Before the International Space Station existed, before U.S. astronauts shared space on Russia's space station Mir, America's first home in Earth orbit was Skylab.

The converted upper stage of a massive Saturn V moon rocket, Skylab was launched 40 years ago today (May 14). The orbital workshop gave NASA its first experience at establishing a long-duration human presence in space, laying the foundation for American astronauts to take up continuous residency almost three decades later on board the International Space Station (ISS).

On Monday (May 13), NASA commemorated four decades of "life off Earth" and the 40th anniversary of Skylab's launch during a roundtable discussion held at its headquarters in Washington, D.C. The event featured Skylab and ISS astronauts, as well as agency managers who are helping to plan the United States' future outposts in space. [Skylab: The First U.S. Space Station (Photos)]

"When these guys went to the final frontier to stay for a long time, they did it as the first ones, the ones who were entering the unknown and to see what it was going to be like and set the stage for us," said astronaut Kevin Ford, who returned from space in March after commanding the International Space Station's Expedition 34. "It is a pleasure for me to be here on the 40th anniversary."

America's first space station

Three crews of three astronauts each launched to the Skylab space station between May and November 1973. Each mission set a record for the amount of time that crewmembers spent in space Skylab 1 for 28 days, Skylab 2 for 59 days and Skylab 3 for 84 days.

"It verified the fact that people could live, work [and] do productive things for long duration, and also took the first steps toward doing the science that we wanted to have aboard," said Owen Garriott, who served as the science pilot for Skylab's second crew.

That astronauts were even able to spend one day aboard Skylab was a testament to the value of having humans in space.

Excessive vibrations during the station's Saturn V liftoff resulted in a critical meteoroid shield being ripped off in flight, which in turn took out one of the orbital workshop's two power-providing solar arrays. Flight controllers moved Skylab's secondary solar panels to face the sun to provide as much electricity as possible, but because of the loss of the debris shield this caused the station's interior to heat up to over 125 degrees Fahrenheit (52 degrees Celsius).

The effort to "save Skylab" fell to its first crew, who had to quickly prepare for a series of unexpected spacewalks in the short time they had between the station's launch and their own. Despite the very tight schedule, the astronauts successfully deployed a parasol (later augmented by a solar shield) to lower the temperature inside the station and freed a snagged second solar array.

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Skylab Legacy: Space Station Astronauts Reflect on 40 Years of Life Off Earth