The Block D upper stage. Copyright © 2011 Anatoly Zak
Block D inside its fairing during processing in Baikonur. Copyright © 2000 Anatoly Zak
A propulsion section of Block D. Copyright © 2000 Anatoly Zak
Project of the Flagman upper stage, which combines Block D and Fregat stages.
A scale model of the head section of the Proton rocket with Block D upper stage and a pair of Yamal satellites. Click to enlarge. Copyright © 2009 Anatoly Zak
The 11D58M engine which powered Block DM. Copyright © 2011 Anatoly Zak
Fuel tank of the Block-DM stage. Click to enlarge. Copyright © 2011 Anatoly Zak
A middle payload fairing for Block DM. Copyright © 2011 Anatoly Zak
The general architecture of the Block D upper stage.
The upper stage known as Block D was originally developed for the L3 lunar expeditionary complex, to be launched by the N1 rocket. During lunar expeditions, Block D was expected to conduct trajectory corrections between the Earth and the Moon, then make a braking maneuver for entering lunar orbit and fire one last time to initiate the initial descent of the LK manned lander on the lunar surface.
Designed for multiple engine firings and multi-day missions in space, the Block D upper stage outlived the program for which it had originally been 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 Soviet circumlunar and unmanned lunar missions and also in unmanned planetary missions to Venus and Mars. Because the stage was no longer intended for multi-day lunar trips, it was simplified for missions not exceeding 12 hours.
A 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 complex, a three-segment fairing was used to mate Block D with Block G below and the lunar orbital spacecraft above. In the Proton rocket configuration, a two-segment shroud is used.
To control the stage during coasting phase of the flight (without thrust) in low Earth orbit, Block D was equipped with small autonomous thrusters burning unsymmetrical dimethyl hydrazine (UDMH) mixed with nitrogen tetroxide (NTO).
The main engine of the stage, burning kerosene and liquid oxygen had a thrust in vacuum of 85 kH (8.7 tons) and a specific impulse of more than 350 seconds. The total burn time (in multiple firings) for this engine could reach more than 600 seconds. The propulsion system designated 11D58M or RD-58M was developed at Korolev's OKB-1, and it was mass-produced by the Voronezh mechanical plant, south of Moscow.
During the launch of the Ekspress AM-2 spacecraft on March 30, 2005, the Block D/DM series upper stage flew its 250th mission, according to RKK Energia.
In the course of its history, Block D underwent numerous upgrades, which recieved designations DM, DM-1, DM-2, DM-3 and DM-SL. The latter upgrade integrated the stage with the Zenit rocket used in the Sea Launch venture. Since mid-1990s, the latest version, known as DM-03, has been in development aiming to increase performance of the Proton rocket, as well as integrate the stage with Rus-M, Angara-5, Energia-K and other proposed launchers.
Block DM (11S86) specifications: