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It's the 53rd anniversary of the Apollo 11 launch, a monolith in mankind's journey to the stars. Celebrate with this compilation of great minds that lended their knowledge to the momentous event.

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Original Videos:
Great Minds: Robert Goddard, Original Rocket Scientist

Great Minds: Katherine Johnson, Human Computer

Great Minds: Margaret Hamilton

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 (00:00) to (02:00)

Thanks to Linode Cloud Computing for supporting this episode of Scishow. You can go to to learn more and get a $100 sixty-day credit on a new Linode account. It's the anniversary of Apollo 11's launch! On July 16th, 1969, we launched the first mission to land humans on the moon. And that's such a momentous part of human history that we made a SciShow documentary about it. But something that big isn't accomplished through one person's blood, sweat, and tears. There were so many great minds behind Apollo 11's success. So, as we celebrate another anniversary of the triumphant Apollo 11 mission, we recognize Robert Goddard, Katherine Johnson, and Margaret Hamilton for their contributions to Apollo 11 and space travel in general, with a space themed compilation video. While today it's well-known that you can take a rocket to the moon, someone had to come up with that technology. That person was Robert Goddard. Here's Reid, one of our SciShow space hosts, to tell the story of the first rocket scientist. In 1920, when physicist Robert Goddard first proposed that a rocket could one day carry a payload to the moon, none other than the New York Times called him out, saying that the notion of a rocket producing thrust in the vacuum of space without any air to push against was absurd. Goddard's response: "Every vision is a joke until the first man accomplishes it; once realized it becomes commonplace." Born way before the Space Age, in 1882, Robert Goddard is today considered one of the original rocket scientists, although his genius wasn't widely recognized during his lifetime. Goddard didn't invent the rocket itself, but he did build and test the world's first liquid-fueled rocket, the basic design of which continues to be used today. Strictly speaking, rockets are simply devices that obtain thrust by releasing gases at high speeds.

 (02:00) to (04:00)

Usually by burning some kind of fuel.  By this definition, credit for the first rocket goes to the 9th century Chinese chemists, who discovered that when you combine saltpeter sulphur and charcoal, you have gunpowder. And, when bamboo tubes are filled with that gunpowder and ignited, you have fireworks which are rockets. Until they explode. Goddard's earliest work focused on the same basic concept, as he tried to improve solid propellant rockets, fuelled by gunpowder.

But by 1915, while teaching physics in his hometown of Worcester, Massachusetts, he began to suspect that a rocket could be better propelled using a more complex liquid fuel. Goddard came up with the design for a rocket that fed liquid fuel under great pressure into a combustion chamber along with an Oxidizer, a compound that supplies Oxygen to make combustion possible. Goddard thought that if the flow of bulk materials into the combustion chamber could be controlled, then you could actually regulate the speed of the rocket. Even turn it off and restart it. Something that fireworks definitely didn't allow for.

In time, he developed a prototype that used gasoline as fuel and oxygen as the oxidizer, each running separately into the combustion chamber. Now you don't have to be a, well, rocket scientist to know that gasoline plus pure oxygen plus ignition equals kaboom. So Goddard had to figure out how to keep the combustion chamber from simply exploding once he ignited the propellants.

He did it by making a pretty simple but revolutionary modification. He used extremely cold liquid oxygen as the oxidizer. By running pipes full of liquid oxygen around the outside of the combustion chamber, he kept the chamber cool while also making the rocket more efficient because less energy is lost as heat.

This method proved so effective that it's still used today. On March 16th 1926 in Auburn Massachutes, Goddard successfully tested the world's first liquid-powered rocket. The flight lasted less than 3 seconds with the rocket reaching an altitude of 12.5 meters and landing 56 meters away. Over the next 15 years, Goddard would successfully launch 35 more liquid-fueled rockets, including one on March 26th 1937 that reached an altitude of 2.73 kilometer in 22 seconds. 

 (04:00) to (06:00)

He continued to improve on the design, adding gyroscopes to control motion, and even a primitive steering system attached to the exhaust jet .

Goddard would also prove to be right in his belief that a rocket didn't need a medium like air, in order to produce thrust.

According to Newton's 3rd law of motion, every action has an equal and opposite reaction. So Goddard knew that while the rocket would push it's exhaust backward, the exhaust would likewise push the rocket forward, whether there was air around it or not.

Starting just a year before his death in 1945, scientists around the world would demonstrate that rockets could travel to and through space just fine, thank you! From German V-2 rockets, to Sputnik, to the Apollo program.

As for that 1920 New York Times editorial? On July 17th 1969, 24 years after Goddard's death, but 3 days before the Apollo 11 landed on the Moon, the paper finally corrected it's criticism of Goddard.

The correction read: "It is not definitely established a rocket can function in a vacuum as well as in an atmosphere. The Times regrets the error."

Better late than never I guess.

Robert Goddard kept his rockets cool under pressure, just like the people who mapped out their flight paths.

After all, Goddard gave the Apollo 11 astronauts the tools to get to the Moon, but they only hit their target thanks to human computers like Katherine Johnson. Here's how Johnson made sure they made it to their destinations.

If you've been following the news recently, you know that getting into space is a tricky business. Even with half a century of experience and plenty of advance technology helping us out.

But in the early days of space-flight, it was a lot harder. In fact, the paths of many of those first missions were calculated entirely by hand, by people like Katherine Johnson; a mathematician who helped plan the missions that sent the first Americans into space, and then into orbit, and finally to the Moon.

Johnson was born in White Sulfur Springs in West Virginia in 1918. An excellent student who's especially good at math, she was ready for high school at the age of 10.

 (06:00) to (08:00)

But in White Sulfur Springs African-American students couldn't attend high school, so the family moved to another part of the State, to a town called Institute.

There she and her siblings continued her education, though their father remained in their original home town to work. When Johnson started college at 15, one of her professors recognised her math skills and encouraged her to pursue the subject. The professor created a course in analytic geometry, the study of shapes using coordinates, just for her.

She became known for asking lots of questions in class, not because she didn't understand, but because she could tell other people didn't even understand enough of what was going on, to ask what they needed to know.

At 18, Johnson graduated college with degrees in French and Mathematics. She originally planned to earn a graduate degree too, but when her husband was diagnosed with cancer, she took up teaching to support her family.

Later at a family gathering, a relative mentioned that the National Advisory Committee for Aeronautics, or NACA, the organisation that would later become NASA, was looking specifically for African-American women, to act as "computers".

NACA needed these skills to check engineer's calculations in the guidance and navigation department. Her work at NACA started in 1953 as one of those so-called "computers in skirts". Reading data from the black boxes of airplanes, and making calculations based on that data, to learn how the flight went.

But she still had a lot of questions. How did these calculations work? And why were they so important? She started going to the researchers meetings to find some answers.

Some people protested at first since women weren't usually invited, but Johnson pointed out that there was no rule against it and was allowed to stay. One of the all-male flight mechanics branch which studied how airplanes fly, needed extra help. Johnson was selected because of her knowledge of the analytic geometry.

At first it was meant to be just a temporary transfer, but her skills proved valuable and she remained on the team until she moved to the Spacecraft control branch, which was responsible for designing space missions and calculating trajectories.

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One of those missions was Freedom 7; Alan Shepard's flight that made him the first American in space.

The goal was just to get him to space and back, a simple-looking parabolic arc, but there were lots of factors to consider. Nasa told Johnson where they wanted Shepard to land and she worked backward from there.

She had to take into account things like how high they wanted the capsule to go, and the burnout conditions; that is, the velocity and position of the rocket when the fuel ran out and entered free fall back to earth. Shepard's space flight lasted 15 minutes and 22 seconds, and travelled 486 kilometers from its launch point. And, thanks to Johnson's calculations, he splashed out right on target in the Atlantic Ocean, where Nasa has a helicopter ready to fish him out.

By the time Nasa was ready to send John Glenn into orbit, they were using digital computers to do the calculations. But even then, they asked Johnson to confirm the computer's results, planning how Glenn would go from launch to three elliptical orbits and fire rockets to slow himself down and land in the ocean. Johnson went on to contribute to Nasa's famous Apollo 11 mission, but this time the planned end-point wasn't the ocean.

You guessed it, the end-point was the moon. This presented a whole new set of challenges for calculating the trajectory because the moon is a moving target, the kind you really don't want to miss. Nasa also needed Apollo 11 to land smoothly on the moon, away from cliffs and craters, so the rocket had to leave Earth during a specific launch window, a time where the moon would be orbiting Earth right in the rocket's path.

And the trajectory wasn't just a straight shot from the Earth to the moon either, Nasa's computers and again, Johnson, had to factor in the Moon's gravitation and plan for the rocket's path to be skewed by it. With Johnson's calculations to back them up, the mission was launched, and on July 20th 1969, Neil Armstrong took his first steps on the moon.

Johnson calculated the path to the moon by hand, so she had to be confident that there were no errors, and Margaret Hamilton was a computer scientist who fixed the astronaut's errors like pushing the wrong button mid-flight.

 (10:00) to (12:00)

Here's an episode from this Scishow channel about how she addressed that human error. 

So you're on your way your way to the moon. It's been a long trip and just as you're finally about to land your spaceship, the computer starts to spit to out error message after error message.

This is an extremely non-ideal situation and sounds really terrifying and it's exactly what happened to astronauts on Apollo 11, the first mission that landed humans on the moon. In the end, the astronauts landed safely, and Margaret Hamilton, a computer scientist who worked for NASA in the 1960s and 70s, was why. 

Margaret rose through the ranks to eventually become the head of the Apollo flight software development team and a pioneer for women in STEM fields. Hamilton has spent her life focused on errors: how to prevent them and how to keep everything running when they come up. And her approach is what saved Apollo 11 from having to abort the mission. 

Hamilton was born on August 17th, 1936 in a small town in southern Indiana. In 1958, she earned a bachelor's degree in math from Earlham College with a minor in philosophy. She taught in a high school for a couple of years and then worked in a few different MIT programming labs. 

Eventually, Hamilton planned to pursue a PhD in abstract math. But then, she got an offer. A lab at MIT was looking for programmers to work on the computer that would take humans to the moon. So she took that job. 

Back then, programming software, the code that tells what computers what to do, wasn't really a thing that people went to school for. The field was pretty new and developing quickly. So when Hamilton, like a lot of early computer scientists, learned on the job. 

One of her first assignments was for an unmanned mission and it involved designing a program that would tell the computer what to do if the mission aborted. According to Hamilton, NASA execs gave her the assignment because they didn't think it was likely that the mission would abort, but then it did, and the computer ended up using her program. 

To write that program, Hamilton had to consider what would happen if a mission failed. Like if a key instrument decided not to work, or the craft ran out of fuel. It was a theme that would continue to come up during her time at NASA and throughout her career.

 (12:00) to (14:00)

Like when it came time to program the computer for Apollo 8, the first manned mission to orbit the Moon. The software team tested their designs using simulators that would run the programs as though they were being used on a mission. While one of these tests was simulating the Spacecraft in flight, Hamilton's four-year-old daughter, who she'd brought into work that day, accidentally started a program that was meant to be used pre-launch, & the simulator crashed. 

Hamilton realized that this was an error that could easily come up during the mission itself. If an astronaut pushed the wrong button by accident. She wanted to program in a work around, but first she needed clearance from NASA and they said no. They didn't think an astronaut would actually make that mistake.

Then Apollo 8 launched and five days into the mission, one of the astronauts (yes) pushed the wrong button, and started the pre-launch program which erased part of the data the computer needed to get the astronauts home. It took NASA engineers nine hours to come up with a fix which involved sending a replacement set of data to the Apollo computer. But the problem could have been prevented if Hamilton had been allowed to plan for it. 

And then came Apollo 11. The errors that cropped up just as the crew was about to land came from the fact that the computer was being asked to do more calculations than it could handle. The extra demand came from the rendezvous radar which the landing module was using to keep track of the command module that stayed in orbit around the moon.

The program for the radar hadn't been set up properly and it was asking the computer to perform 6,400 operations per second, about 13% of the total processing power. That's not so much, except that the computer needed to land on the moon which took 90% of its processing power, so it was overloaded.

Luckily, Hamilton and her team designed Apollo's computer to take priorities into account which was unusual for computers at the time. Instead of trying to do all of the tasks it was assigned in order, which in this case would have crashed the computer, it responded to an overload by focusing only on the high priority tasks. Landing on the moon was rated a much higher priority than messing with the rendezvous radar, so the computer concentrated on landing, and the astronauts made it to the moon's surface.

After Apollo 11, Hamilton continued designing software for NASA, working on the computers used for the rest of the Apollo missions, as well as Skylab, America's first space station. 

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She's now the CEO of Hamilton Technologies, a company she founded in 1986 which provides a way for software engineers to integrate different programs so they act like one big system.

Integrating the programs this way helps prevent errors that can come from interfacing when programs exchange information. Nearly 47 years after Apollo 11, Margaret Hamilton is still working on ways to get rid of software bugs.

So if you liked any of those videos, you'll probably like other SciShow space videos about great minds, technology, and experiments that help us explore this incredible universe. Thanks for watching this video and any others it leads you to. This episode of SciShow is supported by Linode.

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