The International Space Station (ISS) is a large space station assembled and maintained in low Earth orbit by a collaboration of five space agencies: NASA (United States), Roscosmos (Russia), JAXA (Japan), ESA (Europe), CSA (Canada), and their contractors. ISS is the largest space station ever built. Its primary purpose is performing microgravity and space environment experiments.
Operationally the station is divided into two sections: the Russian Orbital Segment assembled by Roscosmos and the US Orbital Segment assembled by NASA, JAXA, ESA and CSA. A striking feature of the ISS is the Integrated Truss Structure, which connects the large solar panels and radiators to the pressurized modules. The pressurized modules are specialized for research, habitation, storage, spacecraft control and airlock functions. Visiting spacecraft dock to the station via its eight docking and berthing ports. The ISS maintains an orbit with an average altitude of 400 kilometres (250 mi) and circles the Earth in roughly 93 minutes, completing 15.5 orbits per day.The ISS programme combines two prior plans to construct crewed Earth-orbiting stations: Space Station Freedom planned by the United States, and the Mir-2 station planned by the Soviet Union. The first ISS module was launched in 1998. Major modules have been launched by Proton and Soyuz rockets and by the Space Shuttle launch system. The first long-term residents, Expedition 1, arrived on 2 November 2000. Since then the station has been continuously occupied for 23 years and 116 days, the longest continuous human presence in space. As of December 2023, 273 individuals from 21 countries have visited the space station. The ISS is expected to have additional modules (the Axiom Orbital Segment, for example) before being de-orbited by a dedicated NASA spacecraft in January 2031.