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Further Reading

UR-100 / SS-11 SEGO

The UR-100/SS-11 liquid propellant light ICBM was the centerpiece of a major Soviet effort to reach numerical strategic parity with the USA. The SS-11 was massively deployed, and as a result was the Soviet counterpart of the US Minuteman system in quantity, size and purpose. It was initially deployed with a single warhead [with a yield of 1.1 MT according to Russian sources, or 0.6 to 1.2 MT according to Western reports] and was not particularly [a CEP of 1.4 km according to Russian sources]. The missile was believed to be only affective against soft targets.

The development of the UR-100 was approved by the government on 30 March 1963. The developer was NPO Mashinostroyenia (OKB-52). The missile was deployed in at least four variants, and was probably tested in at least several additional configurations. Recent published Russian sources, focusing on the physical configuration of the rocket give conflicting reports about these variants when compared with contemporaneous Western sources, which were limited to intelligence derived from observing flight tests. In the middle of the 1970's the UR-100 was replaced by two modernized versions that received the designations UR-100K (15A20) and UR-100U (15A20U).

The UR-100 ICBM is a two-stage, tandem, storable liquid-propellant missile. It is about 64 feet long and 8 feet in diameter. Both stages have the oxidizer and fuel tanks with a common bottom reducing the overall dimensions and launch weight of the missile. The bottom of the oxidizer tank of the first stage was placed inside the tank like an inverted truncated cone. The nozzle of the sustainer of the second stage was included in the formed upper volume. The first stage used a new set of four closed-cycle single-chambered rocket motors, while the second stage incorporated a single-chambered sustainer and a four-chambered control motor. Asymmetrical dimethylhidrazine and nitrogen tetraoxide were used as propellants. The missile uses an inertial guidance system consisting of an autonomous guidance/control system with a gyro-stabilized platform of floating gyros. The command structure also provided an automatic checkout of all systems during flight and automatic preparation of launch.

The missile was deployed in a silo launcher, with a design that was substantially simplified in comparison with earlier silo complexes. A pneumatic driven sliding roof could be closed to protect the silo. The SS-11 was also the first Soviet ICBM to be deployed with a pressurized transport launch canister in which the missile was both delivered to the launch complex and fired from. The engines were isolated from the propellant components during the storage of the missile through membrane-valves that provided their safety during extended times of being in a fueled condition.

Western intelligence considered the SS-11 deployment as similar in concept to the US Minuteman, where a large force was deployed in hardened silos requiring minimum support facilities. Silo and launch control center hardness was estimated at 700 and 400 psi overpressure, respectively, from a 1-MT weapon. The sites were deployed in groups of ten unmanned silos with a single launch control center for each group. Reaction time during normal readiness conditions was assessed by the West as 0.5 to 3.0 min. with an unlimited hold time in this alert condition.

The UR-100 missile was the most extensively deployed ICBM within the Soviet Strategic Rocket Forces. Between 1966 and 1972 a total of 990 of these missiles were deployed along with some 420 launchers of the UR-100K/UR-100U missiles deployed between 1973 and 1977 as the UR-100 missiles were phased out. As of 1991 some 326 remained in service, while by the end of 1994 all but 10 of the UR-100 and UR-100U missiles had been removed from combat duty in compliance with the START-1 treaty. By the end of 1996 all SS-11 missiles had been dismantled.