International Space Station

The International Space Station (ISS) is a large space station that was assembled and is maintained in low Earth orbit by a collaboration of five space agencies and their contractors: NASA (United States), Roscosmos (Russia), ESA (Europe), JAXA (Japan), and CSA (Canada). As the largest space station ever constructed, it primarily serves as a platform for conducting scientific experiments in microgravity and studying the space environment.

The station is divided into two main sections: the Russian Orbital Segment (ROS), developed by Roscosmos, and the US Orbital Segment (USOS), built by NASA, ESA, JAXA, and CSA. A striking feature of the ISS is the Integrated Truss Structure, which connect the station's vast system of solar panels and radiators to its pressurized modules. These modules support diverse functions, including scientific research, crew habitation, storage, spacecraft control, and airlock operations. The ISS has eight docking and berthing ports for visiting spacecraft. The station orbits the Earth at an average altitude of 400 kilometres (250 miles) and circles the Earth in roughly 93 minutes, completing 15.5 orbits per day.

The ISS programme combines two previously planned crewed Earth-orbiting stations: the United States' Space Station Freedom and the Soviet Union's Mir-2. The first ISS module was launched in 1998, with major components delivered by Proton and Soyuz rockets and the Space Shuttle. Long-term occupancy began on 2 November 2000, with the arrival of the Expedition 1 crew. Since then, the ISS has remained continuously inhabited for 24 years and 362 days, the longest continuous human presence in space. As of August 2025^[update], 290 individuals from 26 countries had visited the station.

Future plans for the ISS include the addition of at least one module, Axiom Space's Payload Power Thermal Module. The station is expected to remain operational until the end of 2030, after which it will be de-orbited using the US Deorbit Vehicle.

As the space race drew to a close in the early 1970s, the US and USSR began to contemplate a variety of potential collaborations in outer space. This culminated in the 1975 Apollo-Soyuz Test Project, the first docking of spacecraft from two different spacefaring nations. The ASTP was considered a success, and further joint missions were also contemplated.

One such concept was International Skylab, which proposed launching the backup Skylab B space station for a mission that would see multiple visits by both Apollo and Soyuz crew vehicles. More ambitious was the Skylab-Salyut Space Laboratory, which proposed docking the Skylab B to a Soviet Salyut space station. Falling budgets and rising Cold War tensions in the late 1970s saw these concepts fall by the wayside, along with another plan to have the Space Shuttle dock with a Salyut space station.

In the early 1980s, NASA planned to launch a modular space station called Freedom as a counterpart to the Salyut and Mir space stations. In 1984 the ESA was invited to participate in Space Station Freedom, and the ESA approved the Columbus laboratory by 1987. The Japanese Experiment Module (JEM), or Kibō, was announced in 1985, as part of the Freedom space station in response to a NASA request in 1982.

In early 1985, science ministers from the European Space Agency (ESA) countries approved the Columbus programme, the most ambitious effort in space undertaken by that organization at the time. The plan spearheaded by Germany and Italy included a module which would be attached to Freedom, and with the capability to evolve into a full-fledged European orbital outpost before the end of the century.