FAS
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..
https://fas.org/nuke/guide/russia/icbm/r-7.htm
