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The steering engines of the Soviet R-27 SLBM are the only available engines with low thrust in North Korea and Iran. They are used for various purposes, partially modified, in carrier rockets and missiles:
| Rocket | Stage | Origin | Combustors | Fig. | | Paektusan-1 | 2. | not a 4D10 steering engine | 4 | | | Paektusan-2/Safir IRILV | 4D10 main engine with nozzle extension | 2 with own turbopump | 10,11 | | Unha-1/Simorgh IRILV | 4D10 main engine with nozzle extension | 4 with own turbopumps (2) | | | Unha-2 & Unha-3 | not a 4D10 steering engine | 4 (small thruster) | | | HS-14 | 4D10 main engine with nozzle extension | 2 with own turbopump | | | Unha-3 | 3. | 4D10 main engine with nozzle extension | 2 with own turbopump | 12 | | | | Unha-2 & Unha-3 | 1. | not a 4D10 steering engine | 4 (pressure-fed mode ?) | 3,4 | | HS-12 & HS-14 | 4D10 steering engine | 4 | 8,9 | | HS-10 | 4D10 steering engine | 2 with own turbopump | 6,7 | | HS-13 | 4D10 steering engine | 4 with own turbopums (2) | 5 | |  | Fig. 1 to 2 = R-27 SLBM Fig. 3 to 4 = Unha-2 and -3 (first st.)
(not a 4D10 steerung engine !) Fig. 5 = HS-13 missile Fig. 6 to 7 = HS-10 missile Fig. 8 to 9 = HS-12 and HS-14 missile Fig. 10 to 11 = Safir IRILV (second st.) Fig. 12 = Unha-3 (third st.) | 1. Steering engines in pressure-fed mode for carrier rockets and missiles
Four steering engines, used for the first stage of the North Korean Unha-2 and Unha-3 are not of R-27 SLBM origin. They are homemade, smaller and working in pressure-fed mode The fuel is supplied from additional tanks (debris captured). As control engines for the second (Scud) stage of the Paektusan-1 the same engines worked probably in an other mode. For the second stage of the Unha-2 and Unha-3 are additional to the main engine uses small pressure-fed thruster. 2. Steering engines without own turbpump for missiles
The four steering engines of the H-12 and HS-14 missiles are coupled with the turbopump of the main engine "Pektusan" (RD-250). Probably, the engines were also used for the second (Scud) stage of the Paektusan-1 as control engines. .3. Steering engines with own turbopump for one-stage missiles
In unchanged version, the combination of main engine/steering engines of the R-27 SLBM (with the main engine 4D10) by North Korea is taken over for the HS-10 missile. North Korea is trying to double the engine system in the North Korean HS-13 ICBM. So far, however, no test of the rocket is known, especially since there are obviously great difficulties, to qualify the simplier HS-10 system reliable. 4. Main engine for carrier rockets (2. or 3. stage)
It is believed that the propulsion of the second stage of the Iranian Safir IRILV was built on base the R-27 SLBM technology and comes secondary from North Korea. In fact, there are similarities between the R-27 and the Safir upper stage propulsion. The nature of the turbopump and its placement into the tank and the attachment of the two small engines on the outside of highly curved bulk are striking. The shape of the vernier engines of the R-27 are very similar to the Safir IRILV, but they have only a thrust of about 30 kN with low specific impulse.
Presumably, North Korea has acquired the technology from the R-27. The used two small Soviet steering engines has been upgraded in its performance. This also applies to the turbopump of the R-27 Verniers and their arrangement. This turbopump is located within the tank as in the R-27, however in the centre.
North Korea has probably the changed technology also used in its second stage for the Paektusan-2 and Unha-1. The Paektusan-2 and Unha-1 were tested, but later not more of interest and are now the Iranian Safir IRILV and Simorgh IRILV. North Korea was then focused on the development of the Unha-2 and so on. |
