International Space Station

The International Space Station is a modular space station in low Earth orbit — the largest international cooperative programme in science and technology to date, run as a partnership of 10 European countries, the United States, Japan, Canada and Russia.¹ Five space agencies contributed to its assembly: NASA, Roscosmos, ESA, JAXA and the Canadian Space Agency.² Assembly began with the Russian control module Zarya on 20 November 1998.³ The first resident crew moved aboard on 2 November 2000, and the station has been continuously occupied ever since.⁴

In its third decade of continuous human presence, the station works as a microgravity laboratory, hosting scientific investigations and technology demonstrations from a range of fields.⁸ NASA calls it a classroom, laboratory and proving ground: orbiting 250 miles above Earth at 17,500 miles per hour, it has hosted nearly 300 astronauts from across the globe.⁶ Expedition 75, which began on 26 July 2026 and is scheduled to end in spring 2027, is the current crew, with Jessica Meir serving as commander.⁵

The station does not hover above Earth; it falls around it, flying about 400 km up at 28,800 km/h and completing one circuit of the planet every 92 minutes.⁹ Its orbit is inclined 51.6 degrees to the equator, so that is the farthest north or south it ever reaches.¹⁰ In 24 hours it makes 16 orbits of Earth, and the crew travels through 16 sunrises and 16 sunsets.² Because everything aboard is in free fall, the apparent gravity is only about one millionth of that on Earth.¹¹ From the ground the station appears to travel from west to east, while Earth's own rotation shifts its track 2,200 km westward on each orbit.⁹

Power comes from eight solar arrays generating between 75 and 90 kilowatts, with new iROSA arrays augmenting the originals.² The wingspan of those arrays, 356 feet (109 m), is longer than the world's largest passenger aircraft, the Airbus A380, at 262 feet (80 m).² About eight miles of wiring run through the structure, and its software monitors roughly 350,000 sensors.²

Resupply is expensive, so the station is built to recycle: the Water Recovery System has cut the crew's dependence on water delivered by cargo spacecraft by 65 percent — from about a gallon a day to a third of a gallon.² The same traffic carries oxygen, food and water, exchanges the permanent crew, and replaces the docked lifeboat roughly every six months.¹

The station could not be launched in one piece — no rocket is big enough or powerful enough — so it was taken into space piece by piece and gradually built in orbit about 400 km above Earth.¹ The large modules and other pieces arrived on 42 assembly flights: 37 on U.S. space shuttles and five on Russian Proton/Soyuz rockets.² Assembly depended on spacewalks and robotics; Canadarm2, a 55-foot arm with seven joints and two end-effectors, moved entire modules, deployed science experiments and even transported spacewalking astronauts.²

The station continues to be updated: new iROSA solar arrays augment the eight main arrays, and Prichal, added on 26 November 2021, remains the most recent module installed.² Two commercial modules are also aboard: BEAM, the Bigelow Expandable Activity Module, and the NanoRacks Bishop airlock.²

Inside, the station is larger than a six-bedroom house: it has six sleeping quarters, two bathrooms, a gym and a 360-degree view bay window.² Its habitable volume is 13,696 cubic feet (388 m3) within a pressurized volume of 35,491 cubic feet (1,005 m3).² An international crew of seven lives and works aboard while travelling at five miles per second, and sometimes more are aboard during a crew handover.²

Weightlessness is hard on the body, so to counter the loss of muscle and bone mass in microgravity, astronauts work out at least two hours a day.² Crew members have access to a running treadmill, a cycle ergometer and a resistance exercise device.¹³ Even so, a study of nine crew members found that calf muscle volume decreased about 13 percent after six months aboard, with greater atrophy of the soleus than the gastrocnemius, and peak power 32 percent lower after spaceflight.¹³

Supplies arrive aboard four different cargo spacecraft: Northrop Grumman's Cygnus, SpaceX's Dragon, JAXA's HTV and the Russian Progress.² As many as eight spaceships can be connected to the station at once, and a spacecraft can arrive as soon as four hours after launching from Earth.² The docked lifeboat is replaced roughly every six months.¹

The station is a working laboratory as well as a home: through Expedition 60 it had hosted nearly 3,000 research investigations from researchers in more than 108 countries.² Some instruments sit in open space: Japan's Kibo carries an Exposed Facility directly exposed to space — unique among ISS laboratories — enabling long-term experiments as well as Earth and astronomical observations.¹¹ The Alpha Magnetic Spectrometer measured the cosmic-ray positron fraction from 0.5 to 350 GeV using 6.8 million positron and electron events.¹⁴

Not all of that research belongs to NASA: in 2005 Congress designated the station a U.S. National Laboratory, enabling space research and development access to a broad range of commercial, academic and government users.⁶ The ISS National Lab manages all non-NASA research and investigations aboard.⁸ The peer-reviewed record shows what the setting makes possible: nine in-flight sequencing runs over a six-month period yielded 276,882 reads with no apparent decrease in performance, and automated pipelines demonstrated that sequencing analysis and microbial identification aboard the station are feasible.¹⁵ A six-year survey collected more than 500 samples aboard the station; molecular analysis found nucleic acids of various pathogens, but no viable pathogens were recovered.¹⁶ By the Canadian Space Agency's count, more than 24 Canadian studies have been conducted aboard the station, some of them still under way.³

An international partnership of five space agencies from 15 countries operates the station, and the principals are the space agencies of the United States, Russia, Europe, Japan and Canada.⁶ Five space agencies including NASA, Roscosmos, ESA, JAXA and CSA have contributed to the station's assembly.² Canada is one of the station's partners, along with the United States, Russia, Europe and Japan.³

The project began as an American effort called Freedom, authorised by President Ronald Reagan, and in 1993 the United States and Russia agreed to merge their separate space station plans into a single facility, renamed and expanded internationally.⁴ Launched in 1998 and involving the U.S., Russia, Canada, Japan and the participating countries of the European Space Agency, the station is one of the most complex international collaborations ever attempted.⁶ ESA puts the cost of development, assembly and ten years of operation at about EUR 100 billion, shared over almost 30 years between the United States, Russia, Canada, Japan and 10 European nations.⁷ The 10 ESA member states in the programme are Belgium, Denmark, France, Germany, Italy, the Netherlands, Norway, Spain, Sweden and Switzerland.⁷

Assembly began with the launches of the Russian control module Zarya on 20 November 1998 and the U.S.-built Unity connecting node the following month, which were linked in orbit by U.S. space shuttle astronauts.⁴ In mid-2000 the Russian-built Zvezda, a habitat and control centre, was added, and on 2 November the station received its first resident crew — cosmonauts Sergey Krikalev and Yuri Gidzenko and astronaut William Shepherd, who flew up in a Soyuz spacecraft.⁴ NASA's Destiny microgravity laboratory and other elements were subsequently joined to the station, which grew into a complex of laboratories and habitats along a long truss carrying solar arrays and radiators.⁴ Canadarm2 launched aboard Space Shuttle Endeavour on 19 April 2001; three days later, Chris Hadfield and Scott Parazynski attached the robotic arm to the station.¹²

Construction was interrupted in February 2003, when the space shuttle orbiter Columbia broke up and the fleet was grounded, effectively halting expansion of the station.⁴ The crew was reduced from three to two, and its role was restricted mainly to caretaker status, limiting the amount of science that could be done.⁴

Expansion resumed later in the decade: the European-built American node Harmony was placed on the end of Destiny in October 2007, adding a docking port for the shuttle and connecting ports for a European laboratory, Columbus, and a Japanese laboratory, Kibo.⁴ Columbus was mounted on Harmony's starboard side in February 2008 — Europe's first long-duration crewed space laboratory, containing experiments in such fields as biology and fluid dynamics.⁴ In March, shuttle astronauts brought the Canadian robot Dextre, which was designed to perform tasks that previously required spacewalks, along with the first part of Kibo.⁴ A third node, Tranquility, was installed in 2010, and mounted on it was the Cupola, whose robotic workstation and many windows enabled astronauts to supervise external operations.⁴

The station became fully operational in May 2009 when it began hosting a six-person crew, which required two Soyuz lifeboats to be docked at all times.⁴ After completion of the station, the shuttle was retired from service in 2011, closing the assembly era.⁴ The large modules and other pieces had been delivered on 42 assembly flights: 37 on the U.S. space shuttles and five on Russian Proton/Soyuz rockets.²

Spacewalks have been the station's construction crews — used for building, repairs and the ongoing upgrade programme — and there have been 259 spacewalks at the station since December 1998.⁶ Robots now do part of the work: Canadarm2, 55 feet long with seven joints and two end-effectors, has moved entire modules, deployed science experiments and transported spacewalking astronauts.² Dextre, the Canadian robot, can perform tasks that previously would have required astronauts to make space walks.⁴

Crews arrive aboard vehicles built on both sides of the old space race: during construction a Soyuz remained docked to the station at all times as a lifeboat, and before Crew Dragon all astronauts used Soyuz spacecraft to reach the station.⁴ SpaceX's Crew Dragon had its first flight to the station in 2020; it carried four astronauts, and the station was then able to accommodate a crew of seven.⁴ Boeing's CST-100 Starliner had its first crewed test flight on 5 June 2024, but during the flight to the station five thrusters failed and helium leaks were detected in its propulsion system.⁴ ESA, JAXA, Roscosmos, Northrop Grumman and SpaceX have each launched their own space freighters, while NASA, Roscosmos, SpaceX and Boeing have launched crew ships.⁶

Traffic is heavy and fast: eight spaceships can be connected to the space station at once, and a spacecraft can arrive as soon as four hours after launching from Earth.² The docked lifeboat must also be replaced every six months or so.¹

More than 280 astronauts from 26 different countries have visited the station, and crews typically stay for about six months.⁴ NASA counts over 280 individuals representing 26 countries and five international partners, and nearly 300 astronauts hosted in a quarter of a century.⁶

Some visitors have stayed far longer than six months: on the mission called 'A Year in Space,' cosmonaut Mikhail Korniyenko and astronaut Scott Kelly spent 340 days in orbit from March 2015 to March 2016.⁴ In 2017 Peggy Whitson extended her mission to 289 days — at the time the longest single spaceflight by a woman — and she has spent more than 675 days in space in total, a record for an American and a woman.⁴ Christina Koch surpassed Whitson's consecutive-flight record with 328 days aboard from March 2019 to February 2020, and during that stay she and Jessica Meir performed the first all-female spacewalk.⁴ Cosmonaut Pyotr Dubrov and astronaut Mark Vande Hei stayed 355 days from April 2021 to March 2022, and Vande Hei broke Kelly's record for the longest American spaceflight.⁴

Not everyone who flies is an agency astronaut: eight other individuals paid for seats on Soyuz flights to the station between 2002 and 2021.⁴ Beginning in 2022, the American company Axiom Space has chartered flights on Crew Dragon spacecraft to the station.⁴

The station is easy to see if you know when to look: it can be seen with the naked eye from the ground by looking up at the right time.⁹ To an observer it appears similar to an airplane or a very bright star moving across the night sky, except that it does not have flashing lights or change direction.¹⁰ It also moves faster than a typical airplane: airplanes fly at about 600 mph (965 kph), while the station flies at 17,500 mph (28,000 kph).¹⁰

Sightings happen at specific hours and latitudes: all station sightings occur within a few hours before or after sunrise or sunset, the optimum viewing period, when the Sun reflects off the station against the darker sky.¹⁰ The station orbits with an inclination of 51.6 degrees, so the farthest north or south of the equator it goes is 51.6 degrees latitude; for locations beyond that, including Alaska, it will never go directly overhead.¹⁰

For planning, NASA maintains the Spot the Station service, which helps observers find when the station will pass.¹⁰ The traffic overhead is constant: every day the ISS circles the Earth 16 times, a distance roughly equal to a round trip to the Moon.³

The station's future is now measured in commitments rather than construction milestones: the United States, ESA, Japan and Canada have committed to support the station through 2030, while Russia announced that it would support the station through 2028 and then begin work on its own orbital space station.⁴ On 2 November 2025 the station marked 25 years of continuous human presence aboard.⁶