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

Norbert Brügge, Germany

Update: 07.12.2017

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. I call this engine "Pektusan-B"


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.
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.

 

My second analysis

"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/RD-250). 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)

 

December 06 (The Diplomat) -- According to an unknown U.S. government source the exact flight time of the missile was 53 minutes and 49 seconds. The source added that the missile’s first stage engine burned for 128 seconds and the second stage burned for 161 seconds. The missile did not feature a post-boost vehicle despite the larger payload fairing, which concealed a single reentry vehicle of an unknown weight.
Comment: The stated burning times of the stages are sure wrong.

  

 

 

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

-

tons

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 71 to 72 t. According to my calculations, the projectile reaches a final velocity of about 6700 m sec.


Comparison of North Korea's "Pektusan" engine variants