Modular principle is taken as a basis of the ISS architecture. ISS assembly is implemented by means of replenishment a successive module or block to the station by attaching it to the modules already delivered to orbit. The ISS incorporates the following modules:
Zarya (also known as the Functional Cargo Block or FGB): the first of ISS modules delivered to orbit. Zarya weighs over 20 tons. It is 12.6 meters long and has diameter of 4 meters. The module is equipped with large solar arrays and jet-propulsion engines for ISS orbit correction. The module is expected to be operational for at least 15 years. American financial contribution to Zarya is about $250 million, Russian investment is more than $150 million.
An anti-debris or anti-micrometeoroid shield which was installed according to the requirement of the American part is mounted on the Zvezda module;
Zvezda Service Module holds flight control systems, life-support systems, power and information management centre as well as cabins for cosmonauts. The module weights 24 tons. It is divided into five compartments and has four docking units. All its systems and blocks are made in Russia except for the onboard computer complex developed with participation of European and American experts. The module was launched to orbit in 2000;
Mini-Research Modules or Small Research Modules: two Russian cargo modules named Poisk (Search) and Rassvet (Dawn) intended to store equipment necessary to carry out scientific experiments. Poisk is docked to the zenith docking unit of the Zvezda module whereas Rassvet is connected to the nadir port of Zarya;
MLM or Multipurpose Laboratory Module, is capable to maintain conditions for keeping scientific equipment, carrying out experiments, short-term habitation of crewmembers. It also supports operations of the European Robotic Arm (ERA);
ERA is designed to displace the equipment located outside the station. It will be attached to MLM;
Pressurized Adapter is an airtight mating gathering designed to connect ISS modules against each other and serve as docking device for Space Shuttles;
Tranquility: an ISS module which performs life-support functions. It hosts systems for water refinement, air regeneration, waste recovery, etc. Tranquility is connected to the Unity module;
Unity: the first of the three ISS connecting modules serving as a docking node and an electric power switching center for modules Quest, Node3, truss peace Z1 and transport vehicles docking to it via PMA 3;
Pirs: a docking port designed for docking of the Russian Progress and Soyuz vehicles. It is installed on the Zvezda module;
ESP (External Stowage Platforms): three external unpressurized platforms meant only for cargo and equipment storage;
ITS (Integrated Truss Structure): a structure with mountings for solar arrays , radiators and remote manipulators. It is also designed for non tight storage of cargo and equipment;
Canadarm2 or Mobile Servicing System (MSS): a roboticmanipulator system serving as the main tool for transport vehicles unloading and transfer of external equipment;
Dextre (also known as the Special Purpose Dexterous Manipulator) is a two armed telemanipulator designed for displacement of equipment located outside the station;
Quest: the primary airlock designed for extravehicular astronaut spacewalk. It has denitrogenation (nitrogen removal from human blood) capability;
Harmony, also known as Node 2, is an ISS connection module serving as a docking node and an electric power commutation switch for the three scientific laboratories and transport vehicles docking to it through PMA 3. It contains complementary life-support systems;
Columbus is a European science laboratory which besides scientific equipment hosts network switchboards (hubs) providing connection between ISS pieces of computer equipment The module is docked to the Harmony module;
Destiny module: the primary operating facility for U.S. research payloads aboard the ISS. It is attached to the Harmony module;
Kibo is a Japanese science module consisting of three compartments and one principal remote manipulator. It is the biggest ISS module. It is designed to perform physical, biological, biotechnological and other research experiments in pressurized and unpressurized environments. Besides due to special design it allows to carry out unplanned experiments. Kibo is docked to the Harmony module;
Cupola: a transparent observatory module which hosts the remote manipulator operating console. It is also a place for recreation where crew members can observe space and the Earth. The module is installed on the node module Tranquility;
ExPRESS Logistics Carriers (ELCs): four unpressurised platforms located on the P3 and S3 trusses. They are designed to accommodate the equipment necessary to perform science experiments in vacuum. ELCs provide processing and transfer of experiment-generated data to the station via a high-rate data link.
Except for the components listed above, there are three pressurized logistics modules: Leonardo, Raffaello and Donatello. They are periodically delivered into orbit to resupply the ISS with necessary scientific equipment and other cargoes. The modules having common name Multipurpose Pressurized Logistics Modules are delivered in the payload bay of a Space shuttle and docked to the Unity module.