It is axiomatic to state that all astronauts need a place to stay in space before heading out or going back home. However, the nature of space means that we must provide everything that a person needs to eat and sleep as well as protection from an environment that want to kill them.
Our program involves humans, and humans need to be fed, clothed, and sheltered.
For the orbital locale, the task of bring up sustenance is fairly simple. Going to the Moon, however, is a bit more complicated (read: involves many more Space Shuttle flights). This means that even though the lunar base is smaller, it still needs more than three times the number of Space Shuttles to sustain it than is needed for the space station.
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