The R-7 Semyorka (Russian: Р-7 Семёрка, lit. 'number seven', GRAU index: 8K71) was a Soviet missile developed during the Cold War, and the world's first intercontinental ballistic missile. The basis for the R-7 rocket family, it was adapted into the world's first orbital launch vehicle, Sputnik, and the crewed orbital launch vehicles Vostok. R-7 derivatives are the most launched rocket family ever with over 2,000 flights as of 2026, primarily Soyuz variants. Developed by OKB-1 under Sergei Korolev, the R-7 used a kerolox propellant, with a 37 meter-tall core stage powered by the four-chamber RD-108 engine, and four boosters each powered by one four-chamber RD-107 engines. It carried a thermonuclear warhead of between three and five megatons, based on the RDS-37 design. The R-7 made 28 launches between 1957 and 1961. A derivative, the R-7A, was operational from 1960 to 1968. Western Cold War espionage did not discover the R-7 until its launch, later giving it the NATO reporting name SS-6 Sapwood. In August 1957, it was first tested successfully, flying 6,000 km from Baikonur Cosmodrome to Kura Missile Test Range. Up to six R-7 units were operationally deployed from late 1959, by the newly-formed Strategic Rocket Forces, at five launch sites, one launch pad at Baikonur and four at Plesetsk Cosmodrome. The Soviet Armed Forces initially planned to deploy fifty launch pads for the Soviet nuclear forces. However, the missile's preparation time of 20 hours, maximum alert duration of 24 hours due to liquid oxygen usage, and American Lockheed U-2 spy plane flights, made this infeasible; experts have called its ICBM role as a "blunder" and a "monster". Instead it was R-16 ICBM, developed by the OKB-586 bureau under Mikhail Yangel, which was the first Soviet ICBM deployed en masse, with over 200 units by 1965. Despite its weakness as an ICBM, some American intelligence reports estimated hundreds of R-7s within a few years, beginning fears of a missile gap. The US responded with a Strategic Air Command continuous 24/7 nuclear alert, which lasted another 34 years until 1991, its first ICBM deployment, the SM-65D Atlas, and the deployment of PGM-17 Thor intermediate-range ballistic missiles in the United Kingdom within range of Moscow. It became the basis for the R-7 family which includes Sputnik, Luna, Molniya, Vostok, and Voskhod space launchers, as well as later Soyuz variants. These produced the bulk of early Soviet Space Race achievements, such as the Luna 2 and Luna 3 Moon probes. Various modifications are still in use and it has become the world's most reliable space launcher.
Description
The R-7 was 34 m (112 ft) long, 10.3 m (34 ft) in diameter and weighed 280 metric tons (280 long tons; 310 short tons); it had a single stage with four strap on boosters powered by rocket engines using liquid oxygen (LOX) and kerosene and capable of delivering its payload up to 8,000 km (5,000 mi), with an accuracy (CEP) of around 5 km (3.1 mi). A single thermonuclear warhead could be carried with a nominal yield of 3 megatons of TNT. The launch was boosted by four strap-on liquid rocket boosters with a central 'sustainer' engine powering the central core. Each strap-on booster included two vernier thrusters and the core stage included four. The guidance system was inertial with radio control of the vernier thrusters. The widely used nickname for the R-7 launcher, "Semyorka", is a rough translation of "old number seven" in Russian.
Development Design work began in 1953 at OKB-1 in Kaliningrad in Moscow Oblast (presently Korolyov, Moscow Oblast) and other divisions with the requirement for a missile with a launch mass of 170 to 200 tons, range of 8,500 km and carrying a 3,000 kg (6,600 lb) nuclear warhead, powerful enough to launch a nuclear warhead against the United States. In late 1953 the warhead's mass was increased to 5.5 to 6 tons to accommodate the then planned thermonuclear bomb. On 20 May 1954 the USSR Council of Ministers approved the development of the R-7. The principle of a staged missile, also known as a "rocket packet", was first proposed by Mikhail Tikhonravov at NII-4 in 1947. Korolev became aware of this proposal in 1948 and supported further base studies at NII-4 in 1949–50. This was further refined by Dmitry Okhotsimsky's Department of Applied Mathematics in 1951 and expanded by Korolev's OKB-1 in 1952–53, which concluded that a core and four strap on boosters as the preferred model, which the R-7 used. To lift the 5.5 ton payload required a redesign of the existing RD-105 and RD-106 engines. Valentin Glushko's OKB-456 combined four combustion chambers using a single turbo pump, which provided a cumulative higher thrust than a single engine. Other advantages included an overall lower engine weight and simpler design, test and construction, via standardisation. The main engines for the central core and strap on boosters all used the four combustion chamber configuration. The four strap on propulsion engines were powered by the RD-107 engine providing a sea level thrust of 83 tons, each with two vernier engines to assist with steering. The central core's RD-108 engine provided sea level thrust of 75 tons and included four vernier engines utilized for steering. The rocket had some key features to it that made it unique. Instead of using jet vanes for control, which increased resistance generated at the engine nozzle exhaust outlet, the R-7 used special control engines for steering. These same engines served as the last stage's vernier thrusters. Because of clustered design, each booster had its own propellant tanks. The design team had to develop a system to regulate the propellant component consumption ratio and to synchronize the consumption between the boosters. Instead of a free-standing missile which was launched from a horizontal pad, it turned out that assembling a cluster of a central core and four boosters on the pad is almost impossible without it falling apart. Also, a wind gust could knock the unfuelled missile off of the pad. The solution was to eliminate the pad and to suspend the entire rocket in the trusses that bear both vertical weight load as well as horizontal wind forces. The launch system simulated flight conditions with strap-on boosters pushing the central core forward.
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