A space station, also known as an orbital station or an orbital space station, is a spacecraft capable of supporting crewmembers, which is designed to remain in space (most commonly as an artificial satellite in low Earth orbit) for an extended period of time and for other spacecraft to dock. A space station is distinguished from other spacecraft used for human spaceflight by lack of major propulsion or landing systems. Instead, other vehicles transport people and cargo to and from the station. As of 2018[update], one fully functioning space station is in Earth orbit: the International Space Station (operational and permanently inhabited). Various other components of future space stations, such as Japan's space elevator and U. S. inflatable modules, are also being tested in orbit. Previous stations include the Almaz and Salyut series, Skylab, Mir, and Tiangong-1 and Tiangong-2 . China, Russia, the U. S. , as well as a few private companies are all planning other stations for the coming decades.