Editor's Note: This article is part of a series reflecting on the Apollo 11 mission, 50 years later.
Two men were about to land on the moon, and Mission Control in Houston was thrumming with tension. In the science-operations room, Gerald Schaber, a geologist, needed something to do while he waited for the lunar module to touch down. Schaber had come from northern Arizona, where engineers had warped the desert with dynamite to make a cratered landscape where the astronauts could train. His job didn’t start until Neil Armstrong and Buzz Aldrin stepped out of the lunar module and began to explore the slate-colored surface. And the wait was getting to him.
“Our hearts were beating [fast], of course, everybody’s was,” Schaber told me recently. “So I figured I might as well watch theirs.”
Schaber switched his monitor to the channel displaying biomedical data for the astronauts. Armstrong seemed calmer than some of the folks in Mission Control. The commander’s heart was ticking along at 75 beats per minute, a remarkable rate for someone who was about to, you know, land on the moon. An adult’s normal resting heart rate is between 60 to 100 beats per minute. My heart rate right now, writing this story, is 75, according to a fitness tracker.
Schaber wasn’t surprised. Neil Armstrong, everyone knew, was one of the best flyers in the country. This was the pilot who had ejected himself from his damaged fighter jet in the Korean War with so much force he felt “as if all his body parts had been squeezed into the space the size of a bread box.” The astronaut who once managed to right his capsule in space as it spun ferociously, one revolution per second, and his vision blurred from the tumbling. The lunar commander who ejected himself, once more, from a failing lander simulator less than three seconds before it crashed into the ground and was swallowed in flames—just a year before he’d have to fly the real thing.
The steadiness Schaber had seen didn’t last. Armstrong’s heart began to pound. By the time the module touched down, two hours later, his heart rate was 150.
NASA monitored the Apollo 11 crew’s heart rates, along with other physiological signals, from start to finish. The astronauts wore electrocardiogram sensors on their chests, shaved before launch for maximum stickiness. At a glance, an ECG is little more than black squiggles scratched on a page. But the lines and curves are vocabulary. Strung together, they tell the stories of the mission’s ups and downs, the harrowing maneuvers and playful banter, the moments that distressed flight surgeons. They are proof that, for a short time, the human heart beat on another world.
On the morning of July 16, 1969, the Apollo 11 astronauts walked out of their crew quarters at Kennedy Space Center in their spacesuits, their helmets glinting like soap bubbles, and clambered into a white van bound for the launchpad about 15 minutes away. The Saturn V rocket stood waiting, a hulking beanstalk of modules and engines against the clear Florida sky. An elevator delivered them 34 stories up to their spacecraft. The rocket engines growled to life and 7.5 million pounds of thrust hit the ground. Apollo 11 was on its way.
“We have a report on the launch heart rates now from the flight surgeon,” a NASA officer announced to the public, 36 minutes after launch. “Commander Neil Armstrong’s heart rate, 110. Command Module Pilot Michael Collins, 99. Lunar Module Pilot Buzz Aldrin, 88.”
All three men had already launched to space before. NASA put them through extremely rigorous training, including tumbling through a faint-inducing simulator until their bodies learned to not pass out. “Whereas you and I would say, ‘Oh my god, I’m on top of a 300-foot-tall rocket full of liquid hydrogen that could blow us sky-high,’ for them, it’s like, ‘I’m going to work,’” says John Charles, a retired NASA scientist who worked with astronauts and monitored their health.
Seventeen hours after launch, the Apollo crew settled in for their first sleep in space. Mission Control stayed awake and kept watch, monitoring the men’s vitals as their heart rates dipped into the 40s, a sign of deep sleep. The flight surgeons knew the astronauts were awake before they even called in. The crew made some coffee, fired the module’s engines for a few seconds to set their path moonward, and ate salmon salad as Merrilee Rush crooned “Angel of the Morning” on a cassette player. “Hey, you got any medics down there watching heart rate?” Collins asked Mission Control after breakfast. “I’m trying to do some running in place down here, and I'm wondering just out of curiosity whether it brings my heart rate up.”
“We see your heart beating,” replied Charlie Duke, the spacecraft communicator in Houston. “Mike, we see about a 96 heartbeat now.”
Two days later, Mission Control couldn’t see anything. The command module had looped around to the moon’s far side, out of the reach of radio communications. During this period of silence, the module slowed down and slipped into the moon’s orbit before coming back around. In this moment, as the men succumbed to the gravity of another world, Armstrong’s heart rate was 106, Aldrin’s 70, and Collins’s a cool 66.
The crew would loop around the moon a dozen more times before one spacecraft became two. Collins stayed in the Columbia module, their living quarters, while Armstrong and Aldrin clambered into the Eagle module and boosted it toward the ground. As they descended, the faint tug of the moon’s gravity greeted them. “Their arms sagged. Legs settled within their suits. Their feet pressed downward in their boots as they yielded to their down-rushing speed,” wrote Jay Barbree, a longtime space journalist and Armstrong confidant, in a biography of the astronaut, who died in 2012.
Then an alarm blared; the Eagle’s computers were overloaded with signals. Mission Control told Armstrong to ignore it and keep going. Armstrong could see enough of the jagged terrain through his window to know that they had overshot their target by four miles. They needed a smooth, flat place to land, and the Eagle was now headed toward a crater filled with boulders instead. It was time to shut off the autopilot. Armstrong took control of the Eagle, and manually scooted the module away from the crater. The module was still airborne when the low-fuel light started flashing. (Another propulsion system would launch the astronauts back off the moon.)
Armstrong later said he wasn’t worried about the fuel. They were close enough then that if the engine cut off, the moon’s gentle gravity, one-sixth that of Earth’s, would let them coast safely down. But the descent must have been some adrenaline rush to push the lunar commander’s heart rate to 150. Armstrong’s pulse began to climb after he turned off the autopilot and took the controls in his gloved grip. The fate of the mission was, quite literally, in his hands. Tens of thousands of engineers had helped get him here, but this last bit was up to him. That kind of responsibility would quicken anyone’s pulse.
“Okay. I’m going to step off the LM now.”
Armstrong was outside the module, hovering between a ladder rung and history. As his foot pressed into the lunar regolith, his heart thumped at 125 beats per minute.
The two astronauts bounced along on the surface, setting up science experiments and collecting rocks for geologists like Gerald Schaber, who by this time was tracking the men’s movements in the grainy black-and-white footage at Mission Control. The moon made movement so easy that Armstrong and Aldrin didn’t stop to rest. “At no time during the exercise was there any heavy breathing,” according to a NASA mission report. “For the most part, the astronauts’ heartbeat was lower than expected—lower, in some cases, than that of those at Mission Control who were watching.”
But as the astronauts neared the end of their outing, Armstrong’s heart rate shot to 160. He was loading boxes stuffed with rocks into the module using a pulley system NASA had devised, and it required some effort. Armstrong would hook each box onto a fabric loop and then pull it, hand over hand, until the cargo bounced up to the top of the spacecraft, where Aldrin was waiting. “Neil, this is Houston,” Mission Control piped up, before asking him for an update on his life-support-system stats. They didn’t really need them; they just wanted Armstrong to slow down.
Back in the Eagle, Armstrong and Aldrin had trouble sleeping, and Mission Control could tell long after they’d said good night. Armstrong’s heart rate dipped into the 50s only occasionally before coming back up, suggesting he merely dozed. The module, he would later say, was noisy, cold, and too illuminated even with the shades down. He was wired from the events of the day. Just when he got comfortable, Armstrong realized there was something shining right in his eyes, “just like a light bulb.” It turned out to be the Earth gleaming through the module’s telescope.
The next day, the Eagle launched back into orbit and synced up with Columbia for the return to Earth. Two days from home, a flight surgeon saw something that made him jump out of his chair. Aldrin’s heart rate had risen, incredibly, to 247 beats per minute. “The surgeon is about to die,” Duke told the crew with a laugh. It was just an error; the adhesive paste underneath Aldrin’s sensors had dried out, according to the mission report. “Well, I can assure you my heart’s still working,” Aldrin told Duke.
The Apollo 11 mission transcripts are sprinkled with jokes and light ribbing between the crew and Mission Control, even in the midst of stressful moments. But this one felt especially buoyant. The hardest parts were over now, and the men were almost home safe. The sensors had done their jobs. They’d captured the scares and the spunk, the frenzied maneuvers and relaxed breaks, calling home when the slumbering astronauts couldn’t. Soon, everyone could, at last, rest easy.