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Opinion | Theodore Postol

What North Korea’s rocket launch means — and what it doesn’t

In this undated photo, North Korean leader Kim Jong Un directed his top military leaders.REUTERS

The North Koreans have reportedly launched what they proclaim is a satellite, mounted on an 80-ton rocket called the Unha-3, which has been in development for the past two decades. If the past is any prologue, we can be reasonably assured that the following three elements will shape our public discussion of the event: assertions that this rocket can be readily converted to be an intercontinental ballistic missile; that North Korea could have weaponized a nuclear weapon; and that the launch proves the need for missile defenses.

Indeed, all three elements have emerged in the GOP debate in New Hampshire on Saturday evening.

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We can expect a great deal more threat inflation, saber rattling, and overreacting to a provocative action that is realistically no more than another staged event by the Hermit Kingdom.

This ritual stoking of national anxiety has nothing to do with concerns about real security threats. Instead, it is about increasing the Pentagon’s already bloated arsenal with new, fantastically costly, and nearly useless weapons.

How do we know that this is an inflated threat? Let’s consider each assertion.

Is North Korea able to convert this rocket to an ICBM?

There is considerable information on North Korean rocket capabilities in the public domain, which means the public need not rely on the selective release of classified intelligence assessments to understand the technology and its limitations.

Prior to the successful launch of a satellite in 2012, North Korea allowed the Western press to photograph its Unha-3 launch vehicle on the platform. After the launch, South Korea recovered the first stage of the rocket from the shallow waters of the Yellow Sea. Seoul then published very detailed photographs of essentially all the critical components. These data, along with information about the powered flight path of the rocket, made it possible for knowledgeable analysts outside of the US government to construct a detailed model of the Unha-3 that is totally consistent with the vast body of data that is now publicly available.

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All technically refereed analyses outside of the US government are in agreement — the Unha-3 cannot be converted to an ICBM capable of threatening the US mainland.

The distances are simply too great. In order to reach our shores from theirs, North Korea would need to build an ICBM that weighs in at around 120 tons, rather than their current model which weighs 80 tons. Such an improvement over their existing technology could take a decade or more and the program to do so would be highly visible.

But say the North Koreans eventually built such a giant rocket, in order to threaten the US mainland they’d also need a light and durable nuclear weapon to mount atop it.

Is North Korea close to developing an advanced nuclear weapon?

An advanced first-generation nuclear weapon is typically defined as a device that weighs around one ton and is sufficiently rugged to withstand the violent vibrations and accelerations that occur when it rides inside a ballistic missile screaming around the globe. Those physical forces are formidable, and the technical mastery involved in building such a device is considerable.

There have been four nuclear tests by North Korea over the past 10 years. The first test looks like it failed. This is almost certainly because the explosive lens used in the North Korean device did not properly implode the plutonium fuel into a near perfect sphere.

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The subsequent three tests that followed all appear to have had nuclear yields of well below 10 kilotons. This is most likely because the explosive lens used in the North Korean experimental warhead has not been perfected.

In contrast, the first two nuclear explosions of a likely similar plutonium-based weapon, the Fat Man bomb, built by the United States in 1945, yielded more than 20 kilotons when it was dropped over Nagasaki. Only three years later, a version of the Fat Man, using the same explosive lens from the earlier weapons, produced a yield of 49 kilotons. Within 10 years of the first atomic weapons, the US produced a true multistage thermonuclear weapon that yielded 10,400 kilotons.

No one outside of North Korea seems to have any idea why the yields of North Korean weapons have been so low. However, there is a solid technical reason why this could be the case. Without going into the technical details here, advanced nuclear weapons require that the plutonium core be compressed into a near-perfect spherical shape. It is well known that the Manhattan Project had great difficulties perfecting the explosive lens used in the first plutonium bombs.

We don’t know how far along the North Koreans are in this process. But we do know that there should have been higher yields in all of their tests if the implosive lens worked as designed. The lack of progress over a 10-year time period suggests that North Korea is likely to be a long way off from weaponizing — and miniaturizing — these devices.

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Add this to other technical problems they need to solve, as well as the real limitations on their rocket technologies, and one comes to a shaky but reasonable technical conclusion that the threat of a North Korean nuclear-armed ICBM to the US mainland could easily be decades or more away.

Can US missile defenses stop North Korean nuclear ICBMs if they were eventually developed?

It is now well documented that in order to work, missile defenses have to be able to pick out the weapons from decoys that enemies would launch at the same time. There have been no successful tests — nor will there be — where missile defenses can discern the difference.

But if Washington is truly concerned about this threat, there is a technical solution that would work: a system with fast interceptors carried by drones or airplanes that would shoot down the ICBM while it is in powered flight. Such a system could be built with existing technologies — unlike the current missile defense systems that are being built — no physics-defying magic required.

However, even though this defense could easily be made to work, there is no need for it, because there is no threat that requires building it — unless the real purpose is to defend the Pentagon’s bloated budget.


Theodore Postol has been an adviser to the US Navy’s chief of naval operations on strategic and tactical nuclear weapons systems and on missile defenses. He is professor emeritus of science, technology, and national security policy at MIT.

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