WASHINGTON — As the space race – and the Apollo program – came to an end, NASA shifted the focus of its manned spaceflight program from exploration to science with the launch of the first U.S. space station.


Skylab launched May 14, 1973, on a Saturn 5 rocket from Kennedy Space Center, Fla.


The project, initially dubbed the Apollo Applications Program, began in the mid-1960s, space historian Roger Launius said in a May 1 phone interview. Once the Apollo program ceased, leftover parts were modified for long-duration space missions in Earth orbit, he said.


The Saturn 5’s fuelless third stage was used as the body of Skylab. The rocket’s liquid hydrogen tank was reconfigured to become the astronaut’s living quarters and lab area, while the smaller liquid oxygen tank was used to stow waste. The three-manned Skylab missions were launched on Saturn 1B rockets in modified Apollo command modules leftover from the three canceled Apollo missions.


The Skylab program’s purpose was to enable scientific experiments in a microgravity environment and to make solar and Earth observations. Astronauts both conducted and took part in the experiments, which included examining how the human body copes with long-duration weightlessness. For the first time, a regularly appointed scientist was included in the three-man astronaut crew, the NASA History Web site said.


Skylab hit some obstacles early on. Barely a minute after launch, atmospheric drag tore off the station’s meteoroid and sun shield, which severed one of two solar array wings, and left the second solar array jammed, according to the Web site.


The space station made it to orbit, but was underpowered and temperatures inside were dangerously high. In addition to making it uninhabitable, the excessive heat could have spoiled food supplies, released toxic gas from melting plastics and ruined photographic film, the Web site said.


Skylab’s ground control team devised a series of attitude adjustments to enable the solar arrays to provide the space station with a serviceable amount of power while keeping the internal heat at a tolerable level, according to the Web site.


The first crews to the station made more permanent repairs. The first crew to Skylab, whose launch was delayed by 10 days, installed a parasol-like sun shield and fully extended the jammed solar panel wing, while the second crew deployed a second sun shield, the NASA History Web site said. The successful maintenance proved astronauts could perform meaningful repairs during spacewalks, said Launius, who chairs the National Air and Space Museum’s space history division.


Skylab carried three crews on 28-, 59- and 84-day missions, according to the NASA History Web site. Its last crew left the station in 1974.


NASA had planned to use the space shuttle to send astronauts to Skylab in 1978, but the first shuttle flight was delayed until 1981, Launius said.


But by then Skylab had fallen out of orbit. The station began to lose altitude when peaking solar activity caused Earth’s atmosphere to expand, thereby increasing atmospheric drag. Skylab crashed into the Indian Ocean and the Australian coast in July 1979.


Despite its power problem, Skylab still compared favorably to its Soviet contemporary, the Salyut, Launius said. “Skylab was much larger, had much more capability,” he said.


While there were several Salyuts, there was only one Skylab.


Launius said that while Skylab was orbiting, NASA was “consumed” with its next big project: the space shuttle. Not long after the first space shuttle flight, NASA pitched the idea of another space station, he said.


The U.S. government approved that second station after then-NASA Administrator Jim Beggs showed President Ronald Reagan a current photograph of the Soviet Salyut 7 orbiting Earth, Launius said.