America's first space station, the 75 ton Skylab was launched May 14, 1973 by a two-stage version of the Saturn V booster (the SL-1 mission). Severe damage was sustained during launch, including the loss of the station's micrometeoroid shield/sun shade and one of its main solar panels. Debris from the lost micrometeroid shield further complicated matters by pinning the remaining solar panel to the side of the station, preventing its deployment and thus leaving the station with a huge power deficit. The station underwent a extensive repair by the first crew launched on May 25, 1973 (the SL-2 mission) atop a Saturn 1B. Two additional missions followed on July 28, 1973 (SL-3) and November 16, 1973 (SL-4) with stay times of 28, 59, and 84 days, respectively. The last Skylab crew returned to Earth on February 8, 1974.
Skylab was actually the refitted S-IVB third stage of a Saturn V booster, a leftover from the Apollo program originally intended for one of the canceled moon landing missions (Apollos 18-20). A product of the Apollo Applications program (a program tasked with finding long-term uses for Apollo program hardware), Skylab was originally planned as a minimially-altered S-IVB to be launched on a Saturn IB rocket. The small size of the IB would have required Skylab to double as a rocket stage during launch, only being retrofitted as a space station once on-orbit. With the cancellation of Apollo missions 18-20 a Saturn V was made available and thus the "Wet Workshop" concept, as it was called, was put aside and Skylab was launched dry and fully outfitted. Skylab's grid flooring system is a highly visable legacy of the wet workshop concept.
Following the last mission the Station was positioned in a parking orbit expected to last at least 8 years. Increased solar activity heating the outer layers of the earth's atmosphere and thereby increasing drag on the Station led to an early reentry on July 11, 1979. Skylab disintegrated over Western Australia and the Indian Ocean, casting large pieces of debris in populated areas (without injury). The reentry prevented any further use by the then unfinished Space Shuttle as was envisioned by some at NASA.
Two flight-quality Skylabs were built, the second, a backup, is on display at the National Air and Space Museum in Washington, DC.
With a baseline project now gelling, NASA started to work though the process of obtaining stable funding for the five years the project would take to develop. Here too they found themselves increasingly backed into a corner. NASA's Space Shuttle program is an ongoing endeavor, started in the late 1960s, that has created the world's first partially reusable space launch system, and the first spacecraft capable of carrying large satellites both to and from low Earth orbit. Each shuttle is designed for a projected lifespan of 100 launches. The original purpose of the program was to ferry supplies to a space station. In reality, the Shuttle is the United States' sole manned launch vehicle and has totally dominated NASA's operations since the mid 1970s. With the construction of the International Space Station the Shuttle has finally begun to be used for its original purpose. In January 2004, it was announced that the Shuttle fleet would be replaced by 2010.
