International Space Station

Structure and modules

The ISS is built around two integrated orbital segments: the US Orbital Segment (USOS), contributed by NASA, ESA, JAXA, and CSA, and the Russian Orbital Segment (ROS), contributed by Roscosmos. The segments are physically joined and share power, cooling, communications, and crew access, but each partner agency operates and maintains its own hardware.

The backbone of the station is a 94-metre integrated truss structure from which large solar arrays extend to generate electrical power. The arrays span 73 metres. Attached to the truss and to each other are the pressurised modules where the crew lives and works. Major modules include Russia's Zarya (the first element launched, providing early power and propulsion) and Zvezda (the Russian service module housing living quarters and life support); the US-built Unity, Harmony, Tranquility, and Destiny laboratory; the European Columbus laboratory; Japan's multi-element Kibō complex; the cupola observation bay with its seven windows; the Leonardo permanent multipurpose module; and the more recent Russian additions Nauka and Prichal, the latter docked on 26 November 2021 as the station's most recently installed module. Commercial additions include the Bigelow Expandable Activity Module (BEAM) and the NanoRacks Bishop airlock.

Canada's contribution to the structure is primarily robotic: the 17-metre Canadarm2 robotic arm and the Dextre Special Purpose Dexterous Manipulator are essential for berthing arriving cargo spacecraft and for performing delicate external maintenance tasks, reducing the need for spacewalks.

Notable events, records, and incidents

The ISS holds several defining records in human spaceflight. Its most fundamental achievement is simply that it has been continuously inhabited since 2 November 2000 — a streak lasting more than 25 years by late 2025. Nearly 300 people from 26 countries have visited the station, and at its most crowded — first reached during STS-127 in July 2009 — it has hosted 13 people simultaneously.

Individual duration records have repeatedly been broken aboard the station. Christina Koch spent 328 days continuously on the ISS during 2019–2020, the longest single spaceflight by a woman. Frank Rubio (NASA) set the American record with 371 consecutive days on board in 2022–2023. Peggy Whitson accumulated 675 total days in space across multiple missions, most of it on the ISS.

The station's 259 spacewalks represent an enormous engineering achievement in their own right. The longest single spacewalk associated with ISS construction was 8 hours 56 minutes, performed by James Voss and Susan Helms during STS-102 in 2001. The longest Russian spacewalk from the ISS lasted 8 hours 13 minutes, performed by Alexander Misurkin and Anton Shkaplerov during Expedition 54 to repair a station antenna.

Not all notable events have been straightforward. In July 2013, ESA astronaut Luca Parmitano's helmet filled with water from a cooling-system leak while he was on a spacewalk — a life-threatening situation that required an early termination of the excursion. NASA subsequently overhauled its EVA safety procedures. The station's ammonia-based cooling loops have failed more than once, requiring rapid-response spacewalks to replace pump modules. On 24 December 2013, astronaut Mike Hopkins conducted the second of two spacewalks to replace a faulty external water pump module.

Structural integrity has also required sustained attention. Persistent cracks in the Zvezda service module's transfer tunnel, identified since 2019, have caused small atmosphere leaks; Roscosmos and NASA have applied temporary and permanent sealants while continuing to monitor the situation. The station has also experienced multiple shelter-in-place or partial evacuation events — documented on 13 March 2009, 28 June 2011, 24 March 2012, 16 June 2015, November 2021, and 27 June 2024 — in which crew members closed hatches and took refuge in docked Soyuz vehicles as a precaution against potential debris, leaks, or propulsion anomalies, before normal operations resumed.

Partnership, cost, and governance

The ISS is often described as the most expensive single object ever constructed. Its total programme cost was estimated at approximately US$150 billion as of 2010, shared among the five partner agencies. NASA's share — including US$58.7 billion for the station hardware and an estimated US$50.4 billion for 36 Space Shuttle assembly flights at roughly US$1.4 billion per flight — accounts for approximately US$109 billion of that total. Russia contributed roughly US$12 billion, Europe and Japan approximately US$5 billion each, and Canada approximately US$2 billion. NASA's ongoing annual operations cost is approximately US$3 billion per year, representing about one third of the agency's human spaceflight budget.

The partnership is governed by the Space Station Intergovernmental Agreement (IGA), an international treaty signed on 28 January 1998 by the 15 partner governments. The IGA and associated Memoranda of Understanding define which partner owns which modules, responsibilities for operations and resupply, and the allocation of utilisation rights. Within the US Orbital Segment, utilisation is divided approximately as follows: NASA holds 76.6%, JAXA 12.8%, ESA 8.3%, and CSA 2.3% of crew time and resources. Russia operates and controls its segment independently under the same overarching treaty.

Each partner's hardware contributions reflect these shares. NASA provided the backbone truss, the large solar arrays, and the majority of US segment modules. Russia provided the Zarya and Zvezda modules along with Soyuz crew transport and Progress cargo resupply vehicles. ESA built the Columbus laboratory in Germany and operated the Automated Transfer Vehicle cargo fleet. JAXA contributed the Kibō complex and operated the HTV cargo vehicle series. Canada's CSA provided the Canadarm2 robotic arm and the Dextre dexterous manipulator, indispensable for on-orbit assembly and servicing.

Current status and end-of-life planning

As of late 2025, the ISS remains fully operational and crewed. Expedition 73, with seven people aboard, was active at the station's 25th anniversary of continuous habitation in November 2025. NASA and its international partners plan to keep the station crewed and scientifically productive through 2030.

After 2030, the station will not be abandoned in orbit. Because an uncontrolled reentry of a structure as large as the ISS would pose an unacceptable risk to populated areas, NASA has planned a controlled deorbit. In July 2024, NASA selected SpaceX to develop the US Deorbit Vehicle (USDV), a dedicated spacecraft that will dock with the station near the end of its life. The USDV will perform a series of orbit-lowering burns before executing a final deorbit maneuver targeted so that any surviving debris falls in a remote, uninhabited area of the South Pacific Ocean, commonly referred to as Point Nemo. The final reentry is currently targeted for 2031.

Under the current plan, the last crew will depart the station roughly six months before final reentry, and the deorbit vehicle itself is expected to be launched approximately 1.5 years before the final burn. The station's retirement will mark the end of one era and the planned transition to commercially operated low Earth orbit platforms, which NASA aims to support as successors to the ISS for US government research needs.