Conceptual view of the operations in the equatorial earth orbit. The operation in orbit is principally one of propellant transfer and it not an assembly job. The vehicle being fueled is the third stage of a SATURN II with a lunar landing and return vehicle attached. The third stage of the SATURN II was used in the combination into orbit and has thus expended its propellants. This stage is fueled into orbit by a detachment of approximately ten men after which the vehicle then proceeds on the moon.
Image credit: United States Army
Image source: Project Horizon Reports, NASM