R-7 Semyorka

The R-7  (Р-7 «Семёрка») 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, but was never deployed operationally. A derivative, the R-7A, was deployed from 1959 to 1968. To the West it was known by the NATO reporting name SS-6 Sapwood and within the Soviet Union by the GRAU index 8K71. In modified form, it launched Sputnik 1, the first artificial satellite, into orbit, and became the basis for the R7 family which includes Sputnik, Luna, Molniya, Vostok, and Voskhod space launchers, as well as later Soyuz/L/U/U2/FG/2 variants.

The widely used nickname for the R-7 launcher, "semyorka", means "the digit 7" or a "group of seven" in Russian.

Description
The R-7 was 34 m long, 3.02 m in diameter and weighed 280 MT; it had two stages, powered by rocket engines using liquid oxygen (LOX) and kerosene and capable of delivering its payload up to 8800 km, with an accuracy (CEP) of around 5 km. A single thermonuclear warhead was carried with a nominal yield of 3 megatons of TNT. The initial launch was boosted by four strap-on liquid rocket boosters making up the first stage, with a central 'sustainer' motor powering through both the first and the second stage. 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.

Development
Design work began in 1953 at OKB-1 in Kaliningrad in Moscow oblast (presently Korolev, Moscow Oblast) and other divisions with the requirement for a two-stage missile of 170 MT with a range of 8000 km carrying a 3000 kg warhead. Following first ground tests in late 1953 the initial design was heavily reworked and the final design was not approved until May 1954.

Contrary to statements that the R-7 was based largely on experience and assistance of German scientists, the missile is noteworthy for looking beyond past achievements that had used German ideas. For example, instead of using jet vanes for control, which increased resistance generated at the engine nozzle exhaust outlet, the R-7 used special control engines. 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.

Starting from the R-1, which was a copy of the German V-2, a free-standing missile 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 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.

The first testing of the new missile, codenamed 8K71, was on 15 May 1957 from Baikonur Cosmodrome. A fire in a strap-on rocket led to an unintended crash 400 km from the site. Following another unsuccessful test the first successful long flight, of 6000 km, was made on 21 August 1957. It was announced by TASS on 26 August. A modified version of the missile (8K71PS) placed Sputnik 1 in orbit from Baikonur on 4 October 1957 and Sputnik 2 on 3 November 1957.

Following these first tests certain modifications were found to be needed and test flights were not completed until December 1959. The additional development resulted in the 8K74 (also known as R-7A), which was lighter, had better navigation systems, more powerful engines, extended its range to 12,000 km by carrying more fuel, and increased payload to 5370 kg. The warhead was tested on Novaya Zemlya in October 1957 and again in 1958, yielding an estimated 2.9 Mt.

Operational history
The first strategic-missile unit became operational on 9 February 1959 at Plesetsk in north-west Russia. On 15 December 1959 the R-7 missile was tested at Plesetsk for the first time. The missiles were fully deployed by 1962.

Total service was limited to no more than ten nuclear armed missiles active at any time. A single launch pad was operational at Baikonur and from six to eight were in operation at Plesetsk.

The costs of the system were high, mostly due to the difficulty of constructing in remote areas the large launch sites required. At one point, each launch site was projected to cost 5% of the Soviet defence budget. However, these huge costs were not unique for a first generation missile and the US experienced similar problems.

Besides the cost, the missile system faced other operational challenges. With the U-2 overflights, the huge R-7 launch complexes could not be hidden and therefore could be expected to be destroyed quickly in any nuclear war. Also, the R-7 took almost twenty hours to prepare for launching, and it could not be left on alert for more than a day due to its cryogenic fuel system. Therefore, the Soviet force could not be kept on permanent alert, and could have been subject to an air strike before launching. Additionally the huge payload for which it was designed, adapted to early heavy H-bombs, became irrelevant with the coming of lighter bomb technology.

The limitations of the R-7 pushed the Soviet Union into rapidly developing second-generation missiles which would be more viable weapons systems. The R-7 was phased out of military service by 1968.

While the R-7 turned out to be impractical as a weapon, it became the basis for a series of Soviet expendable space launch vehicles. The derivatives of the R-7 missile became successful space launch vehicles, which are still being used in modified form.

Variants

 * SS-6 Sapwood: NATO reporting name for all versions of the R-7, variants identified by suffix letter on the name portion (e.g. Sapwood-A).
 * R-7 Semyorka: First launch 15 May 1957, last launch 27 February 1961; 27 launch attempts, 18 of which were successful.
 * R-7A Semyorka: First launch 23 December 1959, last launch 25 July 1967; 21 launch attempts, 18 of which were successful.
 * 8K71:The GRAU designation for the R-7 Semyorka missile (GRAU 8K: Missiles 71: model number)
 * 8K74:The GRAU designation for the R-7A Semyorka missile (GRAU 8K: Missiles 74: model number)
 * 8K71PS: ''Sputnik 1 launcher Soyuz-FG	(11A511U-FG) and

Note: Much developed variants of the R-7 are still active:
 * Soyuz-U	(11A511U)
 * Soyuz-FG	(11A511U-FG)
 * Soyuz-2.1a	(14A14A)
 * Soyuz-2.1b	(14A14B)

Operators

 * The Strategic Missile Troops was the only operator of the Semyorka.