RUSSIAN SPACE STATIONS

The Soviet and Russian long duration orbital space stations, Salyut and Mir, were operated from 1971 to 2001. During this period, eight stations were placed into orbit (Table 1). While the stations were in operation, a variety of improvements were made to extend their operational lifetimes and improve their performance. Experience in on-orbit operations enabled the Energia Rocket and Space Corporation (Energia RSC) to develop a Russian space-station concept. This concept was most fully embodied by the Mir space station and the Russian segment of the International Space Station.

The basic principles behind the Energia RSC concept, as actually developed and implemented, were as follows:

1. Use of a modular structure in which modules are classified as either ”service modules” or ”research modules.”
2. Use of a relatively inexpensive transportation infrastructure, including Soyuz manned spacecraft, Progress automated supply spacecraft, Soyuz automated spacecraft, and Raduga research-material return capsules, for station servicing.
3. All space-station equipment is designed for maintainability to increase the usable life span of the equipment.
4. All routine operation of onboard equipment is automated as much as possible to free the crew for research work.
5. For crew safety, a piloted spacecraft is always docked at the station.
6. The stations were used to address a broad range of research goals in science, engineering, and various applied fields.

The major goals of space-station use are as follows:

- research on the behavior of the human body under space conditions to determine a strategy for human space exploration (habitable structures in low Earth orbit, interplanetary flight, and lunar/planetary colonization);
- space research using instruments carried above the atmosphere;
- remote sensing of Earth’s surface and atmosphere for basic research as well as for applications, for example, studies of Earth’s natural resources for human use;
- basic research in materials science and the production of materials and biological substances under microgravity conditions;
- research and development of proposed materials and techniques for future projects (research on the behavior of complex structures; development of tugs, mechanisms, cable systems, and interplanetary spacecraft components).
The long duration orbital space station program began with the launch of the world’s first space station, Salyut, on 19 April 1971. At that time, it was still too early even to mention the idea of an operating concept for an orbital space station. Too many space station operational issues had not yet been resolved.

Table 1. Operation of Soviet and Russian Orbital Space Stations

The issue of crew work assignments and capabilities during station operations had not been fully clarified. Another important consideration was that in 1971, it was still extremely difficult to predict either the station lifetime or the amount of time that crews could work on board the station.
The sole long duration flight before this was the Soyuz-9 spacecraft (crewed by A. Nikolaev and V. Sevast’yanov), which remained in orbit for 18 days; the scheduled duration of the Salyut mission was 3 months because at that time, it was virtually impossible to predict that a complex spacecraft could remain functional for several times that period.
The design for this first space station maximized the use of the design and equipment advances that were available at that time. Many of the on-board systems for the space station were adapted from the Soyuz spacecraft, and the pressure hull and basic structural elements of the main working compartment were adapted from the Almaz space station, which was then under development.
The orbital portion of the space station consisted of a transfer compartment, a working compartment, and a scientific equipment compartment. The 2.1-m-diameter working compartment had a docking system and a set of solar arrays, adapted from the Soyuz spacecraft. The working compartment, which was the largest, had a pressure shell that consisted of two hemispheres 2.9 and 4.1 m in diameter connected by a conical transition section. The 2.1-m-diameter equipment compartment was designed to house the orbital adjust propulsion adapted from the Soyuz spacecraft and a set of newly developed bipropellant attitude thrusters. A second set of solar panels (also adapted from the Soyuz spacecraft) was mounted on the exterior of the compartment. The scientific equipment bay was designed specifically for the Salyut space station, and was installed in the working compartment.
The attitude and flight control system (gyro units, integrator, computer, angular-velocity sensors, manual attitude control system, infrared vertical sensor, ion flux sensors, and pilot’s scope), electrical power system (solar panels, standby chemical battery, charge control system), radio communications and telemetry system, radio orbit monitoring system, command uplink, central pilot control panel, rendezvous system, and life support systems were all adapted from the Soyuz spacecraft. Although the onboard control system was partially adapted from the Soyuz spacecraft, because of the large number of new systems and scientific instrumentation, in particular, it was substantially modified, and additional new equipment was added.
A new temperature control system was developed using the same hardware as that in the Soyuz spacecraft. One of the innovations involved the use of pipes carrying the heat-transfer agent to stabilize the hull temperature; this ensured favorable temperature conditions for the numerous hull gaskets, thereby maintaining integrity of the seals during a long flight.
The scientific equipment aboard the 1.3-metric-ton station included the following: a solar telescope, an X-ray telescope, an infrared telescope/spectrometer, and a 60 x viewer, in addition to various other pieces of equipment. A significant fraction of the equipment was intended for astrophysical research. At that time, it was believed that astrophysical research was the best route to new fundamental scientific results.
The Salyut space station hosted one expedition. A crew consisting of V. Dobrovol’skii, V. Volkov, and V. Patsaev worked for 22 days in orbit. During this expedition, approximately 50 medical experiments were performed, including several experiments involving the cardiovascular system, collection of blood samples, and the blood supply to cerebral vessels, bone density and metabolic studies were also performed. The biological experiments were aimed at determining the effects of weightlessness on living organisms. One such experiment was the Oasis experiment. Seeds and plants were placed in a special container/ greenhouse and were then studied and compared with experimental samples grown on Earth.
An extensive program of astrophysical research was scheduled; however, because the cover on the compartment containing the solar telescope and spec-troscopic instrumentation did not open in orbit, most of the astrophysical research was canceled. The Orion telescope was used to map the sky at ultraviolet wavelengths that are invisible from the ground. Ultraviolet spectra of Vega and Hadar were obtained. Particle fluxes were determined using the Anna-3 gamma-ray telescope. Fixed and manually operated cameras were used to photograph Earth’s surface in regions of greatest interest to geologists and cartographers, i.e. the mining region of Altai, Lake Balkhash, and central Asia. More than 1000 photographs of these regions were obtained.
Unfortunately, the first expedition to the first orbiting space station ended in catastrophe. The crew perished upon landing due to a failure in the Soyuz spacecraft. Significant improvements were made to the Soyuz spacecraft as a result of the accident, and work continued on the orbiting space stations (see Fig. 1). The first Salyut station was followed by the launch of the Salyut-2 and Salyut-3 space stations. These space stations were involved in specialized operations for the Ministry of Defense and were not part of the overall space station program.
The next space station in the program was Salyut-4, which was a significant improvement over the original Salyut space station. The main deficiency of the original Salyut space station was that it was necessary to expend a significant amount of fuel to keep the spacecraft rotating about an axis pointing toward the Sun during the main portion of the flight. This was necessary to keep the rigidly fixed solar arrays, which provided station power, pointing toward the Sun. Thus, the main change made in the space stations from Salyut-4 on (compared with the original Salyut space station) was the addition of three independently steerable solar arrays installed on the working module. To compensate for the increased mass of these solar arrays, the number of propulsion system tanks was reduced, and the station was moved to an altitude of 350 km to reduce fuel requirements for orbital maintenance. The mass of onboard research equipment was increased to 2 metric tons. The independently steerable solar arrays led to an improvement in research capability for Earth and space observations.
This station saw the first installation of the Kaskad cost-effective attitude control system and the Delta experimental navigational system. The temperature control system made the first use of an experimental heat pipe loop system, which turned out to be exceptionally promising for future generations of orbital space stations, and work was begun on developing of a closed-cycle water supply system for the crew, for which a condensate water regeneration system (CWRS) was installed on board the station. Approximately half the water excreted by the crew ends up in the air via the skin; the CWRS collects this water and treats it to make it potable again.

Figure 1. Russian and Soviet orbital space stations.
The Salyut-4 mission placed heavy emphasis on remote sensing of Earth’s surface, and the mid- and southern-latitude territory of the Soviet Union was photographed. During these flights, valuable scientific data were obtained concerning the physical processes in the active region of the Sun, in Earth’s atmosphere, and in outer space across a large portion of the electromagnetic spectrum. This marked the first time in the history of spaceflight that photographic and spectrographic observations were made of the auroras and noctilucent clouds (a rare natural phenomenon of great scientific interest). The effects of long duration spaceflight on the human body were studied, and various methods for treating the unfavorable effects of weightlessness were tested.
Engineering experiments to develop new systems and instruments for future spacecraft and long-term orbiting space stations formed an independent part of the flight plan. Successful performance of these experiments laid the foundation for further improvements in space hardware to be used for ever more complex tasks in space research. The assured on-orbit service life of the space station was extended from 90 days (the original Salyut space station) to half a year. However, the station actually remained functional for more than 2 years. Each successive space station was improved in the following areas: increased operational lifetime, improved capabilities for installation of special-purpose equipment, improvement of station performance for research (improved attitude stabilization, increased electrical power capacity, and improved control system).
Maintaining long duration functionality of an orbiting space station requires an economical supply mechanism. Development of the Progress automated cargo spacecraft was the principal design decision affecting the operational characteristics of subsequent generations of space stations.
The first Progress spacecraft docked with the Salyut-6 space station on 20 January 1978. It delivered consumables for the life-support system, additional research instrumentation, and additional fuel for the space station onboard propulsion system. At this point, it became possible to support effective multiyear station operations. The Salyut-6 space station included an additional transfer compartment with a second docking assembly enabling both a Soyuz spacecraft and a Progress cargo spacecraft to dock simultaneously at the station during resupply and cargo operations or two Soyuz spacecraft to dock at the station during crew changes. The second transfer compartment also provided an opportunity for extravehicular activities (EVA), in which case the transfer compartment became an airlock holding spacesuits and all equipment required to reach the station exterior; special handles on the station hull were available for the cosmonauts to move about and to attach themselves.
Various onboard systems were improved, a color television system was added, and a folding shower was installed in the operations compartment for enhanced crew comfort. The operational service life of the station was increased to 3 years. At this point, the space stations began to have a fairly mobile servicing system. Soyuz spacecraft were used for station crew changes. This spacecraft was continually docked to the station and also served as an assured crew return vehicle. The assured crew return vehicle was simultaneously replaced as each crew changed.
All necessary cargo was transported to orbit using the Progress cargo spacecraft. The cargo manifest depends on the program and might include fuel, consumables for the life-support system, interchangeable equipment for scientific instruments, and/or interchangeable equipment for EVA.
An extremely important avenue for improving space station operating efficiency was opened once onboard maintenance and repair by the cosmonauts themselves became possible. This required overcoming the technological and psychological barriers related to crew safety during repairs while in orbit. The Salyut-6 scientific program resulted in the performance of more than 1550 experiments involving the use of more than 150 scientific instruments that weighed in excess of 2200 kg. More than, 750 kg of scientific instruments were brought on board using the cargo delivery capability. Research was conducted in the fields of astrophysics (submillimeter telescope and radio telescope with 10-meter parabolic dish antenna and others), materials production (Splav and Kristall experimental production systems), geophysics (photographic mapping equipment and multispectral camera), biology, medicine, etc.
One important mission of the orbiting space stations is studying the adaptation of the human body during long flights under weightless conditions. Such research is required to develop a strategy for future human participation in space exploration and can be performed only on board a space station. The longest stay on the Salyut-6 space station was 184 days.
The next space station in this generation was Salyut-7. In many respects, this station was identical to Salyut-6, but Salyut-7 also represented several engineering improvements. For improved efficiency of station operations, a special module contained scientific instrumentation (X-ray system, ultraviolet telescope, etc.), as well as a modern control system based on the Salyut-5B computer, and gyrodines (flywheels) to enable attitude stabilization without fuel consumption. However, it was then decided to use this module on the Mir spacecraft instead. The module came to be known as the Kvant module.
During development of the Salyut-7 space station, it became clear that the solar array area needed to be increased. This change in station design did not seem possible due to problems in fitting the solar arrays under the nose fairing. It was then decided to retrofit the station with solar arrays while in orbit. A system of specialized cables for this purpose was included in the main solar array design, and these cables were used to install the additional panels, once the station was in orbit. Several serious repairs were made during the Salyut-7 flight. One of the fuel lines on the station lost pressure, perhaps due to a meteoroid impact. During a series of six spacewalks, the cosmonauts succeeded in identifying the failed line and hooked up a new line to the propulsion system. A special press for sealed line crimping and special valves mounted on the fuel nozzles, were developed.
In February 1985, during an unmanned portion of the flight, there was a loss of communications with the station due to a failure in the command system and an error by a Flight Control Center operator; the resulting inability to intervene in automated operations from the ground caused a failure in the storage-battery charging mode, the system lost power, and the station failed completely. There was a real risk that the station might be completely lost. The main question was whether it would be possible to dock with a completely uncontrolled station so that repairs could be made. The future crew was given appropriate training to support docking with the station as an ”uncooperative object.” No operation of this type had ever been performed before.
A special mission—cosmonauts V.A. Dzhanibekov and V.P. Savinyi on the Soyuz T-13 spacecraft—was sent into orbit. The crew rendezvoused and docked with the space station under manual control, using instructions from the ground, a laser rangefinder, and the onboard digital computer. The cosmonauts made the repairs, and the station was once again operational.
The main drawback of the Salyut stations was that they consisted only of a single module, which limited the options for placing research instrumentation. Another deficiency was a lack of electromechanical actuators, which implied high fuel consumption for attitude control and, thus, a large amount of cargo traffic from the ground to the space station. The Salyut space stations did not have any communications via relay satellites, meaning that there were large time intervals when the stations were out of communications range. The experience gained on the Salyut space stations with respect to control systems based on digital technology facilitated the transition to modern control systems.
The modular design of the new Mir space station led to enhanced options for housing a large quantity of scientific equipment. The space station consisted of six modules, the base unit and five research modules (Kvant, Kvant-2, Kristall, Spektr, and Priroda). The main service module in the station was the base unit and all of its support equipment. This module was based on the Salyut-7 base unit but had several significant improvements.
The following base-unit systems were modernized. The control system enhanced the capabilities of the station. The new Kurs rendezvous system did not require any rotation of the station during rendezvous operations. The power system capacity was increased, and voltage stabilization was improved. A radio system with a highly directional antenna was added for communications via a relay satellite.
The research modules were based on the FGB (functional cargo block) spacecraft developed by the Khrunichev State Center for Space Science and Space-Related Manufacturing. Initial plans called for attaching the Mir research modules to the station during the first year of flight. However, development and fabrication of the research modules turned out to be more labor-intensive than originally thought, and it actually took several years to install them. Despite this fact, the station continued in use, and the research program was designed around the modules that were present at the station at any given time.
The first research module at the Mir space station was the Kvant module, which included a complete astrophysical observatory with a system of telescopes developed in Russia as well as in various European countries. Note that the division into special-purpose modules and service modules is arbitrary because all modules contain both support equipment and research-oriented equipment. For example, the Kvant module included some support equipment that was vital to the space station as a whole: control-system units and flywheels for attitude stabilization based on gyroscopic forces to reduce fuel consumption. The awkward atmospheric regenerators were replaced by a water electrolysis system to supply the crew with oxygen, as well as a regenerative carbon dioxide absorption system.
The next Mir space station module was the Kvant-2. This module contained research equipment to enhance the space station’s scientific program. In particular, a steerable gimbaled platform carrying photometric, video, and spectro-metric instrumentation was mounted on the exterior of the module. This platform could be controlled either by the space station crew or by Flight Control Center personnel. Scientists could now study, from the ground, any area on Earth’s surface or in the sky. It included a fairly spacious airlock with a large, 1-m diameter exit hatch. The module included an additional set of flywheels installed on the exterior rather than in the interior (as in the Kvant module) of the habitable compartment. Unfortunately, further operational experience with the space station proved that this engineering design solution could not be justified because it turned out to be too difficult to replace the flywheels in the event of failure. This module also provided a new piece of propulsion equipment for use during EVA—the cosmonaut propulsion system (CPS), a ”space motorcycle.” Several cosmonauts used the CPS, flew around the station, and photographed it.
The next research module in the Mir space station was the Kristall module. This module housed a wide variety of research equipment for use in materials-science research, including equipment for research on industrial-scale materials production under microgravity conditions and various pieces of biotechnology equipment. The Kristall module was equipped with a second docking assembly, the androgynous peripheral docking system (APDS) for docking with the Buran space shuttle.
Subsequent research modules, the Spektr and Priroda modules, were initially expected to be outfitted with spectral and laser equipment for remote-sensing observations of Earth, including observations aimed at studying Earth’s natural resources.
The Russian-American Shuttle-Mir program, which occurred against the background of preparatory joint operations for the International Space Station, started before the launch of these modules. Research equipment to support work to be performed by an American astronaut was installed on the Spektr and Priroda modules. Once these modules were docked to the station, Mir began operations in its full configuration. The Shuttle-Mir program consisted of having American astronauts work on board the station; these astronauts were initially delivered via Soyuz spacecraft and eventually via the American Shuttle spacecraft. The American Shuttle spacecraft first docked with the Russian Mir space station on 1 July 1995. The Shuttle initially used the docking port on the Kristall module, but a special docking module with a special hatch was later installed at the space station. During a 3-year period beginning in 1995, the Shuttle docked with the Mir space station nine times as part of this Russian-American program.
June 1997 marked the most hazardous and troublesome event in the history of the Mir space station. During final experimental testing of a remote-control docking mode (manual control by a remote operator) with a Progress M-34 spacecraft, the crew was unable to reduce the approach velocity in time, the spacecraft crashed into the space station, and the Spektr module was depres-surized. This module was isolated from the remainder of the station, thereby preserving the functionality of the station as a whole.
By 23 March 2000, the Mir space station had ceased active operations; in 2000, it was decided that it was not feasible to improve Mir operations at the same time that work was proceeding on the International Space Station. The Mir space station was deorbited and reentered the Earth’s lower atmosphere over the South Pacific. During this 15-year period, the Mir space station performed an extensive program of research and experiments in various areas of science, engineering, and various areas of human activity.
The Kvant module X-ray telescope was the first to detect X-ray emission from Supernova 1987A in the Large Magellanic Cloud and follow the evolution of the supernova spectrum as a function of time. These observations had a high priority. An X-ray source in Cygnus (black-hole candidate) and clusters of galaxies in Perseus were observed. There were, in total, 6200 astrophys-ical observing sessions. A series of photographic cameras with different focal lengths were used to photograph Earth’s surface at spatial resolutions of up to 10 m on multispectral film that had a maximum coverage width of 200 km on the ground. More than 125 million square kilometers of Russia and various foreign countries were photographed, resulting in more than 5000 photographic frames.
Several different control modes, including remote control from the Flight Control Center via a relay satellite, were tested on the spectroscopic instrumentation package that was mounted on the Kvant-2 steerable, gimbaled platform. This remote-controlled, onboard detector system enabled the acquisition of realtime video and spectrometric data refreshed at 2-day intervals.
Plasma-beam ionospheric sounding experiments were performed, in part, to monitor electromagnetic-field variations as earthquake precursors.
While Mir was in operation, final modifications were made to various processes for producing epitaxial silicon structures, in addition to cadmium telluride, zinc oxide, and gallium arsenide monocrystals. Experiments were conducted for zone melting of germanium, silicon, and indium antimonide without crucibles. The semiconductor materials produced on board the Mir space station are being used for research studies, as well as for fabricating experimental devices and microelectronic components. There were more than 290 experiments involving manufacturing processes. Approximately 200 materials (both materials already in use and future materials) were tested during the space-based materials science experiments; the results of these experiments confirmed that space-related factors had a strong effect on structural materials and coatings. During these experiments, coatings for temperature control system radiators were studied, and it was confirmed that they would remain functional for up to 15 years; techniques and coatings were developed to protect materials against exposure to atomic oxygen by depositing thin films based on fluoroplastics, metal oxides, and silicon. In all, there were more than 2450 experimental sessions involving materials science.
Biotechnology is one promising field of research, and several experiments in this field were performed on various pieces of equipment aboard Mir. The most important of these were experiments on protein crystallization and the generation of highly effective producer cells through hybridization and electrophoresis in space. The high productivity and efficiency of the biotechnology processes have now been confirmed, and the necessary engineering data have been obtained to construct a full-scale installation. In all, there were more than 130 experimental sessions involving biotechnology.
Experiments were performed on board Mir to study the growth and development of higher order plants as a function of time and to develop technologies using various growth media. An increase in biological activity by a factor of 5 or 6 relative to control samples occurred in crops exposed to radiation under spaceflight conditions. Research was performed to study changes in the vestibular apparatus of various living organisms, quail, crabs, newts, and snails, under spaceflight conditions. In addition to their practical applications, the results obtained are also of great interest for basic science. More than 200 biological experiments were performed.
Numerous medical experiments and studies led to determination of the basic laws governing human adaptation to long-term space flight. The results enable us to predict with high confidence that longer and longer manned space flights will be possible, including flights to distant planets; the results will also find application in general medical practice. Doctor/cosmonaut V. Polyakov flew on Mir for 437 days. A total of 1400 medical experiments were performed on board Mir.
The engineering experiments enabled more precise determination of the specifications for newly developed structures. One such result was development of a reusable single-leaf solar array based on a hinged-rod beam for on-orbit use; the solar array was installed on the Kristall engineering module. A process and design was developed for a thin-film centrifugally spun 25-m-diameter mirror that could serve as the prototype for the primary element of a space-based system for nighttime illumination of Earth’s surface by reflected sunlight.
A design was developed for a promising system (called the “Topol”) for repeatedly opening and closing the solar panels in a two-leaf solar array for a future power system. A 6.4-m-diameter parabolic dish antenna was deployed at the space station, and it was confirmed that it would be possible to develop large antennas up to 100 meters in diameter. The experience in research on assembly and installation procedures for use in space, the physical and chemical properties of materials (including memory alloys), and the dynamics of large space-frame structures gained during preparations for, and performance of, these experiments suggests that it will be possible to develop specialized power modules with a load-bearing frame, a heat dissipation system, reusable solar arrays, and solar gas-turbine power plants. More than 800 engineering experiments were performed on board Mir.
Like the Salyut-6 and Salyut-7 space stations, the Mir space station also hosted cosmonauts from various countries in the Americas, Europe, and Asia, as well as experiments using foreign equipment. The equipment and instrumentation used also was of scientific and applied interest to the Russians and led to several novel, and, in some cases, important scientific and engineering results, as well as results in the applied sciences. In addition to the international scientific research collaborations, programs were also performed on Mir on a commercial or fee-for-services basis.
In 1990, the first protein crystallization experiment was performed pursuant to the terms of a commercial contract with the U.S. firm, Payload Systems. The Mir space station hosted cosmonauts from Japan, Great Britain, Austria, Germany, France (twice), and the European Space Agency (ESA) (German citizens) on a commercial basis. Flights involving U.S. astronauts were also performed on a commercial basis. More than 31,200 experimental sessions were conducted at the Mir space station in a 15-year period.
The Mir space station was a new-generation space station that absorbed all of the operational experience from orbiting space stations that had been developed in Russia over the years. The new engineering design solutions adopted for Mir enabled it to remain operational for a record period of time — 15 years—an impressive achievement for an orbiting system of such complexity. Of course, it should be noted that the original developers of the space station did not anticipate that it would remain in operation for so long. Many interesting engineering design solutions were adopted for the space station and various related systems and assemblies. The system for supplying the space station with all required items—fuel and cargo—using Progress automated spacecraft is one of the essential features of Russian orbiting space stations. This system is unique in the world (see Fig. 2). Delivery of propellant for the space station thrusters was another logistical element mastered during space station operations. The two propellant components for the onboard propulsion system were transferred from tanks onboard the cargo ship using special airtight connectors.
Scientific research results from the Mir space station were transmitted to Earth via radio downlink or returned together with the crew on a Soyuz spacecraft. In addition, the space station also carried a special Raduga capsule that could be independently returned to Earth. This capsule was a small lander, thermally insulated for passage through the lower atmosphere at velocities nearly equal to the orbital velocity. The capsule is attached to a Progress cargo spacecraft and uses the Progress propulsion system for braking in Earth’s atmosphere. After the spacecraft undocks from the station, it goes through a braking maneuver using its own propulsion system, whereupon the capsule separates from the spacecraft. The Progress spacecraft burns up in the atmosphere, and the capsule lands separately in the specified landing zone.
The solar arrays remained continuously oriented toward the Sun for the entire 15-year mission. The electrical drive for the solar arrays was located within the pressurized compartment, and the torque was transmitted to the solar-array structure through the airtight compartment wall by an electromagnetic field. This engineering design solution, first of all, enabled housing the electric motor under appropriate conditions, and, second, rendered a complex set of seals unnecessary for torque transfer to the solar-array structure on the space-station exterior.
The Mir space station had a stand-alone propulsion system, which was mounted on the 15-meter Sofora truss. The propulsion system was mounted this far from the base module to increase the thrust lever arm for generating the required torques, and thereby reduced the amount of fuel required to eliminate accumulated angular momentum due to drag in Earth’s upper atmosphere and gravitational perturbation torques. The space station control system had been improved from that used in the first Salyut. This system is used for space-station maneuvers and attitude control and determination of the space station’s physical position (i.e., navigation). The Mir control system included a computer system and a set of sensors (Sun and star sensors and magnetometers). Gyrodynes (flywheels) were used as attitude-system effectors. Gyrodynes are single-degree-of-freedom power gyroscopes in magnetic bearings (for longer lifetimes and low noise levels).

Figure 2. Transportation system used for servicing Mir space stations.
Standard procedure called for automatic docking with the Mir space station. However, the capability was always there to perform this operation manually, and this capability was used on occasion. If necessary, a cosmonaut could dock the cargo spacecraft under remote control; the cosmonaut was on the space station, but his “eyes”—television cameras—were on the Progress spacecraft. A total of 75 extravehicular activities and three intravehicular activities (in the depressurized Spektr module), a total of 360 hours, were performed on the Mir space station. The main purposes of these extravehicular/intravehicular activities were as follows: performance of experiments and research related to the behavior of materials in space, development of promising engineering design solutions, enlargement of the space station, and repairs.

Figure 3. Salyut and Mir flights, 1978-1999.
The main deficiency of the Mir space station was limited power. And in spite of the fact that the space station had fairly large installed power in its full configuration, mutual shadowing of the solar panels prevented any fundamental solution of the power problem. The most effective technique was to mount the solar panels on masts extending outward from the basic structure and provide two degrees of freedom instead of one. Our operational experience with the Mir space station indicated that the Kvant-2, Kristall, and other research modules were too large, their weight, their cost, and the labor required to build them were not commensurate with their research equipment capacity. The modules should have used weight more effectively by using standardized bays for transporting modules to the space station.
One deficiency of the Mir space station was the low orbital inclination (51°), which put virtually the entire territory of Russia out of observational range. An orbital inclination of 68° would be required to increase the effectiveness of the space station in natural resources- and geophysics-related research. These changes were made in the design of the new Mir-2 space station. Additional changes include modifications to many of the onboard systems: a closed-loop crew oxygen and water supply system consisting of a water electrolysis system, a water condensate and urine regeneration system, and a system for recovering oxygen from carbon dioxide, and others. The control system was designed as an integrated data processing and control system. The power supply system used a combination of solar cells and a high-voltage (to minimize transmission losses) solar gas turbine with solar concentrator mirrors. Androgynous docking assemblies (APAS) were used.
The Mir-2 design became the design basis for the Russian segment of the International Space Station (ISS). The overall architecture, basic purposes, design of the modules, and equipment complement for the service systems in the Russian segment of the initial ISS configuration were similar to those used in Mir-2. The Salyut and Mir space stations became the first space laboratories to provide many countries around the world the opportunity to implement their own national space programs, because they were the first international space stations (see Fig. 3). The International Space Station project made full use of the operational experience gained on the Salyut and Mir space stations.