If North Korean “Satellite Launch” Impacts Japan-U.S. Alliance, It Will Be by Accident

Question: If North Korea claims that it is a launch of a satellite, would you still consider such a launch to be a target of interception?
Minister: As far as such a launch has any impact on Japan, I would consider it a matter of course to respond to it…According to Article 82-2 of the Self-Defense Forces Act, the subject of our interception consists of “missiles and other objects that are deemed to cause serious damage to human life and property due to their fall and are not aircraft”, so even if it is a rocket, an artificial satellite that has the possibility of going out of control and falling on our country is obviously included, so I think that it is natural to respond to that situation.
—from Defense Minister Yuichi Hamada’s March 3 press conference; the English-language abstract is available here

Sounds reasonable. The United States will be in a similar situation with regard to its own territory. So within minutes after North Korea launches the latest version of the Taepodong, the U.S. surveillance system will calculate the trajectory of the projectile and determine where it is likely to fall. If it is determined that it is likely to fall on Japanese territory, the two AEGIS-equipped destroyersescort vessels currently deployed by the JSDF will attempt to intercept it. (The Land Forces’ Patriot missiles will intercept it on the way down if the AEGIS system fails to do the job.) The half-dozen U.S. AEGIS-equipped vessels in the neighborhood should also be obligated to attempt an intercept under the Mutual Defense Treaty, although I’m not as sure on this point.

However, if it’s determined that the projectile is likely to land on U.S. territory, the Japanese AEGIS system cannot intercept it under the current official interpretation of the Japanese Constitution regarding collective self-defense. Although North Korean authorities would never dare to aim the launch at U.S. (or for that matter Japanese) territory, the rocket does have a long range if there’s any truth to the speculations, and there’s a fairly good chance that the rocket could accidentally go astray at or immediately after the launch.—at which point there is a small but undeniable possibility that this asymmetrical and technically remediable gap in the “mutuality” of the national security relationship will pass from the theoretical to the actual.

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Satoshi Morimoto, my favorite North Korea expert in Japan—he always seems to know what he’s talking about—has a fairly detailed explanation of the technical and political issues in a Sankei column.