KN-20 / Hwasong-14 ICBM
North Korea made significant advances in its missile capabilities since 2015, using Soviet-era engines acquired from illicit networks in Russia and Ukraine. After a number of unsuccessful intermediate-range missile launches in 2016, North Korea made impressive progress the development of longer range missiles. The country illicitly obtained technology for its Hwasong-14 and Hwasong-12 rockets from the European black market. North Korea probably obtained the engines from workers at Yuzhmash, the state-owned Ukrainian aerospace company. The RD-250 engine design used in North Korea was made in a Ukrainian factory for use in Cyclone rockets supplied to Russia.
Some Western analysts saw design elements in the new North Korean missile engine similar to the 1960s-era Soviet RD-250 engine used on the first stage of the R-36-0 [SS-9 SCARP] ICBM of OKB Yangel and the derivative Tsyklon 2 launcher. The Glushko RD-250 (GRAU Index 8D518) is a dual nozzle family of liquid rocket engines burning N2O4 and UDMH, part of the RD-215 family of engines [which includes 16 variants]. For instance, the RD-218 consisted of three RD-217. It had 6 combustion chambers and 3 turbines. It powered the R-16 [SS-7 SADDLER] ICBM of OKB Yangel.
The common feature here is that these missiles were designed and built in Ukraine. This suggests a second line of post-Soviet leakage, in addition to the OKB Makayev leakage from Russia. While the designer [Glushko] is in Russia, the missile designers and constructors in Ukraine would have had intimate knowledge of these engines. Ukraine is hopelessly corrupt, and it is not too hard to imagine money changing hands for some old rocket motors and a few Ukrainian engineers to help bring them back to life.
Theodore A. Postol et al state "It is reported that the bomb design Khan sold to Libya and possibly to North Korea would produce a warhead that weighed about 500 kilograms and yielded about 10 kilotons, if properly implemented... we think that a reasonable guess for the minimum weight of an advanced first-generation weaponized North Korean atomic bomb that is able to survive the extreme environments associated with ICBM delivery could be as low as 500 to 600 kilograms."
But Chuck Hansen reported [Swords of Armageddon, page VI-461] "Livermore believed that lightweight reentry vehicle and warhead combinations in a range of weights between 100 to 150 lbs. were feasible. (The mid- 1964 PEBBLES concept had a total RV plus warhead weight of only 108 lbs.)... Livermore proof-fired during the Operation GUARDIAN Dauphin shot on November 14, 1980 a randomly-selected production line W-68 primary with LX-10 and a boost-gas filling that was somewhat poorer in its D-T mixture than any "aged" gas to be used in the stockpile. This extreme test device performed successfully; yield was less than 20 KT.... The W-68 weighed 367 lbs. and yielded 40 to 50 kilotons. The POSEIDON MK 3 RV had a CEP of about 500-600 yards at a range of 2,500 nautical miles; ten warheads were usually carried by each missile (this number could range between six and fourteen)."
The roughly 170 kg mass of the W-68 / MK3 is about one-third the mass Postol et al attribute to the DPRK. A warhead of this mass would allow the Hwasong-14 to reach a range of roughly 10,000-12,000 km, much of the lower 48 states in the USA.
North Korean leader Kim Jong-un said the second flight test of an intercontinental ballistic missile (ICBM) on 28 July 2017 demonstrated that his country can hit the US mainland. His comments came hours after the launch which left analysts concluding that a wide swath of the United States, including Los Angeles and Chicago, is now in range of North Korean weapons. Analysts had estimated that the North's first ICBM on July 4 could have reached Alaska, and said that the latest missile appeared to extend that range significantly.
Dsvid Wright noted "Los Angeles, Denver, and Chicago appear to be well within range of this missile, and that Boston and New York may be just within range. Washington, D.C. may be just out of range. It is important to keep in mind that we do not know the mass of the payload the missile carried on this test. If it was lighter than the actual warhead the missile would carry, the ranges would be shorter than those estimated...."