[outworlder]

> By the way, since you need to apply thrust from any direction to maneuver flexibly in 3D space (without wind or gravity), wouldn't spherical/disc(saucer) shaped spacecraft be the most efficient?

Definitely not. There's very little need to 'maneuver flexibly in 3D space'. You are mostly interested in rotation. A slight amount of translation if you are trying to dock with something else.

You will likely still prefer to thrust mostly in a 'forward' (wherever forward is) direction. If, for some weird reason, you wanted to have thrusters equally powerful in all directions, just imagine the amount of weight (and plumbing) this would require.