Move over, xenon

My posts here have assumed xenon for propellant, at least up and down our own well. Xenon is expensive even if we buy it from a disused sensor.

Why not argon? Xenon has heavier molecules, but so does mercury which is cheap. Argon is also cheap; what you lose by buying this gas from Air Liquide rather than getting the quicksilver for free, I imagine you save in accident-insurance.

Storage seems to me more serious. Xenon currently gets stored in supercriticality 75-300 bar in ambient Florida summer temperatures. Argon would boil at temperature below 87.302 K where xenon boils 165.051 K [Antarctica: 173.15 K]. There's ongoing research in xenon-storage. Have we considered this research for argon? But we're already good at keeping oxygen liquid (90.188 K) on a launchpad. Is liquid-argon more fluid than -xenon?

As to their use as propellant: Kazunori Takahashi is writing about conversion efficiency, between radio-frequency power to thrust energy. Basically xenon molecules (which are just atoms-with-electrons) won't react but a xenon plasma of ions (lacking the electrons) will. The energies in the usual electric thruster, like a Hall, burn out the electrodes. The magnetic-nozzle rf plasma "helicon" thruster solves this by removing the electrodes, using radio-frequency instead. Problem: 20% efficient under the xenon. Since nobody wants the xenon helicon, we all take the hit on shipping up electrodes we know won't last, instead.

Takahashi used argon and boosted this efficiency to 30%. His paper didn't say if his method would work with xenon; but a xenon solution's not really up to him, since he has beaten all the xenonians already. If it all pans out, Takahashi's plan is best, one imagines, for the long term as mission-duration returns to how Tsiolkovsky intended, with propellant-duration. (And the power-source; but that might just be Sol here.)