one-level Stage separation: Pyrotechnic fastener/hot staging There are two variant upper stages in use, the Blok-I (used on the Soyuz 2.1a) and the Improved Soyuz (Russian: Союз, lit. 'union', as in Soviet Union, GRAU index: 11A511) is a family of Soviet and later Russian expendable, medium-lift launch vehicles initially developed by the OKB-1 design bureau and has been manufactured by the Progress Rocket Space Centre in Samara, Russia. The Soyuz family holds the record for the most launches in the history of spaceflight. Most Soyuz rockets are part o Th… In the early 1990s plans were made for a redesigned Soyuz with a Fregat upper stage. The Fregat engine was developed by NPO Lavochkin from the propulsion module of its Phobos interplanetary probes. Although endorsed by Roscosmos and the Russian Ministry of Defence in 1993 and designated "Rus" as a Russification and modernization of Soyuz, and later renamed Soyuz-2, a funding shortage prevented implementation of the plan. The creation of Starsem in July 1996 provided new funding for the creation of a less ambitious variant, the Soyuz-Fregat or Soyuz-U/Fregat. This consisted of a slightly modified Soyuz-U combined with the Fregat upper stage, with a capacity of up to 1,350 kilograms (2,980 lb) to geostationary transfer orbit. In April 1997, Starsem obtained a contract from the European Space Agency (ESA) to launch two pairs of Cluster II plasma science satellites using the Soyuz-Fregat. Before the introduction of this new model, Starsem launched 24 satellites of the Globalstar constellation in 6 launches with a restartable Ikar upper stage, between 22 September 1999 and 22 November 1999. After successful test flights of Soyuz-Fregat on 9 February 2000 and 20 March 2000, the Cluster II satellites were launched on 16 July 2000 and 9 August 2000. Another Soyuz-Fregat launched the ESA's Mars Express probe from Baikonur in June 2003. The first stage of Soyuz rockets consists of four identical conical liquid booster ro The first Soyuz launcher was introduced in 1966. It was derived from the earlier Vostok launcher, which in turn had been based on the R-7 Semyorka, the world's first intercontinental ballistic missile. The Soyuz used a three-stage design with the Block I third stage. Its first four test flights ended in failure, but subsequent missions achieved success. A four-stage variant, the Molniya, was developed by adding an additional upper stage, enabling launches into highly elliptical Molniya orbits. A later evolution, the Soyuz-U, became the workhorse of the family. During the Cold War, the exact Soviet model designations were not publicly available. In the West, the United States Department of Defense referred to the Soyuz launcher as SL-4, while Charles Sheldon of the Library of Congress devised the A-2 designation. Both systems were eventually abandoned as more accurate information became available. Production of Soyuz rockets peaked at about 60 units per year in the early 1980s. By the 21st century, the Soyuz had become the world's most frequently used space launcher, with more than 1,700 flights. Despite its age, the family has remained in service due to its comparatively low cost, high reliability, and proven performance. In the early 1990s plans were made for a redesigned Soyuz with a Fregat upper stage. The Fregat engine was developed by NPO Lavochkin from the propulsion module of its Phobos interplanetary probes. Although endorsed by Roscosmos and the Russian Ministry of Defence in 1993 and designated "Rus" as a Russification and modernization of Soyuz, and later renamed Soyuz-2, a funding shortage prevented implementation of the plan. The creation of Starsem in July 1996 provided new funding for the creation of a less ambitious variant, the Soyuz-Fregat or Soyuz-U/Fregat. This consisted of a slightly modified Soyuz-U combined with the Fregat upper stage, with a capacity of up to 1,350 kilograms (2,980 lb) to geostationary transfer orbit. In April 1997, Starsem obtained a contract from the European Space Agency (ESA) to launch two pairs of Cluster II plasma science satellites using the Soyuz-Fregat. Before the introduction of this new model, Starsem launched 24 satellites of the Globalstar constellation in 6 launches with a restartable Ikar upper stage, between 22 September 1999 and 22 November 1999. After successful test flights of Soyuz-Fregat on 9 February 2000 and 20 March 2000, the Cluster II satellites were launched on 16 July 2000 and 9 August 2000. Another Soyuz-Fregat launched the ESA's Mars Express probe from Baikonur in June 2003. The first stage of Soyuz rockets consists of four identical conical liquid booster rockets strapped to the second stage core. These boosters are also called Blok-B, V, G, and D. Each engine has four main combustion chambers and two vernier thruster combustion chambers for attitude control. The engine is pump-fed by a hydrogen peroxide gas generator. Propellant tanks are pressurized using liquid nitrogen vaporization. Statistics (each of 4 boosters): The Soyuz booster's second stage, also called Blok-A, is a single, generally cylindrical stage with one motor at the base, activated alongside the first-stage boosters. Like Height: 27.1 metres (88 feet 11 inches) Diameter: 2.95 metres (9 feet 8 inches) Empty mass: 6,545 kilograms (14,429 lb) Gross mass: 99,765 kilograms (219,944 lb) Propellant mass: 90,100 kilograms (198,600 lb) Oxidizer load (liquid oxygen): 63,800 kilograms (140,700 lb) Fuel load (RP-1): 26,300 kilograms (58,000 lb) Powered by: 1 × RD-108A Maximum thrust: At sea level: 792.5 kilonewtons (178,200 lbf) In vacuum: 990.2 kilonewtons (222,600 lbf) Specific impulse: At sea level: 255 seconds (2.50 km/s) In vacuum: 319 seconds (3.13 km/s) Burn time: 286 seconds Throttling: one-level Stage separation: Pyrotechnic fastener/hot staging There are two variant upper stages in use, the Blok-I (used on the Soyuz 2.1a) and the Improved Blok-I (used on the Soyuz 2.1b). Statistics: