RD-855 (РД-855)
Country of originSoviet Union
First flightDecember 16, 1965
Last flightJanuary 30, 2009
DesignerYuzhnoye Design Bureau
ManufacturerYuzhmash
ApplicationVernier
Associated LVR-36, Tsyklon-2 and Tsyklon-3
StatusOut of production
Liquid-fuel engine
PropellantN2O4 / UDMH
Mixture ratio1.97
CycleGas generator
Configuration
Chamber4
Performance
Thrust, vacuum328 kN (74,000 lbf)
Thrust, sea-level285.4 kN (64,200 lbf)
Chamber pressure6.570 MPa (952.9 psi)
Specific impulse, vacuum292 s (2.86 km/s)
Specific impulse, sea-level254 s (2.49 km/s)
Burn timeUp to 127 s
Restarts1
Gimbal range±41°
Dimensions
Length1.74 m (5 ft 9 in)
Diameter3.81 m (12.5 ft)
Dry weight320 kg (710 lb)
Used in
R-36, Tsyklon-2 and Tsyklon-3 first stage vernier
References
References[1][2][3]

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 N2O4, an oxidizer, and UDMH, a propellant.[2] This combination is hypergolic, meaning the two substances ignite on contact, eliminating the need for an external ignition source.

The RD-855 can orient its chambers within a range of ±42° using hydraulic cylinders.[2] 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.[2]

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 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.[3] The engine is housed in a cylindrical structure that surrounds the primary RD-251 engine. This arrangement provides protection for the nozzles and ensures the successful detachment of the rocket's first stage.[2] The RD-855 is activated two seconds before the main RD-251 engine.[2]

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 the potential discontinuation of the program.[4]


See also

References

  1. ↑ "RD-855". Encyclopedia Astronautica. Archived from the original on April 30, 2002. Retrieved 2016-07-06.
  2. 1 2 3 4 5 6 Pillet, Nicolas. "Tsiklone - Le premier étage" [Tsyklon - The first stage] (in French). Kosmonavtika.com. Retrieved 2016-07-06.
  3. 1 2 "RD-855". Yuzhnoye. Archived from the original on 29 May 2015.
  4. ↑ Krebs, Gunter Dirk (2016-04-24). "Tsiklon". Gunter's Space Page. Retrieved 2016-07-05.


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