They Actually Did It
First, this is a lot like an ICBM, even if it is not quite precisely the same thing.
You have undoubtedly read that a three-stage Taepodong-2, which is what we call the Unha-3, could rain death and destruction as far as 15,000 kilometers away. That is an U.S. intelligence community judgment assuming a slightly modified missile with a 500-kilogram payload. North Korea’s plutonium-based nuclear weapons are probably a bit larger than that, and in any event the payload must also accommodate a few hundred kilograms of shielding. (Reentering through the atmosphere is very hot.) A 1,000-kilogram payload would reduce the range of a three-stage Taepodong.
David Wright and Ted Postol, both physicists, estimated that, if the Unha is structurally sound enough to handle 1,000 kilograms of payload, the missile could travel about 10,000 kilometers — far enough to reach about half of the lower 48 states. David wrote me the other night to say that they’ve concluded that is a bit of an overestimate and that I’d be safer to say 8,000-10,000 kilometers. The North Koreans, in any case, have repeatedly said they have missiles that can reach the United States.
Still, the Unha is not an ideal ICBM. In addition to issues with warhead mass reducing range and compromising the structure, there is the issue of fueling the missile. The several-day period during which North Korea erected and fueled the missile has evident drawbacks from a military operations perspective. (Although the quick replacement is worth noting. Perhaps there was a second airframe on site.) North Korea could attempt to deploy the missile in silos or perhaps go the Chinese route of storing the missiles in mountains, rolling them out to launch. They haven’t done that yet.