International Space Station

ISS can also refer to other things. See ISS (disambiguation) for more. The International Space Station is a space station in low Earth orbit. It is run by five space agencies: NASA from the United States, Roscosmos from Russia, ESA from Europe, JAXA from Japan, and CSA from Canada. It is the first space station built, maintained, and crewed through international cooperation, and it is the largest human spacecraft ever built. It is an orbital research station, where scientists perform experiments in microgravity and study the space environment. Since 2 November 2000, it has hosted the longest continuous human presence in space. Along with China's Tiangong, it is one of two space stations that are operating today.

The station circles Earth between 51.64° north and south. It orbits about 400 kilometres (250 miles) above Earth, which keeps it below the Van Allen radiation belts and most space debris. It travels at 7.67 km/s (27,600 km/h; 17,200 mph) and completes an orbit about every 93 minutes, which means it circles Earth 15.5 times a day. Including its solar arrays, it measures 109 m (358 ft) by 73 m (239 ft), about the size of a full-sized football or soccer field. Its pressurised inside space is 1,005 m³ (35,491 ft³), which is similar to that of a Boeing 747 airliner.

The station is a modular space station made of two main parts: the Russian Orbital Segment (ROS), built by Roscosmos, and the US Orbital Segment (USOS), built by NASA, ESA, JAXA, and CSA. The Integrated Truss Structure connects its large solar panels and radiators to its 16 major pressurized modules. These modules support scientific research, crew living, storage, spacecraft control, and airlock operations. The ISS has eight docking and berthing ports for visiting spacecraft, and in total it includes 43 different modules and elements. Crews travel to it on Soyuz and Crew Dragon spacecraft and, in the past, on the Space Shuttle. Supply ships that bring cargo include Progress, Cargo Dragon, Cygnus, Automated Transfer Vehicle, and HTV-X.

The ISS is the political product of the growth of international cooperation in space during the space age. It combines two crewed Earth-orbiting stations that had been planned earlier: the United States' Space Station Freedom and the Soviet Union's Mir-2. The first ISS module was launched in 1998, and its major parts were carried into space by Proton, Soyuz, and Space Shuttle launch vehicles. Long-term living on the station began when the Expedition 1 crew arrived on 2 November 2000. Since then, the ISS has been continuously occupied for 25 years and 345 days, the longest continuous human presence in space. As of August 2025, 290 people from 26 countries had visited the station.

Future plans include adding at least one module, the Payload Power Thermal Module from Axiom Space, which will form the station's commercial part. The station is expected to keep working until the end of 2030, when parts of it are planned to be used for Axiom Station and the Russian Orbital Station. After that, the ISS is planned to be brought down from orbit using the US Deorbit Vehicle. However, some people have criticized this plan and proposed moving the station to a more stable, higher orbit, and as of 2026 this idea has gained support in Congress.

Conception

Purpose

The ISS was first meant to be a laboratory, observatory, and factory. It was also meant to provide transportation, maintenance, and a low Earth orbit staging base for possible future missions to the Moon, Mars, and asteroids. Not all of the uses in the first memorandum of understanding between NASA and Roscosmos have come true. The 2010 United States National Space Policy gave the ISS more jobs, including serving commercial, diplomatic, and educational purposes.

Scientific research is one of the station's main jobs. The ISS has power, data, cooling, and crew to support experiments, and it lets scientists study things that are hard to test on Earth, such as the effects of space on the human body. Main article: Scientific research on the International Space Station

Five space programs and fifteen countries take part in the International Space Station, which makes it the most politically and legally complex space program in history. The main rules for working together come from a 1998 agreement, and later agreements cover other matters, such as rules for visiting astronauts. Countries taking part include Canada, the European Space Agency, Belgium, Denmark, France, Germany, Italy, the Netherlands, Norway, Spain, Sweden, Switzerland, the United Kingdom, Japan, Russia, and the United States.

Brazil was invited to join, the only developing country to receive such an invitation. It was to provide six pieces of equipment in exchange for rights to use the station, but it could not deliver any because of a lack of money and political priority. Brazil officially left the program in 2007. After the 2022 Russian invasion of Ukraine, cooperation between Russia and other countries on the station was put into question. Dmitry Rogozin suggested that Russia leaving could cause the station to fall out of orbit, but NASA said that Northrop Grumman had offered a way to keep it in orbit if needed. In July 2022, Yury Borisov submitted plans to Russian President Vladimir Putin for leaving the program after 2024, but NASA said it had not received any formal notice of this.

Construction

Main article: Manufacture of the International Space Station

Main articles: Assembly of the International Space Station and List of ISS spacewalks

The International Space Station is built from parts made around the world. The Russian modules Zarya and Zvezda, part of the Russian Orbital Segment, were made at the Khrunichev State Research and Production Space Center in Moscow. Zvezda was first made in 1985 for the Mir-2 station, which was never launched. Much of the US Orbital Segment, including Destiny and Unity, the Integrated Truss Structure, and solar arrays, was built at NASA's Marshall Space Flight Center in Huntsville, Alabama and the Michoud Assembly Facility in New Orleans. These parts were prepared for launch at the Operations and Checkout Building and the Space Station Processing Facility (SSPF) at the Kennedy Space Center in Florida. Other parts came from around the world too: the Columbus module from the European Space Agency, built in Germany; the Kibō module from Japan, built at the Tsukuba Space Center and the Institute of Space and Astronautical Science; and the Canadarm2 and Dextre, a joint Canadian-U.S. project. All of these were sent to the SSPF to be prepared for launch.

Assembly of the station, a major project in space architecture, began in November 1998. Russian modules launched and docked on their own, except for Rassvet. Other parts were carried by the Space Shuttle, and astronauts installed them using robotic arms or during extra-vehicular activities (EVAs), more commonly called spacewalks. By 5 June 2011, astronauts had made over 159 EVAs, totaling more than 1,000 hours in space. The first core piece, the Russian-built Zarya, was launched on a Proton rocket on 20 November 1998 and provided attitude control, communications, and power. On 4 December 1998, the American-made Unity was carried by Space Shuttle Endeavour on STS-88 and joined Zarya. The station stayed without a crew for two years until Zvezda launched in July 2000, bringing living quarters and life-support systems. The first crew arrived that November aboard Soyuz TM-31. After the loss of the Space Shuttle Columbia in 2003 grounded the Shuttle fleet, construction paused until 2006, when assembly resumed with STS-115. Later flights added the Harmony, Columbus, Kibō, Tranquility, Cupola, and Leonardo modules, along with Poisk, Rassvet, and Prichal. In 2021, Russia's Nauka research module docked. As of June 2025, NASA says the station has 43 different modules and elements installed.

Structure

The ISS is a modular space station, which means modules can be added or removed to change it. Its first part, Zarya, launched in 1998 and gave the station power, storage, and steering at the start. Unity connects the Russian and U.S. parts of the station. Other living and working modules include Zvezda, Destiny, the Quest Joint Airlock, Poisk, Harmony, Tranquility, Columbus, Kibō, the Cupola, Rassvet, Leonardo, Nauka, and Prichal. The Russian module Pirs was removed in 2021 to make room for Nauka.

The station also has many parts that are not pressurised, meaning people cannot live or work inside them. The largest is the Integrated Truss Structure, which holds the station's main solar arrays and thermal radiators. Robotic arms such as Canadarm2 and Dextre help move and service equipment outside. Axiom Space was given a contract to build a commercial module that will attach to the station, and NASA gave SpaceX a contract to build a vehicle that will bring the station down safely when its working life ends in 2030. Several other planned modules were cancelled during the program.

Onboard systems

Main articles: ISS ECLSS and Chemical oxygen generator

The most important systems keep the crew alive. These include air control, water, food, hygiene, and fire detection and suppression. The Russian part's life-support systems are in the Zvezda service module, and some are backed up by equipment in the USOS. The Nauka laboratory has a complete set of life-support systems. The air on the station is similar to that of Earth, at the same normal pressure as sea level on Earth: 101.3 kPa (14.69 psi). Russian and Soviet spacecraft kept Earth-like air, while American spacecraft used pure oxygen at 5 psi (0.3 atm) after launch. Oxygen is made by the Elektron system in Zvezda and a similar system in Destiny. Backup oxygen comes from bottled oxygen and Solid Fuel Oxygen Generation (SFOG) canisters, a chemical oxygen generator system. The Elektron unit splits water by electrolysis into oxygen and hydrogen, and the hydrogen is vented overboard. The water comes from Earth or is recycled, and Mir was the first spacecraft to use recycled water for oxygen. A second backup uses burning Vika cartridges (see also ISS ECLSS), which are operated by hand. Vozdukh in Zvezda removes carbon dioxide, and activated charcoal filters remove other body by-products such as methane and ammonia. The USOS has backup oxygen from a tank on the Quest airlock, and an ESA-built system in the Tranquility module (Node 3) also makes oxygen.

Main articles: Electrical system of the International Space Station and External Active Thermal Control System

Double-sided solar arrays provide electrical power to the station. These cells collect sunlight on one side and light reflected off Earth on the other. The Russian part uses 28 V low voltage DC from two solar arrays on Zvezda, while the USOS uses 130–180 V DC. A higher distribution voltage allows smaller, lighter wires but is less safe for the crew. The USOS arrays turn to follow the Sun using the alpha gimbal and beta gimbal. The Night Glider mode turns the arrays parallel to the ground at night to reduce drag. The station first used nickel–hydrogen batteries (NiH₂) to power it during the dark part of each orbit, and starting in 2016 these were replaced by lithium-ion batteries. Plasma contactor units help manage electrical current between the station and the space around it. Almost all the power becomes heat, so a passive system and an External Active Thermal Control System keep the temperature workable. The external system uses an ammonia loop and radiators, and the early version was launched on STS-105.

Main articles: Tracking and Data Relay Satellite and Luch (satellite)

See also: ThinkPad § Use in space

The station uses radio links for telemetry, data, and mission control centers, and during rendezvous and docking procedures. The Russian part mainly uses the Lira antenna for ground contact and the Luch relay satellites, which were restored in 2011 and 2012 with Luch-5A and Luch-5B. Voskhod-M provides internal phone calls. The US Orbital Segment uses S band and K_u band links, with the K_u band on the Z1 truss. These signals go through the Tracking and Data Relay Satellite System in geostationary orbit to the Christopher C. Kraft Jr. Mission Control Center in Houston, Texas. Other modules were planned to use the European Data Relay System and a similar Japanese system. UHF radio is used by astronauts on spacewalks and by visiting spacecraft, and the ATV used a laser to dock accurately. About 100 commercial off-the-shelf laptops run Windows or Linux. They were changed to use the station's power and to have extra ventilation. The main computer runs on Debian Linux, after a switch from Windows in 2013, and astronauts connect to it with a laptop through a USB adapter. Other laptops connect to the wireless LAN by Wi-Fi, which reaches the ground through the K_u band. In 2019, speeds were raised to 600 Mbit/s, and crew members have access to the internet.

Operations

Crews live and work on the station for periods called expeditions, which last up to six months. The number of crew members has changed over time. It was reduced to two after the loss of the Space Shuttle Columbia, grew to six around 2010, and has been seven since crews began arriving on larger US commercial spacecraft in 2020. Oleg Kononenko of Roscosmos holds the record for the most time spent in space, with nearly 1,111 days. As of 14 February 2026, 294 people from 26 countries had visited the station. Most were government astronauts, but some were private travellers. The United States has sent the most visitors, followed by Russia. Since 2021, NASA has also allowed private missions to visit the station.

Many spacecraft have carried cargo, crews, and supplies to the station, and it has eight docking ports for visiting craft. Some spacecraft dock automatically, while others are grabbed by a robotic arm and attached by astronauts. Spare parts are kept outside the station and replaced when they wear out or fail. Over the years, astronauts have repaired air leaks, cooling problems, power problems, and damaged solar arrays, often during spacewalks. In June 2026, the crew sheltered in a docked SpaceX Crew Dragon spacecraft because of an air leak on a Russian module, and they later returned to the station. The station's parts are watched by mission control centers in Houston, Moscow, and several other cities around the world.

Orbit, debris and visibility

The ISS flies in a nearly circular path, tilted 51.6 degrees from Earth's equator. This tilt was chosen so that Russian Baikonur Cosmodrome launches can reach it. The station travels with Earth's rotation (prograde) at about 28,000 kilometres per hour, completing 15.5 orbits each day in Low Earth Orbit. Air drag slowly lowers it, so it is sometimes raised again in a reboost. The station also turns itself using reaction wheels and thrusters.

The ISS shares its path with space debris, such as old rocket parts, dead satellites, and tiny pieces from explosions. Some of these pieces are a serious threat. When a collision is possible, the station can move to avoid it in a Debris Avoidance Manoeuvre. Main article: Space debris

Further information: Satellite watching and Satellite flare

From Earth, the ISS can be seen as a bright, moving white dot. It is the brightest artificial object in the sky, and it can be seen from about 95% of inhabited land. Many people enjoy photographing it through telescopes, and astronomers find it interesting when it crosses in front of the Sun.

Environment, safety and crew health

Gravity at the station's height is about 90% as strong as on Earth's surface, but everything in orbit is in continuous freefall, which creates weightlessness known as microgravity. Five effects disturb this: drag from the thin leftover atmosphere, vibration from machines and the crew, the control moment gyroscopes used on board, thruster firings, and gravity-gradient effects, also called tidal effects, which keep the station moving as a rigid body. The station is partly protected by Earth's magnetic field, whose magnetosphere deflects solar wind, but solar flares are still a hazard, and crews may get only a few minutes of warning. In 2005, the crew of Expedition 10 took shelter in a more shielded part of the ROS during the first "proton storm" of an X-3 class solar flare. Crews receive about one millisievert of radiation each day, which raises the risk of cancer. Radiation can damage the DNA and chromosomes of lymphocytes, cells central to the immune system, and it has been linked to more cataracts. Protective shielding and medicines may lower these risks. Protons in space can also create an aurora. Mold can grow in air and water filters, so the LOCAD-PTS test system was developed to find bacteria and molds faster than culturing. In 2018, researchers found five Enterobacter bugandensis strains on the station, none pathogenic to humans. Since 2016, MATISS experiments tested materials for "smart surfaces," and the last one launched on SpaceX CRS-28 in 2023 used pure silica for spectrographic analysis instead of light microsocopy. NASA's 2019 study used molecular-based methods along with culturing. Noise has been a concern since the Apollo missions, and noise control and hearing loss prevention are part of crew health work, with help from acoustical engineers, audiologists, and industrial hygienists. Noise rarely reaches 85 dBA, a level of concern to the Occupational Safety and Health Administration, but crews are exposed around the clock, which can affect sleep and audibility of alarms. Teams use noise barriers and quieter fans to lower ambient noise levels, follow guidance from the National Institute for Occupational Safety and Health and the World Health Organization, and recommend hearing protection devices and engineering controls. The team received the Safe-In-Sound Award in 2020. An onboard fire or toxic gas leak are other possible hazards, since ammonia used in the external radiators could leak into the pressurised modules.

See also: Coronal mass ejection

See also: Microbiological environmental hazards on the Mir space station

In 2019, NASA reported medical results from the Astronaut Twin Study, which compared Scott Kelly, who spent a year in space, with his twin Mark Kelly on Earth. Changes related to DNA and cognition were observed. Researchers also reported blood flow and clot problems in astronauts on the ISS. Stress is another concern, since psychosocial stressors affect crew morale and performance. Cosmonaut Valery Ryumin described difficult conditions on Salyut 6, and NASA has studied psychological stress since its crewed missions began. Living in close quarters with people from different cultures, and being away from family, can add stress, as with NASA astronaut Daniel Tani. Long-term weightlessness affects the physiological body, causing muscle atrophy, bone loss (osteopenia), and a weaker immune system. Sleep is often disturbed, and fans must run constantly because air cannot thermosiphon in freefall. To stay healthy, the station has two TVIS treadmills, the ARED weightlifting device, and a stationary bicycle, and each astronaut exercises at least two hours a day.

Main article: Effect of spaceflight on the human body

Life aboard

The International Space Station (ISS) has living and working space larger than a six-bedroom house. It includes seven private sleeping quarters, three bathrooms, two dining rooms, a gym, and a bay window with a 360-degree view. Long-term crew members have soundproof, person-sized booths for privacy and sleep, and visiting crew use sleeping bags tied to walls. The station's lighting can be dimmed, switched off, and changed in color temperature to support work and rest. A typical day starts at 06:00 and includes exercise, experiments, and maintenance, with the crew working about 10 hours on weekdays and 5 hours on Saturdays. The ISS runs on Coordinated Universal Time (UTC). Windows are covered during sleep because the station has 16 sunrises and sunsets each day.

See also: Space food and Plants in space

Food is packaged to last a long time, reduce waste, and avoid contamination. Because microgravity dulls taste, meals are often seasoned more heavily than on Earth. Crews look forward to resupply missions that bring fresh fruit and vegetables. Drinks are mixed from powder, and crews eat from a galley with food warmers, though many Russian meals come in cans or retort pouches. Astronauts also grow vegetables such as lettuce, Chinese cabbage, mizuna mustard, and red Russian kale, and NASA plans to grow peppers and other crops. The ISS has three Russian-designed toilets, in Zvezda, Tranquility (/w/12), and Nauka. Urine is diverted to a system that turns it into drinking water. The station has no shower, so astronauts clean themselves with wet wipes or a water jet.

End of mission

The ISS was first planned for a 15-year mission, but it has been extended again and again because of its success and support. As a result, its oldest modules have been in orbit for more than 25 years. In 2009, the United States planned to bring the station down in 2016, but later plans extended its operations to 2030. Congress passed similar rules in its CHIPS and Science Act, which U.S. President Joe Biden signed into law in 2022. NASA has suggested going beyond 2030 if Commercial LEO Destinations providers cannot meet its needs. In 2026, members of the United States House Committee on Science, Space, and Technology proposed an amendment, submitted by George T. Whitesides with support from Nick Begich III, Brian Babin and Don Beyer, asking NASA to study moving the station to a safe orbital harbor so it could be reused. In a January 2026 plan, Axiom Station would use science equipment and the Canadarm2 from the ISS. Russia has said it will leave the program after 2025, but its modules will still provide orbital station-keeping until 2028, and its Russian ISS segment was identified as a possible backup for bringing the station down. In late 2025, Russia reconsidered their future space station plans to include ISS modules again.

The station has become less reliable the longer it has operated, and astronauts now spend half of their time on maintenance. Air leaks and mold have raised safety concerns. An unmaintained station would be a space debris and re-entry hazard, and under the Outer Space Treaty, the countries that launched its parts are legally responsible for them. NASA decided that random re-entry was too risky and chose a controlled de-orbit into a remote part of the South Pacific called the spacecraft cemetery, roughly centered on Point Nemo. NASA announced in 2022 that it planned to de-orbit the ISS in January 2031 using the "U.S. Deorbit Vehicle," which is based on a Cargo Dragon spacecraft paired with a longer trunk module. Meanwhile, companies have proposed reusing parts of the station, and in 2025 Elon Musk, who was a Senior Advisor to President Trump, suggested the station be de-orbited sooner. Plans for the future include the Commercial LEO Destinations Program, Russia's planned OPSEK station, and the Exploration Gateway Platform concept, which would have used parts of the station near the Lagrange points.

Cost

The ISS has been described as the most expensive single item ever built. As of 2010, its total cost was US$150 billion. NASA's share was $58.7 billion for the station from 1985 to 2015. Russia spent $12 billion, Europe $5 billion, Japan $5 billion, and Canada $2 billion. The 36 space shuttle flights used to build the station added about $50.4 billion more.

Based on estimates of how many people used the station, each person-day cost less than half of what a person-day cost on Skylab, another space station. NASA still spends about US$3 billion per year on running the station.

In culture

The ISS has become an international symbol of human abilities, especially cooperation and science. It stands for a time of countries working together, instead of a future that is commercialized and militarized. The station has also been used for many public campaigns, and its decades of operation can be explored on an interactive website called ISS in Real Time. The ISS appears in many films. It is the subject of documentaries such as the IMAX films Space Station 3D (2002) and A Beautiful Planet (2016), and it appears in films such as Apogee of Fear (2012) and Yolki 5 (2016). It is also the subject of feature films such as The Day After Tomorrow (2004), Love (2011), and Gravity (2013), where it appears together with the Chinese station Tiangong 1. Other films include Life (2017) and I.S.S. (2023). In 2022, the movie The Challenge (Doctor's House Call) was filmed aboard the ISS, and it was the first feature film in which both professional actors and a director worked together in space.

The station also appears in books and games. Neal Stephenson's 2015 novel Seveneves is set largely on the ISS in its first and second parts. The station is shown mostly as it was when the novel was written, but with a large captured asteroid attached to it. The 2023 novel Orbital by English writer Samantha Harvey is also set on the ISS, and it won the 2024 Booker Prize. Ceridwen Dovey's Only the Astronauts, a 2024 collection of short stories, includes the station, with an inanimate object in space as the narrator of each story. In video games, the ISS is blown up during the Call of Duty: Modern Warfare 2 mission "Second Sun", in which the character Captain Price launches an ICBM into the earth's atmosphere, and the resulting shockwave destroys the station. The ISS also appears in Far Cry New Dawn as an expedition site, where it has fallen to earth during a nuclear war.