I'm not actually worried about atmospheric drag; as I envisioned the diskship as a purely space-traveling vessel. Trinitree had brought up the idea of a disk-ship traveling edge-on for reasons of atmospheric drag. I had merely pointed out that the design I had in mind involved an axis of travel that would be very bad from an atmospheric drag point of view. What I didn't say at the time was that--as Dave pointed out--a true "space ship" doesn't have to worry about atmospheric drag anyway.