Editor’s Note (11/28/17): Scientific American is re-posting the following article, originally published July 6, 2017, in light of claims that North Korea fired its highest-ever intercontinental ballistic missile on November 28. The ICBM was launched from Sain Ni, North Korea, north of Pyongyang, and traveled east about 1,000 kilometers before splashing down in the Sea of Japan, according to the Pentagon. This is North Korea’s third ICBM test this year, following two in July, and the first missile launch of any kind since Sept. 15, when they tested an intermediate range missile.

Many Americans returned to work after the Fourth of July holiday to learn that parts of the U.S. are now within striking distance of a new type of North Korean intercontinental ballistic missile (ICBM). Over the past few years the reclusive country has been active in its efforts to develop nuclear weapons, improve its long-range missiles and launch satellites. Unsettling news to be sure, given Pyongyang’s propensity to threaten the U.S. and its close ally South Korea with a nuclear attack.

North Korea’s latest move could be a wake-up call for Washington to engage directly with the country’s bellicose leader, Kim Jong-un, before he further consolidates the ability to strike the American mainland, says David Wright, co-director and senior scientist with the Union of Concerned Scientists’ Global Security Program. Scientific American spoke with Wright about the significance of North Korea’s first ICBM launch, the state of U.S. missile defense and the best option for easing decades of dangerous tension centered around the volatile Korean Peninsula.

[An edited transcript of the interview follows.]

North Korea has been ramping up its testing of various missiles, rockets and other offensive capabilities in recent years. Why are people so concerned with this latest test?
It’s more symbolic than anything else. People are concerned about the prospect that North Korea could hit the U.S. with a nuclear weapon. South Korea and Japan—not to mention the tens of thousands of U.S. troops stationed in those countries—have been within range of North Korea’s missiles for years. From a technical point of view, the latest test seems to be the next logical step in terms of their missile program. The U.S. has officially said that what North Korea tested was an intercontinental ballistic missile, which would be the first time they’ve successfully launched one of those.

Where does North Korea stand in terms of its military capabilities at this point?
I don’t think anybody really knows. You get a sense from the fact that they’ve been moving ahead relatively quickly—they’ve been doing some new things with a surprising degree of success. It seems as though they spent a few years building up not only their missile engineering capabilities but also other technologies as well. The question is: What else do they have in their back pocket?

Would nuclear weapons be one of those things in their back pocket?
People have generally come to the conclusion that they have a nuclear warhead that is light enough and small enough to put on one of their missiles. If they’re not there yet in terms of making it rugged enough to handle the flight, then they’re probably close. They would need a way to shield a nuclear ICBM from intense heat as it reenters the atmosphere, but they could probably do that using a blunt nose cone to slow down the missile enough to deal with the heat. The trade-off is that you get much less accuracy, which would affect their choice of targets. Assuming Kim Jong-un’s objective is to be able to reach not just Alaska but one of the big population centers up and down the western coast of the United States, then a lack of accuracy becomes less of a problem. That said, you have to consider the reliability of the weapons that North Korea is developing. These are tremendously complicated systems, and North Korea has had problems with them in the past. It’s not clear that if they tried to launch yesterday’s missile again today they would be successful.

To what do you attribute their recent success testing missiles and nuclear weapons?
I think we’re all wondering about that. We may be seeing the fruits of Kim Jong-un pouring a lot of resources over the past two years into developing the country’s systems and building up its engineering capabilities. We’re not just seeing a lot of tests of late; we’re seeing a lot of different systems being tested, including two-stage, solid-fuel missiles that can be launched on land or by submarine and short-range missiles with supposedly a maneuverable warhead—although I’m still a little skeptical about that.

Why has North Korea poured so much of its scarce resources into building such a lethal arsenal?
What North Korea wants most is to preserve its regime. They look at what happened to [former Libyan leader Muammar] Gaddafi, and the invasion of Iraq, and they see that they’re surrounded by countries allied with the U.S. The big military exercises that the U.S. and South Korea conduct together to simulate an invasion of the North probably only add to the paranoia. In that case, it seems that the worst thing you could do is what the U.S. and South Korea did shortly after the North’s latest missile test, which was to run new military exercises. That just gives North Korea the ability to justify the missile test in the first place. Another motive for North Korea’s nuclear buildup is that it wants to use that capability as a negotiating chip with South Korea, maybe to force the U.S. out of South Korea—although I don’t think that’s going to happen.

Could the Terminal High Altitude Area Defense system (THAAD) that the U.S. is installing in South Korea protect the country from an attack by the North?
The problem with relying on missile defenses is that they are not good enough to replace efforts to solve the problem directly through diplomacy. You might think a missile defense system is an insurance policy, but it’s hard to have a lot of confidence in that technology. We did a study a year ago of the U.S. Ground-Based Midcourse Defense system based in California, and found that even under controlled test circumstances it has a 50 percent failure rate. That’s a reflection of several things: One is that it’s a very hard technical problem to hit a bullet with a bullet. Also, the program behind the system has not been run very well. It was exempted by former Pres. George W. Bush from the standard fly-before-you-buy oversight and testing rules, and so it’s been able to go forward without jumping through the hoops that Congress finds—again and again—are important to make these things work. And these intercept tests are incredibly expensive, about $2 million each. The Pentagon’s main tester has said the missile defense system has no demonstrated operational capability, which we agree with. And yet people are saying that they could shoot down North Korean missiles, they have a 90 percent chance of success. I worry about political leaders who don’t understand the technical issues, thinking that they have capability that they don’t actually have. If Pres. Trump thinks that we could launch an attack on North Korea and then defend ourselves using THAAD or the Aegis Ballistic Missile Defense system, then it could lead to bad decisions.

What other options does the U.S. have to defend itself from North Korea’s arsenal?
Most of the defense systems are intended to work as a missile passes out of the atmosphere, during the midcourse phase, because once you’re above the atmosphere things move on a predictable trajectory. The problem is that outside the atmosphere it’s also easier to deploy decoys that can confuse a missile defense system—things have the same trajectory above the atmosphere regardless of their mass. One thing the U.S. doesn’t appear to be working on now—which is a bit of a mystery to me—is so-called boost-phase missile defense, which attempts to hit the missile while it’s still burning early in flight. A missile burns for its initial three to five minutes of flight. During that time it’s a large target that’s moving relatively slowly and is easy to see. The problem is that because boost time is short you need to be relatively close to the launch site to be able to do it. But North Korea is a small country surrounded by water—it was made for boost phase missile defense positioned on ships. If you’re really worried about North Korea and want to develop a missile defense system, that’s probably the way you’d want to go.

What is the best path forward for the U.S.?
The U.S. called for a U.N. Security Council meeting on Wednesday, which is what I would have expected them to do. The Security Council meeting is intended to marshal international forces against North Korea, but I don’t think that solves the problem. Efforts to get China to negotiate with and pressure North Korea on behalf of the U.S. won’t solve the problem either. China doesn’t have as much leverage as the U.S. thinks it has over North Korea. China also views this as an issue between the U.S. and North Korea and, while it’s happy to help, China sees this as something that the U.S. and North Korea have to negotiate between themselves.

There’s a window of opportunity for the U.S. to try to engage with North Korea before they have the capability to reach the United States mainland with their missiles. If people think North Korea crossed a real red line in being able to reach U.S. territories, then reaching the west coast is an even bigger red line, and you have to think outside the box in terms of how you stop that. Everyone, including [Secretary of Defense James] Mattis, seems to agree that there are no good military options. China’s not going to solve this. Sanctions can ramp up pressure, but I don’t see how you get out of this without the two countries finding a way to talk to one another.