From XR-100 to H10

I looked at a Nested Hall Thruster - from 19-22 August 2019. I figured it time for any updates on that tech since sometimes things just fall out of view, like that weedy aerogel fission scheme. In the Hall case, matters are looking better.

Specific-impulse is a function of reach and vice-versa. NASA would like the 3.1 ks which the Dawn ion-drive used to orbit Vesta and on to Ceres. Taxpayers lament, however, Dawn's extreme expense. Plenty of cool rocks remain floating out there; we can settle for something more like Psyche which as of this poast has been running smooth for 1.8 ks. Hall thrusters are cheaper than ion drives such as VASIMR. Hall Thrusters have been for stationkeepers and inter-orbit tugs. That ain't nothin'.

But Hall-effect plasma will degrade the engine. This requires some kind of shield; ablative (somehow) or magnetic. This allows operations in the kilohours, to span something between a day and a few months; when what propellant you'd brought would be used. Here's the focus of the last few years.

Here's JPL's H10.

This is a form of Hall Effect Rocket with Magnetic Shielding which NASA in 2022 was labelling HERMeS. For Hall I_sp, the 2019 presentation had clustered 2 ks; HERMeS in 2022 was 2.78 ks from 12 kW. Now for the real ks, the operating-time...

JPL are saying that over the past few years, their lifespan has improved from the kilohours to 10-30 kh which I'm pretty sure refers to that HERMeS. This lifespan is a gift of the "MeS" side, citing this magnet paper from 2024 (running 8187 h so, slightly over a year). The excited plasma would be krypton or xenon for 50-60% efficiency. This is a lot better than the 20% it used to be; dunno if they'll move to argon.

This occasioned a battle of the kiloseconds, as operating-time feuded with... I_sp. HERMeS ran into a voltage-limit: beyond 500 V, oscillations ruin the flow. Various mitigations are being researched; JPL has decided, for now, not to bother. Instead they increase power density, implicitly a function of mass so W/g here. That shifts the problem to thermodynamics - throwing out all those watts. JPL deal with that, with a segmented radiator that is coupled to high temperature components.

JPL say H10 has tested for peak performance at 800 V, 10 kW of 457 mN thrust, 3400 s specific impulse, and an efficiency of 76%. Its mass is 20 kg for an alpha of 2 kg/kW (lower is better).

I do believe we can supply 10 kW in space with a lightweight heat source, like with neutron-activated enthalpy. How to shield this engine; I don't know if superconductors be possible, or needed.