ISS is used to refer to the International Space Station. Assembly of the station first begin in 1998 as the result of collaboration between the United States and Russia, both aided by other nations.
The operation of the International Space Station builds on the experience gained from Mir, launched by the Soviet Union, and Skylab, a United States project. It is positioned in low Earth orbit, where it is easier to reach than higher orbits but high enough to research the affects of microgravity on humans and other organisms. Its relative isolation from the atmosphere has aided a number of research fields, including exploring the nature of dark matter.