Big in Japan

A friend sends this link from the Australian Broadcasting Corporation, suggesting that despite the US refusal to consider shooting down a North Korean rocket, the Japanese may do it anyway.

Japan has begun moving Patriot guided missiles to the country’s north-east to possibly shoot down a North Korean rocket. … Tokyo is threatening to shoot the North Korean rocket down if it threatens Japanese territory. Meanwhile the US Defence Secretary Robert Gates says the US has no plans to shoot down the missile if the test goes ahead.

But given the nature of the missile system referred to here — Patriot, whose interception envelope occurs when the incoming projectile is in its terminal phase — this will probably only happen as a last resort, if the North Korean is seen headed for Japan. The US refusal to engage the North Korean missile, which may have left Japan with no option but to consider a unilateral response, is an intriguing development. The conceptual lid on Japanese rearmament has always been the tacit assurance that Big Brother USA would take care of Nippon. And although the Japanese government would probably prefer to see the North Korean missile, if it went awry, engaged on an alliance basis, no responsible government in Tokyo would be without an insurance plan in the event the Dear Leader’s missile accidentally, or accidentally on purpose, veered towards the home islands.

The PAC-3 upgrade carried with it a new missile design, nominally known as MIM-104F and called PAC-3 by the Army. The PAC-3 missile dedicated almost entirely to the anti-ballistic missile mission. Miniaturization has made the PAC-3 missile much smaller than the previous Patriot missiles; a single “can” (canister) now holds four missiles where one was once held. The PAC-3 missile is also much more maneuverable than previous variants, thanks to dozens of tiny rocket motors mounted in the forebody of the missile (called ACMs, or Attitude Control Motors). However, the most significant upgrade to the PAC-3 missile is the addition of a Ka band active radar seeker. This allows the missile to drop its uplink to the system and acquire its target itself in the terminal phase of its intercept, which improves the reaction time of the missile against a fast-moving ballistic missile target; the PAC-3 missile is accurate enough to select, target, and home in on the warhead portion of an inbound ballistic missile. The active radar also gives the warhead a “hit-to-kill” capability that completely removes the need for a traditional proximity-fused warhead. This greatly increases the lethality against ballistic missiles of all types.

The PAC-3 upgrade has effectively quintupled the “footprint” that a Patriot unit can defend against ballistic missiles of all types, and has considerably increased the system’s lethality and effectiveness against ballistic missiles. It has also increased the scope of ballistic missiles that Patriot can engage, which now includes several intermediate range. However, despite its increases in ballistic missile defence capabilities, the PAC-3 missile is a less capable interceptor of atmospheric aircraft and air-to-surface missiles. It is slower, has a shorter range, and has a smaller explosive warhead compared to older Patriot missiles (although it generally relies on its kinetic “hit to kill” warhead).