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RD-170 engine



Above: Exterior design of Zenit's first stage.

Previous chapter: Zenit rocket

Originally developed as a strap-on booster of the super-heavy Energia launcher, the same booster also doubled as the first stage of the long-lasting Zenit launch vehicle.

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The architecture of Zenit's first stage, first of all its length and diameter, was dictated primarily by the requirement to fit it into the railway transporter. The price of this advantage was a less-than-optimal distribution of propellant components between two stages. Still, engineers went to a great length to pack maximum propellant volume into the minimal length of both stages.

The second stage is manufactured out of the AMg-6 alloy and welded together to form four main components: oxidizer tank, intertank structure, fuel tank and tail section. These are bolted together to form the first stage.

The long oxidizer tank is comprised of 11 ciclindrical rings and closed off by two hemispheres on both ends. Two rows of titanium tanks for helium gas are located inside the tank close to its bottom. After heating, this gas is used to pressurize both propellant tanks, in order to force their content into the engine. The bottom part of the oxidizer tank connects to the inter-tank ring, which has special hatches used during the rocket's assembly. An oxidizer supply line exits its tank and runs through the fuel tank to reach the engine below.

The lower fuel tank has inverted hemispherical ends designed to save some length of the stage by partially accomodating the end of the oxidizer tank above and the propulsion system below. (264) This volume-saving measures made Zenit one of the most "condensed" launch vehicles in the world. (630)

The tail section with a diameter of 3.7 meters and the fuel tank are connected via a load-bearing ring, which attaches to the launch pad. Launch pad mechanisms hold the rocket by this ring during the liftoff, until the diagnostics system confirms that the main engine had reached the nominal thrust for the flight. The tail section also carries four 8D84 solid-propellant braking motors, which fire as soon as links between two stages of the rocket are cut off in flight to ensure safe separation between two stages. (264)



Specifications of the first stage of the Zenit rocket:

Stage I mass

349 tons

Stage I dry mass

29 tons

Stage I length

32.9 meters

Stage I diameter
3.9 meters
Stage I burn time
~143 seconds from launch
Stage I propulsion

1 (one) four-chamber RD-170 engine (11D520)
4 (four) 8D84 solid-propellant braking motors


Next chapter: Zenit's Stage II


This page is maintained by Anatoly Zak

Last update: February 4, 2013

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Tail ring

An early version of the Zenit rocket featured a skirt-like structure protecting combustion chambers on the first stage. Credit: KB Yuzhnoe

Zenit tail section

A tail section of the Zenit's first stage with a four-chamber RD-171 engine and four 8D84 solid-propellant motors. Copyright © 2000 Anatoly Zak


The RD-171 engine powered the first stage of the Energia rocket. Click to enlarge: 300 by 400 pixels / 56K Copyright © 2005 Anatoly Zak


An interstage structure connecting first and second stages of the Zenit-2 vehicle. Copyright © 2000 Anatoly Zak