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. Apollo-Soyuz Test Project The Apollo-Soyuz Test Project involved a docking in Earth orbit between a CSM and a Soviet Soyuz spacecraft. The mission lasted from July 15 to July 24, 1975. Although the Soviet Union continued to operate the Soyuz and Salyut space vehicles, NASA's next crewed mission would not be until STS-1 on April 12, 1981. Summary of missions References Works cited Apollo program Application 1968 establishments in Washington, D.C. Human missions to Venus