Encyclopedia Astronautica

S5.51 LOK engine
The complex plumbing fed numerous smaller attitude control thrusters at the base of the LOK.
Credit: © Mark Wade
S5.51 LOK engine
Side view of the twin-chamber Isayev S5.51 engine used in the Soyuz 7K-LOK lunar orbiter. The two smaller chambers of the S5.52 supplemental engine protude beyond the main engine bells to either side.
Credit: © Mark Wade
Isayev N2O4/UDMH rocket engine. 33.196 kN. Hardware 1969. Isp=314s. Complex engine used to maneuver the LOK to a rendezvous with the LK lander in lunar orbit, then propel the LOK out of lunar orbit. Verniers included for midcourse corrections.

Burn time main/vernier engines 700 + 300 sec. Oxidizer to fuel ratio 1,85 / 1,76.

Application: Soyuz LOK lunar orbiter.


Chambers: 2 + 1. Throttled thrust(vac): 4.089 kN (919 lbf). Engine: 480 kg (1,050 lb). Thrust to Weight Ratio: 7.05. Oxidizer to Fuel Ratio: 1.85.

AKA: S5.51; 11D68.
Status: Hardware.
Unfuelled mass: 480 kg (1,050 lb).
Height: 2.77 m (9.08 ft).
Thrust: 33.20 kN (7,463 lbf).
Specific impulse: 314 s.
Burn time: 700 s.
First Launch: 1964-72.

More... - Chronology...

Associated Countries
See also
Associated Manufacturers and Agencies
Associated Propellants
  • N2O4/UDMH Nitrogen tetroxide became the storable liquid propellant of choice from the late 1950's. Unsymmetrical Dimethylhydrazine ((CH3)2NNH2) became the storable liquid fuel of choice by the mid-1950's. Development of UDMH in the Soviet Union began in 1949. It is used in virtually all storable liquid rocket engines except for some orbital manoeuvring engines in the United States, where MMH has been preferred due to a slightly higher density and performance. More...

  • Semenov, Yu. P., S P Korolev Space Corporation Energia, RKK Energia, 1994.
  • Haeseler, Dietrich, Visit to the museum of Chemical Machining Design Bureau, Kalinin 1994 via Dietrich Haeseler.

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