It seems that Kim Jung Un’s most recent solid fuel ICBMs have benefited from Russian help. It also explains the increased range.
“Kim’s biggest weapons were saved for the end, when his troops rolled out new ICBMs that were flight-tested in recent months and demonstrated ranges that could reach deep into the U.S. mainland, the Hwasong-17 and Hwasong-18. Some analysts say the missiles are based on Russian designs or know-how.”
If you really think about it, he has never looked away from the image of himself in the mirror.