The RD-855 ( GRAU Index 8D68M ), also known as the RD-68M , is a liquid-fueled rocket engine with four nozzles . As a vernier engine , it provides fine steering adjustments for rockets. It is powered by a combination of N 2 O 4 , an oxidizer, and UDMH , a propellant. This combination is hypergolic, meaning the two substances ignite on contact, eliminating the need for an external ignition source.
5-454: The RD-855 can orient its chambers within a range of ±42° using hydraulic cylinders. Each chamber on the Tsyklon rockets is protected by an aerodynamic cover, and these covers are equipped with small retro-rockets allowing for separation from the second stage. The RD-855 utilizes the gas generator cycle , in which a portion of the propellant is burned in a pre-burner to produce hot gases that drive
10-448: The engine's turbopumps, and then the gases are discarded without passing through the main combustion chamber. It played a key role in rockets such as the R-36 , Tsyklon-2 , and Tsyklon-3 , steering these rockets by adjusting its nozzles . The engine is housed in a cylindrical structure that surrounds the primary RD-251 engine. This arrangement provides protection for the nozzles and ensures
15-409: The potential discontinuation of the program. This rocketry article is a stub . You can help Misplaced Pages by expanding it . Gas-generator cycle The gas-generator cycle , also called open cycle , is one of the most commonly used power cycles in bipropellant liquid rocket engines. Propellant is burned in a gas generator (or "preburner") and the resulting hot gas is used to power
20-466: The propellant pumps before being exhausted overboard and lost. Because of this loss, this type of engine is termed open cycle . The gas generator cycle exhaust products pass over the turbine first. Then they are expelled overboard. They can be expelled directly from the turbine, or are sometimes expelled into the nozzle (downstream from the throat) for a small gain in efficiency. The main combustion chamber does not use these products. This explains
25-634: The successful detachment of the rocket's first stage. The RD-855 is activated two seconds before the main RD-251 engine. Manufactured from 1965 to 1992, the RD-855's inaugural flight was on December 16, 1965, aboard the R-36 missile. Its most recent known flight was on January 30, 2009, with the Tsyklon-3 . Although there were plans to restart its production for the Tsyklon-4 , the engine remains out of production following
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