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
Plants in space of the goals is to grow food for crew consumption. Crops tested at this time include cabbage, lettuce, and mizuna. In 2018, the PONDS system for nutrient deliver in microgravity was tested. In December 2018, the German Aerospace Center launched the EuCROPIS satellite into low Earth orbit. This mission carries two greenhouses intended to grow tomatoes under simulated gravities of the Moon and Mars using by-products of human presence in space as source of nutrients. Plants grown in space include: Some experiments to do with plants include: Plants in space Plants in space is about plants in outer space. In