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Neil Armstrong by the numbers: Tracing the small steps to the moon


Fall 2019 | By Jaehyeok Kim, Class of 2020. Photo by Neil A. Armstrong Collection, Courtesy of Purdue University Libraries, Karnes Archives and Special Collections.


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On July 20, 1969, two valiant men from the Earth visited our closest planetary neighbor and set their feet on the Moon. As Neil Armstrong proclaimed, in his famous first words on the surface, “That's one small step for a man, one giant leap for mankind.” The media celebrated Armstrong and his crew members as conquerors. They praised him, the captain of the mission, as the ultimate hero, a symbol of mankind's glory in the “giant leap.” Yet we also ought to remember Armstrong’s many “small steps” that prepared him to explore space, to pilot a spacecraft, and to fulfill a mission. The two primary instruments of the entire Apollo 11 mission, Armstrong as astronaut and the Lunar Module (LM) he piloted, formed a strong human-machine complex. Each interacted with the other through their journey. Armstrong represented the ultimate human element of the Apollo project. He was at the pinnacle of Apollo’s hierarchies of numbers and functions, stages and modules. And as I explore here, by the measure of his own heartbeat, he helped achieve the Apollo 11 mission’s success.    

The project really began with President John F. Kennedy’s speech on 25 May, 1961, announcing the project of landing a man on the moon, a milestone in the history of science and engineering. David Mindell has defined Apollo 11, quite simply, as “a test flight whose major goal was simply to prove the feasibility of lunar landing with the Apollo system.”[i] But achieving the goal was not easy. The average distance between the Moon and the Earth is 238,855 miles. It took 103 hours, 45 minutes and 7 seconds for Apollo 11 to reach lunar orbit from low earth orbit.[ii] The distance forced NASA to develop a propulsion system to carry supplies, ranging from basic life support elements to research equipment, all the way to the lunar surface. Hence the Saturn V rocket. Out of a total height of 363 feet, the first stage, S-IC, with five F-1 engines produced 1,522,000 pounds of thrust each. The second stage, S-II, had five J-2 engines that produced 228,000 pounds of thrust each. And lastly third stage, the S-IVB, had a single J-2 engine that produced 203,000 pounds of thrust.[iii]

The system was unprecedented in both concept and scope. Glynn Lunney, the Apollo Flight Director, remembered how he “was overwhelmed at the magnitude of it. I mean, we were struggling with Mercury spacecraft that weighed 2,000 or 2,500 pounds. [Now] we were talking about spacecraft that would be 10 or 20 times bigger.”[iv] Humanity had never created such a vast machinery like the Saturn V. In the end, NASA produced 13 of them to deliver missions and crews to the moon. Gene Kranz vividly remembered the launch of Apollo 11 on July 16, 1969. The Kennedy Space Center was very different from any ordinary day of past. The atmosphere in the Mission Control Center (MCC) was tense and heavy. Wrote Kranz, “the pressure I feel asserts itself through nervous kidneys, until commitment of the final GO.” One colleague even had to warn him, in a mock serious voice, “if you don’t settle down, I’m going to have to ask you to leave the room. You’re making me nervous.” MCC engineers were monitoring dozens of screens displaying thousands of functions and numbers, yet their attention was focused on one object: the Saturn V. As the giant white rocket lifted off, against a backdrop of grey cement and orange launch trusses, Dave Reed shouted, “Go, Flight. We are Go!” Kranz responded: “There is no turning back.”[v] 

Like the Apollo missions before and afterward, Apollo 11 reached the moon by way of Lunar Orbit Rendezvous. Through a series of elaborate rendezvouses and dockings, the Command and Service Module (CSM) attached and detached with the LM: on the way to, around, and back home from the moon. The key to this approach was the LM. It had to be light enough to fulfill the weight-carrying limitations of the Saturn V rocket. Hence, the primary focus on designing the LM was to reduce its weight as much as possible. Wrote Norman Mailer, after all, it “was a craft to carry two men in a minimum of space with the maximum fuel.”[vi] The LM also had to be innovative and sophisticated enough to land on the small planetoid of the Moon, with only one-sixth the gravity of Earth, and no atmosphere. As a result, engineers had to design a vehicle to descend to and ascend from the lunar surface without air (or lift and drag). Engineers originally designed it as a sphere, streamlined and aerodynamic, then gradually cut away at its edges to suppress weight of the vehicle. The LM was the first such vehicle to operate in an airless environment, whose reaction forces were the sole source of acceleration.

The guidance and control functions of the craft were centered on the Apollo Guidance Computer, connected by remote controls to the MCC back in Houston and to the propulsion systems of the craft for automated flight, but also through the procedural commands and electrical signals of the pilot, Armstrong. This was an elaborate system of human-machine interaction to execute orders and properly operate the LM, all in order to fulfill the lunar goal. Such a human-machine system was quite common in the era of the Cold War. In fact, it was one of the essential aerospace design trends, applied to a variety of military aircraft. The F-104 Starfighter, for example, designed to intercept Soviet bombers within strict parameters, allowed only a minimum degree of freedom for pilots to control the aircraft. Experimental aircraft like the X-1B and X-15, on the other hand, were unstable and untested, and therefore allowed test pilots fuller autonomy to conduct experiments and learn the full capabilities of the aircraft. Armstrong flew both kinds of planes, but was most familiar with the freer controls of the experimental craft.

Armstrong was an excellent pilot. According to historical sources in the Purdue Archives, he flew over the 50,000 feet altitude at least twelve times, nearly reaching the top of troposphere. He flew jet aircraft a total number of at least 1,000 hours. He flew civilian craft, fighters, transports, and experimental aircrafts.[vii] As a member of the High Speed Flight Station of the National Advisory Committee for Aeronautics, in both simulator and real flights, he mastered the X-15, the world’s highest and fastest flying test aircraft. He even once saved a B-29 bomber when he was a test pilot at Edward Air Force Base. Awaiting an airborne launch under the B-29, a Skyrocket craft accidentally exploded, severely damaging three out of the bomber’s four engines. Yet Armstrong saved both the bomber and the crew.[viii]  In 1962, as he was preparing to become an astronaut, Armstrong summarized these various exploits on a small data-entry card that fit into the palm of his hand.  [Image 1]

Both Armstrong and Buzz Aldrin became the consummate explorers as they entered the LM in lunar orbit, now detached from the CSM, and descending on its ways to the moon’s surface. They were also part and parcel of the LM as a machine, switchboard operators of a kind to monitor and pass on accurate commands to the guidance computer. But Armstrong’s experiences also made him something more: a pilot to control the flight in any extreme or emergency conditions. He was the crucial part of the human-machine complex that was the LM, and on a historic mission that was literally going where no human had gone before. Nothing represents this better than the actual descent of the LM on the historic mission, as the guidance computer controlled the fuel consumption, as recorded by the instrument readings; and Armstrong controlled the guidance computer and landing, as recorded by his heartbeat.

At 102 hours and 23 minutes after the Saturn V’s launch, NASA control sent the LM crew its own command to “GO.” The crew initiated their twelve-minute powered descent under automatic control. Unfortunately, none of it was easy. At 40,000 feet altitude, the computer 1202 error alarm went off, meaning there were too many commands running, an executive overflow. The primary and abort guide system also sounded alarms five times during the descent for the same reason: computing overloads, all a result of the lack of computing power in these early years. When the alarms popped up (between 102:38 and 102:40 into the mission time’s hours and minutes), Armstrong’s heartbeat spiked temporarily but then settled as MCC delivered the order to ignore the error and continue on-course.[ix]

As he and Aldrin approached the lunar surface at about 410 feet altitude, after realizing the original landing site was unreachable, Armstrong took control of the LM for final approach, looking for a smooth plateau upon which to land. He did so without hesitation. The guidance computer immediately accepted Armstrong as its new partner. Computing loads were also lightened, hence the alarms disappeared. The trouble was that the engine of the descent module was constantly burning its fuel to decrease the speed of the vessel. Meanwhile, Armstrong controlled the LM down to the surface, constantly increasing the thrust to compensate for the acceleration on the vehicle. The fuel left at landing was at a critical level: at a thrust level of 25% of maximum thrust, the LM had enough fuel to activate her engine for another 41 more seconds before touchdown. This may not seem like a lot, but it was. Armstrong mentioned this perilous moment for LIFE magazine: “The gauges were registering close to empty and we actually were quite close to a mandatory abort.”[x]

He only had one chance, yet Armstrong did it. He decided to choose a new landing site and precisely brought the craft to the target location, using a limited amount of fuel in the most efficient way possible, by calculating the optimal trajectory in his mind. He did not do this all on his own. He received help from the onboard computer and instruments on the LM, receiving and processing the input data and passing output back to other machines. Yet this proves all the more his central and integral role in the human-machine complex: a human receiving information from the machine to control the other machinery and bring success to the mission. In fact, of all the Apollo moon landings, Armstrong’s was the most precise and coordinated: bringing the LM exactly down to the surface, at the rate of about one foot per second, reflecting a supreme confidence in his ability to bridge distance in time.[xi]

Armstrong’s humanity stands out through all of this.  He was part of the machine, but always human. From the start, his heart rate never went below 100 beats per second, the average for a normal human. But it did rise dramatically as he and Aldrin and the LM descended to the surface, forming an inverse relationship between his human body and the engine’s thrust. Armstrong’s heartbeat spiked up to 120 beats per minute at 2,000 feet and soon rose to 145 beats per minute at 1,000 feet. These sudden jumps in his heartrate matched exactly when the error codes occurred. Despite all his training and experience, his body still reacted. The heartbeats either reduced or returned to their original state, as when the MCC ordered Armstrong to ignore the error codes and continue to descent.

But then his heart beat continued to rise with a new alarm, about 11 minutes into the descent (102:42 in mission time), with the Low Fuel Quantity Light. Despite the intense situation, Armstrong stayed outwardly calm. As he remembered, the indicators were a “distraction that only endangered the landing slightly by prompting him to turn his eyes away from his landmarks.” He may have been worried, but only about the distraction, not about any impending failure. “We were getting good velocities and good altitudes; the principal source of my confidence at that point was the navigation was working fine.” After the “Low Fuel” alarm turned on, the LM passed 160 feet above the lunar surface. With 5% of fuel left or 20 seconds before depletion at the current descent rate, Armstrong had to decide to both save his life and the mission. “We were very aware of the fuel situation. We heard Charlie make the bingo call and we had the quantity light go on in the cockpit, but we were past both of those. I knew we were pretty low by this time. But below one hundred feet was not a time you would want to abort.” With the desire to succeed in the mission and his skill combined, Armstrong landed safely.[xii]

Armstrong’s heartbeat reached its peak at 150 beats per minute about 12 minutes after the descent (102:45 in mission time). This was exactly when he took control of the vehicle to find a new landing site. Surprisingly enough, at this point his heartbeat stayed constant. With confidence, Armstrong controlled the LM and brought her down to the surface. The heartrate only began to decrease a full 1 minute after the landing was completed, and finally stabilized after the MCC announced “GO” for stay. Until this order was given, he stayed sharp and ready, always focused on the task. “We were not concerned with safety, specifically, in these preparations. We were concerned with mission success, with the accomplishment of what we set out to do” said Armstrong in Life.  [Image 2]

How did he do it?  And what did the higher heartrate mean? The official NASA medical judgement, from the mission report, held that it was “indicative of an increased work load and body heat storage.”  But Armstrong’s experience as an X-15 pilot offers another clue. Dr. James Roman’s medical tests in 1965, focused on his physiological readings of special tests of pilots during their flights in high-performance aircraft, found that their heart rates reached 170 beats per minute or even higher. But his conclusion was rather stunning: that the higher rates were more a function of how they took on command responsibility and control rather than nervousness or worry. They happened when the pilots were taking command of their vehicles, despite their calm and confident appearance.[xiii] Armstrong’s higher heartbeat was evidence of this phenomenon. It increased with the error codes and fuel-consumption issues, when the LM was under the control of the guidance computer. But it maintained or decreased dramatically when he took control of the vehicle, at the decisive moment of success, when he became the LM’s command pilot.

Armstrong’s achievement came from many years and many small steps of experience and practice. This included time at work in simulators to practice LM controls during rendezvous, docking, and landing. It included 30 flights in the practice Lunar-Landing Training Vehicle at Ellington Air Force Base. The repeated training taught him to remain outwardly calm, even with higher heartbeats, to avoid surprise or confusion with unexpected events. These experiences taught him to “think like a machine,” to practice processing direct orders from MCC without hesitation and error. In a recent talk at Purdue University, Space Shuttle astronaut, Jerry Ross, highlighted Armstrong’s “comfortable familiarity” with his piloting skills.  “Armstrong was natural at becoming part of the machine,” said Ross. He could “make a plane dance.” Expert pilots like Armstrong became a part of their aircraft, pulling at its maximum capability and pushing its limits, using their training and instincts to improvise their own decisions at critical moments.[xiv]

Armstrong’s story, like the stories of all the Apollo crews and missions, have become the stuff of legend. The Saturn V, the CSM, and the LM, remain icons of modern technology and the “Space Age.” Many young scientists and engineers, including myself, were inspired by the Apollo Project. But we ought not to forget the human equation in the human-machine complex of the Apollo systems. Machines made this all work, but so did the piloting training and experiences of veterans like Armstrong: astronauts with heart.  [Image 3]

[i]  David Mindell, Digital Apollo: Human and Machine in Spaceflight (Cambridge: MIT Press, 2008), chapter 9.

[ii]  Richard Orloff, Apollo by the Numbers: A Statistical Reference (Washington, D.C.: National Aeronautics and Space Administration, 2000), 103-104.

[iii] George C. Marshall Space Flight Center, “Saturn V Flight Manual SA 506,” June 12, 1969, Box 40, Folder 7, Neil A. Armstrong Papers, Purdue University Archives and Special Collections.

[iv] Mark Betancourt, “We Built the Saturn V – Memories of a Giant-in-Progress,” Air & Space Magazine (October, 2017), online.

[v] Gene Kranz, Failure is Not an Option: Mission Control from Mercury to Apollo 13 and Beyond (New York: Simon & Schuster, 2000), 272.

[vi] Norman Mailer, Of a Fire on the Moon (New York: Random House, 2014), 301. Also see Courtney G. Brooks, James M. Grimwood, and Lloyd S. Swenson, Chariots for Apollo: A History of Manned Lunar Spacecraft (Washington, D.C.: NASA, 1979), chapter 12.

[vii] Special Aviation History Card, Box 75, Folder 3, Armstrong Papers.

[viii] Neil Armstrong Speech at Udvar-Hazy Center, Box 178, Folder 2, Armstrong Papers.

[ix] National Aeronautics and Space Administration, “Apollo 11 Mission Report (November 1969), Box 75 Folder 10, Armstrong Papers. Thomas Kelly, Moon Lander, How we Developed the Apollo Lunar Module (Washington, D.C.: Smithsonian Press, 2001), 211.

[x] Neil Armstrong, “The Moon had been awaiting us a Long Time,” Life (August 22, 1969): 24 – 25.

[xi] Keynote Address by Michael D. Griffin, former director of NASA, and currently Under Secretary of Defense for Research and Engineering, at the “Apollo in the Archives” Exhibit, Purdue University Archives (April 5, 2019). Or as Dr. Griffin remembered Armstrong saying: “I can do a lot in thirty seconds.”

[xii] James Hansen, First Man: The Life of Neil A. Armstrong (New York: Simon & Schuster, 2005), 460-471.

[xiii] Heather M. David, “Command Pilots’ Hearts Beat Faster,” Missiles and Rockets (July 5, 1965): 28.

[xiv] Jaehyeok Kim interview with Jerry and Karen Ross, Purdue Archives Reading Room, November 27, 2018.

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