Cheap Shot
On the morning of 14 September 2019, before sunrise, a swarm of fixed-wing drones — in two waves — attacked the Aramco Abqaiq refinery in Saudi Arabia. Fires and explosions soon had the refinery out of operation, with about five percent of the world’s oil production knocked out. Whether missiles were also used in the attack is a matter of dispute.
What is certain is that the attack used cheap industrial drones, each costing about US$25,000-. Modified with explosive packages, the drones became cruise missiles with ranges out to 1000 miles. Moreover, these drones were able to avoid sophisticated multi-layered air defence systems, including short-range Sky-guard batteries. Who was responsible for the attack remains unclear.
The evolution of drone technology is giving terrorists and criminals attack options that are difficult to defeat. Non-state actors can field drones with capabilities until recently enjoyed only by world-class air forces. In 2017, ISIS claimed to have carried out 200 such attacks using a variety of drones, including cheap toys. Disruptions at airports, sightings of drones over sensitive locations such as a submarine base in the US and nuclear facilities in France all add to the threat.
In the Saudi attack, swarming tactics involving between 10 and 25 drones overwhelmed the defences. While guards at the facility engaged the incoming drones with machine-gun fire, at least 19 targets sustained hits.
This attack illustrates the vulnerability of crucial infrastructure to the drones. The events at Gatwick Airport last year made the point that even a sighting of a drone can prove disruptive. Thus as concerns grow about the possible threat posed by drones, counter-drone systems (C-UAS) must evolve.
Below I review the options available and their effectiveness. There are two aspects to consider; detection and then interception. Neither is straightforward.
Drone detection techniques include:
Radar — detects the presence of drones by their radar signature. These systems use algorithms to distinguish between drones and other small, low-flying objects, such as birds.
Radio Frequency — these systems scan the frequencies on which most drones operate and detect their presence. Algorithms pick out and locate RF-emitting devices in the area that are likely to be drones.
Optical — detect drones based on their visual signature.
InfraRed — detect the heat signature of drones
Acoustic — these systems detect drones by recognising the unique sounds from their motors.
Combined Sensors — these systems integrate a variety of different sensor types to enhance detection. For example, a system might include an acoustic sensor that cues an optical camera when it detects a potential drone in the vicinity.
In truth, no detection method is fail-proof. The probability of a successful detection remains low even with combined systems. Even cheap consumer drones present a challenge. These are small and tend to fly at low altitudes, which makes detection by any of these systems difficult.
Further, even if detected, the next matter is how to deal with the drone. It’s known that the world’s most sophisticated air defence systems struggle to bring down rudimentary unmanned aircraft. In July 2016, a simple Russian-made fixed-wing drone flew into Israeli airspace from Syria. It survived two Patriot missile intercepts, as well as an air-to-air missile attack from an Israeli fighter jet. Although on other occasions Israel was successful in deploying Patriot missiles against drones. A hit depends on a variety of factors including the weather.
Options for interdiction include:
RF Jamming — this approach aims to break the link between the drone and its operator. In such cases, the drone should descend, crash or automatically return to its launch point.
GPS Jamming — like RF jamming, this aims at breaking the link to satellites that the drone uses to determine its location. With the GPS gone, the drone will either hover or return to base. GPS blocking used in tandem with RF Jamming is popular.
Spoofing — these systems electronically hijack the drone.
Laser — a directed energy weapon that breaks up the drone causing a crash.
Nets — these aim to capture the drone and bring it out of the air.
Projectile — a shoot-down using ammunition.
Birds — the use of birds of prey to interdict and capture the drone. This method is usually only possible with copter-type drones that are relatively slow-moving.
Collision — deploying another drone to take out a drone.
Of the systems available in the market, RF and GPS jamming enjoy some success and favour. But, drones can be programmed to operate autonomously without an active RF link. Likewise, new technology is emerging that allows drones to fly without a GPS signal as sensors give it terrain-following capabilities.
Moreover, the FAA recently cautioned airports that using jamming systems can interfere with legitimate communications. Meanwhile, kinetic options such as projectiles and collision may be suitable in a military context but not favoured in a civilian setting. The risk of debris falling from the sky cannot be discounted.
In summary, none of the currently available systems is 100% effective in detection or interdiction. Civilian airports face the extra difficulty that their proximity to built-up urban areas may further limit the detection capabilities of any system and the options for interdiction.
At this time, it appears the best option is to limit the inappropriate and illegal use of drones. Pre-installed geofencing non-removable software to prevent flight in restricted areas is a must. Besides, electronic IDs should allow the authorities to identify legitimate drones. Yet, there is no industry standard in this regard.
Compounding the problem is that drone technology continues to advance at a rapid pace and keeping ahead of the game will need vigilance. In the meantime, the three elements identified in my blog last year of deterrent, enforcement and reaction remain valid.