When looking at the Apollo 11 mission, which 50 years ago this week saw humanity first walk on the moon, it's hard not to be both impressed and humbled. The feat is extraordinary under any circumstances, but it is all the more so in that it came just 12 years after the launch of the Soviet Union's Sputnik satellite, the first time anything made by a human-made it into orbit around the Earth. What's more, it came only 66 years after the Wright Brothers became the first humans to achieve any form of flight at all.

RELATED: WHY IS IT TAKING US SO LONG TO GET BACK TO THE MOON?

Which isn't to say that it was easy by any means. The effort to put Neil Armstrong and Edwin "Buzz" Aldrin on the lunar surface was full of all the ups and downs that make for compelling drama, making the details of this historic event all that much more fascinating to revisit.

Aiming for the Moon

After the success of the Mercury and Gemini programs--which put a single astronaut and a pair of astronauts into orbit around the Earth, respectively--the Apollo program originally had a fairly straightforward goal: put a man in orbit around the moon.

US President John F. Kennedy wasn't satisfied with this more conservative goal, though it was a much more reasonable one. Instead, in May 1961, President Kennedy went before the US Congress and said: "I believe that this nation should commit itself to achieving the goal, before this decade is out, of landing a man on the moon and returning him safely to the earth. No single space project in this period will be more impressive to mankind, or more important for the long-range exploration of space, and none will be so difficult or expensive to accomplish."

With that, the stage was set for the unprecedented national effort to put a man on the moon.

Mobilizing for the Moonshot

Neil Armstrong, Edwin Aldrin, and Michael Collins were selected as the commander, lunar module pilot, and command module pilot, respectively, of the Apollo 11 prime crew, with James Lovell--of Apollo 13 fame--, Fred W. Haise, and William A. Anders selected to serve in these roles as a back-up.

While the astronauts involved get the vast majority of the attention, for obvious reasons, it has been estimated that it took the work of around 400,000 people in different capacities to make the mission a success.

Apollo 11 Official Mission Statement

Having originally planned to simply orbit the moon before President Kennedy raised the stakes by promising a moon landing within the decade, NASA still managed to keep the primary mission goal for Apollo 11 as short and simple as possible: "Perform a manned lunar landing and return."

They almost make it sound easy.

The Apollo 11 Crew Designed the Official Mission Insignia Themselves

Continuing a tradition that began with the Gemini V mission, the Apollo 11 crew was tasked with coming up with their own design for the official mission insignia that would be woven into patches. Given the uniquely historic importance of Apollo 11, they broke with tradition and didn't use the names of the mission crew as earlier patches had done.

"We wanted to keep our three names off it because we wanted the design to be representative of everyone who had worked toward a lunar landing and there were thousands who could take a proprietary interest in it, yet who would never see their names woven into the fabric of a patch," said Collins, who took the lead on the insignia design for the crew.

Lovell was the one to suggest the use of the bald eagle in the design, seeing as it is the national bird of the United States, and would be an appropriate symbol of national pride. Running with that idea, Collins also introduced an olive branch into the design at the suggestion of Tom Wilson, who was the simulation instructor for the mission.

After submitting the design, Bob Gilruth, director of NASA's Manned Spacecraft Center, was concerned about the sensitivities around the Apollo 11 mission and thought that the open-taloned bald eagle looked far too aggressive. He had the olive branch moved to the eagle's talons inside, softening the image. Though he liked the end result, Collins reportedly quipped that he "hoped [the eagle] dropped the olive branch before landing."

The Insignia Contains a Notable Mistake

The picture of the Earth in the background, half-cast in shadow, isn't accurate. In the insignia, the left side of the Earth is darkened when in actuality it's the bottom half of the Earth that is cast in shadow when seen from the surface of the moon.

Armstrong's Biggest Concern Ahead of the Launch

At a press availability ahead of the launch, someone asked Armstrong if he would be taking anything personal with him to the moon. "If I had a choice, I would take more fuel," he said.

The Saturn V was the Largest Rocket Ever Successfully Launched

To this day, the Saturn V rocket is the largest rocket to successfully launch. At 363 feet tall, the Saturn V was a bit taller than a football field if you include the endzones, and it stood about 60 feet taller than the Statue of Liberty.

VIP Seating Ain't What it Used to Be

There was enough fuel in the Saturn V rocket that if it exploded on the launch pad--something that could not at all be ruled out--the resulting explosion would have sent shrapnel as heavy as 100 lbs a distance of three miles. As a precaution, VIPs and dignitaries on-site to view the launch had to be kept miles from the launch site, with the closest anyone could get being 3.5 miles from the launch pad.

Lift-Off

To launch the full weight of the Saturn V, which was about 6.2 million pounds when fully fueled, the Saturn V's engines needed to produce about 7.6 million pounds of thrust.

The amount of fuel it burned through during the Apollo 11 mission, if it were used by a car getting about 30 mpg, would be enough for a car to drive around the world 800 times.

The Spirit of St. Louis, which was the first aircraft to make a transatlantic flight in 1927, needed 450 pounds of fuel to make the entire journey. The Saturn V meanwhile, burned through 20 tons of fuel, or 40,000 pounds, per second.

The firing of the Saturn V's first stage engines, the ones that lifted the rocket off of the launch pad, registered at 204 decibels during testing, making it one of the loudest sounds humans have ever recorded. For reference, 150 decibels is the point at which the human eardrum ruptures and 200 decibels would be powerful enough to kill a human outright.

In case you're wondering, this is what ~200 decibels looks like in practice:

In order to protect the Saturn V rocket, as well as the astronauts on board, a sound suppression system had to be developed that used vast quantities of water pumped onto the launch pad.

This dampened the sound waves reflecting off the concrete pad below the engines, soaking up some of the energy of the sound. Otherwise, the sound from the engines alone, at 200 decibels, could have been enough to melt the concrete and the reflected energy could have destroyed the Saturn V rocket on the spot before it ever had a chance to actually lift off.

The Apollo Astronauts were Pretty Relaxed, All Things Considered

With all this going on beneath them--they were sitting on one of the biggest, sustained, and controlled explosions humans ever created after all--you'd imagine that the three men in the crew modules might be a little bit anxious.

The resting heart rate for a human is anywhere from 60 to 100 beats per minute (bpm). The flight surgeon who was monitoring the astronauts' vital signs recorded that at the time of the launch, the heart rates for Armstrong and Collins were 110 bpm and 99 bpm, respectively. Aldrin, meanwhile, registered 88 bpm.

The Columbia and Eagle Modules

The Apollo 11 mission was carried out using three separate modules: the command module, Columbia, and the lunar landing module, Eagle, and the service module.

Columbia and Eagle were the only two modules that had a cockpit for the crew, which were about as roomy as an SUV. The service module contained all the oxygen, water, and power systems used during the mission. It also contained the service propulsion system that was used to enter lunar orbit and rocket the spacecraft back to Earth.

Eagle was a two-stage spacecraft that would carry Armstrong and Aldrin to the lunar surface. Designed to operate entirely in a vacuum, it didn't have to worry about how its shape would affect its flight dynamics and given the weaker gravity on the moon, it didn't need nearly as much fuel as it would take to try to operate it back on Earth.

Columbia remained in orbit around the moon throughout, piloted by Collins who stayed behind while Armstrong and Aldrin were on the surface. Columbia was modeled after the designs of the Mercury and Gemini capsules, so it had the gumdrop-like shape that defined the pre-Space Shuttle spacecraft.

Fizzy Water and Its Side-Effects

All that said, the spacecraft that took the Apollo 11 astronauts still had some issues to work out. In his memoir, Carrying the Fire, Collins wrote: "The drinking water is laced with hydrogen bubbles (a consequence of fuel-cell technology which demonstrates that H 2 and O join imperfectly to form H 2 O). These bubbles produce gross flatulence in the lower bowel, resulting in the not-so-subtle and pervasive aroma which reminds me of a mixture of wet dog and marsh gas."

NASA Hadn't Worked Out How to Deal with Bodily Functions in Space

Gassiness wasn't the only problem, according to Collins: "It seems degrading for Columbia to reach this smelly-old-man stage; I prefer to think of it as a ripe mango ready to fall from the tree--but in any event, it's time to get it on the ground, to end the indignity of having bowel movements in public, and the sooner the better."

It is even reported that one of the Apollo 11 astronauts, though no one will say who it was, apparently loaded up on anti-diarrhea medication so they wouldn't have to deal with the problem at all.

The Flight Computers of the Apollo 11 Mission

There is a lot that can be said about the flight control computer, called the Apollo Guidance Computer (AGC), that powered the Apollo 11 mission.

In some regards, they seem downright archaic from an architecture standpoint relative to today's systems. The programming for the AGC used something called core rope memory to serve as the systems operational memory, which was built out of wires and metal cores so that if a wire went through a core, that represented a one in the binary system, and if the wire went around the core, this would be considered a zero.

After the software engineers--a job title coined by Apollo 11's programming leader, Margaret Hamilton--built the programming that would fly the astronauts to the moon, land on its surface, and return safely, all of the individual programs needed to be sent out to a factory where workers would literally weave the software into a physical system that could be used.

While we might sit here in our new-fangled future with our iPhones and supercomputers, scoffing at the rudimentary electronics of the ACG, we forget that that system successfully landed two men on the moon and then returned them safely back to Earth. We can talk all we want about how a pocket calculator is more advanced technologically than the ACG--and on an architecture level, it is--good luck flying to the moon and back using just a Texas Instruments T-80 calculator.

The Descent to the Surface

Once Apollo 11 made it into orbit around the moon, Collins established a mostly-circular orbit of 62 by 70.2 miles above the lunar surface. After a day or so of preparation and just after 100 hours into the mission, Armstrong and Aldrin entered Eagle through the docking tunnel with Columbia and separated the two modules.

They then began their descent to the lunar surface, entering into a highly elliptical orbit that was 9 by 67 miles above the surface, replicating the trajectory of the Apollo 10 orbit around the moon almost exactly.

Armstrong and Others Weren't Sure They'd Make It

The moon landing itself was a very intricate operation and it wasn't at all certain that Eagle would be able to land safely. This was, after all, the first time anyone in human history had tried to pull this off.

Armstrong, who spent the rest of his post-Apollo 11 life refusing to do interviews about his experience in the Apollo program, broke with past practice and sat for a once in a lifetime, hour-long interview with Alex Malley of the Certified Practicing Accountants of Australia in which he revealed the trepidation that the entire Apollo program felt about the possibility of pulling off the unprecedented landing.

"A month before the launch of Apollo 11, we decided we were confident enough we could try and attempt on a descent to the surface," Armstrong said. "I thought we had a 90% chance of getting back safely to Earth on that flight but only a 50-50 chance of making a landing on that first attempt. There are so many unknowns on that descent from lunar orbit down to the surface that had not been demonstrated yet by testing and there was a big chance that there was something in there we didn't understand properly and we had to abort and come back to Earth without landing."

Armstrong Piloted Eagle Manually During the Landing

At one point during the automated descent, the ACG--which was doing an admirable job all things considered--ran into trouble. A design fault in the antenna suddenly started sucking up desperately needed computational resources, making it harder for the ACG to properly calculate the landing site for the lander. As a result, it tried to set the landing site for Eagle on the slope of a boulder-strewn crater.

"Those slopes are steep, the rocks are very large--the size of automobiles," Armstrong told Malley. Taking manual control, Armstrong piloted Eagle away from the crater and toward a more suitable landing site. "I took it over manually and flew it like a helicopter out to the west direction, took it to a smoother area without so many rocks, and found a level area and was able to get it down there before we ran out of fuel," he told Malley.

Back on Earth, Capsule Communicator (CAPCOM) Charlie Duke, who was responsible for being the communications link between the astronauts and the ground-based mission control, was watching all of this in the data that was being relayed from Eagle back to mission control.

"I was looking at my trajectory plot," Duke said, "[and] Neil leveled off at about 400 feet and was whizzing across the surface…It was far from what we had trained for and seen in the simulations. So I started getting a little nervous, and they weren't telling us what was wrong. It was just that they were flying this strange trajectory."

The Burden of Responsibility Captured in Realtime

When they first launched aboard the Saturn V, Armstrong's heart rate was a surprisingly calm 110 bpm. As he fought to successfully land Eagle, NASA recorded that his heartrate spiked all the way up to 150 bpm, capturing in a single number the moment he must have realized that the fate of the entire moon landing was in his hands alone.

They Almost Didn't Make It

Armstrong was right to worry about the fuel. Rocket scientists have the unenviable task of trying to accomplish the almost impossible within the constraints of the so-called tyranny of the rocket equation. The weight of the fuel, the weight of the payload being carried, and the amount of thrust necessary to accomplish the task at hand are in an incredibly delicate balance that requires providing as close to exactly as much fuel as can do the job with as little extra fuel as possible adding to the mass of the craft.

This leaves so little room for error that the decision to redirect Eagle almost prevented a lunar landing entirely. Alarms began sounding in the lunar module that there was only 60 seconds of fuel remaining before they would have to abort the landing entirely, less than 500 feet from the surface.

"We heard the call of 60 seconds, and a low-level light came on. That, I'm sure, caused concern in the control center," Aldrin remembered. "They probably normally expected us to land with about two minutes of fuel left. And here we were, still a hundred feet above the surface, at 60 seconds."

Another factor that couldn't be ignored was that unexpected conditions, alterations, and speeds during such a descent can reach a point where the laws of physics turn a controlled descent into simply falling from the sky.

Flight Controller for the Apollo 11 mission, Steve Bales, knew that "You never [want to] go under the 'Dead Man's Curve," which he described as "an altitude [where] you just don't have enough time to do an abort before you had crashed."

"Essentially," he added, "you're a dead man."

"When it got down to 30 seconds," Aldrin said, "we were about 10 feet or less. I could sneak a look out, because at that point, I don't think Neil cared what the numbers were. He was looking at the outside."

Then the metal contact rods on the underside of the lander touched the surface of the lunar plain in the Sea of Tranquility, activating a blue light on the control panel marked "CONTACT LIGHT", signaling Aldrin to shut off the descent engines, as they were no longer needed. The Eagle touched down on luna firm, having successfully landed on the surface of the moon.

The First Words Spoken on the Moon

We've probably all learned early on that the first words spoken on the moon as Armstrong's concise, a matter of fact report to CAPCOM: "Houston, Tranquility Base here...the Eagle has landed." It was too perfect a statement to ignore in that it summed up the overwhelming magnitude of what the entire Apollo program just accomplished by stating the simple fact of it.

For each participant in the Apollo program, regardless of their role, those eight simple words would carry an incredibly personal resonance that would be difficult to properly express even to others who took part in the Apollo program. Sometimes, the negative space of things left unsaid says more than we're capable of expressing, so its no wonder that it struck everyone in the moment and is what is remembered today.

Now, if you want to be that guy this week during the Apollo 11 anniversary celebrations, feel free to point out that the actual first words spoken by humanity on the moon were spoken by Aldrin when he reported, "Okay, engine stop," the first step in a checklist that shut down the descent engine for Eagle after it had landed on the surface.

Tranquility Base Wasn't Actually a Thing

Apparently, Tranquility Base wasn't a designated name for the landing site for Eagle once they touched down. Back at mission control, everybody was either too stunned to say anything or they must have figured that the commander of the ship that just landed on the surface of the moon for the first time pretty much gets to call it whatever he wants at that point. From then on, Tranquility Base it was.

The First Meal on the Moon

Aldrin and Armstrong asked mission control for a few moments of silence. Then, Aldrin--a practicing Presbyterian and an elder in his local church back on Earth--performed the rite of communion.

"I ate the tiny Host and swallowed the wine," Aldrin recalled. "I gave thanks for the intelligence and spirit that had brought two young pilots to the Sea of Tranquility. It was interesting for me to think: The very first liquid ever poured on the moon, and the very first food eaten there, were the communion elements."

The Moment Humanity Set Foot on Another World

For the record, the moment humanity first set foot on a world other than the Earth was 10:56 PM Eastern Standard Time.

More Than Half a Billion People Watched the Moon Landing

It is estimated that about 600 million people watched Neil Armstrong's first step onto the lunar surface, a record number of viewers for a live event that no one has come anywhere close to matching, and maybe never will.

What Did Neil Armstrong Actually Say?

We all heard it. It's one of the most famous lines in recorded human history, but what did Neil Armstrong actually say as he set foot on the moon?

"That's one small step for man, one giant leap for mankind" is what everybody heard, but Neil Armstrong himself maintained that that is not what he said. After returning to Earth, Armstrong insisted that what he actually said was "That's one small step for a man, one giant leap for mankind," people simply didn't hear it.

There is a strong case for the indefinite article 'a', as, without it, the remembered quote is actually internally inconsistent and contradictory. Without the 'a', it is not a single man taking a small step, but the abstracted idea of a human being, which is often used when speaking about humanity as a whole.

We have another word for human beings as an abstract class: mankind. So, Armstrong is saying, essentially, "That's one small step for humanity as a whole, one giant leap for humanity as a whole."

It's quite possible that in the excitement of the moment, Armstrong might have flubbed the line a bit--and who could blame him?--and he might have been papering over his mistake; though that would seem a bit out of character for Armstrong. It's also possible that he genuinely remembers himself saying "One small step for a man" when he, in fact, said something else. We do this kind of thing all the time, so why not in this case?



That isn't the whole story, however. In 2006, a computer programmer by the name of Peter Shann Ford found evidence for the missing 'a' in Armstrong's famous words. Using some of the science behind the kinds of software meant to help those unable to speak communicate through computers, Ford downloaded the recording of Armstrong's line from NASA and analyzed the sound waves from the recording.

He was able to identify a 35-millisecond bump in the sound data between the words 'for' and 'man' that coincide with some static over the signal that could have rendered the spoken 'a' undetectable, seeming to provide strong evidence for Armstrong's insistence that he was misquoted.

NASA Originally Planned to Have Armstrong and Aldrin Take a Nap Before Their Moonwalk

Given the intensity of the moon landing itself, which was always going to be stressful, NASA originally planned to have Armstrong and Aldrin take some time to sleep now that they'd touched down on the surface. Not surprisingly, the two men asked for permission to go ahead with the moonwalk immediately, and mission control approved the request.

Buzz Aldrin Makes A Different Kind of History

"It's lonely as hell out there," Aldrin said of the surface of the moon, to an audience at a 40th anniversary celebration of the Apollo 11 landing. "I peed in my pants," which--as far as we'll ever know--also makes Aldrin the first person to urinate on the moon.

They Had to Be Careful Not to Get Locked Out of Eagle

When it came time for Aldrin to join Armstrong on the surface, he had to take care not to lock the door to Eagle since there was no handle to open it again from the outside.

The Moon Smells Like Spent Gunpowder and Wet Ashes

In his memoir, Magnificent Desolation: The Long Journey Back from the Moon, Aldrin revealed some interesting details that only a handful of men have experienced, one of which is what the moon smells like. "A pungent metallic smell," he recalled, "something like gunpowder, or the smell in the air after a firecracker has gone off." While later Apollo astronauts who walked on the moon concur with the spent gunpowder analogy, Armstrong, Aldrin said, described it as the smell of "wet ashes."

Planting the Flag

The decision to plant the American flag on the moon was controversial, even at the time.

Some argued that it ought to be a United Nations flag, to emphasize that this was an achievement for humanity, not America's alone. Others argued that given the investment in time, money, and even the lives of three American astronauts that it took to make it to the moon, some symbol of national pride was warranted. Others thought the idea of planting any flag whatsoever looked downright imperial and should be skipped altogether.

While that debate rages even today, the US Congress later made it official that the only flag that a NASA space mission can plant anywhere is an American flag.

Planting the Flag Was Harder than They Expected

When Apollo 11 landed on the moon, they expected to find the lunar surface to be soft and soil-y, which would make planting a flag much easier than it ended up being. It wasn't until Apollo 11 landed that they found the surface to be a thin layer of dust with a hard, rocky surface underneath, not the kind of substance you can just stick a flag in willy-nilly.

It took serious effort to plant the flag deep enough that it would stand up on its own, which it didn't for very long. Aldrin reported seeing the flag get blown over by the exhaust from the thrusters as the two men left the surface to return to Columbia.

The Flag Was Probably From Sears

The flag itself was reportedly purchased from Sears, but NASA refused to confirm this, not wanting to give the company the kind of free publicity that made Tang a household name during the Mercury program.

The Soviet Union Crashed a Satellite on the Moon During Apollo 11 Landing

While all of this was going on, about 530 miles away, the Soviet Union, having lost the race to the moon, tried to make some kind of notable achievement on the lunar surface in July 1969. The Luna 15 satellite--which was meant to touch down on the lunar surface, collect surface samples, and shoot them back to Earth in a capsule--was orbiting the moon during the Apollo 11 mission and it seriously concerned mission control that the satellite might hit one of the Apollo modules while they were in orbit.

What it did instead was accidentally crash into the surface of the moon a little more than 500 miles from the Sea of Tranquility.

The Moon Plaque

As a compromise between the No-Flag and the America!-Hell-Yeah-Let's-Plant-a-Flag! camps, it was decided that they would plant a flag, but also that they would leave behind a plaque commemorating the event. Armstrong and Aldrin installed the plaque on the moon, which reads:

Here men from the planet Earth first set foot upon the moon, July 1969, A. D. We came in peace for all mankind.

It was signed by Armstrong, Aldrin, and Collins, as well as US President Richard Nixon.

A Day on the Moon

In total, Armstrong and Aldrin spent 21 hours and 36 minutes on the surface of the moon, though they were outside of Eagle for only about two and a half hours, before taking off to rendezvous with Columbia for the return to Earth.

Their Return Was Not Assured

While Armstrong might have been more confident in their ability to return from the surface of the moon as he was that they could land on it, that return was not at all assured.

In their pre-launch quarantine, the Apollo 11 astronauts signed hundreds of photos of themselves in the event that they were unable to return to Earth. NASA would then auction off the photos as a way to support the families of the men who didn't return.

Collins Prepared Himself to Return Home Alone

As Eagle prepared to return to lift off from the surface of the moon, Collins watched from above with some pretty heavy anxiety. "If they fail to rise from the surface," he would later write, recalling his thoughts in that moment, "or crash back into it, I am not going to commit suicide. I am coming home, forthwith, but I will be a marked man for life, and I know it.”

President Richard Nixon Prepared for the Worst

Collins wasn't the only one who was anticipating the worst. President Nixon had a speech [PDF] prepared in the event that Eagle failed in its return from the surface, reprinted below.

Fate has ordained that the men who went to the moon to explore in peace will stay on the moon to rest in peace.

These brave men, Neil Armstrong and Edwin Aldrin, know that there is no hope for their recovery. But they also know that there is hope for mankind in their sacrifice.

These two men are laying down their lives in mankind's most noble goal: the search for truth and understanding.

They will be mourned by their families and friends; they will be mourned by their nation; they will be mourned by the people of the world; they will be mourned by a Mother Earth that dared send two of her sons into the unknown.

In their exploration, they stirred the people of the world to feel as one; in their sacrifice, they bind more tightly the brotherhood of man.

In ancient days, men looked at stars and saw their heroes in the constellations. In modern times, we do much the same, but our heroes are epic men of flesh and blood.

Others will follow, and surely find their way home. Man's search will not be denied. But these men were the first, and they will remain the foremost in our hearts.

For every human being who looks up at the moon in the nights to come will know that there is some corner of another world that is forever mankind.

Reading it is like a glimpse into an alternate history, and it is a humbling reminder that even though we know how this mission would end, no one at the time did, and their anxiety was very, very real.

Saved By a Felt Tip Pen

Had it not been for the quick thinking of Aldrin, that speech might very well be the history that we remember today. When Eagle landed on the moon, a switch for the lander's circuit breaker snapped off, threatening to disable the spacecraft and maroon the two men on the surface. Aldrin wrote in Magnificent Desolation:

Since it was electrical, I decided not to put my finger in, or use anything that had metal on the end. I had a felt-tipped pen in the shoulder pocket of my suit that might do the job. After moving the countdown procedure up by a couple of hours in case it didn't work, I inserted the pen into the small opening where the circuit breaker switch should have been, and pushed it in; sure enough, the circuit breaker held. We were going to get off the Moon, after all.

The Eagle Lifts Off

124 hours and 22 minutes into the Apollo 11 mission, the ascent stage engines on Eagle fired and burned for 435 seconds, lifting Armstrong and Aldrin 11 miles above the lunar surface and into orbit around the moon.

The Things They Left Behind

Behind them, Armstrong and Aldrin left some scientific equipment and other artifacts of their time on the moon. One of which was a mirrored instrument that scientists could use to bounce light off the moon's surface and measure its distance from the earth, an instrument that is still in use today.

Armstrong and Aldrin also left behind medals honoring two Soviet cosmonauts killed in flight accidents--including Yuri Gagarin, the first human to fly in space, as well as the Apollo 1 mission patch--honoring the three Apollo astronauts who were killed when a fire broke out in their crew capsule during an early ground test.

They also left behind messages from 73 world leaders, a gold pin the shape of an olive branch to symbolize peace, and Neil Armstrong's camera.

Docking with Columbia

The process of docking Eagle with Columbia was a nail-biting maneuver that involved several orbital adjustments to line up the two spacecraft in order for them to properly dock. The process took about 4 hours, but 128 hours into the Apollo 11 mission, Eagle successfully docked with Columbia. Armstrong and Aldrin re-entered Columbia and transferred everything from Eagle that they would be taking with them back to Earth.

The docking tunnel was then sealed and four hours after docking with Columbia, Eagle was jettisoned and left behind in lunar orbit.

What They Brought Back With Them

Eagle may not have come home with Columbia, but part of the moon did.

Moon rocks and moon dust in sealed containers gave humans their first real look at the mineral substances that make up the moon. It was found that some of the rocks were as old as 3.7 billion years old, making them a relic of the formation of the moon itself.

The Journey Home

The return journey back was notable for one reason in particular.

As Columbia was coming out from behind the moon for the last time on its way back to Earth, the service propulsion system needed to be fired for just 11.2 seconds to make the only midcourse correction on the return trip from the moon. Margaret Hamilton and the software engineers at NASA had programmed an otherwise flawless return trip for the Apollo 11 astronauts.

Re-Entry and Recovery

Only 44 hours after leaving lunar orbit, traveling at more than five thousand miles an hour, Columbia jettisoned the service module and reoriented itself with its heat shield facing forward. It reentered Earth's atmosphere and a couple of minutes later, successfully deploying its parachutes and splashing down in the Pacific Ocean, about 900 miles west of Hawaii, where it was recovered by the USS Hornet.

Final Mission Figures

The Apollo 11 mission took a total of 195 hours, 18 minutes, and 35 seconds to go from the Earth to the moon and then safely back again, taking about 36 minutes longer than planned.

They returned with 47.84 pounds of moon rocks gathered over Armstrong and Aldrin's 2 hours and 31 minutes walking on the surface of the moon. While there, they traversed a little more than 800 feet of the lunar surface.

Concerns Over Lunar Pathogens

One of the great unknowns at the time was whether or not it was possible for life to exist on the surface of the moon. No one has anticipated moon men or anything, but there was a serious concern about microbial life that might be able to withstand the desolate and harsh lunar environment.

This isn't as strange as it might seem, as microbial life has been found to thrive in some of the most brutally unforgiving environments here on Earth, and we know that some organisms can survive for a time in the vacuum of space. If such an extremophile was able to survive on the moon, the Apollo astronauts could have carried these back with them to a planet where no animal or plant had ever been exposed to them.

This had "end of the world through an alien plague" written all over it, so it's not surprising that the Apollo 11 crew was immediately quarantined the moment they splashed down, where they would remain for 21 days while doctors monitored for any sign of an infection.

Their Quarantine Module

Their mobile quarantine module, which they remained in while being transferred to NASA's Lunar Receiving Laboratory, in Houston, Texas, was quite a bit bigger than the cockpits of Columbia and Eagle. Made from a modified Airstream trailer, the 35-foot-long trailer had living quarters sleeping quarters, a kitchen, and--finally--a bathroom.

They Declared The Moon Rocks with Customs and Submitted Travel Vouchers to NASA

Yes the #Apollo11 crew also signed customs forms. We brought back moon rocks & moon dust samples. Moon disease TBD. pic.twitter.com/r9Sn57DeoW — Buzz Aldrin (@TheRealBuzz) August 2, 2015

#TBT My mission director @Buzzs_xtina's favorite piece of my memorabilia. My travel voucher to the moon. #Apollo11pic.twitter.com/c89UyOfvgY — Buzz Aldrin (@TheRealBuzz) July 30, 2015

The Software Code for the Apollo 11 Flight Computers is Available Online

From start to finish, the Apollo 11 mission was one of greatest--if not the greatest--voyages ever undertaken by human beings. If you're feeling at all inspired to follow in Apollo 11's footsteps, then you're in luck.

Thanks to the digitization efforts undertaken in the past two decades, the Assembly source code that powered the ACG for both Columbia and Eagle is freely available on Github, so you can perform your own re-enactment of the Apollo 11 moon landing if you'd like--assuming you can get 400,000 people to help you do it.