International Space Station
A foreward view of the International Space Station backdropped by the limb of the Earth. In view are the station's four large, maroon-coloured solar array wings, two on either side of the station, mounted to a central truss structure. Further along the truss are six large, white radiators, three next to each pair of arrays. In between the solar arrays and radiators is a cluster of pressurised modules arranged in an elongated T shape, also attached to the truss. A set of blue solar arrays are mounted to the module at the aft end of the cluster.
The ISS on 23 May 2010, as seen from STS-132
ISS insignia.svg
ISS emblem.png
Station statistics
COSPAR ID1998-067A
SATCAT no.25544
Call signAlpha, Station
CrewFully manned: 7
Currently aboard: 7
(Expedition 64) (SpaceX Crew-1)
Launch20 November 1998; 22 years ago (1998-11-20)
Launch pad
Mass419,725 kg (925,335 lb)[1]
Length73.0 m (239.4 ft)[1]
Width109.0 m (357.5 ft)[1]
Pressurised volume915.6 m3 (32,333 cu ft)[1]
Atmospheric pressure101.3 kPa (14.7 psi; 1.0 atm)
oxygen 21%, nitrogen 79%
Perigee altitude418 km (259.7 mi) AMSL[2]
Apogee altitude420 km (261.0 mi) AMSL[2]
Orbital inclination51.64° [2]
Orbital speed7.66 km/s [2]
(27,600 km/h; 17,100 mph)
Orbital period92.68 minutes [2]
Orbits per day15.54 [2]
Orbit epoch03 December 2020 20:45:53 [2]
Days in orbit22 years, 14 days
(4 December 2020)
Days occupied20 years, 1 month, 2 days
(4 December 2020)
No. of orbits116,178 as of May 2019[2]
Orbital decay2 km/month
Statistics as of 9 March 2011
(unless noted otherwise)
References: [1][2][3][4][5]
Configuration
The components of the ISS in an exploded diagram, with modules on-orbit highlighted in orange, and those still awaiting launch in blue or pink
Station elements as of August 2019
(exploded view)

The International Space Station (ISS) is a modular space station (habitable artificial satellite) 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).[6][7] The ownership and use of the space station is established by intergovernmental treaties and agreements.[8] 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.[9][10][11] The ISS is suited for testing the spacecraft systems and equipment required for possible future long-duration missions to the Moon and Mars.[12]

The ISS programme evolved from the Space Station Freedom, an American proposal which was conceived in 1984 to construct a permanently manned Earth-orbiting station,[13] and the contemporaneous Soviet/Russian Mir-2 proposal 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 U.S. Skylab. It is the largest artificial object in space and the largest satellite in low Earth orbit, regularly visible to the naked eye from Earth's surface.[14][15] It maintains an orbit with an average altitude of 400 kilometres (250 mi) by means of reboost manoeuvres using the engines of the Zvezda Service Module or visiting spacecraft.[16] The ISS circles the Earth in roughly 93 minutes, completing 15.5 orbits per day.[17]

The station is divided into two sections: the Russian Orbital Segment (ROS), operated by Russia; and the United States Orbital Segment (USOS), which is shared by many nations. Roscosmos has endorsed the continued operation of ROS through 2024,[18] having previously proposed using elements of the segment to construct a new Russian space station called OPSEK.[19] The first ISS component was launched in 1998, and the first long-term residents arrived on 2 November 2000.[20] The station has since been continuously occupied for 20 years and 32 days,[21] the longest continuous human presence in low Earth orbit, having surpassed the previous record of 9 years and 357 days held by the Mir space station. The latest major pressurised module, Leonardo, was fitted in 2011 and an experimental inflatable space habitat was added in 2016. Development and assembly of the station continues, with several major new Russian elements scheduled for launch starting in 2020. As of December 2018, the station is expected to operate until 2030.[22]

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.[23] The station is serviced by a variety of visiting spacecraft: the Russian Soyuz and Progress, the U.S. Dragon and Cygnus, the Japanese H-II Transfer Vehicle,[6] and, formerly, the European Automated Transfer Vehicle. The Dragon spacecraft allows the return of pressurised cargo to Earth, which is used, for example, to repatriate scientific experiments for further analysis. As of September 2019, 239 astronauts, cosmonauts, and space tourists from 19 different nations have visited the space station, many of them multiple times. This includes 151 Americans, 47 Russians, 9 Japanese, 8 Canadians, 5 Italians, and others.[24]

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 come to fruition.[25] In the 2010 United States National Space Policy, the ISS was given additional roles of serving commercial, diplomatic,[26] and educational purposes.[27]

Scientific research

Comet Lovejoy photographed by Expedition 30 commander Dan Burbank
Expedition 8 Commander and Science Officer Michael Foale conducts an inspection of the Microgravity Science Glovebox
Fisheye view of several labs

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.[28][29]

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.[9][10][11][30][31] 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.[29] 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.[9][32]

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 and is as important as the Hubble Space Telescope according to NASA. Currently docked on station, it could not have been easily accommodated on a free flying satellite platform because of its power and bandwidth needs.[33][34] On 3 April 2013, scientists reported that hints of dark matter may have been detected by the AMS.[35][36][37][38][39][40] 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.[41] Some simple forms of life called extremophiles,[42] as well as small invertebrates called tardigrades[43] can survive in this environment in an extremely dry state through desiccation.

Medical research improves knowledge about the effects of long-term space exposure on the human body, including muscle atrophy, bone loss, and fluid shift. This data will be used to determine whether high duration human spaceflight and space colonisation 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.[44][45]

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.[46][47][48]

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 support 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.[49][50]

Freefall

ISS crew member storing samples
A comparison between the combustion of a candle on Earth (left) and in a free fall environment, such as that found on the ISS (right)

Gravity at the altitude of the ISS is approximately 90% as strong as at Earth's surface, but objects in orbit are in a continuous state of freefall, resulting in an apparent state of weightlessness.[51] This perceived weightlessness is disturbed by five separate effects:[52]

  • 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 interconnected 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 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.[10]

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. In addition, examining reactions that are slowed by low gravity and low temperatures will improve our understanding of superconductivity.[10]

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.[53] 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.[10]

Exploration

A 3D plan of the Russia-based MARS-500 complex, used for conducting ground-based experiments that complement ISS-based preparations for a human mission to Mars

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, mission risks can be reduced and the capabilities of interplanetary spacecraft advanced.[12] Referring to the MARS-500 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".[54] 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.[55]

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."[56] 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.[57] NASA chief Charles Bolden stated in February 2011, "Any mission to Mars is likely to be a global effort".[58] Currently, US federal legislation prevents NASA co-operation with China on space projects.[59]

Education and cultural outreach

Original Jules Verne manuscripts displayed by crew inside the Jules Verne ATV

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, videolink, and email.[6][60] ESA offers a wide range of free teaching materials that can be downloaded for use in classrooms.[61] 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.[62]

JAXA aims to inspire children to "pursue craftsmanship" and to heighten their "awareness of the importance of life and their responsibilities in society".[63] 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.[64][65] 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.[66]

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."[67]

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.[68]

Spoken voice recording by ESA astronaut Paolo Nespoli on the subject of the ISS, produced in November 2017 for Wikipedia

First Orbit is a 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.[69] The film was streamed in a global YouTube premiere in 2011 under a free licence through the website firstorbit.org.[70]

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.[71][72] It was the first music video ever to be filmed in space.[73]

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.[74][75]

Construction

Manufacturing

ISS module Node 2 manufacturing and processing in the Space Station Processing Facility

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.[76]

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.[77]

The European Space Agency Columbus module was manufactured at the EADS Astrium Space Transportation facilities in Bremen, Germany, along with many other contractors throughout Europe.[78] 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.[79]

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.[80]

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.[3] 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); as of 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.[81] The beta angle of the station had to be considered at all times during construction.[82]

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, 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 Pressurised Mating Adapters (PMAs), one connects permanently to Zarya, the other allowed the Space Shuttle to dock to the space station. At that time, the Russian station Mir was still inhabited, and the ISS remained uncrewed for two years. 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 target for a rendezvous with Zarya and Unity: it maintained 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'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.[83][84]

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 Krikalev preferred to the more cumbersome "International Space Station".[85] The name "Alpha" had previously been used for the station in the early 1990s,[86] and its use was authorised for the whole of Expedition 1.[87] 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."[88] 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.[87][89][90]

Expedition 1 arrived 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 US television, additional attitude support needed for the additional mass of the USOS, and substantial solar arrays supplementing the station's four existing solar arrays.[91]

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 Space Shuttle Columbia disaster in 2003 and a resulting hiatus in flights. The Space Shuttle was grounded until 2005 with STS-114 flown by Discovery.[92]

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 in May 2010 by the penultimate Russian module, Rassvet. 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.[93] The last pressurised module of the USOS, Leonardo, was brought to the station in February 2011 on the final flight of Discovery, STS-133.[94] The Alpha Magnetic Spectrometer was delivered by Endeavour on STS-134 the same year.[95]

As of June 2011, the station consisted of 15 pressurised modules and the Integrated Truss Structure. Five modules are still to be launched, including the Nauka with the European Robotic Arm, the Prichal module, and two power modules called NEM-1 and NEM-2.[96] As of May 2020, Russia's future primary research module Nauka is set to launch in the spring of 2021,[97] along with the European Robotic Arm which will be able to relocate itself to different parts of the Russian modules of the station.[98]

The gross mass of the station changes over time. The total launch mass of the modules on orbit is about 417,289 kg (919,965 lb) (as of 3 September 2011).[99] 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

Technical blueprint of components

The ISS is a third generation[100] modular space station.[101] Modular stations can allow modules to be added to 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. The Unity node joins directly to the Destiny laboratory. For clarity, they are shown apart.