Proper engineering: Iron Dome

Ignoring the rights and wrongs of the current Israel-Hamas contretemps, what has been interesting is the performance of Iron Dome, the Israeli counter-rocket missile system.

Iron Dome tackles an odd problem which occurs due to the economic asymmetry between Israel and its guerrilla opponents (here, Hamas). It is relatively cheap for Hamas to acquire rockets, smuggle them into suitable locations and fire them at Israel. The rockets have a substantial terror value; you never know when they will be fired, where they will hit, and there is only 15 seconds or so of warning. If they do hit housing areas then casualties are nearly guaranteed

Iron Dome's two key features are therefore 1) providing a relatively cheap guided missile capable of intercepting and destroying an unguided rocket with a high probability of success, and 2) only aiming at rockets which are likely to endanger civilian areas. 2) is reasonably straight forward - it's just an evolution of counter-battery radar which plots the initial trajectory of a mortar or rocket to locate the firing point. Instead of going backwards, however, it plots the trajectory forwards to identify the probable area of impact, and is programmed with a map of vulnerable versus deserted areas so it knows which areas to defend.

1) is trickier than you might think; it's no good destroying the body of a rocket if the warhead is still mostly intact, since it will continue in its ballistic path and do damage when it lands. There's also a variety of potential rocket targets:

  • Qassam: man-portable, up to 100Kg weight, 20Kg warhead, up to 20km range;
  • Grad: truck-mounted, banks of up to 40 tubes, rockets up to 70Kg weight each with 20Kg warhead and range up to 20km;
  • Fajr-5: truck-mounted, 900Kg rocket with 175Kg warhead, range up to 75Km.
Iron Dome "Tamir" missiles therefore have to be able to disable the largest possible target while still being cheap enough to be a reasonable trade-off for the cheapest missiles (around $800 for a Qassam, presumably plus $200-$500 cost of smuggling it to the right place in Gaza). Tamirs cost around $50K each.

To date in this phase of the conflict, around 800 rockets have been fired by Hamas with a single fatal hit (3 civilians). Iron Dome has been intercepting around 30% of these; presumably 2/3 of all rockets land in unoccupied areas, which doesn't speak well for either their accuracy or skill at aiming.

The economic calculation from the stats we have so far is therefore that firing about 800 Qassams will cost around $800,000. Israel will need to expend 240 Tamirs at $12 million cost, and can expect one hit with a civilian cost of, say $3 million. So the cost ratio is about 16:1. This is not great, but it's certainly far better than previously where no missiles would have been intercepted, 240 missiles could have landed in civilian areas and say 100 of them would cause damage at $50,000 and 10 would have killed 2 civilians so $2 million each - $5 million + $20 million = $25 million. Israel has therefore halved the economic damage of rocket attacks, not to mention nearly eliminating the terror value.

What Hamas has done in this attack is given the Israelis priceless data on real-life volley attacks. Rafael Armaments can continue to tune their algorithm for which rockets to intercept, and improve the performance of Tamirs in effectively wrecking missiles that they intercept. The other issue is that Iron Dome functions as an extremely effective counter-battery locator; the Hamas rocket launching teams will be under rapid attack from artillery and air platforms (drones, Apache or Cobra helicopters) and will have to be lucky to manage a series of attacks without being pounded.

This isn't the end of rocket attacks on Israel. It isn't even the beginning of the end. But maybe it is the end of the beginning.

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