The ISS functions as a modular space station, enabling the addition or removal of modules from its structure for increased adaptability.

Blueprint of ISS (as of 2018)
Rendering of ISS (as of 2023)

Below is a diagram of major station components. The Unity node joins directly to the Destiny laboratory; for clarity, they are shown apart. Similar cases are also seen in other parts of the structure.

Key to box background colors:

Pressurised component, accessible by the crew without using spacesuits
Docking/berthing port, pressurized when a visiting spacecraft is present
Airlock, to move people or material between pressurized and unpressurized environment
Unpressurised station superstructure
Unpressurised component
Temporarily defunct or non-commissioned component
Former, no longer installed component
Future, not yet installed component

Russian
docking port

Means of
attachment of
large payloads

Heat radiator

Poisk

Russian
docking port

Portable workpost

European Robotic Arm

Solar array

Zvezda

Solar array

Solar array

Nauka

Solar array

Pirs ^[a]

Prichal

Solar array^[b]

Zarya

Solar array^[c]

Rassvet

Dextre
robotic arm

Canadarm2
robotic arm

Unity

Cupola

Cargo spacecraft
berthing port

Leonardo

ESP-1

Destiny

PMA / IDA
docking port

Kibō
cargo bay

Kibō
robotic arm

External payloads

Columbus

Harmony

Kibō

Kibō
external platform

Cargo spacecraft
berthing port

PMA / IDA
docking port

Pressurised modules

Zarya

Zarya (Russian: Заря, lit. 'Sunrise'^[d]), also known as the Functional Cargo Block (Russian: Функционально-грузовой блок), was the inaugural component of the ISS. Launched in 1998, it initially served as the ISS's power source, storage, propulsion, and guidance system. As the station has grown, Zarya's role has transitioned primarily to storage, both internally and in its external fuel tanks.^[98]

A descendant of the TKS spacecraft used in the Salyut programme, Zarya was built in Russia but is owned by the United States. Its name symbolizes the beginning of a new era of international space cooperation.^[99]

Unity

Unity, also known as Node 1, is the inaugural U.S.-built component of the ISS.^[100]^[101] Serving as the connection between the Russian and U.S. segments, this cylindrical module features six Common Berthing Mechanism locations (forward, aft, port, starboard, zenith, and nadir) for attaching additional modules. Measuring 4.57 metres (15.0 ft) in diameter and 5.47 metres (17.9 ft) in length, Unity was constructed of steel by Boeing for NASA at the Marshall Space Flight Center in Huntsville, Alabama. It was the first of three connecting nodes – Unity, Harmony, and Tranquility – that forms the structural backbone of the U.S. segment of the ISS.^[102]

Zvezda

Zvezda (Russian: Звезда, lit. 'star') launched in July 2000, is the core of the Russian Orbital Segment of the ISS. Initially providing essential living quarters and life support systems, it enabled the first continuous human presence aboard the station. While additional modules have expanded the ISS's capabilities, Zvezda remains the command and control center for the Russian segment and it is where crews gather during emergencies.^[103]^[104]^[105]

A descendant of the Salyut programme's DOS spacecraft, Zvezda was built by RKK Energia and launched atop a Proton rocket.^[106]

Destiny

The Destiny laboratory is the primary research facility for U.S. experiments on the ISS. NASA's first permanent orbital research station since Skylab, the module was built by Boeing and launched aboard Space Shuttle Atlantis during STS-98. Attached to Unity over a period of five days in February 2001, Destiny has been a hub for scientific research ever since.^[107]^[108]^[109]

Within Destiny, astronauts conduct experiments in fields such as medicine, engineering, biotechnology, physics, materials science, and Earth science. Researchers worldwide benefit from these studies. The module also houses life support systems, including the Oxygen Generating System.^[110]

Quest Joint Airlock

The Quest Joint Airlock enables extravehicular activities (EVAs) using either the U.S. Extravehicular Mobility Unit (EMU) or the Russian Orlan space suit.^[111]

Before its installation, conducting EVAs from the ISS was challenging due to a variety of system and design differences. Only the Orlan suit could be used from the Transfer Chamber on the Zvezda module (which was not a purpose-built airlock) and the EMU could only be used from the airlock on a visiting Space Shuttle, which could not accommodate the Orlan.^[112]

Launched aboard Space Shuttle Atlantis during STS-104 in July 2001 and attached to the Unity module, Quest is a 6.1-metre-long (20 ft), 4.0-metre-wide (13 ft) structure built by Boeing.^[113] It houses the crew airlock for astronaut egress, an equipment airlock for suit storage, and has facilities to accommodate astronauts during their overnight pre-breathe procedures to prevent decompression sickness.^[112]

The crew airlock, derived from the Space Shuttle, features essential equipment like lighting, handrails, and an Umbilical Interface Assembly (UIA) that provides life support and communication systems for up to two spacesuits simultaneously. These can be either two EMUs, two Orlan suits, or one of each design.

Poisk

Poisk (Russian: По́иск, lit. 'Search'), also known as the Mini-Research Module 2 (Russian: Малый исследовательский модуль 2), serves as both a secondary airlock on the Russian segment of the ISS and supports docking for Soyuz and Progress spacecraft, facilitates propellant transfers from the latter.^[114] Launched on 10 November 2009 attached to a modified Progress spacecraft, called Progress M-MIM2.^[115]^[116]

Poisk provides facilities to maintain Orlan spacesuits and is equipped with two inward-opening hatches, a design change from Mir, which encountered a dangerous situation caused by an outward-opening hatch that opened too quickly because of a small amount of air pressure remaining in the airlock.^[117] Since the departure of Pirs in 2021, it's become the sole airlock on the Russian segment.

Harmony

Harmony, or Node 2, is the central connecting hub of the US segment of the ISS, linking the U.S., European, and Japanese laboratory modules. It's also been called the "utility hub" of the ISS as it provides essential power, data, and life support systems. The module also houses sleeping quarters for four crew members.^[118]

Launched on 23 October 2007 aboard Space Shuttle Discovery on STS-120,^[119]^[120] Harmony was initially attached to the Unity^[121]^[122] before being relocated to its permanent position at the front of the Destiny laboratory on 14 November 2007.^[123] This expansion added significant living space to the ISS, marking a key milestone in the construction of the U.S. segment.

Tranquility

Tranquility, also known as Node 3, is a module of the ISS. It contains environmental control systems, life support systems, a toilet, exercise equipment, and an observation cupola.

The European Space Agency and the Italian Space Agency had Tranquility manufactured by Thales Alenia Space. A ceremony on 20 November 2009 transferred ownership of the module to NASA.^[124] On 8 February 2010, NASA launched the module on the Space Shuttle's STS-130 mission.

Columbus

Columbus is a science laboratory that is part of the ISS and is the largest single contribution to the station made by the European Space Agency.

Like the Harmony and Tranquility modules, the Columbus laboratory was constructed in Turin, Italy by Thales Alenia Space. The functional equipment and software of the lab was designed by EADS in Bremen, Germany. It was also integrated in Bremen before being flown to the Kennedy Space Center in Florida in an Airbus Beluga jet. It was launched aboard Space Shuttle Atlantis on 7 February 2008, on flight STS-122. It is designed for ten years of operation. The module is controlled by the Columbus Control Centre, located at the German Space Operations Center, part of the German Aerospace Center in Oberpfaffenhofen near Munich, Germany.

The European Space Agency has spent €1.4 billion (about US$1.6 billion) on building Columbus, including the experiments it carries and the ground control infrastructure necessary to operate them.^[125]

Kibō

Kibō (Japanese: きぼう, lit. 'hope'), also known as the Japanese Experiment Module, is Japan's research facility on the ISS. It is the largest single module on the ISS, consisting of a pressurized lab, an exposed facility for conducting experiments in the space environment, two storage compartments, and a robotic arm. Attached to the Harmony module, Kibō was assembled in space over three Space Shuttle missions: STS-123, STS-124 and STS-127.^[126]

Cupola

The Cupola is an ESA-built observatory module of the ISS. Its name derives from the Italian word cupola, which means "dome". Its seven windows are used to conduct experiments, dockings and observations of Earth. It was launched aboard Space Shuttle mission STS-130 on 8 February 2010 and attached to the Tranquility (Node 3) module. With the Cupola attached, ISS assembly reached 85 per cent completion. The Cupola's central window has a diameter of 80 cm (31 in).^[127]

Rassvet

Rassvet (Russian: Рассвет, lit. 'first light'), also known as the Mini-Research Module 1 (Russian: Малый исследовательский модуль 1) and formerly known as the Docking Cargo Module is primarily used for cargo storage and as a docking port for visiting spacecraft on the Russian segment of the ISS. Rassvet replaced the cancelled Docking and Storage Module and used a design largely based on the Mir Docking Module built in 1995.

Rassvet was delivered in on 14 May 2010 Space Shuttle Atlantis on STS-132 in exchange for the Russian Proton delivery of the US-funded Zarya module in 1998.^[128] Rassvet was attached to Zarya shortly thereafter.^[129]

Leonardo

The Leonardo Permanent Multipurpose Module (PMM) is a module of the International Space Station. It was flown into space aboard the Space Shuttle on STS-133 on 24 February 2011 and installed on 1 March. Leonardo is primarily used for storage of spares, supplies and waste on the ISS, which was until then stored in many different places within the space station. It is also the personal hygiene area for the astronauts who live in the US Orbital Segment. The Leonardo PMM was a Multi-Purpose Logistics Module (MPLM) before 2011, but was modified into its current configuration. It was formerly one of two MPLM used for bringing cargo to and from the ISS with the Space Shuttle. The module was named for Italian polymath Leonardo da Vinci.

Bigelow Expandable Activity Module

The Bigelow Expandable Activity Module (BEAM) is an experimental expandable space station module developed by Bigelow Aerospace, under contract to NASA, for testing as a temporary module on the International Space Station (ISS) from 2016 to at least 2020. It arrived at the ISS on 10 April 2016,^[130] was berthed to the station on 16 April at Tranquility Node 3, and was expanded and pressurized on 28 May 2016. In December 2021, Bigelow Aerospace conveyed ownership of the module to NASA, as a result of Bigelow's cessation of activity.^[131]

International Docking Adapters

The International Docking Adapter (IDA) is a spacecraft docking system adapter developed to convert APAS-95 to the NASA Docking System (NDS). An IDA is placed on each of the ISS's two open Pressurized Mating Adapters (PMAs), both of which are connected to the Harmony module.

Two International Docking Adapters are currently installed aboard the Station. Originally, IDA-1 was planned to be installed on PMA-2, located at Harmony's forward port, and IDA-2 would be installed on PMA-3 at Harmony's zenith. After IDA 1 was destroyed in a launch incident, IDA-2 was installed on PMA-2 on 19 August 2016,^[132] while IDA-3 was later installed on PMA-3 on 21 August 2019.^[133]

Bishop Airlock Module

The NanoRacks Bishop Airlock Module is a commercially funded airlock module launched to the ISS on SpaceX CRS-21 on 6 December 2020.^[134]^[135] The module was built by NanoRacks, Thales Alenia Space, and Boeing.^[136] It will be used to deploy CubeSats, small satellites, and other external payloads for NASA, CASIS, and other commercial and governmental customers.^[137]

Nauka

Nauka (Russian: Наука, lit. 'Science'), also known as the Multipurpose Laboratory Module, Upgrade (Russian: Многоцелевой лабораторный модуль, усоверше́нствованный), is a Roscosmos-funded component of the ISS that was launched on 21 July 2021, 14:58 UTC. In the original ISS plans, Nauka was to use the location of the Docking and Stowage Module (DSM), but the DSM was later replaced by the Rassvet module and moved to Zarya's nadir port. Nauka was successfully docked to Zvezda's nadir port on 29 July 2021, 13:29 UTC, replacing the Pirs module.

It had a temporary docking adapter on its nadir port for crewed and uncrewed missions until Prichal arrival, where just before its arrival it was removed by a departing Progress spacecraft.^[138]

Prichal

Prichal (Russian: Причал, lit. 'pier') is a 4-tonne (8,800 lb) spherical module that serves as a docking hub for the Russian segment of the ISS. Launched in November 2021, Prichal provides additional docking ports for Soyuz and Progress spacecraft, as well as potential future modules. Prichal features six docking ports: forward, aft, port, starboard, zenith, and nadir. One of these ports, equipped with an active hybrid docking system, enabled it to dock with the Nauka module. The remaining five ports are passive hybrids, allowing for docking of Soyuz, Progress, and heavier modules, as well as future spacecraft with modified docking systems. As of 2024, the forward, aft, port and starboard docking ports remain covered. Prichal was initially intended to be an element of the now canceled Orbital Piloted Assembly and Experiment Complex.^[139]^[140]^[141]^[142]

Unpressurised elements

ISS Truss Components breakdown showing Trusses and all ORUs in situ

Construction of the Integrated Truss Structure over New Zealand

The ISS has a large number of external components that do not require pressurisation. The largest of these is the Integrated Truss Structure (ITS), to which the station's main solar arrays and thermal radiators are mounted.^[143] The ITS consists of ten separate segments forming a structure 108.5 metres (356 ft) long.^[8]

The station was intended to have several smaller external components, such as six robotic arms, three External Stowage Platforms (ESPs) and four ExPRESS Logistics Carriers (ELCs).^[144]^[145] While these platforms allow experiments (including MISSE, the STP-H3 and the Robotic Refueling Mission) to be deployed and conducted in the vacuum of space by providing electricity and processing experimental data locally, their primary function is to store spare Orbital Replacement Units (ORUs). ORUs are parts that can be replaced when they fail or pass their design life, including pumps, storage tanks, antennas, and battery units. Such units are replaced either by astronauts during EVA or by robotic arms.^[146] Several shuttle missions were dedicated to the delivery of ORUs, including STS-129,^[147] STS-133^[148] and STS-134.^[149] As of January 2011^[update], only one other mode of transportation of ORUs had been used – the Japanese cargo vessel HTV-2 – which delivered an FHRC and CTC-2 via its Exposed Pallet (EP).^[150]^{[needs update]}

There are also smaller exposure facilities mounted directly to laboratory modules; the Kibō Exposed Facility serves as an external "porch" for the Kibō complex,^[151] and a facility on the European Columbus laboratory provides power and data connections for experiments such as the European Technology Exposure Facility^[152]^[153] and the Atomic Clock Ensemble in Space.^[154] A remote sensing instrument, SAGE III-ISS, was delivered to the station in February 2017 aboard CRS-10,^[155] and the NICER experiment was delivered aboard CRS-11 in June 2017.^[156] The largest scientific payload externally mounted to the ISS is the Alpha Magnetic Spectrometer (AMS), a particle physics experiment 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.^[157]^[158]

The commercial Bartolomeo External Payload Hosting Platform, manufactured by Airbus, was launched on 6 March 2020 aboard CRS-20 and attached to the European Columbus module. It will provide an additional 12 external payload slots, supplementing the eight on the ExPRESS Logistics Carriers, ten on Kibō, and four on Columbus. The system is designed to be robotically serviced and will require no astronaut intervention. It is named after Christopher Columbus's younger brother.^[159]^[160]^[161]

MLM outfittings

MLM outfittings on Rassvet

A wide-angle view of the new module (behind Rassvet) attached to the ROS as seen from the cupola

In May 2010, equipment for Nauka was launched on STS-132 (as part of an agreement with NASA) and delivered by Space Shuttle Atlantis. Weighing 1.4 metric tons, the equipment was attached to the outside of Rassvet (MRM-1). It included a spare elbow joint for the European Robotic Arm (ERA) (which was launched with Nauka) and an ERA-portable workpost used during EVAs, as well as RTOd add-on heat radiator and internal hardware alongside the pressurized experiment airlock.^[162]

The RTOd radiator adds additional cooling capability to Nauka, which enables the module to host more scientific experiments.^[162]

The ERA was used to remove the RTOd radiator from Rassvet and transferred over to Nauka during VKD-56 spacewalk. Later it was activated and fully deployed on VKD-58 spacewalk.^[163] This process took several months. A portable work platform was also transferred over in August 2023 during VKD-60 spacewalk, which can attach to the end of the ERA to allow cosmonauts to "ride" on the end of the arm during spacewalks.^[164]^[165] However, even after several months of outfitting EVAs and RTOd heat radiator installation, six months later, the RTOd radiator malfunctioned before active use of Nauka (the purpose of RTOd installation is to radiate heat from Nauka experiments). The malfunction, a leak, rendered the RTOd radiator unusable for Nauka. This is the third ISS radiator leak after Soyuz MS-22 and Progress MS-21 radiator leaks. If a spare RTOd is not available, Nauka experiments will have to rely on Nauka's main launch radiator and the module could never be used to its full capacity.^[166]^[167]

Another MLM outfitting is a 4 segment external payload interface called means of attachment of large payloads (Sredstva Krepleniya Krupnogabaritnykh Obyektov, SKKO).^[168] Delivered in two parts to Nauka by Progress MS-18 (LCCS part) and Progress MS-21 (SCCCS part) as part of the module activation outfitting process.^[169]^[170]^[171]^[172] It was taken outside and installed on the ERA aft facing base point on Nauka during the VKD-55 spacewalk.^[173]^[174]^[175]^[176]

Robotic arms and cargo cranes

Commander Volkov stands on Pirs with his back to the Soyuz whilst operating the manual
Strela crane (which is holding photographer Oleg Kononenko).

Dextre, like many of the station's experiments and robotic arms, can be operated from Earth, allowing tasks to be performed while the crew sleeps.

The Integrated Truss Structure (ITS) serves as a base for the station's primary remote manipulator system, the Mobile Servicing System (MSS), which is composed of three main components:

Canadarm2, the largest robotic arm on the ISS, has a mass of 1,800 kilograms (4,000 lb) and is used to: dock and manipulate spacecraft and modules on the USOS; hold crew members and equipment in place during EVAs; and move Dextre to perform tasks.^[177]
Dextre is a 1,560 kg (3,440 lb) robotic manipulator that has two arms and a rotating torso, with power tools, lights, and video for replacing orbital replacement units (ORUs) and performing other tasks requiring fine control.^[178]
The Mobile Base System (MBS) is a platform that rides on rails along the length of the station's main truss, which serves as a mobile base for Canadarm2 and Dextre, allowing the robotic arms to reach all parts of the USOS.^[179]

A grapple fixture was added to Zarya on STS-134 to enable Canadarm2 to inchworm itself onto the ROS.^[149] Also installed during STS-134 was the 15 m (50 ft) Orbiter Boom Sensor System (OBSS), which had been used to inspect heat shield tiles on Space Shuttle missions and which can be used on the station to increase the reach of the MSS.^[149] Staff on Earth or the ISS can operate the MSS components using remote control, performing work outside the station without the need for space walks.

Japan's Remote Manipulator System, which services the Kibō Exposed Facility,^[180] was launched on STS-124 and is attached to the Kibō Pressurised Module.^[181] The arm is similar to the Space Shuttle arm as it is permanently attached at one end and has a latching end effector for standard grapple fixtures at the other.

The European Robotic Arm, which will service the ROS, was launched alongside the Nauka module.^[182] 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 two Strela (Russian: Стрела́, lit. 'Arrow') cargo cranes during EVAs for moving crew and equipment around the ROS. Each Strela crane has a mass of 45 kg (99 lb).

Former module

The Pirs module attached to the ISS

ISS-65 Pirs docking compartment separates from the International Space Station.

Pirs

Pirs (Russian: Пирс, lit. 'Pier') was launched on 14 September 2001, as ISS Assembly Mission 4R, on a Russian Soyuz-U rocket, using a modified Progress spacecraft, Progress M-SO1, as an upper stage. Pirs was undocked by Progress MS-16 on 26 July 2021, 10:56 UTC, and deorbited on the same day at 14:51 UTC to make room for Nauka module to be attached to the space station. Prior to its departure, Pirs served as the primary Russian airlock on the station, being used to store and refurbish the Russian Orlan spacesuits.

Planned components

Axiom segment

In January 2020, NASA awarded Axiom Space a contract to build a commercial module for the ISS. The contract is under the NextSTEP2 program. NASA negotiated with Axiom on a firm fixed-price contract basis to build and deliver the module, which will attach to the forward port of the space station's Harmony (Node 2) module. Although NASA has only commissioned one module, Axiom plans to build an entire segment consisting of five modules, including a node module, an orbital research and manufacturing facility, a crew habitat, and a "large-windowed Earth observatory". The Axiom segment is expected to greatly increase the capabilities and value of the space station, allowing for larger crews and private spaceflight by other organisations. Axiom plans to convert the segment into a stand-alone space station once the ISS is decommissioned, with the intention that this would act as a successor to the ISS.^[183]^[184]^[185] Canadarm 2, which will be used to berth the Axiom Space Station modules to the ISS, is planned to continue its operations on the Axiom Space Station after the retirement of ISS in late 2020s.^[186]

As of December 2023, Axiom Space expected to launch the first module, Hab One, at the end of 2026.^[187]

US Deorbit Vehicle

The US Deorbit Vehicle (USDV) is a NASA-provided spacecraft intended to perform a controlled de-orbit and demise of the station after the end of its operational life in 2030. In June 2024, NASA awarded SpaceX a contract to build the Deorbit Vehicle.^[188] NASA plans to de-orbit ISS as soon as they have the "minimum capability" in orbit: "the USDV and at least one commercial station."^[189]

Cancelled components

The cancelled Habitation module under construction at Michoud in 1997

Rendering of the Nautilus-X Centrifuge Demonstrator docked to the ISS (side)

Several modules developed or planned for the station were cancelled over the course of the ISS programme. Reasons include budgetary constraints, the modules becoming unnecessary, and station redesigns after the 2003 Columbia disaster. The US Centrifuge Accommodations Module would have hosted science experiments in varying levels of artificial gravity.^[190] The US Habitation Module would have served as the station's living quarters. Instead, the living quarters are now spread throughout the station.^[191] The US Interim Control Module and ISS Propulsion Module would have replaced the functions of Zvezda in case of a launch failure.^[192] Two Russian Research Modules were planned for scientific research.^[193] They would have docked to a Russian Universal Docking Module.^[194] The Russian Science Power Platform would have supplied power to the Russian Orbital Segment independent of the ITS solar arrays.

Science Power Modules 1 and 2 (Repurposed Components)

Science Power Module 1 (SPM-1, also known as NEM-1) and Science Power Module 2 (SPM-2, also known as NEM-2) are modules that were originally planned to arrive at the ISS no earlier than 2024, and dock to the Prichal module, which is docked to the Nauka module.^[142]^[195] In April 2021, Roscosmos announced that NEM-1 would be repurposed to function as the core module of the proposed Russian Orbital Service Station (ROSS), launching no earlier than 2027^[196] and docking to the free-flying Nauka module.^[197]^[198] NEM-2 may be converted into another core "base" module, which would be launched in 2028.^[199]

Xbase

Designed by Bigelow Aerospace. In August 2016, Bigelow negotiated an agreement with NASA to develop a full-size ground prototype Deep Space Habitation based on the B330 under the second phase of Next Space Technologies for Exploration Partnerships. The module was called the Expandable Bigelow Advanced Station Enhancement (XBASE), as Bigelow hoped to test the module by attaching it to the International Space Station. However, in March 2020, Bigelow laid off all 88 of its employees, and as of February 2024^[update] the company remains dormant and is considered defunct,^[200]^[201] making it appear unlikely that the XBASE module will ever be launched.

Nautilus-X Centrifuge Demonstration

A proposal was put forward in 2011 for a first in-space demonstration of a sufficiently scaled centrifuge for artificial partial-g gravity effects. It was designed to become a sleep module for the ISS crew. The project was cancelled in favour of other projects due to budget constraints.^[202]