RD-250


The RD-250 is the base version of a dual-nozzle family of liquid-fuel rocket engines, burning a hypergolic mixture of unsymmetrical dimethylhydrazine fuel with dinitrogen tetroxide oxidizer in a gas-generator open cycle. The RD-250 was developed by OKB-456 for Yangel's PA Yuzhmash ICBM, the R-36. Its variations were also used on the Tsyklon-2 and Tsyklon-3 launch vehicles. It was supposed to be used on the Tsyklon-4, but since the cancellation of the project it should be considered as out of production.

Versions

The engine has seen different versions made:RD-250 : Base engine of the family. Used on the R-36. A bundle of three RD-250 form the RD-251 cluster.RD-250P : Improved version of the RD-250. Used on the R-36P. A bundle of three RD-250P form the RD-251P cluster.RD-250M : Improved version of the RD-250P. Used on the R-36-O. A bundle of three RD-250M form the RD-251M cluster.RD-250PM : Improved version of the RD-250M. Used on the Tsyklon-3. A bundle of three RD-250PM form the RD-261 cluster.RD-252 : Vacuum optimized version of the RD-250. Used on the R-36 and Tsyklon-2 second stages.RD-262 : Improved version of the RD-252. Used on the Tsyklon-3 second stages.

Modules

Some of these engines were bundled into modules of multiple engines. The relevant modules and auxiliary engines are:RD-251 : A module comprising three RD-250. Propulsion module of the R-36 first stage.RD-251P : A module comprising three RD-250P. Propulsion module of the R-36P first stage.RD-251M : A module comprising three RD-250M. Propulsion module of the R-36-O and Tsyklon-2 first stage.RD-261 : A module comprising three RD-250PM. Propulsion module of the Tsyklon-3 first stage.

Possible technological transfer to North Korea

Several experts think that technology from the RD-250 engine could have been transferred to North Korea from Russia. This transfer would explain the rapid progress of North Korea in the development of two new missiles: the intermediate-range Hwasong-12 and the intercontinental ballistic missile, Hwasong-14. Due to complexity of the technology involved in this type of engine, modifications or reverse engineering seem difficult to achieve. Thus it is believable that complete hardware could have been bought on black market and directly shipped to North Korea, by Russia or Ukraine. Conversely, there is analysis suggesting an alternative mechanism for North Korea to receive R-36 missile engines, or an entire missile, from USSR or Russia.