Blok E

Blok E (or Block E) is the propulsion unit of Soviet lunar module LK, developed in the 1960s by Yuzhnoye Design Bureau as a part of the human lunar landing program.[3]

Blok E

Manufacturer	Yuzhnoye Design Bureau
Country of origin	Soviet Union
Used on	LK
General characteristics
Height	2.38 m (7.8 ft)[1]
Diameter	1.72 m (5.6 ft)[1]
Gross mass	2,950 kg (6,500 lb)[1]
Propellant mass	2,390 kg (5,270 lb)[1]
Empty mass	525 kg (1,157 lb)[1]
Launch history
Status	Retired
Total launches	0a[2]
Successes stage only)	0
Failed	0
Blok E[3]
Powered by	11D410 engine cluster Consisting of: 1x 11D411 1x 11D412 4x Vernier Thrusters
Maximum thrust	20.1 kN (4,500 lbf) (11D411 at 100% Thrust or 11D412) 8.4 kN (1,900 lbf) (11D411 at minimum Throttle)
Specific impulse	315 s (3.09 km/s) (11D411) 285 s (2.79 km/s) (11D411 at minimum Thrust) 312 s (3.06 km/s) (11D412)
Burn time	400 seconds Full Thrust +100 seconds throttled (11D411) 400 seconds (11D412)
Propellant	UDMH/N2O4[4]

Blok E was designed to soft land the LK on the surface of the Moon after orbital velocity was cancelled by Blok D. Later the same stage would fire for the second time for the liftoff and ascent from the Moon to rendezvous with the orbiting Soyuz 7K-LOK.[5][6] Blok E used RD-858 (or 11D411),[7] which has one nozzle and is deeply throttleable (from 2050 kg to 858 kg of thrust),[8] as the primary engine. The backup engine was RD-859 (or 11D412),[7] which has two nozzles.

Together, the two engines formed the propulsion system designated 11D410.[3] Both engines burned a mix of unsymmetrical dimethyl hydrazine and nitrogen tetroxide. The hypergolic propellant components guaranteed their easy storage during a lunar expedition lasting at least 11 or 12 days.

The engines were equipped with clam-shell doors to prevent damaging it while staying on the surface of the Moon. There were four additional vernier engines placed between main and backup engine nozzles. Additionally to the main engine, the backup engine and the verniers, the stage was equipped with eight low-thrust reaction control thrusters feeding off a common propellant reserve.[9] These thrusters had been provided by OKB-300, the Stepanov Aviation Bureau.[10]

11D410
	RD-858 / 11D411	RD-859 / 11D412
Designed	1964
Propellant	N2O4/UDMH
Mixture Ratio	2.03 at 100% Thrust 1.6 fully throttled	1.6
Engine cycles	Open Gas-generator cycle
Pumps	1
Combustion chambers	1	2
Restarts	2
Dry mass	53 kg (117 lb)	57 kg (126 lb)
TWR	38.68 (Full thrust)	35.88
Mass flow	6.5–3.0 kg/s (14.3–6.6 lb/s) depending on throttle	6.6 kg/s (15 lb/s)