The ISS has modules installed by various countries over several missions. Each module serves a specific purpose, like living quarters, labs for science experiments, or storage. This modular design makes the station very flexible. This setup also allows different countries to contribute their own pieces, like the European Columbus module or Japan’s Kibō lab. It’s a collaborative and adaptable way to keep the ISS evolving and ready for future missions! So, let’s take a look at all present, past, and future modules of the International Space Station.
Pressurized Modules
Pressurized modules on the ISS are enclosed, air-filled sections where astronauts can work and live without needing spacesuits. These modules maintain a breathable atmosphere, similar to Earth, with controlled oxygen levels, temperature, and pressure.
They include areas like laboratories (Kibō, Columbus), living quarters, and storage spaces. Pressurized modules also connect to docking ports, allowing spacecraft to attach while keeping the interior environment safe for crew members. Essentially, they’re the “indoor” spaces of the ISS, making long-term life and work in space possible.
Zarya: The First ISS Module
Zarya (Заря, meaning “Sunrise” in Russian), also called the Functional Cargo Block, was the first module of the International Space Station, launched in 1998. Initially, it provided the station with power, storage, propulsion, and guidance capabilities. Over time, as the ISS expanded, Zarya’s primary function shifted to storage inside the module and in its external fuel tanks.
Derived from the TKS spacecraft used in the Soviet Salyut program, Zarya was constructed in Russia but is owned by the United States. Its name reflects the dawn of international cooperation in space exploration.
Unity: The First US-Built Module
Unity, also called Node 1, was the first U.S.-built module of the ISS. Serving as the critical connection point between the U.S. and Russian segments, Unity is a cylindrical module with six berthing ports to attach additional components. These ports are positioned on the forward, aft, port, starboard, zenith, and nadir sides.
Measuring 4.57 meters (15.0 feet) in diameter and 5.47 meters (17.9 feet) in length, Unity was constructed by Boeing for NASA at the Marshall Space Flight Center in Huntsville, Alabama. It is one of three connecting nodes on the ISS, alongside Harmony and Tranquility, forming the structural backbone of the U.S. segment of the station.
Zvezda: The Russian Core
Zvezda (Звезда, meaning “star” in Russian), launched in July 2000, serves as the heart of the Russian Orbital Segment of the ISS. It originally provided living quarters and life support systems, enabling the first long-term human habitation aboard the station. While the ISS has since grown with additional modules, Zvezda remains the command and control hub for the Russian segment and serves as the designated gathering point for crews during emergencies.
Derived from the DOS spacecraft used in the Soviet Salyut program, Zvezda was constructed by RKK Energia and launched aboard a Proton rocket.
Destiny: The Science Lab
The Destiny module is NASA’s primary science laboratory on the ISS and its first permanent orbital research facility since Skylab. Built by Boeing, it was launched aboard Space Shuttle Atlantis during the STS-98 mission in February 2001. Over five days, it was connected to the Unity module, establishing a center for cutting-edge research.
Destiny supports experiments across various fields, including medicine, engineering, biotechnology, physics, materials science, and Earth observation. The findings benefit researchers worldwide. The module also houses critical life support systems, such as the Oxygen Generating System, enhancing the ISS’s long-term functionality.
Quest Joint Airlock
The Quest Joint Airlock facilitates spacewalks (EVAs) using both the U.S. Extravehicular Mobility Unit (EMU) and the Russian Orlan spacesuit. Before Quest’s installation, EVAs on the ISS were complicated due to compatibility issues. The Orlan suit could only be used through Zvezda’s Transfer Chamber, which wasn’t designed as an airlock, while the EMU required the airlock of a visiting Space Shuttle, which couldn’t support Orlan suits.
Launched aboard Space Shuttle Atlantis during STS-104 in July 2001, Quest was attached to the Unity module. The structure, built by Boeing 🔗, measures 6.1 meters (20 feet) long and 4.0 meters (13 feet) wide. It includes a crew airlock for astronaut egress and an equipment airlock for suit storage, as well as facilities for pre-breathe procedures to prevent decompression sickness before EVAs.
The crew airlock, based on Space Shuttle designs, is equipped with handrails, lighting, and an Umbilical Interface Assembly (UIA) that supports life support and communication systems for up to two spacesuits. These can be two EMUs, two Orlan suits, or one of each.
Poisk: Mini-Research
Poisk (Поиск, meaning “Search” in Russian), also known as the Mini-Research Module 2 (MRM-2), serves as an airlock and docking port on the Russian segment of the ISS. It supports Soyuz and Progress spacecraft docking and facilitates propellant transfer from Progress spacecraft.
Launched on November 10, 2009, atop a modified Progress spacecraft (Progress M-MIM2), Poisk is equipped to maintain Orlan spacesuits. It features two inward-opening hatches, a safer design inspired by issues encountered on Mir, where an outward-opening hatch caused an incident due to residual air pressure in the airlock.
Following the removal of the Pirs module in 2021, Poisk became the sole airlock for spacewalks on the Russian segment.
Harmony: The US Central Hub
Harmony, also known as Node 2, serves as the central hub of the U.S. segment of the ISS, connecting the U.S., European, and Japanese laboratory modules. Often referred to as the station’s “utility hub,” it provides power, data connections, and life support, as well as sleeping quarters for four crew members.
Launched on October 23, 2007, aboard Space Shuttle Discovery during the STS-120 mission, Harmony was initially attached to Unity before being moved to its permanent location at the front of the Destiny laboratory on November 14, 2007. This relocation significantly expanded the station’s living and working space, representing a major milestone in the development of the U.S. segment.
Tranquility: Life Support Module
Tranquility, or Node 3, is an ISS module that houses key environmental and life support systems, including air and water filtration, a toilet, and exercise equipment. It also features the Cupola, a multi-windowed observation deck offering stunning views of Earth.
Built by Thales Alenia Space for the European and Italian Space Agencies, Tranquility was formally handed over to NASA during a ceremony on November 20, 2009. The module was launched aboard Space Shuttle Endeavour during the STS-130 mission on February 8, 2010.
Columbus: ESA's Laboratory
Columbus is the primary science laboratory contributed by the European Space Agency (ESA) to the ISS. It is the largest single ESA contribution and supports experiments across various disciplines, including biology, physics, and Earth science.
Constructed by Thales Alenia Space 🔗 in Turin, Italy, and equipped by EADS in Bremen, Germany, Columbus was integrated in Bremen before being transported to the Kennedy Space Center aboard an Airbus Beluga jet. It was launched aboard Space Shuttle Atlantis on February 7, 2008, during the STS-122 mission. Designed for at least 10 years of operation, Columbus is managed by the Columbus Control Centre, located near Munich, Germany.
The ESA invested €1.4 billion (approximately $1.6 billion) in Columbus, including its onboard experiments and the infrastructure needed for its operations.
Kibō: Japan's Flagship
Kibō (きぼう, meaning “hope” in Japanese) is Japan’s flagship research module on the ISS and the largest single module on the station. It includes a pressurized laboratory, an exposed facility for experiments in open space, two storage compartments, and a robotic arm for handling payloads.
Connected to the Harmony module, Kibō was assembled over three Space Shuttle missions: STS-123, STS-124, and STS-127.
Cupola: The Observatory Module
The Cupola is a dome-shaped observatory module designed and built by the European Space Agency (ESA). Its seven large windows provide astronauts with panoramic views for Earth observation, docking operations, and experiments. The module was launched on February 8, 2010, aboard Space Shuttle Endeavour during the STS-130 mission and attached to the Tranquility module (Node 3). The Cupola’s central window, the largest on the ISS, measures 80 cm (31 inches) in diameter. Its addition brought the ISS assembly to 85% completion.
Rassvet: Russia's Mini-Research Module
Rassvet (Рассвет, meaning “first light” in Russian), also known as the Mini-Research Module 1 (MRM-1), serves as a cargo storage unit and docking port for spacecraft on the Russian segment of the ISS. Its design is based on the Mir Docking Module built in 1995, and it replaced the canceled Docking and Storage Module project.
Delivered on May 14, 2010, aboard Space Shuttle Atlantis during the STS-132 mission, Rassvet was provided in exchange for Russia’s 1998 launch of the U.S.-funded Zarya module. Shortly after its arrival, Rassvet was attached to Zarya, further enhancing the station’s capabilities.
Leonardo: Storage
The Leonardo Permanent Multipurpose Module (PMM) is a storage module on the International Space Station. Installed on March 1, 2011, after being launched aboard Space Shuttle Discovery on STS-133 on February 24, it serves as the primary location for storing spares, supplies, and waste, centralizing items previously scattered throughout the station. It also houses the personal hygiene area for astronauts living on the U.S. Orbital Segment.
Originally one of two Multi-Purpose Logistics Modules (MPLMs) used to transport cargo to and from the ISS aboard Space Shuttles, Leonardo was modified into a permanent module before its final installation. It is named after Italian polymath Leonardo da Vinci 🔗.
Bigelow Expandable Activity Module (BEAM)
The Bigelow Expandable Activity Module (BEAM) is an experimental, expandable module designed by Bigelow Aerospace under a NASA contract.
It was launched to the ISS on April 10, 2016, berthed to the Tranquility module (Node 3) on April 16, and expanded and pressurized on May 28, 2016. Initially planned for a temporary trial through 2020, ownership of BEAM was transferred to NASA in December 2021 after Bigelow Aerospace 🔗 ceased operations. The module serves as a testbed for expandable habitat technologies.
International Docking Adapters (IDAs)
The International Docking Adapters (IDAs) are systems that convert the APAS-95 docking mechanism to the NASA Docking System (NDS), allowing spacecraft to dock with the ISS. These adapters are installed on the station’s two open Pressurized Mating Adapters (PMAs), both attached to the Harmony module.
The first adapter, IDA-2, was installed on PMA-2 (Harmony’s forward port) on August 19, 2016, after IDA-1 was lost in a launch failure. IDA-3 was later installed on PMA-3 (Harmony’s zenith port) on August 21, 2019.
Bishop Airlock Module
The NanoRacks Bishop Airlock Module, a commercially funded airlock, was launched to the ISS on December 6, 2020, aboard SpaceX CRS-21. Built by NanoRacks, Thales Alenia Space, and Boeing, Bishop is used to deploy CubeSats, small satellites, and external payloads for NASA, CASIS, and various commercial and governmental clients. The module significantly expands the station’s ability to support external operations.
Nauka: The Lab Upgrade
Nauka (Наука, meaning “Science” in Russian), officially the Multipurpose Laboratory Module-Upgrade, is a Roscosmos-funded addition to the ISS. It was launched on July 21, 2021, and docked to the station on July 29, replacing the Pirs module. Initially, Nauka was planned to occupy the location of the Docking and Stowage Module (DSM), but the DSM was relocated to Zarya’s nadir port and replaced by the Rassvet module. Nauka now occupies Zvezda’s nadir port.
Before the arrival of the Prichal module, Nauka temporarily housed a docking adapter for crewed and uncrewed missions. This adapter was removed by a departing Progress spacecraft just prior to Prichal’s docking.
Prichal: Docking Hub
Prichal (Причал, meaning “Pier” in Russian) is a spherical docking hub module for the Russian segment of the ISS. Launched in November 2021, it adds five additional docking ports for Soyuz and Progress spacecraft, as well as potential future modules.
The module features six docking ports: one active hybrid port for its initial attachment to the Nauka module, and five passive hybrid ports designed to support Soyuz, Progress, heavier modules, and future spacecraft with updated docking systems. As of 2024, the forward, aft, port, and starboard ports remain covered.
Prichal was originally conceived as part of the canceled Orbital Piloted Assembly and Experiment Complex but now plays a key role in expanding the docking capabilities of the ISS’s Russian segment.
ISS Unpressurised Modules
The ISS features numerous external components that do not require pressurization, the largest being the Integrated Truss Structure (ITS). This 108.5-meter (356-foot) framework supports the station’s main solar arrays and thermal radiators.
Other external elements include robotic arms, three External Stowage Platforms (ESPs), and four ExPRESS Logistics Carriers (ELCs), which store spare Orbital Replacement Units (ORUs). These ORUs—such as pumps, antennas, and batteries—can be replaced by astronauts during EVAs or by robotic arms. Several shuttle missions, including STS-129 and STS-134, and the Japanese cargo vessel HTV-2, have delivered ORUs to the ISS.
MLM Outfittings
In May 2010, equipment for the Nauka module was delivered on STS-132 and attached to Rassvet. This included a spare elbow joint and workpost for the European Robotic Arm (ERA), the RTOd radiator for additional cooling, and a pressurized experiment airlock. The RTOd radiator, essential for Nauka’s experiments, was transferred and activated during a series of spacewalks but malfunctioned due to a leak, limiting Nauka’s capabilities.
A four-segment payload attachment system (SKKO) was also installed on Nauka in 2023 for securing large payloads.
Robotic Arms and Cranes
The ISS features advanced robotic systems for operations and maintenance:
- Canadarm2: A 1,800 kg robotic arm for docking, module manipulation, and assisting astronauts during EVAs.
- Dextre: A 1,560 kg manipulator with precision tools for replacing equipment and performing fine tasks.
- Mobile Base System (MBS): A rail-mounted platform enabling Canadarm2 and Dextre to access the entire U.S. segment.
- European Robotic Arm (ERA): Launched with Nauka, it services the Russian segment.
Former ISS Modules and Canceled Components
At the time of writing this article (December 2024), there is only one module that was detached from the ISS to make space for another one: Pirs.
Pirs
Pirs (Пирс, meaning “Pier” in Russian) was launched on September 14, 2001, as part of ISS Assembly Mission 4R aboard a Soyuz-U rocket. It used a modified Progress spacecraft, Progress M-SO1, as its upper stage.
For nearly two decades, Pirs functioned as the primary airlock for the Russian segment of the ISS, supporting spacewalks and housing Orlan spacesuits for storage and refurbishment. On July 26, 2021, Pirs was undocked by Progress MS-16 at 10:56 UTC and deorbited later that day at 14:51 UTC to clear the way for the Nauka module’s installation.
Canceled ISS Modules
Several modules originally planned for the ISS were also canceled due to budget constraints, shifting priorities, or redesigns following the 2003 Columbia disaster.
- The Centrifuge Accommodations Module was designed for experiments under varying levels of artificial gravity.
- The Habitation Module was intended as centralized living quarters but was deemed unnecessary as living spaces were distributed across existing modules.
- The Interim Control Module and Propulsion Module were backup plans to replace Zvezda’s functions in case of a launch failure.
- Two Russian Research Modules were proposed for scientific studies and would have docked to a Universal Docking Module.
- The Russian Science Power Platform was envisioned to provide independent power to the Russian Orbital Segment but was rendered redundant by the ITS solar arrays.
