When Alan Shepard became the first American in space in 1961, he rode in a Mercury capsule packed with the world’s most cutting-edge technology.

It had almost everything you’d expect a spaceship to have, from a heat shield to plenty of oxygen. But it was missing one really big thing: a computer!

Somehow, our first mission to space relied on Newton’s good ‘ole “what goes up, must come down” idea about gravity. Thankfully, we’ve come a long way since those early days. And as computers have gotten more powerful, they’ve completely transformed how we explore the solar system.

And along the way, the space industry gave computer science a boost, too. By the time NASA was getting serious about landing on the Moon, everyone knew the Mercury system wouldn’t cut it. Mission control in Houston provided most Apollo flight control data, but there were still critical times when the astronauts couldn’t rely on Earth.

And the most important time was during lunar landing. Because the Moon is so far and signals can only travel so fast, there’s a round-trip communication delay of about two and half seconds between Earth and the Moon. Which was just way too long during landing.

So each Apollo mission needed computers capable of doing everything necessary to reach the lunar surface. The problem was that computers back then fit in whole rooms, not on desks, and the Apollo missions needed something with as little mass as possible. So computer engineering had to step it up.

NASA assigned this huge task to MIT, which proposed using a new technology: the integrated circuit. In the 1950s, computers were being made with transistors, tiny electronic switches that form the foundation of digital circuits. But all the wires needed to connect them together still left a bulky, sometimes unreliable end result -- which is not good if you only get one chance to land on the Moon!

Integrated circuits solve this problem by printing the transistor and its wiring directly on a thin sheet of silicon, which increases reliability and decreases weight. Using integrated circuits in the Apollo Guidance Computer was a huge risk because they’d never been tried outside a prototype — but they worked! The final computers weighed only about 32 kilograms — or about as much as a golden retriever — and each one performed flawlessly in flight.

To build them, MIT also bought basically the whole world’s supply of integrated circuits, which really helped out the computer industry. In 1961, a single circuit cost about $32, and each Apollo computer used them by the thousands. With all that demand, the price plummeted to just a buck-twenty-five a decade later, and today every computerized product on Earth is built from integrated circuits.

Thanks, Apollo! Of course, we had plenty of robotic missions in the 1960s, too. And since those didn’t have astronauts, they definitely needed computers.

But they were super basic! Back then, they weren’t even called computers; instead these so-called sequencers just stored a list of commands and the time they should be executed. Once the mission was in flight, everything was totally out of our hands.

The first mission to break this mold didn’t come until 1969, when Mariner 6 and 7 flew past Mars. The Mariner 6 flyby happened first, and then scientists could use the data it collected to reprogram Mariner 7 mid-flight. That way, when Mariner 7 showed up at Mars five days later, it could get an even better data return.

Now, almost 50 years later, our flight sequencing has gotten a lot more complicated, thanks to more powerful computers. When Cassini made its final dives between Saturn and its rings this fall, it was executing the last commands of a 294-orbit mission. Something that complicated could never have been planned out years in advance, so it was critical that mission controllers could update the computer along the way.

Cassini’s flight computer is simple compared to what’s in your phone, but it successfully flipped and spun the spacecraft to make sure every instrument was pointed in the right place at the right time. And all those flips and turns have taught us a lot about Saturn’s moons, weather, and more. Modern computers are also enabling missions we wouldn’t have dreamed of in the past — like the Sky Crane that dropped the Curiosity rover on Mars in 2012.

Curiosity is way too big for an airbag-style landing, like what we used for the Opportunity rover, so engineers built the parachute, rocket, and winch combo of the Sky Crane to lower it to the ground. Like with the Apollo landings, there’s a communications delay between Earth and Mars, so everything was up to the flight computer. But unlike a sequencer, the computer had split-second decisions to make.

After being dropped from the parachute, the Sky Crane had just moments to find its elevation and velocity, determine its orientation, account for the local wind speed, and fire its rockets to get balanced. And it had to decide when to lower Curiosity and when to cut it loose. All before anyone on Earth even knew it was entering the atmosphere.

Spoilers: It worked! And now Curiosity is living a happy, productive life on Mars. Without computers powerful enough to collect that data and make those decisions, Curiosity may have never made it to Mars in the first place.

And luckily there’s no sign this innovation will slow down. Opportunity and Curiosity can already pick some of their own objects to study, and Curiosity can drive itself over short distances like a self-driving car. That’s a heck of a long way to come in sixty years, and there’s no telling what will come next.

Thanks for watching this episode of SciShow Space, brought to you by our awesome patrons on Patreon who make everything we do possible! If you want to learn more about the human computers who helped Alan Shepherd and other Mercury astronauts get to space, check out one of my all time favorite SciShow Space videos on Katherine Johnson.