Mauro Gilli is senior researcher in military technology and international security at the Swiss Federal Institute of Technology in Zurich (ETH-Zurich). His research focuses on air defense, military operations, the defense industry and great powers competition. In this exclusive interview with Kyiv Post, Gilli explains the technology behind air defense systems operations, and how Ukraine’s systems are responding to Russia’s on-going threat.

How does an air defense system detect that a missile or airplane is approaching?

Air defense systems depend on multiple sensors, primarily radars, as they provide day-and-night, all-weather, and long-range detection capability. Most countries rely on ground-based and airborne radars, while some might possess satellite-based radars and additional types of sensors (Ukraine, for example, developed a system for acoustic detection of incoming missiles).


Radars emit electro-magnetic pulses and capture their echoes when they are reflected from an incoming missile or aircraft. Once a radar system detects a return of potential interest, it tries to identify and to track it.

Does an air defense system work differently in detecting a missile from an airplane?

Actually, no – the process is exactly the same. Radars scan the sky searching for possible intruders, and a radar return produced by any aerial vehicle alerts the air defense system of a potential incoming threat. The main differences between missiles and aircraft are their flight profiles and shapes. Cruise missiles, for instance, have a specific shape (i.e., with very few protuberances) intended to reflect limited radar returns, which in turn means that they can be detected only later in their flight journey, thus limiting the available response time to air defenses for identifying, tracking and engaging the target. The same is true for stealth aircraft.

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Along the same lines, cruise missiles and jet fighters generally fly at very low altitudes to postpone the moment of detection by ground-based radars (as encapsulated by the metaphor "flying below the radar"). Conversely, ballistic missiles follow a ballistic [upward then downward] trajectory which exposes them to detection by ground-based radars, but their sustained speed during the descent phase makes their interception more difficult. 


How does modern technology differ from air defense systems from, say, 50 years ago?

The principles behind the workings of radar systems are exactly the same as they were in the past. The difference compared to 50 or even 80 years ago stems from progress in electronics and computing. Advances in materials, primarily in semiconductors, have led to much more sensitive and powerful sensors, while advances in processors, big data and signal processing have dramatically expanded the capacity to collect, store and analyze data.

In medical diagnostics, these developments have led to unprecedented advances: this is why, for example, through big data and machine learning, it is possible to detect markers that indicate cancer cells much earlier than a very well-trained physician. The same is true for air defense systems. Powerful sensors, together with large amounts of data, lower the threshold of what it takes to detect an incoming missile or aircraft. Of course, the technology has also advanced for the attacking side, which can take advantage of different tools to its own advantage.


After an incoming missile is detected, what happens next? Does it pass this information to a person? Or is it automated to prepare an air defense response and turn on the air raid warning siren?

The answer is that it depends – on many factors, including the capabilities, in particular the technologies, of the country under scrutiny. For countries that have the most advanced technologies, many steps are automated (such as target detection, target recognition, etc.), but, at some point, the information goes through people in charge, as they have to make specific judgement calls.

In general, long-range radars detect an incoming missile or volley of missiles, and then pass this information to command-and-control centers, which decide on the subsequent course of action and task specific units that are within range of the incoming threat to engage it.

How does air defense pinpoint where a missile will land? How does it calculate where and at what point to shoot it down?

The impact point is estimated by identifying the trajectory of a missile, and then calculating (or projecting) its subsequent path. The Israeli missile defense system, Iron Dome, uses this calculation to assess whether a given enemy missile is likely to strike inhabited areas, in which case it will fire an interceptor missile. Otherwise, if the estimated impact point of the enemy missile is an uninhabited area, it will not engage it.


Determining where to shoot down a missile depends on a variety of factors. When possible, missile defense systems try to intercept an enemy missile over rural or inhabited areas to minimize risks for the population. But such a goal is not always possible. For instance, for drones or missiles flying at low altitudes, there might be just a very tight window to shoot them down.

Can an incoming object go too fast for air defense to detect it?

In general, speed is not a problem for radar detection. But it might be a problem for tracking or engaging a target. This means that we might be able to see an incoming threat, but we might not be able to aim at it or to shoot it down. This is the "bet" behind hypersonic missiles that many countries have invested in.

Russia is now using drones to "distract" the air defense system, force Ukraine to use-up its air defense missiles, and to locate Ukraine’s air defense systems. Is there a way to avoid this? Hypothetically, could Russia not just send 10,000 drones and use up all of Ukraine's air defense missiles?

I don't think it is possible to "avoid" what is happening – or at least, to avoid it, Ukraine would have to strike deposits of Russian drones to take care of the threat at the source. As long as Russia has supplies of drones, what Ukraine can do is what it has already done – that is, employing countermeasures.


The drones which Russia has been using to strike Ukrainian territory are very cheap, but this also means that they have a limited payload and can be shot down with cheaper systems. Ukraine has adopted different types of active and passive countermeasures: protecting critical infrastructure, such as electric plants, with air defense systems that have short ranges but are highly effective; warning the population so that it can take cover to minimize deaths; and creating a system of acoustic sensors strategically placed so as to enhance capacity to detect incoming attacks by capturing sound emissions of missiles that try to avoid radar detection (such as flying very low, for example over rivers). Other solutions might be on the way in the near future.

Unfortunately, providing 100 percent protection is inherently impossible, as the age of terrorism has taught us. Hypothetically, Russia could launch an unlimited number of drones. But since these drones have relatively limited payloads, what is most important for Ukraine is actively defend its critical infrastructure and employ the countermeasures just described.


Do Russian air defenses work differently to the Ukrainian equivalent? How was it possible that a drone recently exploded over the Kremlin?

Unfortunately, I do not know the specifics of how the Russian and Ukrainian air defense networks work. In principle, air defenses operate in a similar fashion because of the nature of the technologies involved. Russia and Ukraine also share many similar key components of their air defense systems, as a legacy of the Soviet Union (the Buk, Kub, the Strela, the S-300 for example).

As to the attacks within Russian territory, Ukraine has so far carried out a couple such attacks. I think that whereas in some instances it was probably a drone that was launched from within Ukrainian borders, in other instances the drone was fairly small and carried a very limited payload, which suggests that it was brought close to the target by undercover Ukrainian forces.

Thank you.

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