Not sure if anyone else has done this yet, but I just calculated the "equivalent" Isp of a 6 fuel cell per ion engine setup. 1 ion engine require 8.74 charge / second, and each fuel cell produces 1.5 charge / second. So you need 6 fuel cells. 6 fuel cells (which in total weigh 0.3 tons, btw) use 0.01 liquid fuel / second and 0.0124 oxidizer / second, or 0.112 kg / second of reaction mass. The ion engine uses 0.486 xenon / second, or 0.0486 kg / second of reaction mass. Add the two up and plug it into the Isp formula, you get 2kN/(0.1606 kg/s * 9.81 m/s^2) = 1,269.4 s of Isp. It comes out to around 1,269 s, which is a big drop from the 4200 s of just an ion engine, but still higher than a nuclear engine. So it might be more worth it to just spam solar panels / batteries / RTGs. Thoughts?
