North Korea's ultimate nuclear ICBM "Hwasong-15" (HS-15)
(How the Unha-3 converted to an ICBM)

Norbert Brügge, Germany

Update: 17.02.201
8

We may have been wrong about the rating of the HS-15 as ICBM. The launch of the HS-15 was probably the test of the second stage of the new North Korean Unha-X SLV, and the whole staging of an ICBM is only for propaganda.
.
This monstrous vehicle HS-15 is a airframe of the Unha-3 launcher that is not suitable for flat ballistic trajectories.The gimbaled "Pektusan-B" engine could support the assumption that this is a second stage for a new big SLV.

On the other hand, the completed conversion of four from originally six available 8-axle TEL's actually speaks also for the use as ICBM, at least theoretically (right).

Note: The latest suppositions of some analysts that the HS-15 is based on old Soviet ICBM technology is nonsense. The called R-37/R-38 ICBM's were only project studies of a "light ICBM" of OKB-586 (Yangel).

   
2018, Febr. 08 - North Korea presents four HS-15 during the parade

2017, November 29 (KCNA) -- The government of the Democratic People's Republic of Korea announced a statement over the successful test-fire of new-type Hwasong-15.
The HS-15 intercontinental ballistic missile tipped with super-large heavy warhead. This system has much greater advantages in its tactical and technological specifications and technical characteristics than HS-14.
The rocket soared to the highest altitude of 4,475 km and then flew the distance of 950 km. After making a 53-minute flight along its present orbit, the rocket accurately landed in the target waters set in the open sea in the East Sea of Korea.



 

They seem to have found a way to gimbal mount the two combustors of the engine. The platform to which the turbopump and  combustors are rigidly connected can no longer be recognized. The turbopump is mounted higher.


The assumption that the HS-15 is a completely new ICBM has been confirmed. The HS-15 is a large two stage missile. Unclear is, if the projectile inside the shroud has an own propulsion. I think it is a dummy.
So far, it is only certain that for the first time the complete engine "Pektusan" (RD-250 clone) with two combustors and a common turbopump was used. This increases the take-off thrust compared to the
HS-14 only to 170% (788 kN SL) because the steering engines are missing. The function of the steering engines assumes the advertised thrust vector control of the main engine. KCNA also reports that the thrust is even controllable in some way ("speed correction in the mid-flight section").
The burning time of the engine must be longer as the observed 127 or 129 sec. The propulsion of the second stage is completely unclear. It should not come as a surprise, however, when to use two single engines from Unha's second stage.

Dimensions of the missile
The scale for determining the dimensions of the missile was the length of the new transporter. By the adding an axis makes it 1.80 m longer than the previous TEL. This results in the length of the HS-15 of 22.5 m. The diameter is 2.40 m from the photo.

 

"It is my guess that the HS-15 is a converted Unha-3. So far nobody has repeated this. But, I am almost sure though. Diameter and length of the first stage are strikingly in agreement. Only the engines were replaced ("Pektusan").
The second stage is probably a down-scaled Unha-3 second stage.
The HS-15 was launched at a steep angle. After burning out (5 min or longer, when the second stage ignited after a coast-phase), the warhead had a long free-flight phase up to speed 0 up to a height of 4475 km, and then dropped back. I can not say anything about the range of the warhead when the missile launching along a low ballistic trajectory. I have to leave that to the specialists. It is spoken by 13000 km.
About the final speed of the rocket after end burn time can only be speculated, because we not accurate know the weight/thrust ratios. However, I assume that the necessary speed will be missed significantly in order to send a warhead into the earth orbit (FOB)." (My Interview with Difesa Online, Roma, Dec. 04)

  

 

 

Stage

Engines

Thrust s.l.

Isp s.l.

Thrust vac

Isp vac

Propellant

Burn time

Flow rate

Total Imp

kN

N*s/kg

kN

N*s/kg

-

t

s

t/s

MN*s (vac)

1

RD-250

788.3

2644

881.3

2956

UDMH/N204

56.35

189

0.2982

166.6

2

LRE-X (2)

    62.5 2501 UDMH/N2O4 5.50 220 0.0250 13.8

The takeoff weight of the HS-15 is estimated at approximately 69 to 70 t. According to my calculations, the projectile reaches a final velocity of about 6700 m/sec.


Comparison of North Korea's "Pektusan" engine variants