How can be interpreted pictures of
an unknown rocket engine combustor
Iran presented as Simorgh future second stage engine
and used as Unha second stage main
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 one picture, 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
It was here also reported that this engine is a
newer engine for the second stage of the Simorgh.
This combustor (engine called
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 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.
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
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).
With 70 cm the combustor would be still 1.9
times higher as that from the LRE-4. By an additional skirt for the
expansion of the nozzle may be achieved a total length of about 95 cm
as second stage vacuum engine for the North Korean Unha SLV. Such nozzle
extension skirts were presented in North Korea and Iran (4,
5). The total thrust of the four engines
is unknown, but could be between
10 and 15 tons.
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.
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