MirMir Mir Mir (, ; ) was a space station that operated in low Earth orbit from 1986 to 2001, operated by the Soviet Union and later by Russia. "Mir" was the first modular space station and was assembled in orbit from 1986 to 1996. It had a greater mass than any previous spacecraft. At the time it was the largest artificial satellite in orbit, succeeded by the International Space Station (ISS) after "Mir"<nowiki>'</nowiki>s orbit decayed. 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 held the record for the longest continuous human presence in space at 3,644 days, until it was surpassed by the ISS on 23 October 2010. It holds the record for the longest single human spaceflight, with Valeri Polyakov spending 437 days and 18 hours on the station between 1994 and 1995. "Mir" was occupied for a total of twelve and a half years out of its fifteen-year lifespan, having the capacity to support a resident crew of  three, or larger crews for short visits. Following the success of the Salyut programme, "Mir" represented the next stage in the Soviet Union's space station programme. The first module of the station, known as the core module or base block, was launched in 1986 and followed by six further modules. Proton rockets were used to launch all of its components except for the docking module, which was installed by US Space Shuttle mission STS-74 in 1995. When complete, the station consisted of seven pressurised modules and several unpressurised components. Power was provided by several photovoltaic arrays attached directly to  the modules. The station was maintained at an orbit between and altitude and travelled at an average speed of 27,700 km/h (17,200 mph), completing 15.7 orbits per day. The station was launched as part of the Soviet Union's crewed spaceflight programme effort to maintain a long-term research outpost in space, and following the collapse of the USSR, was operated by the new Russian Federal Space Agency (RKA). As a result, most of the station's occupants were Soviet; through international collaborations such as the Intercosmos, 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). Origins. "Mir" was authorised by a 17 February 1976 decree, to design an improved model of the Salyut DOS-17K space stations. Four Salyut space stations had been launched since 1971, with three more being launched during "Mir"'s development. It was planned that the station's core module (DOS-7 and  the backup DOS-8) would be equipped with a total of four docking ports; two at either end of the station as with the Salyut stations, and an additional two ports on either side of a docking sphere at the front of the station to enable further modules to expand the station's capabilities. By August 1978, this had evolved to the final configuration of one aft port and five ports in a spherical compartment at the forward end of the station. It was originally planned that the ports would connect to modules derived from the Soyuz spacecraft. These modules would  have used a Soyuz propulsion module, as 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 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 and 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 the Salyut 5B digital flight control computer and gyrodyne flywheels (taken from Almaz), Kurs automatic rendezvous system, "Luch" satellite communications system, Elektron oxygen generators, and Vozdukh carbon dioxide scrubbers. By early 1984, work on "Mir" had halted while all resources were being put into the Buran programme in order 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 orbital assembly of "Mir" began on 19 February 1986 with the launch of the "Proton-K" rocket. Four 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 main "Mir" complex. Firstly, the module would be launched independently on its own Proton-K and  chase the station automatically. It would then dock to the forward docking port on the core module's docking node, then extend its Lyappa arm to mate with a fixture on the node's exterior. The arm would then lift the module away from the forward docking port and rotate it on to the radial port where it was to mate, before lowering it to dock. 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 expansion modules, "Kvant"-1 in 1987 and the docking module in 1995, followed different procedures. "Kvant"-1, having, unlike the four modules mentioned above, no engines of its own, was launched attached to a tug based on the TKS spacecraft which delivered the module to the aft end of the core module instead of the docking node. Once hard docking had been achieved, the tug undocked and deorbited itself. The docking module, meanwhile, was launched aboard during STS-74 and mated to the orbiter's Orbiter  Docking System. "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 three truss structures, several experiments and other unpressurised elements were also mounted to the exterior of the station by cosmonauts conducting a total of eighty spacewalks 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 . 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 when collapsed, but when extended using a hand crank were 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 (PV) 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 m (409 ft) 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 kW from a 22 m (237 ft) area. "Kvant"-2, launched in 1989, provided two 10 m (32.8  ft) long panels which supplied 3.5 kW each, whilst "Kristall" was launched with two collapsible, 15 m (49.2 ft) 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 m (1360 ft) of array with a 16 kW supply. Two further arrays were flown to the station on board the 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 and an average apogee of , 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; in order 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, in order 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: Life support. "Mir"<nowiki>'</nowiki>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. 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, and is much safer than the alternative, a pure oxygen atmosphere, because of increased fire risk such as occurred with Apollo 1. International cooperation. Interkosmos. Interkosmos () was a Soviet Union space exploration programme which allowed members from 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 fourteen missions consisted of an expedition to "Mir" but none resulted in an extended stay  in the station: European involvement. Various European astronauts visited "Mir" as part of several cooperative programmes: 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. Life on board. Inside, the "Mir" resembled a cramped labyrinth, 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 up to a month. 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 to be expected given it had been lived in for ten to eleven years without being brought home and cleaned. Crew schedule. The time zone used on board "Mir" was Moscow Time (). 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, 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 comrades on "Mir" did not "improvise" in this way, and as a medical doctor he observed the effects of stress on his comrades that he believed was the outcome of following an itinerary without making modifications to it. Despite this, he commented that his comrades 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" saying "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 and run the equivalent of 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 was recycled back into drinking water, although this 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", phonebox-sized booths 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 100 g of protein, 130 g of fat and 330 g 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 samples of extremophile molds were  taken from "Mir". Ninety species of micro-organisms were found in 1990, four years after the station's launch. By the time of its decommission in 2001, the number of known different micro-organisms had grown to 140. As space stations get older, the problems with contamination get worse. Molds that develop aboard space stations can produce acids that degrade metal, glass and rubber. The molds in "Mir" were found growing behind panels and inside air-conditioning equipment. The molds 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. 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 twelve different nations, making it the most visited spacecraft in history (a record later surpassed by the ISS). Early existence. 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. The initial rendezvous of the "Kvant"-1 module with "Mir" on 5 April 1987 was troubled by the failure of the onboard control system. After the failure of the second attempt to dock, the resident cosmonauts , Yuri Romanenko and Aleksandr Laveykin, conducted an EVA to fix the problem. They found a trash bag which had been left in orbit after the departure of one of the previous cargo ships and was now located between the module and the station, which prevented the docking. After removing the bag, docking was completed on 12 April. The Soyuz TM-2 launch was the beginning of a string of 6 Soyuz launches and three long-duration crews between 5 February 1987 and 27 April 1989. This period also saw the first international visitors, Muhammed Faris (Syria), Abdul Ahad Mohmand (Afghanistan) and  Jean-Loup Chrétien (France). With the departure of EO-4 on Soyuz TM-7 on 27 April 1989 the station was again left unoccupied. Third start. The launch of Soyuz TM-8 on 5 September 1989 marked the beginning of the longest human presence in space, until 23 October 2010, when this record was surpassed by the ISS. It also marked the beginning of "Mir's" second expansion. The Kvant-2 and "Kristall" modules were now ready for launch. Alexander Viktorenko and Aleksandr Serebrov docked with "Mir" and brought the station out of its five-month hibernation. On 29 September the cosmonauts installed equipment  in the docking system in preparation for the arrival of "Kvant"-2, the first of the 20 tonne add-on modules based on the TKS spacecraft from the Almaz programme. After a 40-day delay caused by faulty computer chips, "Kvant"-2 was launched on 26 November 1989. After problems deploying the craft's solar array and with the automated docking systems on both "Kvant"-2 and "Mir", the new module was docked manually on 6 December. "Kvant"-2 added a second set of control moment gyroscopes (CMGs, or "gyrodynes") to "Mir", and brought the new life support systems for recycling water and generating  oxygen, reducing dependence on ground resupply. The module featured a large airlock with a one-metre hatch. A special backpack unit (known as "Ikar"), an equivalent of the US Manned Maneuvering Unit, was located inside "Kvant"-2's airlock. Soyuz TM-9 launched EO-6 crew members Anatoly Solovyev and Aleksandr Balandin on 11 February 1990. While docking, the EO-5 crew noted that three thermal blankets on the ferry were loose, potentially creating problems on reentry, but it was decided that they would be manageable. Their stay on board "Mir" saw the addition of the "Kristall" module, launched 31 May 1990. The first  docking attempt on 6 June was aborted due to an attitude control thruster failure. "Kristall" arrived at the front port on 10 June and was relocated to the lateral port opposite "Kvant"-2 the next day, restoring the equilibrium of the complex. Due to the delay in the docking of "Kristall", EO-6 was extended by 10 days to permit the activation of the module's systems and to accommodate an EVA to repair the loose thermal blankets on Soyuz TM-9. "Kristall" contained furnaces for use in producing crystals under microgravity conditions (hence the choice of name for the module). The module  was also equipped with biotechnology research equipment, including a small greenhouse for plant cultivation experiments which was equipped with a source of light and a feeding system, in addition to equipment for astronomical observations. The most obvious features of the module were the two Androgynous Peripheral Attach System (APAS-89) docking ports designed to be compatible with the "Buran" spacecraft. Although they were never used in a "Buran" docking, they were useful later during the Shuttle-"Mir" programme, providing a berthing location for US Space Shuttles. The EO-7 relief crew arrived aboard Soyuz TM-10 on 3 August 1990. The new crew arrived  at "Mir" with quail for "Kvant"-2's cages, one of which laid an egg en route to the station. It was returned to Earth, along with 130 kg of experiment results and industrial products, in Soyuz TM-9. Two more expeditions, EO-8 and EO-9, continued the work of their predecessors whilst tensions grew back on Earth. Post-Soviet period. The EO-10 crew, launched aboard Soyuz TM-13 on 2 October 1991, was the last crew to launch from the USSR and continued the occupation of "Mir" during the fall of the Soviet Union. The crew launched as Soviet citizens and returned to  Earth on 25 March 1992 as Russians. The newly formed Russian Federal Space Agency (Roscosmos) was unable to finance the unlaunched "Spektr" and "Priroda" modules, instead putting them into storage and ending "Mir's" second expansion. The first human mission flown from an independent Kazakhstan was Soyuz TM-14, launched on 17 March 1992, which carried the EO-11 crew to "Mir", docking on 19 March before the departure of Soyuz TM-13. On 17 June, Russian President Boris Yeltsin and US President George H. W. Bush announced what would later become the Shuttle-"Mir" programme, a cooperative venture which proved useful to the  cash-strapped Roskosmos (and led to the eventual completion and launch of "Spektr" and "Priroda"). EO-12 followed in July, alongside a brief visit by French astronaut Michel Tognini. The following crew, EO-13, began preparations for the Shuttle-"Mir" programme by flying to the station in a modified spacecraft, Soyuz TM-16 (launched on 26 January 1993), which was equipped with an APAS-89 docking system rather than the usual probe-and-drogue, enabling it to dock to "Kristall" and test the port which would later be used by US space shuttles. The spacecraft also enabled controllers to obtain data on the dynamics of  docking a spacecraft to a space station off the station's longitudinal axis, in addition to data on the structural integrity of this configuration via a test called "Rezonans" conducted on 28 January. Soyuz TM-15, meanwhile, departed with the EO-12 crew on 1 February. Throughout the period following the collapse of the USSR, crews on "Mir" experienced occasional reminders of the economic chaos occurring in Russia. The initial cancellation of "Spektr" and "Priroda" was the first such sign, followed by the reduction in communications as a result of the fleet of tracking ships being withdrawn from service by Ukraine. The  new Ukrainian government also vastly raised the price of the "Kurs" docking systems, manufactured in Kyivthe Russians' attempts to reduce their dependence on "Kurs" would later lead to accidents during TORU tests in 1997. Various Progress spacecraft had parts of their cargoes missing, either because the consumable in question had been unavailable, or because the ground crews at Baikonur had looted them. The problems became particularly obvious during the launch of the EO-14 crew aboard Soyuz TM-17 in July; shortly before launch there was a black-out at the pad, and the power supply to the nearby city of Leninsk  failed an hour after launch. Nevertheless, the spacecraft launched on time and arrived at the station two days later. All of "Mir"<nowiki>'</nowiki>s ports were occupied, and so Soyuz TM-17 had to station-keep 200 metres away from the station for half an hour before docking while Progress M-18 vacated the core module's front port and departed. The EO-13 crew departed on 22 July, and soon after "Mir" passed through the annual Perseid meteor shower, during which the station was hit by several particles. A spacewalk was conducted on 28 September to inspect the station's hull, but  no serious damage was reported. Soyuz TM-18 arrived on 10 January 1994 carrying the EO-15 crew (including Valeri Polyakov, who was to remain on "Mir" for 14 months), and Soyuz TM-17 left on 14 January. The undocking was unusual in that the spacecraft was to pass along "Kristall" in order to obtain photographs of the APAS to assist in the training of space shuttle pilots. Due to an error in setting up the control system, the spacecraft struck the station a glancing blow during the manoeuvre, scratching the exterior of "Kristall". On 3 February 1994, "Mir" veteran Sergei Krikalev became  the first Russian cosmonaut to launch on a US spacecraft, flying on during STS-60. The launch of Soyuz TM-19, carrying the EO-16 crew, was delayed due to the unavailability of a payload fairing for the booster that was to carry it, but the spacecraft eventually left Earth on 1 July 1994 and docked two days later. They stayed only four months to allow the Soyuz schedule to line up with the planned space shuttle manifest, and so Polyakov greeted a second resident crew in October, prior to the undocking of Soyuz TM-19, when the EO-17 crew arrived in Soyuz TM-20 . Shuttle–"Mir". The 3 February launch of , flying STS-63, opened operations on "Mir" for 1995. Referred to as the "near-"Mir"" mission, the mission saw the first rendezvous of a Space Shuttle with "Mir" as the orbiter approached within of the station as a dress rehearsal for later docking missions and for equipment testing. Five weeks after "Discovery" departure, the EO-18 crew, including the first US cosmonaut Norman Thagard, arrived in Soyuz TM-21. The EO-17 crew left a few days later, with Polyakov completing his record-breaking 437-day spaceflight. During EO-18, the "Spektr" science module (which served as living and working  space for American astronauts) was launched aboard a Proton rocket and docked to the station, carrying research equipment from America and other nations. The expedition's crew returned to Earth aboard following the first Shuttle–"Mir" docking mission, STS-71. "Atlantis", launched on 27 June 1995, successfully docked with "Mir" on 29 June becoming the first US spacecraft to dock with a Russian spacecraft since the ASTP in 1975. The orbiter delivered the EO-19 crew and returned the EO-18 crew to Earth. The EO-20 crew were launched on 3 September, followed in November by the arrival of the docking module during STS-74 . The two-man EO-21 crew was launched on 21 February 1996 aboard Soyuz TM-23 and were soon joined by US crew member Shannon Lucid, who was brought to the station by "Atlantis" during STS-76. This mission saw the first joint US spacewalk on "Mir" take place deploying the Mir Environmental Effects Payload package on the docking module. Lucid became the first American to carry out a long-duration mission aboard "Mir" with her 188-day mission, which set the US single spaceflight record. During Lucid's time aboard "Mir", "Priroda", the station's final module, arrived as did French visitor  Claudie Haigneré flying the "Cassiopée" mission. The flight aboard Soyuz TM-24 also delivered the EO-22 crew of Valery Korzun and Aleksandr Kaleri. Lucid's stay aboard "Mir" ended with the flight of "Atlantis" on STS-79, which launched on 16 September. This, the fourth docking, saw John Blaha transferring onto "Mir" to take his place as resident US astronaut. His stay on the station improved operations in several areas, including transfer procedures for a docked space shuttle, "hand-over" procedures for long-duration American crew members and "ham" amateur radio communications, and also saw two spacewalks to reconfigure the station's  power grid. Blaha spent four months with the EO-22 crew before returning to Earth aboard "Atlantis" on STS-81 in January 1997, at which point he was replaced by physician Jerry Linenger. During his flight, Linenger became the first American to conduct a spacewalk from a foreign space station and the first to test the Russian-built Orlan-M spacesuit alongside Russian cosmonaut Vasili Tsibliyev, flying EO-23. All three crew members of EO-23 performed a "fly-around" in Soyuz TM-25 spacecraft. Linenger and his Russian crewmates Vasili Tsibliyev and Aleksandr Lazutkin faced several difficulties during the mission, including the most severe  fire aboard an orbiting spacecraft (caused by a malfunctioning "Vika"), failures of various systems, a near collision with Progress M-33 during a long-distance TORU test and a total loss of station electrical power. The power failure also caused a loss of attitude control, which led to an uncontrolled "tumble" through space. Linenger was succeeded by Anglo-American astronaut Michael Foale, carried up by "Atlantis" on STS-84, alongside Russian mission specialist Elena Kondakova. Foale's increment proceeded fairly normally until 25 June when during the second test of the "Progress" manual docking system, TORU, Progress M-34 collided with solar arrays  on the "Spektr" module and crashed into the module's outer shell, puncturing the module and causing depressurisation on the station. Only quick actions on the part of the crew, cutting cables leading to the module and closing "Spektr's" hatch, prevented the crews having to abandon the station in Soyuz TM-25. Their efforts stabilised the station's air pressure, whilst the pressure in "Spektr", containing many of Foale's experiments and personal effects, dropped to a vacuum. In an effort to restore some of the power and systems lost following the isolation of "Spektr" and to attempt to locate  the leak, EO-24 commander Anatoly Solovyev and flight engineer Pavel Vinogradov carried out a risky salvage operation later in the flight, entering the empty module during a so-called "intra-vehicular activity" or "IVA" spacewalk and inspecting the condition of hardware and running cables through a special hatch from "Spektr's" systems to the rest of the station. Following these first investigations, Foale and Solovyev conducted a 6-hour EVA outside "Spektr" to inspect the damage. After these incidents, the US Congress and NASA considered whether to abandon the programme out of concern for the astronauts' safety, but NASA administrator  Daniel Goldin decided to continue. The next flight to "Mir", STS-86, carried David Wolf aboard "Atlantis". During the orbiter's stay, Titov and Parazynski conducted a spacewalk to affix a cap to the docking module for a future attempt by crew members to seal the leak in "Spektr"s hull. Wolf spent 119 days aboard "Mir" with the EO-24 crew and was replaced during STS-89 with Andy Thomas, who carried out the last US expedition on "Mir". The EO-25 crew arrived in Soyuz TM-27 in January 1998 before Thomas returned to Earth on the final Shuttle–"Mir" mission, STS-91. Final days and  deorbit. Following the 8 June 1998 departure of "Discovery", the EO-25 crew of Budarin and Musabayev remained on "Mir", completing materials experiments and compiling a station inventory. On 2 July, Roskosmos director Yuri Koptev announced that, due to a lack of funding to keep "Mir" active, the station would be deorbited in June 1999. The EO-26 crew of Gennady Padalka and Sergei Avdeyev arrived on 15 August in Soyuz TM-28, alongside physicist Yuri Baturin, who departed with the EO-25 crew on 25 August in Soyuz TM-27. The crew carried out two spacewalks, one inside "Spektr" to reseat some power cables  and another outside to set up experiments delivered by Progress M-40, which also carried a large amount of propellant to begin alterations to "Mir"s orbit in preparation for the station's decommissioning. 20 November 1998 saw the launch of "Zarya", the first module of the ISS, but delays to the new station's service module "Zvezda" had led to calls for "Mir" to be kept in orbit past 1999. Roscosmos confirmed that it would not fund "Mir" past the set deorbit date. The crew of EO-27, Viktor Afanasyev and Jean-Pierre Haigneré, arrived in Soyuz TM-29 on 22 February 1999  alongside Ivan Bella, who returned to Earth with Padalka in Soyuz TM-28. The crew carried out three EVAs to retrieve experiments and deploy a prototype communications antenna on "Sofora". On 1 June it was announced that the deorbit of the station would be delayed by six months to allow time to seek alternative funding to keep the station operating. The rest of the expedition was spent preparing the station for its deorbit; a special analog computer was installed and each of the modules, starting with the docking module, was mothballed in turn and sealed off. The crew loaded their results  into Soyuz TM-29 and departed "Mir" on 28 August 1999, ending a run of continuous occupation, which had lasted for eight days short of ten years. The station's control moment gyroscopes (CMGs, or "gyrodynes") and main computer were shut down on 7 September, leaving Progress M-42 to control "Mir" and refine the station's orbital decay rate. Near the end of its life, there were plans for private interests to purchase "Mir", possibly for use as the first orbital television/movie studio. The privately funded Soyuz TM-30 mission by MirCorp, launched on 4 April 2000, carried two crew members , Sergei Zalyotin and Aleksandr Kaleri, to the station for two months to do repair work with the hope of proving that the station could be made safe. This was to be the last crewed mission to "Mir"—while Russia was optimistic about "Mir" future, its commitments to the ISS project left no funding to support the aging station. "Mir"s deorbit was carried out in three stages. The first stage involved waiting for atmospheric drag to reduce the station's orbit to an average of . This began with the docking of Progress M1-5, a modified version of the Progress-M carrying  2.5 times more fuel in place of supplies. The second stage was the transfer of the station into a 165 × 220 km (103 × 137 mi) orbit. This was achieved with two burns of Progress M1-5's control engines at 00:32 UTC and 02:01 UTC on 23 March 2001. After a two-orbit pause, the third and final stage of the deorbit began with the burn of Progress M1-5's control engines and main engine at 05:08 UTC, lasting 22+ minutes. Atmospheric reentry (arbitrarily defined beginning at 100 km/60 mi AMSL) occurred at 05:44 UTC near  Nadi, Fiji. Major destruction of the station began around 05:52 UTC and most of the unburned fragments fell into the South Pacific Ocean around 06:00 UTC. 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 fourteen-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. In order 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's striking the station, damaging "Spektr" and causing decompression). In addition to the routine Soyuz and Progress flights, it was anticipated that "Mir" would also be the destination for flights by the Soviet "Buran" space shuttle, which was intended to deliver extra modules (based on  the same "37K" bus as "Kvant"-1) and provide a much improved cargo return service to the station. "Kristall" carried two Androgynous Peripheral Attach System (APAS-89) docking ports designed to be compatible with the shuttle. One port was to be used for "Buran"; the other for the planned "Pulsar" X-2 telescope, also to be delivered by "Buran". The cancellation of the "Buran" programme meant these capabilities were not realised until the 1990s when the ports were used instead by US Space Shuttles as part of the Shuttle-"Mir" programme (after testing by the specially modified Soyuz TM-16 in 1993). Initially, visiting  Space Shuttle orbiters docked directly to "Kristall", but this required the relocation of the module to ensure sufficient distance between the shuttle and "Mir"s solar arrays. To eliminate the need to move the module and retract solar arrays for clearance issues, a Mir Docking Module was later added to the end of "Kristall". The shuttles provided crew rotation of the American astronauts on station and carried cargo to and from the station, performing some of the largest transfers of cargo of the time. With a space shuttle docked to "Mir", the temporary enlargements of living and working areas amounted to  a complex that was the largest spacecraft in history at that time, with a combined mass of . Mission control centre. "Mir" and its resupply missions were controlled from the Russian mission control centre () 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: 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. Ageing systems and atmosphere. 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) Accidents. 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. Radiation and orbital debris. Without the protection of the Earth's atmosphere, cosmonauts were  exposed to higher levels of radiation from a steady flux of cosmic rays and trapped protons from the South Atlantic Anomaly. The station's crews were exposed to an absorbed dose of about 5.2 cGy over the course of the Mir EO-18 expedition, producing an equivalent dose of 14.75 cSv, or 1133 µSv per day. This daily dose is approximately that received from natural background radiation on Earth in two years. The radiation environment of the station was not uniform; closer proximity to the station's hull led to an increased radiation dose, and the strength of radiation shielding varied  between modules; "Kvant"-2's being better than the core module, for instance. The increased radiation levels pose a higher risk of crews developing cancer, and can cause damage to the chromosomes of lymphocytes. These cells are central to the immune system and so any damage to them could contribute to the lowered immunity experienced by cosmonauts. Over time, in theory, lowered immunity results in the spread of infection between crew members, especially in such confined areas. To avoid this only healthy people were permitted aboard. Radiation has also been linked to a higher incidence of cataracts in cosmonauts. Protective shielding  and protective drugs may lower the risks to an acceptable level, but data is scarce and longer-term exposure will result in greater risks. At the low altitudes at which "Mir" orbited there is a variety of space debris, consisting of everything from entire spent rocket stages and defunct satellites, to explosion fragments, paint flakes, slag from solid rocket motors, coolant released by RORSAT nuclear powered satellites, small needles, and many other objects. These objects, in addition to natural micrometeoroids, posed a threat to the station as they could puncture pressurised modules and cause damage to other parts of the  station, such as the solar arrays. Micrometeoroids also posed a risk to spacewalking cosmonauts, as such objects could puncture their spacesuits, causing them to depressurise. Meteor showers in particular posed a risk, and, during such storms, the crews slept in their Soyuz ferries to facilitate an emergency evacuation should "Mir" be damaged. Mir Mir (, ; ) was a space station that operated in low Earth orbit from 1986 to 2001, operated by the Soviet Union and later by Russia. "Mir" was the first modular space station and was assembled in orbit from 1986 to 1996. It had a greater mass than any