Structure

The ISS is a third generation modular space station. Modular stations can allow modules to be added to or removed from the existing structure, allowing greater flexibility.

Below is a diagram of major station components. The blue areas are pressurised sections accessible by the crew without using spacesuits. The station's unpressurised superstructure is indicated in red. Other unpressurised components are yellow. The Unity node joins directly to the Destiny laboratory. For clarity, they are shown apart.

Russian docking port

Solar array

Zvezda DOS-8 (service module)

Solar array

Russian docking port

Poisk (MRM-2) airlock

Pirs airlock

Russian docking port

Nauka lab to replace Pirs

European robotic arm

Prichal

Solar array (retracted)

Zarya FGB (first module)

Solar array (retracted)

Rassvet (MRM-1)

Russian docking port

PMA 1

Cargo spacecraft berthing port

Leonardo cargo bay

BEAM habitat

Quest airlock

Unity Node 1

Tranquility Node 3

Bishop airlock

ESP-2

Cupola

Solar array

Solar array

Heat radiator

Heat radiator

Solar array

Solar array

ELC 2, AMS

Z1 truss

ELC 3

S5/6 Truss

S3/S4 Truss

S1 Truss

S0 Truss

P1 Truss

P3/P4 Truss

P5/6 Truss

ELC 4, ESP 3

ELC 1

Dextre robotic arm

Canadarm2 robotic arm

Solar array

Solar array

Solar array

Solar array

ESP-1

Destiny laboratory

Kibō logistics cargo bay

IDA 3 docking adapter

Cargo spacecraft berthing port

PMA 3 docking port

Kibō robotic arm

External payloads

Columbus laboratory

Harmony Node 2

Kibō laboratory

Kibō external platform

PMA 2 docking port

IDA 2 docking adapter

Axiom modules

Pressurised modulesedit

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Zaryaedit

Unityedit

Zvezdaedit

Destinyedit

Questedit

Pirs and Poiskedit

Pirs (Russian: Пирс, lit. 'Pier') and Poisk (Russian: По́иск, lit. 'Search') are Russian airlock modules, each having two identical hatches. An outward-opening hatch on the Mir space station failed after it swung open too fast after unlatching, because of a small amount of air pressure remaining in the airlock. All EVA hatches on the ISS open inwards and are pressure-sealing. Pirs was used to store, service, and refurbish Russian Orlan suits and provided contingency entry for crew using the slightly bulkier American suits. The outermost docking ports on both airlocks allow docking of Soyuz and Progress spacecraft, and the automatic transfer of propellants to and from storage on the ROS.

Pirs 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. Poisk was launched on 10 November 2009 attached to a modified Progress spacecraft, called Progress M-MIM2, on a Soyuz-U rocket from Launch Pad 1 at the Baikonur Cosmodrome in Kazakhstan.

Harmonyedit

Tranquilityedit

Columbusedit

Kibōedit

Cupolaedit

Rassvetedit

Leonardoedit

Bigelow Expandable Activity Moduleedit

International Docking Adapteredit

Unpressurised elementsedit

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. The ITS consists of ten separate segments forming a structure 108.5 metres (356 ft) long.

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). 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. Several shuttle missions were dedicated to the delivery of ORUs, including STS-129, STS-133 and STS-134. As of January 2011update, only one other mode of transportation of ORUs had been utilised—the Japanese cargo vessel HTV-2—which delivered an FHRC and CTC-2 via its Exposed Pallet (EP).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, and a facility on the European Columbus laboratory provides power and data connections for experiments such as the European Technology Exposure Facility and the Atomic Clock Ensemble in Space. A remote sensing instrument, SAGE III-ISS, was delivered to the station in February 2017 aboard CRS-10, and the NICER experiment was delivered aboard CRS-11 in June 2017. 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.

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.

Robotic arms and cargo cranesedit

The Integrated Truss Structure 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 around to perform tasks.
• 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.
• 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.

A grapple fixture was added to Zarya on STS-134 to enable Canadarm2 to inchworm itself onto the Russian Orbital Segment. 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. 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, was launched on STS-124 and is attached to the Kibō Pressurised Module. 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.

Planned componentsedit

European Robotic Armedit

The European Robotic Arm, which will service the Russian Orbital Segment, will be launched alongside the Multipurpose Laboratory Module in 2020. 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).

Naukaedit

Nauka (Russian: Нау́ка, lit. 'Science'), also known as the Multipurpose Laboratory Module (MLM), (Russian: Многофункциональный лабораторный модуль, or МЛМ), is a component of the ISS that has yet to be launched into space. The MLM is funded by the Roscosmos State Corporation. 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. Planners now anticipate that Nauka will dock at Zvezda's nadir port, replacing the Pirs module.

The launch of Nauka, initially planned for 2007, has been repeatedly delayed for various reasons. As of May 2020update, the launch to the ISS is assigned to no earlier than spring 2021. After this date, the warranties of some of Nauka's systems will expire.

Prichaledit

Prichal, also known as Uzlovoy Module or UM (Russian: Узловой Модуль Причал, lit. 'Nodal Module Berth'), is a 4-tonne (8,800 lb) ball-shaped module that will allow docking of two scientific and power modules during the final stage of the station assembly, and provide the Russian segment additional docking ports to receive Soyuz MS and Progress MS spacecraft. UM is due to be launched in the third quarter of 2021. It will be integrated with a special version of the Progress cargo ship and launched by a standard Soyuz rocket, docking to the nadir port of the Nauka module. One port is equipped with an active hybrid docking port, which enables docking with the MLM module. The remaining five ports are passive hybrids, enabling docking of Soyuz and Progress vehicles, as well as heavier modules and future spacecraft with modified docking systems. The node module was intended to serve as the only permanent element of the cancelled OPSEK.

Science Power Modules 1 and 2edit

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 are planned to arrive at the ISS not earlier than 2024. They will dock to the Prichal module, which is planned to be attached to the Nauka module. If Nauka is cancelled, then Prichal, SPM-1, and SPM-2 would dock at the zenith port of the Zvezda module. SPM-1 and SPM-2 would also be required components for the OPSEK space station.

Bishop Airlock Moduleedit

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

Axiom segmentedit

In January 2020, NASA awarded Axiom Space a contract to build a commercial module for the ISS with a launch date of 2024. 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.

Cancelled componentsedit

Several modules 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. The US Habitation Module would have served as the station's living quarters. Instead, the living quarters are now spread throughout the station. The US Interim Control Module and ISS Propulsion Module would have replaced the functions of Zvezda in case of a launch failure. Two Russian Research Modules were planned for scientific research. They would have docked to a Russian Universal Docking Module. The Russian Science Power Platform would have supplied power to the Russian Orbital Segment independent of the ITS solar arrays.