The largest modular space station currently in low Earth orbit. It is a multinational collaborative project involving five participating space agencies:

• NASA (United States)
• Roscosmos (Russia)
• JAXA (Japan)
• ESA (Europe)
• CSA (Canada)

It maintains an orbit with an average altitude of 400 kilometres (250 mi) by means of reboost manoeuvres using the engines of the Zvezda Service Module or visiting spacecraft. The ISS circles the Earth in roughly 93 minutes, completing 15.5 orbits per day.

The station serves as a microgravity and space environment research laboratory in which scientific research is conducted in astrobiology, astronomy, meteorology, physics, and other fields. The ISS is suited for testing the spacecraft systems and equipment required for possible future long-duration missions to the Moon and Mars.

The station is divided into two sections: the Russian Orbital Segment (ROS) is operated by Russia, while the United States Orbital Segment (USOS) is run by the United States as well as by the other states. The Russian segment includes six modules. The US segment includes ten modules, whose support services are distributed 76.6% for NASA, 12.8% for JAXA, 8.3% for ESA and 2.3% for CSA.

References

• ISS National Laboratory, ^About*
• [NASA, 20 Years Ago: Station Partners Sign Intergovernmental Agreement (IGA)