Editing Mir (section)

==Station structure==

===Assembly===
[[File:Mir Docking Cone Placement and Module Movements.pdf|right|thumb|upright|A diagram showing the ''Konus'' drogue and module movements around ''Mir'''s docking node<ref name="SSA">{{cite book|title=Space Shuttle Almanac|isbn=978-0-9696313-0-9|orig-year=1992|year=2011|author1=Joel W. Powell|author2=Lee Brandon-Cremer|publisher=Microgravity Press |name-list-style=amp|url=http://www.spaceshuttlealmanac.com/|access-date=23 August 2011|archive-date=2 October 2011|archive-url=https://web.archive.org/web/20111002020622/http://www.spaceshuttlealmanac.com/|url-status=live}}</ref>]]
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|''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.<ref name="MirBIS"/><ref name="SSSM"/>{{page needed|date=February 2021}}

The other two expansion modules, [[Kvant-1|''Kvant''-1]] in 1987 and the [[Mir Docking Module|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 {{OV|104}} 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.<ref name="SSSM"/>{{rp|248–249}}<ref name="STS-74"/> 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.<ref name="SSSM"/>{{page needed|date=February 2021}}

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 (spacecraft)|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.<ref name="SSSM"/>{{page needed|date=February 2021}}

===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 {{OV|104}}.
{{Clear}}
{{sticky header}}
{| class="wikitable sticky-header" style="width:auto; margin:auto;"
|- style="background:#EFEFEF;"
! Module
! Expedition
! Launch date
! Launch system
! style="width:100px;"| Nation
! style="width:82px;"| Isolated view
! style="width:82px;"| Station view
|-
| rowspan="2" | ''[[Mir Core Module]]''<br /><small>(Core Module)</small>
| N/A
| 19 February 1986
| [[Proton-K]]
| Soviet Union
| rowspan="2" | [[File:RP1357 p103 Mir base block.svg|80px]]
| rowspan="2" | [[File:Mir Core Module.JPG|center|40px]]
|- style="border-bottom: 3px solid gray"
| colspan="4" | The base block for the entire ''Mir'' complex, the core module, or DOS-7, provided the main living quarters for resident crews and contained environmental systems, early attitude<!--It's supposed to be ATTitude, meaning orientation – please don't change this to aLTitude.--> control systems and the station's main engines. The module was based on hardware developed as part of the [[Salyut program]]me, and consisted of a stepped-cylinder main compartment and a spherical 'node' module, which served as an airlock and provided ports to which four of the station's expansion modules were berthed and to which a Soyuz or Progress spacecraft could dock. The module's aft port served as the berthing location for [[Kvant-1|''Kvant''-1]].<ref name="MHH">{{cite book|url=http://en.wikisource.org/wiki/Mir_Hardware_Heritage|title=Mir Hardware Heritage|author=David S. F. Portree|publisher=NASA|date=March 1995|access-date=8 July 2009|archive-date=15 July 2009|archive-url=https://web.archive.org/web/20090715235246/http://en.wikisource.org/wiki/Mir_Hardware_Heritage|url-status=live}}{{page needed|date=February 2021}}</ref>{{page needed|date=February 2021}}
|-
| rowspan="2" | [[Kvant-1|''Kvant''-1]]<br /><small>(Astrophysics Module)</small>
| [[Mir EO-2|EO-2]]
| 31 March 1987
| [[Proton-K]]
| Soviet Union
| rowspan="2" | [[File:RP1357 p162 Kvant module.svg|80px]]
| rowspan="2" | [[File:Mir-kvant.jpg|80px]]
|- style="border-bottom: 3px solid gray"
| colspan="4" | The first expansion module to be launched, ''Kvant''-1 consisted of two pressurised working compartments and one unpressurised experiment compartment. Scientific equipment included an [[X-ray telescope]], an [[Ultraviolet astronomy|ultraviolet telescope]], a wide-angle camera, high-energy X-ray experiments, an X-ray/gamma ray detector, and the Svetlana electrophoresis unit. The module also carried six [[Gyroscope|gyrodynes]] for attitude<!--It's supposed to be ATTitude, meaning orientation – please don't change this to aLTitude.--> control, in addition to life support systems including an [[Elektron (ISS)|Elektron]] oxygen generator and a [[ISS ECLSS#Vozdukh|Vozdukh]] carbon dioxide scrubber.<ref name="MHH"/>{{page needed|date=February 2021}}
|-
| rowspan="2" | [[Kvant-2|''Kvant''-2]]<br /><small>(Augmentation Module)</small>
| [[Mir EO-5|EO-5]]
| 26 November 1989
| [[Proton-K]]
| Soviet Union
| rowspan="2" | [[File:RP1357 p164 Kvant 2 module.svg|80px]]
| rowspan="2" | [[File:Mir Kvant 1-Base Block-Kvant 2.jpg|80px]]
|- style="border-bottom: 3px solid gray"
| colspan="4" | The first [[TKS spacecraft|TKS]] based module, ''Kvant''-2, was divided into three compartments: an [[Extra-vehicular activity|EVA]] airlock, an instrument/cargo compartment (which could function as a backup airlock), and an instrument/experiment compartment. The module also carried a Soviet version of the [[Manned Maneuvering Unit]] for the [[Orlan space suit]], referred to as [[Astronaut Propulsion Unit#Soviet SPK|''Ikar'']], a system for regenerating water from urine, a shower, the ''Rodnik'' water storage system and six [[gyroscopes|gyrodynes]] to augment those already located in ''Kvant''-1. Scientific equipment included a high-resolution camera, spectrometers, X-ray sensors, the Volna 2 fluid flow experiment, and the Inkubator-2 unit, which was used for hatching and raising [[quail]].<ref name="MHH"/>{{page needed|date=February 2021}}
|-
| rowspan="2" | ''[[Kristall]]''<br /><small>(Technology Module)</small>
| [[Mir EO-6|EO-6]]
| 31 May 1990
| [[Proton-K]]
| Soviet Union
| rowspan="2" | [[File:RP1357 p166 Kristall module.svg|80px]]
| rowspan="2" | [[File:Mir from Soyuz TM-17.jpg|80px]]
|- style="border-bottom: 3px solid gray"
| colspan="4" | ''Kristall'', the fourth module, consisted of two main sections. The first was largely used for materials processing (via various processing furnaces), astronomical observations, and a biotechnology experiment utilising the Aniur electrophoresis unit. The second section was a docking compartment which featured two [[APAS-89]] [[Spacecraft docking|docking ports]] initially intended for use with the [[Buran programme|''Buran'' programme]] and eventually used during the [[Shuttle-Mir Program|Shuttle-''Mir'' programme]]. The docking compartment also contained the Priroda 5 camera used for Earth resources experiments. ''Kristall'' also carried six [[control moment gyroscope]]s (CMGs, or "gyrodynes") for attitude<!--It's supposed to be ATTitude, meaning orientation – please don't change this to aLTitude.--> control to augment those already on the station, and two collapsible solar arrays.<ref name="MHH"/>{{page needed|date=February 2021}}
|-
| rowspan="2" | ''[[Spektr]]''<br /><small>(Power Module)</small>
| [[Mir EO-18|EO-18]]
| 20 May 1995
| [[Proton-K]]
| Russia
| rowspan="2" | [[File:Spektr module drawing.png|80px]]
| rowspan="2" | [[File:Mir from STS-74.jpg|80px]]
|- style="border-bottom: 3px solid gray"
| colspan="4" | ''Spektr'' was the first of the three modules launched during the Shuttle-''Mir'' programme; it served as the living quarters for American astronauts and housed [[NASA]]-sponsored experiments. The module was designed for remote observation of Earth's environment and contained atmospheric and surface research equipment. It featured four solar arrays which generated approximately half of the station's electrical power. The module also had a science airlock to expose experiments to the vacuum of space selectively. ''Spektr'' was rendered unusable following the collision with [[Progress M-34]] in 1997 which damaged the module, exposing it to the vacuum of space.<ref name="SSSM"/>{{page needed|date=February 2021}}
|-
| rowspan="2" | [[Mir Docking Module|Docking Module]]
| [[Mir EO-20|EO-20]]
| 15 November 1995
| {{OV|104}}<br />([[STS-74]])
| US
| rowspan="2" | [[File:Mir Docking Module drawing.svg|80px]]
| rowspan="2" | [[File:Mir from STS-74PLB.jpg|80px]]
|- style="border-bottom: 3px solid gray"
| colspan="4" | The docking module was designed to help simplify [[Space Shuttle]] [[spacecraft docking|dockings]] to ''Mir''. Before the first shuttle docking mission ([[STS-71]]), the ''[[Kristall]]'' module had to be tediously moved to ensure sufficient clearance between ''Atlantis'' and ''Mir'''s solar arrays. With the addition of the docking module, enough clearance was provided without the need to relocate ''Kristall''. It had two identical [[APAS-89]] docking ports, one attached to the distal port of ''Kristall'' with the other available for shuttle docking.{{r|SSSM|p=247–249}}
|-
| rowspan="2" | ''[[Priroda]]''<br /><small>(Earth Sensing Module)</small>
| [[Mir EO-21|EO-21]]
| 26 April 1996
| [[Proton-K]]
| Russia
| rowspan="2" | [[File:Priroda module drawing.svg|80px]]
| rowspan="2" | [[File:Mir from STS-81.jpg|80px]]
|- style="border-bottom: 3px solid gray"
| colspan="4" | The seventh and final ''Mir'' module, ''Priroda'''s primary purpose was to conduct Earth resource experiments through remote sensing and to develop and verify remote sensing methods. The module's experiments were provided by twelve different nations, and covered microwave, visible, near infrared, and infrared spectral regions using both passive and active sounding methods. The module possessed both pressurised and unpressurised segments, and featured a large, externally mounted [[synthetic aperture radar]] dish.<ref name="SSSM"/>{{rp|251–253}}
|}

=== Unpressurised elements ===
{{anchor|VDU}}
[[File:Mir unpressurised elements.jpg|thumb|The Travers radar antenna, ''Sofora'' girder, VDU thruster block, SPK unit and a ''Strela'' crane, alongside [[Kvant-2|''Kvant''-2]] and ''[[Priroda]]'']]
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.<ref name="SSSM"/>{{page needed|date=February 2021}} 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|''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.<ref name="SSSM"/>{{page needed|date=February 2021}}

To assist in moving objects around the exterior of the station during [[Extra-vehicular activity|EVAs]], ''Mir'' featured two [[Strela (crane)|''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 {{convert|6|ft|m|order=flip}} when collapsed, but when extended using a hand crank were {{convert|46|ft|m|order=flip}} long, meaning that all of the station's modules could be accessed during spacewalks.<ref>{{cite book|title=Leaving Earth: Space Stations, Rival Superpowers and the Quest for Interplanetary Travel|publisher=Henry (Joseph) Press|isbn=978-0-309-08548-9|url=https://books.google.com/books?id=0e2vl0sev2IC&pg=PA297|author=Robert Zimmerman|date=3 September 2003|page=297|access-date=27 February 2018|archive-date=5 August 2020|archive-url=https://web.archive.org/web/20200805233521/https://books.google.com/books?id=0e2vl0sev2IC&pg=PA297|url-status=live}}</ref>

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.<ref name="MHH"/>{{page needed|date=February 2021}} ''Kvant''-2 also featured several scan platforms and was fitted with a mounting bracket to which the [[Astronaut Propulsion Unit#Soviet SPK|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 [[Mir EO-5|EO-5]].<ref name="SSSM"/>{{page needed|date=February 2021}}

In addition to module-specific equipment, ''Kvant''-2, ''Kristall'', ''Spektr'' and ''Priroda'' were each equipped with one [[Lyappa arm|''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.<ref name="MHH"/>{{page needed|date=February 2021}}

===Power supply===
[[File:Spektr before collision - cropped.jpg|thumb|The four solar arrays on ''[[Spektr]]'']]
[[Photovoltaic system#Photovoltaic arrays|Photovoltaic (PV) arrays]] powered ''Mir''. The station used a 28&nbsp;[[volt]] [[direct current|DC]] supply which provided 5-, 10-, 20- and 50-[[Ampere|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 battery|nickel-cadmium storage batteries]] installed throughout the station.<ref name="SSSM"/> The arrays rotated in only one degree of freedom over a 180° arc, and tracked the Sun using [[Sun sensor]]s 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&nbsp;[[Ampere hour|Ah]] capacity, were then used to power the station until the arrays recovered their maximum output on the day side of Earth.<ref name="SSSM"/>

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&nbsp;m<sup>2</sup> (409&nbsp;ft<sup>2</sup>) in area, were launched on the core module, and together provided a total of 9&nbsp;kW of power. A third, [[Dorsum (anatomy)|dorsal]] panel was launched on ''Kvant''-1 and mounted on the core module in 1987, providing a further 2&nbsp;kW from a 22&nbsp;m<sup>2</sup> (237&nbsp;ft<sup>2</sup>) area.<ref name="SSSM"/> ''Kvant''-2, launched in 1989, provided two 10&nbsp;m (32.8&nbsp;ft) long panels which supplied 3.5&nbsp;kW each, whilst ''Kristall'' was launched with two collapsible, 15&nbsp;m (49.2&nbsp;ft) long arrays (providing 4&nbsp;kW each) which were intended to be moved to ''Kvant''-1 and installed on mounts which were attached during a spacewalk by the [[Soyuz TM-11|EO-8]] crew in 1991.<ref name="SSSM"/><ref name="MHH"/>

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&nbsp;m<sup>2</sup> (1360&nbsp;ft<sup>2</sup>) of array with a 16&nbsp;kW supply.<ref name="SSSM"/> Two further arrays were flown to the station on board the {{OV|104}} 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&nbsp;kW.<ref name="SSSM"/> 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.<ref name="SSSM"/>

===Orbit control===
[[File:MirOrbitalManoeuvres.svg|thumb|Graph showing the changing altitude of ''Mir'' from 19 February 1986 until 21 March 2001]]
''Mir'' was maintained in a near circular orbit with an average perigee of {{convert|354|km|mi|0|abbr=on}} and an average apogee of {{convert|374|km|mi|0|abbr=on}}, travelling at an average speed of 27,700&nbsp;km/h (17,200&nbsp;mph) and completing 15.7 orbits per day.<ref name="MirBIS"/><ref name="FinalBIS"/><ref name="OrbitCalc"/> 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.<ref name="SSSM"/>

Attitude<!--It's supposed to be ATTitude, meaning orientation – please don't change this to aLTitude.--> control was maintained by a combination of two mechanisms; in order to hold a set attitude<!--It's supposed to be ATTitude, meaning orientation – please don't change this to aLTitude.-->, a system of twelve [[control moment gyroscope]]s (CMGs, or "gyrodynes") rotating at 10,000&nbsp;[[Revolutions per minute|rpm]] kept the station oriented, six CMGs being located in each of the ''Kvant-1'' and ''Kvant-2'' modules.<ref name="MHH"/><ref name="MirGyros">{{cite report|title=Further Analysis of the Microgravity Environment on Mir Space Station during Mir-16|date=June 1996|url=http://gltrs.grc.nasa.gov/cgi-bin/GLTRS/browse.pl?1996/TM-107239.html|author1=DeLombard R.|author2=Ryaboukha S.|author3=Hrovat K.|author4=Moskowitz M.|publisher=NASA|url-status=dead|archive-url=https://web.archive.org/web/20090507111807/http://gltrs.grc.nasa.gov/cgi-bin/GLTRS/browse.pl?1996%2FTM-107239.html|archive-date=7 May 2009}}</ref> When the attitude<!--It's supposed to be ATTitude, meaning orientation – please don't change this to aLTitude.--> 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<!--It's supposed to be ATTitude, meaning orientation – please don't change this to aLTitude.--> and the CMGs were reengaged.<ref name="MirGyros"/> 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.<ref name="SSSM"/> Conversely, materials processing experiments required the minimisation of movement on board the station, and so ''Mir'' would be oriented in a [[Gravity-gradient stabilization|gravity gradient]] attitude<!--It's supposed to be ATTitude, meaning orientation – please don't change this to aLTitude.--> for stability.<ref name="SSSM"/> Prior to the arrival of the modules containing these gyrodynes, the station's attitude<!--It's supposed to be ATTitude, meaning orientation – please don't change this to aLTitude.--> 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.<ref name="SSSM"/><ref name="Dragonfly"/>{{page needed|date=February 2021}}

===Communications===
[[Radio|Radio communications]] provided [[telemetry]] and scientific data links between ''Mir'' and the [[TsUP|RKA Mission Control Centre]] (TsUP). Radio links were also used during [[Space rendezvous|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 (ISS)|''Lira'']] [[Antenna (radio)|antenna]] mounted to the [[Mir Core Module|core module]]. The ''Lira'' antenna also had the capability to use the [[Luch (satellite)|''Luch'']] data relay satellite system (which fell into disrepair in the 1990s) and the network of Soviet [[tracking ship]]s deployed in various locations around the world (which also became unavailable in the 1990s).<ref name="SSSM"/> [[Ultra high frequency|UHF radio]] was used by cosmonauts conducting [[Extra-vehicular activity|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.<ref name="SSSM"/>

===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 [[Micro-g environment|microgravity]]. This state of perceived weightlessness was not perfect, being disturbed by five separate effects:<ref name="gravity">{{cite web|url=http://www.spaceflight.esa.int/users/downloads/userguides/physenv.pdf|title=European Users Guide to Low Gravity Platforms|access-date=13 July 2011|date=6 December 2005|publisher=European Space Agency|pages=1–3|archive-url=https://web.archive.org/web/20090327101925/http://www.spaceflight.esa.int/users/downloads/userguides/physenv.pdf|archive-date=27 March 2009}}</ref>
* 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&nbsp;rpm, producing vibrations of 166.67&nbsp;[[Hertz|Hz]]<ref name="MirGyros"/>) or thrusters;
* [[Tidal force]]s. Any parts of ''Mir'' not at exactly the same distance from Earth tended to [[Gravity-gradient stabilization|follow separate orbits]]. As each point was physically part of the station, 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===
{{see also|ISS ECLSS}}
''Mir''<nowiki>'</nowiki>s [[ISS ECLSS|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 (ISS)|''Elektron'']] system generated oxygen [[electrolysis|electrolytically]], venting hydrogen to space. Bottled oxygen and [[chemical oxygen generator|solid fuel oxygen generation]] (SFOG) canisters, a system known as [[Vika oxygen generator|''Vika'']], provided backup. Carbon dioxide was removed from the air by the ''[[ISS ECLSS#Vozdukh|Vozdukh]]'' system.<ref name="SSSM"/> Other byproducts of human metabolism, such as methane from the intestines and ammonia from sweat, were removed by [[Activated carbon|activated charcoal]] filters. Similar systems are presently used on the ISS.

The atmosphere on ''Mir'' was similar to [[Atmosphere of Earth|Earth's]].<ref>{{cite web|url=http://science.howstuffworks.com/space-station2.htm|title=How Space Stations Work|last=Craig Freudenrich|publisher=Howstuffworks|date=20 November 2000|access-date=23 November 2008|archive-date=12 December 2008|archive-url=https://web.archive.org/web/20081212014934/http://science.howstuffworks.com/space-station2.htm|url-status=live}}</ref> Normal air pressure on the station was 101.3&nbsp;[[kilopascal|kPa]] (14.7&nbsp;[[Pounds per square inch|psi]]); the same as at sea level on Earth.<ref name="SSSM"/> An Earth-like atmosphere offers benefits for crew comfort.<ref>{{Cite web |last1=Magazine |first1=Smithsonian |last2=Goss |first2=Heather |title=Why Living in Space Can be a Pain in the Head |url=https://www.smithsonianmag.com/air-space-magazine/why-living-space-can-be-pain-head-180951507/ |access-date=2024-10-16 |website=Smithsonian Magazine |language=en}}</ref>