Soyuz-U (GRAU index: 11A511U) was a Soviet and later Russian expendable medium-lift launch vehicle designed by the TsSKB design bureau and constructed at the Progress factory in Samara, Russia. The U designation stands for unified, as the launch vehicle was the replacement for the Voskhod rocket and several earlier Soyuz rocket variants. The Soyuz-U is part of the larger R-7 rocket family, which evolved from the R-7 Semyorka, the first intercontinental ballistic missile. The first Soyuz-U flight took place on 18 May 1973, carrying as its payload Kosmos 559, a Zenit military surveillance satellite. The final flight of a Soyuz-U rocket took place on 22 February 2017, carrying Progress MS-05 to the International Space Station. Soyuz-U was in use continuously for almost 44 years. Production of R-7 derived launch vehicles peaked in the late 1970s-early 1980s at 55–60 a year. Soyuz-U held the world record of highest launch rate in a year in 1979 with 47 flights until this was beaten by SpaceX's Falcon 9 in 2022. Over its operational lifetime, the Soyuz-U variant flew a total of 786 missions, another world record. Soyuz-U has also been one of the most reliable launchers, with a success rate of 97.3%.
Development The original Soyuz rocket, introduced in 1966, represented the first attempt to standardize the R-7 design. It was largely identical to the Molniya booster but omitted the fourth stage. Two variants of the original Soyuz were produced, with at least three additional variants planned but ultimately canceled. By the mid-1970s, the Soviet Union was operating a wide range of R-7 variants, including the Molniya, Voskhod, and various Vostok models. To address this fragmentation, the Soyuz-U was introduced as a unified platform. The "U" stood for "unified," as it replaced both the Voskhod and original Soyuz rockets. This model featured an upgraded core with enhanced RD-117/118 engines to mitigate issues like in-flight vibration and combustion instability. Complete adoption of the Soyuz-U was not achieved until 1977, when the remaining stock of the original Soyuz boosters was depleted. However, despite the move toward standardization, some variants persisted. The Vostok-2M and Molniya-M continued to serve specialized roles, launching satellites into higher orbits until 1991 and 2010, respectively.
Versions Two versions of Soyuz-U were fitted with an additional upper stage:
Soyuz-U/Ikar with the Ikar upper stage, produced by Progress is used to deliver various payloads with masses of 750 to 3,920 kg (1,650 to 8,640 lb) to heights of 250 to 1,400 km (160 to 870 mi). The performance of the Ikar upper stage is lower than that of the Fregat upper stage, but it offers more precise maneuvering and longer autonomous operation. This version was launched six times in 1999, carrying four GlobalStar satellites on each mission. The Ikar was replaced by the improved Volga upper stage which remains in use with the Soyuz-2. Soyuz-U/Fregat with the Fregat upper stage, developed and produced by Lavochkin flew four times in 2000. The Fregat upper stage was subsequently flown regularly atop Soyuz-FG and Soyuz-2 boosters. An older variant of Soyuz-U, the Soyuz-U2 launcher, first flown in 1982, had the same hardware as the basic Soyuz-U. Instead of standard RP-1, it used a high energy, synthetic version, Syntin, as the first stage fuel. This variant, mainly used to transport crew and cargo to the Mir space station, last flew in 1995, after production of Syntin ended due to cost reasons. Soyuz-U was the basic platform for the development of the Soyuz-FG variant, which used an all-new first stage and took over crew transport to the ISS in 2002. Since 2013, both Soyuz-U and Soyuz-FG are gradually being replaced by the modernized Soyuz-2 launch vehicle.
Human spaceflight The first use of a Soyuz-U to launch a crewed mission took place 2 December 1974, when the Soyuz 16 crew was launched in preparation for the Apollo–Soyuz Test Project (ASTP). Soyuz 19, which as part of the ASTP docked with the last Apollo spacecraft ever flown, was also launched by a Soyuz-U rocket. On 6 July 1976, a Soyuz-U launched Soyuz 21, which took a crew of two to the Salyut 5 space station. Many subsequent space station crews were launched on Soyuz-U launchers. The final crewed mission to use the Soyuz-U was Soyuz TM-34, a Soyuz ferry flight to the International Space Station. A spectacular accident occurred on 26 September 1983, when the launcher for the Soyuz T-10a mission was destroyed by fire on the launch pad. The crew was saved by activation of the launch escape system a few seconds before the explosion.
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