As a vernier engine, it provides fine steering adjustments for rockets.
It is powered by a hypergolic mixture of unsymmetrical dimethylhydrazine (UDMH) fuel with dinitrogen tetroxide (N2O4) oxidizer.
[2] The RD-855 utilizes the gas generator cycle, in which a portion of the propellant is burned in a pre-burner to produce hot gases that drive the engine's turbopumps, and then the gases are discarded without passing through the main combustion chamber.
This arrangement provides protection for the nozzles and ensures the successful detachment of the rocket's first stage.
[2] Manufactured from 1965 to 1992, the RD-855's inaugural flight was on December 16, 1965, aboard the R-36 missile.