How many Skylab missions were there?

Skylab was the United States' first space station, orbiting Earth from 1973 to 1979. Launched and operated by NASA, Skylab included a workshop, a solar observatory, and other systems necessary for crew survival and scientific experiments. It was launched unmanned by a modified Saturn V rocket, with a weight of 170,000 pounds (77,111 kg).

To transport astronauts to Skylab, there were a total of three manned expeditions to the station, conducted between May 1973 and February 1974. Each of these missions delivered a three-astronaut crew, carried in the Apollo Command/Service Module (Apollo CSM) launched atop the Saturn IB rocket, which is much smaller than the Saturn V. For the final two manned missions to Skylab, a backup Apollo CSM/Saturn IB was assembled and made ready in case an in-orbit rescue mission was needed, but this backup vehicle was never flown.