Jon Goff has some useful thoughts on in-space transportation elements. Dave Salt has a salty comment:
If you go back a couple of decades (circa 1985) you’ll find NASA was developing your “tug” and calling it the Orbital Maneuvering Vehicle (OMV), while what you term a “ferry” was being developed as the Orbital Transfer Vehicle (OTV) – astronautics.com has some nice pages describing each.
They were (and still are) logical elements in any reusable LEO infrastructure that uses space stations/platforms/depots as transportation nodes to enable sustainable deep-space missions… which is probably why they don’t feature in ESAS 🙂
Of course, if I were doing the OMV/OTV these days, I’d probably do it completely differently. They do serve as good examples of the general concept we’ve been discussing though.
~Jon
I would say a “ferry” is a roll on, roll off cargo carrier, be it be people, cars, trucks, or rail cars. A “tug” would just be a propulsion unit. A tug can be used to move other craft or push large bulk cargo barges across oceans.
Thus I would feel more comfortable with a “tug”. A space tug could be nothing more than motors, fuel, and guidance, built into an airframe robust enough to push or pull stuff around. It could be a remotely piloted vehicle or just dock a crew quarters to it and have it manned.
If you build it modular you might be able to slave several tugs together to give you enough power to go anywhere. Ocean going tugs and barges ain’t purty be they can move truly large quanities of stuff over large distances.
Even though the Russian Kliper seems permanently stalled isn’t the Parom space-tug moving foreard?