The RD-858 was the primary engine for the Soviet LK manned lunar lander. The propulsion cluster provided the variable thrust needed for a soft landing onto the lunar surface. The same engine was then restarted for lift-off from the moon and injection of the LK into a lunar elliptical orbit. Testing of the engine on the ground and in earth orbital tests confirmed the high reliability of the design.
The autonomous single-chamber two-mode double-start pump-fed engine featured deep thrust throttling using hypergolic propellants and used a gas generator scheme (using the main engine propellants, without generator gas afterburning). During the first run of the engine (lunar landing), maximum thrust was followed by deep thrust throttling. The engine restart for ascent used the full thrust mode without throttling. During startup the turbine's rotor was spun up by a pyrotechnic device. The inlet valves were opened using gas tapped from the manifold of the pyrotechnic device. The valves were operated by fuel pressure delivered from the pump's discharge branch.
Engine shutdown was performed by pyrovalves under commands of the control system. The engine featured control systems for thrust and mixture ratio regulation. Transducers provided the data to control chamber pressure according to the operating mode.
The engine was designed for a total burn time of 470 seconds. This included up to 50 seconds in full-thrust mode during descent to the surface; followed by up to 100 seconds of deep-throttled firing during the soft landing; and then 350 seconds at full thrust during the ascent back to lunar orbit. The full engine installation on the LK consisted of the RD-858 main engine and the RD-859 back-up engine:
Engine RD-858 RD-859 No of chambers: 1 2 Operating regime nominal throttled Thrust in vacuum 2050 kg 858 kg 2045 kg 20104 N 8414 N 20055 N spec. vac. impulse 315 s 285 s 312 s 3089 Ns/kg 2795 Ns/kg 3060 Ns/kg Mixture ratio O/F 2.03 1.6 2.0 Thrust variation +/- 9.8 % +/- 35 % +/- 9.8 % Mixture ratio deviation 3 % 3 % Chamber pressure 80 kg/cm^2 33.8 kg/cm^2 80 kg/cm^2 78.5 bar 33.15 bar 78.5 bar Nozzle exit pressure 0.07 kg/cm^2 0.021 kg/cm^2 0.07 kg/cm^2 Operation time 50 + 350 s 100 s 400 s Propellants N2O4 / UDMH N2O4 / UDMH Engine mass 53 kg 57 kg Propulsion system height 1090 mm Propulsion system width 1102 mm
Application: LK lunar lander main engine.
Throttled thrust(vac): 8.414 kN (1,892 lbf). Engine: 53 kg (116 lb). Chamber Pressure: 78.50 bar. Thrust to Weight Ratio: 38.67. Oxidizer to Fuel Ratio: 2.03.
Unfuelled mass: 53 kg (116 lb).
Height: 1.09 m (3.57 ft).
Diameter: 1.10 m (3.62 ft).
Thrust: 20.10 kN (4,519 lbf).
Specific impulse: 315 s.
Burn time: 470 s.
First Launch: 1964-72.