I don't know about KSP simple, but Elmer is an GNU-licensed (iirc) open source multiphysical simulator, including magnetics. https://www.csc.fi/web/elmer https

I don't know about KSP simple, but Elmer is an GNU-licensed (iirc) open source multiphysical simulator, including magnetics. https://www.csc.fi/web/elmer https://www.csc.fi/web/elmer