The old Soviet SLBM "R-27"
and the re-use of the technology
for the North Korean and Iranian rocket development

Norbert Brügge, Germany


The Soviet R-27 submarine-launched ballistic missile is a single-stage, storable liquid-propellant missile. Development work resulted from a proposal by SKB-385 in late 1961 for the development of a launch system with a light single-stage missile for strikes against strategic land targets. In 1962 the project was officially authorized.
One distinctive innovation in this design was the placement of the rocket engines within the fuel tank in order to reduce the external dimensions of the vehicle. The missile body was made of aluminium alloys, and the fuel and two oxidizer tanks had common bottoms. The propulsion system has a single-chamber sustainer and a dual-chamber control engine. The thrust chambers of the attitude control engine were oriented at an angle of 45 degrees from the stabilization axis of the missile. The R-27 had a total length of 8.75 (later 9.65) meters, and a total length without warhead of 7.10 meters.
Because the propellants are so corrosive, once they were fueled they would not be in a condition to transfer. Moreover, the design of the R-27 had the main engine submerged in the propellant ,so these engines could not be salvaged for reuse. The smaller steering engines were outside the fuel tank and could have been salvaged.
A second version, the R-27A, with increased range, began flight tests in October 1972 and entered service in 1974. A third version, the R-27U carried three Re-entry Vehicles (RVs), and also entered service in 1974.
The two-stage R-27K were fitted in upgraded project. A report in 1999 suggested that a single warhead anti-radar version had also been developed, with a reduced range, and with a passive radar seeker to track ship surveillance radars during the terminal phase. This project was cancelled in 1975.
The R-27 SLBM in North Korea has used as a template for the development of its own missile, the so-called "Musudan".

Engine first stage Thrust (s.l.) Isp (s.l.) Thrust (vac) Isp (vac) Propellant Mass (t) Burn time (sec) Flow rate (t/sec)

Total Impulse (vac)

1x Isayev  4D10  216.5 2579 238.7 2844 UDMH/AK-27P 12.65 128.5 0.0839  34.7 MN*s
2x Vernier 28.4 1961 31.3 2157 0.0145
1x Isayev  4D10 233.9 2638 257.4 2903 UDMH/N2O4 12.65 122 0.0887  35.4 MN*s
2x Vernier 29.4 1961 32.4 2157 0.0150


R-27 SLBM with 1.50 m diameter

R-27 propulsion arrangement
Source: Forum Novosti Kosmonavtiki

R-27 Vernier engine (15 kN thrust only)


R-27 SLBM main engine arrangement  (Source: Forum Novosti Kosmonavtiki)

R-27 Vernier turbo-aggregat


Unha/Safir upper 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 now secundary 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 engines 4D10 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 used in its new second stage for the Unha-1. The Unha-1 (not the Paektusan / Taepodong-1) was tested only once without success and is now successful in Iran as Safir IRILV in use. North-Korea is now focused on the development of the Unha-2. The Unha-2 used a larger version of the second stage, with about 465% more fuel. But probably are used two new engines like for the Iranian Simorgh.

 Engines Thrust (s.l.) Isp (s.l.) Thrust (vac) Isp (vac) Propellant Mass (t) Burn time (sec) Flow rate (t/sec) Total Impulse (vac)
 LRE-4 (2) 31.7 2707 33.3 2844 UDMH/AK-27 3.05 260 0.0117 8.7 MN*s

Safir IRILV engine without nozzle extension

Engine without and with nozzle extension


Safir IRILV engine with nozzle extension

Safir IRILV second stage tail


Similarities between the turbo-units of R-27 Verniers and the Safir IRILV