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R-7 - SS-6 SAPWOOD

The R-7/SS-6 Sapwood, the first Soviet intercontinental ballistic missile developed and programmed for operational deployment in the USSR, is a one and one-half stage, cryogenic liquid-propellant missile. According to Western estimates it was capable of delivering a 9000 lb reentry vehicle to a maximum operational range of 6500 nm with a CEP of approximately 2 nm.

The R-7 missile became the first Soviet intercontinental ballistic missile. It was based on plans laid out in the governmental order from February 13, 1953 to develop a two-stage ballistic missile with a range of 7000-8000 km. The original design plans provided for a total weight of the nose cone plus warhead of 3 tons. However, soon after the first tests in October 1953 were carried out, the design was substantially changed. The total weight of the nose cone was increased to carry a thermonuclear warhead of 3 tons. To preserve the previous maximum range it was necessary to redesign the missile completely since the launch weight was increased from 170 up to 280 ton. The development of this two-stage ballistic missile was approved on May 20, 1954.

The R-7 missile employs a unique parallel division of stages, consisting of one central sustainer and four strap-on boosters, all of which were started simultaneously at liftoff. The strap-on boosters formed the first stage, and the central sustainer constituted the second stage. This tandem structure allowed the start and control of all engines at normal atmospheric pressure [the Atlas first-generation American ICBM employed a similar principle, while using common propellant tanks for both booster and sustainer engines]. Each of the stages featured a four-chamber open-cycle rocket engine using liquid oxygen and kerosene. Flight control was achieved by vernier engines located on the strapon boosters and the core sustainer. Aerodynamic fins located on the aft bay of the strap-ons also provided for flight control.

The missile had a combined command structure consisting of both an independent autonomous system and a radio command system. The independent autonomous system provided attitude control for the missile with respect to the vehicle's center of mass and motion on the planned trajectory. It also controlled the synchronous draining of the propellant tanks in all units of the first stage. The system of radio control carried out in-flight trajectory corrections and provided for an increase of delivery accuracy.

The flight tests of the 8K71 missile began on 15 May 1957. The spectacular launch of the first Sputnik satellite in October 1957 revealed a rocket with a thrust far in excess of anything the United States could then produce. The Soviet feat caused the United States to review its missile programs in order to narrow the rocket-booster gap. To sustain morale, several small American satellites using the Jupiter and Vanguard boosters were launched in 1958, but it would take considerable time to construct engines equaling those already developed by the Russians.

The results of the first six tested R-7 (two of which were used in a modified version to place the first two Sputnik satellites into orbit) led to a modification of the nose cone and its mode of separation. During the first launches the nose cone collided after its' separation with a missile body and was destroyed during atmospheric reentry. Between 29 March and 10 July 1958 the new design with a modified nose cone was successfully tested and between 24 1958 and 27 November 1959 16 flight tests were conducted to assure the reliability of the design. Following the completion of tests in December 1959 the first launch complexes were put on an alert, and on 20 January 1960 deployment of the R-7 missile started..

During the test phase of the R-7 missile, on 02 July 1958, a ministerial decree was issued for the development of an improved ICBM based on the R-7 design. The new R-7A (8K74) included a modernized lighter warhead, more powerful engines and an increased propellant volume. Thus maximum range was increased from 8000 up to 12000 km. A newly developed gyroscopic inertial navigation system, replacing the previous radio-command control system, improved the missile's accuracy. Flight tests of this variant were conducted from December 1959 through July 1960. In January 1960 for the first time a successful test of a long-range missile carried out with successful delivery of the nose cone into the Pacific Ocean. Eight missile launches were carried out of which seven were successful. In early 1960 theR-7A missile was put on active alert.

The 8K71 and 8K74 missiles were put on alert at test facilities at the Baikonur cosmodrome and at "Angara" in the Arkhangelsk area (subsequently known as Plesetsk). They were deployed at five sites that consisted of six launch facilities in total. The SS-6 ICBM system has had limited deployment in fixed soft sites in northwestern USSR. The system reaction time in the normal readiness condition was approximately ten hours. Because of the cryogenic oxidizer, the allowable hold time in the maximum alert condition (reaction time equals five to ten minutes) was approximately one hour. By mid-1968 the SS-6 ICBM had been phased out of the operational inventory. Use of the SS-6 is now restricted to space applications.

Sources and Resources

• Russian Strategic Nuclear Weapons, Pavel Podvig, ed., IzdAT, Moscow, 1998, 492 pp. (in Russian). Authors: Oleg Bukharin, Timur Kadyshev, Eugene Miasnikov, Pavel Podvig, Igor Sutiagin, Maxim Tarasenko, Boris Zhelesov
• R-7 @ Encyclopedia Astronautica by Mark Wade
• SS-6 Sapwood @ US Naval Institute Military Database
• "A History of Strategic Arms Competition 1945-1972" (U), Volume 3, A Handbook Of Selected Soviet Weapon and Space Systems, United States Air Force, June 1976. pgs 128-133

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