North Korea's new missile could hit any US state - but the immediate threat of a nuclear strike is less clear

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The estimated trajectory of North Korea's Nov. 29, 2017, intercontinental ballistic missile test-launch.

• North Korea test-launched its most powerful intercontinental ballistic missile yet on Wednesday.
• The high arc of the missile, called Hwasong-15, shows it could reach anywhere in the US.
• However, weapons experts say a real nuclear warhead would significantly weigh down the missile.
• That weight may be enough to keep American cities out of striking distance - for now.

Early Wednesday morning, North Korea test-launched an intercontinental ballistic missile to a record-breaking speed and altitude for the isolated nation.

North Korea's new show of force follows an ICBM test launch in July and a powerful thermonuclear test blast in September.

Officials in the US, Japan, and South Korea confirmed that North Korea launched the new missile, called Hwasong-15, from Sain Ni, North Korea. Its payload soared about 2,800 miles into space before falling back to Earth, ultimately landing in the Sea of Japan some 53 minutes later and about 620 miles away from the launch pad.

For reference, the International Space Station orbits Earth from about 250 miles above the planet's surface.

David Wright, a physicist and missile expert at the Union of Concerned Scientists, said this arc avoids flying of Japan to limit political fallout and is a "very impressive" feat. This is because the new missile, if tilted toward the US during launch instead of nearly straight up, could give it a top speed of more than 17,000 miles per hour - and a target radius of roughly 8,100 miles.

"This missile could reach all of the United States," Wright told Business Insider, adding a critical caveat: "But it doesn't mean much without considering the payload."

The nuclear threat of an ICBM

KCNA via Reuters

The intended payload for North Korea's ICBM program is a nuclear warhead (although chemical weapons like VX nerve agent, which the nation allegedly possesses and has used, are another option).

Wright said ICBMs burn rocket fuel for about three to five minutes before deploying a warhead on top. The warhead continues coasting through space for another 30 minutes or so, falling toward Earth under the force of gravity until it reenters the atmosphere, reaches its target, and detonates.

This alarms North Korea's adversaries, since the nation recently detonated a thermonuclear device that yielded the energy of perhaps 300 kilotons of TNT - about 20 times as much as the bomb the US detonated over Hiroshima in 1945.

However, Wright doubts such a weapon, also known as a hydrogen bomb, will be miniaturized into a missile-ready warhead by North Korea anytime soon. Rather, he thinks the first type of warhead North Korea may be capable of launching is a less-powerful, Hiroshima-style atomic weapon.

Being able to deliver such firepower "is still a big deal," he said, but is by no means a proven capability.

"There's a big debate going on in the technical community that works on these things, and it's exactly about how heavy the warhead would be that North Korea could build, and what capabilities they can get out of their rocket engines," he said.

'This is not a fluke'

Thomson Reuters

North Korea's leader Kim Jong Un stands before what may be a miniaturized thermonuclear weapon.

For now, experts like Wright assume North Korea's recent ICBM launched with a very lightweight dummy payload to give the missile alarming show of range.

An actual warhead built by North Korea might weigh "several hundred kilograms," or more than 600 pounds.

"That's going to significantly reduce the distance," Wright said - likely enough to keep an armed missile payload from striking American cities.

What's more, the current estimated accuracy of North Korea's weapons may be as poor as six to twelve miles. (US and Russian missiles can hit a target within a couple of hundred feet.) If North Korea targeted San Francisco, for example, there's a chance the bomb could miss the city entirely and detonate over the Pacific Ocean.

"It's kind of like throwing a baseball," Wright said. "The farther away your target is, the harder it is to hit. If the speed or aim is off by a tiny amount, those small errors add up to big distances over intercontinental ranges."

Wright said Wednesday's test launch is an incremental step for North Korea's nuclear weapons program, but emphasized that it's important not to dismiss.

"IT shows this is not a fluke, that they're continuing this progress toward something more and more capable," Wright said. "If things continue along they way they're going, I think there's little doubt North Korea will eventually have the capability to hit targets in the US with nuclear weapons."