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
Soyuz-U crewed mission took place 2 December 1974, when the Soyuz 16 crew was launched in preparation for the Apollo-Soyuz Test Project (ASTP). Soyuz 19, which as part of the ASTP docked with the last Apollo spacecraft ever flown, was also launched by a Soyuz-U rocket. On 6 July 1976 a Soyuz-U launched Soyuz 21, which took a crew of two to the Salyut 5 space station. Many subsequent space station crews were launched on Soyuz-U launchers. The final crewed mission to utilize the Soyuz-U was Soyuz TM-34, a Soyuz ferry flight to the International Space Station. A spectacular accident occurred