Apollo 11 Aimed for the Moon While the World Watched

By James Donovan
NASA

The unknowns were rampant. 

— Neil Armstrong

“APOLLO 11. APOLLO 11. Good morning from the Black team.”

It was six a.m. Michael Collins, loosely belted and floating over the left seat with his headset on, took a while to wake up. “Good morning, Houston… you guys wake up early.”

“It looks like you guys were really sawing them away,” said CapCom Ron Evans.

A few minutes later, the spacecraft disappeared around the moon’s left side for the ninth time. None of them had slept long—six hours at most. Buzz Aldrin had had a fitful night, but the other two had slept soundly. All three ate breakfast. In Mission Control, when Evans saw their craft reappear around the right edge of the moon, he read them the day’s headlines. He reported that Miss Philippines had won the Miss Universe crown the night before, that congregations in churches around the world were including the Apollo 11 crew in their prayers, and that the Russian Luna probe was still circling the moon, though its purpose remained a mystery and its orbit far from theirs. After the crew heard the latest updates on their families, it was time to get down to business. 

In Mission Control, there was about to be a changing of the guard. Glynn Lunney’s Black team had been there most of the night while the crew slept, and they were about to hand over the console to Gene Kranz’s White team. They wouldn’t go far—Black was also the ascent team and had to be present during the descent in case of an emergency liftoff, so most of them would stick around, sitting in chairs behind their replacements. The two teams compared notes, and the White team began computing numbers for the upcoming maneuvers.

Kranz arrived carrying two bags. Others in NASA, especially the younger flight controllers, had let their hair grow out, but not him; he still sported a crew cut. His sharp features and intense gaze gave his face the look of a bird of prey. The larger bag held his lunch, several snacks, and candy bars—he liked to eat his way through a shift. In the other bag was his new mission vest, made by his wife, Marta—a tradition started back in Gemini. Each one was slightly different and always a surprise for the controllers. This one, which he called his landing vest—the first—was white-and-silver brocade. Kranz made his way to his console on the second row—there were four rows in all, with preassigned consoles—and put the food in a drawer and his vest on. When Chris Kraft walked in and passed by Kranz, he patted him on the shoulder and said, “Good luck, young man.” He took a seat on the level above, management row, where he was soon joined by most of NASA’s top brass: Bob Gilruth, Robert Seamans, George Low, and Sam Phillips. Kraft and Low had determined that the overall probability of success for the entire mission was roughly 56 percent. Now Low turned to him and said, “I’ve never seen this place so tense.”

A Brief History of the Apollo Mission (Photos)

The glass-fronted viewing room overlooking the MOCR seated 74.  On this occasion, there were many more than that standing in the aisles, on the sides, on the steps. The  gathering was an illustrious collection of NASA officials and other dignitaries, among them Wernher von Braun, Eberhard Rees,  Kurt Debus, Rocco Petrone, John Houbolt, Thomas Paine, Bill Tindall, Guy Thibodaux, and several astronauts, including the first American in orbit, John Glenn. On the right side of the MOCR  was the simulation-control area, where instructors lined the windows to watch. In staff support rooms throughout the building, systems experts and contractor representatives sat, ready to aid in any way they could.

As Kranz settled in at his console, he looked up into the viewing room and saw Tindall there. He waved him down into the MOCR. Tindall declined, but Kranz insisted. If anyone deserved to be there, it was Tindall; he had been instrumental in making this moment a reality. Tindall made his way in and Kranz cleared off a chair right next to him.

The evening before, after their short four-hour shift had ended at about nine, Steve Bales, Jay Greene, and a couple of other controllers on the descent team had gone out to Perusina’s, a good steak house on the Gulf Freeway in Dickinson. They’d returned to the Mission Control Center building and gone to sleep in the controller dormitory above the MOCR. It was large enough to sleep 20 and had its own showers. Bales had woken up refreshed, eaten at the temporary cafeteria set up in the lounge next door, and walked into the MOCR at 7:30 a.m. feeling good. It would be eight hours before the landing attempt, and he had a roomful of computer experts, including Jack Garman, standing by in a staff support room down the hall as well as a bunch of MIT engineers, the men who had created the computer, sitting in a Cambridge, Massachusetts, classroom listening in on a dedicated line. Every flight controller had a similar support network.

But Bales’s good mood was short-lived. As his team began their shift, the pressure they felt was evident. No one was smiling. He took his seat at the far right on the bottom row, near the rear-projected screens in front, with the rest of the flight dynamics team.

At his right sat Granville Paules, a tall, blond guidance officer who would support Bales on the guidance systems, including the on-board computer.  To their left was flight guidance officer (FIDO) Jay Greene, a pipe-smoker from Brooklyn, who would handle trajectory—where the spacecraft was and where it was going. He was not shy in making his opinions known. To his left, retrofire officer (RETRO) Chuck Deiterich, a native Texan, would manage its return, whether nominal or an emergency; he would be ready with possible abort options if necessary. Like most members of the Trench, he had an attitude that said, We’re the guys really running the show—the rest of you are just plumbers. These men thought of themselves as astronauts on the ground, the ones who really did the job of running the spacecraft.

In the next row up were the flight systems controllers. Right behind Bales, on the last console on the right, was dry, imperturbable Bob Carlton, the veteran controller in charge of the LM’s guidance, navigation, and control. At 39, he was considered the old man of the group; the average age of the rest of the White team was 26. They called him the Silver Fox, for his gray hair. On the extreme left side of the row sat the flight surgeon. Next to him was the CapCom, astronaut Charlie Duke, who spoke with a light southern drawl. He hadn’t been assigned to a flight yet, but he’d done such a good job in the same role for Apollo 10 that Neil Armstrong had requested him for the descent. Duke knew the LM propulsion systems well, and that wouldn’t hurt. His job was important, and difficult, for he would have to sort through several voice loops to get the information the astronauts would need and then deliver it to them on the ground-to-air loop—the only one they would communicate on. Jim Lovell and Fred Haise sat on his left, and behind Duke was Deke Slayton, drawing on a cigarillo. Pete Conrad and Dave Scott, preparing for Apollo 12, sat nearby. Three other systems controllers sat between the CapCom and Carlton.

At about 7:45 a.m., Kranz and his controllers donned their headsets, plugged into their consoles, and began punching up various controllers’ voice loops to monitor; depressing a foot switch or activating a control on a headset would allow them to speak on a loop. Most of them were smokers—cigarettes, cigarillos, or pipes—and one of their first orders of business was to empty the amber ashtrays, still full from the evening before, and light up.

Some members of the Black team left, wishing the White team good luck on their way out. John Hodge, the former flight director who had overseen Neil Armstrong and Dave Scott’s Gemini 8 near catastrophe three years before and then moved into management, stopped to talk to Kranz.

Apollo 11 was still completing an orbit of the moon every two hours. In the command module, all three suited up—Armstrong and Aldrin in their liquid-cooled undergarments that would keep their temperature  down on the hot lunar surface, Collins in his own suit—and then attended to various housekeeping chores. After that, Aldrin pulled himself through the tunnel and did more systems checks to Eagle while Armstrong, with Collins’s help, struggled into his EVA suit in the navigation bay. Then Aldrin and Armstrong switched places, and Aldrin put on his suit. It took each man a half an hour to fully suit up, with their helmets and gloves locked into place, though fortunately their suits were only half pressurized for now, so they weren’t as stiff as usual. About 9:30 a.m., Armstrong entered the Lunar Module (LM). Once Collins had reinstalled the LM drogue and the command-module probe, Armstrong sealed the upper hatch. 

An hour later, Duke said, “Apollo 11, Houston. We’re go for undocking.”

Three  minutes later,  Columbia, the command-service module, and Eagle, the lunar module, disappeared around the moon. When they reappeared at the right edge of the large map of the moon on a front screen in Mission Control, there would be two radar dots, not one. Kranz told his team to take five, and there was a mad rush to the restroom. It would be the last break before descent.

When everyone returned, Kranz directed his flight controllers to a private communications loop.

“We are about to make history,” he told them. “We have trained and prepared for this moment and we are ready. But I want you to know this—whatever happens when we walk out of this room, we walk out together as a team.” Then he switched back to the flight director’s loop, ordered the doors to the MOCR locked until the landing attempt was over, and lit up another Kent.

 “You cats take it easy on the lunar surface,” said Collins on the other side of the moon. “If I hear you huffing and puffing, I’m going to start bitching at you.” He was as aware as anyone of how strenuous an EVA could be—and how dangerous.

“Okay, Mike,” said Aldrin.

Collins retracted the probe, vented the air in the tunnel connecting the two spacecraft, and, at 12:46 p.m., threw a switch that opened the capture latches. The release of the remaining air in the tunnel caused the two vehicles to gradually drift 50 feet apart. Armstrong maneuvered with his thrusters to regain the precise orbital parameters. Then he detonated explosive bolts that released Eagle’s spring-loaded landing gear. There was a shudder and a click as the four legs, including the spindly, 67-inch landing probes extending from three of them, swung out and locked into place.

They flew formation together—station-keeping—as Armstrong rotated Eagle one full revolution so that Collins in Columbia could inspect it for damage and make sure the legs and probes were in position. The 23-foot-high LM consisted of two parts. The descent stage was essentially four large fuel tanks and a gimballed rocket engine encased in an octagonal metal chassis with four legs sprouting from it. Above that was the ascent stage, a hodgepodge of tanks, boxes, antennas, and radar surrounding a pressurized cabin just large enough for two astronauts in spacesuits, with another rocket engine underneath it. The cabin’s walls were an aluminum alloy skin, about twelve-thousandths of an inch thick—the width of three layers of tinfoil. Most of the bottom half and the four slender legs were wrapped with gold Mylar insulation, and the top half was black, silver, and gray. It might have been mistaken for a large alien insect from another galaxy.

Collins made sure the landing gear was down and locked. A few minutes later, he said, “I think you’ve got a fine-looking flying machine there, Eagle, despite the fact that you’re upside down.”

“Somebody’s upside down,” Armstrong said. 

“There you go... you guys take care.”

“See you later,” Armstrong said, as if he and Aldrin were going out to get a bite to eat and would be back soon.

So far, things had gone as planned. Collins fired the service-module engine to move two miles away. In Eagle, more system activations and reviews followed; they checked on their spacesuits, the guidance system, the control thrusters, the descent propulsion system, and its helium fuel. The radio signal was weak and staticky, and the air-to-ground from Eagle was dropping out, so they adjusted the antennas to improve it. Though the rendezvous radar wouldn’t be needed for the descent, they powered it up so it would be ready in case they had to make a quick abort.

There were no seats in the LM, so both men stood shoulder to shoulder in the cramped, gray-painted cabin. Armstrong was on the left and Aldrin on the right, their boots secured and waists tethered, an array of controls, gauges, switches, and displays before them. Each man had a hand controller on either side of him, at waist level, and a small, upside-down triangular window 16 inches in front of his face.

In Mission Control, 15 minutes after separation, a radar dot appeared on the right side of the large moon map. It was Columbia, in a higher orbit now than Eagle and visible first.

A few minutes later,  Eagle emerged from behind the moon, moving at about four thousand miles an hour, and reestablished radio contact.

“How does it look, Neil?” said Duke.

“The Eagle has wings,” Armstrong said.

After Kranz polled his controllers, Duke said, “You’re go for DOI”—descent-orbit insertion. Seven minutes later,  Eagle disappeared behind the moon’s left side again, followed by Columbia. Both would be out of contact until they reappeared 30 minutes later.

In the middle of Eagle’s passage across the far side, Armstrong maneuvered the LM so that its rocket engine was aimed forward, in the direction it was traveling. That meant he and Aldrin were looking down, so they could track their progress by landmarks they had studied for months. He fired the descent engine just about opposite the landing area on the near side. The burn, like the others, had to be precise, twenty-eight and a half seconds; a few seconds too long could cause the LM to crash into the moon. This one went perfectly and slowed Eagle enough to allow the moon’s gravity to pull it down to fifty thousand feet. Columbia remained 60 miles above them and behind. Armstrong and Aldrin could feel a slight gravitational pull—maybe a third of a g. The glycol pumps circulating coolant were loud and constant.

The  altitude of fifty thousand feet was not arbitrarily chosen. Since the moon has no atmosphere and little gravity, an orbit could theoretically be set for any altitude, as close to the ground as possible—but that was theoretically. An orbit was never perfectly circular, and the moon was not a perfect, smooth sphere; lunar terrain altitudes could vary by twenty thousand feet or so, and uncertainties in the guidance system by another fifteen thousand. To be on the safe side, fifty thousand feet had been chosen for the LM’s beginning orbit altitude.

From that altitude, the descent to the lunar surface 260 miles downrange — powered-descent initiative (PDI)—was planned to take 12 minutes. The braking phase would come first, a steady burn of eight and a half minutes to drop them down to about seven thousand feet and slow them to four hundred miles per hour while covering all but four and a half miles. Then  the short final approach of one minute and forty seconds would begin, during which they would travel the remaining distance, drop to five hundred feet, and further slow their speed, to about twenty miles per hour. The last minute or so, mostly a vertical drop to the surface two thousand feet downrange, would be the landing phase. The onboard computer was programmed to land the LM, but the crew could take control at any time. It was expected that Armstrong would assume control as Eagle came within a few hundred feet of the surface.

Collins in Columbia came around the left edge of the moon first. He had been visually monitoring Eagle continually since separation in case there was an emergency.

“How did it go?” said Duke, the CapCom in Mission Control. 

“Listen,  babe. Everything’s going swimmingly. Beautiful,” Collins said. It was the first report of the LM burn. 

“Great. We’re standing by for Eagle,” said Duke. 

“OK. He’s coming along.”

Two minutes later,  Eagle acquired signal—16 minutes to PDI. In Mission Control, telemetry began to pour in, and flight controllers scanned through the constantly moving green numbers on their CRT screens to make sure it was safe to begin powered de-scent. Tindall scooted his chair closer to Kranz. The flight director realized his palms were sweating, but he said to his crew, “We’re off to a good start. Play it cool.”

Slayton, sitting next to Duke, told the astronauts hanging around the CapCom  station to find other consoles for the rest of the flight—it was too crowded, and Duke didn’t need any distractions. Conrad moved down next to Greene at the FIDO console in the first row and plugged in his headset. Scott sat on a step over on the left.

As Eagle came into view and radio communications were restored, Aldrin confirmed a quality burn. A minute later, the signal was lost, and both voice and telemetry were glitchy. Eagle’s high-gain antenna must have been pointed toward Earth, but it was out of position, and the spacecraft itself was interfering. As Eagle descended, the LM system back room scrambled to find an alternate antenna. Without the exact altitude, Mission Control would be unable to precisely compute the descent engine ignition point.

Communications improved briefly, just enough for the LM crew to provide the data. Duke struggled to maintain radio contact and suggested Armstrong change Eagle’s attitude slightly to improve reception but couldn’t tell if Eagle had received his suggestion. Some telemetry data managed to get through, just enough for Kranz to decide to go forward—to try a landing. He polled his team for PDI, five minutes away. Each one responded with a “Go.” 

“You’re go for powered descent,” Duke said, but he was unable to speak directly to Eagle, so he relayed the go order through Collins in Columbia, 55 miles above his crewmates. The signal was lost again, then reacquired after Eagle made the change Duke had suggested.

The landing radar locked onto the surface and began transmitting info, and Bales knew right away that something was wrong.

“Flight,” Bales said, “we’re out on our radial velocity—we’re halfway to our abort limits. I don’t know what’s caused it, but I’m going to keep watching it.” (Bales would later find out that the tunnel’s unvented air had combined with thruster burns and other variables to add a bit of movement to Eagle at undocking and increased its velocity—“like popping a cork,” as Kranz would put it later—just enough to make a difference down the flight path.) Bales was worried, and with good reason—what if it was a guidance- system problem? It might get worse. His nightmare might even happen—he would have to call an abort. He had quit smoking a few months ago after an X-ray had shown a shadow in his lung, and now he fleetingly wished he hadn’t.

But after 30 seconds, he determined that it wasn’t a guidance-system issue but a navigation problem. It was holding steady, though that meant a new problem: Eagle would be landing about three miles farther down range than planned. But at least he wouldn’t have to call an abort.

Bales relaxed a bit. It looked like his problem was over. He turned to Greene on his left, busy recomputing potential abort modes, and said, “We’re in great shape.”

Four minutes later, at 4:05 p.m., Eagle’s descent engine roared to life at 10 percent power for 26 seconds to settle the fuel in the tanks, then powered up close to full throttle. Facedown and feet forward, the two astronauts could feel the brake through their boots as their speed and their altitude began decreasing.  While Aldrin kept his eyes glued to the computer display and the other gauges, Armstrong watched the features below as they sped over the brownish-gray lunar surface—craters, hills, ridges, and cracks, their long shadows stretching westward before the rising sun. When they passed one called Boot Hill, he said, “Our position checks downrange show us to be a little long.” That  corroborated what Bales had told Kranz.

“We confirm that,” Bales said.

“Rog,” said Kranz. The far western end of the targeted landing area, he knew, was rougher terrain. Landing would be more difficult for the fragile LM.

A minute later, he went around the room polling on whether to continue powered descent. When he got to his guidance officer, Bales shouted, “Go!”

Kranz chuckled, but it relieved some of the tension. Duke said, “You are go to continue powered descent.”

At forty thousand feet, there was lots of static on the radio as Armstrong used his right-hand controller to roll over to windows-up, the astronauts’ feet still forward. The Earth came into view, and the landing radar antenna, now pointing down at the moon, began acquiring the velocity and altitude the computer needed to calculate rate of descent. As it continued to descend, Eagle swayed left and right every few seconds as the engine’s fuel sloshed back and forth.

Five seconds later, a warbling alarm sounded in their headsets, and both Armstrong and Aldrin looked down at the computer display between them to see a yellow caution light.

“Program alarm,” Armstrong said with some urgency, and Aldrin punched in a command to ask the computer to define the problem. They both looked down and saw 1202 on the digital readout.

“It’s a twelve-oh-two,” said Armstrong. He and Aldrin looked at each other. Neither of them had heard of this alarm. They could probably find it in the book they’d brought along, but neither of them had a spare second for that. They were trying to land a strange spacecraft that had never landed before on an alien world no human had ever touched, and in a low-gravity vacuum. Was the computer going to die on them?

Duke,  flustered, said,  “Twelve—twelve-oh-two alarm,” and looked toward Bales. A silence of several seconds followed. “It’s the same one we had in training,” Duke said on the flight director’s loop.

In Mission Control, more than one heart skipped a beat. This was the alarm that had caused Bales to call an abort two weeks before. It meant that the computer was being overloaded with data—the unnecessary rendezvous radar that had been turned on added just enough to kick its computational load over 100 percent—and it was going to ignore that secondary task, reboot, and restart selected programs where they had been before the reboot. In other words, it would continue with more important tasks, as it had been programmed to do. The simple but sturdy rope-core memory assembled by the little-old-ladies method was doing its job, but no one in Mission Control knew that. The radar had been on during simulations with no problems.

Bales had been busy assessing the fresh radar telemetry when the

1202 sounded. He said, “Stand by,” and reached for his notebook. Garman had made him a copy of his cheat sheet, and Bales had stuck it in there. Next to him, Paules said, “That’s like the one we had in the sim.”

To Garman, on the dedicated GUIDO loop that only the two of them shared, Bales said, “What’s that?”

Garman had seen the alarm appear on his screen seconds after it sounded—the time it took the LM telemetry to reach Earth—and he was already looking at the cheat sheet under the Plexiglas on his console. His back room was on a dedicated, open line to a roomful of engineers at MIT, but he wasn’t sure they knew, and he didn’t need them anyway. He told Bales, slowly and calmly,  “It’s executive overflow. If it does not occur again, we’re fine... that has not occurred again—OK, we’re go. Continue.”

On the air-to-ground loop, Armstrong asked, as insistently as anyone had ever heard him, “Give us a reading on that twelve-oh-two program alarm.” Usually Aldrin talked to Mission Control about such things, since Armstrong’s attention was on the window in front of him and the ground coming toward them. But Armstrong’s eyes were now fixed on the instrument panel. To the right of Armstrong’s window lay the red abort and abort stage buttons.

Bales said, “We’re... we’re go on that, Flight.” Go  in this case meant “nothing to worry about.”

Kranz said, “We’re go on that alarm?”

Kranz was about to accept Bales’ decision, but Duke had heard it and he didn’t wait for Flight to confirm, as CapComs usually did. As a pilot, he knew the men in the LM were thinking abort, and they needed an answer fast, so 21 seconds after Armstrong first mentioned the alarm, he said, “Roger. We got you—we’re go on that alarm.”

“It’s—if it doesn’t recur, we’re go,” said Bales.

Garman, on the GUIDO loop, reassured him. “If it’s continuous, that makes it a no-go. If it reoccurs”—he meant with at least several seconds in between—“we’re fine.” Sitting next to him was 37-year-old Russ Larson, MIT’s representative to the LM crews, almost a foot shorter than Garman. He didn’t know what the alarms were and was too scared to speak. He could only give Garman a weak thumbs-up.

Someone in a backroom loop said, “Hey, this is just like a simulation,” and for some reason, everyone relaxed a bit. The computer was still doing its job of firing thruster jets and navigating, and it appeared the problem was gone.

Fifteen seconds later, the same 1202 alarm sounded with another yellow light.

On the GUIDO loop, Garman said, “Tell ’em to leave it alone and we’ll monitor it, OK?”

Bales passed the word along, as did Duke.

Aldrin was worried about further overloading the computer, so he stopped asking it for landing radar data. He had begun calling out critical info: velocity rate and descent speed in feet per second, and altitude. The  engine throttled down—a good sign; it meant the computer was still working—and at twenty- one thousand feet and seven minutes into the descent, Eagle began to pitch over so the astronauts faced forward, standing again. Forty seconds later, when the craft was at sixteen thousand feet, the lunar surface began to creep into the bottom of Armstrong’s window.

Kranz said, “Everyone hang tight. Seven and a half minutes.” Bales told him, “The landing radar has fixed everything; the LM velocity is beautiful.” More than a minute had gone by since the last alarm, and they were receiving a clear signal. To Greene he said, “Jay, we’re in good shape now, babe.”

The LM was dropping quickly, at a hundred feet per second, and at almost nine minutes, it was five thousand feet above the surface. To  test his manual controls, Armstrong checked the right-hand controller, which adjusted attitude; he moved the toggle switch from auto to attitude hold, tested yaw and pitch, and pushed it back to auto. He knew he’d need it soon.

Kranz polled the room for the last time, now asking whether or not to land. Bales gave another resounding “Go!” At three thousand feet, Duke gave them a go for landing, and ten seconds later, there was a familiar sound.

Aldrin said, “Program alarm,” paused, then said, “Twelve-oh-one.” Both Garman and Bales were all over it; it was a similar alarm.

“Same type,” said Bales. “We’re go, Flight.”

Duke didn’t bother waiting for confirmation. “We’re go. Same type, we’re go.”

The alarms had caused Armstrong and Aldrin to spend too much time monitoring gauges. When Armstrong was finally able to devote his full attention to the triangular window in front of him, he realized he’d lost track of the landmarks he had studied at such great length. At two thousand feet, he could see a crater coming up. He asked Aldrin for a reading for the landing point. Aldrin punched the question into the computer, then read the answer. “Forty-seven degrees.”

Both panes of Armstrong’s window were inscribed with a grid that was calibrated to his height and eye level in degrees, and it showed where the computer, which didn’t know the LM was going long, planned to land them. He moved his head to align the grids and looked out, about a mile or so away. “That’s not a bad-looking area,” he said at a thousand feet.

He changed his mind a few seconds later. The computer was about to land them on the side of a crater about the size of a football stadium with boulders as big as cars surrounding it. For a second, Armstrong considered trying to land there—maybe he could find an open, level space just short of the crater where the slope wasn’t more than 15 degrees, roughly the maximum safe angle estimated for a successful ascent. A much sharper angle and the LM might tip over; even in the one-sixth gravity of the moon, it would be impossible to right. But they were moving too fast to try landing.

“Twelve-oh-two alarm,” said Aldrin. 

“Roger, no sweat,” Garman said to Bales. 

“Roger, twelve-oh-two, we copy it,” said Duke.

Aldrin, the Mechanical Man, began to coolly call out the critical data Armstrong needed: rate of descent, in feet per second, and altitude. Seconds later they were at six hundred feet. Another 1202 alarm. Everyone ignored it.

There  was an old saying among pilots: When in doubt, land long—what was up ahead of you was easier to see than what was under you. Armstrong decided to do that.

He said, “I’m going to...” but he didn’t need to finish. Everyone knew he was taking over manual control. He quickly slowed the descent to almost zero by switching the autopilot from auto to attitude hold—that would also ease the computational burden and prevent further program alarms. The computer was still involved, but he would be telling it what to do; he, not the computer, would now control the landing. Armstrong pitched Eagle forward to almost level and guided it over the rim of the large crater and its boulder field, bending the trajectory slightly left to avoid a particularly large rock and then resuming his original course. The LM flew better than he had expected; all those hours in the unforgiving LLTV had been worth it.

The ground was getting closer—500 feet below them. They were moving faster than they ever had at this point in a sim and still slowly descending over what looked like the lifeless bed of an ancient lake.

 In Mission Control, a controller reported, “We’re on attitude hold,” and Duke said, “Attitude hold.”

Slayton slapped his arm and said, “Shut up, Charlie,  let ’em land.”

Duke said, “Yes, sir,” then said to Kranz, “I think we better be quiet, Flight.”

“Rog,” said Kranz. He told his team, “Okay, the only callouts from now on will be fuel.”

 Aldrin mentioned the forward velocity for the first time: “Fifty-eight forward”—about 40 miles an hour.

“No problem,” Armstrong said calmly, though his heartbeat had doubled to 150. With his right hand, he carefully tilted Eagle back to allow the rocket engine to slow their velocity, and with his left, he toggled the controller switch, one click at a time, adjusting his rate of descent by one foot per second. Between the noise of the rocket engine below them and the frequent cracks made by the 16 small thrusters arrayed around the exterior, it was loud in the cabin. Up ahead, he could see a relatively smooth area between some large craters and a boulder field. It wasn’t perfect, but it would have to do.

He said, “How’s the fuel?” The LM descent engine didn’t carry more than about 12 minutes’ worth.

“Eight percent,” said Aldrin.

“OK. Here’s a—looks like a good area here.”

Aldrin shot a quick glance out his window and saw the LM’s shadow on the ground beneath them and ahead—the sun was low behind them. “I got the shadow out there,” he said.

They were at 200 feet and had slowed to 13 miles an hour. They scooted over a small crater.

By this time in every simulation, the LM had touched down, crashed, or aborted. Their new landing site wasn’t even in view, and fuel was getting low. Propellant slosh in the tank meant that an accurate fuel-level reading was impossible. Like seafaring explorers centuries before, they were now in terra incognita. They continued skimming over the brightly lit gray surface a hundred feet below them. Another 1202 alarm sounded.

 Duke said, “You’re GO,” though they knew that already.

Duke knew Armstrong had no intention of aborting; he was going to try to land, alarms or not, just like he’d told them he would in all those planning sessions. No one on the ground knew why Eagle hadn’t landed yet—it should have—but they all knew there had to be a good reason. A display on one of the front screens showed the plot of the expected trajectory; Eagle had followed this graph closely at first, but not anymore.

Aldrin looked at the fuel reading—a red light had just come on. “Five percent,” he said. “Quantity light.” If they were still aloft in 90 seconds, they were supposed to make a decision: land within 20 seconds or abort. Aldrin was concerned, but there was nothing he could do. The last thing he wanted to do was disturb his commander’s concentration. He continued to read out numbers—attitude and rate-of-descent speed and forward velocity in feet per second. “Sixty feet, down two and a half… two forward… two forward… that’s good.”

A red low-fuel-level light had flashed on Bob Carlton’s console also. He had started a stopwatch and was now counting down the seconds before the  Eagle ran out of fuel. “Sixty-five, sixty-four, sixty-three, sixty-two, sixty-one, sixty . . .”

Duke said, “Sixty seconds”—one minute until the mandatory abort-or-land decision.

The ground was close now. They had entered the dead man’s zone, an old helicopter term meaning that if they tried to abort at this point, their downward velocity would crash them into the ground before they could ignite the ascent engine. Armstrong wanted to maintain a slight forward speed so they wouldn’t fall into a hole that he couldn’t see under or behind them.

Aldrin said, “Forty feet, down two and a half. Picking up some dust... thirty feet, two and a half down. Faint shadow.”

Armstrong had noticed it too. A sheet of dust dislodged by the engine exhaust flared up from the surface and made it almost impossible for him to judge his rate of descent or determine where the  ground was. He could see some rocks ahead through the slowly moving dust, and he tried to base his velocity decisions on that.

 Everyone in Mission Control was silent except for Carlton, who called out, “Thirty seconds,” and Duke said, “Thirty seconds,” but Armstrong was coming down and fuel was not a factor for him anymore; if the engine quit, they would just fall to the ground. He figured the compressible landing gear could absorb a fall from 30 or 40 feet.

“Drifting forward just a little bit—that’s good,” said Aldrin.

They were moving left when a blue light flashed on the control panel: lunar contact. One of the probes had touched the surface.

Aldrin said, “Contact light.”

Armstrong said, “Shutdown,” and quickly turned off the engine—the back pressure could cause an explosion.

Aldrin said, “Okay. Engine stop.”

Neither of them felt the touchdown, but they had stopped moving. Armstrong watched, fascinated, as dust particles continued to race out to the horizon, which appeared surprisingly close, and then disappeared over it. Except for the glycol pumps, it was silent.

At 2:17:39 p.m. Houston time, Armstrong and Aldrin grinned at each other and shook hands firmly, then checked to make sure that everything, especially the engine arming control, was off.

Duke half collapsed onto his console in relief and said, “We copy you down, Eagle.”

“Engine arm is off,” said Armstrong. “Houston, uh... ” He waited a couple of seconds, and then with added spirit, he said, “Tranquility Base here. The Eagle has landed.”

 In Mission Control, when Armstrong shut down the engine, everyone started to breathe again. Carlton looked at his stopwatch. It said 18 seconds—meaning 18 seconds of fuel left, roughly, though no one could know for sure. Later it would be determined that they had as much as 45 seconds left, but with fuel slosh, it was hard to tell at the moment.

Steve Bales had just started his abort procedures when he heard “Contact light.” Now he was puzzled—Tranquility Base? In every one of the hundreds of sims they’d done, he’d never heard that call sign. Then he thought: What a wonderful name.

The only person Armstrong and Aldrin had mentioned the base name to was Charlie Duke. Now he said, “Roger, Twan... Tranquility. We copy you on the ground. You got a bunch of guys about to turn blue. We’re breathing again. Thanks a lot.”

Aldrin said, “Thank you.”

In Mission Control, a few arms were thrust in the air, but the White team stayed in their chairs; there was still work to do. On the top row, Gilruth wiped his eyes and shook hands with Kraft, who then walked down to the GUIDO console and clapped Bales on the shoulder. The viewing room erupted in cheers as people stood or drummed their feet. The instructors did the same in the simulation control area on the right. In the back rooms, men jumped to their feet, screaming and shouting. Von Braun, with tears in his eyes, turned to Houbolt, the man who had crusaded so tirelessly for the lunar-orbit rendezvous. He gave him an OK sign and said, “Thank you, John.”

Excerpted from Shoot for the Moon: The Space Race and the Extraordinary Voyage of Apollo 11. Copyright © 2019 by James Donovan. Used with permission of Little, Brown and Company, New York. All rights reserved.

Read more at The Daily Beast.

Get our top stories in your inbox every day. Sign up now!

Daily Beast Membership: Beast Inside goes deeper on the stories that matter to you. Learn more.