Ahlywog

...seem to be pretty much worthless now? Maybe I'm missing something? I was playing around with a probe. I wanted to see if I could land one, using 8x Ion engines, on Minmus, refuel (Kethane mod) then take off again only to notice 3.88 u/s fuel consumption. 16 KN/s thrust with 3.88 units of Xenon gas/sec? Thoughts?

Let's take Larry Niven's approach. At least in regards to his Ring World book series. All stars have a sort of event horizon. In the case of Earth (and yes I know KSP doesn't involve Earth) it starts just outside the Kuiper belt. Within this event horizon normal Newtonian physics applies. Outside of it normal Newtonian physics applies except in the case of the speed of light being the universal speed limit.