International Space Station

Purpose

The ISS was originally intended to be a laboratory, observatory, and factory while providing transportation, maintenance, and a low Earth orbit staging base for possible future missions to the Moon, Mars, and asteroids. However, not all of the uses envisioned in the initial memorandum of understanding between NASA and Roscosmos have been realised. In the 2010 United States National Space Policy, the ISS was given additional roles of serving commercial, diplomatic, and educational purposes.

Scientific research

The ISS provides a platform to conduct scientific research, with power, data, cooling, and crew available to support experiments. Small uncrewed spacecraft can also provide platforms for experiments, especially those involving zero gravity and exposure to space, but space stations offer a long-term environment where studies can be performed potentially for decades, with ready access by human researchers.

The ISS simplifies individual experiments by allowing groups of experiments to share the same launches and crew time. Research is conducted in a wide variety of fields, including astrobiology, astronomy, physical sciences, materials science, space weather, meteorology, and human research including space medicine and the life sciences. Scientists on Earth have timely access to the data and can suggest experimental modifications to the crew. If follow-on experiments are necessary, the routinely scheduled launches of resupply craft allows new hardware to be launched with relative ease. Crews fly expeditions of several months' duration, providing approximately 160 man-hours per week of labour with a crew of six. However, a considerable amount of crew time is taken up by station maintenance.

A notable ISS experiment is the Alpha Magnetic Spectrometer (AMS), which is intended to detect dark matter and answer other fundamental questions about the universe. According to NASA, the AMS is as important as the Hubble Space Telescope. It is docked on the station, and could not have been easily accommodated on a free flying satellite platform because of its power and bandwidth needs. On 3 April 2013, scientists reported that hints of dark matter may have been detected by the AMS. According to these scientists, "The first results from the space-borne Alpha Magnetic Spectrometer confirm an unexplained excess of high-energy positrons in Earth-bound cosmic rays".

The space environment is hostile to life. Unprotected presence in space results in exposure to intense radiation (consisting primarily of protons and other subatomic charged particles from the solar wind, in addition to cosmic rays), vacuum, extreme temperatures, and microgravity. Some simple forms of life called extremophiles, as well as small invertebrates called tardigrades, can survive in this environment in an extremely dry state through desiccation.

Medical research improves knowledge about the effects of long-term space exposure on the human body, including muscle atrophy, bone loss, and fluid shift. This data will be used to determine whether long-lasting human spaceflight and space colonisation is feasible. In 2006, data on bone loss and muscular atrophy suggested that there would be a significant risk of fractures and movement problems if astronauts landed on a planet after a lengthy interplanetary cruise, such as the six-month interval required to travel to Mars.

Exploration

The ISS provides a location in the relative safety of low Earth orbit to test spacecraft systems that will be required for long-duration missions to the Moon and Mars. This provides experience in operations, maintenance, and repair and replacement activities on-orbit. This will help develop essential skills in operating spacecraft farther from Earth, reduce mission risks, and advance the capabilities of interplanetary spacecraft. Referring to the MARS-500 experiment, a crew isolation experiment conducted on Earth, ESA states, "Whereas the ISS is essential for answering questions concerning the possible impact of weightlessness, radiation and other space-specific factors, aspects such as the effect of long-term isolation and confinement can be more appropriately addressed via ground-based simulations". Sergey Krasnov, the head of human space flight programs for Russia's space agency, Roscosmos, in 2011 suggested a "shorter version" of MARS-500 may be carried out on the ISS.

In 2009, noting the value of the partnership framework itself, Sergey Krasnov wrote, "When compared with partners acting separately, partners developing complementary abilities and resources could give us much more assurance of the success and safety of space exploration. The ISS is helping further advance near-Earth space exploration and realisation of prospective programs of research and exploration of the Solar system, including the Moon and Mars." A crewed mission to Mars may be a multinational effort involving space agencies and countries outside the current ISS partnership. In 2010, ESA Director-General Jean-Jacques Dordain stated his agency was ready to propose to the other four partners that China, India, and South Korea be invited to join the ISS partnership. NASA chief Charles Bolden stated in February 2011, "Any mission to Mars is likely to be a global effort." Currently, US federal legislation prevents NASA co-operation with China on space projects without approval by the FBI and Congress.

Education and cultural outreach

The ISS crew provides opportunities for students on Earth by running student-developed experiments, making educational demonstrations, allowing for student participation in classroom versions of ISS experiments, and directly engaging students using radio, and email. ESA offers a wide range of free teaching materials that can be downloaded for use in classrooms. In one lesson, students can navigate a 3D model of the interior and exterior of the ISS, and face spontaneous challenges to solve in real time.

The Japanese Aerospace Exploration Agency (JAXA) aims to inspire children to "pursue craftsmanship" and to heighten their "awareness of the importance of life and their responsibilities in society". Through a series of education guides, students develop a deeper understanding of the past and near-term future of crewed space flight, as well as that of Earth and life. In the JAXA "Seeds in Space" experiments, the mutation effects of spaceflight on plant seeds aboard the ISS are explored by growing sunflower seeds that have flown on the ISS for about nine months. In the first phase of Kibō utilisation from 2008 to mid-2010, researchers from more than a dozen Japanese universities conducted experiments in diverse fields.

Cultural activities are another major objective of the ISS program. Tetsuo Tanaka, the director of JAXA's Space Environment and Utilization Center, has said: "There is something about space that touches even people who are not interested in science."

Amateur Radio on the ISS (ARISS) is a volunteer program that encourages students worldwide to pursue careers in science, technology, engineering, and mathematics, through amateur radio communications opportunities with the ISS crew. ARISS is an international working group, consisting of delegations from nine countries including several in Europe, as well as Japan, Russia, Canada, and the United States. In areas where radio equipment cannot be used, speakerphones connect students to ground stations which then connect the calls to the space station. Other licensed operators are able to contact the station freely via various methods, including NFM , APRS and SSTV (Only during events, and downlink only)

First Orbit is a 2011 feature-length documentary film about Vostok 1, the first crewed space flight around the Earth. By matching the orbit of the ISS to that of Vostok 1 as closely as possible, in terms of ground path and time of day, documentary filmmaker Christopher Riley and ESA astronaut Paolo Nespoli were able to film the view that Yuri Gagarin saw on his pioneering orbital space flight. This new footage was cut together with the original Vostok 1 mission audio recordings sourced from the Russian State Archive. Nespoli is credited as the director of photography for this documentary film, as he recorded the majority of the footage himself during Expedition 26/27. The film was streamed in a global YouTube premiere in 2011 under a free licence through the website firstorbit.org.

International co-operation

Involving five space programs and fifteen countries, the International Space Station is the most politically and legally complex space exploration program in history. The 1998 Space Station Intergovernmental Agreement sets forth the primary framework for international cooperation among the parties. A series of subsequent agreements govern other aspects of the station, ranging from jurisdictional issues to a code of conduct among visiting astronauts.

Brazil was also invited to participate in the program, the only developing country to receive such an invitation. Under the agreement framework, Brazil was to provide six pieces of hardware, and in exchange, would receive ISS utilization rights. However, Brazil was unable to deliver any of the elements due to a lack of funding and political priority within the country. Brazil officially dropped out of the ISS program in 2007.

Following the 2022 Russian invasion of Ukraine, continued cooperation between Russia and other countries on the International Space Station has been put into question. Roscosmos Director General Dmitry Rogozin insinuated that Russian withdrawal could cause the International Space Station to de-orbit due to lack of reboost capabilities, writing in a series of tweets, "If you block cooperation with us, who will save the ISS from an unguided de-orbit to impact on the territory of the US or Europe? There's also the chance of impact of the 500-ton construction in India or China. Do you want to threaten them with such a prospect? The ISS doesn't fly over Russia, so all the risk is yours. Are you ready for it?" (This latter claim is untrue: the ISS flies over all parts of the Earth between 51.6 degrees latitude north and south, approximately the latitude of Saratov.) Rogozin later tweeted that normal relations between ISS partners could only be restored once sanctions have been lifted, and indicated that Roscosmos would submit proposals to the Russian government on ending cooperation. NASA stated that, if necessary, US corporation Northrop Grumman has offered a reboost capability that would keep the ISS in orbit.

On 26 July 2022, Yury Borisov, Rogozin's successor as head of Roscosmos, submitted to Russian President Vladimir Putin plans for withdrawal from the program after 2024. However, Robyn Gatens, the NASA official in charge of the space station, responded that NASA had not received any formal notices from Roscosmos concerning withdrawal plans.

Participating countries

Canada

European Space Agency

Belgium

Denmark

France

Germany

Italy

Netherlands

Norway

Spain

Sweden

Switzerland

United Kingdom

Japan

Russia

United States

Construction

Manufacturing

The International Space Station is a product of global collaboration, with its components manufactured across the world.

The modules of the Russian Orbital Segment, including Zarya and Zvezda, were produced at the Khrunichev State Research and Production Space Center in Moscow. Zvezda was initially manufactured in 1985 as a component for the Mir-2 space station, which was never launched.

Much of the US Orbital Segment, including the Destiny and Unity modules, the Integrated Truss Structure, and solar arrays, were built at NASA's Marshall Space Flight Center in Huntsville, Alabama and Michoud Assembly Facility in New Orleans. These components underwent final assembly and processing for launch at the Operations and Checkout Building and the Space Station Processing Facility (SSPF) at the Kennedy Space Center in Florida.

The US Orbital Segment also hosts the Columbus module contributed by the European Space Agency and built in Germany, the Kibō module contributed by Japan and built at the Tsukuba Space Center and the Institute of Space and Astronautical Science, along with the Canadarm2 and Dextre, a joint Canadian-U.S. endeavor. All of these components were shipped to the SSPF for launch processing.

Assembly

The assembly of the International Space Station, a major endeavour in space architecture, began in November 1998.

Modules in the Russian segment launched and docked autonomously, with the exception of Rassvet. Other modules and components were delivered by the Space Shuttle, which then had to be installed by astronauts either remotely using robotic arms or during spacewalks, more formally known as extra-vehicular activities (EVAs). By 5 June 2011 astronauts had made over 159 EVAs to add components to the station, totaling more than 1,000 hours in space.

The beginning of the core of the ISS's tenure in orbit was the launch of the Russian-built Zarya module atop a Proton rocket on 20 November 1998. Zarya provided propulsion, attitude control, communications, and electrical power. Two weeks later on 4 December 1998, the American-made Unity was ferried aboard Space Shuttle Endeavour on STS-88 and joined with Zarya. Unity provided the connection between the Russian and US segments of the station and would provide ports to connect future modules and visiting spacecraft.

While the connection of two modules built on different continents by nations that were once bitter rivals was a significant milestone, these two initial modules lacked life-support systems and the ISS remained unmanned for the next two years. At the time, the Russian station Mir was still inhabited.

The turning point arrived in July 2000 with the launch of the Zvezda module. Equipped with living quarters and life-support systems, Zvezda enabled continuous human presence aboard the station. The first crew, Expedition 1, arrived that November aboard Soyuz TM-31.

The ISS grew steadily over the following years, with modules delivered by both Russian rockets and the Space Shuttle.

Expedition 1 arrived midway between the Space Shuttle flights of missions STS-92 and STS-97. These two flights each added segments of the station's Integrated Truss Structure, which provided the station with Ku band communications, additional attitude control needed for the additional mass of the USOS, and additional solar arrays. Over the next two years, the station continued to expand. A Soyuz-U rocket delivered the Pirs docking compartment. The Space Shuttles Discovery, Atlantis, and Endeavour delivered the American Destiny laboratory and Quest airlock, in addition to the station's main robot arm, the Canadarm2, and several more segments of the Integrated Truss Structure.

Structure

The ISS functions as a modular space station, enabling the addition or removal of modules from its structure for increased adaptability.

Below is a diagram of major station components. The Unity node joins directly to the Destiny laboratory; for clarity, they are shown apart. Similar cases are also seen in other parts of the structure.

Key to box background colors:

Pressurised component, accessible by the crew without using spacesuits

Docking/berthing port, pressurized when a visiting spacecraft is present

Airlock, to move people or material between pressurized and unpressurized environment

Unpressurised station superstructure

Unpressurised component

Temporarily defunct or non-commissioned component

Former, no longer installed component

Future, not yet installed component

Pressurised modules

Zarya (Russian: Заря, lit. 'Sunrise'), also known as the Functional Cargo Block (Russian: Функционально-грузовой блок), was the inaugural component of the ISS. Launched in 1998, it initially served as the ISS's power source, storage, propulsion, and guidance system. As the station has grown, Zarya's role has transitioned primarily to storage, both internally and in its external fuel tanks.

A descendant of the TKS spacecraft used in the Salyut program, Zarya was built in Russia but is owned by the United States. Its name symbolizes the beginning of a new era of international space cooperation.

Unity, also known as Node 1, is the inaugural U.S.-built component of the ISS. Serving as the connection between the Russian and U.S. segments, this cylindrical module features six Common Berthing Mechanism locations (forward, aft, port, starboard, zenith, and nadir) for attaching additional modules. Measuring 4.57 metres (15.0 ft) in diameter and 5.47 metres (17.9 ft) in length, Unity was constructed of steel by Boeing for NASA at the Marshall Space Flight Center in Huntsville, Alabama. It was the first of three connecting nodes – Unity, Harmony, and Tranquility – that forms the structural backbone of the U.S. segment of the ISS.

Zvezda (Russian: Звезда, lit. 'star') launched in July 2000, is the core of the Russian Orbital Segment of the ISS. Initially providing essential living quarters and life-support systems, it enabled the first continuous human presence aboard the station. While additional modules have expanded the ISS's capabilities, Zvezda remains the command and control center for the Russian segment and it is where crews gather during emergencies.

A descendant of the Salyut program's DOS spacecraft, Zvezda was built by RKK Energia and launched atop a Proton rocket.

The Destiny laboratory is the primary research facility for U.S. experiments on the ISS. NASA's first permanent orbital research station since Skylab, the module was built by Boeing and launched aboard Space Shuttle Atlantis during STS-98. Attached to Unity over a period of five days in February 2001, Destiny has been a hub for scientific research ever since.

Unpressurised elements

The ISS has a large number of external components that do not require pressurisation. The largest of these is the Integrated Truss Structure (ITS), to which the station's main solar arrays and thermal radiators are mounted. The ITS consists of ten separate segments forming a structure 108.5 metres (356 ft) long.

The station was intended to have several smaller external components, such as six robotic arms, three External Stowage Platforms (ESPs) and four ExPRESS Logistics Carriers (ELCs). While these platforms allow experiments (including MISSE, the STP-H3 and the Robotic Refueling Mission) to be deployed and conducted in the vacuum of space by providing electricity and processing experimental data locally, their primary function is to store spare Orbital Replacement Units (ORUs). ORUs are parts that can be replaced when they fail or pass their design life, including pumps, storage tanks, antennas, and battery units. Such units are replaced either by astronauts during EVA or by robotic arms. Several shuttle missions were dedicated to the delivery of ORUs, including STS-129, STS-133 and STS-134. As of January 2011, only one other mode of transportation of ORUs had been used – the Japanese cargo vessel HTV-2 – which delivered an FHRC and CTC-2 via its Exposed Pallet (EP).

There are also smaller exposure facilities mounted directly to laboratory modules; the Kibō Exposed Facility serves as an external "porch" for the Kibō complex, and a facility on the European Columbus laboratory provides power and data connections for experiments such as the European Technology Exposure Facility and the Atomic Clock Ensemble in Space. A remote sensing instrument, SAGE III-ISS, was delivered to the station in February 2017 aboard CRS-10, and the NICER experiment was delivered aboard CRS-11 in June 2017. The largest scientific payload externally mounted to the ISS is the Alpha Magnetic Spectrometer (AMS), a particle physics experiment launched on STS-134 in May 2011, and mounted externally on the ITS. The AMS measures cosmic rays to look for evidence of dark matter and antimatter.

The commercial Bartolomeo External Payload Hosting Platform, manufactured by Airbus, was launched on 6 March 2020 aboard CRS-20 and attached to the European Columbus module. It will provide an additional 12 external payload slots, supplementing the eight on the ExPRESS Logistics Carriers, ten on Kibō, and four on Columbus. The system is designed to be robotically serviced and will require no astronaut intervention. It is named after Christopher Columbus's younger brother.

Former module

Pirs (Russian: Пирс, lit. 'Pier') was launched on 14 September 2001, as ISS Assembly Mission 4R, on a Russian Soyuz-U rocket, using a modified Progress spacecraft, Progress M-SO1, as an upper stage. Pirs was undocked by Progress MS-16 on 26 July 2021, 10:56 UTC, and deorbited on the same day at 14:51 UTC to make room for the Nauka module to be attached to the space station. Prior to its departure, Pirs served as the primary Russian airlock on the station, being used to store and refurbish the Russian Orlan spacesuits.

Planned components

In January 2020, NASA awarded Axiom Space a contract to build a commercial module for the ISS. The contract is under the NextSTEP2 program. NASA negotiated with Axiom on a firm fixed-price contract basis to build and deliver the module, which will attach to the forward port of the space station's Harmony (Node 2) module. Although NASA only commissioned one module, Axiom planned to build an entire segment (Axiom Orbital Segment) consisting of five modules, including a node module, an orbital research and manufacturing facility, a crew habitat, and a "large-windowed Earth observatory". The Axiom segment was expected to greatly increase the capabilities and value of the space station, allowing for larger crews and private spaceflight by other organisations. Axiom planned to convert the segment into a stand-alone space station (Axiom Station) once the ISS is decommissioned, with the intention that this would act as a successor to the ISS. Canadarm2 is planned to continue its operations on Axiom Station after the retirement of ISS in 2030. In December 2024, Axiom Space revised their station assembly plans to require only one module to dock with the ISS before assembling Axiom Station in an independent orbit. The module docked to the ISS will feature storage for established ISS hardware to be transferred to and retained at the Axiom module and later station.

As of December 2024, Axiom Space expects to launch one module, the Payload Power Thermal Module (PPTM), to the ISS no earlier than 2027. PPTM is expected to remain at the ISS until the launch of Axiom's Habitat One (Hab-1) module about one year later, after which it will detach from the ISS to join with Hab-1.

The US Deorbit Vehicle (USDV) is a NASA-provided spacecraft intended to perform a controlled de-orbit and demise of the station after the end of its operational life in 2030. In June 2024, NASA awarded SpaceX a contract to build the Deorbit Vehicle. NASA plans to de-orbit ISS as soon as they have the "minimum capability" in orbit: "the USDV and at least one commercial station."

Cancelled components

Several modules developed or planned for the station were cancelled over the course of the ISS program. Reasons include budgetary constraints, the modules becoming unnecessary, and station redesigns after the 2003 Columbia disaster. The US Centrifuge Accommodations Module would have hosted science experiments in varying levels of artificial gravity. The US Habitation Module would have served as the station's living quarters. Instead, the living quarters are now spread throughout the station. The US Interim Control Module and ISS Propulsion Module would have replaced the functions of Zvezda in case of a launch failure. Two Russian Research Modules were planned for scientific research. They would have docked to a Russian Universal Docking Module. The Russian Science Power Platform would have supplied power to the Russian Orbital Segment independent of the ITS solar arrays.

Science Power Module 1 (SPM-1, also known as NEM-1) and Science Power Module 2 (SPM-2, also known as NEM-2) are modules that were originally planned to arrive at the ISS no earlier than 2024, and dock to the Prichal module, which is docked to the Nauka module. In April 2021, Roscosmos announced that NEM-1 would be repurposed to function as a core module of the proposed Russian Orbital Service Station (ROS), launching no earlier than 2027 and docking to the free-flying Nauka module. NEM-2 may be converted into another core "base" module, which would be launched in 2028. As of December 2025, NEM-1—now referred to simply as NEM—is expected to be launched to the ISS in 2029, where it will dock with the Universal Node module replacing Prichal prior to the separation of the ROS modules around 2030.

In August 2016, Bigelow Aerospace negotiated an agreement with NASA to develop a full-size ground prototype Deep Space Habitation based on the B330 under the second phase of Next Space Technologies for Exploration Partnerships. The module was called the Expandable Bigelow Advanced Station Enhancement (XBASE), as Bigelow hoped to test the module by attaching it to the International Space Station. However, in March 2020, Bigelow laid off all 88 of its employees, and as of February 2024 the company remains dormant and is considered defunct, making it appear unlikely that the XBASE module will ever be launched.

A proposal was put forward in 2011 for a first in-space demonstration of a sufficiently scaled centrifuge for artificial partial-g gravity effects. It was designed to become a sleep module for the ISS crew. The project was cancelled in favour of other projects due to budget constraints.

Onboard systems

Life support

The critical systems are the atmosphere control system, the water supply system, the food supply facilities, the sanitation and hygiene equipment, and fire detection and suppression equipment. The Russian Orbital Segment's life-support systems are contained in the Zvezda service module. Some of these systems are supplemented by equipment in the USOS. The Nauka laboratory has a complete set of life-support systems.

The atmosphere on board the ISS is similar to that of Earth. Normal air pressure on the ISS is 101.3 kPa (14.69 psi), the same as at sea level on Earth. While the crew would remain healthy at a lower pressure, some equipment is very pressure-sensitive.

Earth-like atmospheric conditions have been maintained on all Russian and Soviet spacecraft, while American spacecraft used pure oxygen atmospheres at 5 psi (0.3 atm) after launch.

The Elektron system aboard Zvezda and a similar system in Destiny generate oxygen aboard the station. The crew has a backup option in the form of bottled oxygen and Solid Fuel Oxygen Generation (SFOG) canisters, a chemical oxygen generator system. Carbon dioxide is removed from the air by the Vozdukh system in Zvezda. Other by-products of human metabolism, such as methane from the intestines and ammonia from sweat, are removed by activated charcoal filters.

Part of the ROS atmosphere control system is the oxygen supply. Triple-redundancy is provided by the Elektron unit, solid fuel generators, and stored oxygen. The primary supply of oxygen is the Elektron unit which produces O2 and H2 by electrolysis of water and vents H2 overboard. The 1 kW (1.3 hp) system uses approximately one litre of water per crew member per day. This water is either brought from Earth or recycled from other systems. Mir was the first spacecraft to use recycled water for oxygen production. The secondary oxygen supply is provided by burning oxygen-producing Vika cartridges (see also ISS ECLSS). Each 'candle' takes 5–20 minutes to decompose at 450–500 °C (842–932 °F), producing 600 litres (130 imp gal; 160 US gal) of O2. This unit is manually operated.

The US Orbital Segment (USOS) has redundant supplies of oxygen, from a pressurised storage tank on the Quest airlock module delivered in 2001, supplemented ten years later by ESA-built Advanced Closed-Loop System (ACLS) in the Tranquility module (Node 3), which produces O2 by electrolysis. Hydrogen produced is combined with carbon dioxide from the cabin atmosphere and converted to water and methane.

Power and thermal control

Double-sided solar arrays provide electrical power to the ISS. These bifacial cells collect direct sunlight on one side and light reflected off from the Earth on the other, and are more efficient and operate at a lower temperature than single-sided cells commonly used on Earth.

The Russian segment of the station, like most spacecraft, uses 28 V low voltage DC from two rotating solar arrays mounted on Zvezda. The USOS uses 130–180 V DC from the USOS PV array. Power is stabilised and distributed at 160 V DC and converted to the user-required 124 V DC. The higher distribution voltage allows smaller, lighter conductors, at the expense of crew safety. The two station segments share power with converters.

The USOS solar arrays are arranged as four wing pairs, for a total production of 75 to 90 kilowatts. These arrays normally track the Sun to maximise power generation. Each array is about 375 m2 (4,036 sq ft) in area and 58 m (190 ft) long. In the complete configuration, the solar arrays track the Sun by rotating the alpha gimbal once per orbit; the beta gimbal follows slower changes in the angle of the Sun to the orbital plane. The Night Glider mode aligns the solar arrays parallel to the ground at night to reduce the significant aerodynamic drag at the station's relatively low orbital altitude.

The station originally used rechargeable nickel–hydrogen batteries (NiH2) for continuous power during the 45 minutes of every 90-minute orbit that it is eclipsed by the Earth. The batteries are recharged on the day side of the orbit. They had a 6.5-year lifetime (over 37,000 charge/discharge cycles) and were regularly replaced over the anticipated 20-year life of the station. Starting in 2016, the nickel–hydrogen batteries were replaced by lithium-ion batteries, which are expected to last until the end of the ISS program.

The station's large solar panels generate a high potential voltage difference between the station and the ionosphere. This could cause arcing through insulating surfaces and sputtering of conductive surfaces as ions are accelerated by the spacecraft plasma sheath. To mitigate this, plasma contactor units create current paths between the station and the ambient space plasma.

The station's systems and experiments consume a large amount of electrical power, almost all of which is converted to heat. To keep the internal temperature within workable limits, a passive thermal control system (PTCS) is made of external surface materials, insulation such as MLI, and heat pipes. If the PTCS cannot keep up with the heat load, an External Active Thermal Control System (EATCS) maintains the temperature. The EATCS consists of an internal, non-toxic, water coolant loop used to cool and dehumidify the atmosphere, which transfers collected heat into an external liquid ammonia loop. From the heat exchangers, ammonia is pumped into external radiators that emit heat as infrared radiation, then the ammonia is cycled back to the station. The EATCS provides cooling for all the US pressurised modules, including Kibō and Columbus, as well as the main power distribution electronics of the S0, S1 and P1 trusses. It can reject up to 70 kW. This is much more than the 14 kW of the Early External Active Thermal Control System (EEATCS) via the Early Ammonia Servicer (EAS), which was launched on STS-105 and installed onto the P6 Truss.

Communications and computers

The ISS relies on various radio communication systems to provide telemetry and scientific data links between the station and mission control centers. Radio links are also used during rendezvous and docking procedures and for audio and video communication between crew members, flight controllers and family members. As a result, the ISS is equipped with internal and external communication systems used for different purposes.

The Russian Orbital Segment primarily uses the Lira antenna mounted on Zvezda for direct ground communication. It also had the capability to utilize the Luch data relay satellite system, which was in a state of disrepair when the station was built, but was restored to operational status in 2011 and 2012 with the launch of Luch-5A and Luch-5B. Additionally, the Voskhod-M system provides internal telephone communications and VHF radio links to ground control.

The US Orbital Segment (USOS) makes use of two separate radio links: S band (audio, telemetry, commanding – located on the P1/S1 truss) and Ku band (audio, video and data – located on the Z1 truss) systems. These transmissions are routed via the United States Tracking and Data Relay Satellite System (TDRSS) in geostationary orbit, allowing for almost continuous real-time communications with Christopher C. Kraft Jr. Mission Control Center (MCC-H) in Houston, Texas. Data channels for the Canadarm2, European Columbus laboratory and Japanese Kibō modules were originally also routed via the S band and Ku band systems, with the European Data Relay System and a similar Japanese system intended to eventually complement the TDRSS in this role.

UHF radio is used by astronauts and cosmonauts conducting EVAs and other spacecraft that dock to or undock from the station. Automated spacecraft are fitted with their own communications equipment; the ATV used a laser attached to the spacecraft and the Proximity Communications Equipment attached to Zvezda to accurately dock with the station.

The US Orbital Segment of the ISS is equipped with approximately 100 commercial off-the-shelf laptops running Windows or Linux. These devices are modified to use the station's 28V DC power system and with additional ventilation since heat generated by the devices can stagnate in the weightless environment. NASA prefers to keep a high commonality between laptops and spare parts are kept on the station so astronauts can repair laptops when needed.

Operations

Expeditions

Each permanent crew is given an expedition number. Expeditions run up to six months, from launch until undocking, an 'increment' covers the same time period, but includes cargo spacecraft and all activities. Expeditions 1 to 6 consisted of three-person crews. After the destruction of NASA's Space Shuttle Columbia, Expeditions 7 to 12 were reduced to two-person "caretaker" crews who could maintain the station, because a larger crew could not be fully resupplied by the small Russian Progress cargo spacecraft. After the Shuttle fleet returned to flight, three person crews also returned to the ISS beginning with Expedition 13. As the Shuttle flights expanded the station, crew sizes also expanded, eventually reaching six around 2010. With the arrival of crew on larger US commercial spacecraft beginning in 2020, crew size has been increased to seven, the number for which ISS was originally designed.

Oleg Kononenko of Roscosmos holds the record for the longest time spent in space and at the ISS, accumulating nearly 1,111 days in space over the course of five long-duration missions on the ISS (Expedition 17, 30/31, 44/45, 57/58/59 and 69/70/71). He also served as commander three times (Expedition 31, 58/59 and 70/71).

Peggy Whitson of NASA and Axiom Space has spent the most time in space of any American, accumulating over 675 days in space during her time on Expeditions 5, 16, and 50/51/52 and Axiom Missions 2 and 4.

Private flights

As of June 2023, 13 individuals have paid for their own travel to visit the ISS. In news coverage, such travellers are often referred to as "space tourists"; however, many have objected to the term, as they typically undergo professional training and conduct scientific, educational, or outreach activities while on orbit. Accordingly, Roscosmos and NASA classify them as spaceflight participants.

Initially, privately funded access to the ISS was provided exclusively by Roscosmos through seats on Soyuz spacecraft, either during crew rotations or on dedicated missions. These seats were marketed by Space Adventures at prices of about US$40 million. NASA and the ESA initially criticised the practice, and NASA resisted training Dennis Tito, the first person to pay for an ISS stay.

Beginning in 2021, NASA also began authorizing commercially organized visits known as Private Astronaut Missions (PAMs). These flights are required to use a NASA-certified U.S. commercial vehicle and to include a mission commander who is a former NASA astronaut, responsible for spacecraft operations and oversight of the other spaceflight participants. The first PAM, Axiom Mission 1, launched in 2022 with one Axiom commander and three private passengers, followed in 2023 by Axiom Mission 2, with one private passenger and two astronauts from the Saudi Space Agency. As of 2025, NASA offers up to two PAM opportunities per year. In addition to private individuals, PAMs are frequently used by ESA and other national governments to fly astronauts for short-term missions.

Fleet operations

Various crewed and uncrewed spacecraft have supported the station's operations. Flights to the ISS have included 95 Progress, 73 Soyuz, 52 SpaceX Dragon, 37 Space Shuttle, 22 Cygnus, 10 HTV/HTV-X, 5 ATV, and 2 Boeing Starliner missions.

There are currently eight docking ports for visiting spacecraft, with four additional ports installed but not yet put into service:

Harmony forward (with PMA 2 & IDA 2)

Harmony zenith (with PMA 3 & IDA 3)

Harmony nadir (CBM port)

Unity nadir (CBM port)

Prichal aft

Prichal forward

Prichal nadir

Prichal port

Prichal starboard

Poisk zenith

Rassvet nadir

Zvezda aft

Forward ports are at the front of the station in its usual orientation and direction of travel. Aft is the opposite, at the rear. Nadir points toward Earth, while zenith points away from it. Port is to the left and starboard to the right when one's feet are toward Earth and one is facing forward, in the direction of travel.

Cargo spacecraft that will perform an orbital re-boost of the station will typically dock at an aft, forward or nadir-facing port.

As of 14 February 2026, a total of 294 individuals from 26 countries have visited the ISS, including both government-sponsored astronauts and privately funded spaceflight participants. The United States accounted for 172 of these visitors, followed by Russia with 65, Japan with 11, and Canada with 9. Italy had 6 visitors, France had 5 and Germany had 4. Saudi Arabia, Sweden, and the United Arab Emirates each had 2 individuals visit the ISS. One person has traveled to the ISS from each of the following countries: Belarus, Belgium, Brazil, Denmark, Hungary, India, Israel, Kazakhstan, Malaysia, the Netherlands, Poland, South Africa, South Korea, Spain, Turkey, and the United Kingdom.

Repairs

Orbital Replacement Units (ORUs) are spare parts that can be readily replaced when a unit either passes its design life or fails. Examples of ORUs are pumps, storage tanks, controller boxes, antennas, and battery units. Some units can be replaced using robotic arms. Most are stored outside the station, either on small pallets called ExPRESS Logistics Carriers (ELCs) or share larger platforms called External Stowage Platforms (ESPs) which also hold science experiments. Both kinds of pallets provide electricity for many parts that could be damaged by the cold of space and require heating. The larger logistics carriers also have local area network (LAN) connections for telemetry to connect experiments. A heavy emphasis on stocking the USOS with ORU's occurred around 2011, before the end of the NASA shuttle program, as its commercial replacements, Cygnus and Dragon, carry one tenth to one quarter the payload.

Unexpected problems and failures have impacted the station's assembly time-line and work schedules leading to periods of reduced capabilities and, in some cases, could have forced abandonment of the station for safety reasons. Serious problems include an air leak from the USOS in 2004, the venting of fumes from an Elektron oxygen generator in 2006, and the failure of the computers in the ROS in 2007 during STS-117 that left the station without thruster, Elektron, Vozdukh and other environmental control system operations. In the latter case, the root cause was found to be condensation inside electrical connectors leading to a short circuit.

During STS-120 in 2007 and following the relocation of the P6 truss and solar arrays, it was noted during unfurling that the solar array had torn and was not deploying properly. An EVA was carried out by Scott Parazynski, assisted by Douglas Wheelock. Extra precautions were taken to reduce the risk of electric shock, as the repairs were carried out with the solar array exposed to sunlight. The issues with the array were followed in the same year by problems with the starboard Solar Alpha Rotary Joint (SARJ), which rotates the arrays on the starboard side of the station. Excessive vibration and high-current spikes in the array drive motor were noted, resulting in a decision to substantially curtail motion of the starboard SARJ until the cause was understood. Inspections during EVAs on STS-120 and STS-123 showed extensive contamination from metallic shavings and debris in the large drive gear and confirmed damage to the large metallic bearing surfaces, so the joint was locked to prevent further damage. Repairs to the joints were carried out during STS-126 with lubrication and the replacement of 11 out of 12 trundle bearings on the joint.

Mission control centers

The components of the ISS are operated and monitored by their respective space agencies at mission control centers across the globe, primarily the Christopher C. Kraft Jr. Mission Control Center in Houston and the RKA Mission Control Center (TsUP) in Moscow, with support from Tsukuba Space Center in Japan, Payload Operations and Integration Center in Huntsville, Alabama, U.S., Columbus Control Center in Munich, Germany and Mobile Servicing System Control at the Canadian Space Agency's headquarters in Saint-Hubert, Quebec.

Orbit, debris and visibility

Altitude and orbital inclination

The ISS is currently maintained in a nearly circular orbit with an eccentricity of 0.0002267 and at an inclination of 51.6 degrees to Earth's equator. This orbit was selected because it is the lowest inclination that can be directly reached by Russian Soyuz and Progress spacecraft launched from Baikonur Cosmodrome at 46° N latitude without overflying China or dropping spent rocket stages in inhabited areas. As a result, it makes more polar latitudes accessible and observable, for example the Chinese Space Station orbits more equatorial with an inclination of 41.47°. The ISS travels prograde (with Earth's rotation, west to east) at an average speed of 28,000 kilometres per hour (17,000 mph), and completes 15.5 orbits per day (93 minutes per orbit).

The station orbits in Low Earth Orbit (LEO) at a minimum mean altitude of 370 km (230 mi) and a maximum of 460 km (290 mi), in the center of the thermosphere. The altitude was in the past allowed to fall around the time of each NASA Space Shuttle flight to permit heavier loads to be transferred to the station. After the retirement of the shuttle, the nominal orbit of the space station was raised in altitude (from about 350 km to about 400 km). Other, more frequent supply spacecraft do not require this adjustment as they are substantially higher performance vehicles.

Atmospheric drag reduces the altitude by about 2 km a month on average. To reduce drag the ISS puts its solar arrays while in the dark of Earth's night side edge on toward the flight direction into Night Glider mode. For station keeping, to bring the station back to a higher altitude, a so-called reboost is performed, which takes approximately two orbits (three hours) to be completed. Maintaining ISS altitude uses about 7.5 tonnes of chemical fuel per annum at an annual cost of about $210 million.

Orbital boosting can be performed by the station's two main engines on the Zvezda service module, or Russian or European spacecraft docked to Zvezda's aft port. The Automated Transfer Vehicle is constructed with the possibility of adding a second docking port to its aft end, allowing other craft to dock and boost the station.

The Russian Orbital Segment contains the Data Management System, which handles Guidance, Navigation and Control (ROS GNC) for the entire station. Initially, Zarya, the first module of the station, controlled the station until a short time after the Russian service module Zvezda docked and was transferred control. Zvezda contains the ESA built DMS-R Data Management System. Using two fault-tolerant computers (FTC), Zvezda computes the station's position and orbital trajectory using redundant Earth horizon sensors, Solar horizon sensors as well as Sun and star trackers. The FTCs each contain three identical processing units working in parallel and provide advanced fault-masking by majority voting.

Orientation

Zvezda uses gyroscopes (reaction wheels) and thrusters to turn itself. Gyroscopes do not require propellant; instead they use electricity to 'store' momentum in flywheels by turning in the opposite direction to the station's movement. The USOS has its own computer-controlled gyroscopes to handle its extra mass. When gyroscopes 'saturate', thrusters are used to cancel out the stored momentum. In February 2005, during Expedition 10, an incorrect command was sent to the station's computer, using about 14 kilograms of propellant before the fault was noticed and fixed. When attitude control computers in the ROS and USOS fail to communicate properly, this can result in a rare 'force fight' where the ROS GNC computer must ignore the USOS counterpart, which itself has no thrusters.

Docked spacecraft can also be used to maintain station attitude, such as for troubleshooting or during the installation of the S3/S4 truss, which provides electrical power and data interfaces for the station's electronics.

Orbital debris threats

The low altitudes at which the ISS orbits are also home to a variety of space debris, including spent rocket stages, defunct satellites, explosion fragments (including materials from anti-satellite weapon tests), paint flakes, slag from solid rocket motors, and coolant released by US-A nuclear-powered satellites. These objects, in addition to natural micrometeoroids, are a significant threat. Objects large enough to destroy the station can be tracked, and therefore are not as dangerous as smaller debris. Objects too small to be detected by optical and radar instruments, from approximately 1 cm down to microscopic size, number in the trillions. Despite their small size, some of these objects are a threat because of their kinetic energy and direction in relation to the station. Spacewalking crew in spacesuits are also at risk of suit damage and consequent exposure to vacuum.

Ballistic panels, also called micrometeorite shielding, are incorporated into the station to protect pressurised sections and critical systems. The type and thickness of these panels depend on their predicted exposure to damage. The station's shields and structure have different designs on the ROS and the USOS. On the USOS, Whipple Shields are used. The US segment modules consist of an inner layer made from 1.5–5.0 cm-thick (0.59–1.97 in) aluminium, a 10 cm-thick (3.9 in) intermediate layers of Kevlar and Nextel (a ceramic fabric), and an outer layer of stainless steel, which causes objects to shatter into a cloud before hitting the hull, thereby spreading the energy of impact. On the ROS, a carbon fibre reinforced polymer honeycomb screen is spaced from the hull, an aluminium honeycomb screen is spaced from that, with a screen-vacuum thermal insulation covering, and glass cloth over the top.

Space debris is tracked remotely from the ground, and the station crew can be notified. If necessary, thrusters on the Russian Orbital Segment can alter the station's orbital altitude, avoiding the debris. These Debris Avoidance Manoeuvres (DAMs) are not uncommon, taking place if computational models show the debris will approach within a certain threat distance. Ten DAMs had been performed by the end of 2009. Usually, an increase in orbital velocity of the order of 1 m/s is used to raise the orbit by one or two kilometres. If necessary, the altitude can also be lowered, although such a manoeuvre wastes propellant. If a threat from orbital debris is identified too late for a DAM to be safely conducted, the station crew close all the hatches aboard the station and retreat into their spacecraft in order to be able to evacuate in the event the station was seriously damaged by the debris. Partial station evacuations have occurred on 13 March 2009, 28 June 2011, 24 March 2012, 16 June 2015, November 2021, and 27 June 2024.

Visibility from Earth

The ISS is visible in the sky to the naked eye as a visibly moving, bright white dot, when crossing the sky and being illuminated by the Sun, during twilight, the hours after sunset and before sunrise, when the station remains sunlit, outside of Earth's shadow, but the ground and sky are dark. It crosses the skies at latitudes between the polar regions. Depending on the path it takes across the sky, the time it takes the station to move across the horizon or from one to the other may be short or up to 10 minutes, while likely being only visible part of that time because of it moving into or out of Earth's shadow. It then returns around every 90 minutes, with the time of the day that it crosses the sky shifting over the course of some weeks, and therefore before returning to twilight and visible illumination.

Because of the size of its reflective surface area, the ISS is the brightest artificial object in the sky (excluding other satellite flares), with an approximate maximum magnitude of −4 when in sunlight and overhead (similar to Venus), and a maximum angular size of 63 arcseconds.

Tools are provided by a number of websites such as Heavens-Above (see Live viewing below) as well as smartphone applications that use orbital data and the observer's longitude and latitude to indicate when the ISS will be visible (weather permitting), where the station will appear to rise, the altitude above the horizon it will reach and the duration of the pass before the station disappears either by setting below the horizon or entering into Earth's shadow.

In November 2012 NASA launched its "Spot the Station" service, which sends people text and email alerts when the station is due to fly above their town. The station is visible from 95% of the inhabited land on Earth, but is not visible from extreme northern or southern latitudes.

Under specific conditions, the ISS can be observed at night on five consecutive orbits. Those conditions are 1) a mid-latitude observer location, 2) near the time of the solstice with 3) the ISS passing in the direction of the pole from the observer near midnight local time. The three photos show the first, middle and last of the five passes on 5–6 June 2014.

Using a telescope-mounted camera to photograph the station is a popular hobby for astronomers, while using a mounted camera to photograph the Earth and stars is a popular hobby for crew. The use of a telescope or binoculars allows viewing of the ISS during daylight hours.

Environment, safety and crew health

Environment

Gravity at the altitude of the ISS is approximately 90% as strong as on Earth's surface, but objects in orbit are in continuous freefall, resulting in a state of weightlessness known as microgravity. This perceived weightlessness is disturbed by five effects:

Drag from the residual atmosphere.

Vibration from the movements of mechanical systems and the crew.

Actuation of the on-board attitude control moment gyroscopes.

Thruster firings for attitude or orbital changes.

Gravity-gradient effects, also known as tidal effects. Items at different locations within the ISS would, if not attached to the station, follow slightly different orbits. Being mechanically connected, these items experience small forces that keep the station moving as a rigid body.

The ISS is partially protected from the space environment by Earth's magnetic field. From an average distance of about 70,000 km (43,000 mi) from the Earth's surface, depending on Solar activity, the magnetosphere begins to deflect solar wind around Earth and the space station. Solar flares are still a hazard to the crew, who may receive only a few minutes warning. In 2005, during the initial "proton storm" of an X-3 class solar flare, the crew of Expedition 10 took shelter in a more heavily shielded part of the ROS designed for this purpose.

Subatomic charged particles, primarily protons from cosmic rays and solar wind, are normally absorbed by Earth's atmosphere. When they interact in sufficient quantity, their effect is visible to the naked eye in a phenomenon called an aurora. Outside Earth's atmosphere, ISS crews are exposed to approximately one millisievert each day (about a year's worth of natural exposure on Earth), resulting in a higher risk of cancer. Radiation can penetrate living tissue and damage the DNA and chromosomes of lymphocytes; being central to the immune system, any damage to these cells could contribute to the lower immunity experienced by astronauts. Radiation has also been linked to a higher incidence of cataracts in astronauts. Protective shielding and medications may lower the risks to an acceptable level.

Overall health effects

On 12 April 2019, NASA reported medical results from the Astronaut Twin Study. Astronaut Scott Kelly spent a year in space on the ISS, while his identical twin Mark Kelly spent the year on Earth. Several long-lasting changes were observed, including those related to alterations in DNA and cognition, when one twin was compared with the other.

In November 2019, researchers reported that astronauts experienced serious blood flow and clot problems while on board the ISS, based on a six-month study of 11 healthy astronauts. The results may influence long-term spaceflight, including a mission to the planet Mars, according to the researchers.

There is considerable evidence that psychosocial stressors are among the most important impediments to optimal crew morale and performance. Cosmonaut Valery Ryumin wrote in his journal during a particularly difficult period on board the Salyut 6 space station: "All the conditions necessary for murder are met if you shut two men in a cabin measuring 18 feet by 20 [5.5 m × 6 m] and leave them together for two months."

NASA's interest in psychological stress caused by space travel, initially studied when their crewed missions began, was rekindled when astronauts joined cosmonauts on the Russian space station Mir. Common sources of stress in early US missions included maintaining high performance under public scrutiny and isolation from peers and family. The latter is still often a cause of stress on the ISS, such as when the mother of NASA astronaut Daniel Tani died in a car accident, and when Michael Fincke was forced to miss the birth of his second child.

A study of the longest spaceflight concluded that the first three weeks are a critical period where attention is adversely affected because of the demand to adjust to the extreme change of environment. ISS crew flights typically last about five to six months.

The ISS working environment includes further stress caused by living and working in cramped conditions with people from very different cultures who speak a different language. First-generation space stations had crews who spoke a single language; second- and third-generation stations have crew from many cultures who speak many languages. Astronauts must speak English and Russian, and knowing additional languages is even better.

Life aboard

Living quarters

The living and working space aboard the International Space Station (ISS) is larger than a six-bedroom house, equipped with seven private sleeping quarters, three bathrooms, two dining rooms, a gym, and a panoramic 360-degree-view bay window.

The station provides dedicated crew quarters for long-term crew members. Two are located in Zvezda, one in Nauka, and four in Harmony. These soundproof, person-sized booths offer privacy, ventilation, and basic amenities such as a sleeping bag, a reading lamp, and storage for personal items. The quarters in Zvezda include a small window but have less ventilation and soundproofing.

Visiting crew members use tethered sleeping bags attached to available wall space or inside their spacecraft. While it is possible to sleep floating freely, this is generally avoided to prevent collisions with sensitive equipment. Proper ventilation is critical, as astronauts risk oxygen deprivation if exhaled carbon dioxide accumulates in a bubble around their heads.

The station's lighting system is adjustable, allowing for dimming, switching off, and color temperature changes to support crew activities and rest.

Crew activities

The ISS operates on Coordinated Universal Time (UTC). A typical day aboard the ISS begins at 06:00 with wake-up, post-sleep routines, and a morning inspection of the station. After breakfast, the crew holds a daily planning conference with Mission Control, starting work around 08:10. Morning tasks include scheduled exercise, scientific experiments, maintenance, or operational duties. Following a one-hour lunch break at 13:05, the crew resumes their afternoon schedule of work and exercise. Pre-sleep activities, including dinner and a crew conference, begin at 19:30, with the scheduled sleep period starting at 21:30.

The crew works approximately 10 hours on weekdays and 5 hours on Saturdays, with the remaining time allocated for relaxation or catching up on tasks. Free time often involves enjoying personal hobbies, communicating with family, or gazing out at Earth through the station's windows. The crew can watch TV aboard the station.

When the Space Shuttle was operating, the ISS crew aligned with the shuttle crew's Mission Elapsed Time, a flexible schedule based on the shuttle's launch.

To simulate night conditions, the station's windows are covered during designated sleep periods, as the ISS experiences 16 sunrises and sunsets daily due to its orbital speed.

Reflection and material culture

Reflection of individual and crew characteristics are found particularly in the decoration of the station and expressions in general, such as religion. The latter has produced a certain material economy between the station and Russia in particular.

The micro-society of the station, as well as wider society, and possibly the emergence of distinct station cultures, is being studied by analyzing many aspects, from art to dust accumulation, as well as archaeologically how material of the ISS has been discarded.

Food

Food aboard the International Space Station (ISS) is preserved and packaged to withstand long storage times, minimize waste, and prevent contamination of station systems. Because microgravity dulls taste, meals are often seasoned more heavily than on Earth. Crews particularly look forward to resupply missions, which deliver perishable items such as fresh fruit and vegetables. To reduce the risk of crumbs and spills damaging equipment, foods are prepared in specialized packaging, liquid condiments are preferred over powdered ones, and containers are secured with Velcro or magnets. Drinks are delivered as powders to be mixed with water, while soups and beverages are sipped from plastic bags with straws. Solid foods are eaten with utensils attached to trays by magnets, and any stray food must be collected to prevent it from clogging air filters and other systems.

The first galley was installed in Zvezda, equipped with an electro-resistive can warmer and a water dispenser for both hot and ambient water. Many Russian meals are still packaged in cans, which are eaten directly, while others are provided in retort pouches rehydrated with the water dispenser.

A second galley was later added to Unity to support the station's larger crew. It contains two briefcase-shaped food warmers, a refrigerator (added in 2008), and a water dispenser. Most food in the U.S. Orbital Segment is packaged in retort pouches, which are rehydrated if necessary and heated or chilled in a food warmer or refrigerator as desired.

While crews occasionally gather for group meals in Unity, especially during holidays or special occasions, they more often eat in small groups because of differing schedules. Russian cosmonauts also retain the option of dining separately in Zvezda, where the can warmer is located. With the growing diversity of NASA's astronaut corps and the large number of international astronauts who have flown to the ISS, the variety of food available has expanded significantly. Efforts are made to provide meals that reflect astronauts' cultural backgrounds and personal preferences, and food is often shared among crew members.

Experiments have also been conducted aboard the ISS to grow fresh vegetables in orbit. These studies aim to supplement astronauts' diets with additional nutrients, provide psychological benefits, and advance space agricultural techniques needed for long-duration missions to the Moon and Mars. As of 2023, crops grown include three types of lettuce, Chinese cabbage, mizuna mustard, and red Russian kale. Some of the plants are harvested and eaten by the crew, while others were returned to Earth for analysis. In the future, NASA plans to grow tomatoes and peppers, and eventually berries, beans, and other nutrient-rich foods. Such crops could offer not only improved nutrition, but also potential protection against space radiation for crew members who consume them.

Personal hygiene

The ISS is equipped with three Russian-designed toilets, located in Zvezda, Tranquility and Nauka. Inside these "Waste and Hygiene Compartments" the occupant fastens themselves to the toilet seat, which is equipped with spring-loaded restraining bars to ensure a proper seal. A lever activates a powerful fan while opening a suction port at the bottom of the toilet bowl, and the airstream carries waste away. Solid waste is stored in individual bags placed in an aluminium container, which is later transferred to cargo spacecraft that will burn up on reentry. Liquid waste is collected through a hose with anatomically shaped funnel adapters so that both men and women can use the same system. The urine is diverted to the Water Recovery System, where it is processed into drinking water.

Showers were first introduced on space stations in the early 1970s aboard Skylab and Salyut 3. However, crews complained about the complexity of showering, and by the time of Salyut 6 in the early 1980s, it had been reduced to a monthly activity. The ISS, like later Russian stations after, has no shower; instead, astronauts clean themselves with wet wipes or with a water jet and using soap dispensed from a toothpaste-like tube. Rinseless shampoo and edible toothpaste are also provided to conserve water.

End of mission

The ISS was originally intended for a 15-year mission, but the mission has been repeatedly extended due to its success and support. As a result, the oldest modules of the ISS have been in orbit for more than 25 years.

The US planned in 2009 to deorbit the ISS in 2016. But on 30 September 2015, Boeing's contract with NASA as prime contractor for the ISS was extended to 30 September 2020. Part of Boeing's services under the contract related to extending the station's primary structural hardware past 2020 to the end of 2028. In July 2018, the Space Frontier Act of 2018 was intended to extend operations of the ISS to 2030. This bill was unanimously approved in the Senate, but failed to pass in the U.S. House. In September 2018, the Leading Human Spaceflight Act was introduced with the intent to extend operations of the ISS to 2030, and was confirmed in December 2018. Congress later passed similar provisions in its CHIPS and Science Act, signed into law by U.S. President Joe Biden on 9 August 2022.

NASA has suggested extending ISS operations beyond 2030 if Commercial LEO Destinations providers prove insufficient to accommodate NASA's needs. In February 2026, during a vote to approve the NASA Reauthorization Act of 2026, members of the United States House Committee on Science, Space, and Technology introduced an amendment requiring NASA to explore the feasibility of relocating the ISS to a safe orbital harbor following its end-of-life so that it can be preserved for potential re-use, as an alternative to destructive atmospheric re-entry, with the amendment submitted by George T. Whitesides with bipartisan support from Nick Begich III, Brian Babin and Don Beyer.

In a January 2026 plan, Axiom Station, while a segment of the ISS, would pick up and use established science hardware and the Canadarm2 from the ISS.

Russia meanwhile has stated that it plans to pull out of the ISS program after 2025. However, Russian modules will provide orbital station-keeping until 2028. Recommendations by the U.S.-Russian Joint Commission identified the thrusters of the Russian ISS segment as a deorbit backup. In late 2025 Russia has under budget constraints reconsidered their future space station plans to again include modules from the ISS.

End of mission considerations

The reliability of the station has decreased over its longer than designed operation. Astronauts have been having to spend half of their time on station maintenance, and air leaks, as well as mold, have increasingly called the safety of the station into doubt. Furthermore station-keeping needs funds, which have been suggested to be used elsewhere, while its preservation, as an institution or landmark, has also been raised.

An unmaintained station would pose a space debris and re-entry hazard. According to the Outer Space Treaty, the parties are legally responsible for all spacecraft or modules they launch.

Post mission

NASA considered originally several possible options for the station's fate after its mission: natural orbital decay with random reentry (as with Skylab), boosting the station to a higher altitude (which would delay reentry), and a controlled de-orbit targeting a remote ocean area.

NASA determined that random reentry carried an unacceptable risk of producing hazardous space debris that could hit people or property and re-boosting the station would be costly and could also create hazards.

Prior to 2010, plans had contemplated using a slightly modified Progress spacecraft to de-orbit the ISS. However, NASA concluded Progress would not be adequate for the job, and decided on a spacecraft specifically designed for the task.

In January 2022, NASA announced a planned date of January 2031 to de-orbit the ISS using the "U.S. Deorbit Vehicle" and direct any remnants into a remote area of the South Pacific Ocean that has come to be known as the spacecraft cemetery. NASA plans to launch the deorbit vehicle in 2030, docking at the Harmony forward port. The deorbit vehicle will remain attached, dormant, for about a year as the station's orbit naturally decays to 220 km (140 mi). The spacecraft would then conduct one or more orientation burns to lower the perigee to 150 km (93 mi), followed by a final deorbiting burn.

NASA began planning for the deorbit vehicle after becoming wary of Russia pulling out of the ISS abruptly, leaving the other partners with few good options for a controlled reentry. In June 2024, NASA selected SpaceX to develop the U.S. Deorbit Vehicle, a contract potentially worth $843 million. The vehicle will consist of an existing Cargo Dragon spacecraft which will be paired with a significantly lengthened trunk module which will be equipped with 46 Draco thrusters (instead of the normal 16) and will carry 30,000 kg (66,000 lb) of propellant, nearly six times the normal load. NASA is still working to secure all the necessary funding to build, launch and operate the deorbit vehicle.

On 20 February 2025, Elon Musk, CEO of SpaceX and Senior Advisor to President Trump, suggested in a tweet that the International Space Station be de-orbited "two years from now" as Musk believes the station has "served its purpose" and has "very little incremental utility". Despite this, no official decisions on moving up the de-orbiting date have been made yet by the president.

Follow up plans

The follow-up to NASA's program/strategy is the Commercial LEO Destinations Program, meant to allow private industry to build and maintain their own stations, and NASA procuring access as a customer, starting in 2028. Similarly, the ESA has been seeking new private space stations to provide orbital services, as well as retrieve materials, from the ISS. Axiom Station is planned to begin as a single module temporarily hosted at the ISS in 2027. Additionally, there have been suggestions in the commercial space industry that the ISS could be converted to commercial operations after it is retired by government entities, including turning it into a space hotel.

Russia previously has planned to use its orbital segment for the construction of its OPSEK station after the ISS is decommissioned. The modules under consideration for removal from the current ISS included the Multipurpose Laboratory Module (Nauka; MLM), launched in July 2021, and the other new Russian modules that are proposed to be attached to Nauka. These newly launched modules would still be well within their useful lives in 2024. At the end of 2011, the Exploration Gateway Platform concept also proposed using leftover USOS hardware and Zvezda 2 as a refuelling depot and service station located at one of the Earth–Moon Lagrange points. However, the entire USOS was not designed for disassembly and will be discarded.

In 2022, companies such as CisLunar suggested using the ISS as a platform to develop orbital salvage capacities. They propose to repurpose components from the station, or at least to use space debris for its raw materials, or fuel, instead of plunging it into the ocean.

In July 2024, NASA stated that it had not seen any viable proposals for reuse of the ISS or parts of it.

Cost

The ISS has been described as the most expensive single item ever constructed. As of 2010, the total cost was US$150 billion. This includes NASA's budget of $58.7 billion ($89.73 billion in 2021 dollars) for the station from 1985 to 2015, Russia's $12 billion, Europe's $5 billion, Japan's $5 billion, Canada's $2 billion, and the cost of 36 shuttle flights to build the station, estimated at $1.4 billion each, or $50.4 billion in total. Assuming 20,000 man-days of use from 2000 to 2015 by two- to six-person crews, each man-day would cost $7.5 million, less than half the inflation-adjusted $19.6 million ($5.5 million before inflation) per man-day of Skylab. NASA spends about US$3 billion per year on operational costs.

In culture

The ISS has become an international symbol of human capabilities, particularly human cooperation and science, defining a cooperative international approach and period, instead of a looming commercialized and militarized interplanetary world.

Outreach

The station has hosted and been used for many public campaigns and engagement.

The decades long operation documentation has been made accessible with an interactive website called ISS in Real Time.

Film

Beside numerous documentaries such as the IMAX documentaries Space Station 3D from 2002, or A Beautiful Planet from 2016, and films like Apogee of Fear (2012) and Yolki 5 (2016) the ISS is the subject of feature films such as The Day After Tomorrow (2004), Love (2011), together with the Chinese station Tiangong 1 in Gravity (2013), Life (2017), and I.S.S. (2023).

In 2022, the movie The Challenge (Doctor's House Call) was filmed aboard the ISS, and was notable for being the first feature film in which both professional actors and director worked together in space.

Literature

Neal Stephenson's 2015 novel Seveneves is set largely on the ISS for the first and second parts of the novel. The ISS is depicted largely as it was when the novel was written, but with the addition of a large captured asteroid attached to the station.

The 2023 novel Orbital by English writer Samantha Harvey is set on the ISS. It won the 2024 Booker Prize.

Ceridwen Dovey's Only the Astronauts, a 2024 collection of short stories in which the narrator in each story is an inanimate object in space, includes the International Space Station.

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; the resulting shockwave destroys the station.

The ISS is present in Far Cry New Dawn as an expedition site, having fallen to earth during a nuclear war.