3 ms·
So efficiency is always going to be some A divided by some B. Traditionall with rocket engines it means impulse divided by propellant mass expended. But given
by Symmetry 6y ago
So efficiency is always going to be some A divided by some B. Traditionall with rocket engines it means impulse divided by propellant mass expended. But given that there are both electric thrusters with much higher ISP and electric thrusters with much lower ISP (e.g. resistojets) I'm not seeing any reasonable efficiency metric under which I think the claim is plausible. Even in terms of losses electric thrusters that don't have to ionize their propellant have a pretty big advantage.
- binarycoffee 6y agoI am not sure I understand the objection (or maybe there wasn't one?) but since there seems to be some confusion in this thread on this point, the electrical efficiency of electric thrusters is very well defined, it is: η = ½Q·(Isp·g₀)² / P where Q is the mass flow rate (kg/s) and P is the input electrical power. Hall thrusters have efficiencies typically ranging from 30% (small HTs) to 60% (large HTs). Gridded ion thrusters have slightly better efficiencies (add 5-10%), mainly because they operate at higher Isp (they would actually have worse efficiency than Hall thrusters when operating in the 1000-1500s range). Why I object to the (admittedly common) characterization of Isp as an efficiency: it is always better to have a high efficiency, whereas Isp is always a trade-off between mass budget and power budget so optimal Isp is always mission-dependent.