Base camps

An analogy to mountain climbing as applied to space travel.  Plenty of analogies can be made, not just this one.  For example, aerial refueling in the military.  There's even talk about the Navy making its own fuel so they don't have to carry it around everywhere.  In situ resourcing and refueling are game changers in space as well as on the ground:

...destinations are less important than capabilities. Put an off-planet space-transportation infrastructure in place, and the entire solar system (including Europa and Enceladus) is opened up to us--- Rand Simberg

To add my own comment to this, I've suggested using the big SLS rocket to emplace some of the architecture needed for these "base camps".