This is meant to be a colony starter. The cylinder holds colonists and supplies, and detaches upon arrival at whatever planet is being colonized. It then serves as an orbital platform for the new colony. The upper section returns to the shipyard, where it's outfitted with a new cylinder. It can also serve as a generic cargo hauler, if necessary.

I'm working on a full-blown Baloo type writeup. But for now...take a look.