Is a 10 or 100 MW, or even GW class electric thruster on anyone's radar? Are there fundamental reasons why that would be much more difficult than 100 kW class thrusters?
Ahah, but you've failed to consider that I want to use them to go to Mercury, where solar panels are 5-10 times as powerful per area. That means my mission planning can consider the state of the art to be less than 1 kg/kW, and that opens up solar-electric vehicles with substantial payload mass fraction.
Anyway, you're right that it would be large, though. If it's assembled in LEO, though, it only ever has to withstand less than 1E-2 m/s^2 acceleration, which ought to afford further mass reductions. I don't see a way any such thing gets underway sooner than 2030, so I think planning for assembly in LEO is not much of a compromise.
What's the largest object that we could land on/take off from (or maybe "rendezvous" would be more accurate for very small asteroids etc.) with current-technology electric propulsion?I think the NSTAR engine used by Dawn would be (barely) good enough for tiny objects like Bennu (Wikipedia claims Bennu's gravity is 6.7 micro-g, so 0.09 N should be able to accelerate 1200 kg at 0.000075 m/s = about 7.6 micro-g, unless my math is off).But how much better could we do? Can we trade Isp for thrust to land on, say, Deimos?
If so, of that 40% waste, how much of the waste heat goes out with the reaction mass (the ions) and thus doesn't have to be mitigated, and how much of that 40% has to be radiated away with special radiators?
7.3.3 Dominant Power Loss MechanismsIn preparation for examining the terms that drive the efficiency of Hall thrusters, it is useful to examine the dominant power-loss mechanisms in the thruster. Globally, the power into the thruster comes from the discharge power supply. The power out of the thruster, which is equal to the input power, isgiven to first order byPd = Pb + Pw + Pa + PR + Pion , (7.3-27)where Pb is the beam power given by IbVb , Pw is the power to the channel walls due to ion and electron loss, Pa is the power to the anode due to electron collection, PR is the radiative power loss from the plasma, and Pion is the power to produce the ions that hit the walls and become the beam. Additional loss terms, such as the power that electrons take into the beam, the ion power to the anode, etc., are relatively small and can usually be neglected.In Hall thrusters with dielectric walls, the power loss due to electron and ion currents flowing along the radial magnetic field through the sheath to the channel walls ( Pw ) represents the most significant power loss.
Quote from: InterestedEngineer on 03/05/2023 11:20 pmIf so, of that 40% waste, how much of the waste heat goes out with the reaction mass (the ions) and thus doesn't have to be mitigated, and how much of that 40% has to be radiated away with special radiators?AIUI, most of the energy not producing thrust is spent ionising the propellant, so it's not really "waste" as such, and it definitely goes out with the exhaust.