North Korea still mastering how to deliver a nuke

WASHINGTON — U.S. intelligence officials are pretty sure North Korea can put a nuclear warhead on an intercontinental missile that could reach the United States. But experts aren’t convinced the bomb could make it all that way intact.

They cite lingering questions about North Korean leader Kim Jong Un’s nuclear know-how.

“I don’t think North Korea has a good measure of how accurate the missile is at this point,” said Michael Elleman, an expert with the International Institute for Strategic Studies. “They don’t know if the re-entry technologies will really hold up — whether the bomb will survive the trip.”

North Korea has shortrange missiles that can hit its neighbors. It has tested an intermediate one that could strike Guam, a U.S. territory, as well as a longerrange missile that could reach Hawaii and perhaps the U.S. West Coast. The intermediate and long-range missiles still are being developed, and it’s still questionable whether they can reliably strike targets.

The North must conduct more tests to master what is known as “re-entry” in missile parlance, experts believe. The process involves shielding a nuclear warhead from the high temperatures and force it faces when it re-enters the Earth’s atmosphere at about 15,500 mph.

“In principle, Kim Jong Un could hit the United States with a nuclear weapon,” said Elleman, a former scientist at Lockheed Martin’s Research and Development Laboratory who also worked as missile expert for U.N. weapons inspection missions. “In practice, I think they are probably a half-year to a full year away from having something that will work more often than it would fail.”

John Schilling, a consultant with 38 North, a respected website on North Korea at Johns Hopkins University’s School of Advanced International Studies, said the success of North Korean missiles also depends on the weight of the payload — the weight of the nuclear weapon plus its heat-shielding re-entry system. North Korea is able to make one that weighs between 1,100 and 1,300 pounds. One that size might reach West Coast targets, Schilling said, but North Korea would need to make one lighter to strike farther east.

“It needs to be light in order to achieve range, but it also needs to be built fairly tough to survive, and those two things are at odds with one another,” Schilling said. “Too light is a problem in that the payload would be too fragile and won’t survive the trip, particularly atmospheric re-entry at the far end.”