> As you and several others pointed out last year, the energy considerations here are good enough to invalidate the scheme.
The only "energy consideration" in that thread is this, from "ballenarosada":
"The potential is 0 at infinity, positive at the first plate and negative at the second. An incoming ion starts at 0 potential, climbs a big hill to get through the first plate, then falls down below 0. Then on the way out it has to climb back to 0 potential at infinity. So the ions gain energy inside the plates but lose it all back on either side."
In order to believe this to be correct, you must fail to understand that the device is electrically neutral. As you move away from it, the distance between the plates becomes negligible compared to your distance from it, and all you see is a neutral object exerting a negligible attraction on the ion.
This is, of course, the principle behind multipole expansions [1].
"balenarosada" thought he or she could just use the dipole term of the expansion to model the capacitor, maybe misled by the name "dipole drive". In hindsight, maybe Zubrin should have gone with "capacitor drive" to prevent this misunderstanding.
The only "energy consideration" in that thread is this, from "ballenarosada":
"The potential is 0 at infinity, positive at the first plate and negative at the second. An incoming ion starts at 0 potential, climbs a big hill to get through the first plate, then falls down below 0. Then on the way out it has to climb back to 0 potential at infinity. So the ions gain energy inside the plates but lose it all back on either side."
In order to believe this to be correct, you must fail to understand that the device is electrically neutral. As you move away from it, the distance between the plates becomes negligible compared to your distance from it, and all you see is a neutral object exerting a negligible attraction on the ion.
This is, of course, the principle behind multipole expansions [1].
"balenarosada" thought he or she could just use the dipole term of the expansion to model the capacitor, maybe misled by the name "dipole drive". In hindsight, maybe Zubrin should have gone with "capacitor drive" to prevent this misunderstanding.
[1] https://en.wikipedia.org/wiki/Multipole_expansion