Twenty years after deorbit, Mir’s legacy lives on in today’s space projects

by William Graham

At 05:59 UTC on 23 March 2001 Russia’s Mir space station burned up as it re-entered Earth’s atmosphere, concluding its storied fifteen-year mission. Twenty years on, the successes and lessons learned aboard Mir live on in its successor, the International Space Station, and in the proposed next-generation space stations being developed by national agencies, international partnerships and commercial organizations around the world.

Mir was the first space station to adopt a truly modular design, with multiple components launching separately and being joined in orbit. This allowed a much larger complex to be constructed than had been possible with the previous Salyut stations, whose size was constrained by the capabilities of the Proton rockets which carried them into orbit.

The Soviet Union began developing space stations towards the end of the space race of the 1960s, focusing on long-duration missions in low Earth orbit when it became clear that they would not beat the United States to land a man on the moon.

The first station, Salyut 1, was launched in April 1971, with its first crew coming aboard through the Soyuz 11 mission in June after the previous Soyuz 10 mission had failed to dock. The three cosmonauts aboard Soyuz 11 – Georgy Dobrovolsky, Vladislav Volkov and Viktor Patsayev were the only crew to visit Salyut 1, but they were tragically killed during their return to Earth after a valve in the Soyuz capsule malfunctioned and their spacecraft depressurized.

After losing the next three stations to launch and early-mission anomalies, the next Soviet station to host a crew was Salyut 3 in 1974, one of three military Almaz space stations to be designated as part of the Salyut program. Two crewed missions visited Salyut 3, with the same number travelling to the subsequent Salyut 4 and 5 stations, the latter of which was another Almaz.

A scale model of Salyut 7 with docked Soyuz and Progress spacecraft on display in Moscow, Russia – via Don S. Montgomery, USN (Ret.)

Building on the lessons of these early stations, the Soviet Union then progressed to the second-generation Salyut 6. This was designed for longer service, with a second docking port added to allow an additional spacecraft to dock.

This meant the station could be resupplied by automated Progress spacecraft and short-duration visiting crewed missions could dock during the course of a longer principal expedition. This helped to extend long-duration missions, as they were no longer constrained by the provisions they could bring with them or by how long their Soyuz spacecraft could remain on orbit – since a visiting crew could bring up a fresh Soyuz and depart in the principal crew’s original spacecraft.

Six long-duration expeditions to Salyut 6 were carried out between 1977 and 1981 – with the fourth and longest remaining aboard for half a year. Another second-generation station, Salyut 7, was launched in 1982 and also hosted several long-duration missions.

Large TKS logistics spacecraft were also docked to both stations. TKS was originally developed as part of the military Almaz project, and at least one of the craft carried reconnaissance systems. The TKS effectively served as an additional module, remaining docked for extended periods of time and providing additional space for the crew as well as for instruments and experiments.

Salyut 7 suffered from reliability problems – the fourth principal expedition in 1985 had to conduct repairs after finding it drifting without power upon their arrival. In the early morning of 20 February 1986 (19 February UTC), a Proton-K rocket lifted off from pad 200/39 at the Baikonur Cosmodrome with its replacement. The DOS-7 spacecraft was an evolution of the later Salyut stations with additional docking ports that would allow it to become the core of a new type of space station.

The Mir core module, highlighted, as seen from Space Shuttle Atlantis during STS-71 – via NASA

The Soviet Union announced the name of its new outpost – Mir (Cyrillic Мир), which can be translated into English as “peace” or “world”.

Mir’s core module had six docking ports: one at the aft end of the spacecraft and five arranged in a docking node at the forward end. This would allow additional modules to remain permanently docked without affecting the arrival of new crews and resupply missions.

Mir’s first crew, veteran cosmonauts Leonid Kizim and Vladimir Solovyov, arrived aboard Soyuz T-15 on 15 March. The Soviets had intended to operate Mir alongside Salyut 7 in the short term, and in May the two cosmonauts departed Mir for a short stay aboard the older Salyut, before returning to Mir at the end of June and then to Earth the following month.

The Soyuz T-15 mission remains the only time that a crew has transferred between two different space stations in orbit, however it also marked the last time that cosmonauts would visit Salyut 7. Although Salyut was boosted into a higher orbit to preserve it for future use, subsequent missions either using the Soyuz spacecraft or the Buran spaceplane, then under development, failed to materialize, and it re-entered in 1991.

Cosmonaut Leonid Kizim on board Mir – via TASS

The arrival of a second principal expedition to Mir, EO-2, in February 1987 marked the start of over two years of continuous occupation. This included three expedition crews, with replacement crew arriving before the outgoing expedition departed so that the station did not need to be de-crewed during the handover period.

During the EO-2 mission, Mir’s first expansion module – the Kvant-1 astrophysics laboratory – was delivered by a disposable TKS-derived propulsion module. This was docked to the aft port of the core module. Kvant-1 included forward and aft docking ports, with its own aft port being used for subsequent Soyuz and Progress dockings.

It was during this first period of continuous occupation that cosmonauts Vladimir Titov and Musa Manarov became the first humans to spend over 365 days continuously in space, although as 1988 was a leap year, they returned home 81 minutes short of a full calendar year after their launch.

Mir was briefly left without a crew when the EO-4 expedition ended in April 1989. A new crew arrived in September 1989 to begin a decade of continuous human presence in space.

Three months later, the Kvant-2 module – incorporating a new airlock, life support systems and scientific instruments – docked at the station’s forward port. Two days later, the Lyappa crane arm was used to swing it around to the zenith, or upper, port.

The Kristall module as seen by the crew of Space Shuttle Atlantis during STS-81 – via NASA

During the subsequent EO-6 expedition, the Kristall module, a materials science laboratory, arrived. Following the same process as Kvant-2, it was berthed at the nadir, or Earth-facing, port of the core module.

The Kristall module incorporated a pair of Androgynous Peripheral Attach System (APAS) docking ports intended for future docking of the crewed Buran spacecraft, which the Soviet Union had been developing to rival the American Space Shuttle. While Buran would only fly to space once, and never carry a crew or visit Mir, these docking ports would later be used by US shuttles visiting Mir in a new era of international cooperation.

Principal expeditions to Mir typically lasted between four and six months, although some cosmonauts remained aboard for two back-to-back expeditions. A typical crew aboard Mir in the early 1990s would consist of two cosmonauts.

When Soyuz spacecraft were used for crew rotations, a third crewmember would typically accompany the principal crew and spend a few days aboard Mir before returning to Earth with the departing crew. Many of these short-duration visitors were part of international partnerships such as Interkosmos and Euromir.

An example of this was the flight of Helen Sharman, the first British person to visit space, who launched aboard Soyuz TM-12 in May 1991 and after five-and-a-half days on Mir returned to Earth with the outgoing EO-8 cosmonauts. Sharman’s flight was to have been paid for by a consortium of UK businesses, but when they were unable to raise the required funds Soviet President Mikhail Gorbachev directed that the mission should go ahead anyway.

The crew of Soyuz TM-12, from left to right: Anatoly Artsebarsky, Helen Sharman, and Sergei Krikalev – via TASS

Sharman’s launch also carried Anatoly Artsebarsky and Sergei Krikalev of the station’s long-duration EO-9 crew. Krikalev remained aboard Mir as part of EO-10, joined by Aleksander Volkov who arrived in October. In space until March 1992, the two cosmonauts returned to a very different world from the one they had left. The Soviet Union had ceased to exist, with Gorbachev formally declaring its dissolution on 25 December 1991. Krikalev and Volkov were now both Russian citizens, and the newly-independent Russian Federation had taken over most of the former Soviet space program.

The new Russian Space Agency, RKA, would continue to operate Mir into the 1990s. This agency would be renamed Rosaviakosmos in 1999, before taking on its modern name Roscosmos in 2005.

Following a 1993 agreement between Russia and the United States to deepen their co-operation in space, plans were drawn up for NASA’s involvement in the Mir program as the first step to developing a new space station as a joint venture: a project which would become the International Space Station. This partnership included joint missions and the addition of new modules to Mir.

In February 1995, Space Shuttle Discovery carried cosmonaut Vladimir Titov aboard its STS-63 mission and performed a rendezvous with Mir. The following month, astronaut Norman Thagard became the first American to go aboard Mir when he lifted off aboard the Soyuz TM-21 spacecraft – remaining aboard for three months as part of the EO-18 expedition.

Space Shuttle Discovery lands on Runway 15 at the Kennedy Space Center at the conclusion of STS-63 – via NASA

It was during EO-18 that the Spektr module arrived – containing living and working areas for NASA crew aboard the station as well as solar panels to boost Mir’s overall power production. Spektr’s arrival necessitated a reshuffle of Mir’s modules, with Kristall moving to the starboard docking port and Spektr occupying the nadir position thus vacated.

Discovery’s February 1995 mission paved the way for STS-71, flown by Space Shuttle Atlantis in June of the same year. Two days after lifting off from the Kennedy Space Center, Atlantis docked with Mir’s Kristall module, which had been temporarily relocated again to the core’s forward docking port to provide sufficient clearance from Mir’s solar panels for the orbiter to dock. The Shuttle mission performed a crew rotation, bringing the three-man EO-18 home and leaving cosmonauts Anatoly Soloveyev and Nikolai Budarin aboard Mir in their place as EO-19.

Atlantis would visit Mir a total of seven times between 1995 and 1997. On its second visit to the station, STS-74, it delivered a new docking module, Stykovochnyy Otsek. This would provide a small amount of internal and external storage space for Mir, but its primary purpose was to increase the clearance between the Space Shuttle and Mir so that dockings could take place with Kristall in its normal position, instead of having to relocate it as had been done for STS-71. The module was attached to Atlantis’ docking port prior to its arrival at Mir, and left connected to the port at the end of the Kristall module when the Shuttle departed.

Two solar arrays were brought up to Mir with the docking module, and later attached to the Kvant 1 module. The docking module itself hosted the external Mir Environmental Effects Payload which was installed during the STS-76 mission and returned to Earth a year and a half later during Atlantis’ final visit, STS-86.

The Shuttle-Mir missions carried cargo, supplies and experiments to Mir, as well as rotating American astronauts aboard the station, although aside from STS-71, Russian crew rotations continued to use the Soyuz.

Space Shuttle Atlantis docked to Mir during STS-71, as seen from Soyuz TM-21 – via NASA

Mir’s final module, Priroda, arrived in April 1996 after launch on a Proton rocket and carried remote sensing and Earth sciences experiments. This was located on the port side of the core module’s docking node, opposite Kristall.

With the International Space Station on the horizon, the beginning of the end for Mir came in 1997 with a series of serious incidents aboard the station. First, on 24 February a defective Vika oxygen generator ignited like a blowtorch, filling Mir with smoke. Although the crew were able to extinguish the fire after about fourteen minutes, worse was to come.

With Russia’s space program buckling under financial pressures, RKA considered eliminating the Kurs automated docking system from its Progress resupply ships, proposing that crews instead perform the dockings manually using the TORU remote control system carried as a backup. A test was carried out in March 1997 using Progress M-33, but cosmonauts were unable to complete the docking because of radio interference which prevented them seeing the feed from the Progress vehicle’s cameras and a collision was narrowly avoided.

The docking test was to be repeated with the next Progress spacecraft. Progress M-34 arrived on 8 April following its launch aboard a Soyuz-U rocket, docking through the automated Kurs system. After being unloaded and re-filled with trash for disposal, the Progress undocked on 24 June, returning the following day for its docking demonstration.

Cosmonaut Vasily Tsibliyev took manual control using the TORU system, but Mir’s crew were unable to track the spacecraft visually as it approached Mir. Suddenly Progress appeared from behind a solar panel, on a collision course, and the cosmonauts were unable to prevent it from hitting the Spektr module.

The Spektr module’s damaged solar panels – via NASA

The collision between Progress M-34 and Mir damaged the solar panels on the Spektr module – responsible for much of Mir’s power generation at the time – and punctured the skin of the module causing air to leak out. Aboard the station cosmonauts had to cut power and data cables into the module in order to seal its hatch before the space station depressurized.

While subsequent repair work allowed partial power to be restored from the solar panels, the module was left unusable for crew operations and aside from these repairs which had to be done by crewmembers in full spacesuits due to the loss of atmosphere, it was left sealed for the remainder of Mir’s career.

With Atlantis entering an Orbiter Maintenance Down Period (OMDP) for a refit in 1997, the final two Shuttle-Mir flights were made by Endeavour and Discovery: STS-89 and STS-91 in January and June 1998 respectively. Mir’s final regular crew, EO-27, departed aboard Soyuz TM-30 on 27 August, leaving the station without cosmonauts aboard for the first time since 1989.

A final crew, cosmonauts Sergei Zalyotin and Aleksander Kaleri, launched to reactivate Mir in April 2000, under the privately-funded MirCorp project which had intended to re-boost the station into a higher orbit and repair and refurbish it for future commercial flights. The pair spent two and a half months aboard Mir, undocking for the last time at 21:24 UTC on 15 June.

After their departure, and the arrival of a subsequent uncrewed Progress cargo mission with supplies for the next crew, funding for MirCorp fell through. Mindful of the size of the station and the potential, however remote, that debris from an uncontrolled re-entry could do damage on the ground, Rosaviakosmos decided to dispose of the aging space station safely through a controlled deorbit.

Mir, as seen by the crew of Space Shuttle Atlantis during STS-71 – via NASA

The final decision to deorbit Mir was taken in November 2000 and signed off by the Russian government the following month, although the operation was postponed to ensure that Mir would reach its fifteenth anniversary in orbit first.

The station’s orbit would be allowed to decay naturally until the station was below 250 kilometers (155 miles, 135 nautical miles) in altitude – at which point a docked Progress spacecraft would fire its thrusters and main engine in a series of deorbit burns to ensure a re-entry over an unpopulated area of the Pacific Ocean.

Progress M1-5 was launched from the Baikonur Cosmodrome on 24 January 2001, arriving at Mir after an extended three-day chase to conserve fuel. The Progress-M1 vehicles were variants of the standard Progress-M resupply vehicles in use at the time, designed to carry additional propellant – either for its own use or transfer to a space station – at the expense of other types of cargo.

Progress M1-5 carried 2,678 kilograms (5,904 lb) of propellant, in the form of unsymmetrical dimethylhydrazine and dinitrogen tetroxide. A standard Soyuz-U rocket carried the Progress into orbit, with the launch taking place from Baikonur’s historic Site 1/5.

In parallel with the Progress launch campaign, a Soyuz-TM spacecraft – which would later fly to the International Space Station as Soyuz TM-32 – was made ready to fly cosmonauts Gennady Padalka and Nikolai Budarin to Mir should the Progress fail to dock. Padalka and Budarin were chosen for this role as they had previously trained for a similar contingency mission to perform a manual docking of the Zvezda module to the International Space Station should it have encountered difficulties.

In the event, neither mission was required, and the crew were stood down once Mir’s orbit dropped too low for a crewed mission to be attempted safely.

With Progress M1-5 docked at the aft port of Kvant-1, Mir was placed into a spin to keep it stabilized and powered down as atmospheric drag slowly reduced its altitude. The target altitude to perform the deorbit was reduced to 220 kilometers (137 miles, 119 nautical miles) in order to reduce the amount of fuel required, meaning a shorter burn and less chance that something might go wrong. In mid-March, Mir was reactivated and prepared for its final maneuvers.

The deorbit was carried out in the morning of 23 March, over the course of three orbits. The first two burns used smaller thrusters, lowering the perigee, or lowest point, of Mir’s orbit to 188 kilometers (117 miles, 102 nautical miles) and 158 kilometers (98 miles, 85 nautical miles) respectively.

The final burn began at 05:07 UTC, with Progress M1-5’s S5.80 main engine firing as well as the thrusters. This burn lasted over twenty minutes, with Progress commanded to fire its engines until its propellant was exhausted. At 05:30 the last signals were received from Mir, with the station moving out of range of the last tracking station along its route.

Mir entered the atmosphere fourteen minutes later to the east of New Zealand, beginning to disintegrate shortly afterwards. According to a Rosaviakosmos press release, the mission ended at 05:59:24 when Mir “ceased to exist”.

The crews of STS-71, EO-18, and EO-19 on board Mir – via NASA

In all, 39 crewed missions to Mir were flown by Soyuz spacecraft and the Space Shuttle fleet. These carried 104 space travelers from 12 different countries on a total of 137 individual trips to the station. These included 28 long-duration principal expeditions.

Seventy-eight spacewalks were made from Mir, with two additional EVAs being made from an airlock on the docked Space Shuttle Atlantis during two of the Shuttle-Mir missions. The spacewalks conducted from Mir included both extravehicular activities (EVAs) outside of the spacecraft and intravehicular activities (IVAs) where the crew entered depressurized parts of the station’s interior – such as the Spektr module after its collision with Progress M-34.

Over 23,000 experiments were conducted aboard Mir during its fifteen-year mission, contributing to scientific fields from astrophysics to geology and materials research to life sciences.

Mir’s greatest legacy remains in orbit in the form of the International Space Station, which took the lessons that NASA and Roscosmos learned through Mir and applied them to construct the largest, most complex, and most expensive spacecraft ever built.

Assembly began while Mir was still operational, with the first module – Zarya – lifting off aboard a Proton-K rocket in November 1998. Space Shuttle Endeavour lifted off a fortnight later on the first of 37 Space Shuttle missions that would visit the station, delivering the Unity module.

Zarya and Unity, the first two modules of the International Space Station – via NASA

The third major component of the ISS – the Zvezda service module, which joined the outpost in 2000 – was refurbished from a backup module built for Mir’s original core, which had also previously been considered as the first element of a Russian-only successor station.

Like Mir, the International Space Station uses a modular structure, with most Russian segment modules launching on Proton and Soyuz rockets, while the majority of the US and international components were delivered by the Shuttle.

Although most assembly had been completed by the time of the Shuttle’s retirement, components continue to be added to the complex. Russia’s long-delayed Nauka laboratory module is currently slated to launch between May and June, beginning a new phase of construction on the Russian segment, and NASA selected Axiom Space last year to develop a new commercial extension to the US segment of the station.

Render of the Tianhe core module of China’s upcoming Tiangong space station – via Mack Crawford for NSF/L2

China will soon begin launching its first modular space station, with the core module – Tianhe – expected to fly aboard a Chang Zheng 5B rocket as early as next month. Like Russia, China used two smaller single-module Tiangong stations to gain experience before progressing to the larger modular design. If this launch goes as planned, a Tianzhou cargo spacecraft will join it in May, before the first crew arrives aboard the Shenzhou 12 mission in June.

One particular field which Mir advanced was the study of the effects of long-term spaceflight on the human body. Cosmonaut Valeri Polyakov spent over 437 days in space aboard Mir, launching aboard Soyuz TM-18 as part of the EO-15

crew in January 1994 and remaining aboard for EO-16 and EO-17, before returning with Soyuz TM-20 in March 1995.

Polyakov’s record for continuous days spent in orbit still stands. Studies of long-duration stays aboard Mir have played a big role in keeping crews safe and healthy aboard the International Space Station and will continue to do so as humans begin to venture beyond the Earth and Moon.

The Lunar Gateway conducts a maneuver using its ion thrusters – via NASA

The Lunar Gateway, which NASA plans to build with its international and commercial partners in the next decade will be one of the first steps in this journey, standing on the shoulders of Mir and the International Space Station. The Gateway will use a modular design, as pioneered by Mir, to support longer-duration missions with astronauts in lunar orbit.

Meanwhile, SpaceX is developing the Starship vehicle which it hopes will one day take humans to Mars. When it does, it will be lessons in long-duration spaceflight learned aboard Mir that keep the crew alive on their long voyage.

While the International Space Station may have surpassed Mir’s records for size, length of service and continuous habitation, it has been able to do so because of the technology, science and partnerships that its predecessor helped to develop and refine. Space stations will be at the forefront of future space exploration, and these projects have been made possible because of the trail blazed by Mir.

(Lead photo of Mir as seen from Space Shuttle Atlantis on STS-74 – via NASA)

Related Articles