At present, GUNNS only models DC and has no ability to model alternating current. Space vehicles are mostly DC anyway. Sometimes they’ll have a few AC loads like AC motors or wall outlets for AC-powered crew equipment. These will usually be small, isolated secondary circuits powered by an AC inverter. In such cases, we can simply represent the AC sub-circuit as a constant-power load at the AC inverter’s DC input.

I think that GUNNS could model AC circuits with a separate solution of [A]{x}={b} for each phase, similar to how the radiation aspect has a separate solver and solution for each EM frequency band. However there would be a few important limitations in the AC case. Firstly, AC analysis is often concerned with the frequency domain, as resistance (impedance) of AC circuits is dependent on frequency, etc., and GUNNS is strictly a time domain model with no applicability to frequency domain solutions, that I’m aware of. The steady-state solution of voltages and currents of an AC phase would represent the RSS value over the time step, but extra code could be written to compute the actual values at a given time based on the AC waveform shape (sinusoid, etc.) As with the radiation aspect, this multi-solver approach would require a custom network class and architecture, as well as a whole set of new or upgraded links.