Bang bang, you shot me down

Take me out: creating ‘No-Drone Zones’ around airports

Image credit: MPL

The criminal use of drones around busy airports is on the rise. Techniques must be developed to prevent incidents like the disruptions at Gatwick Airport last Christmas from happening again.

On Wednesday 19 December 2018, London’s Gatwick Airport received a startling wake-up call: drone sightings were reported in the restricted airspace. The airport was forced to suspend operations just as thousands of travellers were heading there to get home or get away for Christmas.

The next 48 hours were beset with uncertainty. At one point, runways were briefly re-opened, only to be closed again 45 minutes later following another possible sighting. Finally, at 6:30pm on Friday 21 December, flights were given the all-clear to resume. However, for an estimated 110,000 passengers it was too late, as countless Christmases were ruined. A culprit is yet to be identified and we still do not have a full picture of what happened.

What we do know, however, is that incidents involving drones are becoming more common. In August 2018, a drone appeared to attempt an attack on Venezuelan President Nicolas Maduro while he addressed a military parade in Caracas. Furthermore, incidents involving drones coming into close contact with aircraft are steadily increasing. In 2018, UK Airprox, the body responsible for investigating air crashes and near-misses, counted 117 incidents – up from 93 in 2017, and 71 in 2016.

“The vast majority of critical infrastructure around the world is completely unprepared for the widespread use of drones,” says Luke Fox, CEO of WhiteFox Defense, the company that recently secured a $12m investment as it develops technologies for a “counter unmanned aerial system (C-UAS)”, which Fox calls a “highway patrol in the sky”.

“[Incidents at] all of these airports are just the tipping point in the overall recognition that drones are part of society,” he says.

Drones aren’t going to go away, so what are the options for taking them down? What technologies are available if something like the Gatwick nightmare happens again?


Drone detection

Before a drone can be taken down, it needs to be detected. And the C-UAS companies are also active here. “Our Galaxy security platform combines input from multiple sensors to detect anomalies in the sky, at ranges of up to a 25-mile radius,” explains Jaz Banga, co-founder and CEO of Airspace Systems. “Detection comprises three crucial functions: radio frequency (RF) sensors that use drone-to-operator communication links to identify a drone’s serial number and operator location, a camera array to minimise false alarms and improve localisation, and communication alerts to the Galaxy operator.”

What’s particularly clever is that the Galaxy system takes all the detected metadata and uses machine learning to create “actionable intelligence” on what the incoming threat is. This means that rather than just telling you where the incoming drone is, it can also identify the make and model – and thus the anticipated payload – to enable operators to assess more accurately how much of a threat the detected drone actually is.

One of the most obvious ways to take out a drone is jamming. If signals between the drone and its controller can be disrupted, then that could render the unauthorised drone no longer a threat. But with jamming, there is a problem: if a device simply blankets the local area with jamming signals, it could disrupt other devices and communications. This is where DroneDefender comes in.

First developed by Alex Morrow and Dan Stamm in 2014, DroneDefender is a rifle-like weapon designed for the battlefield. But instead of firing bullets, pulling the trigger directs a narrow beam of energy capable of knocking out a drone’s remote-control signal and its GPS. In principle this means that once a drone has been caught in the DroneDefender’s sight, it should simply descend to the ground gracefully as on-board software defaults to a controlled landing.

Currently the device is marketed primarily to agencies in the US government and its allies – not least because sale or use of the device requires the permission of the US State Department. Morrow says that at present they’ve sold over 300 systems in the “tens of thousands” of dollars price range – but, unsurprisingly, he isn’t at liberty to divulge much when asked when his device has been used in the real world. “I don’t get a lot of insight into engagement scenarios, but the same customers have continued to buy,” he quips.

However, this method has limitations. Earlier this year, the BBC’s Quentin Sommerville tweeted about drone attacks on the Iraqi forces fighting ISIS and, although he didn’t name the brand, he remarked that jamming rifles “weren’t terribly effective”.

The biggest problem with jamming is that even if the beam can be directed, it is still a relatively blunt instrument. Jamming devices will block whatever falls into range, which could cause problems at a challenging location like Gatwick Airport, for example, where if any of the sensitive instruments or SCADA control systems are inadvertently jammed, it could lead to unintended consequences. This is why Fox’s WhiteFox Defense promotes a method he calls “signal substitution” – or what we might call hacking.

The premise behind this approach is simple: instead of jamming, the intercepting device attempts to take control of the hostile drone by spoofing control signals and attempting to fool it into thinking that the signals are coming from the real controller. This means that such a counter-drone device could land the drone safely or change its flight path and divert it to a safe location.

There is one other advantage. If you can lock on to the software of the hostile drone, you don’t need to act on the incident immediately. “We can monitor it and make an informed decision about whether we shut down this airspace or leave it operating,” explains Fox. In a future where drones are more common, if signal substitution – which enables a more finely tuned approach – can be used not every drone incident will require the shutting down of entire airports.

Fox describes WhiteFox as “one of the most pro-drone counter-drone companies”, and talks about how the entire drone industry has the same goal of a secure sky.

‘The vast majority of critical infrastructure around the world is completely unprepared for the widespread use of drones.’

Luke Fox, WhiteFox Defense

The reality of signal substitution, however, arguably exposes a fundamental tension between drone developers and counter-drone companies: both sides are in a similar arms race to the one software developers find themselves in with hackers. Once a security hole is discovered in the software of a drone, which could be used for signal substitution, drone manufacturers will want to patch the hole so that their drones are more secure. Security holes –  like drones themselves – can be used for both good and bad, so ultimately this approach isn’t completely foolproof.

The great benefit of jamming and hacking is that it doesn’t damage the drone. Jamming is “a non-destructive tool enabling you to recover the asset and do whatever you want with it after that point”, explains DroneDefender developer Morrow. It’s easy to imagine why this might be advantageous: if the technology is used on the wrong target, there is no harm done. Also, capturing the drone could enable the authorities to more effectively identify and track down the perpetrators.

If these defences fail, ultimately you want to take what is called a ‘kinetic’ approach in the industry’s military parlance. In other words, you want to use force.

One obvious approach is to simply shoot it down – but this is more difficult than it looks and comes with risk of collateral damage. “If you’re in an urban area, you’re not going to be shooting rounds up into the sky... that’s not what you want to do,” says Morrow.

Airspace is another company that is positioning itself as a fully-integrated drone-defence ‘platform’, offering technology to detect and identify drone threats, as well as take them out. It has previously protected the Major League Baseball World Series, where it detected 53 rogue drone operators over the course of three days.

How does it remove drones from the sky? By using an even bigger drone equipped with a net.

The company has developed a defence system that sends up a drone of its own to autonomously lock on to the rogue drone, fly into position and fire a net to capture it. Airspace’s drone can then simply fly the captured goods to a safe landing site, away from anyone else, which is especially useful when there is a risk that an unknown drone may contain explosives.

Another kinetic solution that is similarly old-fashioned is birds.

An eagle catching a drone. There's something you don't see every day.

Image credit: AFP

Birds of prey have long been used around airports to keep other avians away, but now the technique is being applied to the drone threat. A company called Guard from Above, based in The Netherlands, has a specialised team of birds and handlers and offers consultancy on “C-UAS Bird of Prey Capability” – boasting that it already has boots and talons on the ground in Afghanistan.

“What we found with the peregrines was that they were using the same underlying feedback law as is used by most missiles, but tuned a little bit differently,” explains Professor Graham Taylor of Oxford University’s Department of Zoology, who has conducted research into how birds of prey hunt – which suggests why birds might be effective at tackling threats from drones.

“Imagine drawing a line between the bird and the target, measuring the rate at which that line’s direction changes and feeding that back to control the turning – it’s known as ‘proportional navigation’ and has been the standard in missiles since the 1960s.”

Taylor explains that birds are more sophisticated than missiles because a missile navigates simply by locking on to a heat source, whereas birds have high-resolution visual systems and are capable of stabilising their gaze against a moving background. In other words, birds might be perfectly suited for hunting down drones despite drones being smaller than missiles and moving in less predictable paths.

There are, however, two problems with this strategy on the grounds of both animal welfare and practicality.

“For a falcon going and grabbing a small DJI [consumer drone], it shouldn’t be much of a problem but for anything larger it could be really quite serious,” Taylor explains. “So, I think the majority of people in the falconry community have quite significant reservations about the welfare of using birds.

“On the practicality side, the way that falconry works is the birds are kept hungry, so it’s different from training a dog. To make this work, you would need the birds to be motivated to chase targets because they were hungry, which means keeping a flying team of birds in a continuously hungry state.”

So, what’s the best way to knock a drone out of sky? Unfortunately, there are no simple answers – but this is something C-UAS makers readily admit. “You really need to have multiple modalities for your detection, identification and defeat, allowing you to escalate and ramp up your engagement level,” says DroneDefender’s Morrow.

“There’s no silver bullet, there’s no one system that’s perfect for the entire kill-chain.”


Homebrew drone defence

Counter-UAS isn’t just for the professionals, as demonstrated by hacker and researcher Samy Kamkar. He has invented what he calls the Skyjack drone. It essentially does something similar to WhiteFox’s signal substitution technique: it flies into the air and looks for the wireless signals coming from other drones. Once it finds a target, its software forcibly disconnects the drone’s owner and attempts to take control.

What makes it remarkable is how it was made. It doesn’t require any fancy kit, as it is just a standard consumer Parrot AR Drone 2 with a tiny Raspberry Pi computer, USB battery and wireless transmitter bolted on – and much of the onboard software is open-source. So why not build your home some counter-drone defences?

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