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N1

Block A

Block B

Block V

The fourth stage of the N1 rocket was designated Block G after the fourth letter in the Russian alphabet. Block G was also considered to be a part of the L3 expeditionary complex, because it was delivered with the rest of the payload into the initial parking orbit around the Earth by the three booster stages of the N1 rocket — Blocks A, B and V.

Previous chapter: Block V (Stage III) of the N1 rocket

Known specifications of Block G (Stage IV of the N1 rocket):

During a lunar expedition, Block G, equipped with a single NK-21 engine burning a mix of kerosene and liquid oxygen, had the job of sending the L3 expeditionary complex from the initial low-Earth orbit toward the Moon. During the six-minute maneuver, the propulsion system of Block G was to burn until full consumption of the propellant in its tanks. Once empty, Block G was expected to separate from the L3 vehicle, leaving it to the still-attached Block D stage to correct the newly formed trans-lunar trajectory.

Sergei Korolev's OKB-1, later TsKBEM, based in Podlipki, near Moscow, was responsible for the overall design of Block G, while the development of the production documentation and the actual manufacturing of the stage were delegated to the Progress factory and its design bureau in Kuibyshev (now Samara), along with all the booster stages of the N1 rocket.

The Block G during assembly.

Like other components of the L3 payload, Block G was enclosed into the payload fairing of the N1-L3 system. Going from bottom to top, Block G's structure consisted of an aft section with the engine, a torus-shaped fuel tank, an inter-tank truss, a spherical oxidizer tank with a cylindrical insert at its equator and a top adapter interfacing with the fifth stage (Block D).

OKB-276, based in Kuibyshev and led by Nikolai Kuznetsov, developed Block G's NK-21 engine, which was also used on the N1's third stage (Block V).

In its original design, Block G was apparently expected to carry one or two thruster pods, known as SOZ (from Sistema Obespecheniya Zapuska) with the 11D74 multi-engine propulsion system. SOZ thrusters would provide initial attitude control and acceleration to the vehicle, ensuring reliable propellant supply to the main engine of Block G before its ignition in the weightlessness of space. The SOZ unit was to be developed at Turaev MKB Soyuz in Lytkarino, near Moscow, which built a simular unit for Block D. However, the drawings showing the final architecture of the Block G stage lacked SOZ, seemingly confirming reports and available film footage showing small solid-propellant motors apparently serving as the ullage system for the main engine on Block G.

The N1 rocket development roadmap and the prospective L3M lunar exploration architecture (INSIDER CONTENT) envisioned replacing the kerosene-burning Block G with the hydrogen-fueled Block S and, later, with Block Sr, but their development was not completed.

Next chapter: Block D (Stage V) of the N1 rocket

Page author: Anatoly Zak; last update: April 3, 2025

Page editor: Alain Chabot; last edit: April 3, 2025

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Block G fires, sending the L3 complex toward the Moon. Click to enlarge Copyright © 2002 Anatoly Zak

Block G under assembly. Credit: RKTs Progress