A space station is an orbiting satellite that allows astronauts to live in space for weeks or months at a time. The first U.S. space station, called Skylab, was launched unmanned on May 14, 1973. In 1973 and 1974, three more manned missions followed with Skylab, during which astronauts observed Earth, solar flares, and the comet Kohoutek. Skylab included a solar observatory, a laboratory for studying the effects of microgravity, and a refrigerator that held prime rib, German potato salad, and ice cream. Skylab orbited Earth 2,476 times during the 171 days and 13 hours of its three manned missions.