How can be interpreted pictures of an unknown rocket engine combustor

 in Iran presented as Simorgh future second stage engine

and used as Unha second stage main engine ?

Norbert Brügge, Germany

Upload: 2017;  Update:24.06.2020

Until this day it is a mystery what kind of engines are used for the second stage of the North Korean Unha SLV. All presented speculations are not suitable to solve the problem. There is only two pictures, on which in the open adapter three main engines and two control thruster are to be seen (above).
Images from the on board camera the Unha-3 flight # 3 confirm that worked more than one engine in the second stage (below).
In this context are interesting two pictures of an unknown engine in Iran. An illustration was shown by Tal Inbar, Israel, and another was a long time ago (April 2012) on an Iranian forum presented, now untraceable (
right).  In the Iranian source of the image was reported that during the initial tests there were many malfunctions. Finally they could increase the burn time to 150, 320 and then 350 seconds.
It was here also reported that this engine is a
newer engine for the second stage of the Simorgh.

This combustor (engine called here LRE-X) is not identical to that of the steering engines LRE-15 in the first stage of the Simorgh (as originally thought). The steering engines for the first stage of the Simorgh are of other origin, with a thrust of total 15 tons (
see end of this page).

So it is therefore more than likely that this LRE-X engine is used in the vacuum version (nozzle extension) for the second stage of the North Korean Unha SLV. Added are four small control thrusters.



1. Combustor
The engine seems to have a very old design. Striking is a large combustion chamber and a typical old KB Isayev engines ripple structure on the nozzle. On the combustion chamber are devices for the pivoting of the engine mounted. The cooling system for the combustor is unique (
2, 3). There are each a ring for the inflow and outflow of fuel mounted on the nozzle. It looks as if the combustion chamber is not regeneratively cooled because of outflow ring is located directly at the edge of the nozzle and connected is with the injector directly. However, it is likely that a part stream of the cooling flows upward through the wall of the combustion chamber.

The dimensions of the combustor we can determine only in an indirect way, with the assumption that the label nearby the LRE-4 combustor (4D10 steerimg engine) is written on a paper in A6 format (
1) and the label on the LRE-X combustor also in A6 format (2).

1 2 3

With 70 cm the combustor would be still 1.9 times higher as that from the LRE-4. By an possible additional skirt for the expansion of the nozzle may be achieved a total length of about 95 cm for the second stage vacuum engine of the North Korean Unha SLV. The total thrust of the four engines is unknown, but could be between 10 and 15 tons (125 kN ?).
Some nozzle extension skirts were presented in North Korea and Iran (
4, 5). An assignment is not clear to clarify.


2. Control thruster
The added four small control thrusters at the main engines of the second stage of the Unha might be working pressure-fed. In Iran and North Korea  pictures are presented of such thrusters (
6 to 8). The statement that these thrusters can be switched on and off, supports the presumption that they are used in the second stage of the Unha.


4 5 6 7 8



3. Simorgh first stage steering engines (LRE-15 engine)
I do no longer think that the LRE-X combustor is used as steering engine for the first stage of the Simorgh. A comparison with the images of the steering engines at the Simorgh, which were presented in 2015, but not enlightening (11). The only certainty is that the four steering engines of the Simorgh is connected with its own (fifth) turbopump.

The performance of the engine is unclear. The sources mention permanently the term "attitude control engine" or "fifth engine" with a thrust of 15 or 13.6 tons for the Simorgh rocket. This meant of magnitude of about 147.0 or 133.4 kN thrust. So we assume that this engine a thrust generated of 4 x 33.34 kN (s.l.) and 4 x 36.77 kN (vac).

What kind of engines they are, remains unresolved up to now. Perhaps there is a connection with a combustor, of which a picture was shown in 2013 (11).

9 10 11 Comparison