Missile R-7 Semyorka

The R-7 Semyorka (GRAU index 8K71, NATO reporting name SS-6 Sapwood) was the first intercontinental ballistic missile to enter service. Design work began in 1953 at the OKB-1 bureau against a requirement for a missile able to deliver a nuclear warhead against targets in the United States; later that year the warhead mass requirement was raised to accommodate a thermonuclear device. The USSR Council of Ministers approved development on 20 May 1954. The staged "rocket packet" concept underlying the design had been proposed in 1947 and refined through the early 1950s, converging on a central core with four strap-on boosters. Existing test facilities at Kapustin Yar were inadequate, and a new site in Kazakhstan — later the Baikonur Cosmodrome — was approved on 12 February 1955.

The missile burned liquid oxygen and kerosene. Four strap-on boosters were each powered by a four-chamber RD-107 engine, and the central sustainer core by a four-chamber RD-108. Rather than jet vanes, steering was accomplished by vernier engines: two on each strap-on booster and four on the core. Guidance was inertial with radio correction applied to the vernier thrusters, giving a circular error probable of several kilometres. Because each booster carried its own propellant tanks, a system was required to regulate and synchronise propellant consumption across the cluster. The assembled vehicle could not stand on a conventional pad without collapsing or being toppled by wind, so it was suspended in a truss structure carrying both vertical and horizontal loads. Armament was a single thermonuclear warhead of three to five megatons based on the RDS-37 design.

The first flight attempt on 15 May 1957 ended when a booster fire led to breakup 88 seconds after liftoff. A second attempt on 11 June was destroyed by an electrical short that caused uncontrolled roll. The first successful long-range flight, 6,000 km from Baikonur to the Kura range on Kamchatka, took place on 21 August 1957, though the dummy warhead disintegrated in the upper atmosphere; a repeat on 7 September produced the same reentry failure. A second test series ran from December 1958 to December 1959 with seven of eight launches successful, and the missile was declared operational on 20 January 1960.

The Strategic Missile Troops were the sole operator. The first unit went on alert at Plesetsk on 15 December 1959. The improved R-7A (8K74), with a lighter warhead, fully inertial guidance and a range of 12,000 km, became the standard version from 12 September 1960. Preparation for launch took roughly twenty hours, and the cryogenic propellant limited alert duration to about a day. The launch complexes were large, expensive to build in remote areas, and visible to U-2 overflights. A planned deployment of fifty complexes was cut to six — five for the strategic forces at Baikonur and Plesetsk, plus one space-launch pad — and no more than six missiles were fielded at a time. Those shortcomings drove development of the R-16, which became the first Soviet ICBM deployed in quantity, and the R-7 was withdrawn from military service by mid-1968.

Its second career outlasted the first. A modified missile, the 8K71PS, placed Sputnik 1 in orbit on 4 October 1957, and the airframe became the basis of the Sputnik, Luna, Vostok, Voskhod, Molniya and Soyuz launch vehicles. R-7 derivatives have since flown well over 1,800 times, and the modernised Soyuz-2 remains in service — more than sixty years of operational use for a design that lasted eight years as a weapon.