The RD-250 (GRAU Index 8D518) is the base version of a dual nozzle family of liquid rocket engines, burning N2O4 and UDMH in the oxidizer rich staged combustion cycle. The RD-250 was developed by OKB-456 for Yangel's PA Yuzhmash ICBM, the R-36 (missile) (8K67). 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.
The engine has seen different versions made:
RD-250 (GRAU Index 8D518): Base engine of the family. Used on the R-36. A bundle of three RD-250 form the RD-251 cluser.
RD-250P (GRAU Index 8D518P): Improved version of the RD-250. Used on the R-36P. A bundle of three RD-250P form the RD-251P cluser.
RD-250M (GRAU Index 8D518M): Improved version of the RD-250P. Used on the R-36-O. A bundle of three RD-250M form the RD-251M cluser.
RD-250PM (GRAU Index 8D518PM): Improved version of the RD-250M. Used on the Tsyklon-3. A bundle of three RD-250PM form the RD-261 cluser.
RD-252 (GRAU Index 8D724): Vacuum optimized version of the RD-250. Used on the R-36 and Tsyklon-2 second stages.
RD-262 (GRAU Index 11D26): Improved version of the RD-252. Used on the Tsyklon-3 second stages.
Some of these engines were bundled into modules of multiple engines. The relevant modules and auxiliary engines are:
RD-251 (GRAU Index 8D723): A module comprising three RD-250. Propulsion module of the R-36 (8K67) first stage.
RD-251P (GRAU Index 8D723P): A module comprising three RD-250P. Propulsion module of the R-36P (8K68) first stage.
RD-251M (GRAU Index 8D723M): A module comprising three RD-250M. Propulsion module of the R-36-O (8K69) and Tsyklon-2 first stage.
RD-261 (GRAU Index 11D69): A module comprising three RD-250PM. Propulsion module of the Tsyklon-3 first stage.
