America's first space station Skylab turns 40

Before the International Space Station andviral videos from space, there was Skylab -- America's first space station.

Skylab launched into space by the unmanned Saturn V rocket on May 14, 1973 from launch pad 39A at the Kennedy Space Center.

The space station went unmanned for over a week until Commander Charles C. Conrad Jr., Paul J. Weitz and Joseph Kerwin arrived on May 25, 1973.

In the 1977 book "Skylab, Our First Space Station," author Leland F. Belew describes the highlights of Skylab's mission.

According to Belew, the first crew made repairs to the ship that occurred during take-off and conducted solar astronomy and Earth resources experiments, as well as medical studies and five student experiments. Two more teams of astronauts made missions to Skylab in July and November of 1973.

Researchers on Skylab performed nearly 300 experiments including studies of the Earth's crust, oceans and surfaces, comets, meteors, planets and stars.

Astronauts were able to study the sun like never before because they could observe X-ray and ultraviolet emissions that could not be examined from Earth. And for the first time, remote parts of the Earth could be accurately measured.

Skylab researchers were able to study physiological and psychological effects from prolonged periods of zero-gravity. A total of 16 biomedical experiments were conducted.

"Skylab's success proved many things. Chief among these is man's capability not only to sustain long periods of weightlessness but to live and work effectively in the space environment," Belew wrote. "And the program provided a vast amount of scientific data which scientists will be analyzing for many years."

Skylab returned to Earth on July 7, 1979. Over 100 experiments by scientist from 28 nations conducted experiments on space station.