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The International Space Station (ISS) is a habitable artificial satellite in low Earth orbit. It follows the Salyut, Almaz, Skylab and Mir as the ninth space station to be inhabited. The station is operated by Expedition crews, and has been continuously occupied for having exceeded the previous record of almost 10 years (or 3,644 days) held by Mir, in 2010. The ISS serves as a microgravity and space environment research laboratory in which crew members conduct experiments in biology, human biology, physics, astronomy, meteorology and other fields. The station is suited for the testing of spacecraft systems and equipment required for missions to the Moon and Mars. The ISS is a modular structure whose first component was launched in 1998. It has since grown to become the largest and most expensive space station ever built. Other modular space station projects include MIR, OPSEK and Tiangong 3.

The International Space Station combines three space station projects with the Japanese Kibō module and Canadian robotics. Budget constraints led to the merger of the Soviet/Russian Mir-2, the American Freedom, and the European Columbus, into a single multi-national programme. The ISS programme is a joint project between five participating space agencies, the American NASA, the Russian RKA, the Japanese JAXA, the European ESA, and the Canadian CSA. The ISS consists of pressurised modules, external trusses, solar arrays and other elements. ISS components have been launched by American Space Shuttles as well as Russian Proton and Soyuz rockets.

The ownership and use of the space station is established by intergovernmental treaties and agreements. The station is divided into two sections, the Russian orbital segment (ROS) and the United States orbital segment (USOS), which is shared by many nations. The station is serviced by Soyuz spacecraft, Progress spacecraft, the Automated Transfer Vehicle and the H-II Transfer Vehicle, and has been visited by astronauts and cosmonauts from 15 different nations. The ISS is maintained at an orbital altitude of between 330 km and 410 km. It completes 15.7 orbits per day. Like many artificial satellites, the station can be seen from Earth with the naked eye. The ISS is expected to remain in operation until at least 2020, and potentially to 2028. Some elements of the ISS are expected to be separated to form the planned Russian OPSEK facility before the remainder is deorbited.

Purpose
According to the original Memorandum of Understanding between NASA and RSA, the International Space Station was intended to be a laboratory, observatory and factory in space. It was also planned to provide transportation, maintainence, and act as a staging base for possible future missions to the Moon, Mars and asteroids. 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 that cannot be performed in any other way. While unmanned spacecraft can provide platforms for zero gravity and exposure to space, the ISS offers a long term environment where studies can be performed potentially for decades, combined with ready access by human researchers over periods that exceed the capabilities of manned spacecraft. Kibō is intended to accelerate Japan's progress in science and technology, gain new knowledge and apply it to such fields as industry and medicine. The Alpha Magnetic Spectrometer (AMS), which NASA compares to the Hubble telescope, could not be accommodated on a free flying satellite platform, due in part to its power requirements and data bandwidth needs. The Station simplifies individual experiments by eliminating the need for separate rocket launches and research staff.

The primary fields of research include Space weather, human research, space medicine, life sciences, physical sciences, astronomy and meteorology. Scientists on Earth have access to the crew's data and can modify experiments or launch new ones; benefits generally unavailable on unmanned spacecraft. Crews fly expeditions of several months duration, providing approximately 160 man-hours a week of labor with a crew of 6.

Research on the ISS 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 lengthy human spaceflight and space colonization are feasible. As of 2006, data on bone loss and muscular atrophy suggest 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 and 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.

Microgravity
Gravity is the only significant force acting upon the ISS, which is in constant freefall. This state of freefall, or perceived weightlessness, is not perfect however, being disturbed by four separate effects: One, the drag resulting from the residual atmosphere, when the ISS enters the Earth's shadow, the main solar panels are rotated to minimise this aerodynamic drag, helping reduce orbital decay. Two, vibration caused by mechanical systems and the crew on board the ISS. Three, orbital corrections by the on-board gyroscopes or thrusters. Four, the spatial separation from the real centre of mass of the ISS. Any part of the ISS not at the exact center of mass will tend to follow its own orbit. That is, parts on the underside, closer to the Earth are pulled harder, towards the Earth. Conversely, parts on the top of the station, farther from Earth, try to fling off into space. However, as each point is physically part of the station, this is impossible, and so each component is subject to small forces which keep them attached to the station as it orbits. This is also called the tidal force.

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 this 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.

The investigation of the physics of fluids in microgravity will allow researchers to model the behaviour of fluids better. Because fluids can be almost completely combined in microgravity, physicists investigate fluids that do not mix well on Earth. In addition, an examination of reactions that are slowed by low gravity and temperatures will give scientists a deeper 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 the low gravity environment on combustion, through the study of the efficiency of burning and control of emissions and pollutants. These findings may improve current knowledge about energy production, and lead to economic and environmental benefits. Future plans are for the researchers aboard the ISS to examine aerosols, ozone, water vapour, and oxides in Earth's atmosphere, as well as cosmic rays, cosmic dust, antimatter, and dark matter in the universe.

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, which will be essential skills in operating spacecraft farther from Earth. Leveraging this and other experience, mission risks can be reduced and the capabilities of interplanetary spacecraft advanced. Referring to the Mars500 experiment, 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 Mars500 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 manned mission to Mars, however, may be a multinational effort acceding the current ISS partnership and involving space agencies and countries outside of it. In 2010 ESA Director-General Jean-Jacques Dordain stated his agency was ready to propose to the other 4 partners that China, India and South Korea be invited to join the ISS partnership. NASA chief Charlie Bolden stated in Feb 2011 "Any mission to Mars is likely to be a global effort". Currently, American legislation prevents NASA co-operation with China on space projects.

Education and cultural outreach
The ISS crew provide 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, videolink 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 3-D model of the interior and exterior of the ISS, and face spontaneous challenges to solve in real time.

JAXA aims both to 'Stimulate the curiosity of children, cultivating their spirits, and encouraging their passion to pursue craftsmanship', and to 'Heighten the child's awareness of the importance of life and their responsibilities in society.' Through a series of education guides, a deeper understanding of the past and near-term future of manned space flight, as well as that of Earth and life, will be learned. In the JAXA Seeds in Space experiments, the mutation effects of spaceflight on plant seeds aboard the ISS is explored. Students grow sunflower seeds which flew on the ISS for about nine months as a start to ‘touch the Universe’. 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. 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 which inspires 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 9 countries including several countries 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 station.

First Orbit is a feature-length documentary film about Vostok 1, the first manned space flight around the Earth. By matching the orbit of the International Space Station 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, during Expedition 26/27, filmed the majority of the footage for this documentary film, and as a result is credited as its director of photography. The film was streamed through the website www.firstorbit.org in a global YouTube premiere in 2011, under a free license.

Origins
The International Space Station represents a combination of three national space station projects, NASA's Freedom, the RSA's Mir-2, and the European Columbus space stations. In September 1993, American Vice-President Al Gore, Jr., and Russian Prime Minister Viktor Chernomyrdin announced plans for a new space station, which eventually became the International Space Station. They also agreed, in preparation for this new project, that the United States would be involved in the Mir programme, including American Shuttles docking, in the Shuttle-Mir Program. According to the plan, the International Space Station programme would combine the proposed space stations of 3 participant agencies with Canadian robotics and the Japanese Kibō laboratory.

NASA's Freedom
In the early 1980s, NASA planned to launch a modular space station called Freedom as a counterpart to the Soviet Salyut and Mir space stations. Although approved by then-president Ronald Reagan and announced in the 1984 State of the Union Address, "We can follow our dreams to distant stars, living and working in space for peaceful economic and scientific gain", Freedom was never constructed or completed as originally designed, and after several cutbacks, the remnants of the project became part of the ISS. Several NASA Space Shuttle missions in the 1980s and early 1990s included spacewalks to demonstrate and test space station construction techniques.

NASA's first cost assessment in 1987 revealed the 'Dual Keel' Station would cost $14.5 billion. This caused a political uproar in Congress, and NASA and Reagan Administration officials reached a compromise in March 1987 which allowed the agency to proceed with a cheaper $12.2-billion Phase One Station that could be completed after 10 or 11 Shuttle assembly flights. This design initially omitted the $3.4-billion 'Dual Keel' structure and half of the power generators. The new Space Station configuration was named 'Freedom' by Reagan in June 1988. Originally, Freedom would have carried two 37.5 kW solar arrays. However, Congress quickly insisted on adding two more arrays for scientific users. The Space Station programme was plagued by conflicts during the entire 1984-87 definition phase. In 1987, the Department of Defense (DoD) briefly demanded to have full access to the Station for military research, despite strong objections from NASA and the international partners. Besides the expected furor from the international partners, the DoD position sparked a shouting match between Defense Secretary Caspar Weinberger and powerful members of Congress that extended right up to the final Fiscal 1988 budget authorisation in July 1987. Reagan wanted to invite other NATO countries to participate in the U.S-led project, since the Soviet Union had been launching international crews to their Salyut space stations since 1971. At one point, then-anonymous disgruntled NASA employees calling themselves "Center for Strategic Space Studies" suggested that instead of building Freedom, NASA should take the back-up Skylab from display in the National Air and Space Museum in Washington and launch that.

The space station was also going to tie the emerging European and Japanese national space programmes closer to the U.S.-led project, thereby preventing those nations from becoming major, independent competitors too. An agreement signed in September 1988 allocated 97% of the US lab resources to NASA while the Canadian CSA would receive 3% in return for its contribution to the programme. Europe and Japan would retain 51% of their own laboratory modules. Six Americans and two international astronauts would be permanently based on Space Station Freedom.

Russia's Mir-2
The Russian Orbital Segment (ROS or RS) is the eleventh Soviet-Russian space station. Mir ("Peace") and the ISS are successors to the Salyut ("Fireworks") and Almaz ("Diamond") stations. Mir-2 was originally authorised in the February 1976 resolution setting forth plans for development of third generation Soviet space systems. The first MIR-2 module was launched in 1986 by an Energia heavy-lift expendable launch system. The launcher worked properly, however the Polyus payload fired its engines to insert itself into orbit whilst in the wrong position due to a programming error, and re-entered the atmosphere. The planned station changed several times, but Zvezda was always the service module, containing the stations critical systems such as life support. The station would have used the Buran spaceplane and Proton rockets to lift new modules into orbit. The spaceframe of Zvezda, also called DOS-8 serial number 128, was completed in February 1985 and major internal equipment was installed by October 1986.

The Polyus module or spacecraft, which would have served the same function as Zarya, looked like a "Salyut" slightly modified for this task and would have served as the FGB, a foundation which provides propulsion and guidance, but lacks life support. There are two different descriptions of the weapon systems. In one, Polyus is described as a space-borne nuclear bomber, in another it is described as a satellite interceptor, carrying a 1 MegaWatt carbon dioxide laser. The module had a length of almost 37 m and a diameter of 4.1 m weighed nearly 80 t and included 2 principal sections, the smallest, the functional service block (FGB) and the largest, the aim module.

In 1983, the design was changed and the station would consist of Zvezda, followed by several 90 metric ton modules and a truss structure similar to the current station. The draft was approved by NPO Energia Chief Semenov on 14 December 1987 and announced to the press as 'Mir-2' in January 1988. This station would be visited by the Soviet Buran, but mainly resupplied by Progress-M2 spacecraft. Orbital assembly of the station was expected to begin in 1993. In 1993 with the collapse of the Soviet Union, a redesigned smaller Mir-2 was to be built whilst attached to Mir, just as OPSEK is being assembled whilst attached to the ISS.

Japan's Kibō
Conceived in 1985, the Japanese Experiment Module (JEM) or Kibō consists of a pressurised laboratory dedicated to advanced technology experiments, education and art, a cargo bay, an unpressurised pallet for vacuum experiments in space plus a robotic arm. While the proposed space station was redesigned many times around Kibō, the only significant change has been the placement of its ballistic shielding. Its final position at the front of the station increases the risk of damage from debris. The Japanese National Space Development Agency (NASDA) formally submitted the JEM proposal to NASA in March 1986.

In 1986 the Japanese contribution was estimated to be worth $1.9-3.2 billion for a JEM launch in 1995. By 1990, the schedule had slipped by three years due to NASA budget cuts and space station cost overruns. The delays increased the JEM's total cost slightly, from $2.3 billion in 1986 to $2.63 billion in 1993, when the launch was postponed to 1999. Final hardware production began in the mid-1990s and the Japanese robotic arm was tested on a NASA Space Shuttle flight in August 1997. According to plans prior to the Columbia disaster, the JEM would be launched in 2002-03.

In 2010, Kibō won the Good Design Award, a 67 year old consumer and industry award which identifies the best of Japanese craftsmanship. During August 2011, an observatory mounted on Kibō, which utilises the ISS's orbital motion to image the whole sky in the X-ray spectrum, detected for the first time the moment a star was swallowed by a black hole.

ESA's Columbus
In 1988, Europe proposed to participate with three elements, the Columbus module, the Man-Tended Free Flyer (MTFF), and the Polar Platform (PPF), supported by the Ariane-5 launcher and the Hermes spaceplane.

The Columbus Man-Tended Free Flyer (MTFF) was a European Space Agency (ESA) programme to develop a space station that could be used for a variety of microgravity experiments while serving ESA's needs for an autonomous manned space platform. The Hermes spaceplane is comparable in function to the American and Soviet spaceplanes, with a smaller crew of up to 6 (reduced to 3 with ejection seats after the Columbia disaster) and substantially smaller cargo capacity, 4,550 kg, comparable to ISS unmanned cargo ships.

By 1991 the Columbus and Hermes pre-development activities were good enough to progress into full development, however profound geopolitical changes prompted examining broader international cooperation, in particular with the Russian Federation. ESA Member States approved the complete development of the Attached Pressurised Module (APM) and the Polar Platform (PPF) for Columbus, but the Man-Tended Free-Flyer (MTFF) was abandoned. The Hermes programme was reoriented into the Manned Space Transportation Programme (MSTP), and a three-year period extending from 1993 to 1995 was agreed on in order to define a future manned space transportation system in cooperation with Russia, including joint development and use of Mir-2.

Station structure
The ISS follows Salyut, Almaz, "Cosmos 557", Skylab, and Mir as the 11th space station launched, as the Genesis prototypes were never intended to be manned. The ISS is a third generation modular space station.

Other examples of modular station projects include the Soviet/Russian MIR, Russian OPSEK, and Chinese Tiangong 3. The first space station, Salyut 1, and other one-piece or 'monolithic' first generation space stations, such as Salyut 2,3,4,5, DOS 2, Kosmos 557, Almaz and NASA's Skylab stations were not designed for re-supply. Generally, each crew had to depart the station to free the only docking port for the next crew to arrive, Skylab had more than one docking port but was not designed for resupply. Salyut 6 and 7 had more than one docking port and were designed to be resupplied routinely during crewed operation. Modular stations can allow the mission to be changed over time and new modules can be added or removed from the existing structure, allowing greater flexibility.

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. Other unpressurised components are yellow. Note that the Unity node joins directly to the Destiny laboratory. For clarity, they are shown apart.

Assembly


The assembly of the International Space Station, a major endeavour in space architecture, began in November 1998. Russian modules launch and dock 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 SSRMS and EVAs;, they had added 159 components during more than 1,000 hours of EVA activity. 127 of these spacewalks originated from the station, while 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, as the station's beta angle is directly related to the percentage of its orbit that the station (as well as any docked or docking spacecraft) is exposed to the sun; the Space Shuttle would not perform optimally above a limit called the "beta cutoff". Rassvet was delivered by NASA's Atlantis Space Shuttle in 2010 in exchange for the Russian Proton delivery of the United States-funded Russian-built Zarya Module in 1998. Robot arms rather than EVAs were utilised in its installation (docking).

The first segment of the ISS, Zarya, was launched on 20 November 1998 on an autonomous Russian Proton rocket. It provided propulsion, orientation control, communications, electrical power, but lacked long-term life support functions. Two weeks later a passive NASA module Unity was launched aboard Space Shuttle flight STS-88 and attached to Zarya by astronauts during EVAs. This module has two Pressurized Mating Adapters (PMAs), one connects permanently to Zarya, the other allows the Space Shuttle to dock to the space station. At this time, the Russian station Mir was still inhabited. The ISS remained unmanned for two years, during which time Mir was de-orbited. On 12 July 2000 Zvezda was launched into orbit. Preprogrammed commands on board deployed its solar arrays and communications antenna. It then became the passive vehicle for a rendezvous with the Zarya and Unity. As a passive "target" vehicle, the Zvezda maintained a stationkeeping orbit as the Zarya-Unity vehicle performed the rendezvous and docking via ground control and the Russian automated rendezvous and docking system. Zarya's computer transferred control of the station to Zvezda's computer soon after docking. Zvezda added sleeping quarters, a toilet, kitchen, CO2 scrubbers, dehumidifier, oxygen generators, exercise equipment, plus data, voice and television communications with mission control. This enabled permanent habitation of the station.

The first resident crew, Expedition 1, arrived in November 2000 on Soyuz TM-31, midway between the flights of STS-92 and STS-97. These two Space Shuttle flights each added segments of the station's Integrated Truss Structure, which provided the station with Ku-band communication for U.S. television, additional attitude support needed for the additional weight of the USOS, and substantial solar arrays supplementing the station's existing 4 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 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 by the destruction of the NASA space shuttle Columbia on STS-107 in 2003, with the resulting hiatus in the Space Shuttle programme halting station assembly until the launch of Discovery on STS-114 in 2005.

The official resumption of assembly was marked by the arrival of Atlantis, flying STS-115, 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 followed shortly after 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, closely followed in May 2010 by the penultimate Russian module, Rassvet, delivered by Space Shuttle Atlantis on STS-132. The last pressurised module of the USOS, Leonardo, was brought to the station by Discovery on her final flight, STS-133, followed by the Alpha Magnetic Spectrometer on STS-134, delivered by Endeavour.



The station consisted of fifteen pressurised modules and the Integrated Truss Structure. Still to be launched are the Russian Multipurpose Laboratory Module Nauka and a number of external components, including the European Robotic Arm. Assembly is expected to be completed by 2012, by which point the station will have a mass in excess of 400 metric tons (440 short tons).

The gross mass of the station is not possible to calculate with precision. The total launch weight of the modules on orbit is 417289 kg (as of 03/09/2011). The weight 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. Gas (Hydrogen) is constantly vented overboard by the Oxygen generators.

Pressurised modules
Zarya (Заря́; lit. dawn), also known as the Functional Cargo Block or FGB (ФГБ), was the first module of the station, launched on 20 November 1998 on a Russian Proton rocket from Baikonur Cosmodrome Site 81 in Kazakhstan to a 400 km high orbit. After parking in orbit, the Zarya Module provided orientation control, communications and electrical power for itself, and for the passive Node 1 (Unity) attached later, while the station awaited launch of the third component, a Russian-provided crew living quarters and early station core, the service module Zvezda. The Service Module enhanced or replaced many functions of Zarya. The FGB is a descendant of the TKS spacecraft designed for the Russian Salyut programme. 6,100 kg of propellant fuel can be stored and transferred automatically to and from ships docked to the Russian portion of the station – the Russian Orbital Segment (ROS). Zarya was originally intended as a module for the Russian Mir space station, but was not flown as of the end of the Mir-1 programme. Development costs for Zarya were paid for by Russia (and the former Soviet Union), spread across previous space station programmes, and some construction and preparation costs were paid for by the United States. Unity, a passive connecting module was the first U.S.-built component of the Station. It is cylindrical in shape, with six berthing locations facilitating connections to other modules. Unity was carried into orbit as the primary cargo of STS-88 in 1998.

Zvezda (Звезда, meaning "star"), DOS-8, also known as the Service Module or SM (СМ). It provides all of the station's critical systems, its addition rendered the station permanently habitable for the first time, adding life support for up to six crew and living quarters for two. Zvezda's DMS-R computer handles guidance, navigation & control for the entire space station. A second computer which performs the same functions is installed in the Nauka FGB-2. The rocket used for Zvezda's launch was one of the first to carry advertising. The space frame was completed in February 1985, major internal equipment was installed by October 1986, and it was launched on 12 July 2000. Zvezda is at the rear of the station according to its normal direction of travel and orientation, its engines are used to boost the station's orbit. Alternatively Russian and European spacecraft can dock to Zvezda's aft (rear) port and use their engines to boost the station.

Destiny is the primary research facility for United States payloads aboard the ISS. In 2011, NASA solicited proposals for a not-for-profit group to manage all American science on the station which does not relate to manned exploration. The module houses 24 International Standard Payload Racks, some of which are used for environmental systems and crew daily living equipment. Destiny also serves as the mounting point for the station's Truss Structure.

Quest is the only USOS airlock, Quest hosts spacewalks with both United States EMU and Russian Orlan spacesuits. Quest consists of two segments; the equipment lock, that stores spacesuits and equipment, and the crew lock, from which astronauts can exit into space. This module has a separately controlled atmosphere. Crew sleep in this module, breathing a low nitrogen mixture the night before scheduled EVAs, to avoid decompression sickness (known as "the bends") in the low pressure suits.

Pirs (Пирс, meaning "pier"), (Стыковочный отсек, "docking module", SO-1 or DC-1 (docking compartment), and Poisk (По́иск; lit. Search), also known as the Mini-Research Module 2 (MRM 2), Малый исследовательский модуль 2, or МИМ 2. Pirs and Poisk are Russian airlock modules. Each of these modules have 2 identical hatches. An outward opening hatch on the MIR space station failed after it swung open too fast after unlatching, due to a small amount of air pressure remaining in the airlock. A different entry was used, and the hatch repaired. All EVA hatches on the ISS open inwards and are pressure sealing. Pirs 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 ports on both airlocks allow docking of Soyuz and Progress spacecraft, and the automatic transfer of propellants to and from storage on the ROS.

Harmony, is the second of the station's node modules and the utility hub of the USOS. The module contains four racks that provide electrical power, bus electronic data, and acts as a central connecting point for several other components via its six Common Berthing Mechanisms (CBMs). The European Columbus and Japanese Kibō laboratories are permanently berthed to two of the radial ports, the other two can used for the HTV. American Shuttle Orbiters docked with the ISS via PMA-2, attached to the forward port. Tranquility is the third and last of the station's U.S. nodes, it contains an additional life support system to recycle waste water for crew use and supplements oxygen generation. Three of the four berthing locations are not used, one has the cupola installed and one has the docking port adapter installed.

Columbus, the primary research facility for European payloads aboard the ISS, provides a generic laboratory as well as facilities specifically designed for biology, biomedical research and fluid physics. Several mounting locations are affixed to the exterior of the module, which provide power and data to external experiments such as the European Technology Exposure Facility (EuTEF), Solar Monitoring Observatory, Materials International Space Station Experiment, and Atomic Clock Ensemble in Space. A number of expansions are planned for the module to study quantum physics and cosmology. ESA’s development of technologies on all the main areas of life support has been ongoing for more than 20 years and are/have been used in modules such as Columbus and the ATV.

Kibō (きぼう, "hope") is the largest single ISS module. This laboratory is used to carry out research in space medicine, biology, Earth observations, materials production, biotechnology, communications research, and has facilities for growing plants and fish. The laboratory contains a total of 23 racks, including 10 experiment racks and has a dedicated airlock for experiments. In a 'shirt sleeves' environment, crew attach an experiment to the sliding drawer within the airlock, close the inner, and then open the outer hatch. By extending the drawer and removing the experiment using the dedicated robotic arm, payloads are placed on the external platform. The process can be reversed and repeated quickly, allowing access to maintain external experiments without the delays caused by EVA's. Only the Russian and Japanese laboratories have this feature. A smaller pressurised module is attached to the top of Kibō, serving as a cargo bay. The dedicated Interorbital communications system allows large amounts of data to be beamed from Kibō's ICS, first to the Japanese KODAMA satellite in geostationary orbit, then to Japanese ground stations. When a direct communication link is used, contact time between the ISS and a ground station is limited to approximately 10 minutes per visible pass. When KODAMA relays data between a LEO spacecraft and a ground station, real-time communications are possible in 60% of the flight path of the spacecraft. Ground staff use tele-present robotics to conduct on-orbit research without crew intervention.

Cupola is an observatory, named after the raised observation deck on an American railroad caboose, its seven windows are used to make observations of Earth and dock spacecraft. The Cupola project was started by NASA and Boeing, but canceled due to budget cuts. A barter agreement between NASA and the ESA resulted in the Cupola's development being resumed in 1998 by the ESA. The module comes equipped with robotic workstations for operating the station's main robotic arm and shutters to protect its windows from damage caused by micrometeorites. It features a 80 cm round window, the largest window on the station.

Rassvet (Рассве́т; lit. "dawn"), also known as the Mini-Research Module 1 (MRM-1) (Малый исследовательский модуль, МИМ 1) and formerly known as the Docking Cargo Module (DCM), is similar in design 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 NASA's on the STS-132 mission and connected in May 2010,  Rassvet is the only Russian owned module launched by NASA, to repay for the launch of Zarya, which is Russian designed and built, but partially paid for by NASA. Rassvet was launched with the Russian Nauka Laboratory's Experiments airlock temporarily attached to it, and spare parts for the European Robotic Arm.

Leonardo PPM The three NASA Space Shuttle MPLM cargo containers Leonardo, Raffaello and Donatello, were built for NASA in Turin, Italy by Alcatel Alenia Space, now Thales Alenia Space. The MPLMs are provided to the ISS programme by the Italy (independent of Italy's role as a member state of ESA) to NASA and are considered to be U.S. elements. In a bartered exchange for providing these containers, the U.S. has given Italy research time aboard the ISS out of the U.S. allotment in addition to that which Italy receives as a member of ESA. The Permanent Multipurpose Module was created by converting Leonardo into a module that could be permanently attached to the station.

Scheduled additional modules
Nauka (Нау́ка; lit. Science), also known as the Multipurpose Laboratory Module (MLM) or FGB-2, (Russian: Многофункциональный лабораторный модуль, or МЛМ), is the major Russian laboratory module. This module will be separated from the ISS before de-orbit with support modules and become the OPSEK space station, it contains an additional set of life support systems and orientation control, and power provided by its solar arrays will mean the ROS no longer relies on power from the USOS main arrays. Nauka's mission has changed over time, during the mid 1990's it was intended as a backup for the FGB, and later as a universal docking module (UDM), its docking ports will be able to support automatic docking of both space craft, additional modules and fuel transfer. Prior to the arrival of the MLM, a progress robot spacecraft will dock with PIRS, depart with that module, and both will be discarded. Nauka will then use its own engines to attach itself to the ROS in 2012.

Node Module (UM)/(NM) This 4-ton ball shaped module will support the docking of two scientific and power modules during the final stage of the station assembly and provide the Russian segment additional docking ports to receive Soyuz TMA (transportation modified anthropometric) and Progress M spacecraft. NM is to be incorporated into the ISS in 2012. It will be integrated with a special version of the Progress cargo ship and launched by a standard Soyuz rocket. The Progress would use its own propulsion and flight control system to deliver and dock the Node Module to the nadir (Earth-facing) docking port of the Nauka MLM/FGB-2 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. However more importantly, the node module was conceived to serve as the only permanent element of the future Russian successor to the ISS, OPSEK. Equipped with six docking ports, the Node Module would serve as a single permanent core of the future station with all other modules coming and going as their life span and mission required. This would be a progression beyond the ISS and Russia's modular MIR space station, which are in turn more advanced than early monolithic first generation stations such as Skylab, and early Salyut and Almaz stations.

Science Power Modules 1 & 2 (NEM-1, NEM-2) (Научно-Энергетический Модуль-1 и -2)

Cancelled components
The US Habitation Module would have served as the station's living quarters. Instead, the sleep stations are now spread throughout the station. The US Interim Control Module and ISS Propulsion Module were intended to replace functions of Zvezda in case of a launch failure. The Russian Universal Docking Module, to which the cancelled Russian Research modules and spacecraft would have docked. The Russian Science Power Platform would have provided the Russian Orbital Segment with a power supply independent of the ITS solar arrays, and two Russian Research Modules that were planned to be used for scientific research.

Unpressurised elements
The ISS features a large number of external components that do not require pressurisation. The largest such component 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 m (356 ft) long.

The station in its complete form has several smaller external components, such as the six robotic arms, the three External Stowage Platforms (ESPs) and four ExPrESS Logistics Carriers (ELCs). Whilst these platforms allow experiments (including MISSE, the STP-H3 and the Robotic Refuelling Mission) to be deployed and conducted in the vacuum of space by providing electricity and processing experimental data locally, the platforms' primary function is to store Orbital Replacement Units (ORUs). ORUs are spare parts that can be replaced when the item either passes its design life or fails. Examples of ORUs include pumps, storage tanks, antennas and battery units. Such units are replaced either by astronauts during EVA or by robotic arms. While spare parts were routinely transported to and from the station via Space Shuttle resupply missions, there was a heavy emphasis on ORU transport once the NASA Shuttle approached retirement. Several shuttle missions were dedicated to the delivery of ORUs, including STS-129, STS-133 and STS-134. To date only one other mode of transportation of ORUs has been utilised – 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 JEM Exposed Facility serves as an external 'porch' for the Japanese Experiment Module 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, is due to be delivered to the station in 2014 aboard a Dragon capsule. The largest such scientific payload externally mounted to the ISS is the Alpha Magnetic Spectrometer (AMS), a particle physics experiment, was 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.

Cranes and robotic arms
The largest robotic arm on the ISS, Canadarm2 has a mass of 1,800 kilograms and is used to dock and manipulate spacecraft and modules on the USOS, and hold crew members and equipment during EVAs. 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 2 Strela (Стрела; lit. Arrow) cargo cranes during EVAs for moving crew and equipment around the ROS. Each Strela crane has a mass of 45 kg. The Russian and Japanese laboratories both have airlocks and robotic arms. The Integrated Truss Structure serves as a base for the main remote manipulator system called the Mobile Servicing System (MSS). This consists of the Mobile Base System (MBS), the Canadarm2, and Dextre. The MBS rolls along rails built into some of the ITS segments to allow the arm to reach all parts of the United States segment of the station. The MSS had its reach increased an Orbiter Boom Sensor System in May 2011, used to inspect tiles on the NASA shuttle, and converted for permanent station use. To gain access to the extreme extents of the Russian Segment the crew also placed a "Power Data Grapple Fixture" to the forward docking section of Zarya, so that the Canadarm2 may inchworm itself onto that point.

The European Robotic Arm, which will service the Russian Orbital Segment, will be launched alongside the Multipurpose Laboratory Module in 2012. The Japanese Experiment Module's Remote Manipulator System (JFM RMS), which services the JEM Exposed Facility, was launched on STS-124 and is attached to the JEM Pressurised Module.

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 Service Module Zvezda. Some of these systems are supplemented by equipment in the USOS. The MLM Nauka laboratory has a complete set of life support systems.

Atmospheric control systems
The atmosphere on board the ISS is similar to the Earth's. Normal air pressure on the ISS is 101.3 kPa (14.7 psi); the same as at sea level on Earth. An Earth-like atmosphere offers benefits for crew comfort, and is much safer than the alternative, 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 spacecraft.



ECLSS controls atmospheric pressure, fire detection and suppression, oxygen levels, waste management and water supply. The highest priority for the ECLSS is maintaining the onboard atmosphere, but the system also collects, processes, and stores waste and water produced and used by the crew—a process that recycles water from the sink and toilet, and condensation from the air. 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 Elektron unit is the primary oxygen supply, and  are produced by electrolysis, with the  being vented overboard. The 1 kW system uses approximately 1 liter of water per crew member per day from stored water from Earth, or water recycled from other systems. MIR was the first spacecraft to use recycled water for oxygen production. The secondary oxygen supply is provided by burning producing Vika cartridges (see also ISS ECLSS). Each 'candle' takes 5–20 minutes to decompose at 450–500 °C, producing 600 liters 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.

Food


Most of the food eaten by station crews is stored frozen, refrigerated or canned. Menus are prepared by the astronauts, with the help of a dietitian, before the astronauts' flight to the station. As the sense of taste is reduced in orbit because of fluid shifting to the head, spicy food is a favourite of many crews. Each crewmember has individual food packages and cooks them using the onboard galley, which features two food warmers, a refrigerator, and a water dispenser that provides both heated and unheated water. Drinks are provided in dehydrated powder form and are mixed with water before consumption. Drinks and soups are sipped from plastic bags with straws, while solid food is eaten with a knife and fork, which are attached to a tray with magnets to prevent them from floating away. Any food that does float away, including crumbs, must be collected to prevent it from clogging up the station's air filters and other equipment.

Hygiene
Showers on space stations were introduced in the early 1970's on Skylab and Salyut 3. By Salyut 6, in the early 1980's, crew complained of the complexity of showering in space, which was a monthly activity. The ISS does not feature a shower, instead, crewmembers wash using a water jet and wet wipes, with soap dispensed from a toothpaste tube-like container. Crews are also provided with rinseless shampoo and edible toothpaste to save water.

There are two space toilets on the ISS, both of Russian design, located in Zvezda and Tranquility. These Waste and Hygiene Compartments use a fan-driven suction system similar to the Space Shuttle Waste Collection System. Astronauts first fasten themselves to the toilet seat, which is equipped with spring-loaded restraining bars to ensure a good seal. A lever operates a powerful fan and a suction hole slides open: the air stream carries the waste away. Solid waste is collected in individual bags which are stored in an aluminium container. Full containers are transferred to Progress spacecraft for disposal. Liquid waste is evacuated by a hose connected to the front of the toilet, with anatomically correct "urine funnel adapters" attached to the tube so both men and women can use the same toilet. Waste is collected and transferred to the Water Recovery System, where it is recycled back into drinking water.

Power supply
Double-sided solar, or Photovoltaic arrays, provide electrical power for the ISS. These bifacial cells are more efficient and operate at a lower temperature than single-sided cells commonly used on Earth, by collecting sunlight on one side and light reflected off the Earth on the other.

The Russian segment of the station, like the Space Shuttle and most spacecraft, uses 28 volt DC from four rotating solar arrays mounted on Zarya and 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 ROS uses low voltage. The two station segments share power with converters.

The USOS solar arrays are arranged as four wing pairs, with each wing producing nearly 32.8 kW. These arrays normally track the sun to maximise power generation. Each array is about 375 m2 (450 yd2) in area and 58 m long. In the complete configuration, the solar arrays track the sun by rotating the alpha gimbal once per orbit while 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 uses rechargeable nickel-hydrogen batteries (NiH2) for continuous power during the 35 minutes of every 90 minute orbit that it is eclipsed by the Earth. The batteries are recharged on the day side of the Earth. They have a 6.5 year lifetime (over 37,000 charge/discharge cycles) and will be regularly replaced over the anticipated 20-year life of the station.

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 (PCU)s create current paths between the station and the ambient plasma field.

Thermal Control System
The large amount of electrical power consumed by the station's systems and experiments is turned almost entirely into heat. The heat which can be dissipated through the walls of the stations modules is insufficient to keep the internal ambient temperature within comfortable, workable limits. Ammonia is continuously pumped through pipework throughout the station to collect heat, and then into external radiators exposed to the cold of space, and back into the station.

The International Space Station (ISS) External Active Thermal Control System (EATCS) maintains an equilibrium when the ISS environment or heat loads exceed the capabilities of the Passive Thermal Control System (PTCS). Note Elements of the PTCS are external surface materials, insulation such as MLI, or Heat Pipes. The EATCS provides heat rejection capabilities for all the US pressurised modules, including the JEM and COF as well as the main power distribution electronics of the S0, S1 and P1 Trusses. The EATCS consists of two independent Loops (Loop A & Loop B), they both use mechanically pumped Ammonia in fluid state, in closed-loop circuits. The EATCS is capable of rejecting up to 70 kW, and provides a substantial upgrade in heat rejection capacity from the 14 kW capability 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 crewmembers, 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, used for communications with Mir, fell into disrepair during the 1990s, and as a result is no longer in use, although two new Luch satellites—Luch-5A and Luch-5B—are planned for launch in 2011 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 also provides a VHF radio link to ground control centres via antennas on Zvezda's exterior.

The US Orbital Segment (USOS) makes use of two separate radio links mounted in the Z1 truss structure: the S band (used for audio) and Ku band (used for audio, video and data) systems. These transmissions are routed via the United States Tracking and Data Relay Satellite System (TDRSS) in geostationary orbit, which allows for almost continuous real-time communications with NASA's Mission Control Center (MCC-H) in Houston. Data channels for the Canadarm2, European Columbus laboratory and Japanese Kibō modules are routed via the S band and Ku band systems, although the European Data Relay Satellite System and a similar Japanese system will eventually complement the TDRSS in this role. Communications between modules are carried on an internal digital wireless network.

UHF radio is used by astronauts and cosmonauts conducting EVAs. UHF is employed by other spacecraft that dock to or undock from the station, such as Soyuz, Progress, HTV, ATV and the Space Shuttle (except the shuttle also makes use of the S band and Ku band systems via TDRSS), to receive commands from Mission Control and ISS crewmembers. Automated spacecraft are fitted with their own communications equipment; the ATV uses a laser attached to the spacecraft and equipment attached to Zvezda, known as the Proximity Communications Equipment, to accurately dock to the station.

The ISS is equipped with approximately 100 IBM and Lenovo ThinkPad model A31 and T61P laptop computers. 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. Laptops aboard the ISS are connected to the station's wireless LAN via Wi-Fi and are connected to the ground at 3 Mbit/s up and 10 Mbit/s down, comparable to home DSL connection speeds.

Docking
Spacecraft from Russia and Europe are able to launch and fly themselves without human intervention, both Russian manned and unmanned spacecraft dock using the automated Kurs radio telemetry system, this is comparable to the docking system used on the Chinese Tiangong-1. The American Space Shuttle was manually docked, and on missions with a Multi-Purpose Logistics Module, the MPLM would be berthed to the Station with the use of manually controlled robot arms. The Japanese H-II Transfer Vehicle parks itself in progressively closer orbits to the station, and then awaits 'approach' commands from the crew, until it is close enough for the crew to grapple it with a robotic arm and berth it to the USOS. Berthed craft can transfer International Standard Payload Racks. Japanese spacecraft berth for 1–2 months. Russian and European Supply craft can remain at the ISS for 6 months, allowing great flexibility in crew time for loading and unloading of supplies and trash. NASA Shuttles could remain docked for 11–12 days.

The American Manual approach to docking allows greater initial flexibility and less complexity. The downside to this mode of operation is that each mission becomes unique and requires specialised training and planning, making the process more labor-intensive and expensive. The Russians pursued an automated methodology that used the crew in override or monitoring roles. Although the initial development costs were high, the system has become very reliable with standardisations that provide significant cost benefits in repetitive routine operations. An automated approach could allow assembly of modules orbiting other worlds prior to manned missions.

Soyuz manned spacecraft for crew rotation also serve as lifeboats for emergency evacuation, they are replaced every six months and have been used once to remove excess crew after the Columbia disaster. Expeditions require, on average, 2 722 kg of supplies, and as of 2011, crews had consumed a total of around 22 000 meals. Soyuz crew rotation flights and Progress resupply flights visit the station on average two and three times respectively each year, with the ATV and HTV planned to visit annually from 2010 onwards. Following retirement of the NASA Shuttle Cygnus and Dragon will fly cargo to the station until at least 2015.

From 26 February 2011 to 7 March 2011 four of the governmental partners (United States, ESA, Japan and Russia) had their spacecraft (NASA Shuttle, ATV, HTV, Progress and Soyuz) docked at the ISS, the only time this has happened to date.

Scheduled launches and dockings
As of 2011 03 09, there have been 25 Soyuz, 41 Progress, 2 ATV, 2 HTV and 35 Space Shuttle flights to the station.

All dates are UTC. Dates are the earliest possible dates and may change. Forward ports are at the front of the station according to its normal direction of travel and orientation (attitude). Aft is at the rear of the station, used by spacecraft boosting the station's orbit. Nadir is closest the Earth, Zenith is on top.

Unmanned cargo docking is in light blue. Manned spacecraft docking is light green. TBD = Yet to be decided/determined.

Expeditions
Each permanent crew is given an expedition number. Expeditions have an average duration of half a year, and they commence following the official handover of the station from one Expedition commander to another. Expeditions 1 through 6 consisted of three person crews, but the Columbia accident led to a reduction to two crew members for Expeditions 7 to 12. Expedition 13 saw the restoration of the station crew to at least three. Several expeditions, such as Expedition 16, have consisted of up to six Crew members, who are flown to and from the station on separate flights. When crew size was increased to six in 2010, space tourism was halted until 2013. With the arrival of the American Commercial Crew vehicles in the middle of the 2010s, expedition size may be increased to seven crew members, the number ISS is designed for. The International Space Station is the most-visited spacecraft in the history of space flight.

Crew activities
A typical day for the crew begins with a wake-up at 06:00, followed by post-sleep activities and a morning inspection of the station. The crew then eats breakfast and takes part in a daily planning conference with Mission Control before starting work at around 08:10. The first scheduled exercise of the day follows, after which the crew continues work until 13:05. Following a one-hour lunch break, the afternoon consists of more exercise and work before the crew carries out its pre-sleep activities beginning at 19:30, including dinner and a crew conference. The scheduled sleep period begins at 21:30. In general, the crew works ten hours per day on a weekday, and five hours on Saturdays, with the rest of the time their own for relaxation or work catch-up.

The station provides crew quarters for each member of the expedition's crew, with two 'sleep stations' in the Zvezda and four more installed in Harmony. The American quarters are private, approximately person-sized soundproof booths. The Russian crew quarters include a small window, but do not provide the same amount of ventilation or block the same amount of noise as their American counterparts. A crewmember can sleep in a crew quarter in a tethered sleeping bag, listen to music, use a laptop, and store personal items in a large drawer or in nets attached to the module's walls. The module also provides a reading lamp, a shelf and a desktop. Visiting crews have no allocated sleep module, and attach a sleeping bag to an available space on a wall—it is possible to sleep floating freely through the station, but this is generally avoided because of the possibility of bumping into sensitive equipment. It is important that crew accommodations be well ventilated; otherwise, astronauts can wake up oxygen-deprived and gasping for air, because a bubble of their own exhaled carbon dioxide has formed around their heads.

Mission control centres
The components of the ISS are operated and monitored by their respective space agencies at control centres across the globe, including:
 * Roskosmos's Mission Control Center at Korolyov, Moscow Oblast, controls the Russian Orbital Segment which handles Guidance, Navigation & Control for the entire Station., in addition to individual Soyuz and Progress missions.
 * ESA's ATV Control Centre, at the Toulouse Space Centre (CST) in Toulouse, France, controls flights of the unmanned European Automated Transfer Vehicle.
 * JAXA's JEM Control Centre and HTV Control Centre at Tsukuba Space Centre (TKSC) in Tsukuba, Japan, are responsible for operating the Japanese Experiment Module complex and all flights of the 'White Stork' HTV Cargo spacecraft, respectively.
 * NASA's Mission Control Center at Lyndon B. Johnson Space Center in Houston, Texas, serves as the primary control facility for the United States segment of the ISS and also controls the Space Shuttle missions that visit the station.
 * NASA's Payload Operations and Integration Center at Marshall Space Flight Center in Huntsville, Alabama, coordinates payload operations in the USOS.
 * ESA's Columbus Control Centre at the German Aerospace Centre (DLR) in Oberpfaffenhofen, Germany, manages the European Columbus research laboratory.
 * CSA's MSS Control at Saint-Hubert, Quebec, Canada, controls and monitors the Mobile Servicing System, or Canadarm2.

Orbit
The ISS is maintained in a nearly circular orbit with a minimum mean altitude of 330 km (205 mi) and a maximum of 410 km (255 mi), in the centre of the Thermosphere, at an inclination of 51.6 degrees to Earth's equator, necessary to ensure that Russian Soyuz and Progress spacecraft launched from the Baikonur Cosmodrome may be safely launched to reach the station. Spent rocket stages must be dropped into uninhabited areas and this limits the directions rockets can be launched from the spaceport. The orbital inclination chosen was also low enough to allow American space shuttles launched from Florida to reach the ISS.

It travels at an average speed of 27,724 kilometres (17,227 mi) per hour, and completes 15.7 orbits per day. The station's altitude was allowed to fall around the time of each NASA shuttle mission. Orbital boost burns would generally be delayed until after the shuttle's departure. This allowed shuttle payloads to be lifted with the station's engines during the routine firings, rather than have the shuttle lift itself and the payload together to a higher orbit. This trade-off allowed heavier loads to be transferred to the station. After the retirement of the NASA shuttle, the nominal orbit of the space station was raised in altitude. Other, more frequent supply ships don't require this adjustment as they are substantially lighter vehicles.

Orbital boosting can be performed by the station's two main engines on the Zvezda service module, or Russian and American spacecraft docket to Zvezda's aft port. The ATV has been designed with the possibility of adding a second docking port to its other end, allowing it to remain at the ISS and still allow other craft to dock and boost the station. It takes approximately two orbits (three hours) for the boost to a higher altitude to be completed. In December 2008 NASA signed an agreement with the Ad Astra Rocket Company which may result in the testing on the ISS of a VASIMR plasma propulsion engine. This technology could allow station-keeping to be done more economically than at present.

The Russian orbital segment handles Guidance, Navigation & Control 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. Zvezda computes the station's position and orbital trajectory using redundant Earth horizon sensors, Sun and Solar horizon sensors, and star trackers. The USOS and ROS both have experimental position sensing equipment, which use the GPS and Russian GLONASS systems. Amongst the problems with these experimental systems are the stations path and speed. GPS was not initially designed for orbital navigation and high speed (25,000 km/h). Once, during Expedition 10, an incorrect command was sent to the station's computer, and the CMG system became 'saturated' (when the set of CMGs exceed their operational range or cannot track a series of rapid movements ) Attitude control was automatically taken over by the Russian Attitude Control System thrusters for about one orbit, using about 14 kilograms of propellant before the fault was noticed and fixed. Thrusters are deactivated during EVAs for crew safety. When a Space Shuttle or Soyuz is docked to the station, it can also be used to maintain station attitude such as for troubleshooting. Shuttle control was used exclusively during installation of the S3/S4 truss, which provides electrical power and data interfaces for the station's electronics.

Sightings
Before sunrise or after sunset, the ISS can appear to observers on the ground, with the naked eye as a slow moving, bright, white dot, slowly crossing the sky in 2 to 5 minutes. This happens before dawn and after dusk when the ISS is sunlit but the ground and sky are dark, which is typically the case up to a few hours after sunset or before sunrise. Because of the size of its reflective surface area, the ISS is the brightest man made object in the sky, with an approximate maximum brightness of −4 when overhead, similar to Venus. The ISS can also produce flares as sunlight glints off reflective surfaces as it orbits of up to 8 or 16 times the brightness of Venus. The ISS is also visible during broad daylight conditions, albeit with a great deal more effort.

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

The station is visible from 95% of the inhabited land on Earth, but is not visible from extreme northern or southern latitudes.

Safety aspects
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. Some simple forms of life including Tardigrades can survive in this environment in a desiccated state.

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

Without the protection of the Earth's atmosphere, astronauts are exposed to higher levels of radiation from a steady flux of cosmic rays. Subatomic charged particles, primarily protons from solar wind, penetrate living tissue and damage DNA. The station's crews are exposed to about 1 millisievert of radiation each day, which is about the same as someone would get in a year on Earth, from natural sources. This results in a higher risk of astronauts' developing cancer. High levels of radiation can cause damage to the chromosomes of lymphocytes. These cells are central to the immune system and so any damage to them could contribute to the lowered immunity experienced by astronauts. Over time lowered immunity results in the spread of infection between crew members, especially in such confined areas. Radiation has also been linked to a higher incidence of cataracts in astronauts. Protective shielding and protective drugs may lower the risks to an acceptable level, but data is scarce and longer-term exposure will result in greater risks.

Despite efforts to improve radiation shielding on the ISS compared to previous stations such as Mir, radiation levels within the station have not been vastly reduced, and it is thought that further technological advancement will be required to make long-duration human spaceflight further into the Solar System a possibility. Large, acute doses of radiation from coronal mass ejections can cause radiation sickness and can be fatal. Without the protection of the Earth's magnetosphere, interplanetary manned missions are especially vulnerable.

The radiation levels experienced on ISS are about 5 times greater than those experienced by airline passengers and crew. The Earth's electromagnetic field provides almost the same level of protection against solar and other radiation in low Earth orbit as in the stratosphere. Airline passengers, however, experience this level of radiation for no more than 15 hours for the longest intercontinental flights. For example, on a 12 hour flight an airline passenger would experience 0.1 millisievert of radiation, or a rate of 0.2 millisieverts per day; only 1/5 the rate experienced by an astronaut in LEO.

Crew health
The most significant adverse effects of long-term weightlessness are muscle atrophy and deterioration of the skeleton, or spaceflight osteopenia. Other significant effects include fluid redistribution, a slowing of the cardiovascular system, decreased production of red blood cells, balance disorders, and a weakening of the immune system. Lesser symptoms include loss of body mass, nasal congestion, sleep disturbance, excess flatulence, and puffiness of the face. These effects begin to reverse quickly upon return to the Earth.

To prevent some of these adverse physiological effects, the station is equipped with two treadmills (including the COLBERT), the aRED (advanced Resistive Exercise Device) which enables various weightlifting exercises, and a stationary bicycle; each astronaut spends at least two hours per day exercising on the equipment. Astronauts use bungee cords to strap themselves to the treadmill. Researchers believe that exercise is a good countermeasure for the bone and muscle density loss that occurs when humans live for a long time without gravity.

Orbital debris
At the low altitudes at which the ISS orbits there is a variety of space debris, consisting of many different objects including entire spent rocket stages, dead satellites, explosion fragments—including materials from anti-satellite weapon tests, paint flakes, slag from solid rocket motors, coolant released by RORSAT nuclear powered satellites and some of the 750,000,000 small needles from the American military Project West Ford. These objects, in addition to natural micrometeoroids, are a significant threat. Large objects can destroy the station, but are less of a threat as their orbits can be predicted. 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 still a threat because of their kinetic energy and direction in relation to the station. Spacesuits of spacewalking crew could puncture, causing exposure to vacuum.

Space debris objects are tracked remotely from the ground, and the station crew can be notified. This allows for a Debris Avoidance Manoeuvre (DAM) to be conducted, which uses thrusters on the Russian Orbital Segment to alter the station's orbital altitude, avoiding the debris. DAMs are not uncommon, taking place if computational models show the debris will approach within a certain threat distance. Eight DAMs had been performed prior to March 2009, the first seven between October 1999 and May 2003. Usually the orbit is raised by one or two kilometres by means of an increase in orbital velocity of the order of 1 m/s. Unusually there was a lowering of 1.7 km on 27 August 2008, the first such lowering for 8 years. There were two DAMs in 2009, on 22 March and 17 July. 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 Soyuz spacecraft, so that they would be able to evacuate in the event it was damaged by the debris. This partial station evacuation has occurred twice, on 13 March 2009 and 28 June 2011. Ballistic panels, also called micrometeorite shielding, is incorporated into the station to protect pressurised sections and critical systems. The type and thickness of these panels varies depending upon their predicted exposure to damage.

Repairs
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, had these problems not been resolved.

During STS-120 on 2007, following the relocation of the P6 truss and solar arrays, it was noted during the redeployment of the array that it had become torn and was not deploying properly. An EVA was carried out by Scott Parazynski, assisted by Douglas Wheelock, the men took extra precautions 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 race ring at the heart of the joint, and so the joint was locked to prevent further damage. Repairs to the joint were carried out during STS-126 with lubrication of both joints and the replacement 11 of 12 trundle bearings on the joint.

In 2009, the engines on Zvezda were issued an incorrect command which caused resonant vibrations to propagate throughout the station structure which persisted for over two minutes. While no damage to the station was immediately reported, some components may have been stressed beyond their design limits. Further analysis confirmed that the station was unlikely to have suffered any structural damage, and it appears that "structures will still meet their normal lifetime capability". 2009 also saw damage to the S1 radiator, one of the components of the station's cooling system. The problem was first noticed in Soyuz imagery in September 2008, but was not thought to be serious. The imagery showed that the surface of one sub-panel has peeled back from the underlying central structure, possibly due to micro-meteoroid or debris impact. It is also known that a Service Module thruster cover, jettisoned during an EVA in 2008, had struck the S1 radiator, but its effect, if any, has not been determined. On 15 May 2009 the damaged radiator panel's ammonia tubing was mechanically shut off from the rest of the cooling system by the computer-controlled closure of a valve. The same valve was used immediately afterwards to vent the ammonia from the damaged panel, eliminating the possibility of an ammonia leak from the cooling system via the damaged panel.

Early on 1 August 2010, a failure in cooling Loop A (starboard side), one of two external cooling loops, left the station with only half of its normal cooling capacity and zero redundancy in some systems. The problem appeared to be in the ammonia pump module that circulates the ammonia cooling fluid. Several subsystems, including two of the four CMGs, were shut down.

Planned operations on the ISS were interrupted through a series of EVAs to address the cooling system issue. A first EVA on 7 August 2010, to replace the failed pump module, was not fully completed due to an ammonia leak in one of four quick-disconnects. A second EVA on 11 August successfully removed the failed pump module. A third EVA was required to restore Loop A to normal functionality.

The USOS's cooling system is largely built by the American company Boeing, which is also the manufacturer of the failed pump.

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 which left the station without thruster, Elektron, Vozdukh and other environmental control system operations, the root cause of which was found to be condensation inside the electrical connectors leading to a short-circuit.

International co-operation


International co-operation in space began in the early 1970s with the docking of Soyuz 19 and Apollo 18, known in the US as the Apollo-Soyuz programme, and in the USSR as the Soyuz-Apollo programme. From 1978–1987 the USSR's Interkosmos programme included allied Warsaw Pact countries, and countries which were not Soviet allies, such as India, Syria and France, in manned and unmanned missions to Space stations Salyut 6 and 7. In 1986 the USSR extended this co-operation to a dozen countries in the MIR programme. In 1994–98 NASA Space Shuttles and crew visited MIR in the Shuttle-Mir programme. In 1998 the ISS programme began.

Ownership of modules, station utilisation by participant nations, and responsibilities for station resupply are established by the Space Station Intergovernmental Agreement (IGA). This international treaty was signed on 28 January 1998 by the primary nations involved in the Space Station project; the United States of America, Russia, Japan, Canada and eleven member states of the European Space Agency (Belgium, Denmark, France, Germany, Italy, The Netherlands, Norway, Spain, Sweden, Switzerland, and the United Kingdom). A second layer of agreements was then achieved, called Memoranda of Understanding (MOU), between NASA and ESA, CSA, RKA and JAXA. These agreements are then further split, such as for the contractual obligations between nations, and trading of partners' rights and obligations. Use of the Russian Orbital Segment is also negotiated at this level.

In addition to these main intergovernmental agreements, Brazil originally joined the programme as a bilateral partner of the United States by a contract with NASA to supply hardware. In return, NASA would provide Brazil with access to its ISS facilities on-orbit, as well as a flight opportunity for one Brazilian astronaut during the course of the ISS programme. However, due to cost issues, the subcontractor Embraer was unable to provide the promised ExPrESS pallet, and Brazil left the programme. Italy has a similar contract with NASA to provide comparable services, although Italy also takes part in the programme directly via its membership in ESA. Expanding the partnership would require unanimous agreement of the existing partners. Chinese participation has been prevented by unilateral US opposition. The heads of both the South Korean and Indian space agency ISRO announced at the first plenary session of the 2009 International Astronautical Congress that their nations wished to join the ISS programme, with talks due to begin in 2010. The heads of agency also expressed support for extending ISS lifetime. European countries not part of the programme will be allowed access to the station in a three-year trial period, ESA officials say.

The Russian part of the station is operated and controlled by the Russian Federation's space agency and provides Russia with the right to nearly one-half of the crew time for the ISS. The allocation of remaining crew time (three to four crew members of the total permanent crew of six) and hardware within the other sections of the station is as follows: Columbus: 51% for the ESA, 46.7% for NASA, and 2.3% for CSA. Kibō: 51% for the JAXA, 46.7% for NASA, and 2.3% for CSA. Destiny: 97.7% for NASA and 2.3% for CSA. Crew time, electrical power and rights to purchase supporting services (such as data upload and download and communications) are divided 76.6% for NASA, 12.8% for JAXA, 8.3% for ESA, and 2.3% for CSA.

China
China is not an ISS partner, and no Chinese nationals have been aboard. China has its own contemporary manned space program, project 921, and has carried out comprehensive cooperation and exchanges with countries such as Russia and Germany, amongst others in manned and unmanned space projects. China launched its first space station, Tiangong 1, in September 2011, and has officially initiated its programme for a modular station. In 2007, Chinese vice minister of science and technology Li Xueyong stated that China would like to participate in the ISS, then, in 2010 ESA Director-General Jean-Jacques Dordain stated his agency was ready to propose to the other 4 partners that China be invited to join the partnership, but this needs to be a collective decision by all the current partners.

Chinese participation in this project is blocked by America. American concerns over the transfer of technology which could be used for military purposes, and Human rights echo similar concerns with Russia prior to their membership. It turned out Russian crew capsules saved the Station when the Shuttles were grounded after the Columbia accident in 2003, and again after the NASA Shuttle's retirement in 2011. China believes that international exchanges and cooperation in the field of aerospace engineering should be intensified on the basis of mutual benefit, peaceful use and common development. China's manned Shenzhou spacecraft use the Russian-designed APAS docking system, and Shenzhou spacecraft could to dock to the International Space Station if it became politically feasible, Shenzhou 7 passed within about 50 kilometers of the ISS.

American co-operation with China in space is limited, efforts have been made by both sides to improve relations, but in 2011 new American legislation further strengthened legal barriers to co-operation, preventing NASA co-operation with China or Chinese owned companies, even the expenditure of funds used to host Chinese visitors at NASA facilities, unless specifically authorized by new laws, at the same time China, Europe and Russia have a co-operative relationship in several space exploration projects. Between 2007 and 2011, the space agencies of Europe, Russia and China carried out the ground-based preparations in the Mars500 project, which complement the ISS-based preparations for a manned mission to Mars.

End of mission
According to a 2009 report, RKK Energia is considering methods to remove from the station some modules of the Russian Orbital Segment when the end of mission is reached and use them as a basis for a new station, known as the Orbital Piloted Assembly and Experiment Complex (OPSEK). The modules under consideration for removal from the current ISS include the Multipurpose Laboratory Module (MLM), currently scheduled to be launched in May 2012, with other Russian modules which are currently planned to be attached to the MLM until 2015. Neither the MLM nor any additional modules attached to it would have reached the end of their useful lives in 2016 or 2020. The report presents a statement from an unnamed Russian engineer who believes that, based on the experience from Mir, a thirty-year life should be possible, except for micrometeorite damage, because the Russian modules have been built with on-orbit refurbishment in mind.

According to the Outer Space Treaty the United States is legally responsible for all modules it has launched. In ISS planning, NASA examined options including returning the station to Earth via shuttle missions (deemed too expensive, as the station (USOS) is not designed for disassembly and this would require at least 27 shuttle missions ), natural orbital decay with random reentry similar to Skylab, boosting the station to a higher altitude (which would simply delay reentry) and a controlled targeted de-orbit to a remote ocean area.

The technical feasibility of a controlled targeted deorbit into a remote ocean was found to be possible only with Russia's assistance. At the time ISS was launched, the Russian Space Agency had experience from de-orbiting the Salyut 4, 5, 6, and 7 space stations, while NASA's first intentional controlled de-orbit of a satellite (the Compton Gamma Ray Observatory) would not occur for another two years. NASA currently has no spacecraft capable of de-orbiting the ISS at the time of decommissioning. Skylab, the only space station built and launched entirely by the US, decayed from orbit slowly over 5 years, and no attempt was made to de-orbit the station using a deorbital burn. Remains of Skylab hit populated areas of Esperance, Western Australia. without injuries or loss of life.

While the entire USOS cannot be reused and will be discarded, some Russian modules are planned to be reused. Nauka, the Node module, two science power platforms and Rassvet, launched between 2010 and 2015 and joined to the ROS will be separated to form OPSEK. The Nauka module of the ISS will be used in the station, whose main goal is supporting manned deep space exploration. OPSEK will orbit at a higher inclination of 71 degrees, allowing observation to and from all of the Russian federation.

Agency websites

 * 🇺🇸 American, 🇨🇦 Canadian, 🇨🇳 Chinese, European, 🇮🇹 Italian, 🇯🇵 Japanese,🇷🇺 RSC Energia, 🇷🇺 Russian Federal,

Space Agency Youtube channels

 * 🇺🇸 American, 🇨🇦 Canadian, European, 🇯🇵 Japanese, 🇷🇺 Russian

Youtube
View the motion picture First Orbit, the story of the first man in space.
 * ISS: Video (01:02): Earth (Time-Lapse)
 * ISS: Video (00:27): Earth and Auroras (Time-Lapse)

Live viewing
Simple instructions on where and when to look for the ISS may be found on Heavens-above or see list of satellite trackers for a complete list.
 * ISS: Current position (NASA)
 * ISS: "Live" Webcam

Image galleries

 * ISS: Interactive Reference Guide
 * ISS: Image Gallery Search Page
 * ISS: Assembly Sequence: Animation
 * Commons

Research

 * Daily ISS Reports
 * NASA: Station Science
 * ESA: Columbus
 * JAXA: Space Environment Utilization and Space Experiment
 * RSC Energia: Science Research on ISS Russian Segment