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Comment by lordgrenville | Hacker News Reader

a) Attack missiles need to hit a stationary target, whereas the defenders need to hit a moving target. So defenders are more expensive.

b) A human defender can hunker down in a safe space and shoot at attackers. The attackers need to move and are more vulnerable

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As a counter to point (a), Iranian missile salvos against Israel in recent years are stated by analysts to be militarily ineffective (or a failure) even if Iran has a 10:1 cost advantage. Reasons include:

1. US+Israel economies have a 100:1 size advantage over Iran's economy.

2. Israel is a very small area to defend, dramatically reducing the cost of anti-ballistic missile defence required. As little as 4 missile defence launch sites may cover the entire country.

Perun's video on the cost effectiveness of missile defence vs. attack is more focussed towards the economics of defence of an expansive country or region such as the United States, Saudi Arabia or the gulf region generally, where many missile defence sites would be required. Israel is a bit of an exception due to the small area needing to be defended.

Another minus specifically for Iran in the Iran/US+Israel war is being forced to build underground factories at much greater expense than an above-ground factory for Israeli interceptor missiles. I don't think analysts have been considering this long term cost in their cost comparison ratios. However, for both Iran and Israel--they're importing a lot of the components and materials from overseas anyway.

Attack missiles generally need to travel much farther which increases the cost. How it balances out it an open question and different for each system of missile/interceptor.

If your interceptors are good eventually the enemy is going to give up on that attack mode. - you have more incentive to defend than they do to conduct useless attacks.

If attackers are cheaper than defenders, the attacker might be able to bankrupt the defender, or at least temporarily deplete their supply of defenders. So not useless at all.

attackers are not cheap though.

Ukraine's interceptors for cheap drones are drones that are even cheaper and so advantage defender.

The consideration made in Perun's video, and I know it's quite different geographically for drones versus missiles, is a defender having to defend all important sites as if the attacker sent every drone or missile to a single target.

For a facility that Ukraine has decided would cause $10m in economic damage if hit by a Russian drone, how much should Ukraine spend on interception for that site to not make it worth Russia's expense to target it? Let's assume a Russian drone is $100k (current estimate in news for Geran-5 jet-powered drones). But Ukraine can build their Bars interceptor drone for half the cost at just $50k (low estimate from public rumours/reports). It wouldn't be worth Russia's expense to send more than 100 drones in a salvo at this target. For Ukraine, they should defend the site with $5m worth of Bars interceptor drones, assuming a very favourable 100% success rate (actual reported success rates are reported by media to be just 30%). Russia has now made every $10m facility in Ukraine cost $15m (+50% increase).

The defender is essentially forced to find a 10:1 or better cost advantage for their interceptors vs. incoming drones. This is hard to do when an interceptor and attack drone are substantially the same except for larger fuselage (cheap), larger fuel tank (cheap) and larger engine (possibly cheaper than making a small engine).

And perhaps that is the reason Russia and Ukraine are largely focussed on attack rather than defence in the hope of being first to cripple the other's economy and supply chain for munitions.

> Attack missiles generally need to travel much farther which increases the cost.

This is likely a a flattened curve after you enter ballistic missile territory.

Distance does have cost, but that's mostly a brute force solution of strapping more fuel on. The really expensive piece is the tracking and flight control systems that enable interception of fast targets.

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