For more than 40 years, scientists have sought to learn how well human beings can adapt to long periods in space. The International Space Station continues to provide valuable knowledge about spaceflight. But an earlier space station, Skylab, helped make the current space project possible. Canadian astronaut Chris Hadfield sang aboard the International Space Station on May 12, 2013. His music video has become extremely popular. The astronaut played his own version of David Bowie's song Space Oddity. He performed while floating weightlessly, with images of planet earth and space appearing in the window behind him. Chris Hadfield recently returned home after nearly five months on the space station. For him, the long flight produced a hit video on YouTube and no major physical problems. But 40 years ago, scientists did not know how humans would react to long-term spaceflight. To find out, NASA, the American space agency, launched Skylab in May, 1973. Over nearly a year, three teams of astronauts visited Skylab for stays of between 28 to 84 days. They learned how people react to extended periods in space. Gerald Carr commanded Skylab 4. He spoke at a NASA event marking the 40th anniversary of Skylab's launch. He said that the loss of the body's muscle mass was a main concern. Astronauts on Skylab used exercise equipment to stay strong. The astronauts spent their workdays carrying out experiments, including biomedical   research. Marshall Porterfield is the director of NASA's Space Life and Physical Sciences Division. He says the Skylab astronauts' understanding of their own ability to deal with long-term spaceflight continues to help current astronauts. NASA says the next step for life away from Earth is a year-long space station mission, set for 2015. For what purpose did NASA launch Skylab?
To research on whether human beings could stay in space. To gather up information on setting up a space station. To study the changes in the body when staying long in space. To find out the possibility of doing experiments in space.