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Comment by ISL | Hacker News Reader

If the trajectory was measured and expected to miss Japan, there would be no need to use any defense system.

Those playing defense have a lot of incentive to keep their plans and capabilities quiet and uncertain until they are absolutely required. Once the defensive strategies are employed openly, the offense can more-reliably develop countermeasures.

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It went over Japan. ICBMs are capable of adjusting their target mid-flight. There's no way to know it wasn't going to hit Japan.

It is (from my extreme sideline position) unknowable whether or not this particular weapon was capable of adjusting trajectory mid-flight. The point, however, is that it didn't and no shield test was deemed necessary. If it was calculated that it wasn't going to hit Japan, whatever was used to calculate it ended up being correct.

Using a missile shield when it's not needed reveals the location of installations, which can make them deliberate future targets.

That is an unreasonable conclusion to reach given the evidence. You cannot reasonably allow a missile, potentially carrying a dirty bomb to enter your airspace, and relatively centrally so, and not act. Occam's razor suggests there is no shield.

Or it is known that the current state of the shield matches the first generation of Patriot interceptors, which means that it in a case where hail mary is not needed the US would not engage it.

Invoking philosophical razors does not change the reality that the missile did not hit anything of importance.

If you throw a punch and miss me (whether intentional or not), and I do not immediately react, it does not imply that I am incapable of defending myself.

It demonstrated clearly that Kim can hit any town in Japan and surrounding territories if he so chooses. The Japanese government went to some trouble to disseminate that information via SMS. If they could shoot down that missile and not terrify their own population they would have done so.

> they would have done so

What actually happened proves that this would have been unnecessary.

It's not exactly your "airspace" at 550km (the reported apogee) as, among other things, there's no air. That's 150km higher than the ISS orbits. It won't be a perfect ballistic curve due to the boost phase not being instantaneous and drag during the endoatmospheric periods, but based on how far it flew and how far it overshot Japan by, the halfway point between launch and landing is just at or just west of the Japanese coast. So a conservative estimate would be that when it crossed over a Japanese land mass, it was at least 500km up. So saying "you can't reasonably allow it" is a little odd when I don't think they could physically have stopped it at that altitude. By the time it dropped down into the reported range of THAAD, it'd have been well past Japan.

From what I've read, the most reliable period to shoot down these things is on their down-trajectory. At which point it was probably already no longer over Japan.

edit: for instance this Reddit comment https://www.reddit.com/r/japan/comments/6wmnxp/north_korea_f...

> The THAAD system that is deployed in Japan intercepts an incoming missile as it is coming down on the target, with a maximum altitude of about 150 km.

Which gets you to reading https://en.wikipedia.org/wiki/Terminal_High_Altitude_Area_De...

> Terminal High Altitude Area Defense (THAAD), formerly Theater High Altitude Area Defense, is an American anti-ballistic missile defense system designed to shoot down short, medium, and intermediate range ballistic missiles in their terminal phase (descent or reentry) by intercepting with a hit-to-kill approach.

The most reliable time to shoot down a missile is when it is just lifting off. It's moving slowly, lots of fuel, etc. All it takes is a high powered laser hitting it almost anywhere in its cross section.

Well the most reliable time to destroy a missile is before it's built, but beggars can't be choosers :)

So you're saying all Japan needs to do is station high-powered lasers near all North Korean missile sites? Seems easy enough.

https://en.wikipedia.org/wiki/Boeing_YAL-1

If it was ballistic then sure, you can ignore it. But a missile can change course so I don't buy this excuse that 'we knew it would miss'

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