[SciShow intro plays]   Hank: Stop me if you've hear this one before: "back in the 1960s, NASA spent several years and millions of dollars developing a pen that could write in outer space. Their Soviet rivals, on the other hand, when faced to the same problem, they just used a pencil.” As usual, the truth is more complicated.   First of all, in the early days of spaceflight, both American astronauts and cosmonauts used pencils during their missions. And secondly, NASA didn’t design the pen. It was invented by the American pen manufacturer Paul C. Fisher. The space pens were a much better tool for the job – so much so that cosmonauts started using them too. But there are lots of stories about the space pen floating around the Internet, so let’s get down-to-Earth.   You might think a pencil would be a handy writing tool on Earth and in space. It’s erasable, it doesn’t have any liquids that can leak out and float around a spacecraft’s cabin, but it does have wooden shavings and flecks of graphite that can get everywhere. Including your instrument panels. Or your eyeball.   Pencils are also flammable, which is the last thing you need in an oxygen-rich environment, surrounded by tanks of rocket fuel. So why didn’t we just give astronauts regular ballpoint pens? Well, the pens we use here on Earth every day need gravity to create a steady flow of ink. If they aren’t pointing down, they don’t work.   If you have been lying on your back, trying to write in a notebook over your head? You know that you might as well be scribbling with an empty straw. So NASA started looking for a better solution to help astronauts write precisely in space.   Paul C. Fisher, of the Fisher Pen Company, brought his AG7 anti-gravity pen to NASA’s attention in 1965, after he spent a million dollars on research and development. He just wanted to make a better pen that wouldn’t leak, and started dreaming up new features – like working at extreme temperatures. One of the pen’s main features was a pressurized ink cartridge, which forced the ink out the tip, whether gravity was helping it or not. That way, it could write upside-down, or even in the microgravity of space.   Early prototypes used vents in the body of the pen to pressurize the ink when you clicked the button on top and extended the tip. Eventually, the pens were pressurized with nitrogen gas. But forcing the ink out meant that the pen ink could leak uncontrollably, which is the exact opposite of what Fisher wanted. So he developed special ink for his special pen. By adding a little resin, his researchers turned the ink into a non-Newtonian fluid: a special type of fluid that can change how easily it flows – or its viscosity – when it’s under stress. Basically, sometimes it acts like a solid, and sometimes it acts like a liquid.   There are lots of different kinds of non-Newtonian fluids, but this ink acts a lot like ketchup. When it’s at rest, it’s in a gel-like state. But as you compress it or shake it up, it lowers its viscosity and flows more easily. We call this kind of non-Newtonian fluid thixotropic. So even when the ink is stored in the pressurized main cartridge, it’s thicker and won’t flow very easily. But when the ink is in the tight ballpoint socket and you push down to write, there’s even more pressure on the ink. This changes the ink’s viscosity, and lets it flow out. NASA tested the AG7 pen for over a year to make sure it worked.   And in 1968, it flew to space for the first time, with the astronauts on Apollo 7. Fisher’s pen designs have accompanied astronauts into space ever since – including cosmonauts, who didn’t waste their time and money designing their own space pen.   Now, it’s an innovative design, and useful for writing precisely, but Fisher’s space pen can’t do everything. Fisher liked to tell a story about how his pen helped with an emergency repair in space: See, Apollo 11 astronauts Neil Armstrong and Buzz Aldrin accidentally broke a circuit breaker switch on the lunar lander, which they needed to turn on the ascent engine when it was time to leave.   Fisher claimed that Aldrin stuck his space pen into the slot where the switch went, to fix the problem. But NASA astronauts also bring up other writing tools, like markers, for different things they need to jot down. According to Aldrin, himself, he used a felt-tipped marker to push in the switch and start the engine.   The marker’s plastic body was less likely to cause a short circuit than the metal body of the space pen. It just goes to show, even though the myths surrounding the space pen might make for good stories, you can’t believe everything you read on the Internet.    Thanks for watching this episode of SciShow Space, and thank you especially to all of our supporters on Patreon. If you’d like to support more videos like this one, you can go to Patreon.com/SciShow. And don’t forget to go to YouTube.com/SciShowSpace and subscribe!