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Hank: Orion. If you have heard this word, not in reference to a constellation, you’re probably thinking of the crew capsule NASA’s planning to use to bring humans to Mars. NASA’s Orion could complete a trip from Earth to the Red Planet in about 240 days. But almost 70 years ago, Project Orion meant something very different. It was a working design for a huge, nuclear-powered spaceship -- one that would have been able to get to Mars -- and back! -- in just 125 days.

In 1957, the Soviet Union kick-started the Space Race when they successfully launched Sputnik, the world’s first artificial satellite. The US developed its own space exploration program -- one that eventually landed us on the Moon. Meanwhile, a group of US scientists was secretly working on a totally different way to explore space -- one that would use the explosive power of nuclear bombs. And eventually, they hoped to use the technology to tour the entire solar system -- and maybe even visit other stars. They called it Project Orion.

The idea of blowing something up to launch a spaceship wasn’t new. Back in the 1880s, a Russian scientist proposed a craft that would use charges of gunpowder exploding inside of a chamber to propel it forward. The idea was way ahead of its time, but it probably would have also killed everyone on board.

Early US nuclear rocket designs were also based around a combustion chamber, but combustion chambers and nuclear power don’t go together very well. I mean, you’re trying to contain nuclear reactions in a small, enclosed area. All that heat and force is going to melt your combustion chamber, or just blow it apart.

Then, in 1946, a scientist working on the Manhattan Project proposed a different idea: What if you put the nuclear bombs outside the spaceship? They could be relatively small bombs, and you could use the force of the blast to propel the spaceship along. You know, in theory.

In 1955, General Atomics, a US defense contractor, decided to study the idea. By 1958, they’d assembled a team of engineers and scientists to create a practical design, including mathematician Freeman Dyson. They came up with a spaceship that looked a lot like a skyscraper, with shock absorbers connecting it to a giant steel pusher plate. The plate would eject nuclear bombs from a hole in the middle, about one per second, which would detonate at a set distance from the ship. The bombs would create a series of explosions that would propel the ship forward. Sounds like a nice, smooth ride, doesn’t it?

Orion’s shock absorbers would transfer the power from the explosion to the spaceship, but they’d also dampen the intensity, which would hopefully keep everyone on the ship from turning into jelly. The team actually tested this ridiculous idea: they made a few models based on Orion’s design, but that used chemical explosives instead of nuclear ones. And they worked!

Orion’s design would have supported all kinds of different spaceships, depending on the scale of the mission. One version would have been able to tour the solar system with up to 150 people on board. It would have weighed more than 3600 metric tons -- about as much as 40 space shuttles. Another could have gotten to Alpha Centauri, our nearest-neighbor star system, in about a century.

But Orion was never built, for reasons that now seem pretty obvious. For one thing, the nuclear test ban treaty of 1963 would have made a launch illegal. They might have been able to get an exception for peaceful use, but there were health concerns, too. The team estimated that it would take 800 small explosions to get Orion from Earth to orbit, and Dyson calculated that the nuclear fallout from the launch would cause 10 people to die of cancer. The project ran out of funding in 1964, and Orion was quietly shelved. But for a while, humans were planning to visit space by exploding nuclear bombs at the back of their spaceship.

Thanks for watching this episode of SciShow Space, and thank you especially to all of our patrons on Patreon who enable us to make videos like this- talking about the ridiculous ideas people have had to get us out into our solar system through the vast desert of space. So thanks, to all of you. If you want to become one of those people, you can go to patreon.com/scishow. And don’t forget to go to youtube.com/scishowspace and subscribe!