her breast, showed her generosity of spirit in these anxious moments by thinking of the lonely vigil of Mike Collins. “The tension rose to a peak each step of the way,” recalled Viola. “The tense period between the separation of the Lem [sic] from Columbia, when Buzz and Neil left Mike, really pulled on my heartstrings. We felt sorry for him because he was alone and could not go along with the other two. We were so proud of him because he was so faithful.”

  PDI came at 4:05 P.M. EDT. Strapped into restraining belts and cables that worked like shock absorbers, neither Neil nor Buzz felt the motion, so they looked quickly at their computer to make sure the engine was in fact firing. For the first twenty-six seconds—a quantity that programmers of the LM propulsion system called “zoom time”—the two astronauts kept the engine firing at merely 10 percent of maximum thrust. The gentle power gave the guidance computer the leeway it needed to sense when the lunar module was in the proper geometric position to go full throttle. “Basically, you liked to be at a pretty high thrust for good fuel efficiency,” Armstrong notes. “But if something was wrong and you were at too high of a throttle for too long, you couldn’t sync to your target. So there was a strategy for the throttle profile—for throttling the engine to start at point A and end up at point B with a relative maximum efficiency.”

  As power from the engine grew, the motion became noticeable to the astronauts; even though the LM was falling at a rate of thirty feet per second, it seemed no more dramatic than a trip down several floors in a quiet hotel elevator. As they fell, Armstrong watched his instruments for proper readings while Aldrin made sure that the numbers from PNGS and AGS were correlating with preestablished figures written onto a stack of note cards that Buzz had placed between Neil and himself.

  By his own admission, Buzz chattered the entire way down, “like a magpie,” as he continually read out numbers from the computers, whereas very little was heard from Neil in the minutes leading up to landing.

  If Neil had had his way, nothing from either one of them would have been heard by the outside world. Late in training Armstrong had asked about the possibility of keeping all the talking in the LM during the last minutes of descent off the radio, so as to minimize distractions. Mission Control quickly rejected the notion because it wanted to hear what was being said; the flight directors wanted their teams at the consoles to be fully informed. The idea was that one of the many experts on the ground might be able to help out the crew even in the very last seconds if a problem popped up. “Whenever I wanted to talk to the outside world,” states Neil, “normally I used the push-to-talk mode,” meaning he squeezed a switch. “We had a voice-activated [VOX] position as well, and I think Buzz used that during the descent.”

  In the first minutes after PDI, while flying with the engine forward and windows down, Neil tracked his surface landmarks in order to confirm Eagle’s pathway and its timing down along it. Three minutes into descent, he noticed they were passing over the crater known as Maskaleyne W. a few seconds early:

  Neither Neil nor Buzz could be sure why they were over the crater a little early. They guessed that PDI must have started a little bit late. “Our downrange position appeared to be good at the minus-three and minus-one minute points prior to ignition,” Neil reported during Apollo 11’s postflight debriefing. On a chart placed in front of them, he had premarked where PDI was supposed to start but, when PDI actually began, things were too hectic for him to pay careful attention to precisely where it had happened. “I did not accurately catch the ignition point because I was watching the engine performance. But it appeared to be reasonable, certainly in the right ballpark. Our cross-ra
nge position was difficult to tell accurately because of the skewed yaw attitude that we were obliged to maintain for communications. However, the downrange position-marks on my window after ignition indicated that we were long.” From one mark to another represented two or three seconds farther downrange, with every second corresponding to roughly a mile of distance. “The fact that throttle-down essentially came on time, rather than being delayed, indicated that the computer was a little confused as to what our downrange position was. Had the computer known where it was, it would have throttled down later to kill a little velocity. Landmark visibility was very good. We had no difficulty determining our position throughout all the facedown phase of powered descent.”*

  The reason for the slight delay in starting PDI was not analyzed by NASA until after the mission: what it involved were very small perturbations in the motion of the lunar module—in engineering terms, small delta-v inputs—that had occurred back at the instant the LM and CSM had separated. Very likely, residual pressure in the tunnel between the two modules had given Eagle a little extra “kick,” a force resulting, some eighty minutes (and over one orbit) later, in a velocity-induced positional error that put Eagle a sizable distance away from where it was supposed to be. Incomplete venting of the tunnel was not considered a serious matter before Apollo 11, but it was afterwards. In all subsequent Apollo missions, Mission Control made sure to double-check the status of the tunnel pressure before approving the LM’s undocking.

  Armstrong had no time to worry that his descent path was taking him a little long, topographically speaking. “It wasn’t a sure thing that we were going to be long because we didn’t know how accurately the markings on the window would turn out be. Anyway, it wasn’t a big deal as to exactly where we were going to set down. There wasn’t going to be any welcoming committee there anyway.”

  His first indication that Eagle might be overflying its landing spot came just as he began to turn the LM into a faceup, feet-forward position. The reason for moving into this unusual position (via a yawing maneuver that took a little more time than expected) was to get the LM’s radar antenna pointing down at the Moon. “We needed to get landing radar into the equation pretty soon because Earth didn’t know how close we were and we didn’t want to get too close to the lunar surface before we got that radar. If we found there was a big difference between where we were and where we were supposed to be, we might have to make some rather wild maneuvers to try and get us back on a proper trajectory, and we wanted to avoid that. So it was a matter of rolling over so that our landing radar was getting contact. It was a Doppler radar that gave three components of velocity and altitude, a pretty unique device.” As it turned out, it was good that the radar was working because it showed an altitude of 33,500 feet, some 2,900 feet lower than what PNGS was indicating because PNGS was programmed into the mean surface height, not the actual height above the surface at any one place.

  Completing the roll, what the crew saw right out in front of them was their home planet in all the rare beauty and security it represented. “We got the Earth right out our front window,” Buzz said to Neil, looking up from the computer. “Sure enough,” was the limit of Neil’s response.

  With a reliable radar reading coming in, Neil prepared for the onboard computer to pitch the LM over so that it would be almost upright. As that happened, he would get a great view of the landmarks down below, leading like roadside signs down what the astronauts (in reference to the main north-south route from New York to Florida pre-dating the 1950s–1960s construction of the Interstate Highway System) had been calling “U.S. Highway 1,” the pathway to the landing site on the Sea of Tranquility.

  It was at that instant—at 04:06:38:22 elapsed time—that a yellow caution light came on and the first of what turned out to be several computer program alarms sounded inside the LM. With only the slightest touch of urgency in his voice, Neil squeezed his comm switch and told Houston: “Program alarm,” adding three seconds later after moving his eyes down to the computer display, “It’s a 1202.” “Give us a reading on the 1202 program alarm,” Neil quickly asked, not knowing which of the dozens of alarms 1202 represented.

  It took Mission Control only fifteen seconds to respond: “We got you…we’re Go on that alarm.” The problem with the computer was not a critical one. Eagle’s descent could continue.

  “We had gone that far and we wanted to land,” Neil asserts. “We didn’t want to practice aborts. We were focusing our attention on doing what was required in order to complete the landing.”

  What caused the 1202 alarm was an overload in the onboard computer incited by the inflow of the just-arriving landing radar data. Fortunately, one of the brilliant young minds in the Houston control room—that belonging to twenty-six-year-old Steve Bales, the GUIDO (pronounced gido, with a long i) or lead specialist in LM navigation and computer software on Flight Director Gene Kranz’s White Team—very quickly determined that the landing would not be jeopardized by the overflow, because the computer had been programmed to recognize landing radar data as being of secondary importance. The computer would ignore that data whenever there were more important computations to make.

  Two more times in the next four minutes, the same computer alarm, 1202, flashed on, the second time just after Armstrong had “throttled down” to reduce his engine thrust for the final approach to landing. At that moment, Eagle was only 3,000 feet above the lunar surface.

  Seven seconds after the third 1202 alarm, the situation grew more intense when a new alarm came on—a 1201.

  It took Mission Control only an instant to realize that the 1201 alarm, like the 1202, was not in itself a dangerous problem.

  The massive international television audience that was tuned in to the coverage of Apollo 11 had no idea what the alarms meant. On CBS, an oblivious Cronkite told his viewers after hearing the crew’s reference to the 1201 alarm, “These are space communications, simply for readout purposes.” Schirra said nothing to correct the newsman.

  One can imagine how sensational the live coverage would have been if on-air commentators such as Cronkite had had an inkling of the alarm call’s significance. Even in the years after Apollo 11, people telling the story of the mission have exaggerated the sounding of the alarms into an urgent life-or-death drama. In a sense, even Aldrin has done this by writing in his 1973 autobiography:

  At six thousand feet above the lunar surface a yellow caution light came on and we encountered one of the few potentially serious problems in the entireflight, a problem which might have caused us to abort, had it not been for a man on the ground [Steve Bales] who really knew his job. When the yellow program alarm light came on, we routinely asked the computer to define its problem. The coded answer it gave was that the machine was overloaded; it was being asked to do too much in too little time. It turned out that the men at MIT, who had designed the landing computer program that interrogated the landing radar, had never talked to the men who designed the rendezvous radar program. The combination overloaded our onboard computer. The problem had never come up in the simulators because we were using special-purpose computers. Back in Houston, not to mention on board the Eagle, hearts shot up into throats while we waited to learn what would happen.

  Armstrong never felt this way about the alarms. For him, they were mainly a distraction that only endangered the landing slightly by prompting him to turn his eyes away from his landmarks. “We were getting good velocities and good altitudes; the principal source of my confidence at that point was the navigation was working fine. There were no anomalies other than the fact that the computer was saying, ‘Hey, I’ve got a problem.’ Everything else was working right and seemed to be calculating fine. There were no anomalies in the information that was being presented, and nothing was jiggling or acting erratic. Everything was very steady and working just like you would expect it to work if the computer were not complaining.

  “My inclination was just to keep going ahead as long as everything looked like it was fine.
There had never been an abort from this situation, and aborting at this point at rather low altitude would not have been a low-risk maneuver. I didn’t want to do that unless I was absolutely out of all other alternatives—and I wasn’t out of alternatives at this point.

  “So going ahead looked like the very best thing to me. But I was listening to the ground because I had great respect for the information and help it could provide. When you get that close, why go put yourself intentionally in what was expected to be a dangerous situation—an abort—just because you had a warning light saying you might have a problem.”

  Armstrong gave no thought at the time as to how worried Aldrin might have been about the alarms. “Buzz was trying to get all the information he could out of the ground and trying to come up with a position that would be helpful,” explains Neil. “I didn’t have a bit of complaint about any of the information he was providing. I am not sure how he felt about it. I don’t know if he had the same confidence level that I did that we should keep going.”

  Neil would have been less distracted by the computer alarms if he had known more about a simulation that had been conducted at Mission Control just a few days before the launch. The mastermind behind the “sim” was Richard Koos, the so-called SimSup, or simulation supervisor, at the Manned Spacecraft Center. A thin guy who wore wire-rimmed glasses, Dick Koos had been with the Army Missile Command at Fort Bliss, Texas, before joining the Space Task Group in 1959. Previously an expert in computer guidance for guided missiles, for Projects Mercury and Gemini Koos became one of Houston’s foremost authorities in the computer simulation of spaceflight missions. For Apollo, it was his job to cook up the most intense training sessions imaginable and put every aspect of the vital relationship between a crew in flight and the ground team at Mission Control through trials by fire.