UR-100 / SS-11 SEGO
SS-11 Variant-1 UR-100
The flight-design tests were conducted at the Baikonur cosmodrome between April 1965 and October 1966. The first silo-launch was conducted on 17 July 1965. The Variant 1 reentry vehicle had a ballistic coefficient of 310 lb per sq ft and a CEP assessed by Western intelligence at 1.0 nm. Western intelligence assessed that an initial operational capability was reached in early 1966. According to Russian sources the first three regiments with UR-100 missiles were put on alert in November 1966 with operational employment beginning on 21 July 1967. According to Russian sources the missile was initially equipped with two different types of warheads: a light one for intercontinental targets in North America, and a heavier one for medium range targets in Eurasia.
SS-11 Variant -1 UR-100UTTh
Upgrades to the UR-100 missile provided a different nose cone that improved flight characteristics and a modified command structure that reduced the time for pre-launch operations. The modified version was designated UR-100UTTh (8K84UTTh). It differed from former missiles with improved warhead technology, improved launching equipment, and an autonomous power supply system, which ensured extended storage in fueled conditions. The flight-design tests of the UR-100UTTh missile were conducted between July 1969 and March 1971.
SS-11 Variant -2 UR-100K
The development of the UR-100K (15A20) missile [known in the West as the SS-11 Variant -2] began in the middle of the 1960s. The main design changes found in the UR-100k concerned lengthening of the first stage to increase the amount of propellant and modifications to the propulsion systems of both stages. These measures allowed for an increase in the launch weight to 8 tons and a 60 percent increase of throw weight. The maximum range of the UR-100K was increased up to 12,000 km, and through the use of improved sensors the accuracy was increased by a factor of 1.5 to a CEP of 1 Km. The Variant 2 reentry vehicle had a ballistic coefficient of 900 lb per sq ft and a CEP assessed by Western intelligence at 0.6 nm. The missile also dispensed decoys at the end of the boost phase of the trajectory before the separation of the reentry vehicle. The reentry vehicle itself had radio-reflecting properties. The sophisticated control system allowed an increase of combat readiness of a missile through the use of boosted spin-ups of gyros. The silo had its own system of power supply allowing remote changes of its mission and launch. The flight-design tests of the UR-100K missile were conducted from February 1971 through November 1971. According to Russian sources the missile was initially deployed in December 1971. Western intelligence assessed that an initial operational capability was reached in 1973.
SS-11 Variant-3 UR-100U
The UR-100U (15A20U) missile differed from the UR-100K missile by the number of warheads. Instead of a single warhead it carried three warheads, though with a reduced maximum range. The tests of the UP-100U were conducted from July 1971 through January 1973, and according to Russian sources, its deployment started on 26 September 1974. According to Western sources, the first Variant 3 flight test was in September 1969, and they assessed that an initial operational capability was reached in 1973. Development of this missile system centered on increasing its survivability. The silos were hardened and the shock-absorption of the transport-launch canister was improved. The silo consists of a monolithic ferro-concrete trunk with a steel hardware compartment, rigidly attached to it. The trunk was covered with an accident protection device in the form of a sliding roof.
The Variant -4 missile differed from the Variant-3 missile by the number of warheads -- instead of three warheads it carried six. This variant was tested but not deployed.
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