Apollo Applications Program - Skylab

Skylab

Originally, AAP missions would alternate with Apollo lunar missions, starting in 1969. However when NASA's 1969 budget was cut, focus was shifted to the Skylab space station proposal, which managed to accommodate the equipment already specified for some of the AAP missions. Specifically, Skylab included the Apollo Telescope Mission (renamed the Apollo Telescope Mount) attached to the docking station used by the CSMs. Since the first two stages of the Saturn V had enough payload capability by themselves to place a pre-fabricated S-IVB workshop into the appropriate orbit, this enabled the "dry workshop" concept. This allowed the interior space to be better fitted out, although many design concepts from the "wet" workshop, notably the open flooring that allowed fuel to flow through it, were kept in Skylab.

The concept of launching another Skylab into lunar orbit using a spare S-IVB was briefly discussed around the same time, but no justification could be found for it, so the project was abandoned early on.