Kuwait says it intercepted Iranian drones in its airspace this week. A drone found beside a German runway carried explosives. So how do you actually stop one?

The news behind the question

The Kuwaiti defence ministry reported that its military detected and intercepted Iranian drones entering the country’s airspace, according to Kuwait Times reporting. Days earlier, a drone carrying an explosive device was found near a runway in Germany.

Step one: see it

This is harder than it sounds. Traditional air defence radar is built to spot fast, metal, high-flying aircraft. Many drones are small, slow, partly plastic and fly low — closer to a bird than a fighter jet on a radar screen. Detection therefore combines radar with radio-frequency sensors that listen for the link between drone and operator, plus cameras and acoustic sensors.

Step two: stop it

Broadly, defenders choose between two families of response. Non-destructive methods cut the drone’s radio or satellite-navigation link so it lands or returns home. Destructive methods physically bring it down. Both have obvious drawbacks over a city or an airport: jamming can disturb other systems, and anything shot down still falls somewhere.

The economics of the problem

Here is the uncomfortable arithmetic that defines modern air defence: the drone can cost a few thousand kroner, while the missile traditionally used to intercept an aircraft costs a fortune. An attacker who can force a defender to spend a hundred times more per exchange is winning even when every drone is stopped. That imbalance is why so much current research goes into cheaper defences.

We describe the general principles here; we do not publish operational detail about defeating specific systems.

Source: Kuwait Times, as collected by Wikipedia’s current events portal.