|Country of origin||Soviet Union|
|First flight||December 16, 1965|
|Last flight||January 30, 2009|
|Designer||Yuzhnoye Design Bureau|
|Associated L/V||R-36, Tsyklon-2 and Tsyklon-3|
|Status||Out of production|
4 / UDMH
|Thrust (vac.)||54.23 kN (12,190 lbf)|
|Chamber pressure||7.160 MPa (1,038.5 psi)|
|Isp (vac.)||280.5 s (2.751 km/s)|
|Burn time||up to 163s|
|Gimbal range||+/- 30°|
|Length||0.9 m (2 ft 11 in)|
|Diameter||3.35 m (11.0 ft)|
|Dry weight||112.5 kg (248 lb)|
|R-36, Tsyklon-2 and Tsyklon-3 second stage vernier|
The RD-855 (GRAU Index 8D69M), also known as the RD-69M, is a four nozzle liquid rocket vernier engine, burning N2O4 and UDMH in a gas generator cycle. It was used on the R-36, Tsyklon-2 and Tsyklon-3 second stage as thrust vector control by gimbaling of its nozzle. The engine is distributed through a cylindrical structure that is integrated around the main engine RD-252 module. The structure includes aerodynamic protection for the nozzles. The engine was started by a pyrotechnic ignitor.
The engine was serially produced between 1965 and 1992. It was first launched on December 16, 1965 on an R-36 and its last launch was on January 30, 2009 with the last launch of the Tsyklon-3. The production capability was restarted for the Tsyklon-4 but with the apparent cancellation of the program the engine would still be out of production.
- R-36 - The Soviet ICBM for which the RD-856 was created.
- Tsyklon-2 - A Soviet small rocket that uses the RD-856.
- Tsyklon-3 - A Soviet small rocket that uses the RD-856.
- Tsyklon-4 - A Ukrainian small rocket project that would have used the RD-856.
- Yuzhnoe Design Bureau - The RD-856 designer bureau.
- "RD-856". Encyclopedia Astronautica. Retrieved 2016-07-06.
- Pillet, Nicolas. "Tsiklone - Le deuxième étage" [Tsyklon - The second stage] (in French). Kosmonavtika.com. Retrieved 2016-07-06.
- "RD-856". Yuzhnoye. Retrieved 2016-07-06.
- Krebs, Gunter Dirk (2016-04-24). "Tsiklon". Gunter's Space Page. Retrieved 2016-07-05.
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