Editing Skylab (section)

=== Wet workshop ===
{{main|Wet workshop}}
[[File:Wet Workshop.svg|left|thumb|An early "[[wet workshop]]" version of Skylab]]

In November 1964, von Braun proposed a more ambitious plan to build a much larger station built from the [[S-II]] second stage of a Saturn V. His design replaced the S-IVB third stage with an aeroshell, primarily as an adapter for the CSM on top. Inside the shell was a {{convert|10|ft}} cylindrical equipment section. On reaching orbit, the [[S-II]] second stage would be vented to remove any remaining [[hydrogen]] fuel, then the equipment section would be slid into it via a large inspection hatch. This became known as a "[[wet workshop]]" concept, because of the conversion of an active fuel tank. The station filled the entire interior of the S-II stage's hydrogen tank, with the equipment section forming a "spine" and living quarters located between it and the walls of the booster. This would have resulted in a very large {{convert|33|by|45|ft}} living area. Power was to be provided by [[solar cell]]s lining the outside of the S-II stage.<ref>{{harvp|Benson|Compton|1983|p=22}}.</ref>

One problem with this proposal was that it required a dedicated Saturn V launch to fly the station. At the time the design was being proposed, it was not known how many of the then-contracted Saturn Vs would be required to achieve a successful Moon landing. However, several planned Earth-orbit test missions for the LM and CSM had been canceled, leaving some Saturn IBs free for use. Further work led to the idea of building a smaller "wet workshop" based on the S-IVB, launched as the second stage of a Saturn IB.

A number of S-IVB-based stations were studied at MSC from mid-1965, which had much in common with the Skylab design that eventually flew. An [[airlock]] would be attached to the hydrogen tank, in the area designed to hold the [[Apollo Lunar Module|LM]], and a minimum amount of equipment would be installed in the tank in order to avoid taking up too much fuel volume. Floors of the station would be made from an open metal framework that allowed the fuel to flow through it. After launch, a follow-up mission launched by a Saturn IB would launch additional equipment, including solar panels, an equipment section and docking adapter, and various experiments. [[Douglas Aircraft Company]], builder of the S-IVB stage, was asked to prepare proposals along these lines. The company had for several years been proposing stations based on the S-IV stage, before it was replaced by the S-IVB.<ref>{{harvp|Benson|Compton|1983|p=25}}.</ref>

On April 1, 1966, MSC sent out contracts to Douglas, [[Grumman]], and [[McDonnell Aircraft Corporation|McDonnell]] for the conversion of an S-IVB spent stage, under the name Saturn S-IVB spent-stage experiment support module (SSESM).<ref>{{harvp|Benson|Compton|1983|p=30}}.</ref> In May 1966, astronauts voiced concerns over the purging of the stage's hydrogen tank in space. Nevertheless, in late July 1966, it was announced that the Orbital Workshop would be launched as a part of Apollo mission AS-209, originally one of the Earth-orbit CSM test launches, followed by two Saturn I/CSM crew launches, AAP-1 and AAP-2.

The Manned Orbiting Laboratory (MOL) remained AAP's chief competitor for funds, although the two programs cooperated on technology. NASA considered flying experiments on MOL or using its [[Titan IIIC]] booster instead of the much more expensive Saturn IB. The agency decided that the Air Force station was not large enough and that converting Apollo hardware for use with Titan would be too slow and too expensive.<ref>{{harvp|Benson|Compton|1983|pp=45–48}}.</ref> The DoD canceled MOL in June 1969.<ref>{{harvp|Benson|Compton|1983|p=109}}.</ref>