Ben Krasnow, a hardware hacker employed by Valve, has built a hybrid rocket engine in his garage — out of clear acrylic, so that you can actually see the rocket’s inner workings. Either Valve’s getting into the jet pack business, Half-Life 3 will come with a DIY rocket launcher, or Gabe Newell doesn’t work his employees hard enough.

In this case, Krasnow has built a hybrid rocket engine — where the acrylic tube itself is the solid fuel, and pure oxygen is added to allow the acrylic to burn. This is quite different from the liquid rocket motors found in many rockets, such as the the Space Shuttle engines, where the two liquid propellants are mixed together and ignited. The overall construction and end result, though, are the same: A combustion chamber where the two propellants are mixed together, and a whole lot of thrust (and awesome noise) pushed out of the nozzle at the end.

After watching the video and being suitably humbled by Krasnow’s DIY skills, I came away with two main thoughts: a) It’s very easy to build a rocket engine, and b) Solid acrylic can be used as rocket fuel? Really, it seems like building a rocket engine involves a bit of drilling, a couple of aluminium end plates, some silicon o-rings, and a bit of tubing.

This simple design also illustrates just how rudimentary rocket engines are, too: Fuel combusts, creating lots of hot gas (just as in a car’s internal combustion engine). This gas is pushed out through a small nozzle at the back, which increases the speed of the gas, thus creating more thrust. This process repeats until you run out of fuel. Voila, a rocket engine.

The solid acrylic rocket fuel took a little longer to get my head around, but really it’s more a matter of oxygen’s ability to oxidize almost anything; in a pure oxygen environment, just about anything will combust, including acrylic. In a famous episode of Mythbusters, they even make a hybrid rocket from a hollowed-out salami — oxygen is that awesome.

In some ways, we’re rather lucky that Earth’s atmosphere is just 21% oxygen. If there was just a little more oxygen in the atmosphere — say, 25% in total — spontaneous combustion would be quite common, rather than the reserve of eerie X-Files episodes. Likewise, if there was less oxygen in the atmosphere, it’d be almost impossible to make fire.

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