Skylab, America's first space station, launched in May 1973 and came crashing back to Earth on July 11, 1979.
Related: Skylab: The First U.S. Space Station (Photos) Skylab leveraged Apollo hardware that was left over after the final three missions of the moon program were canceled in the early 1970s.
NASA's Skylab plans called for three crewed missions, each lofting three astronauts.
No more crews visited Skylab, and the station's orbit steadily decayed over the next few years, bringing it closer and closer to a fiery death in Earth's atmosphere.
NASA considered ways to boost Skylab's orbit using gear launched aboard the space shuttle, but the winged orbiter didn't come online until 1981.
Skylab showed that astronauts could live and work in space for long durations, paving the way for the International Space Station (ISS), which has hosted rotating crews continuously since November 2000.
ISS astronauts generally serve six-month stints, though NASA's Scott Kelly and cosmonaut Mikhail Korniyenko stayed aboard the station for 11 months, from March 2015 through March 2016.