Or, what NASA did next. Originally Skylab was the '
Apollo Applications Project', a set of missions designed to make use of left-over hardware, a project which included the Apollo/Soyuz linkup. The main body of the station was actually a
Saturn V second stage, whilst the shuttles used to service it were none other than Apollo Command/Service Modules.
The station was initially fraught with problems, most pressing of which was that, during launch and deployment, vibrations caused the meteoroid / heat shield that covered the habitation module to break off. In turn, this caused the 'topmost' (looking at the ASCII diagram above) solar 'wing' to become detatched from the station. Thus, the first crew spent their time fitting a makeshift shield, essentially a large rectangle of golden foil. As with Apollo 13 this was considered more of a learning experience than a failure; for the first time men had performed real, extremely hard work during EVA.
After 1974 the station was put into a parking orbit, designed to keep it aloft until the mid 1980s, by which time it would have been a destination for the Space Shuttle. Indeed an early Shuttle mission was to have attached a booster rocket in order to raise Skylab's orbit. The Shuttle was however delayed, and unexpectedly high levels of solar activity destabilised Skylab, such that by 1977 it became apparent that the station was going to re-enter the atmosphere. This was something of a media event at the time, immortalised in song by Devo ('Space Junk') and in the popular British computer game Manic Miner. Eventually poor Skylab re-entered in 1979, burning up over the Indian Ocean and Australia. Some parts fell in suburban Perth whilst the rest were spread over the western desert.
The station was something of a consolation prize for astronauts who would have gone to the moon on the cancelled Apollo missions - Gerald Carr and William Pogue were to have been LM and CM pilots respectively for Apollo 19, whilst Paul Weitz and Jack Lousma were to have performed the same roles for Apollo 20 (all four eventually went on to the Space Shuttle project). Both Alan Bean and Pete Conrad had already walked on the moon, of course. The AAP was renamed Skylab in 1970, the name devised by a Mr Donald L. Steelman of the USAF. It is not to be confused with Spacelab, the small laboratory carried in the cargo bay of the Shuttle on certain missions.
Skylab and the Apollo command modules which were used to service it did not however use up all of the left-over Apollo hardware, and a second Skylab was planned for launch in 1975. This was eventually cancelled in order to save money. The rest of Apollo (an assortment of Saturn boosters, three CMs and two Lunar Modules) was instead sold off to museums. By 1976, Apollo was over and done with. With the end of Skylab, all the capital NASA had gained during its heyday had been mothballed, burnt or smashed to pieces.
Skylab was nonetheless a success, packing a great deal of science and industry into its relatively low cost, all the hardware and personnel being reused. It was useful as both a scientific instrument (its infra-red camera produced many spectacular and useful images of solar activity and vegation on earth - indeed for a time all popular science books were obliged to include Skylab images of dying vegetation / drying lakes / industrial heat waste - and the comet Kohoutek), and as a way of improving NASA's experience with long-duration missions, particularly in the field of on-the-spot repairs - something NASA needed if the shuttle was to be of any use. Certainly Skylab was larger and more impressive than the Russian Salyut stations, albeit that it only operated for two years. The station itself had devolved from early, grandiose plans for a manned station as a waypoint for missions to the Moon and Mars; despite the ISS, NASA has still not regained the momentum it once had.
As a tiny trivia point The Six Million Dollar Man had a large and prominent Skylab mission patch on his jacket. For even more information, http://www.astronautix.com/project/skylab.htm has details of the station, its cancelled sequel, and several other promising missions that never were.