RD-0255
# RD-0255

The RD-0255 is a propulsion module composed of an RD-0256 main engine and a RD-0257 vernier engine. Both are liquid rocket engine, burning UDMH in $N_2O_4.$ The RD-0256 main engine operates in the oxidizer rich staged combustion cycle, while the vernier RD-0257 uses the simpler gas generator cycle. It was used on the R-36MUTTKh (GRAU:15A18) and R-36M2 (GRAU:15A18M). Subsequently, it has been in the Dnepr second stage and as of 2016 it is still in active service.

The RD-0256 is an improved version of the RD-0228 (GRAU: 15D84), itself composed of an RD-0229 (GRAU: 15D84) main engine and a RD-0230 (GRAU: 15D79) vernier engine. The RD-0228 was developed between 1967 and 1974 for the first generation of R-36M (GRAU: 15D83) ICBM second stage, but was replaced on subsequent iterations by the RD-0256. The RD-0228 debut was on January 21, 1973. With the START I and START II the RD-0228 was retired and its successor, the RD-0256, only continued as the Dnepr.

