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modified: Nov 10, 2012

UR-100 (Russian: универсальная ракета, universal rocket) was a Soviet light ICBM developed in the 1960s. It was the main ICBM adopted for use by the RVSN. Between 1966 and 1972, 990 launchers were deployed. In the mid-1970s, many of the UR-100 missiles were replaced by upgraded UR-100K and UR-100U missiles.

A government decree issued on March 30, 1963 authorized work on the missile. OKB-52 (Central Machine-Building Design Bureau) was selected as the head developer.

The UR-100 was a two-stage single-warhead missile. The oxidizer and propellant tanks of both stages had shared dividers to reduce the missile's size and weight. Furthermore, the top of the first-stage oxidizer tank had the shape of an inverted cone. This configuration provided the space to host the nozzle of the second-stage engine.

The first stage had four gimbaled closed-cycle liquid-fuel sustainer and a four-chamber liquid-fuel steering engine. The separation of the stages was achieved with the aid of dedicated solid-propellant motors. The missile was equipped with a fully autonomous inertial guidance system that guided the missile along a predetermined trajectory. The control and guidance system also provided for the automatic remote control of the state of the missile, automatic launch preparations, and the automatic launch of the missile.

The missile can carry a light warhead to be used at intercontinental ranges, or a heavy intermediate range warhead. The missile could be used only against soft, unprotected targets because the missile had a relatively low accuracy and the warhead yield was small. The missile was kept in a simple and inexpensive silo with a flat, pneumatically driven sliding roof.

The UR-100 was the first missile to be used with a sealed transport and launch container (TPK). It was fully assembled and loaded into the sealed container at the manufacturing plant and then transported to the launch complex in the container. The container was inserted into the silo and secured. The missile was fueled through the container's outlets, after which the missile and canister were ampulized and kept in a permanent state of readiness for launch. When the missile was ampulized, the engines were isolated from the fuel components by membranes, securing their preservation when the missile was kept fueled for a long time.

The UR-100 underwent flight tests at the Fifth Scientific Research Test Range (Baikonur) between April 19, 1965 and October 27, 1966. The first silo launch was conducted on July 17, 1965. The missile was accepted for service on July 21, 1967. On November 24, 1966, the first three regiments with UR-100 missiles were put on combat duty.

UR-100M was an upgraded version of the UR-100. The UR-100M was equipped with a lighter warhead that had better flight performance characteristics. It was also equipped with a new control and guidance system that improved prelaunch operations and expanded the missile's re-targeting capabilities. The UR-100M had improved launch equipment and an autonomous power supply system. Flight tests were conducted between July 23, 1969 and March 15, 1971.

UR-100K was an upgraded version developed starting in the mid-1960s. It had a bigger first stage and improved propulsion systems. These modifications increased the throw weight by 60 percent and increased the launch weight by 8 tonnes.

The range was increased to 12,000km. By using improved sensors, accuracy was increased by about 50 percent reducing the CEP to 1km. Furthermore, the missile contained decoys that were released at the end of the boost phase before the separation of the warhead. The warhead was covered with a radar-absorbing material.

The improved control and guidance system enhanced the missile's combat readiness significantly by employing accelerated revving of gyros and allowed the missile's targeting information to be changed remotely. The enhanced endurance of the autonomous power supply system in the silo launcher allowed all launch preparation procedures including re-targeting to be completed in autonomous mode.

The UR-100K underwent flight tests between February 2 and November 24, 1971. It was accepted for service on December 28, 1971.

UR-100U was an upgraded MRV version. It was equipped with a three-warhead MRV but the maximum range of the MRV was shorter than that of the single-warhead variant. The three warheads were placed on a platform covered by a fairing that was released after the missile had passed through the lower atmosphere.

Flight tests of the UR-100U were conducted between July 1971 and January 1973. It was accepted for service on September 26, 1974.

During the development of the UR-100U, the silo was hardened and the launch container shock absorbers improved. The silo launcher consisted of a monolithic reinforced concrete tube with a steel launch equipment compartment. The tube was covered with a lid that was driven by an explosive charge. The canister and missile were suspended from two supports at the top and stabilized by horizontal shock absorbers at the bottom. These measures increased the hardness of the silo by more than one order of magnitude.

Overall, 420 UR-100K and UR-100U launchers were deployed between 1973 and 1977. Because of the expiration of their service life and in accordance with the START I Treaty, all of the UR-100K and UR-100U missiles had been removed from combat duty by the end of 1994.