R-7 Semyorka

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 R-7 made 28 launches between 1957 and 1961. A derivative, the R-7A, was operational from 1960 to 1968. To the West it was unknown until its launch (later it would get the NATO reporting name SS-6 Sapwood). In modified form, it launched Sputnik 1, the first artificial satellite, into orbit, and became the basis for the R-7 family which includes Sputnik, Luna, Molniya, Vostok, and Voskhod space launchers, as well as later Soyuz variants. Various modifications are still in use and it has become the world's most reliable space launcher.

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.

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.