RD-250

The RD-250 (GRAU Index 8D518) is the base version of a dual-nozzle family of liquid rocket engines, burning N2O4 and UDMH in the oxidizer rich staged combustion cycle. The RD-250 was developed by OKB-456 for Yangel's PA Yuzhmash ICBM, the R-36 (8K67). Its variations were also used on the Tsyklon-2 and Tsyklon-3 launch vehicles. It was supposed to be used on the Tsyklon-4, but since the cancellation of the project it should be considered as out of production.

RD-250 (РД-250)
Country of originUSSR
First flightDecember 16th, 1965
DesignerOKB-456
ManufacturerPA Yuzhmash
Associated L/VR-36, Tsyklon-2 and Tsyklon-3
StatusOut of Production
Liquid-fuel engine
PropellantN2O4 / UDMH
Mixture ratio2.6
CycleGas-generator
Configuration
Chamber2
Performance
Thrust (vac.)882 kN (198,000 lbf)
Thrust (SL)788 kN (177,000 lbf)
Chamber pressure8.33 MPa (1,208 psi)
Isp (vac.)301 s (2.95 km/s)
Isp (SL)270 s (2.6 km/s)
Dimensions
Dry weight788 kg (1,737 lb)
Used in
R-36, Tsyklon-2 and Tsyklon-3 first stage
References
References[1][2][3][4][5][6]

Versions

The engine has seen different versions made:

  • RD-250 (GRAU Index 8D518): Base engine of the family. Used on the R-36. A bundle of three RD-250 form the RD-251 cluster.
  • RD-250P (GRAU Index 8D518P): Improved version of the RD-250. Used on the R-36P. A bundle of three RD-250P form the RD-251P cluster.
  • RD-250M (GRAU Index 8D518M): Improved version of the RD-250P. Used on the R-36-O. A bundle of three RD-250M form the RD-251M cluster.
  • RD-250PM (GRAU Index 8D518PM): Improved version of the RD-250M. Used on the Tsyklon-3. A bundle of three RD-250PM form the RD-261 cluster.
  • RD-252 (GRAU Index 8D724): Vacuum optimized version of the RD-250. Used on the R-36 and Tsyklon-2 second stages.[4]
  • RD-262 (GRAU Index 11D26): Improved version of the RD-252. Used on the Tsyklon-3 second stages.[7]

Modules

Some of these engines were bundled into modules of multiple engines. The relevant modules and auxiliary engines are:

  • RD-251 (GRAU Index 8D723): A module comprising three RD-250. Propulsion module of the R-36 (8K67) first stage.[3]
  • RD-251P (GRAU Index 8D723P): A module comprising three RD-250P. Propulsion module of the R-36P (8K68) first stage.
  • RD-251M (GRAU Index 8D723M): A module comprising three RD-250M. Propulsion module of the R-36-O (8K69) and Tsyklon-2 first stage.
  • RD-261 (GRAU Index 11D69): A module comprising three RD-250PM. Propulsion module of the Tsyklon-3 first stage.[8]

Comparison
RD-250 Family of Engines[1]
Engine RD-250 RD-250P RD-250M RD-250PM RD-252 RD-262
GRAU 8D5188D518P8D518M8D518PM8D72411D26
Module RD-251RD-251PRD-251MRD-261N/AN/A
Module GRAU 8D7238D723P8D723M11D69N/AN/A
Development 1962-19661967-19681966-19681968-19701962-19661968-1970
Propellant N2O4/UDMH
Combustion chamber pressure 8.336 MPa (1,209.0 psi) 8.924 MPa (1,294.3 psi)
Thrust, vacuum 881.6 kN (198,200 lbf)881.6 kN (198,200 lbf)881.6 kN (198,200 lbf)881.7 kN (198,200 lbf)940.8 kN (211,500 lbf)941.4 kN (211,600 lbf)
Thrust, sea level 788.5 kN (177,300 lbf)788.5 kN (177,300 lbf)788.5 kN (177,300 lbf)788.7 kN (177,300 lbf)N/AN/A
Isp, vacuum 301 s (2.95 km/s)301 s (2.95 km/s)301 s (2.95 km/s)301.4 s (2.956 km/s)317.6 s (3.115 km/s)318 s (3.12 km/s)
Isp, sea level 270 s (2.6 km/s)270 s (2.6 km/s)270 s (2.6 km/s)269.6 s (2.644 km/s)N/AN/A
Length 2,600 mm (100 in)2,600 mm (100 in)2,600 mm (100 in)N/A2,190 mm (86 in)2,190 mm (86 in)
Diameter 1,000 mm (39 in)1,000 mm (39 in)1,000 mm (39 in)N/A2,590 mm (102 in)2,590 mm (102 in)
Dry weight 728 kg (1,605 lb)728 kg (1,605 lb)728 kg (1,605 lb)N/A715 kg (1,576 lb)715 kg (1,576 lb)
Use R-36 (8K67) 1st stageR-36P (8K67P) 1st stageR-36-O (8K67-O) and Tsyklon-2 1st stageTsyklon-3 1st stageR-36, R36P, R-36-O, Tsyklon-2 2nd stageTsyklon-3 2nd stage

Possible technological transfer to North Korea

Several experts think that technology from the RD-250 engine could have been transferred to North Korea (from Ukraine). This transfer would explain the rapid progress of North Korea in the development of two new missiles: the intermediate-range Hwasong-12 and the intercontinental ballistic missile (ICBM), Hwasong-14. Due to complexity of the technology involved in this type of engine, modifications or reverse engineering seem difficult to achieve. Thus it's believable that complete hardware could have been bought on black market and directly shipped to North Korea, by Russia or Ukraine.[9] Conversely, there is analysis[10] suggesting an alternative mechanism for North Korea to receive R-36 missile engines, or an entire missile, from USSR or Russia.

See also

References
  1. "NPO Energomash list of engines". NPO Energomash. Retrieved 2015-06-20.
  2. "RD-250". Encyclopedia Astronautica. Retrieved 2015-06-20.
  3. "RD-251". Encyclopedia Astronautica. Retrieved 2015-06-20.
  4. "RD-252". Encyclopedia Astronautica. Retrieved 2015-06-20.
  5. Pillet, Nicolas. "Tsiklone - Le premier étage" [Tsyklon - The first stage] (in French). Kosmonavtika.com. Retrieved 2016-07-04.
  6. Pillet, Nicolas. "Tsiklone - Le deuxième étage" [Tsyklon - The second stage] (in French). Kosmonavtika.com. Retrieved 2016-07-04.
  7. "RD-262". Encyclopedia Astronautica. Retrieved 2015-06-20.
  8. "RD-261". Encyclopedia Astronautica. Retrieved 2015-06-20.
  9. "The secret to North Korea's ICBM success". www.iiss.org. Retrieved 2017-08-15.
  10. North Korean Missile Engines: Not from Ukraine, Mariana Budjeryn & Andrew Zhalko-Tytarenko, Atlantic Council, 2017-09-12
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