In principle it is easy to shoot down an enemy ballistic missile like a Russian Grad or Iranian Fajr. First you need to know the location, in three dimensions, the speed, the bearing, also in three dimensions, and the shape of the incoming projectile. Modern radar can provide information about location, speed and bearing. It can also identify the type of projectile which gives information as to shape.
Then you need software that can calculate an interception course for an anti-missile. Add in some terminal guidance on your anti-missile for mid-course corrections and, bang, a hit is guaranteed.
Oh, and make the system smart enough that it ignores missile that are going to land in open areas where they won't do any damage. That way you don't go off wasting expensive ordinance.
Well that's the theory. Iron Dome is the first system to bring all these elements together in a cost-effective manner. The Israeli designed and built radar and battle management systems as well as the Israeli designed and built Tamir interceptor missiles all performed above expectation.
According to the Israeli Ministry of Defence, Iron Dome knocked down over 400 incoming rockets. Only 70 landed in urban areas implying a success rate of around 85%. Rockets that were headed for open country where they were unlikely to do much harm were ignored.
Even more amazing, only 500 Tamirs were launched meaning that almost every interceptor missile found its target.
The cost of a Tamir interceptor missile is around $50,000. However this is an estimate of full cost including an allowance for amortising R & D. With mass production the marginal cost of could probably be reduced to below $10,000. This means that the cost of shooting down a missile may be comparable to the cost of the incoming projectile – a cost effective defence in every sense of the word.
One of the keys to a successful missile defence system is ultra-fast computers. I doubt if even five years ago Iron Dome could have performed as it did. My guess is that the designers of the system counted on computing power catching up with their requirements.
Another requirement is versatile software. There are reports that software engineers were monitoring performance and updating the system with improvements even while the conflict was under way. This from Business Week:
Typical command-and-control software for military gear is highly customized and hard to modify. The key to [Iron Dome's success]…. is that the command-and-control software is simple and modular, so customers can quickly adapt it without reprogramming. The Israeli army was able to recalibrate Iron Dome batteries almost immediately, without a software rewrite, when Hamas fighters began to fire longer-range missiles.