Interesting Concept

People are looking into using metals for reaction mass in electrical spacecraft propulsion. (Alternate link)

We are talking about things like Hall Effect Thrusters, Ion Drives, and Plasma Drives.

They are looking at replacing various noble gasses, like xenon, krypton, and argon, with cheaper and denser metals, like zinc, bismuth, and the like.

I do recall that cesium was favored as a reaction mass a few decades ago, but that is corrosive and difficult to handle:

Move aside, xenon, krypton and argon. There is a new, heavier-weight class of spacecraft propellant: metals.

This year, several startups are testing electric thrusters that run on metal propellants. The companies say the hard stuff packs a greater punch for its volume and is cheaper and easier to handle than conventional gases.

In March, propulsion company Benchmark Space Systems launched its Xantus plasma thruster system, which uses molybdenum as a propellant, on Orion Space Solutions’ 12U cubesat. In August, Neumann Space and the University of Melbourne announced the successful completion of on-orbit tests of the Neumann Drive, an ion thruster that also uses molybdenum, on a nanosatellite. And in January, Starlight Engines plans to test its Crucible Hall-effect thruster on orbit using zinc propellant.

Metal propellants work inside electric propulsion systems in a similar way to gaseous propellants: After being vaporized, they are ionized and then accelerated out the back of the system using an electrical field. Because metal propellants have greater atomic weight, the elements require less storage volume to generate equivalent thrust.

Typically such systems provide very low thrust, from the 10s of micronewtons to a few millinewtons, but they provide somewhere between 4 and 10 times the ISP (Fuel efficiency) meaning that for station keeping in orbit or long duration missions, they can offer significantly better performance once in space.

I'm keeping my eye on this.