ISS Expedition 43 Patch

The International Space Station (ISS) is the largest modular space station currently in low Earth orbit. It is a multinational collaborative project involving five participating space agencies: NASA (United States), Roscosmos (Russia), JAXA (Japan), ESA (Europe), and CSA (Canada). The ownership and use of the space station is established by intergovernmental treaties and agreements. The station serves as a microgravity and space environment research laboratory in which scientific research is conducted in astrobiology, astronomy, meteorology, physics, and other fields. The ISS is suited for testing the spacecraft systems and equipment required for possible future long-duration missions to the Moon and Mars.

The ISS programme evolved from the Space Station ''Freedom'', a 1984 American proposal to construct a permanently crewed Earth-orbiting station, and the contemporaneous Soviet/Russian '' Mir-2'' proposal from 1976 with similar aims. The ISS is the ninth space station to be inhabited by crews, following the Soviet and later Russian ''Salyut'', Almaz, and ''Mir'' stations and the American Skylab. It is the largest artificial object in the solar system and the largest satellite in low Earth orbit, regularly visible to the naked eye from Earth's surface. It maintains an orbit with an average altitude of by means of reboost manoeuvres using the engines of the '' Zvezda'' Service Module or visiting spacecraft. The ISS circles the Earth in roughly 93 minutes, completing orbits per day.

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

Roscosmos had previously endorsed the continued operation of ROS through 2024, having proposed using elements of the segment to construct a new Russian space station called OPSEK. However, continued cooperation has been rendered uncertain by the 2022 Russian invasion of Ukraine and subsequent international sanctions on Russia, who theoretically, may lower, redirect, or cut funding from their side of the space station due to the sanctions set on them.

The first ISS component was launched in 1998, and the first long-term residents arrived on 2 November 2000 after being launched from the Baikonur Cosmodrome on 31 October 2000. The station has since been continuously occupied for , the longest continuous human presence in low Earth orbit, having surpassed the previous record of held by the ''Mir'' space station. The latest major pressurised module, ''Nauka'', was fitted in 2021, a little over ten years after the previous major addition, ''Leonardo'' in 2011. Development and assembly of the station continues, with an experimental inflatable space habitat added in 2016, and several major new Russian elements scheduled for launch starting in 2021. In January 2022, the station's operation authorization was extended to 2030, with funding secured within the United States through that year. There have been calls to privatize ISS operations after that point to pursue future Moon and Mars missions, with former NASA Administrator Jim Bridenstine stating: "given our current budget constraints, if we want to go to the moon and we want to go to Mars, we need to commercialize low Earth orbit and go on to the next step."

The ISS consists of pressurised habitation modules, structural trusses, photovoltaic solar arrays, thermal radiators, docking ports, experiment bays and robotic arms. Major ISS modules have been launched by Russian Proton and Soyuz rockets and US Space Shuttles. The station is serviced by a variety of visiting spacecraft: the Russian Soyuz and Progress, the SpaceX Dragon 2, and the Northrop Grumman Space Systems Cygnus, and formerly the European Automated Transfer Vehicle (ATV), the Japanese H-II Transfer Vehicle, and SpaceX Dragon 1. The Dragon spacecraft allows the return of pressurised cargo to Earth, which is used, for example, to repatriate scientific experiments for further analysis. , 251 astronauts, cosmonauts, and space tourists from 20 different nations have visited the space station, many of them multiple times.

History

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, combined 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 person-hours per week of labour with a crew of six. However, a considerable amount of crew time is taken up by station maintenance.

Perhaps the most notable ISS experiment is the Alpha Magnetic Spectrometer (AMS), which is intended to detect dark matter and answer other fundamental questions about our universe. According to NASA, the AMS is as important as the Hubble Space Telescope. Currently docked on station, it 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 the 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 is characterised by an intense radiation field (consisting primarily of protons and other subatomic charged particles from the solar wind, in addition to cosmic rays), high vacuum, extreme temperatures, and microgravity. (see Space Environment on page 122) 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. These data will be used to determine whether high duration human spaceflight and space colonisation are 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.

Medical studies are conducted aboard the ISS on behalf of the National Space Biomedical Research Institute (NSBRI). Prominent among these is the Advanced Diagnostic Ultrasound in Microgravity study in which astronauts perform ultrasound scans under the guidance of remote experts. The study considers the diagnosis and treatment of medical conditions in space. Usually, there is no physician on board the ISS and diagnosis of medical conditions is a challenge. It is anticipated that remotely guided ultrasound scans will have application on Earth in emergency and rural care situations where access to a trained physician is difficult.

In August 2020, scientists reported that bacteria from Earth, particularly ''Deinococcus radiodurans'' bacteria, which is highly resistant to environmental hazards, were found to survive for three years in outer space, based on studies conducted on the International Space Station. These findings supported the notion of panspermia, the hypothesis that life exists throughout the Universe, distributed in various ways, including space dust, meteoroids, asteroids, comets, planetoids or contaminated spacecraft.

Remote sensing of the Earth, astronomy, and deep space research on the ISS have dramatically increased during the 2010s after the completion of the US Orbital Segment in 2011. Throughout the more than 20 years of the ISS program researchers aboard the ISS and on the ground have examined aerosols, ozone, lightning, and oxides in Earth's atmosphere, as well as the Sun, cosmic rays, cosmic dust, antimatter, and dark matter in the universe. Examples of Earth-viewing remote sensing experiments that have flown on the ISS are the Orbiting Carbon Observatory 3, ISS-RapidScat, ECOSTRESS, the Global Ecosystem Dynamics Investigation, resulting in an apparent state of weightlessness. 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.

Researchers are investigating the effect of the station's near-weightless environment on the evolution, development, growth and internal processes of plants and animals. In response to some of the data, NASA wants to investigate microgravity's effects on the growth of three-dimensional, human-like tissues and the unusual protein crystals that can be formed in space.

Investigating the physics of fluids in microgravity will provide better models of the behaviour of fluids. Because fluids can be almost completely combined in microgravity, physicists investigate fluids that do not mix well on Earth. Examining reactions that are slowed by low gravity and low temperatures will improve our understanding of superconductivity.

The study of materials science is an important ISS research activity, with the objective of reaping economic benefits through the improvement of techniques used on the ground. Other areas of interest include the effect of low gravity on combustion, through the study of the efficiency of burning and control of emissions and pollutants. These findings may improve knowledge about energy production and lead to economic and environmental benefits.

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 as well as 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 that "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 programmes 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 programmes 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.

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 programme. 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 programme 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.

'' 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''.

In May 2013, commander Chris Hadfield shot a music video of David Bowie's "Space Oddity" on board the station, which was released on YouTube. It was the first music video ever to be filmed in space.

In November 2017, while participating in Expedition 52/ 53 on the ISS, Paolo Nespoli made two recordings of his spoken voice (one in English and the other in his native Italian), for use on Wikipedia articles. These were the first content made in space specifically for Wikipedia.

In November 2021, a virtual reality exhibit called The Infinite featuring life aboard the ISS was announced.

Construction

Manufacturing

Since the International Space Station is a multi-national collaborative project, the components for in-orbit assembly were manufactured in various countries around the world. Beginning in the mid-1990s, the U.S. components ''Destiny'', ''Unity'', the Integrated Truss Structure, and the solar arrays were fabricated at the Marshall Space Flight Center and the Michoud Assembly Facility. These modules were delivered to the Operations and Checkout Building and the Space Station Processing Facility (SSPF) for final assembly and processing for launch.

The Russian modules, including '' Zarya'' and '' Zvezda'', were manufactured at the Khrunichev State Research and Production Space Center in Moscow. ''Zvezda'' was initially manufactured in 1985 as a component for '' Mir-2'', but was never launched and instead became the ISS Service Module.

The European Space Agency (ESA) ''Columbus'' module was manufactured at the EADS Astrium Space Transportation facilities in Bremen, Germany, along with many other contractors throughout Europe. The other ESA-built modules'' Harmony'', ''Tranquility'', the ''Leonardo'' MPLM, and the ''Cupola''were initially manufactured at the Thales Alenia Space factory in Turin, Italy. The structural steel hulls of the modules were transported by aircraft to the Kennedy Space Center SSPF for launch processing.

The Japanese Experiment Module ''Kibō'', was fabricated in various technology manufacturing facilities in Japan, at the NASDA (now JAXA) Tsukuba Space Center, and the Institute of Space and Astronautical Science. The ''Kibo'' module was transported by ship and flown by aircraft to the SSPF.

The Mobile Servicing System, consisting of the Canadarm2 and the ''Dextre'' grapple fixture, was manufactured at various factories in Canada (such as the David Florida Laboratory) and the United States, under contract by the Canadian Space Agency. The mobile base system, a connecting framework for Canadarm2 mounted on rails, was built by Northrop Grumman.

Assembly

The assembly of the International Space Station, a major endeavour in space architecture, began in November 1998. Russian modules launched and docked robotically, with the exception of '' Rassvet''. All other modules were delivered by the Space Shuttle, which required installation by ISS and Shuttle crewmembers using the Canadarm2 (SSRMS) and extra-vehicular activities (EVAs); by 5 June 2011, they had added 159 components during more than 1,000 hours of EVA. 127 of these spacewalks originated from the station, and the remaining 32 were launched from the airlocks of docked Space Shuttles. The beta angle of the station had to be considered at all times during construction.

The first module of the ISS, ''Zarya'', was launched on 20 November 1998 on an autonomous Russian Proton rocket. It provided propulsion, attitude control, communications, and electrical power, but lacked long-term life support functions. A passive NASA module, ''Unity'', was launched two weeks later aboard Space Shuttle flight STS-88 and attached to ''Zarya'' by astronauts during EVAs. The ''Unity'' module has two Pressurised Mating Adapters (PMAs): one connects permanently to ''Zarya'' and the other allowed the Space Shuttle to dock to the space station. At that time, the Russian (Soviet) station ''Mir'' was still inhabited, and the ISS remained uncrewed for two years. On 12 July 2000, the ''Zvezda'' module was launched into orbit. Onboard preprogrammed commands deployed its solar arrays and communications antenna. ''Zvezda'' then became the passive target for a rendezvous with ''Zarya'' and ''Unity'', maintaining a station-keeping orbit while the ''Zarya''–''Unity'' vehicle performed the rendezvous and docking via ground control and the Russian automated rendezvous and docking system. ''Zarya'' computer transferred control of the station to ''Zvezda'' computer soon after docking. ''Zvezda'' added sleeping quarters, a toilet, kitchen, CO₂ scrubbers, dehumidifier, oxygen generators, and exercise equipment, plus data, voice and television communications with mission control, enabling permanent habitation of the station.

The first resident crew, Expedition 1, arrived in November 2000 on Soyuz TM-31. At the end of the first day on the station, astronaut Bill Shepherd requested the use of the radio call sign "''Alpha''", which he and cosmonaut Sergei Krikalev preferred to the more cumbersome "''International Space Station''". The name "''Alpha''" had previously been used for the station in the early 1990s, and its use was authorised for the whole of Expedition 1. Shepherd had been advocating the use of a new name to project managers for some time. Referencing a naval tradition in a pre-launch news conference he had said: "For thousands of years, humans have been going to sea in ships. People have designed and built these vessels, launched them with a good feeling that a name will bring good fortune to the crew and success to their voyage." Yuri Semenov, the President of Russian Space Corporation Energia at the time, disapproved of the name "''Alpha''" as he felt that ''Mir'' was the first modular space station, so the names "''Beta''" or "''Mir'' 2" for the ISS would have been more fitting.

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 communication for US television, additional attitude support needed for the additional mass of the USOS, and substantial solar arrays to supplement the station's four existing 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 ''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.

The expansion schedule was interrupted in 2003 by the Space Shuttle '' Columbia'' disaster and a resulting hiatus in flights. The Space Shuttle was grounded until 2005 with STS-114 flown by ''Discovery''. Assembly resumed in 2006 with the arrival of STS-115 with ''Atlantis'', which delivered the station's second set of solar arrays. Several more truss segments and a third set of arrays were delivered on STS-116, STS-117, and STS-118. As a result of the major expansion of the station's power-generating capabilities, more pressurised modules could be accommodated, and the ''Harmony'' node and ''Columbus'' European laboratory were added. These were soon followed by the first two components of '' Kibō''. In March 2009, STS-119 completed the Integrated Truss Structure with the installation of the fourth and final set of solar arrays. The final section of ''Kibō'' was delivered in July 2009 on STS-127, followed by the Russian '' Poisk'' module. The third node, ''Tranquility'', was delivered in February 2010 during STS-130 by the Space Shuttle ''Endeavour'', alongside the ''Cupola'', followed by the penultimate Russian module, ''Rassvet'', in May 2010. ''Rassvet'' was delivered by Space Shuttle ''Atlantis'' on STS-132 in exchange for the Russian Proton delivery of the US-funded ''Zarya'' module in 1998. The last pressurised module of the USOS, ''Leonardo'', was brought to the station in February 2011 on the final flight of ''Discovery'', STS-133. The Alpha Magnetic Spectrometer was delivered by ''Endeavour'' on STS-134 the same year.

By June 2011, the station consisted of 15 pressurised modules and the Integrated Truss Structure. Two power modules called NEM-1 and NEM-2. are still to be launched. Russia's new primary research module ''Nauka'' docked in July 2021, along with the European Robotic Arm which will be able to relocate itself to different parts of the Russian modules of the station. Russia's latest addition, the nodal module '' ''Prichal'' docked in November 2021.

The gross mass of the station changes over time. The total launch mass of the modules on orbit is about (). The mass of experiments, spare parts, personal effects, crew, foodstuff, clothing, propellants, water supplies, gas supplies, docked spacecraft, and other items add to the total mass of the station. Hydrogen gas is constantly vented overboard by the oxygen generators.

Structure

The ISS is a modular space station. Modular stations can allow modules to be added to or removed from the existing structure, allowing greater flexibility.

File:ISS blueprint.png, Technical blueprint of components.
File:View_of_the_ISS_taken_during_Crew-2_flyaround_(ISS066-E-081311).jpg, The ISS exterior and steelwork taken on 8 November 2021, from the departing SpaceX Crew-2 capsule.
File:Iss after installation of first 3 roll out solar arrays.jpg, Diagram structure of International Space Station after installation of iROSA solar arrays (as of 2022).

Below is a diagram of major station components. The blue areas are pressurised sections accessible by the crew without using spacesuits. The station's unpressurised superstructure is indicated in red. Planned components are shown in white, non installed, temporarily defunct or non-commissioned components are shown in brown and former ones in gray. Other unpressurised components are yellow. 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.

Pressurised modules

''Zarya''

''Zarya'' (russian: Заря, , Dawn), also known as the Functional Cargo Block or FGB (from the russian: "Функционально-грузовой блок", , ''Funktsionalno-gruzovoy blok'', links=no or ''ФГБ''), is the first module of the ISS to have been launched.NASA, International Space Station
Zarya
(accessed 19 Apr. 2014) The FGB provided electrical power, storage, propulsion, and guidance to the ISS during the initial stage of assembly. With the launch and assembly in orbit of other modules with more specialized functionality, ''Zarya,'' as of August 2021'','' is primarily be used for storage, both inside the pressurized section and in the externally mounted fuel tanks. The ''Zarya'' is a descendant of the TKS spacecraft designed for the Russian ''Salyut'' program. The name ''Zarya'' ("Dawn") was given to the FGB because it signified the dawn of a new era of international cooperation in space. Although it was built by a Russian company, it is owned by the United States.

''Unity''

The ''Unity'' connecting module, also known as Node 1, is the first U.S.-built component of the ISS. It connects the Russian and U.S. segments of the station, and is where crew eat meals together.

The module is cylindrical in shape, with six berthing locations (forward, aft, port, starboard, zenith, and nadir) facilitating connections to other modules. ''Unity'' measures in diameter, is long, made of steel, and was built for NASA by Boeing in a manufacturing facility at the Marshall Space Flight Center in Huntsville, Alabama. ''Unity'' is the first of the three connecting modules; the other two are ''Harmony'' and ''Tranquility''.

''Zvezda''

''Zvezda'' (russian: Звезда, links=no, meaning "star"), ''Salyut'' DOS-8, is also known as the ''Zvezda'' Service Module. It was the third module launched to the station, and provides all of the station's life support systems, some of which are supplemented in the USOS, as well as living quarters for two crew members. It is the structural and functional center of the Russian Orbital Segment, which is the Russian part of the ISS. Crew assemble here to deal with emergencies on the station.

The module was manufactured by RKK Energia, with major sub-contracting work by GKNPTs Khrunichev. ''Zvezda'' was launched on a Proton rocket on 12 July 2000, and docked with the ''Zarya'' module on 26 July 2000.

''Destiny''

The ''Destiny'' module, also known as the U.S. Lab, is the primary operating facility for U.S. research payloads aboard the ISS. It was berthed to the ''Unity'' module and activated over a period of five days in February 2001. ''Destiny'' is NASA's first permanent operating orbital research station since Skylab was vacated in February 1974. The Boeing Company began construction of the research laboratory in 1995 at the Michoud Assembly Facility and then the Marshall Space Flight Center in Huntsville, Alabama. ''Destiny'' was shipped to the Kennedy Space Center in Florida in 1998, and was turned over to NASA for pre-launch preparations in August 2000. It launched on 7 February 2001, aboard the Space Shuttle ''Atlantis'' on STS-98. Astronauts work inside the pressurized facility to conduct research in numerous scientific fields. Scientists throughout the world would use the results to enhance their studies in medicine, engineering, biotechnology, physics, materials science, and Earth science.

''Quest''

The Joint Airlock (also known as "Quest") is provided by the U.S. and provides the capability for ISS-based Extravehicular Activity (EVA) using either a U.S. Extravehicular Mobility Unit (EMU) or Russian Orlan EVA suits. Before the launch of this airlock, EVAs were performed from either the U.S. Space Shuttle (while docked) or from the Transfer Chamber on the Service Module. Due to a variety of system and design differences, only U.S. space suits could be used from the Shuttle and only Russian suits could be used from the Service Module. The Joint Airlock alleviates this short-term problem by allowing either (or both) spacesuit systems to be used.
The Joint Airlock was launched on ISS-7A / STS-104 in July 2001 and was attached to the right hand docking port of Node 1. The Joint Airlock is 20 ft. long, 13 ft. in diameter, and weighs 6.5 tons. The Joint Airlock was built by Boeing at Marshall Space Flight Center. The Joint Airlock was launched with the High Pressure Gas Assembly. The High Pressure Gas Assembly was mounted on the external surface of the Joint Airlock and will support EVAs operations with breathing gases and augments the Service Module's gas resupply system.
The Joint Airlock has two main components: a crew airlock from which astronauts and cosmonauts exit the ISS and an equipment airlock designed for storing EVA gear and for so-called overnight "campouts" wherein Nitrogen is purged from astronaut's bodies overnight as pressure is dropped in preparation for spacewalks the following day. This alleviates the bends as the astronauts are repressurized after their EVA.

The crew airlock was derived from the Space Shuttle's external airlock. It is equipped with lighting, external handrails, and an Umbilical Interface Assembly (UIA). The UIA is located on one wall of the crew airlock and provides a water supply line, a wastewater return line, and an oxygen supply line. The UIA also provides communication gear and spacesuit power interfaces and can support two spacesuits simultaneously. This can be either two American EMU spacesuits, two Russian ORLAN spacesuits, or one of each design.

''Poisk''

''Poisk (russian: По́иск, , Search, links=no)'' was launched on 10 November 2009 attached to a modified Progress spacecraft, called Progress M-MIM2, on a Soyuz-U rocket from Launch Pad 1 at the Baikonur Cosmodrome in Kazakhstan. ''Poisk'' is used as the Russian airlock module, containing two identical EVA hatches. An outward-opening hatch on the ''Mir'' space station failed after it swung open too fast after unlatching, because of a small amount of air pressure remaining in the airlock. All EVA hatches on the ISS open inwards and are pressure-sealing. Poisk is used to store, service, and refurbish Russian Orlan suits and provides contingency entry for crew using the slightly bulkier American suits. The outermost docking port on the module allows docking of Soyuz and Progress spacecraft, and the automatic transfer of propellants to and from storage on the ROS. Since the departure of the identical Pirs module on July 26, 2021, Poisk has served as the only airlock on the ROS.

''Harmony''

''Harmony'', also known as ''Node 2'', is the "utility hub" of the ISS. It connects the laboratory modules of the United States, Europe and Japan, as well as providing electrical power and electronic data. Sleeping cabins for four of the crew are housed here.

''Harmony'' was successfully launched into space aboard Space Shuttle flight STS-120 on 23 October 2007. After temporarily being attached to the port side of the ''Unity'' node, it was moved to its permanent location on the forward end of the ''Destiny'' laboratory on 14 November 2007. ''Harmony'' added to the station's living volume, an increase of almost 20 percent, from . Its successful installation meant that from NASA's perspective, the station was considered to be "U.S. Core Complete".

''Tranquility''

''Tranquility'', also known as Node 3, is a module of the ISS. It contains environmental control systems, life support systems, a toilet, exercise equipment, and an observation cupola.

The European Space Agency and the Italian Space Agency had ''Tranquility'' manufactured by Thales Alenia Space. A ceremony on 20 November 2009 transferred ownership of the module to NASA. On 8 February 2010, NASA launched the module on the Space Shuttle's STS-130 mission.

''Columbus''

''Columbus'' is a science laboratory that is part of the ISS and is the largest single contribution to the station made by the European Space Agency.

Like the ''Harmony'' and ''Tranquility'' modules, the ''Columbus'' laboratory was constructed in Turin, Italy by Thales Alenia Space. The functional equipment and software of the lab was designed by EADS in Bremen, Germany. It was also integrated in Bremen before being flown to the Kennedy Space Center in Florida in an Airbus Beluga. It was launched aboard Space Shuttle ''Atlantis'' on 7 February 2008, on flight STS-122. It is designed for ten years of operation. The module is controlled by the Columbus Control Centre, located at the German Space Operations Center, part of the German Aerospace Center in Oberpfaffenhofen near Munich, Germany.

The European Space Agency has spent €1.4 billion (about US$2 billion) on building ''Columbus'', including the experiments it carries and the ground control infrastructure necessary to operate them.

''Kibō''

The Japanese Experiment Module (JEM), nicknamed , is a Japanese science module for the International Space Station (ISS) developed by JAXA. It is the largest single ISS module, and is attached to the ''Harmony'' module. The first two pieces of the module were launched on Space Shuttle missions STS-123 and STS-124. The third and final components were launched on STS-127.

''Cupola''

The ''Cupola'' is an ESA-built observatory module of the ISS. Its name derives from the Italian word ', which means " dome". Its seven windows are used to conduct experiments, dockings and observations of Earth. It was launched aboard Space Shuttle mission STS-130 on 8 February 2010 and attached to the ''Tranquility'' (Node 3) module. With the ''Cupola'' attached, ISS assembly reached 85 percent completion. The ''Cupola'' central window has a diameter of .

''Rassvet''

'' Rassvet'' (russian: Рассвет; lit. "dawn"), also known as the Mini-Research Module 1 (MRM-1) (russian: Малый исследовательский модуль, ) and formerly known as the Docking Cargo Module (DCM), is a component of the International Space Station (ISS). The module's design is similar to the ''Mir'' Docking Module launched on STS-74 in 1995. ''Rassvet'' is primarily used for cargo storage and as a docking port for visiting spacecraft. It was flown to the ISS aboard Space Shuttle ''Atlantis'' on the STS-132 mission on 14 May 2010, and was connected to the ISS on 18 May 2010. The hatch connecting ''Rassvet'' with the ISS was first opened on 20 May 2010. On 28 June 2010, the Soyuz TMA-19 spacecraft performed the first docking with the module.

MLM outfittings

In May 2010, equipment for ''Nauka'' was launched on STS-132 (as part of an agreement with NASA) and delivered by Space Shuttle ''Atlantis''. Weighing 1.4 metric tons, the equipment was attached to the outside of ''Rassvet'' (MRM-1). It included a spare elbow joint for the European Robotic Arm (ERA) (which was launched with ''Nauka'') and an ERA-portable workpost used during EVAs, as well as RTOd heat radiator, internal hardware and an experiment airlock for launching CubeSats to be positioned on the modified passive forward port near the nadir end of the ''Nauka'' module.

The RTOd radiator will be used to add additional cooling capability to ''Nauka'', which will enable the module to host more scientific experiments. The airlock will be used only to pass experiments inside and outside the module, with the aid of ERAvery similar to the Japanese airlock and Nanoracks Bishop Airlock on the U.S. segment of the station.

The ERA will be used to remove the RTOd radiator and airlock from ''Rassvet'' and transfer them over to ''Nauka''. This process is expected to take several months. A portable work platform will also be transferred over, which can attach to the end of the ERA to allow cosmonauts to "ride" on the end of the arm during spacewalks.

Another MLM outfitting is a 4 segment external payload interface called means of attachment of large payloads (Sredstva Krepleniya Krupnogabaritnykh Obyektov, SKKO). Delivered in two parts to Nauka by Progress MS-18 (LCCS part) and Progress MS-21 (SCCCS part) as part of the module activation outfitting process. It was taken outside and installed on the ERA aft facing base point on Nauka during the VKD-55 spacewalk.

''Leonardo''

The ''Leonardo'' Permanent Multipurpose Module (PMM) is a module of the International Space Station. It was flown into space aboard the Space Shuttle on STS-133 on 24 February 2011 and installed on 1 March. ''Leonardo'' is primarily used for storage of spares, supplies and waste on the ISS, which was until then stored in many different places within the space station. It is also the personal hygiene area for the astronauts who live in the US Orbital Segment. The ''Leonardo'' PMM was a Multi-Purpose Logistics Module (MPLM) before 2011, but was modified into its current configuration. It was formerly one of two MPLM used for bringing cargo to and from the ISS with the Space Shuttle. The module was named for Italian polymath Leonardo da Vinci.

Bigelow Expandable Activity Module

The Bigelow Expandable Activity Module (BEAM) is an experimental expandable space station module developed by Bigelow Aerospace, under contract to NASA, for testing as a temporary module on the International Space Station (ISS) from 2016 to at least 2020. It arrived at the ISS on 10 April 2016, was berthed to the station on 16 April at Tranquility Node 3, and was expanded and pressurized on 28 May 2016.

International Docking Adapters

The International Docking Adapter (IDA) is a spacecraft docking system adapter developed to convert APAS-95 to the NASA Docking System (NDS). An IDA is placed on each of the ISS's two open Pressurized Mating Adapters (PMAs), both of which are connected to the ''Harmony'' module.

Two International Docking Adapters are currently installed aboard the Station. Originally, IDA-1 was planned to be installed on PMA-2, located at ''Harmony'''s forward port, and IDA-2 would be installed on PMA-3 at ''Harmony'''s zenith. After IDA 1 was destroyed in a launch incident, IDA-2 was installed on PMA-2 on 19 August 2016, while IDA-3 was later installed on PMA-3 on 21 August 2019.

Bishop Airlock Module

The NanoRacks Bishop Airlock Module is a commercially funded airlock module launched to the ISS on SpaceX CRS-21 on 6 December 2020. The module was built by NanoRacks, Thales Alenia Space, and Boeing. It will be used to deploy CubeSats, small satellites, and other external payloads for NASA, CASIS, and other commercial and governmental customers.

''Nauka''

''Nauka'' (russian: Наука, links=no, 3=Science), also known as the Multipurpose Laboratory Module-Upgrade (MLM-U), (Russian: ''Многоцелевой лабораторный модуль'', усоверше́нствованный, or ''МЛМ-У)'', is a Roscosmos-funded component of the ISS that was launched on 21 July 2021, 14:58 UTC. In the original ISS plans, ''Nauka'' was to use the location of the Docking and Stowage Module (DSM), but the DSM was later replaced by the ''Rassvet'' module and moved to ''Zarya''s nadir port. ''Nauka'' was successfully docked to ''Zvezda''s nadir port on 29 July 2021, 13:29 UTC, replacing the ''Pirs'' module.

It had a temporary docking adapter on its nadir port for crewed and uncrewed missions until Prichal arrival, where just before its arrival it was removed by a departuring Progress spacecraft.

''Prichal''

''Prichal'', also known as ''Uzlovoy'' Module or UM (russian: Узловой Модуль Причал, links=no, 3=Nodal Module Berth), is a ball-shaped module that will provide the Russian segment additional docking ports to receive Soyuz MS and Progress MS spacecraft. UM was launched in November 2021. It was integrated with a special version of the Progress cargo spacecraft and launched by a standard Soyuz rocket, docking to the nadir port of the ''Nauka'' module. One port is equipped with an active hybrid docking port, which enables docking with the MLM module. The remaining five ports are passive hybrids, enabling docking of Soyuz and Progress vehicles, as well as heavier modules and future spacecraft with modified docking systems. The node module was intended to serve as the only permanent element of the cancelled Orbital Piloted Assembly and Experiment Complex (OPSEK).

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 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. , only one other mode of transportation of ORUs had been utilisedthe Japanese cargo vessel HTV-2which 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.

Robotic arms and cargo cranes

The Integrated Truss Structure serves as a base for the station's primary remote manipulator system, the Mobile Servicing System (MSS), which is composed of three main components:
* Canadarm2, the largest robotic arm on the ISS, has a mass of and is used to: dock and manipulate spacecraft and modules on the USOS; hold crew members and equipment in place during EVAs; and move Dextre around to perform tasks.
* Dextre is a robotic manipulator that has two arms and a rotating torso, with power tools, lights, and video for replacing orbital replacement units (ORUs) and performing other tasks requiring fine control.
* The Mobile Base System (MBS) is a platform that rides on rails along the length of the station's main truss, which serves as a mobile base for Canadarm2 and Dextre, allowing the robotic arms to reach all parts of the USOS.

A grapple fixture was added to ''Zarya'' on STS-134 to enable Canadarm2 to inchworm itself onto the Russian Orbital Segment. Also installed during STS-134 was the Orbiter Boom Sensor System (OBSS), which had been used to inspect heat shield tiles on Space Shuttle missions and which can be used on the station to increase the reach of the MSS. Staff on Earth or the ISS can operate the MSS components using remote control, performing work outside the station without the need for space walks.

Japan's Remote Manipulator System, which services the ''Kibō'' Exposed Facility, was launched on STS-124 and is attached to the ''Kibō'' Pressurised Module. The arm is similar to the Space Shuttle arm as it is permanently attached at one end and has a latching end effector for standard grapple fixtures at the other.

The European Robotic Arm, which will service the Russian Orbital Segment, was launched alongside the ''Nauka'' module. The ROS does not require spacecraft or modules to be manipulated, as all spacecraft and modules dock automatically and may be discarded the same way. Crew use the two '' Strela'' (russian: Стрела́, , Arrow) cargo cranes during EVAs for moving crew and equipment around the ROS. Each Strela crane has a mass of .

Former module

''Pirs''

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 ''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

Axiom segment

In January 2020, NASA awarded Axiom Space a contract to build a commercial module for the ISS with a launch date of 2024. 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 has only commissioned one module, Axiom plans to build an entire 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 is expected to greatly increase the capabilities and value of the space station, allowing for larger crews and private spaceflight by other organisations. Axiom plans to convert the segment into a stand-alone space station once the ISS is decommissioned, with the intention that this would act as a successor to the ISS. Canadarm 2 will also help to berth the Axiom Space Station modules to the ISS and will continue its operations on the Axiom Space Station after the retirement of ISS in late 2020s.

Proposed components

Xbase

Made by Bigelow Aerospace. In August 2016 Bigelow negotiated an agreement with NASA to develop a full-sized ground prototype Deep Space Habitation based on the B330 under the second phase of Next Space Technologies for Exploration Partnerships. The module is called the Expandable Bigelow Advanced Station Enhancement (XBASE), as Bigelow hopes to test the module by attaching it to the International Space Station.

Independence-1

Nanoracks, after finalizing its contract with NASA, and after winning NextSTEPs Phase II award, is now developing its concept Independence-1 (previously known as Ixion), which would turn spent rocket tanks into a habitable living area to be tested in space. In Spring 2018, Nanoracks announced that Ixion is now known as the Independence-1, the first 'outpost' in Nanoracks' Space Outpost Program.

Nautilus-X Centrifuge Demonstration

If produced, this centrifuge will be the first in-space demonstration of sufficient scale centrifuge for artificial partial-g effects. It will be designed to become a sleep module for the ISS crew.

Cancelled components

Several modules planned for the station were cancelled over the course of the ISS programme. 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 Modules 1 and 2 (Repurposed Components)

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 currently docked to the ''Nauka'' module. In April 2021, Roscosmos announced that NEM-1 would be repurposed to function as the core module of the proposed Russian Orbital Service Station (ROSS), launching no earlier than 2025 and docking to the free-flying ''Nauka'' module either before or after the ISS has been deorbited. NEM-2 may be converted into another core "base" module, which would be launched in 2028.

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.

Atmospheric control systems

The atmosphere on board the ISS is similar to that of Earth. Normal air pressure on the ISS is ; the same as at sea level on Earth. An Earth-like atmosphere offers benefits for crew comfort, and is much safer than a pure oxygen atmosphere, because of the increased risk of a fire such as that responsible for the deaths of the Apollo 1 crew.
Earth-like atmospheric conditions have been maintained on all Russian and Soviet spacecraft.

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 and by electrolysis of water and vents overboard. The 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 , producing of . This unit is manually operated.

The US Orbital Segment 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 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 in area and 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 () 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 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

Radio communications provide telemetry and scientific data links between the station and mission control centres. 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 communicates directly with the ground via the '' Lira'' antenna mounted to ''Zvezda''. The ''Lira'' antenna also has the capability to use the '' Luch'' data relay satellite system. This system fell into disrepair during the 1990s, and so was not used during the early years of the ISS, although two new ''Luch'' satellites''Luch''-5A and ''Luch''-5Bwere launched in 2011 and 2012 respectively to restore the operational capability of the system. Another Russian communications system is the Voskhod-M, which enables internal telephone communications between ''Zvezda'', ''Zarya'', ''Pirs'', ''Poisk'', and the USOS and provides a VHF radio link to ground control centres via antennas on ''Zvezda'' exterior.

The US Orbital Segment (USOS) makes use of two separate radio links: S band (audio, telemetry, commanding – located on the P1/S1 truss) and K_u 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. Data channels for the Canadarm2, European ''Columbus'' laboratory and Japanese ''Kibō'' modules were originally also routed via the S band and K_u band systems, with the European Data Relay System and a similar Japanese system intended to eventually complement the TDRSS in this role. Communications between modules are carried on an internal wireless network.

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 uses a laser attached to the spacecraft and the Proximity Communications Equipment attached to ''Zvezda'' to accurately dock with the station.

The ISS is equipped with about 100 IBM/Lenovo ThinkPad and HP ZBook 15 laptop computers. The laptops have run Windows 95, Windows 2000, Windows XP, Windows 7, Windows 10 and Linux operating systems. Each computer is a commercial off-the-shelf purchase which is then modified for safety and operation including updates to connectors, cooling and power to accommodate the station's 28V DC power system and weightless environment. Heat generated by the laptops does not rise but stagnates around the laptop, so additional forced ventilation is required. Portable Computer System (PCS) laptops connect to the Primary Command & Control computer (C&C MDM) as remote terminals via a USB to 1553 adapter. Station Support Computer (SSC) laptops aboard the ISS are connected to the station's wireless LAN via Wi-Fi and ethernet, which connects to the ground via K_u band. While originally this provided speeds of 10 Mbit/s download and 3 Mbit/s upload from the station, NASA upgraded the system in late August 2019 and increased the speeds to 600 Mbit/s. Laptop hard drives occasionally fail and must be replaced. Other computer hardware failures include instances in 2001, 2007 and 2017; some of these failures have required EVAs to replace computer modules in externally mounted devices.

The operating system used for key station functions is the Debian Linux distribution. The migration from Microsoft Windows to Linux was made in May 2013 for reasons of reliability, stability and flexibility.

In 2017, an SG100 Cloud Computer was launched to the ISS as part of OA-7 mission. It was manufactured by NCSIST of Taiwan and designed in collaboration with Academia Sinica, and National Central University under contract for NASA.

ISS crew members have access to the Internet, and thus the web. This was first enabled in 2010, allowing NASA astronaut T.J. Creamer to make the first tweet from space. Access is achieved via an Internet-enabled computer in Houston, using remote desktop mode, thereby protecting the ISS from virus infection and hacking attempts.

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. Expeditions 7 to 12 were reduced to the safe minimum of two following the destruction of the NASA Shuttle ''Columbia''. From Expedition 13 the crew gradually increased to six around 2010. With the arrival of crew on US commercial vehicles beginning in 2020, NASA has indicated that expedition size may be increased to seven crew members, the number ISS was originally designed for.

Gennady Padalka, member of Expeditions 9, 19/ 20, 31/ 32, and 43/ 44, and Commander of Expedition 11, has spent more time in space than anyone else, a total of 878 days, 11 hours, and 29 minutes. Peggy Whitson has spent the most time in space of any American, totalling 665 days, 22 hours, and 22 minutes during her time on Expeditions 5, 16, and 50/ 51/ 52.

Private flights

Travellers who pay for their own passage into space are termed spaceflight participants by Roscosmos and NASA, and are sometimes referred to as "space tourists", a term they generally dislike. , seven space tourists have visited the ISS; all seven were transported to the ISS on Russian Soyuz spacecraft. When professional crews change over in numbers not divisible by the three seats in a Soyuz, and a short-stay crewmember is not sent, the spare seat is sold by MirCorp through Space Adventures. Space tourism was halted in 2011 when the Space Shuttle was retired and the station's crew size was reduced to six, as the partners relied on Russian transport seats for access to the station. Soyuz flight schedules increased after 2013, allowing five Soyuz flights (15 seats) with only two expeditions (12 seats) required. The remaining seats were to be sold for around US$40 million to members of the public who could pass a medical exam. ESA and NASA criticised private spaceflight at the beginning of the ISS, and NASA initially resisted training Dennis Tito, the first person to pay for his own passage to the ISS.

Anousheh Ansari became the first self-funded woman to fly to the ISS as well as the first Iranian in space. Officials reported that her education and experience made her much more than a tourist, and her performance in training had been "excellent." She did Russian and European studies involving medicine and microbiology during her 10-day stay. The 2009 documentary ''Space Tourists'' follows her journey to the station, where she fulfilled "an age-old dream of man: to leave our planet as a 'normal person' and travel into outer space."

In 2008, spaceflight participant Richard Garriott placed a geocache aboard the ISS during his flight. This is currently the only non-terrestrial geocache in existence. At the same time, the Immortality Drive, an electronic record of eight digitised human DNA sequences, was placed aboard the ISS.

Fleet operations

A wide variety of crewed and uncrewed spacecraft have supported the station's activities. Flights to the ISS include 37 Space Shuttle missions, 83 Progress resupply spacecraft (including the modified M-MIM2, M-SO1 and M-UM module transports), 63 crewed Soyuz spacecraft, 5 European ATVs, 9 Japanese HTVs, 1 Boeing Starliner

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