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To Protect Japan, Target North Korean Rockets in Boost Stage
The members of Japan Self-defense Force prepare the Patriot Advanced Capability-3 missile for interception right after North Korea's rocket launch on February 7, 2016 in Ishigaki, Okinawa, Japan. (The Asahi Shimbun/The Asahi Shimbun via Getty Images)

To Protect Japan, Target North Korean Rockets in Boost Stage

Arthur Herman

North Korea’s latest round of nuclear and missile tests has set off alarm bells around East Asia, as well as in Washington.

South Korea and the U.S. have even entered into talks to deploy the U.S. Army’s antimissile system known as Thaad, or Terminal High Altitude Area Defense, which targets missiles in flight. Now there is talk Japan might do the same.

And no wonder. Kim Jong Un’s missile arsenal has become as menacing as his nuclear arsenal. His Unha-3 ballistic missile, for example, has morphed into an intercontinental ballistic missile capable of reaching California, not to mention Tokyo and any other target in Japan.

Japan already has the U.S.-built Patriot and Aegis antimissile systems. Yet these, like Thaad, are designed to hit a missile during its final, or descent, phase. A miss could mean catastrophe. Even more disturbing, none has been tested against a long-range ballistic missile like the Unha-3.

Yet, there is a simpler way to stop the missile, in its earlier boost stage instead — and Japan could soon have the means at its fingertips.


Large, multistage rockets require high-thrust booster engines to push them out of the atmosphere. Theoretically, destroying a missile in this boost phase has all kinds of advantages. It is the easiest for infrared sensors to detect and identify. It is also the slowest phase of its flight. Above all, a boost-phase intercept, or BPI, doesn’t allow time for the missile to take evasive countermeasures.

How would such a BPI work? First, it would not operate from a ground- or sea-based system like Thaad or Aegis, but from an unmanned aerial vehicle stationed at an altitude of 55,000 feet (16,764 meters) and equipped with infrared sensors able to detect a missile launch from 350 miles (563km) outside North Korean airspace.

Secondly, the UAV would be equipped with an agile antimissile interceptor of 225kg or more — more than enough firepower to bring down a large ICBM like the Unha-3 or its variants. The interceptor’s 3.5km-per-second velocity would give the UAV’s ground operators nearly a minute after detection to decide to intercept. That is more than enough time to prevent a mistake. And since there are already American-built UAVs capable of carrying up to four interceptors of this size, the chances that Kim’s missile could evade destruction and get into orbital flight shrink to almost nil.

This isn’t science fiction or laboratory theory. As the former science and technology director of the Pentagon’s Ballistic Missile Defense Organization Leonard Caveny has pointed out, all the technologies for an operating BPI system not only exist, but have been tested and qualified for use.

The U.S. is working on a similar UAV missile-intercept system using lasers, but it could be a half-decade or more before it sees practical application. Since BPI relies on proven technologies, Japan could take the lead in developing the system now, using U.S.-built UAVs, with Japanese companies building the interceptor’s motors, sensors and other components. Caveny has estimated the system could be ready for testing in 18 months at minimal cost.

It would also come with two geopolitical advantages: While easily deterring boost-phase ballistic missile launches from North Korea, BPI would not be feasible for doing the same for launches from the far larger land mass of China, thus reassuring Beijing that the system is not aimed at it. And if a shoot-down did become necessary, any debris will fall into the Sea of Japan instead of into South Korea or Japan itself.

Once successfully tested, a Japan-designed BPI system could be a game changer in the effort to halt North Korea’s nuclear blackmail. Turkey and Europe would see a working BPI system in the same way, as a means to prevent nuclear blackmail by Iran.

It’s not often that a lethal military technology can be redesigned and redeployed to save lives and prevent nuclear disaster. A Japanese government that takes UAV-based BPI seriously could make East Asia rest easier and help make the threat of rogue ballistic missile attacks a thing of the past.

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