KN-21

US military intelligence identified and designated a new type of North Korean short-range ballistic missile (SRBM). The missile is assessed to be a modification of North Korea’s existing Scud-B missiles, U.S. government sources with knowledge of the latest U.S. intelligence assessments on North Korea tell The Diplomat. The missiles were a new type of short-range ballistic missile, a Scud-B variant designated as the KN-21, The Diplomat reported 14 September 2017, citing U.S. government sources. According to one source who spoke to The Diplomat, the SRBMs that were tested had “similar guidance capabilities as the KN18.” The missiles are distinct from the KN18 in that they were unitary, non-separating Scuds with terminal maneuverability. The KN18, based on the Scud-C, has a separating warhead.

Scud-ER

© C. P. Vick 2008 All Rights Reserved

The North Korean Scud–ER was first observed through intelligence imagery in 2005 in North Korea but was first revealed publicly in the 75 th anniversary of the Korean People’s Army, military parade held in Pyongyang on April 25, 2007. Its development was completed in 2003 with deployment that followed.

The Scud-ER (extended range) Scud derivation utilizes a single stage with storable propellants. This Scud variant range has been extended from the Scud-C range of 500 kilometers with a conventional warhead mass of 700-800 kilograms to a range of 750-800 kilometers or more with a conventional warhead mass of 450 kilograms or more.

Its engine stage combination is believed to be the same as used for the second stage on the Taepo-dong-1 satellite launch vehicle with its SAM-2 step throttled engine and propellant change. In its Taep’o-dong-1 second stage configuration it utilized an altitude thrust chamber verses the Scud-ER sea level thrust chamber. By Step throttling the turbine fed engine drives the Scud-ER over a longer range with a smaller mass warhead of 450 kilograms or more. This is not done merely or exclusively by reducing the warhead mass but also by using the higher launch thrust lower than that of the Scud-B but then step throttling the thrust at altitude down to a lower sustainer thrust level that extends the missile range performance. Literally the range performance can be shortened or extended by the phases of the thrust level performance from 100 % at launch to as low 65% or less at altitude which can in turn lengthen the single stage burn time or shorten it for a given propellant mass. That is the primary key to understanding the Scud-ER performance characteristics.

Scud Evolution

Scud-ER Performance Estimates

 Designation - Scud –ER

Range - 750-800 or more km

Diameter - 0.855 m

Height - 9.5 – 11.37 meters depending on warhead size

Fin Span - 1.8 - 2.0 m

Launch Weight - 5,300 – 5,600 kg

Dry weight - 1,100 kg minus warhead

Guidance - Strap-down inertial

Thrust - 13,150 kgf max to [ 8,300 kgf at launch and 5,000 kgf at altitude]

Derivation on the SAM-2 step throttled engine using Scud-B propellants.

Thrust Chambers - 1

Steering - Rotating vanes in the exhaust jet (-4 to -5 sec Isp losses)

Isp. - 226 – 263 sec actual sea level to vac.

Mp - 3,771 – 3760 kg

Fuel - TM-185 =20% Gasoline, 80% Kerosene

Oxidizer - AK-27I =27% N2O4 + 73% HNO3 with Iodium inhibitor Nitrogen Tetroxide & Nitric Acid

Thrust/Weight -1.48 – 1.56 Gee’s

Burn time - Variable over flight duration

Warhead mass - 700 - 450 kg