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 short-range missiles that can hit its neighbors. It has tested an intermediate one that could strike Guam, a U.S. territory, as well as a longer-range missile that could reach Hawaii and perhaps the U.S. West Coast. The intermediate and long-range missiles are still 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 (7 kilometers a second).
“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.”