The RD-0233 (GRAU Index 15D95) and RD-0234 (GRAU Index 15D96) are liquidrocket engines, burning N2O4 and UDMH in the oxidizer rich staged combustion cycle.[3][1][2] The only difference between the RD-0233 and the RD-0234 is that the latter has a heat exchanger to heat the pressuring gasses for the tanks.[4] Three RD-0233 and one RD-0234 are used on the first stage of the UR-100UTTKhICBM.[5] While the engine is out of production, the ICBM as well as Rokot and Strela remain operational as of 2015.[5]