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 origin	USSR
First flight	December 16th, 1965
Designer	OKB-456
Manufacturer	PA Yuzhmash
Associated L/V	R-36, Tsyklon-2 and Tsyklon-3
Status	Out of Production
Liquid-fuel engine
Propellant	N2O4 / UDMH
Mixture ratio	2.6
Cycle	Gas-generator
Configuration
Chamber	2
Performance
Thrust (vac.)	882 kN (198,000 lbf)
Thrust (SL)	788 kN (177,000 lbf)
Chamber pressure	8.33 MPa (1,208 psi)
Isp (vac.)	301 s (2.95 km/s)
Isp (SL)	270 s (2.6 km/s)
Dimensions
Dry weight	788 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	8D518	8D518P	8D518M	8D518PM	8D724	11D26
Module	RD-251	RD-251P	RD-251M	RD-261	N/A	N/A
Module GRAU	8D723	8D723P	8D723M	11D69	N/A	N/A
Development	1962-1966	1967-1968	1966-1968	1968-1970	1962-1966	1968-1970
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/A	N/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/A	N/A
Length	2,600 mm (100 in)	2,600 mm (100 in)	2,600 mm (100 in)	N/A	2,190 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/A	2,590 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/A	715 kg (1,576 lb)	715 kg (1,576 lb)
Use	R-36 (8K67) 1st stage	R-36P (8K67P) 1st stage	R-36-O (8K67-O) and Tsyklon-2 1st stage	Tsyklon-3 1st stage	R-36, R36P, R-36-O, Tsyklon-2 2nd stage	Tsyklon-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

• R-36 (missile) - ICBM for which this engine was originally developed for.
• Tsyklon-2 - launch vehicle based on the R-36.
• Tsyklon-3 - Three stage launch vehicle developed from the Tsyklon-2.
• Cyclone-4M - launch vehicle based on the R-36
• Rocket engine using liquid fuel

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

External links

• Yuzhmash official information on the RD-261.
• Encyclopedia Astronautica information on RD-250 base engine.