Mir (Russian: Мир, IPA: [ˈmʲir]; lit. 'peace' or 'world') was a space station operated in low Earth orbit from 1986 to 2001, first by the Soviet Union and later by the Russian Federation. Mir was the first modular space station and was assembled in orbit from 1986 to 1996. At the time it was the largest artificial satellite in orbit, only being succeeded by the International Space Station (ISS) after Mir's deorbiting in 2001. The station served as a microgravity research laboratory in which crews conducted experiments in biology, human biology, physics, astronomy, meteorology, and spacecraft systems with a goal of developing technologies required for permanent occupation of space.
Mir was the first continuously inhabited long-term research station in orbit and previously held the record for the longest continuous human presence in space at 3,644 days, until it was surpassed by the ISS in 2010. It holds the record for the longest single human spaceflight, Valeri Polyakov, who spent 437 days on the station from 1994 until 1995. Mir's typical crew size was 3, though larger short-term crews made an appearance, peaking at ten during STS-71. Occupied for twelve and a half years out of its fifteen-year lifespan, 105 cosmonauts and astronauts from 12 different nations visited the station, and conducted 80 spacewalks.
Mir was the next stage of the Soviet space programme's station development, following the success of six crewed single-module stations under the Salyut programme; its inaugural flight, Soyuz T-15, also conducted the only station-to-station trip, docking with Salyut 7 during its mission. Consisting of seven pressurised modules and several unpressurised components, its initial Core Module was launched in 1986. Proton rockets launched all components, except the Docking Module, which was installed by the Space Shuttle on STS-74. Power was provided by several photovoltaic arrays attached directly to the modules. The station was maintained at an orbit between 296 and 421 km (184 and 262 mi) altitude, completing 15.7 orbits per day at an inclination of 51.6°.
Initially, the station was operated by NPO Energia with subcontracting to KB Salyut. Following the dissolution of the Soviet Union, Mir was operated by the Russian Federal Space Agency (RKA). Most of the station's occupants were Soviet/Russian; through international collaborations such as the Interkosmos, Euromir and Shuttle–Mir programmes, the station was made accessible to space travellers from several Asian, European and North American nations. Mir was deorbited in March 2001 after funding was cut off. The cost of the Mir programme was estimated by former RKA General Director Yuri Koptev in 2001 as $4.2 billion over its lifetime (including development, assembly and orbital operation). As of 2026, five of the ten longest human spaceflights ever were aboard Mir.
Mir was authorised by a 17 February 1976 decree, to design an improved model of the Salyut space stations. Four Salyut space stations had been launched since 1971; three more were launched during Mir's development. It was planned that the station's core module (DOS-7 and the backup DOS-8) would have a total of four docking ports: one at each end of the station (as in the Salyut stations) and one on each side of a docking sphere at the front of the station to allow more modules to expand the station's capabilities. By August 1978, this had evolved to the final configuration: one aft port and five ports in a spherical compartment at the fore.
It was originally planned that the ports would connect to 7.5-tonne (8.3-short-ton) modules derived from the Soyuz spacecraft. These modules would have used a Soyuz propulsion module, as used in Soyuz and Progress; and the descent and orbital modules would have been replaced with a long laboratory module. Following a February 1979 governmental resolution, the programme was consolidated with Vladimir Chelomei's crewed Almaz military space station programme. The docking ports were reinforced to accommodate 20-tonne (22-short-ton) space-station modules based on the TKS spacecraft. NPO Energia was responsible for the overall space station, with work subcontracted to KB Salyut, due to ongoing work on the Energia rocket, Salyut 7, Soyuz-T, and Progress spacecraft. KB Salyut began work in 1979, and drawings were released in 1982 and 1983. New systems incorporated into the station included gyrodyne flywheels (taken from Almaz), Kurs automatic rendezvous system, Luch satellite communications system, Elektron oxygen generators, and Vozdukh carbon dioxide scrubbers and the Salyut 5B digital flight control computer, although the Salyut 5B computer was not installed until the delivery of the Kvant-2 module.
In early 1984, work on Mir had halted while all resources were being put into the Buran programme to prepare the Buran spacecraft for flight testing. Funding resumed in early 1984 when Valentin Glushko was ordered by the Central Committee's Secretary for Space and Defence to orbit Mir by early 1986, in time for the 27th Communist Party Congress.
It was clear that the planned processing flow could not be followed and still meet the 1986 launch date. It was decided on Cosmonaut's Day (12 April) 1985 to ship the flight model of the base block to the Baikonur Cosmodrome and conduct the systems testing and integration there. The module arrived at the launch site on 6 May, with 1100 of 2500 cables requiring rework based on the results of tests to the ground test model at Khrunichev. In October, the base block was rolled outside its cleanroom to carry out communications tests. The first launch attempt on 16 February 1986 was scrubbed when the spacecraft communications failed, but the second launch attempt, on 19 February 1986 at 21:28:23 UTC, was successful, meeting the political deadline.
The assembly of Mir began on 20 February 1986 with the launch of the Mir core module. Four out of the six modules which were later added (Kvant-2 in 1989, Kristall in 1990, Spektr in 1995 and Priroda in 1996) followed the same sequence to be added to the Mir station:
The module would launch independently on a Proton-K rocket, and rendezvous with the station automatically. It would then dock with the forward (-X) docking node on the core module, and then use its Lyappa arm to attach itself to a fixture on the core module, then lift the module away and rotate the arm to another port, before mating and docking with the new docking port. The node was equipped with only two Konus drogues, which were required for dockings. This meant that, prior to the arrival of each new module, the node would have to be depressurised to allow spacewalking cosmonauts to manually relocate the drogue to the next port to be occupied.
The other two modules, Kvant-1 and the docking module did not follow this procedure.
Kvant-1 was originally designed to be installed on the Salyut 7 station, and did not feature a propulsion system of its own. Instead, Kvant-1 would be assisted by a space tug based on the TKS spacecraft, which delivered the module to the aft docking node of the core module instead of the forward docking node. Kvant-1 successfully docked on 11 April 1987, and the tug disposed of itself the next day.
The docking module was launched on STS-74 by Space Shuttle Atlantis on 12 November 1995, and was mated to the orbiter's docking system via the Canadarm. Atlantis then docked, via the module, to Kristall, then left the module behind when it undocked later in the mission. Various other external components, including two Strela cranes, three truss structures and several experiments and other unpressurised elements were also mounted to the exterior of the station over the course of the station's history.
The station's assembly marked the beginning of the third generation of space station design, being the first to consist of more than one primary spacecraft (thus opening a new era in space architecture). First generation stations such as Salyut 1 and Skylab had monolithic designs, consisting of one module with no resupply capability; the second generation stations Salyut 6 and Salyut 7 comprised a monolithic station with two ports to allow consumables to be replenished by cargo spacecraft such as Progress. The capability of Mir to be expanded with add-on modules meant that each could be designed with a specific purpose in mind (for instance, the core module functioned largely as living quarters), thus eliminating the need to install all the station's equipment in one module.