Move over, xenon: II

That Hall thruster is still being worked on. Here's the krypton Hall. Parallel to the argon Not-Hall.

These Hall-ish designs all share the same constraint: electrodes do not last under raging ions. That argon drive swapped out electrodes for propellant-efficiency (30%). Efficiency is a problem we can handle with argon on account there's so much of it. At least, over the major inner planets.

There isn't a lot of xenon - nor of krypton for that matter (1/5 the atmospheric fraction of helium). University of Michigan, competing with that argon alternative, are making the most of what noble-gas they have. By using a 9 kW Hall at MAX POWER 45 kW - not possible with xenon - they got more efficiency, with krypton. Ten times the force per unit-area.

Krypton was krap-ton at lower energies, so it's a credit to the team that they wondered what it might do at higher energies.

And 45 kW is just the power the university allowed to the team. What if they had more...?

All this said, I'll fault the article for flinging percentages around. 80% of its nominal efficiency got me all excited until I read further to an overall efficiency of about 49%, not far off the 62% efficiency. So "nominal" is not "100%"; it's 62%, and 49 is indeed 79% of 62. 49% is however better than 30% and that's a bar which competitors must clear.