Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

Missile defense is NP-complete

smu160.github.io

Post reply on HN
Print view View original

141–150 of 446 posts

Re: Missile defense is NP-complete

#141

Post by maratc »

owenmarshall wrote: post #69
maratc wrote: post #32

Earlier quoted context omitted.

That's a false comparison. You want to compare between the actual options you have, which are either (a) firing an interceptor (or several); or (b) repairing the damage caused by a non-intercepted missile.

Your first option comes with the major caveat that each interceptor you fire comes from a limited stockpile whose replacement rate[0] today isn't sufficient for even going 1:1, let alone accepting that multiple interceptors are required. I'd say the real options in the near term when faced with an inbound missile is a) deciding to deplete your stockpile of interceptors with an incredibly limited replenishment rate; o…

In theory; in practice however, there's been rocket fire from Gaza towards Israel where the offence was literally a metallic tube with a bit of TNT at a cost of about $800 per rocket [0] while the defence was $100,000+ per interceptor [1]. This has been going on for years, and as far as I'm aware there was no depletion observed.

[0] https://en.wikipedia.org/wiki/Qassam_rocket [1] https://en.wikipedia.org/wiki/Iron_Dome

Re: Missile defense is NP-complete

#142

Post by hedora »

cpgxiii wrote: post #25
dboreham wrote: post #2

It's been known since the 1960s that effective anti ballistic missile defense is impossible.

There are several different levels of ballistic missiles. ICBMs, for which the GBI is intended, are the most challenging to defend against and show the least interceptor success. In contrast, we do have some pretty definitive evidence that theater and "lower" MRBM/IRMB ballistic missiles can be intercepted successfully. If you define "effective defense" as "most missiles that would cause damage are intercepted", then…

If you define "effective" in terms of cost ratios: R = (cost of defense system + cost from failed intercepts) / (cost of attack system)

then N There's no magic Pareto-optimal point where investing the right amount in missile defense means that starting a war against a medium-sized country makes economic sense. Russia figured this out in Ukraine, and the US figured it out in Iran.

Israel's genocide worked pretty well tactically, but is a long-term strategic disaster. If the US continues to be a democracy, polls say that it will cause us to withdraw support sometime this decade. Also, it only works if you have an incredibly asymmetric fight.

Re: Missile defense is NP-complete

#143

Post by koakuma-chan »

hedora wrote: post #137
koakuma-chan wrote: post #86

Why does a ground based interceptor cost $75M? High idiot index?

$1M, but we can only make 600 / year, globally.

From the article,

"Each GBI costs approximately $75 million, and as of 2024, 44 are deployed across Alaska and California [3]."

Re: Missile defense is NP-complete

#144

Post by teleforce »

lejalv wrote: post #53
1234letshaveatw wrote: post #21

Earlier quoted context omitted.

That seems like an acceptable trade off to get some real world experience with what works and what doesn't with regards to massed drones and swarming. There is a lot we can learn in this conflict with relatively low stakes

Stakes for whom? >100 kids got murdered the first day of this "low stakes" war

Imagine the NATO reaction if on the very first day of Russo-Ukrainian war offensive is by Russia performing missiles bombing murdering 100 kids studying in Ukraine primary school.

Trump candid reaction to the Iranian school incident when asked by reporter was "I can live with that".

Re: Missile defense is NP-complete

#145

Post by DoctorOetker »

orwin wrote: post #52
jvanderbot wrote: post #26

Earlier quoted context omitted.

Ah yes, but then you also have to add GDP + targetting/defense radii. Great Britian alone has 10x the GDP of Iran. So an interceptor costing 10:1 is (at first approx) breakeven just for GB, who would have to intercept much less than the total manufacturing capability of Iran anyway. Then you have every rich nation surrounding Iran as well. Let alone the USA who cannot be reached but throws their weight behind interce…

> total manufacturing capability" is set to decline in any prolonged engagement with an Iran-like nation That was what Russia thought about Ukraine. Effectively, they needed East European tanks and munitions for the first two years, but munitions production ramped up, and now they produce more per year that what they received over two years. A resource-rich country like the Iran that is effectively fight a death war…

> And imho, while Kurds accepting to be betrayed by the US for the third time in less than two decade won't have any real long term impact, an independent Baluchistan can easily destabilise Pakistan.

Not to confuse my prediction from prescription, but what prevents all the neighboring (direct or indirect over a sea) nation states from deciding to divide Iran like Germany was during the cold war? Thats not an independent Balochistan, at some point they will want reparations for all the damage, terrorism and intimidation they have incurred from Iran...

At some point the people in Iran will have to be forced to teach their innocent children the equivalent of the Nuremberg trials: there is no excuse in order to stop thinking, just following orders is not a valid legal defense.

Every population has the moral responsibility to keep the local aspiring autocrats in check, because if they don't and external power deconstructs the regime, the onus will be on the population!

Re: Missile defense is NP-complete

#146

Post by dlisboa »

energy123 wrote: post #121
hedora wrote: post #107

Earlier quoted context omitted.

Offense doesn't work at scale. As the cost of drones goes to zero, the expected damage you take is roughly proportional to how much you have to lose. This means larger / richer economies cannot win these sorts of wars. To see what I mean, check out this desalination plant map: https://www.theguardian.com/world/2026/mar/23/iran-threat-to... It doesn't help if your commander in chief is incompetent and your invasion st…

It's heavily dependent on geography. Iran is geographically "lucky" it's positioned near the Strait of Hormuz and near the oil facilities of multiple Gulf states, allowing it to exert extreme asymmetric pressure through a small amount of drones etc. Most states can't replicate that luck. Good luck to South Africa if they ever decide to wage a similar war. Strategic depth also largely nullifies the role of one-way att…

Israel is similiarly lucky that it is surrounded by neighbors with US bases that can intercept missiles and drones before they get to it. All of its more competent enemies are very far away. In a different scenario there'd be no motivation for a country like Iraq or Jordan to help.

They can afford to try to destroy Iran's offensive capabilities because in-between countries allow their airspace to be used.

Wars are usually between neighbors. If a neighbor has a huge stockpile of drones they can launch a first salvo that'll overwhelm whatever defensive capabilities the other country has before they even get to the point of destroying launchers/manufacturing.

Threats of massive drones strikes are the closest deterrent a country can get to nuclear weapons without developing nuclear weapons. If Iran had 5 million drones instead of 50 thousand this war wouldn't even be happening.

Re: Missile defense is NP-complete

#147

Post by maratc »

mamonster wrote: post #136
maratc wrote: post #79

Earlier quoted context omitted.

Cluster munitions are great against infantry in open field; less so against population centres equipped with advance warning systems. As it stands, they fail to even cause the damage worth offsetting by firing interceptors. The damage these inflict on Israel is not unsustainable, and they don't do much to create deterrence. Given a choice of conventional 500-800 kg warhead or cluster munitions warhead, I think that t…

>The damage these inflict on Israel is not unsustainable, and they don't do much to create deterrence. Has there been a study on this? What is the GDP loss of having however many Israelis go to bunkers due to incoming ballistics instead of working ? If a trash cluster missile that costs 100k USD to build causes 1mio USD worth of GDP to not be produced (numbers completely made up) then it's very worth it.

No idea about studies or GDP; just observing that the losses inflicted by Iran on Israel in June 2025 did nothing to deter Israel from going on offence again eight months later.

Re: Missile defense is NP-complete

#148

Post by maxglute »

Voultapher wrote: post #124
maxglute wrote: post #111

>Hence, for one warhead, a defender can launch 4 interceptors and have a 96% chance of successfully intercepting the incoming warhead. >Unfortunately, those numbers are optimistic. This part worth stressing, ceiling for more performant missiles, i.e. faster, terminal maneuvering, decoys are geometrically harder to intercept. Past mach ~10 terminal and functionally impossible because intercept kinematics will break in…

Lasers. No really, near-future laser systems with adaptive optics and good spotting - for example distributed SAR satellites - dramatically shift that balance [0]. [0] https://toughsf.blogspot.com/2025/05/the-laser-revolution-pa...

Maybe for subsonic, high end missiles I'm extremely skeptical. Need 5-10MW to get useful dwell power on high end hypersonic inherently shielded against reentry thermals. Speculative laser defense are infra size defense, not mobile trailer size. Factor in duty cycles (i.e. shots per minute) and it seems dead end. Half of economics of missile defense is mobility - building density relative to threats by moving platforms. Last 2 parts real constraints, high-end adversaries coordinate salvos to arrive in time. Interceptor magazine depth limited = still throw 100s of interceptors to engage multiple targets if required. Lasers = serial visual range engagement. Figure out dwell time + duty cycle to saturate. Hypersonic can go from over horizonal to hit target in 10 seconds, a laser couldn't engage more than 1-2 missiles in that time. Technically 1, because by the time you fried 1st target the 2nd is so close the shrapnel will hit on momentum.

Re: Missile defense is NP-complete

#149

Post by jandrewrogers »

owenmarshall wrote: post #109
hedora wrote: post #59

Earlier quoted context omitted.

Currently, we're using $1M interceptors to take out $30K drones. This asymmetry is here to stay. The end game probably involves At that point, it turns into a logistics problem that's much easier for the attacker than the defender. Iran's already demonstrated that one successful drone can do $100B-1T in damages, so a hit rate of 0.1% means a 1:100K cost:damage ratio.

This leans towards my belief that the US is fundamentally fighting last century's war against adversaries that have _massively_ evolved. Look at the Ukranians: they are currently fielding an entire suite of counter-drone tech: fast pursuit systems to hit Russian drones on launch, cheap FPV drones for last-mile intercept, integrated radar/acoustic monitoring to target and respond to launches... and of course, the Russ…

This betrays your ignorance of drone defense tech.

The US had APKWS (anti-drone guided missiles) operational in the 2010s and these have been widely deployed. They are effective and cost less than a Shahed. These are just mods of an existing dirt-cheap rocket for which the US has an effectively unlimited supply. The Europeans have similar systems under development.

The US has deployed high-power anti-drone laser systems for a few years now with several operational kills. These are still new but are expected to replace CIWS. It can kill a drone for the cost of a Starbucks coffee and has a virtually unlimited magazine.

US pioneered military drones and defenses decades before the Ukraine/Russia war. There are many operational lessons to be learned from that war but both sides are using drone defense tech that is considerably less sophisticated than what the US has available.

Re: Missile defense is NP-complete

#150

Post by hedora »

tonnydourado wrote: post #65
myrmidon wrote: post #50

Earlier quoted context omitted.

You are basically complaining that the article is not about a your preferred, different topic. Directed energy defense does not really compete with a system like GMD at all , because the range is extremely limited by comparison. The US might be able to justify throwing a few billion at a few dozens of ICBM interceptors stationed in a handful of sites, but protecting every potential target (city, military base) with s…

Gotta say, did not know direct energy weapons were actually leaving science fiction and entering the real world yet, but it seems they're. It's obviously not star trek level, but it's way more advanced than I expected

They are, but only have a range of 1.2 miles in earth's atmosphere. Since they're on the ground, and presumably near the target (not the launcher), that means they're aimed at the warhead just before it hits the ground.

I looked up the numbers, and, interestingly, ICBMs have to slow down before they hit their target. In the midrange flight, they travel at 15,000 mph, but at re-entry the warheads are only traveling at 1900 mph, or 0.58 miles per second.

So, in the best case (the warhead is headed to the laser), the laser only gets 2.5 seconds of dwell time to intercept it. This rapidly decreases as the distance from the laser to the target increases (to 0 seconds of dwell time at 1.2 miles). Also, if the ICBM fires multiple warheads, or chaff, then you'd need to scale up the number of lasers or scale down the dwell time linearly, assuming they're all conveniently aimed within a small fraction of a mile of the laser (again, I'm assuming best-case).

Current direct energy weapons have only been demoed against UAVs, probably for this reason.

edit: my math is completely wrong: Modern nukes are optimally detonated at about 5000 ft above ground level. So, you get about 0.33 seconds of dwell time, assuming the attacker doesn't just set the warhead to detonate at a non-optimal (but still devastating) 1.2 mile altitude.

https://remm.hhs.gov/zones_nucleardetonation.htm

Post reply on HN