They are everywhere and they are becoming increasingly dangerous. Just yesterday, an out of control drone interrupted a match at the U.S. Open. On September 15, 2013 a supposed prankster landed one on the podium from which German Chancellor Angela Merkel was speaking. Last May, a man was detained for attempting to fly a drone into the White House. There have been reports from JFK to Ben Gurion airport of near collisions between airliners and drones.
To date these events do not seem to be the work of terrorists or hostile states. Moreover, the drones in question have all been the hobby shop versions that are small, short range, slow flying and with limited payload capacities. But they are hard to detect and defeat. So even with a few pounds of plastic explosives, terrorists could turn these toys into lethal tools of assassination. Operating in swarms, small drones, in theory, could attack airfields, military convoys, critical infrastructure and even large public events.
Countering the threat posed by small drones has two steps. First, it is necessary to detect and track them. Because they fly low and slow they are hard to see with the naked eye or even with cameras unless they receive some form of cueing. Most small drones are made primarily of plastics. This makes them difficult to detect with many currently deployed air surveillance radars. Rotary wing drones — mini-helicopters and quadrotors — may be able to avoid detection by some sensors simply by hovering in one place.
There is a new family of lightweight, even portable, radars with sufficient fidelity to detect extremely small, lightweight drones and quadrotors. One of these systems, the Manportable Aerial Radar System (MARS-K), has been tested by several U.S. agencies with the idea of acquiring a number of them for surveillance of ultra-light aircraft and small drones operating in sensitive airspace. The MARS-K can detect and track a wide variety of small drones. It has even had success identifying hovering quadrotors by the small movements operators must make to maintain a stable position against wind gusts. An electro-optical camera can be added to the system to permit the operator to refine the target identification provided by the radar. The MARS-K will make its public debut in the U.S. in mid-October at the Association of the U.S. Army annual meeting in Washington, D.C.
Detecting a small drone operating in restricted airspace is the first step. Defeating one with hostile intent and, potentially, a lethal payload is the second. They can be brought down by kinetic fires, assuming a very accurate rifleman or targeting system. This creates the potentially serious problem of falling debris and collateral damage. If the drone is carrying a biological weapon or nuclear material, kinetic fires may simply cause greater destruction. The U.S. has tested low power lasers against small and medium drones with great success. But the problem of potential collateral damage would still remain.
It appears that the best techniques for defeating small, hostile drones involve some form of electronic or cyber attack. Jamming the drone’s guidance system or the link between the platform and its controller would at least turn a precision weapon into a dumb flying bomb. But it could still go off. The drone also could be guided by a small computer with selected waypoints pre-programmed in it. This could defeat a defense based on jamming. A better approach would be to block the drone’s command detonation circuit, assuming it has one.
The best way of defeating this threat appears to be some sort of cyber or electronic defense that could take control of the drone away from its operator or the on-board guidance system and force it to land at a safe spot. This would require very sophisticated, fast electronic defenses because of the relatively short timelines involved. But it is possible.
The threat from improperly operated and hostile drones in U.S. airspace is only going to get worse. While it is impossible to surveil and defend the entirety of low altitude airspace against such threats, it is a relatively straightforward problem to provide protection for critical airspace, high value infrastructure and important individuals and events. But meeting this challenge must start with the ability to detect and track small, lightweight drones flying close to the ground.
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