 |
Backgrounder: Information About Russian Space Station Mir
Russian space authorities have set March 22 as a deadline for the space station Mir's fiery reentry into Earth's atmosphere. Following is some developments of the Mir's 15-year history.
The first element of Mir was launched on February 20, 1986 at an inclination of 51.6 degrees. The current Mir Space Station is actually a third-generation Russian space station and a complex of different modules that have been pieced together.
The Salyut stations of the late 1970s and early 1980s were successful programs from which Mir grew.
In July, a cosmonaut disconnected a power plug prematurely, setting the station adrift. A month later, the main computer failed during a cargo ship docking, setting the station adrift again.
In early 1999, Russia announced Mir would be taken out of orbit in 2000 unless new funds could be found, and a crew that waswidely expected to be the station's last returned to the Earth onAugust 27.
In the year, Russian cosmonaut Sergei Avdeyev set the record for total time spent in space -- 747 days in three missions.
Last year, the Netherlands-based MirCorp, backed by private investors, reached an agreement to lease Mir. Then, MirCorp paid for a cargo ship and a 73-day mission to Mir, and announced ambitious plans for the future. In November, the Russian government said MirCorp had not met its obligations and announced that Mir will be dumped.
Russia uses the Soyuz-TM spacecraft to transport crews and cargo to and from Mir, and uses the Progress-M spacecraft as a cargo and supply vehicle to send science equipment and data to and from Mir. The latter can also be used to conduct experiments either while attached to the complex or during free flight. When sent back to Earth, it removes waste materials from the station.
Typically, two or three crew members aboard a Soyuz-TM spacecraft begin a two-day space flight from the Baikonur cosmodrome in Kazakhstan to the Mir. After docking, crews make the hand-over activities and the returning crew members use the resident Soyuz- TM for the flight home.
Mir consists of six modules arranged in a T-shape, including a core module and five other components. With a cargo ship and an escape capsule attached, it weighs up to 154 tons with its onboarde quipment manufactured in 27 countries.
Mir's normal orbit is about 250 miles above the Earth. It circles the planet about 16 times a day at a speed of about 28,163 kilometers per hour.
Building and maintaining Mir cost 4.2 billion U.S. dollars, including the overall 3- billion-dollar cost of building Mir, according to the Russian Space Agency.
Since the launch of its core module, Mir has had 104 people aboard, including 42 Russian cosmonauts, seven U.S. NASA (NationalAeronautics and Space Administration) astronauts and others fromBritain, France, Germany and other countries.
Cosmonauts and astronauts staged a total of 78 spacewalks, lasting 352 hours altogether, and the champion space walker is Russian cosmonaut Anatoly Solovyov with a record of 16 spacewalks totaling 77 hours.
During its 15-year life, Mir has witnessed more than 16,500 experiments conducted aboard and 24 international programs have been realized on it.
The station's development resulted in more than 600 new technologies, which later turned out to be useful to industry. The most important ones are: spacecraft assembly and launch from orbit,illumination of the polar regions of Earth Construction of space-tether systems, refining laser-communication systems and probing Earth's ionosphere from low orbit.
At early hours on March 22, or one day earlier or later, the 137-ton, 33-meter long and 30-meter wide Mir will be thrust to plunge into the waters of latitude 47 degrees south and a longitude of 140 degrees west in the south Pacific Ocean. Enditem
The Mir module, the first module of the complex placed in orbit,is the main module of the station. It provides docking ports forthe other modules to attach to. There are five docking ports onthe transfer compartment of the Mir module. One is located along the long axis of the module, and four along the radius in 90-degree increments.
There is another docking port on the aft end of the Mir module.The various modules attached to the docking ports can be movedaround to different configurations.
The Soviet Union successfully launched the core module of Mir on February 20, 1986, and predicted the station would last three to five years. The first crew took off for the station on March 13.
In 1987, the station's second component, Kvant 1, arrived at Mir but had trouble docking as crew members found refuse stuck on the docking port.
In 1991, a cargo ship went out of control during its final approach to the station, nearly colliding with Mir. The chaos and financial troubles accompanying the collapse of the Soviet Union forced Mir's crew to stay in orbit months longer than scheduled.
In 1995, Russian cosmonaut Valery Polyakov returned from a 438-day mission, more than 14 months, which is the longest continuous human space flight. Later, Norman Thagard became the first American astronaut to visit Mir.
On February 23, 1997, a series of dramatic accidents started with an oxygen- generating canister bursting into flames and nearly forcing the crew to evacuate. On June 25, a cargo ship rammed the station during a practice manual docking, puncturing a laboratory module, but the crew quickly sealed it off, saving the station.
Russia's Mir Destruction PlanFifteen years ago, on February 20, 1986, the launching of the Core Block marked the beginning of the construction of the Mirorbital station, which is undoubtedly one of the most important cosmonautic engineering achievements in the 20th century. In these years, Mir has become essentially a flying test bed for many technological solutions and processing techniques to be used at the International Space Station.
Last week, the Russian Space Agency set Mir's final critical orbit approximately at 210 kilometers, instead of the original planned 250 kilometers. At that point the Progress tanker will stabilize Mir's rotation and lower the perigee to 160 kilometers over the selected reentry area in two burns. The final braking maneuver is scheduled for wee hours Wednesday, maybe one or two days later, depending on the solar activity and density of the atmosphere.
The world community has expressed a great interest and, in some sense, concern about forthcoming deorbiting of Mir.
Mir's unburned fragments will reenter atmosphere and splash into an area of the southern Pacific Ocean between Australia and South America, which is free from shipping routes and is usually used for sinking debris of launch vehicles and spacecraft by Russia and other countries.
The foreseen controlled deorbit of the Mir station would cover three stages. They are: 1. Passive waiting of the date when the orbital altitude decreases to 250-240 kilometers, the so-called pre-descent orbit.This stage started after the docking of the Progress M1 cargovehicle on January 27, 2000 and was completed in early March 2001. 2. Construction of the approximately 160-230 kilometers descentorbit with a perigee located above the sinking area by usingseveral burns of the Progress M1 cargo vehicle engines. Thisprocess is still going on. 3. Progress M1 executes the final deorbit impulse to make Mir pass to the reentry trajectory, which is slated for Wednesday.
Undestroyed station fragments could impact the outlined Pacific area from three diurnal orbits. A basic estimate shows that the final deorbit impulse will be executed at the orbit arc from the Gulf of Guinea to the Caucasus.
During Mir descending along the last reentering orbit, the station's main body and its external elements will sustain progressively increasing stress and thermal loads as atmosphere density increases. Outer antennas and solar panels will burn first at altitudes of 110-100 kilometers. The destruction of the mainbody structural elements and hence the primary fragmentation ofthe whole object can take place at altitudes 90-80 kilometers.
The separate fragments will continue their descent in the atmosphere independently. They can further split into parts, and the fragmentation process will terminate at altitudes of 50-40kilometers. The majority of fragments will melt and completely burn down, but the most heavy and high-melting ones can reach theEarth surface.
Aerodynamic characteristics of separate fragments can differ essentially and hence their descent downranges are also different. That forms the fragments dispersion area. Moreover, the descent downranges of fragments depend on the altitudes where they are formed. The width of the dispersion area is determined by the lateral force coefficient of each fragment during its motion in the atmosphere.
The development of the destruction model for a complex artificial space object is a non-deterministic problem that cannot be solved precisely, at least at the present time. The mainreasons of this situation are the following:
-- A sequence of the fragments separation and their shapes are determined by an initial object orientation and the uncontrolled object motion relative to the center of mass under the action of aerodynamic moments is impossible to analyze precisely.
-- Precise determination of aerodynamic characteristics of separate fragments along the descent trajectory is not possible due to the uncertainty of their shape and also fragments rotation around their centers of mass.
Therefore it is practically impossible to determine a complete set of fragments formed during the object reentry into the atmosphere, and longitudinal and lateral dispersion of the fragments. So, the problem of successive disintegration of the Mir into fragments and that of their final set was solved only in an approximate way.
A total estimated mass of unburned fragments would be 20-25 tons with a total expected number of fragments up to about 1500 pieces. Length of the fragment impact area along the reentry path is estimated to be 6,000 kilometers long and 200 kilometers wide.
In Anfimov's opinion, the nominal implementation of the developed Mir deorbit and sinking plan practically entirely excludes any damage infliction. Nevertheless, it is not possible to exclude entirely an occurrence of contingencies onboard the station or in the flight control loop.
All such possible situations have been analyzed and methods to control them have been developed, including a launch of the Soyuz transport vehicle with the crew to dock the station and to performrepair work there, said Anfimov.
If the final stage of Mir's crash does not go well, an option remains to correct the station trajectory by using engines or changing an orientation of the station or its separate solar panels in order to avoid hitting the land. Thus the risk of the Mir deorbit in a completely uncontrolled mode and fragments falling on the land is inessential.
According to the above-analyzed program, Anfimov concluded that the set of implemented preparatory efforts and the developed program of controlled Mir station deorbit should provide a safe sinking of unburned fragments in pre-determined area with a high enough reliability.
Russian Space Stations' Development HistoryThe station Mir lasting out its final days in orbit is the eighth orbital station in the history of Russian space exploration and the first and last station of the third generation. The firstand main element of Mir, a core module, was launched into orbit on February 20, 1986.
The current Mir is actually a complex of different modules that have been pieced together, grew from the Salyut stations of thelate 1970s and early 1980s.
According to the Russian Aerospace Agency, the first five stations of the Salyut type, also the first-ever space orbiters inhuman history, belong to the first generation. They could not be used for manned missions on a large scale because they had onlyone docking unit.
The first station of the Salyut type, launched in April 1971, was on an unmanned mission for 170 days. Although Salyut-2 spent only 26 days in orbit, it was in manned mode for 23 days. Salyut-3spent a total of 213 days in orbit with 15 days in manned mode.
The lifetime of Salyut-4, which was launched into orbit in December 1974, was much longer -- 774 days. Ninety-three days of the total it was in manned mode. The last station of the first generation, Salyut-5, was in orbit for 441 days, with 62 days ofthese in manned mode. Salyut-4 and Salyut-5 were in orbit simultaneously for nearly eight months.
Another two Salyuts belong to second-generation orbital stations. They had two docking units, which made it possible for crews of astronauts to make wider use of such stations. Their life in orbit ran into years rather than days.
Salyut-6, which was launched in September 1977, revolved around the earth for four years and ten months, including 617 days inmanned mode. The last of the Salyuts, Salyut-7, stayed in spacenearly twice as long -- eight years and ten months, with successive crews spending a total 1,075 days aboard it.
Cargo ships of the Kosmos type became a landmark event in supplying Salyut-6 and Salyut-7. For example, the Kosmos-929 cargo ship included a capsule that returned to earth a month later afterlaunch. On that occasion, however, the mission plan did notenvisage a docking with the orbital station.
By contrast, Kosmos-1267 was designed to effect a docking maneuver but without forming a transfer tunnel to Salyut-6. Acapsule abroad it returned to earth 30 days after launch together with the orbital station.
Kosmos-1443 performed its mission jointly with Salyut-7. A tunnel was formed for transfer to the orbiting station, and acapsule aboard it returned to earth 5.5 months after the start of the space mission. A transfer tunnel was formed after Kosmos-1686 docked with Salyut-7. A set of scientific equipment was a substitute for the usual onboard capsule.
The aim of the cargo ships was to adjust orbit, orient and stabilize orbiting stations during scientific experiments, ferry supplies from earth and back and play the role of "tug" placing orbiters in new orbits.
Besides, cargo ships were equipped with docking devices makingit possible for large and heavy space ships to link up in orbit.It was that docking system that sustained Salyut-7 in orbit formore than eight years. This means that apart from their supply andtug function they represented additional working modules of thespace complex.
The Mir multi-purpose complex is a fundamentally new station of the third generation. It is designed to fulfill Russia's national program of space exploration and tackle down-to-earth economicproblems. Given that it was possible to modernize it during operation, this paved the way for effective use under international cooperation programs.
Mir has been the pride of Russia's space program for over decade years, giving Moscow by far the world's greatest experience in long-term manned space flight.
After Mir, Russia, the United States and 14 other Western countries have started a joint project of building the International Space Station (ISS). Russia launched the first long-duration crew for the ISS with the Russian spaceship Soyuz TM-31in late 2000 and deliver the first crew to the first internationalspace station instead of the outdated Mir.
The 16-nation ISS worth 114 billion US dollars will be built by 2006 and comprise 47 main parts, including 17 hermetic compartments. It will weigh 450 tons with a length of 108 meters and a width of 75 meters, capable of allowing seven astronauts to permanently live in the station. It is designed to contain 15 menat most for scientific work.
In This Section
|