WASHINGTON When the cosmonauts departed from the MIR space station today and began their return to Earth, they did more than end the last major visit to the aging space facility thats been an orbital home to international crews for 13 years. The cosmonauts climbed aboard what may be one of the final voyages of the most flown spacecraft in history, an orbital workhorse that has been "reinvented" repeatedly over the course of more than three decades of human spaceflight.

The Soyuz spacecraft carrying the cosmonauts home to Mother Russia has a history and a space-going pedigree unlike any other, with connections to the birth of the once glorious Soviet space program as well as its evolving end. Along the way, Soyuz became the basis not only for station-bound cosmonauts space taxi trips, but unpiloted commercial capsules, military satellites, resupply tankers, and a host of other experimental and commercial space systems. Many of these missions have vaulted into space from the same pad as that used by the once great Sputniks and even the first space flyer, Cosmonaut Major Yuri Gagarin himself.

And Soyuz was even more than a spaceship - it was also a launch vehicle that began the first Space Age, as well as shaped the competitive nature of the new Space Age to come.

The project was the dream of Soviet Chief Space Designer Sergi Korolev, who in the late 1950s designed the first generation of Russian piloted spacecraft called Vostok. Lifted into space aboard a modified version of the R-7 ballistic missile, the single-seat Vostok was but a prelude to a series of advanced piloted spaceship designs to flow from Korolevs genius. These included adding an airlock to the one-man Vostok and then squeezing in two and three person flights in October 1964 and March 1965, the latter conducting the worlds first walk in space. But Korolev knew that his Vostoks and space-walking Voshkods were limited space capsules that could not change their orbits or perform extended operations while in flight. For those roles the Russian designer envisioned the Soyuz; a three-part modular space capsule system that could support up to three Cosmonauts in space and provide extensive operations while aloft. Soyuz was to house a reentry capsule for the Cosmonauts to return in, but also a circular living quarters and an equipment module for oxygen and supplies for the crew. While the Vostoks couldnt do much more than keep their occupants alive in space, Soyuz could act as a true transport ship, tracking down international stations, docking with them, and staying attached for months at a time before returning its crew to a land landing using a retrorocket tucked in the capsules tail to cushion the touchdown at the last second.

Korolev gave the basic R-7 an upgrade to lift Soyuz, with a more powerful set of liquid engines and lengthened upper stage. On December 14, 1966 the first Soyuz lifted from the Soviet space complex at Baikonur on the first unpiloted test flight of the new design.

This and additional tests were followed in April 1967 by the piloted Soyuz 1 carrying Cosmonaut Vladimir Komarov. But Soyuz was not yet ready for human spaceflight, and a series of system malfunctions caused the mission, which was to see a rendezvous in space with Soyuz 2, cut short. Komarovs capsule tumbled during reentry and its parachute lines fouled. The craft hit the ground at hundreds of miles per hour, killing the Cosmonaut.

An extensive redesign of Soyuz took place. Korolev died in January 1966, but several versions of the basic Soyuz that he had dreamt about were built and flown. The Soyuz became the basis of a Russian military photoreconnaissance space capsule. Another version became a possible piloted lunar spacecraft called Zond before that project, to beat the Americans to the Moon, was canceled. The baseline Soyuz was modified with a new flight computer as the heavier Soyuz T spacecraft, used to dock with the Russian Salyut space stations in the 1970s. Another upgrade, the Soyuz TM, was introduced in the 1980s, and a variant is the one the Mir Cosmonauts rode home in.

Since its beginnings, Soyuz spacecraft has been used primarily as a transport. An unpiloted version, called Progress, is an automated robotic cargo vehicle that is used to carry food, water, supplies, equipment and even books to the orbiting stations beginning with the Salyut 6 on January 20, 1978. A yet more updated version, Progress M, entered service on August 23, 1989, docking with MIR.

The R-7 space booster has been repeatedly upgraded with more powerful booster engines and different upper stages for the differing space missions of the Russian civil, military, and even commercial space projects. Versions named after the launchers payloads have included the Vostok, Voshkod, Luna, Molnyia, Progress, Soyuz, Soyuz U and Soyuz/Itar variants. The last version is being sold commercially by the Russian design bureau that builds the rocket in a partnership with the European launch company Arianespace.

It is not yet clear how many more Soyuz vehicles will be flown to the new International Space Station, or when the basic Soyuz launcher will be replaced. But one mission for a Soyuz is set: next year. An unpiloted Progress tanker version of Soyuz will be used to gently nudge the MIR complex out of its orbit and down through the Earths atmosphere in a fiery end to its 13 years of space history.