Plasma thrusters may very well be the future of space propulsion. They're small, light, reliable, highly efficient, and are mostly powered by electricity. They do also need reaction mass to function, and researchers at the Australian National University have developed a new plasma thruster that runs on almost anything, including astronaut pee.
ANU's helicon double layer plasma thruster (HDLT) is similar in design to the VASIMIR plasma thruster that we wrote about last year. Plasma thrusters work by using radio waves to inject energy into a gas, turning into a plasma, and then using a magnetic field to exhaust the plasma out the back of the engine at very high speed to generate thrust. There are basically zero moving parts, no electrodes or anything that might function or degrade, and the only parts of the engine that come in contact with the exhaust gases are made of glass or ceramic, which can shrug off the heat without any issues.
While VASIMIR ran on argon (and other plasma and ion engines use other noble gases like xenon), the HDLT seems to be far less picky about its reaction mass. According to professor Rod Boswell, the project's chief researcher:
We can use any type of propellant, including piss. In the International Space Station, there's a system that extracts water from urine, known as the 'Russian piss-presser'. The result ends up with a pH around one — we could easily use that. Xenon is expensive — why not use what's already there?"
This, wondrously, is only the second idea we've heard about turning astronaut pee into a propulsion source. What times we live in!
The HDLT will soon undergo testing in a custom-built space simulation chamber, and ANU expects that the plasma thruster could be used on an operational satellite for station keeping or maneuvering within two years.