A space station, also known as an orbital station or an orbital space station, is a spacecraft capable of supporting a crew, 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 September 2016 three space stations are in orbit: the International Space Station, which is permanently manned, China's Tiangong-1 (defunct) and Tiangong-2 (launched 15 September 2016, unmanned most of the time). Previous stations include the Almaz and Salyut series, Skylab, and most recently Mir.