I've been thinking about hypothetical cargo spacecraft, for transporting materials from planet to planet. Say we're talking container-ship scale. I was wondering if it would be more efficient to, rather than have the whole massive ship take off or land on a planet, to have the cargo carried in containers that can each take off and land themselves. I was thinking that possibly it would be more efficient because containers would only need enough fuel to reach orbit and dock with the cargo vessel, whereas a launching cargo vessel would need to take off with enough fuel to reach orbit and then to get to its destination. On the other hand, each container would have the added weight of engines that would be absent if the whole craft lands and launches. Maybe if the cargo vessel is not designed to land or launch (ie, constructed in space), it could be made larger/lighter/cheaper than one massive vessel that must survive re-entry and launch? Any thoughts? Would this design be viable?