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Lunar program guide:

Program chronology

Chronology of the Moon Race

N1

L3

N1/Block G

N1/Block D

LK/Block E

LOK/Block I

N1 launch facilities

Soviet plans for lunar base

The upper stage, known as Block D, was originally developed for the L3 lunar expeditionary complex, launched by the N1 rocket. During the lunar expedition, Block D was expected to conduct trajectory corrections in transit from the Earth to the Moon, a breaking maneuver for entering the lunar orbit and another breaking maneuver for the initial descent of the LK module on the lunar surface.

Designed for multiple engine firings and long-duration performance, the Block D upper stage outlived the program, for which it was originally created. In fact, it has become the most significant heritage of the Soviet lunar effort.

Incorporated into the Proton rocket as its fourth stage, Block D was used in the Soviet circumlunar and unmanned lunar missions and also in unmanned planetary missions to Venus and Mars.

The new modification of the stage, introduced in 1974 and designated Block DM, allowed the USSR to reach geostationary orbit for the first time.

Two modified versions of Block D were also introduced: DM2 in 1982 and DM3 in 1996. In the 1990's, Block D was proposed as a basis for an upper stage in several rockets, such as Zenit-3, Energia-M and the air-launched Polyot booster.

Block D has a length of 5.5 meters and a diameter of 4 meters. Although the stage has its own energy source and avionics, its overall control and data relay is usually performed by the payload. Within the configuration of the N1-L3 rocket system, a three-segment fairing was used to mate Block D with Block G below it and the lunar orbital spacecraft above. In the Proton rocket configuration, two segments are normally used.

To control the stage during coasting phase of flight in the low-Earth orbit, Block D is equipped with small autonomous engines burning unsymmetrical dimethyl hydrazine (UDMH) mixed with nitrogen tetroxide (NTO).

The main engine of the stage, burning kerosene and liquid oxygen has a thrust in vacuum of 85 kH (8.7 tons) and a specific impulse of more than 350 seconds. Total burn time (in multiple firings) could reach more than 600 seconds. The propulsion system for the stage, designated 11D58M or RD-58M, was developed in Korolev's OKB-1, and it is mass-produced by the Voronezh mechanical plant, south of Moscow.

During the launch of the Express AM-2 spacecraft on March 30, 2005, the Block D/DM series upper stage flew its 250th mission, according to RKK Energia.