International Space Station: History of the ISS Since 1998

The International Space Station (ISS) is a large, permanently crewed laboratory orbiting the Earth about 400 kilometres up. Its first module was launched on 20 November 1998, and since November 2000 people have lived aboard without interruption. Built and run by the United States, Russia, Europe, Japan and Canada, it is the largest structure ever assembled in space and one of the most ambitious engineering projects in history.

Origins: from Freedom to a joint station

Space stations were not new. The Soviet Union had flown the Salyut series from 1971 and the modular Mir from 1986, while the United States had launched Skylab in 1973. In January 1984 President Ronald Reagan directed NASA to build a permanently crewed station within a decade, and invited America’s allies to take part.

The project, named Space Station Freedom in 1988, attracted partners in Europe, Japan and Canada. But it was repeatedly redesigned as costs rose, and by the early 1990s it faced cancellation in Congress, surviving one House vote in 1993 by a single vote.

The end of the Cold War changed the picture. In 1993 the Clinton administration ordered a cheaper redesign and invited Russia, whose experience with long-duration flight and reliable rockets was valuable, to join. Russia’s planned Mir-2 hardware was merged into the project. As a first step, the Shuttle–Mir programme from 1995 to 1998 saw American shuttles dock with Mir and American astronauts live aboard the Russian station.

Russian participation had practical consequences for the design. The station’s orbit was set at an inclination of 51.6 degrees to the equator so that rockets launched from Baikonur in Kazakhstan could reach it, even though this made shuttle launches from Florida carry less cargo. Russia also brought proven hardware, including the Soyuz spacecraft, which could serve as a lifeboat for the crew.

The formal framework came on 29 January 1998, when 15 governments signed the Intergovernmental Agreement in Washington: the United States, Russia, Japan, Canada and 11 member states of the European Space Agency.

Assembly in orbit, 1998-2011

The station was built in space, one piece at a time, because no rocket could launch it whole. The first module, Zarya (“Dawn”), was built in Russia under a US contract and launched on a Proton rocket from Baikonur on 20 November 1998. In December the shuttle Endeavour carried up the American Unity node and astronauts joined the two modules together.

The Russian service module Zvezda, which provided living quarters and engines, followed in July 2000. On 2 November 2000 the first resident crew, Expedition 1, arrived aboard a Soyuz: American commander William Shepherd with Russian cosmonauts Yuri Gidzenko and Sergei Krikalev. They were the first of an unbroken line of crews.

Assembly continued with the US Destiny laboratory in February 2001 and the Canadian robotic arm Canadarm2 in April 2001. Large sections of the integrated truss, which carries the solar arrays and radiators, were added from 2002 onwards.

Building the station was a feat of remote engineering. Modules made in different countries, often never joined together on the ground, had to fit perfectly in orbit. Assembly required dozens of shuttle flights and Russian launches, and astronauts and cosmonauts carried out well over a hundred spacewalks to connect power lines, fluid lines and structures. Robotic arms supplied by Canada did much of the heavy lifting.

The Columbia setback and recovery

The loss of the shuttle Columbia on 1 February 2003, described in Space Shuttle Columbia Disaster, grounded the shuttle fleet for more than two years. Without shuttles, the station could not grow, and crews were cut from three to two to conserve supplies.

Russia’s Soyuz crew ferries and Progress cargo craft kept the station supplied during this period. Shuttle flights resumed in 2005, and assembly picked up again in 2006 with new truss segments and solar arrays.

The two-person “caretaker” crews of 2003-2006 kept the station’s systems running and carried on a reduced programme of research. In July 2006 the German astronaut Thomas Reiter of the European Space Agency became the first long-duration crew member from a partner other than the United States and Russia, restoring a three-person crew.

The European laboratory Columbus arrived in February 2008, and Japan’s Kibo complex, the station’s largest single laboratory, was delivered in three flights between March 2008 and July 2009. In May 2009 the permanent crew was raised to six. The space shuttle made its final flight to the station in July 2011, and NASA declared the US segment essentially complete.

Life and work aboard

Crews usually spend about six months aboard, although a few stays have exceeded a year. They exercise for around two hours a day to limit bone and muscle loss, eat packaged food, and sleep in small crew cabins. Water is recycled from humidity and urine.

The station keeps Coordinated Universal Time (UTC), a neutral choice between the control centres in Houston and Moscow. English and Russian are its working languages, and every long-stay crew member trains in both. Control is shared among several centres, including Houston, Moscow, Munich in Germany and Tsukuba in Japan, each responsible for its own partner’s modules.

The ISS hosts thousands of experiments in biology, human physiology, materials science, fluid physics, Earth observation and astronomy. A major focus has been learning how the human body responds to long periods of weightlessness and radiation, knowledge needed for future missions to the Moon and Mars. The Alpha Magnetic Spectrometer, a particle physics detector installed in 2011, searches for antimatter and dark matter in cosmic rays.

More than 270 people from around 20 countries had visited the station by the mid-2020s. They include professional astronauts and a small number of paying visitors, the first of whom flew in 2001.

Commercial supply and crew

After the shuttle’s retirement, NASA relied on Russian Soyuz seats to carry its astronauts, while turning to private companies for cargo. A SpaceX Dragon became the first commercial spacecraft to berth with the station in May 2012, and Orbital Sciences’ Cygnus followed in 2013. These craft grew out of NASA’s Commercial Orbital Transportation Services programme, begun in 2006, which paid private firms to develop vehicles that NASA would then buy services from rather than own. European ATV and Japanese HTV cargo ships also served the station.

In May 2020 SpaceX’s Crew Dragon carried NASA astronauts to the ISS, the first crewed orbital flight from US soil since 2011. Boeing’s Starliner made its first crewed test flight to the station in 2024, although problems with its thrusters led NASA to bring its two astronauts home on a Crew Dragon instead. Russia added the Nauka laboratory module in July 2021, the last major module to date.

By the numbers

Cost estimates vary widely depending on what is counted, such as shuttle flights and partner contributions, so no single figure is definitive.

Tensions, challenges and the future

The ISS has survived political strains between its partners, including tensions after 2014 and 2022 over Ukraine. Cooperation in orbit has generally continued, with Russian and American crews still swapping seats on each other’s vehicles.

Technical problems have included ammonia coolant leaks, failed gyroscopes, a hole drilled in a Soyuz in 2018 and persistent small air leaks in a Russian transfer tunnel. None has forced a permanent evacuation of the station.

The ISS grew from a Cold War project into a partnership between former rivals, following the precedent of the Apollo–Soyuz Test Project. It has kept humans in orbit continuously for more than a quarter of a century, building up practical experience of living and working in space.

NASA and its partners plan to operate the station until around 2030, after which a dedicated deorbit vehicle is intended to bring it down over a remote ocean area. Commercial stations are being developed to take over its role in low Earth orbit.

Myths and facts

A common belief is that astronauts float because there is no gravity in orbit. In fact gravity at the station’s height is roughly 90 per cent as strong as on the ground; crews are weightless because the station and everyone in it are in continuous free fall around the Earth.

Another is that the ISS can be seen only with a telescope. It is often the third-brightest object in the night sky after the Moon and Venus, and can be seen with the naked eye as a fast-moving point of light.

Timeline

• 1984, January: President Reagan announces plans for a permanently crewed US space station.
• 1993: The station is redesigned and Russia is invited to join.
• 1998, 29 January: Fifteen governments sign the Intergovernmental Agreement.
• 1998, 20 November: Zarya, the first module, is launched from Baikonur.
• 2000, 2 November: Expedition 1 arrives; continuous occupation begins.
• 2001, February: The US Destiny laboratory is installed.
• 2003, 1 February: The Columbia disaster halts shuttle assembly flights.
• 2008: The European Columbus and the first parts of Japan’s Kibo laboratory are added.
• 2011, July: The final shuttle mission to the station, STS-135, is flown.
• 2020, May: Crew Dragon carries astronauts to the ISS on the first commercial crew flight.

Why it matters

The International Space Station is the most expensive and complex object humans have built, and it has given people a permanent foothold in space since 2000. It demonstrated that rival nations could share a single, delicate machine for decades, and its research underpins plans for longer journeys to the Moon and Mars.