[Pontiac]

Sand is more abrasive than interstellar gas

No moving parts to wear out but I think heating elements resistance rises when they get thinner.

[TXnMA]

In order for solid particles to be in suspension at that altitude, they would have to be colloidal in size or smaller. And, they would be just about as rare as oxygen atoms in low lunar orbit.

[TXnMA]

Come to think of it, I doubt that resistance heating would be employed. My guess is that there would be a plethora of pointed, field-emission electrodes -- as used in a Coates & Welter field emission scanning electron microscope (in lieu of an I²R-heated filament emitter, as is common in other SEM designs).