U.S. space exploration history on U.S. stamps also the only space station NASA launched alone. The 100-ton space station was in Earth's orbit from 1973 to 1979 and it was visited by crews three times in 1973 and 1974. Circling 50 degrees north and south of the equator at an altitude of , Skylab had an orbital period of 93 minutes. There were a plethora of UV astronomy experiments done during the Skylab lifetime, as well as detailed X-ray studies of the Sun. The station was active until July 11, 1979, when it fell out of orbit. The 10-cent Skylab commemorative stamp first day of release took
International Space Station leftover USOS hardware and '"Zvezda" 2' as a refuelling depot and service station located at one of the Earth-Moon Lagrange points, L1 or L2. The entire USOS cannot be reused and will be discarded, but some Russian modules are planned to be reused. "Nauka", the Uzlovoy Module, two science power platforms and "Rassvet", launched between 2010 and 2015 and joined to the ROS, may be separated to form OPSEK. "Nauka" will be used in the station, whose main goal is supporting manned deep space exploration. OPSEK will orbit at a higher inclination of 71 degrees, allowing observation to and from