Sen—Approaching a half a century in operation, the Russian Soyuz is the world's longest-serving spacecraft designed to carry humans in space. The seven-ton, three-seat spacecraft became the second-generation flagship of the Soviet manned space program, replacing a one-seat Vostok capsule and its "pushed-to-the-limit" derivative, Voskhod.
Unlike its predecessors, the Soyuz for the first time sported a multi-purpose propulsion system for active maneuvering in space, a sophisticated autopilot system enabling fully automated rendezvous with other objects in space, and a docking port making it possible to conduct orbital assembly.
The descent module of the spacecraft introduced an aerodynamic control during the reentry into the Earth's atmosphere, reducing G-loads on its crew and making landing more accurate.
The first unmanned prototype of Soyuz made it into orbit in 1966 in a midst of an intense race between the USSR and the U.S. to put the first man on the Moon.
Rushed to the launch pad before all its glitches had been resolved, the first Soyuz mission with a pilot onboard in March 1967 ended tragically with the death of Vladimir Komarov. In 1971, another fatal accident during the return to Earth of Soyuz-11 claimed the lives of Georgy Dobrovolsky, Vladislav Volkov and Viktor Patsaev. The Soyuz has operated safely ever since these tragedies.
After the end of the Moon Race, the Soyuz was adapted for the new role of delivering crews to the Soviet orbiting space stations. Along with Russian cosmonauts, travellers from around two dozen countries took a ride onboard Soyuz to the Salyut-6, Salyut-7, Mir and to the International Space Station, ISS.
The Soyuz also became the space tourist vehicle for a few very wealthy individuals willing to pay tens of millions of dollars for the privilege of participating in a spaceflight.
These days, serving as a lifeboat for the entire crew of the ISS, at least one Soyuz is always docked at the outpost when the station hosts a three-member crew. However, most of the time, two ships are parked at the station to guarantee a ticket back to Earth for the entire six-person population on the outpost.
With its operational lifetime of around six months, four Soyuz spacecraft had to be launched every year to support the ISS after its construction had been completed in 2008.
With the retirement of the Space Shuttle in 2011, and at least until 2017—when the U.S. expects to be ferrying crew aboard U.S. built commercial space taxis—the Soyuz will be the only spacecraft certified to carry humans to the ISS.
While the effort to replace Soyuz with a new-generation spacecraft faces financial uncertainty in Russia, the classic vehicle has good chances to remain in service well into 2020s. Moreover, with a behind-the-scene effort to design a low-cost lunar exploration program, the Soyuz might finally reclaim its original role as the lunar transport ship.
Over the years, a number of attempts have been made in the USSR and in Russia to build a bigger, better replacement to the Soyuz. However, for a variety of financial and technical reasons none of them have materialized so far.
In the meantime, while retaining its overall architecture, the Soyuz has undergone numerous (even though incremental) upgrades, which have increased sophistication of its electronics, saved mass, improved safety and ergonomics of its cramped interior.
So many changes have been made over the years, that the Soyuz developers are seemingly running out of designations for all the variants of the spacecraft: Soyuz-T, Soyuz-TM, Soyuz-TMA and Soyuz TMA-M. Yet, another upgrade for the spacecraft is now promised in about a year under name Soyuz-MS.