of the booster. This would have resulted in a very large living area. Power was to be provided by solar cells lining the outside of the S-II stage. 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 a number of 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 LM, and a minimum amount of equipment would be installed in the tank itself 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. On April 1, 1966, MSC sent out contracts to Douglas, Grumman, and McDonnell for the conversion of an S-IVB spent stage, under the name Saturn S-IVB spent-stage experiment support module (SSESM). 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