>>>Canadian astronaut Chris Hadfield's music video has gone viral.

In the popular video, Hadfield plays David Bowie's rock classic Space Oddity on his acoustic guitar and sings the lyrics about a space traveler. The real draw, beyond Hadfield's ability to play and carry a tune, is that he performed while floating weightless aboard the International Space Station, at times with a view of our planet out the window.    

Canadian astronaut Hadfield, who recently wrapped up nearly five months on the space station, has clearly adjusted to life away from Earth.

But only four decades ago, scientists didn't know if humans could adapt to long-duration spaceflight.

Skylab

NASA attempted to answer that with its Skylab module, which was launched unmanned into Earth orbit in May 1973. During its nearly year-long operation, three teams of astronauts visited the outpost for missions ranging from 28 to 84 days, learning how people react to extended periods in space.    

Gerald Carr, who commanded Skylab 4, appeared on a NASA panel in Washington for the 40th anniversary of the launch. He said muscle atrophy was a major concern.

"What we learned was that simple exercise takes care of the problem, and there's no reason why a person can't stay in a weightless environment for a long, long time," Carr said.  

Archival video shows an astronaut in a harness connected to waist-high elastic bands that secured him to Skylab's floor. This primitive sort of treadmill allowed him to run in place. Other video shows astronauts flying through their large, open workspace or performing graceful somersaults outside the bounds of gravity.   

The astronauts spent their workdays conducting experiments, including biomedical research, in microgravity. Skylab also served as a solar observatory and a pioneering platform to study Earth.

That is Skylab's legacy, said Owen Garriott, the science pilot of Skylab 3.
"Forty years out, I think we're still impressed with the amount of work that was accomplished and the foresight of the investigators in planning the experiments," Garriott said.

High school students also had the opportunity to propose scientific experiments to be performed on the orbiting lab. This kind of collaboration between students and astronauts still exists aboard the International Space Station.

Adaptability

The astronauts' insights into their own ability to handle long-duration flight laid the groundwork for life in space today, says Marshall Porterfield, director of NASA's Space Life and Physical Sciences Division.

"Now we've built on that, and what they found in terms of bone and muscle health changes that occur in space," said Porterfield. "And those are still significant areas in our research portfolio now."  

But Skylab had setbacks.  A meteoroid shield broke off during launch, tearing a solar panel off with it. The first crew, which arrived 11 days later, had to deploy a parasol-like sun shield through Skylab's airlock and later perform a spacewalk to release a jammed solar array wing.

These challenges allowed astronauts to prove a point, says Allan Needell, a curator at the Smithsonian National Air and Space Museum in Washington.

"One of the first things that they learned was yes, indeed, humans were capable of reacting to situations unanticipated," said Needell. "Remember, we didn't have the space shuttle that could go up and do a repair at that time."

Skylab's End

The third and final crew left Skylab in February 1974. NASA wanted the station to remain in orbit into the 1980s, with the idea that the planned space shuttle fleet could bring astronauts back to the lab. However, greater than expected solar activity compromised the outpost. 
 
Skylab plummeted back toward Earth in 1979 and disintegrated in the atmosphere. Debris fell across a sparsely populated part of western Australia and the southeastern Indian Ocean.

Present and Future

NASA transferred the backup Skylab Orbital Workshop to the Smithsonian National Air and Space Museum in 1975, where it remains a major draw for visitors.       

Looking to the future, NASA says the next step for life away from Earth is a year-long Space Station mission, featuring an astronaut and a cosmonaut, that is set for 2015.