UR-100N / SS-19 STILLETO

Once regarded as the "backbone" of the Soviet ICBM force, the fourth generation UR-100N / SS-19 intercontinental ballistic missile was a tandem two-stage, storable liquid-propellant ICBM. The missile was approximately 80 feet long and 8 1/2 feet in diameter. It was a competing design with the SS-17 Spanker, and both were eventually deployed to partially replace the aging SS-11 force as the SS-11 reached its operational life expectancy.

The UR-100N was similar to the UR-100 in some respects, but with an increased diameter and longer propellant tanks its launch weight was more than doubled and the throw-weight was increased over three-fold than that of the UR-100. Like many 4th generation systems, the UR-100N used asymmetrical dimethylhidrazine and nitrogen tetraoxide propellants. The first stage consisted of four autonomous closed-cycle single-chambered rocket motors, while the second stage had a closed-cycle single chambered sustainer and a four chambered open cycle control motor with four rotating nozzles.

The guidance and control system of the SS-19 was identical to the SS-18 and permitted remote monitoring of missile status while on alert. Remote monitoring also allowed for automatic pre-launch preparation, remote missile targeting before launch and in-flight control of the missile via a flexible pitch control program. Unlike the UR-100MR, the UR-100N could not use existing silos. As a result new silos were constructed at the same sites as the UR-100U silos. The silos were later completely dismantled and rebuilt to increase the survivability of the new missiles. The UR-100N was launched in the hot mode through the thrust of the first stage sustainer engine.

The SS-19 was deployed in three configurations.

• SS-19 Variant-1 - Through the increase of throw-weight and reduction of the size of the warheads relative to the UR-100 the UR-100N was able to carry six MIRV warheads with a yield of 550 KT according to Russian sources or a a yield of one- to two-megatons suggested by Western estimates. According to Western estimates the booster system was limited to a range of 4900 nm but the total system ( booster plus PBV) was believed to be capable of delivering all six RVs to a maximum range of 5200 nm. Development for the SS-19 Variant 1 was approved on 19 August 1970 and developed by V. N. Chelomey. The flight tests of the UR-100N were conducted at the Baikonur cosmodrome from April 1973 through October 1975. The missile was initially deployed in December 1975, Western intelligence believed it achieved an initial operational capability in 1974. The first regiment with UR-100N missiles was put on alert in April 1975 and by the end of 1975 a total of 60 launchers were deployed. The missile utilized an inertial guidance system that was is estimated by some Western sources to have an operational CEP of 0.3 nm in 1975 with a potential CEP of 0.25 nm by 1980. However hasty development of system failed to notice serious problems associated with resonant oscillations that was only discovered following training launches. The resonant oscillations significantly reduced its overall accuracy. Subsequently all deployed missiles were modified to eliminate the problems.
• SS-19 Variant -2 - Otherwise similar to the Variant-1, this variant carries a single warhead with a yield reported by Russian sources of between 2.5 and 5 MT rather than the MIRV system found on variant-1. Between 1976 and 1978 the UR-100N reached its maximum operational inventory of 180 missiles. Sixty of which carried a single warhead. Both of these SS-19 M variants were attributed "hard target kill" capabilities by the West.
• SS-19 Variant -3 -The development of an improved version was authorized on 16 August 1976. The upgrades to the missile involved the development of improved engines and modification of the command system as well as further hardening of SS-19 silos. The protection from a nuclear strike at their silos was considerably improved. The flight-design tests of the improved version that received the designation UR-100NUTTH were conducted between June 1979 and October 1979. Its deployment began in November 1979.

The first complex with UR-100N missiles was commissioned in 1975 with the guarantee period of 10 years. All the best engineering solutions were implemented in this complex validated by the previous generation of “100s”. High reliability indices of the missile and the complex, achieved during exploitation, allowed the military leadership of our country to set a challenge for the Ministry of Defense, the General Staff, Strategic Missile Forces Command, the leading designer to extend the complex service life from 10-15 to 25 years and then from 25 to 30 years. At present the operation life of the complex is extended to over 36 years.

The accomplishment of such complicated task required cooperation of “JSC MIC Mashinostroyenia” , as the head designer with the other enterprises for development of the new methodic approaches and close interaction with the scientific research institutes, MoD organizations, operating units and services of Strategic Missile Forces.

The task for such long service life of the complex with the same combat and technical performance was solved for the first time in the world. The great number of scientific surveys and R&D had to be conducted combined into the single complex program. The approaches for prediction of the complex status were developed for not less than 2-3 years ahead based on the “Calculation – Experiment – Prediction - Solution” principle.

In this connection the strength margins of the load-bearing structures are estimated, the condition of fuel tank walls is checked, the condition of the propellant components is analyzed, the accelerated tests are conducted in the environmental chambers to simulate the equivalent effects of the environmental parameters on the units and mechanisms of the complex. The gained experience is universal and it can be used for the service life extension of all complexes with the liquid-propellant missiles, including RS-20 “Voevoda”.

The annual launches of UR-100N UTTKh missiles from Baikonur cosmodrome is the important part for confirmation of the missile basic specifications. The missile with the longest service life is selected for such launch. The calculations demonstrated that having the UR-100N UTTKh missiles in Strategic Missile Forces saved several billion roubles for the other important national tasks. The extension of missile service life contributed to implementation of the “Strela” LV program for launching of spacecraft with the minimum expenses.