Comment by adewinter | Hacker News Reader

Comment by adewinter | Hacker News Reader

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The two systems are definitely not in the same league (agreed!), if that's what you're pointing out.

That said, the time required to calculate an intercept point is not the hard problem, so 1-2 seconds versus 30 minutes is not really super relevant.

Arguably more relevant factors are detection, precision, accuracy and ultimate intercept effectiveness.

In the case of ICBM you're essentially trying to hit one bullet with another bullet... hundreds of miles away. It doesn't matter that you have 30 minutes to think about it. It's still ridiculously hard to actually know there's an icbm, where it is, and then be able to hit it with another missile (and have that make a difference).

RPGs around a armored vehicle are way more straightforward by comparison. The projectile is easier to detect, it's a much smaller volume of space (easier to scan continuously) and the projectiles are traveling slower!

Still I imagine it's quite a trick detecting incoming then swiveling, aiming and firing (accurately) your defense auto-cannon all in 1-2 seconds. It would be very impressive to see that in action.

The Trophy and other APSs don't really have to deal with countermeasures either. Anti-ballistic missiles that try to intercept the warheads as they're on their way back down have to deal with loads of decoys that can be packed into an ICBM vs a single rocket with very limited movement and a much more well defined final target (ie a rocket that isn't going to hit the tank isn't much of a concern vs a warhead that could be aimed anywhere in the country).

The other issue with intercepting an ICBM is that the ballistics are much more difficult. You have to factor in the curvature of the earth, atmospheric conditions (is there a storm front between the interceptor pad and the missile?), and the changing nature of the projectile (is it a MIRV? some missiles can jink now, how do you handle that?).

One of my friends is a rocket scientist (aerospace engineer). I asked him about kill vehicles once, and he said that intercepting Russian ICBMs is a losing battle even if you can identify the ICBM and intercept it reliably. Russian ICBMs have inflatable decoy payloads in them that are balloons for all intents and purposes. Since ICBMs deploy their payload while in space, where there is no atmosphere, the decoy balloons behave just like the actual nuclear warheads, despite the huge difference in mass. Once they hit the atmosphere the decoy payloads slow down quickly, however you should target the ICBM and its payload much earlier than this if you want to reliably defeat it. The decoys are much less expensive than the intercept vehicles, and the balloon decoys are light, so Russia can afford to put a whole mess of them in each ICBM.

*edited for clarity.

It's still a fight worth fighting.

Multi-layer defense works. Yes, yes, it sucks when a city gets nuked, but things go way worse if you just give up on the problem and thus allow 1000 cities to get nuked. Think of it like computer network defense. You don't just give up because there is a chance of failure.

You start with treaties, export control, diplomacy, and a threat to respond in kind. Next it's sabotage, both physical and cyber. Next it's launch-phase attack... and if they move their launch sites to a less-desirable location to avoid your attack, it's still a partial win. Next it's an attack right before engine cut-out, possibly from orbit. Next it's an attack on the warheads in space; those balloons sure are vulnerable to lasers. Next it's an attack right after reentry. Next is building codes, bomb shelters, and emergency services.

Every layer has value, even if imperfect. It's negligent to leave out even one layer.

New Russian (and Chinese by extend, the tech was sold about 10 years ago) warheads are also maneuverable on re-entry.

There's also the element of unit cost. An anti ballistic missile system can easily be worth spending billions on even if effective against low numbers of weapons thanks to North Korea. An anti RPG system is going to be protecting against hardware valued in the hundreds of thousands of dollars.

    > * It's still ridiculously hard to actually know there's
    >     an icbm,
    > * where it is
    > * be able to hit it with another missile
    > * (and have that make a difference)

Are these tasks all equally difficult, or is one part of that substantially harder than the others? I had (naively?) assumed the first two pieces would be reasonably easy.

Yeah, for me, it's the intercepting projectile. One is a bullet fired from auto-aiming system, the other a rocket with a guidance system. Bullets vs. rockets definitely not the same thing.

Still, the performance of Trohpy is impressive. And, it has actually been proven to work in combat, something we pray to never see with ICBMs.

Heh. The missile defense systems are super controversial even now exactly because we have been unable to effectively demonstrate that they work[1].

This stuff sounds like it already works in the field. Nice.

[1]: Tests are run and performance is usually quite horrible, until they make them way way easier than real world conditions. https://www.google.com/search?q=missile+defense+effectivenes...

They do work? https://news.usni.org/2015/12/10/aegis-ashore-scores-in-firs...

Why would the Russians use it if it doesn't work?

You don't have 1 cannon. Better option is to have round battery with mini rockets on top of the vehicle. Your reaction time will be milliseconds for the first target. And you could intercept two targets if they are offset enough.

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