Sometimes you just build a rocket in your spare time. Or at least that’s what you do if you’re Valve hardware hacker Ben Krasnow.

Krasnow, a self-described “hacker extraordinaire,” has several videos on YouTube showing his crazy electrical and mechanical projects. But his latest is a real doozy.

In it, Krasnow shows off the “hybrid rocket engine” he built from an acrylic rod (which serves as the fuel source) and a few other parts. The way the engine is built allows Krasnow to throttle it and shut it off, something you can’t usually do with solid-fuel rockets. He writes:

I built a small rocket engine for demonstration purposes. The engine is built from a 2″ diameter acrylic rod through which I drilled a 0.5″ hole. The oxygen at 80 psi or less is passed through the hole and then is forced through a convergent-divergent nozzle at the tail end. The nozzle’s throat is about 0.25″ and expands to 0.625″. I lit the engine by inserting a burning cotton swab (with wooden stick) while a small amount of oxygen was flowing. The acrylic catches fire very easily in a pure oxygen environment. The engine can be throttled and shut off completely, which is a major benefit to hybrid engine designs. Solid-fuel rockets cannot be throttled or shut off, which makes them difficult to control.

Check out the awesome video above.

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