The International Space Station (ISS) is a multi-nation construction project that is the largest single structure humans ever put into space. Its main construction was completed between 1998 and 2011, although the station continually evolves to include new missions and experiments. It has been continuously occupied since Nov. 2, 2000.
The ISS is not owned by one single nation and is a “co-operative programme” between Europe, the United States, Russia, Canada and Japan, according to the European Space Agency (ESA).
As of April 2021, 244 individuals from 19 countries have visited the International Space Station. Top participating countries include the United States (153 people) and Russia (50 people). Astronaut time and research time on the space station is allocated to space agencies according to how much money or resources (such as modules or robotics) that they contribute. The ISS includes contributions from 15 nations. NASA (United States), Roscosmos (Russia) and the European Space Agency are the major partners of the space station who contribute most of the funding; the other partners are the Japanese Aerospace Exploration Agency and the Canadian Space Agency.
Current plans call for the space station to be operated through at least 2024, with the partners discussing a possible extension until 2028. Afterwards, plans for the space station are not clearly laid out. It could be deorbited, or recycled for future space stations in orbit.
Crews aboard the ISS are assisted by mission control centers in Houston and Moscow and a payload control center in Huntsville, Ala. Other international mission control centers support the space station from Japan, Canada and Europe. The ISS can also be controlled from mission control centers in Houston or Moscow.
How to see the International Space Station
The Space Station flies at an average altitude of 248 miles (400 kilometers) above Earth. It circles the globe every 90 minutes at a speed of about 17,500 mph (28,000 km/h). In one day, the station travels about the distance it would take to go from Earth to the moon and back.
The space station can rival the brilliant planet Venus in brightness and appears as a bright moving light across the night sky. It can be seen from Earth without the use of a telescope by night sky observers who know when and where to look.
For more information on how to see and track the ISS check out our guide.
What work do astronauts do aboard the ISS?
There is typically an international crew of 7 people that live and work on the ISS. However, during the changeover of crew members this number can vary, for example in 2009, 13 crew members visited the ISS. This is also the record for the most people in space at one time.
Typically, astronauts travel to the space station via a Russian Soyuz capsule (first launched in 1967), which has long been the only spacecraft that ferries people to the ISS, since NASA’s space shuttle programme retired in 2011. However, on Mar. 3, 2020, SpaceX’s Crew Dragon capsule became the first privately-owned spacecraft to transport people to the ISS.
Once at the station, astronauts will typically spend a mission period of around 6 months conducting various science experiments and maintaining and repairing the ISS. Outside of work, astronauts will spend at least 2 hours on exercise and personal care. They also occasionally perform spacewalks, conduct media/school events for outreach, and post updates to social media. The first astronaut to tweet from space was Mike Massimino, who did it from a space shuttle in May 2009.
The ISS is a platform for long-term research for human health, which NASA bills as a key stepping stone to letting humans explore other solar system destinations such as the moon or Mars.
Human bodies change in microgravity, including alterations to muscles, bones, the cardiovascular system and the eyes; many scientific investigations are trying to characterize how severe the changes are and whether they can be reversed. Astronauts also participate in testing out products – such as an espresso machine or 3D printers – or doing biological experiments, such as on rodents or plants, which the astronauts can grow and sometimes eat in space. As the only microgravity laboratory in existence, the ISS has facilitated more than 3,600 researchers to conduct more than 2,500 experiments to date.
In 2019, NASA executives announced that the space station would open its airlocks to commercial businesses and private astronauts. This allows the private sector to test out new technologies and train astronauts under microgravity. There are also plans for Houston-based company Axiom Space to build a new commercial module on the space station to spur the growth of an off-Earth economy.
Crews are not only responsible for science, but also for maintaining the station. Sometimes, this requires that they venture on spacewalks to perform repairs. From time to time, these repairs can be urgent — such as when a part of the ammonia system fails, which has happened a couple of times. Spacewalk safety procedures were changed after a potentially deadly 2013 incident when astronaut Luca Parmitano's helmet filled with water while he was working outside the station. NASA now responds quickly to "water incursion" incidents. It also has added pads to the spacesuits to soak up the liquid, and a tube to provide an alternate breathing location should the helmet fill with water.
NASA has produced several machines to reduce the need for space walks, including the humanoid Robonaut 2. The dexterous machine joined the ISS crew back in 2011, however, after discovering a fault in the machine, Robonaut 2 was sent home to Earth in 2018, for repairs. Also onboard the ISS are several external robotic arms that can tackle maintenance issues remotely, such as the Special Purpose Dexterous Manipulator (SPDM) - also known as Dextre - and the Canadarm2 (a 57.7-foot-long robotic arm).
Related: How to Photograph the ISS
What are the parts of the ISS?
The space station, including its large solar arrays, spans the area of a U.S. football field, including the end zones, and has a mass of 925,335 lbs. (419,725 kilograms), not including visiting vehicles. The complex now has more livable room than a conventional 6-bedroom house, and has 2 bathrooms, gym facilities and a 360-degree bay window. Astronauts have also compared the space station's living space to the cabin of a Boeing 747 jumbo jet.
The International Space Station was taken into space piece-by-piece and gradually built in orbit using spacewalking astronauts and robotics. Most missions used NASA's space shuttle to carry up the heavier pieces, although some individual modules were launched on single-use rockets. The ISS includes modules and connecting nodes that contain living quarters and laboratories, as well as exterior trusses that provide structural support, and solar panels that provide power.
The first module, the Russia Zarya, launched on Nov. 20, 1998, on a Proton rocket. Two weeks later, space shuttle flight STS-88 launched the NASA Unity/Node 1 module. Astronauts performed spacewalks during STS-88 to connect the two parts of the station together; later, other pieces of the station were launched on rockets or in the space shuttle cargo bay. [Rare Photos: Space Shuttle at Space Station]. Some of the other major modules and components include:
- The truss, airlocks and solar panels (launched in stages throughout the ISS lifetime; docking adapters were launched in 2017 for new commercial spacecraft)
- Zvezda (Russia; launched in 2000)
- Destiny Laboratory Module (NASA; launched 2001)
- Canadarm2 robotic arm (CSA; launched 2001). It was originally used only for spacewalks and remote-controlled repairs. Today it also is regularly used to berth cargo spacecraft to the space station – spacecraft that can't use the other ports.
- Harmony/Node 2 (NASA; launched 2007)
- Columbus orbital facility (ESA; launched 2008)
- Dextre robotic hand (CSA; launched 2008)
- Japanese Experiment Module or Kibo (launched in stages between 2008-09)
- Cupola window and Tranquility/Node 3 (launched 2010)
- Leonardo Permanent Multipurpose Module (ESA; launched for permanent residency in 2011, although it was used before that to bring cargo to and from the station)
- Bigelow Expandable Activity Module (private module launched 2016)
- NanoRacks Bishop Airlock (launched 2020)
- Nauka, Multipurpose Laboratory Module (launched 2021)
What else visits the ISS?
Besides the space shuttle and Soyuz, the space station has been visited by many other kinds of spacecraft. Uncrewed Progress (Russia) vehicles make regular visits to the station. Europe's Automated Transfer Vehicle and Japan's H-II Transfer Vehicle used to do visits to the ISS as well, until their programs were retired.
NASA began developing commercial cargo spacecraft to the space station under the Commercial Orbital Transportation Services program, which lasted from 2006 to 2013. Starting in 2012, the first commercial spacecraft, SpaceX's Dragon, made a visit to the space station. Visits continue today with Dragon and Orbital ATK's Antares spacecraft under NASA's Commercial Resupply Services program.
Records in space
The ISS has had several notable milestones over the years, when it comes to crews:
- Most consecutive days in space by an American: 340 days, which happened when Scott Kelly took part in a one-year mission to the International Space Station in 2015-16 (along with Russian cosmonaut Mikhail Kornienko). The space agencies did a comprehensive suite of experiments on the astronauts, including a "twin study" with Kelly and his Earth-bound former astronaut twin, Mark.
- Longest single spaceflight by a woman: 328 days, during American astronaut Christina Koch’s 2019-20 mission aboard the space station.
- Most total time spent in space by a woman: Again, that's Peggy Whitson, who racked up most of her 665 days in space on the ISS.
- Most women in space at once: This happened in April 2010 when women from two spaceflight missions met at the ISS. This included Tracy Caldwell Dyson (who flew on a Soyuz spacecraft for a long-duration mission) and NASA astronauts Stephanie Wilson and Dorothy Metcalf-Lindenburger and Japan's Naoko Yamazaki, who arrived aboard the space shuttle Discovery on its brief STS-131 mission.
- Biggest space gathering: 13 people, during NASA's STS-127 shuttle mission aboard Endeavour in 2009. (It's been tied a few times during later missions.)
- Longest single spacewalk: 8 hours and 56 minutes during STS-102, for an ISS construction mission in 2001. NASA astronauts Jim Voss and Susan Helms participated.
- Longest Russian spacewalk: 8 hours and 13 minutes during Expedition 54, to repair an ISS antenna. Russian astronauts Alexander Misurkin and Anton Shkaplerov participated.
- Discover more about the ISS with this Haynes manual: International Space Station: An insight into the history, development, collaboration, production and role of the permanently manned earth-orbiting complex (Owners' Workshop Manual)
- Look out the windows of the ISS with this amazing visual guide: Interior Space: A Visual Exploration of the International Space Station: Photographs by Paolo Nespoli & Roland Mille
- Scott Kelly's account of life aboard the ISS: Endurance: A Year in Space, a Lifetime of Discovery
This article was updated on Oct. 12, 2021 by Space.com staff writer Scott Dutfield.
Additional reporting by Space.com Reference Editor Tim Sharp.