Mir

Origins

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.

Station structure

Assembly

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.

Pressurised modules

In its completed configuration, the space station consisted of seven different modules, each launched into orbit separately over a period of ten years by either Proton-K rockets or Space Shuttle Atlantis.

Unpressurised elements

In addition to the pressurised modules, Mir featured several external components. The largest component was the Sofora girder, a large scaffolding-like structure consisting of 20 segments which, when assembled, projected 14 metres from its mount on Kvant-1. A self-contained thruster block, the VDU (Vynosnaya Dvigatyelnaya Ustanovka), was mounted on the end of Sofora and was used to augment the roll-control thrusters on the core module. The VDU's increased distance from Mir's axis allowed an 85% decrease in fuel consumption, reducing the amount of propellant required to orient the station. A second girder, Rapana, was mounted aft of Sofora on Kvant-1. This girder, a small prototype of a structure intended to be used on Mir-2 to hold large parabolic dishes away from the main station structure, was 5 metres long and used as a mounting point for externally mounted exposure experiments.

To assist in moving objects around the exterior of the station during EVAs, Mir featured two Strela cargo cranes mounted to the sides of the core module, used for moving spacewalking cosmonauts and parts. The cranes consisted of telescopic poles assembled in sections which measured around 1.8 metres (6 ft) when collapsed, but when extended using a hand crank were 14 metres (46 ft) long, meaning that all of the station's modules could be accessed during spacewalks.

Each module was fitted with external components specific to the experiments that were carried out within that module, the most obvious being the Travers antenna mounted to Priroda. This synthetic aperture radar consisted of a large dish-like framework mounted outside the module, with associated equipment within, used for Earth observations experiments, as was most of the other equipment on Priroda, including various radiometers and scan platforms. Kvant-2 also featured several scan platforms and was fitted with a mounting bracket to which the cosmonaut manoeuvring unit, or Ikar, was mated. This backpack was designed to assist cosmonauts in moving around the station and the planned Buran in a manner similar to the US Manned Maneuvering Unit, but it was only used once, during EO-5.

In addition to module-specific equipment, Kvant-2, Kristall, Spektr and Priroda were each equipped with one Lyappa arm, a robotic arm which, after the module had docked to the core module's forward port, grappled one of two fixtures positioned on the core module's docking node. The arriving module's docking probe was then retracted, and the arm raised the module so that it could be pivoted 90° for docking to one of the four radial docking ports.

Power supply

Photovoltaic arrays powered Mir. The station used a 28 volt DC supply which provided 5-, 10-, 20- and 50-amp taps. When the station was illuminated by sunlight, several solar arrays mounted on the pressurised modules provided power to Mir's systems and charged the nickel-cadmium storage batteries installed throughout the station. The arrays rotated in only one degree of freedom over a 180° arc, and tracked the Sun using Sun sensors and motors installed in the array mounts. The station itself also had to be oriented to ensure optimum illumination of the arrays. When the station's all-sky sensor detected that Mir had entered Earth's shadow, the arrays were rotated to the optimum angle predicted for reacquiring the Sun once the station passed out of the shadow. The batteries, each of 60 Ah capacity, were then used to power the station until the arrays recovered their maximum output on the day side of Earth.

The solar arrays themselves were launched and installed over a period of eleven years, more slowly than originally planned, with the station continually suffering from a shortage of power as a result. The first two arrays, each 38 m2 (410 ft2) in area, were launched on the core module, and together provided a total of 9 kW of power. A third, dorsal panel was launched on Kvant-1 and mounted on the core module in 1987, providing a further 2.5 kW from a 22 m2 (240 ft2) area. Kvant-2, launched in 1989, provided two 10 metres (33 feet) long panels which supplied 3.5 kW each, whilst Kristall was launched with two collapsible, 15 metres (49 feet) long arrays (providing 4 kW each) which were intended to be moved to Kvant-1 and installed on mounts which were attached during a spacewalk by the EO-8 crew in 1991.

This relocation was begun in 1995, when the panels were retracted and the left panel installed on Kvant-1. By this time all the arrays had degraded and were supplying much less power. To rectify this, Spektr (launched in 1995), which had initially been designed to carry two arrays, was modified to hold four, providing a total of 126 m2 (1,360 ft2) of array with a 16 kW supply. Two further arrays were flown to the station on board the Space Shuttle Atlantis during STS-74, carried on the docking module. The first of these, the Mir cooperative solar array, consisted of American photovoltaic cells mounted on a Russian frame. It was installed on the unoccupied mount on Kvant-1 in May 1996 and was connected to the socket that had previously been occupied by the core module's dorsal panel, which was by this point barely supplying 1 kW. The other panel, originally intended to be launched on Priroda, replaced the Kristall panel on Kvant-1 in November 1997, completing the station's electrical system.

Orbit control

Mir was maintained in a near circular orbit with an average perigee of 354 km (220 mi) and an average apogee of 374 km (232 mi), travelling at an average speed of 27,700 km/h (17,200 mph) and completing 15.7 orbits per day. As the station constantly lost altitude because of slight atmospheric drag, it needed to be boosted to a higher altitude several times each year. This boost was generally performed by Progress resupply vessels, although during the Shuttle-Mir programme the task was performed by US Space Shuttles, and, prior to the arrival of Kvant-1, the engines on the core module could also accomplish the task.

Attitude control was maintained by a combination of two mechanisms; to hold a set attitude, a system of twelve control moment gyroscopes (CMGs, or "gyrodynes") rotating at 10,000 rpm kept the station oriented, six CMGs being located in each of the Kvant-1 and Kvant-2 modules. When the attitude of the station needed to be changed, the gyrodynes were disengaged, thrusters (including those mounted directly to the modules, and the VDU thruster used for roll control mounted to the Sofora girder) were used to attain the new attitude and the CMGs were reengaged. This was done fairly regularly depending on experimental needs; for instance, Earth or astronomical observations required that the instrument recording images be continuously aimed at the target, and so the station was oriented to make this possible. Conversely, materials processing experiments required the minimisation of movement on board the station, and so Mir would be oriented in a gravity gradient attitude for stability. Prior to the arrival of the modules containing these gyrodynes, the station's attitude was controlled using thrusters located on the core module alone, and, in an emergency, the thrusters on docked Soyuz spacecraft could be used to maintain the station's orientation.

Communications

Radio communications provided telemetry and scientific data links between Mir and the RKA Mission Control Centre (TsUP). Radio links were also used during rendezvous and docking procedures and for audio and video communication between crew members, flight controllers and family members. As a result, Mir was equipped with several communication systems used for different purposes. The station communicated directly with the ground via the Lira antenna mounted to the core module. The Lira antenna also had the capability to use the Luch data relay satellite system (which fell into disrepair in the 1990s) and the network of Soviet tracking ships deployed in various locations around the world (which also became unavailable in the 1990s). UHF radio was used by cosmonauts conducting EVAs. UHF was also employed by other spacecraft that docked to or undocked from the station, such as Soyuz, Progress, and the Space Shuttle, to receive commands from the TsUP and Mir crew members via the TORU system.

Microgravity

At Mir's orbital altitude, the force of Earth's gravity was 88% of sea level gravity. While the constant free fall of the station offered a perceived sensation of weightlessness, the onboard environment was not one of weightlessness or zero gravity. The environment was often described as microgravity. This state of perceived weightlessness was not perfect, being disturbed by five separate effects:

The drag resulting from the residual atmosphere;

Vibratory acceleration caused by mechanical systems and the crew on the station;

Orbital corrections by the on-board gyroscopes (which spun at 10,000 rpm, producing vibrations of 166.67 Hz) or thrusters;

Tidal forces. Parts of Mir that weren't at the exact the same distance from Earth as other parts tended to follow separate orbits. As each point was physically part of the station, remedying this was impossible, and so each component was subject to small accelerations from tidal forces;

The differences in orbital plane between different locations on the station.

Life support

Mir's environmental control and life support system (ECLSS) provided or controlled atmospheric pressure, fire detection, oxygen levels, waste management and water supply. The highest priority for the ECLSS was the station's atmosphere, but the system also collected, processed, and stored waste and water produced and used by the crew—a process that recycles fluid from the sink, toilet, and condensation from the air. The Elektron system generated oxygen electrolytically, venting hydrogen to space. Bottled oxygen and solid fuel oxygen generation (SFOG) canisters, a system known as Vika, provided backup. Carbon dioxide was removed from the air by the Vozdukh system. Other byproducts of human metabolism, such as methane from the intestines and ammonia from sweat, were removed by activated charcoal filters. Similar systems are presently used on the ISS.

The atmosphere on Mir was similar to Earth's. Normal air pressure on the station was 101.3 kPa (14.7 psi); the same as at sea level on Earth. An Earth-like atmosphere offers benefits for crew comfort.

International cooperation

Interkosmos

Interkosmos (Russian: Интеркосмос) was a Soviet space exploration programme which allowed members from foreign countries allied with the Soviet Union to participate in crewed and uncrewed space exploration missions. Participation was also made available to governments of countries such as France and India.

Only the last three of the programme's 14 missions consisted of an expedition to Mir but none resulted in an extended stay in the station:

Muhammed Faris – EP-1 (1987) Syria Turkey

Aleksandr Panayatov Aleksandrov – EP-2 (1988) Bulgaria

Abdul Ahad Mohmand – EP-3 (1988) Afghanistan

European involvement

Various European astronauts visited Mir as part of several cooperative programmes, on both the Soyuz and the Space Shuttle:

Jean-Loup Chrétien – Aragatz (1988) France

Helen Sharman – Project Juno (1991) UK

Franz Viehböck – Austromir '91 (1991) Austria

Klaus-Dietrich Flade – Mir '92 (1992) Germany

Michel Tognini – Antarès (1992) France

Jean-Pierre Haigneré – Altair (1993) France

Ulf Merbold – Euromir '94 (1994) Germany

Thomas Reiter – Euromir '95 (1995) Germany

Claudie Haigneré – Cassiopée (1996) France

Reinhold Ewald – Mir '97 (1997) Germany

Jean-François Clervoy – STS-84 (1997) France

Jean-Loup Chrétien – STS-86 (1997) France

Léopold Eyharts – Pégase (1998) France

Jean-Pierre Haigneré – Perseus (1999) France

Ivan Bella – Stefanik (1999) Slovakia

Shuttle–Mir program

In the early 1980s, NASA planned to launch a modular space station called Freedom as a counterpart to Mir, while the Soviets were planning to construct Mir-2 in the 1990s as a replacement for the station. Because of budget and design constraints, Freedom never progressed past mock-ups and minor component tests and, with the fall of the Soviet Union and the end of the Space Race, the project was nearly cancelled entirely by the United States House of Representatives. The post-Soviet economic chaos in Russia also led to the cancellation of Mir-2, though only after its base block, DOS-8, had been constructed. Similar budgetary difficulties were faced by other nations with space station projects, which prompted the US government to negotiate with European states, Russia, Japan, and Canada in the early 1990s to begin a collaborative project. In June 1992, American president George H. W. Bush and Russian president Boris Yeltsin agreed to cooperate on space exploration. The resulting Agreement between the United States of America and the Russian Federation Concerning Cooperation in the Exploration and Use of Outer Space for Peaceful Purposes called for a short joint space programme with one American astronaut deployed to the Russian space station Mir and two Russian cosmonauts deployed to a Space Shuttle.

In September 1993, US vice president Al Gore Jr., and Russian prime minister Viktor Chernomyrdin announced plans for a new space station, which eventually became the ISS. They also agreed, in preparation for this new project, that the United States would be heavily involved in the Mir programme as part of an international project known as the Shuttle–Mir Programme. The project, sometimes called "Phase One", was intended to allow the United States to learn from Russian experience in long-duration spaceflight and to foster a spirit of cooperation between the two nations and their space agencies, the US National Aeronautics and Space Administration (NASA) and the Russian Federal Space Agency (Roskosmos). The project prepared the way for further cooperative space ventures, specifically, "Phase Two" of the joint project, the construction of the ISS. The programme was announced in 1993; the first mission started in 1994, and the project continued until its scheduled completion in 1998. Eleven Space Shuttle missions, a joint Soyuz flight, and almost 1000 cumulative days in space for US astronauts occurred over the course of seven long-duration expeditions.

Other visitors

Toyohiro Akiyama – Kosmoreporter (1990) Japan

Chris Hadfield – STS-74 (1995) Canada

A British con artist, Peter Rodney Llewellyn, almost visited Mir in 1999 on a private contract after promising US$100 million for the privilege.

Life on board

Inside, the 130-tonne (140-short-ton) Mir was crowded with hoses, cables and scientific instruments—as well as articles of everyday life, such as photos, children's drawings, books and a guitar. It commonly housed three crew members, but was capable of supporting as many as six for short stays. The station was designed to remain in orbit for around five years; it remained in orbit for fifteen. As a result, NASA astronaut John Blaha reported that, with the exception of Priroda and Spektr, which were added late in the station's life, Mir did look used; which is a result of its aged condition.

Crew schedule

The time zone used on board Mir was Moscow Time (MSK; UTC+03). The windows were covered during night hours to give the impression of darkness because the station experienced 16 sunrises and sunsets a day. A typical day for the crew began with a wake-up at 08:00 MSK, followed by two hours of personal hygiene and breakfast. Work was conducted from 10:00 until 13:00, followed by an hour of exercise and an hour's lunch break. Three more hours of work and another hour of exercise followed lunch, and the crews began preparing for their evening meal at about 19:00. The cosmonauts were free to do as they wished in the evening, and largely worked to their own pace during the day.

In their spare time, crews were able to catch up with work, observe the Earth below, respond to letters, drawings, and other items brought from Earth (and give them an official stamp to show they had been aboard Mir), or make use of the station's ham radio. Two amateur radio call signs, U1MIR and U2MIR, were assigned to Mir in the late 1980s, allowing amateur radio operators on Earth to communicate with the cosmonauts. The station was also equipped with a supply of books and films for the crew to read and watch.

NASA astronaut Jerry Linenger related how life on board Mir was structured and lived according to the detailed itineraries provided by ground control. Every second on board was accounted for and all activities were timetabled. After working some time on Mir, Linenger came to feel that the order in which his activities were allocated did not represent the most logical or efficient order possible for these activities. He decided to perform his tasks in an order that he felt enabled him to work more efficiently, be less fatigued, and suffer less from stress. Linenger noted that his fellow astronauts on Mir did not "improvise" in this way, and as a medical doctor he observed the effects of stress on his companions that he believed was the outcome of following an itinerary without making modifications to it. Despite this, he commented that his fellow astronauts performed all their tasks in a supremely professional manner.

Astronaut Shannon Lucid, who set the record for longest stay in space by a woman while aboard Mir (surpassed by Sunita Williams 11 years later on the ISS), also commented about working aboard Mir: "I think going to work on a daily basis on Mir is very similar to going to work on a daily basis on an outstation in Antarctica. The big difference with going to work here is the isolation, because you really are isolated. You don't have a lot of support from the ground. You really are on your own."

Exercise

The most significant adverse effects of long-term weightlessness are muscle atrophy and deterioration of the skeleton, or spaceflight osteopenia. Other significant effects include fluid redistribution, a slowing of the cardiovascular system, decreased production of red blood cells, balance disorders, and a weakening of the immune system. Lesser symptoms include loss of body mass, nasal congestion, sleep disturbance, excess flatulence, and puffiness of the face. These effects begin to reverse quickly upon return to the Earth.

To prevent some of these effects, the station was equipped with two treadmills (in the core module and Kvant-2) and a stationary bicycle (in the core module); each cosmonaut was to cycle the equivalent of 10 kilometres (6.2 mi) and run the equivalent of 5 kilometres (3.1 mi) per day. Cosmonauts used bungee cords to strap themselves to the treadmill. Researchers believe that exercise is a good countermeasure for the bone and muscle density loss that occurs in low-gravity situations.

Hygiene

There were two space toilets (ASUs) on Mir, located in the core module and Kvant-2. They used a fan-driven suction system similar to the Space Shuttle Waste Collection System. The user is first fastened to the toilet seat, which was equipped with spring-loaded restraining bars to ensure a good seal. A lever operated a powerful fan and a suction hole slid open: the air stream carried the waste away. Solid waste was collected in individual bags which were stored in an aluminium container. Full containers were transferred to Progress spacecraft for disposal. Liquid waste was evacuated by a hose connected to the front of the toilet, with anatomically appropriate "urine funnel adapters" attached to the tube so both men and women could use the same toilet. Waste was collected and transferred to the Water Recovery System, where it could be recycled back into drinking water, but was usually used to produce oxygen via the Elektron system.

Mir featured a shower, the Bania, located in Kvant-2. It was an improvement on the units installed in previous Salyut stations, but proved difficult to use due to the time required to set up, use, and stow. The shower, which featured a plastic curtain and fan to collect water via an airflow, was later converted into a steam room; it eventually had its plumbing removed and the space was reused. When the shower was unavailable, crew members washed using wet wipes, with soap dispensed from a toothpaste tube-like container, or using a washbasin equipped with a plastic hood, located in the core module. Crews were also provided with rinse-less shampoo and edible toothpaste to save water.

On a 1998 visit to Mir, bacteria and larger organisms were found to have proliferated in water globules formed from moisture that had condensed behind service panels.

Sleeping in space

The station provided two permanent crew quarters, the Kayutkas, phonebooth sized boxes set towards the rear of the core module, each featuring a tethered sleeping bag, a fold-out desk, a porthole, and storage for personal effects. Visiting crews had no allocated sleep module, instead attaching a sleeping bag to an available space on a wall; US astronauts installed themselves within Spektr until a collision with a Progress spacecraft caused the depressurisation of that module. It was important that crew accommodations be well ventilated; otherwise, astronauts could wake up oxygen-deprived and gasping for air, because a bubble of their own exhaled carbon dioxide had formed around their heads.

Food and drink

Most of the food eaten by station crews was frozen, refrigerated or canned. Meals were prepared by the cosmonauts, with the help of a dietitian, before their flight to the station. The diet was designed to provide around 300 grams (11 oz) of protein, 130 grams (4.6 oz) of fat and 330 grams (12 oz) of carbohydrates per day, in addition to appropriate mineral and vitamin supplements. Meals were spaced out through the day to aid assimilation. Canned food such as jellied beef tongue was placed into a niche in the core module's table, where it could be warmed in 5–10 minutes. Usually, crews drank tea, coffee and fruit juices, but, unlike the ISS, the station also had a supply of cognac and vodka for special occasions.

Microbiological environmental hazards

In the 1990s, 90 species of micro-organisms were found inside Mir, four years after the station's launch. By the time of its decommissioning in 2001, the number of known different microorganisms had grown to 140. As space stations get older, the problems with contamination get worse. Moulds that develop aboard space stations can produce acids that degrade metal, glass and rubber. The moulds in Mir were found growing behind panels and inside air-conditioning equipment. The moulds also caused a foul smell, which was often cited as visitors' strongest impression. Researchers in 2018 reported, after detecting the presence on the International Space Station (ISS) of five Enterobacter bugandensis bacterial strains, none pathogenic to humans, that microorganisms on ISS should be carefully monitored to continue ensuring a medically healthy environment for the astronauts.

Some biologists were concerned about the mutant fungi being a major microbiological hazard for humans, and reaching Earth in the splashdown, after having been in an isolated environment for 15 years. On the other hand, some scientists are conducting research on whether this situation can be used for life in space. Scientists have discovered that fungi could actually assist space travel and detect liveable environments for humankind in space. In fact, these resilient and frequently underestimated organisms might hold the key to our future on other planets. Fungi play a dramatic role in creating innovative and sustainable building materials. Most fungi possess mycelia, hair-like root structures that grow and spread across surfaces. As mycelia expand, they bind surrounding materials, as wood chips, sawdust, or regolith (the loose material covering solid rock on planetary bodies like the Moon or Mars). This growth process results in a dense, interconnected network that creates a remarkably strong and durable substance. The resulting mycelium-based material offers notable thermal insulation and radiation protection, making it an ideal candidate for construction, particularly in severe environments like outer space or other interplanetary habitats.

Station operations

Expeditions

Mir was visited by a total of 28 long-duration or "principal" crews, each of which was given a sequential expedition number formatted as EO-X. Expeditions varied in length (from the 72-day flight of the crew of EO-28 to the 437-day flight of Valeri Polyakov), but generally lasted around six months. Principal expedition crews consisted of two or three crew members, who often launched as part of one expedition but returned with another (Polyakov launched with EO-14 and landed with EO-17). The principal expeditions were often supplemented with visiting crews who remained on the station during the week-long handover period between one crew and the next before returning with the departing crew, the station's life support system being able to support a crew of up to six for short periods. The station was occupied for a total of four distinct periods; 12 March–16 July 1986 (EO-1), 5 February 1987 – 27 April 1989 (EO-2–EO-4), the record-breaking run from 5 September 1989 – 28 August 1999 (EO-5–EO-27), and 4 April–16 June 2000 (EO-28). By the end, it had been visited by 104 different people from 12 different nations, making it the most visited spacecraft in history (a record later surpassed by the ISS).

Due to pressure to launch the station on schedule, mission planners were left without Soyuz spacecraft or modules to launch to the station at first. It was decided to launch Soyuz T-15 on a dual mission to both Mir and Salyut 7.

Leonid Kizim and Vladimir Solovyov first docked with Mir on 15 March 1986. During their nearly 51-day stay on Mir, they brought the station online and checked its systems. They unloaded two Progress spacecraft launched after their arrival, Progress 25 and Progress 26.

On 5 May 1986, they undocked from Mir for a day-long journey to Salyut 7. They spent 51 days there and gathered 400 kg of scientific material from Salyut 7 for return to Mir. While Soyuz T-15 was at Salyut 7, the uncrewed Soyuz TM-1 arrived at the unoccupied Mir and remained for 9 days, testing the new Soyuz TM model. Soyuz T-15 redocked with Mir on 26 June and delivered the experiments and 20 instruments, including a multichannel spectrometer. The EO-1 crew spent their last 20 days on Mir conducting Earth observations before returning to Earth on 16 July 1986, leaving the new station unoccupied.

The second expedition to Mir, EO-2, launched on Soyuz TM-2 on 5 February 1987. During their stay, the Kvant-1 module, launched on 30 March 1987, arrived. It was the first experimental version of a planned series of '37K' modules scheduled to be launched to Mir on Buran. Kvant-1 was originally planned to dock with Salyut 7; due to technical problems during its development, it was reassigned to Mir. The module carried the first set of six gyroscopes for attitude control. The module also carried instruments for X-ray and ultraviolet astrophysical observations.

Visiting spacecraft

Mir was primarily supported by the Russian Soyuz and Progress spacecraft and had two ports available for docking them. Initially, the fore and aft ports of the core module could be used for dockings, but following the permanent berthing of Kvant-1 to the aft port in 1987, the rear port of the new module took on this role from the core module's aft port. Each port was equipped with the plumbing required for Progress cargo ferries to replace the station's fluids and also the guidance systems needed to guide the spacecraft for docking. Two such systems were used on Mir; the rear ports of both the core module and Kvant-1 were equipped with both the Igla and Kurs systems, whilst the core module's forward port featured only the newer Kurs.

Soyuz spacecraft provided personnel access to and from the station allowing for crew rotations and cargo return, and also functioned as a lifeboat for the station, allowing for a relatively quick return to Earth in the event of an emergency. Two models of Soyuz flew to Mir; Soyuz T-15 was the only Igla-equipped Soyuz-T to visit the station, whilst all other flights used the newer, Kurs-equipped Soyuz-TM. A total of 31 (30 crewed, 1 uncrewed) Soyuz spacecraft flew to the station over a 14-year period.

The uncrewed Progress cargo vehicles were only used to resupply the station, carrying a variety of cargoes including water, fuel, food and experimental equipment. The spacecraft were not equipped with reentry shielding and so, unlike their Soyuz counterparts, were incapable of surviving reentry. As a result, when its cargo had been unloaded, each Progress was refilled with rubbish, spent equipment and other waste which was destroyed, along with the Progress itself, on reentry. To facilitate cargo return, ten Progress flights carried Raduga capsules, which could return around 150 kg of experimental results to Earth automatically. Mir was visited by three separate models of Progress; the original 7K-TG variant equipped with Igla (18 flights), the Progress-M model equipped with Kurs (43 flights), and the modified Progress-M1 version (3 flights), which together flew a total of 64 resupply missions. Whilst the Progress spacecraft usually docked automatically without incident, the station was equipped with a remote manual docking system, TORU, in case problems were encountered during the automatic approaches. With TORU, cosmonauts could guide the spacecraft safely in to dock (with the exception of the catastrophic docking of Progress M-34, when the long-range use of the system resulted in the spacecraft striking the station, damaging Spektr and causing decompression).

Mission control centre

Mir and its resupply missions were controlled from the Russian mission control centre (Russian: Центр управления полётами) in Korolyov, near the RKK Energia plant. Referred to by its acronym ЦУП ("TsUP"), or simply as 'Moscow', the facility could process data from up to ten spacecraft in three separate control rooms, although each control room was dedicated to a single programme; one to Mir; one to Soyuz; and one to the Soviet space shuttle Buran (which was later converted for use with the ISS). The facility is now used to control the Russian Orbital Segment of the ISS. The flight control team were assigned roles similar to the system used by NASA at their mission control centre in Houston, including:

The Flight Director, who provided policy guidance and communicated with the mission management team;

The Flight Shift Director, who was responsible for real-time decisions within a set of flight rules;

The Mission Deputy Shift Manager (MDSM) for the MCC was responsible for the control room's consoles, computers and peripherals;

The MDSM for Ground Control was responsible for communications;

The MDSM for Crew Training was similar to NASA's 'capcom,' or capsule communicator; usually someone who had served as the Mir crew's lead trainer.

Unused equipment

Three command and control modules were constructed for the Mir program. One was used in space; one remained in a Moscow warehouse as a source of repair parts if needed, and the third was sold to an educational and entertainment complex in the US in 1997. Tommy Bartlett Exploratory purchased the unit and had it shipped to Wisconsin Dells, Wisconsin, where it became the centrepiece of the complex's Space Exploration wing.

Safety aspects

In the later years of the programme, particularly during the Shuttle-Mir programme, Mir suffered from various systems failures. It had been designed for five years of use, but eventually flew for fifteen, and in the 1990s was showing its age, with frequent computer crashes, loss of power, uncontrolled tumbles through space and leaking pipes. Jerry Linenger in his book about his time on the facility says that the cooling system had developed tiny leaks too small and numerous to be repaired, that permitted the constant release of coolant. He says that it was especially noticeable after he had made a spacewalk and become used to the bottled air in his spacesuit. When he returned to the station and again began breathing the air inside Mir, he was shocked by the intensity of the smell and worried about the possible negative health effects of breathing such contaminated air.

Various breakdowns of the Elektron oxygen-generating system were a concern; they led crews to become increasingly reliant on the backup Vika solid-fuel oxygen generator (SFOG) systems, which led to a fire during the handover between EO-22 and EO-23. (see also ISS ECLSS)

Several accidents occurred which threatened the station's safety, such as the glancing collision between Kristall and Soyuz TM-17 during proximity operations in January 1994. The three most alarming incidents occurred during EO-23. The first was on 23 February 1997 during the handover period from EO-22 to EO-23, when a malfunction occurred in the backup Vika system, a chemical oxygen generator later known as solid-fuel oxygen generator (SFOG). The Vika malfunction led to a fire which burned for around 90 seconds (according to official sources at the TsUP; astronaut Jerry Linenger insists the fire burned for around 14 minutes), and produced large amounts of toxic smoke that filled the station for around 45 minutes. This forced the crew to don respirators, but some of the respirator masks initially worn were broken. Some of the fire extinguishers mounted on the walls of the newer modules were immovable.

The other two accidents concerned testing of the station's TORU manual docking system to manually dock Progress M-33 and Progress M-34. The tests were to gauge the performance of long-distance docking and the feasibility of removal of the expensive Kurs automatic docking system from Progress spacecraft. Due to malfunctioning equipment, both tests failed, with Progress M-33 narrowly missing the station and Progress M-34 striking Spektr and puncturing the module, causing the station to depressurise and leading to Spektr being permanently sealed off. This in turn led to a power crisis aboard Mir as the module's solar arrays produced a large proportion of the station's electrical supply, causing the station to power down and begin to drift, requiring weeks of work to rectify before work could continue as normal.