By Tony Reeves of level 7 Expertise
“Taking down a drone – it can’t be that hard, can it?” There is, in fact, a surprising knowledge gap about the optimum means of defeating a rogue drone once the threat has been identified.
There are three ways to defeat a rogue drone – neutralise it, make it go away or destroy/capture it. But there are only a few options open to most civilian or commercial entities and even operators of critical infrastructure installations face a large number of constraints that will include legal, technological, operational and physical.
Defeating an unwanted drone is problematic and is subject to legal restrictions in most countries; however, many governments are seeking to tighten regulations and enable more robust defence of key sites. For example, RF jamming in the UK without a licence is illegal but the use of specific C-UAS jammers can be approved with appropriate controls and authorisations. The UK Civil Aviation Authority has defined Article 240 of the Air Navigation Order (“A person must not recklessly or negligently act in a manner likely to endanger an aircraft, or any person in an aircraft.”) as not applicable to small UAS below 20kg take-off weight, thereby opening up the potential use of C-UAS devices against these systems. In some countries – Jordan for example – it is illegal for anyone other than state security forces to operate drones.
Directed Energy Weapons (DEW) have historically been the province of the military but are the most effective tool in the C-UAS arena.
- Radio Frequency (RF) Jamming is the most commonly employed method of stopping an unwanted drone, in which an RF signal is directed at the drone to either overwhelm the datalink and disrupt the control from the ground controller, or to interfere with the drone’s GPS receiver, forcing it into a reversionary flight mode. The resulting effect is dependent upon the sophistication of the drone itself. For most COTS drones in the Phantom / Mavic class, jamming the datalink will either send the vehicle back to its origin (until it regains link), or continue on its pre-planned mission (but without link), or go to a pre-set ‘rally point’. Jamming the datalink and GPS simultaneously usually results in the drone landing at its current location. However, taking this approach with an unsophisticated drone is likely to result in it crashing. Jamming a Radio-Controlled aircraft operating under positive control will result in a crash. Use of high-power jamming devices can result in RF fratricide and unintended disruption of other services in the vicinity. Some companies offer GPS spoofing devices which disrupt the positional information available to the drone, and there are a number of vendors who claim a capability to conduct a ‘hostile takeover’ of the target drone and a safe landing to be made.
- Electro-Magnetic Pulses (EMP) use high power microwave devices to send a targeted pulse that disrupts or destroys electronic components in the target. These devices are directional but there is a high likelihood of unintended impacts on other devices in the area and other forms of interference. The systems on board the target drone will be disrupted instantly, with the drone likely to crash to the ground. These devices are costly and as far as I can tell, unproven in the commercial / civilian context.
- High Energy Lasers are being developed by a number of manufacturers, and vary between 5 – 30kW in output power although this is on an upward trend. Trials so far have been moderately encouraging but the target illumination time required is longer than ideal and the lasers themselves are enormously costly. As there are no projectiles involved, the risk of collateral or unintended damage is much reduced, which is a clear advantage over gun-based systems. Dependent upon the output power and national legislation, lasers are often classed as weapons so are likely to remain in the domain of the military and specialist security forces for the foreseeable future.
- Guns are a robust battlefield solution and offer a lower cost-per-kill than guided weapons, although the fall of shot and collateral damage considerations are significant; the likelihood of employment of these systems in a non-military context is very low. Hitting a manoeuvring small airborne target is hard, even when the guns are directed by radar, and as such the number of rounds fired in order to be assured of a kill is commensurately high. There are a number of manufacturers developing fragmentation munitions to reduce the number of rounds fire whilst increasing the kill ratio. The use of small arms to bring down drones has some – but very limited – utility.
- Missiles / Guided Munitions are another option for the battlefield, and following the report of Saudi Arabian forces firing a £3M Patriot missile at a small COTS drone in 2017, the extensive use of explosive-laden long-range drones by Houthi rebels has resulted in a number of missile engagements in recent months. In addition, Russian Air Defence troops deployed to Syria used a combination of radar-directed guns and missiles in a layered defence response to drone attacks by Syrian rebel forces. There is a lot of research being done into lowering the cost-per-kill of this weapon type and the likely shift to a drone “hittile” is discussed further below.
- Ground-based net guns have been deployed with security forces and have been seen in and around a number of UK airports. The gun fires a small canister which contains a net which then deploys in proximity to the target drone, snaring its rotors and bringing it to the ground. In many of these systems the canister is classified as a weapon projectile and subject to legal constraints; the effective ranges are also limited – in the case of the OpenWorks Skywall the ranges are in the region of 100-150m for the shoulder-launched versions and up to 300m for the turreted version. The time required to get a net gun to the target drone area on a large installation will be significant, with the other alternative being a large number of net guns positioned around the installation; either way, this is not ideal and therefore these systems are limited to close-in, ‘point’ defence at the time of writing. However, by comparison they are far cheaper than other effectors and the training requirement is reasonably low. There are developments in the pipeline that seek to extend the effective range and mobility options of these devices.
- Airborne net and entanglement systems are being offered by a number of manufacturers, using either a forward-firing net gun (sometimes in combination with a jamming system to force the target to hover) or using an underslung net or cable. The use of parachute devices to deliver a more controlled landing is becoming more common. The advantages of these systems are low risk of collateral damage / third-party risk, and the possibility of retrieving the target drone undamaged for forensic examination. However, the three-dimensional aerial ballet required to snare a manoeuvring aerial target should not be underestimated, and there is a lot of work being done to develop AI-based solutions resulting in more autonomous engagements.
Drone “Hittiles” are becoming more prevalent, in which a drone is used to deliberately ram the target with intent to damage it sufficiently to bring it down. There are a limited number of solutions ranging from small quad-rotor devices to larger military-use tube-launched systems that carry an explosive warhead (and therefore technically a missile rather than a hittile). This is an area which is showing some promise and a number of academic institutions are carrying out additional research into swarming “drone-on-drone” capabilities. The most challenging issue is that vectoring a small device to impact a manoeuvring air target is hard; the two main schools of thought rely on a radar-guided engagement in which the hittile is directed by ground-based command systems; or increasingly, the provision of autonomy, AI and machine learning into the hittile. A recent development was published in Unmanned Airspace in May 2019.
Other innovations are constantly being sought and we’ve all seen the amazing pictures of eagles snatching drones from the air mid-flight; these images seem to be the default for every mainstream C-UAS news article and online publication. The sad thing is that the trials with birds of prey did not work all that well. The birds were hard to train and could not be relied upon to engage the drone outside of a training environment. There was also a report from the French trial in which an eagle attacked a small child; the enquiry suggested it was because the child was wearing a top of the same colour the drone was trained to catch.
Back to the drawing board, it seems!