So why not a disk, for interplanetary travel?

A central core comprising the main engine; with storage, living, and equipment spaces radiating outwards.

RCS thrusters around the outer rim, including thrusters to impart spin (roll?) for artificial gravity.

I'd say put the acceleration couches/nav porthole/storm cellar on top of the main engine, along the main thrust axis. The crew would stay there during powered flight, and then spin the craft while coasting so they could walk around the living quarters and lab areas.

Obvious problems (well, obvious to me, anyway), would have to do with questions like, "how big a radius can the disk have, before it flexes too much to maintain integrity under main thrust?", and, "how strong would the structure have to be, to maintain integrity while spinning?"

One huge problem solved would be the elmination of complex and weight-adding joints and apertures to allow portions of a craft to spin while the rest does not.

I'm sure the board can come up with more problems and solutions. Any takers?