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

Norbert Brügge, Germany

Update: 18.04.2012

R-27 SLBM


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 7.1 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.
  

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

Total Impulse (vac)
R-27
1x Isayev  4D10  225.5 2687 238.7 2844 UDMH/AK-27P 12.65 128 0.0839  35.3 MN*s
2x Vernier  29.4 2279 32.4 2507 148 0.0113
R-27U
1x Isayev  4D10 233.9 2638 257.4 2903 UDMH/AK-27P 12.65 122 0.0887  36.0 MN*s
2x Vernier 29.4 2279 32.4 2507 142 0.0113

   
R-27 SLBM with 1.50 m diameter



R-27 propulsion arrangement
Source: Forum Novosti Kosmonavtiki


R-27 Vernier engine (15 kN thrust ongly)


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


      
R-27 Vernier turbo-aggregat

 

North-Korea's R-27 successor ?


2003 it was reported that North Korea was working on a new missile, is based on the Soviet R-27 submarine-launched missile. North Korea was thought to have acquired the technology sometime between 1992 and 1998.
In 2004 it was reported that prior to the parades on 09 September 2003, as many as ten of the missiles and five launchers were to Mirim Airbase, the preparation site for the parades. Although the missiles were not featured in the celebrations, they were noticed by Western intelligence, which prompted the news reports a few days later. In 2007 it was established that North Korea had fully deployed the missile in it road-mobile-mode.
By March 2009 it had been realized that the missile was deployed in North Korea as a separate strategic rocket forces military division charged with it deployment. The reported 1.5 m diameter is indeed consistent with that of the Soviet R-27 SLBM, but the reported length of about 12 meters (better is 10.75 m, or less ) is a bit puzzling. The R-27 had a total length of 8.75 meters, and a total length without warhead of 7.1 meters.

For Russia, the “Musudan” is a mysterious missile. Russia has not seen any evidence of this missile being developed or tested. References to the missile existence are more in the domain of political speculation than technical fact.

The presented North Korean "missile" has no official name. Both the name "Musudan" or "BM-25" are without foundation. A missile BM-25 entered service with the Soviet army in the 1950s and is the largest caliber MRS (Multiple Rocket System "Katyusha") to have been deployed since WWII by any member of the Warsaw Pact.


Comparison between the Soviet R-27 SLBM and the mysterious "Musudan"

(The interior of   "Musudan" vehicles  is just a guess by me)



Newest picture of the vehicle on the parade in 2012, April 15
 



First pictures of the vehicle on the parade in 2010, Oct. 10

 

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 30 kN. That is not enough for the Safir IRILV.
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 450% 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)     37.3 2849 UDMH/AK-27 3.270 250 0.0131 9.3 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 (below) and the Safir IRILV


Turbo-unit of Safir in work



Comparison between Unha and Safir IRILV upper stages dimensions
 


Safir second stage engine LRE-4 (left) and probably Unha/Simorgh new second stage engine LRE-15 (right)
-- both were presented by Iran, and are advanced Verniers from the R-27 SLBM --