Team Name: Dye HardTeam Captain: Ollie Poole DoB 17/06/02, email: pooleoj@tonbridge-school.orgTeam Member 1: Chris Leigh DoB 08/10/01Team Member 2: Ben Burgess DoB 14/10/01School: Tonbridge SchoolAddress: Tonbridge School, High Street, Tonbridge, Kent, TN9 1JPPhone number : 01732 365555Adult sponsor: Phil Deakin, Head of Physics, email: phil.deakin@tonbridge-school.org

Classification:It is important to classify the particular operators of small UAVs and analysing the potential threats these different types could pose before assigning general preventative and confrontational solutions.

Intrusion type 1: Unintentional intrusions. These operators will be causing no harm, they will have entered sensitive locations by accident.

Intrusion type 2: Intentional intrusions by unsophisticated operators with benign intentions. These operators will be trying to simply protest, make a nuisance or act recklessly. Take for example someone operating a UAV and directing it to fly or hover over an airport or around a government building.

Intrusion type 3: Intentional intrusions by sophisticated operators with malign intentions. These operators will be capable of either manufacturing their own UAV from components or hacking the software and hardware of commercial UAVs. The threats these operators would be posing would be espionage and reconnaissance, as well as physical attack. For instance, a UAV hovering outside a government building and listening to conversations or photographing classified documents, or a UAV with firearms or explosives attached and prepared to physically attack the UK’s infrastructure such as airports, embassies, stadiums or nuclear plants.

Solution 1 - LegislationThe UK already has its ‘Drone Code’ which outlines procedures every UAV owner should abide by.1 However, just like owning a car, the owner does have the ability to break said restrictions, just like breaking the speed limit on the motorway. Always flying within sight, not flying above 400m and keeping away from sensitive areas are great for preventing type 1 intruders, but we are looking at the types of flyers who have the specific intention to cause trouble. They will obviously not be adhering to these rules, and therefore any other non-physically binding legislation is useless at stopping type 3 intruders.

There are advantages to these measures however, as they clear the airspace of all accidental intrusions, meaning that it is easier for real threats to be dealt with by appropriate measures. In terms of concrete measures, the most popular are Geofences. For example, all DJI drones are pre-programmed and updated with maps that contain three types of zones warning against flight.2 The most severe will stop all movement of the UAV when they are entered, causing them to ground or return home immediately. Although these measures have proven to be effective, they are able to be overcome, and most other companies do not take these zones as seriously, relying on the person controlling the UAV to know about these zones beforehand, or to act on passive warnings.

Physically binding legislation will act as the first layer of defence to prevent types 1 and 2, then a combination of detection methods will allow for accurate and reliable tracking to ensure countermeasures can be used effectively in order to combat type 3.

Detection and trackingLaid out by the US budget, the most common threat (found in warzones, at least) are commercially bought quad copters equipped with IED’s, or improvised explosive devices, which “pose a direct threat to U.S. and coalition forces”. According to the Joint Improvised-Threat Defeat Agency’s spokesperson David Small, “the Pentagon office that has worked to combat improvised explosive devices since the 2003 Iraq war, has seen Islamic State fly quad copters and fixed-wing type UAVs you can buy commercially”.3 These types of UAVs are as available in the UK as in the USA, so we expect to see the bulk of type 3 intruders using this style of UAV. However our solutions are not specific to quad-copters and will work on all styles of small UAV.

These commercially bought UAVs are often smaller than 300x300x400mm and can move quickly with devastating accuracy provided by on-board cameras. The main difference between classes of UAVs is whether they have GPS or not. Any UAV that can set a home, has a return to sender feature, or allows uncontrolled flight has on-board GPS, and it is these UAVs which allow users to fly to specific targets and can be controlled remotely without a line of sight. Any user that wants to carry out an attack would be forced to use said system, as any other would simply not be feasible due to a very limited range and accuracy.

1 https://www.heliguy.com/blog/2019/01/08/new-uk-drone-legislation-announced/2 https://www.dji.com/uk3 https://www.telegraph.co.uk/news/2016/07/07/islamic-state-fighters-using-drones-with-ieds-and-spy-cameras-sa/

Figure 1.1: A characteristic commercially available quadcopter used by the Islamic

State

There are four main avenues to go down when looking at UAV detection and tracking; radio frequency, electro-optical, acoustic and radar. A combination of all four of these would be the most effective.

Radio FrequencyAny UAV that has an on-board camera and is transmitting that video, or any UAV that is being controlled via an operator, will be emitting RF waves. Almost all commercial UAVs use either 2.4GHz or 5.8GHz, and this data is sent back to the controller via a wireless data link. These emissions can be detected and triangulated by using a network of synchronised ground stations or a directional antenna and the position of the user can be found.

Disadvantages to this are that the UAV’s transmissions must be sufficiently persistent and powerful. Also, the UAV’s operator could program the UAV with a path and actions, and it would execute these whilst in “radio silence” by which it doesn’t transmit any radio signals. The system we use must also first have knowledge of the emission centre frequency and bandwidth.

Electro-opticalElectro-optics can be used in a variety of ways, often combined, to give a precise location. Visual cameras can be used to identify all possible targets, whilst infrared cameras can be used to detect the heat from inside the UAV’s motor and differentiate between birds and UAVs, due to birds having a lower thermal image. This is cheap to implement, and the synchronisation requirements are trivial. With a large area around a location fitted with visual and thermal cameras, we can survey a large geographical network. These cameras work in day and night and give a good 3-dimensional indication of the UAV’s location.

A disadvantage is that the quality of the infrared detections relies on the strength of the thermal emissions from the UAV.

AcousticPrecise acoustics can be used as UAVs emit very distinctive sounds. This is most well-known for its use in leakage detection, UAVs can be tracked via the sounds generated by their rotors. This is also relatively inexpensive and highly effective when combined with electro-optical sensing to distinguish UAVs from any potential UAV imposter.

This is most effective when in open environments with limited interference however noisy environments are often where such countermeasures are needed the most, such as an airport. Not only this, but acoustics would be unable to detect UAVs in free fall or greater than a 500-metre range.

RadarRadar is often the most popular method and for a good reason. It uses the information from reflected radio waves to gauge the position of objects precisely and accurately.

However radar is far worse at distinguishing between birds and UAVs. Not only can radar mistake birds for UAVs, but worse, mistake UAVs for birds. This is due to both parties being very small and manoeuvrable, and even with similar flight speeds. In order for increased accuracy, wavelengths of mere millimetres are essential. Also a UAV could be built of poorly radar-reflective material to evade radar.

Solution 2 – Hijacking The large majority of commercial UAVs rely on civil GPS for navigation. When an operator uploads a flight path for their UAV, the surrounding GPS satellites help orientate the UAV in a 3-dimensional grid. The UAV’s autopilot carries out the flight plan.

It is possible to hijack the UAV by tricking it into thinking you are a ground control system. The UAV has a GPS receiver inside which has a “correlation peak” which relates to the authentic, original signal. This is shown by the three dots in figure 2.2 which are the tracking points which try to keep themselves concentrated on the peak. By hijacking, you cause a false peak to appear, which interferes with the true peak and causes it to move to one side. This changes the UAV’s perceived location to a false one. This results in the false “ghost” UAV going to the target destination, and so the real UAV overshoots or undershoots the location desired by the controller.4

Limitations:

4 https://www.youtube.com/watch?v=6qQXVUze8oE

Figure 1.2: A quadcopter detected with an IR camera

Figure 2.1: UAV in 3-Dimensional Grid used for navigation

Figure 1.3: Schematic of how radar can be used to detect and locate a

UAV near or inside a no-fly zone

Figure 2.2: 3 red dots shown are tracking points

Figure 2.3: Hijacker peak approaching real peak

Figure 2.4: Hijacker peak interfering with real peak

Figure 2.5: Real peak changed position, and new peak is moved, it is now

representing the false location of the

- This only works with UAVs using GPS to navigate; it is possible for an intruder to configure the autopilot to ignore any GPS signals in the approach to the target, rendering hijacking useless.

Solution 3 – JammingAll non-autonomous UAVs require radio signals to pass between the controller and the UAV. A transmitter can emit a signal on the same frequency and the same modulation as the source to be jammed. Examples of modulation types are FM and AM. For basic modulation types, it is very easy to jam the signal. You need more power on the jamming transmitter than on the UAV’s transmitter. Music or random sounds or whatever desired can be played through the transmitter and if this signal is strong enough, the controller won’t be able to communicate with the UAV, and vice versa for images and any other information being sent back to the controller. This is because the receiver can’t identify the correct modulations to signify binary code or instructions.

However, some digital modulation types are more complicated. For example, PSK (phase-shift keying). Sudden shifts in the phase of the carrier wave correspond to binary strings, these are obvious and result in large changes to the wave that are hard to drown out by jamming. Mostly, these can be worked around. Some form of handshaking is usually required between the transmitter and receiver to establish security settings and the method of transmission, so the jammer can initiate contact, but never complete the handshake, effectively locking the receiver in a cycle where it is unable to receive any other communications.

Another method of resistance to jamming is spread spectrum communication. A signal is sent over a wider bandwidth or a wider range of frequencies. The jamming power is effectively spread over the whole range and to get around this, we just need to take the “more power” approach and put in more power across the whole range.

Limitations- Range: The power drops off fairly quickly but only in the order of kilometres, so this is unlikely to be an issue for

protecting airports and similar locations, especially if multiple jammers are used.- Identifying the right frequency and modulation type: Identifying the frequency is easy enough, all you need is a

computer with a receiver to come up with a list of frequencies in use nearby that aren’t recognised as part of the location’s. To identify the modulation type, it is a more difficult process, you need to resiliently try every possible type. This process can be sped up using multiple computers testing each modulation type.

Solution 4 – LasersNo longer a comical fantasy, the development of more efficient and powerful lasers has led to some exciting new applications. The introduction of 4 level lasers, which utilise a metastable level of 3, can achieve a population inversion far more easily between levels 3 and 2 than any other previous iterations. This, combined with increased research into the more effective cores which require less energy for pumping, has led to weapons such as the XN-1 LaWS. This is a prime example of a concept which was initially met with a lot of interest, but the technology was not initially there. But years of commercial development in other areas has brought down the overall cost, allowing for some exceptional uses.

The XN-1 is so effective as it only requires electricity to use. No storage, manufacture or transportation of projectiles are required for its use. And its range of uses, from disabling motors of motorboats, to exploding missiles mid-air, show how truly versatile it is. Focusing more on its anti-air capabilities, outlined by the US Defence Journal it is able to take down “a range of UAV’s”; an expected lack of detail, but with reports from having even had success after testing against helicopters. Its range is again classified, but its maximum operating power is 30kW, which is ridiculously cheap to run compared to the missiles that cost tens of thousands of pounds per use. Its ability and strength however are not withheld, being able to burn through necessary amounts to disable its targets within 2 seconds. However, the main benefit of these laser weapons is its targeting, precision, and speed of use. The system can track and shoot at, quite literally, the speed of light, allowing for immediate response. It can track multiple targets at once, allowing for an instantaneous transfer of target when there are multiple threats. Its accuracy is obviously currently unmatched, even being able to take out motors from drones, and with videos showing it taking down rocket propelled grenades mid-flight.

Despite the large development cost of $40 million, this is only roughly 0.00005% of our Government’s annual budget. In addition, these laser defence weapons are expected to become even more common as they are developed further and prices continue to fall. Our proposition is that these are used by airports or other equally important, large and vulnerable pieces of infrastructure, at a rate of roughly one per airport, depending on range. This would allow complete protection of the surrounding airspace, which can all be done automatically without any required human input.

Figure 2.5: Real peak changed position, and new peak is moved, it is now

representing the false location of the

Figure 3.1: XMTR represents the transmitter i.e. the operator transmitting the desired signal for the UAV

(RCVR). The jammer also transmits a signal to the UAV to confuse it.

Figure 4.1: XN-1 LaWS on a US navy ship

Limitations: - There is a potential for the laser causing any explosives on the UAV to detonate, if the laser hits the UAV in the right

place. Despite the precision of the laser making this unlikely, the laser must be configured so that it shoots its beam directly at a fatal point on the engine or in the operating system, incapacitating the UAV.

- Collateral damage is potential; however the beam’s precision makes this highly unlikely.

Solution 5 – Physical confrontation

a) Birds: Police departments across the Netherlands are using teams of eagles to take down rogue small UAVs, and they are no match for eagles. Eagles have very sharp talons which can destroy an operating system or a motor inside a UAV, either preventing it from understanding and carrying out instructions or from flying at all. The talons combined with the sharp eyesight allow the eagles to very swiftly take down a UAV. Hawks also have the skills required to eliminate any threat posed. Both birds come away unharmed from the impact most of the time.

Limitations:- The birds need to be trained sufficiently to carry out very specific instructions as

soon as they are released, and carry the UAV away instantly.- If the UAV contains explosives, it may detonate in the air, killing the bird and causing damage to the surrounding area.- There are maintenance costs to keep care of the birds- Even though they are trained, the birds can potentially be distracted by their surroundings and not concentrate on

taking down a dangerous UAV.- If there were multiple simultaneous intrusions, multiple birds would be required to eliminate all threats simultaneously

b) Nets: Having detected and tracked an intruding UAV, one could send out a UAV of their own with a large net attached, as police in Tokyo have done.5 Simply fly the net towards the target UAV and it becomes tangled up and unable to move.

A different way would be to have the personal UAV shoot a net out of the front, similar to the commercially available product called DroneCatcher developed by Delft Dynamics6. Their product can fly up to 20 metres per second and can shoot its net up to 20 metres. It is able to lock onto a target and shoot the net at it, the captured UAV then falls out the sky with a parachute. A potential modification to this would be to have the net attached to the personal UAV, so it is able to fly the captured UAV away.

A more effective way would be to have multiple UAVs all connected to the same net and wrap it around the intruding UAV, so there is no chance of it disconnecting from the net.

Limitations:- The target UAV could fly away making it difficult to catch.- The net could miss, and the UAV(s) would be wasted and would depend on

back-up of other similar UAVs to attempt the same thing.- The personal UAV(s) would either need a skilled operator or a sophisticated

set of instructions, especially if using multiple UAVs connected to the same net

- Again, if there were multiple simultaneous intrusions, multiple UAVs would be required to eliminate all threats simultaneously

Catching the UAV in freefall

Several of our ideas may result in the UAV falling having been separated from its operator. If the UAV had explosives on it, they may detonate on impact, and we would be doing the intruder’s work for them. It is therefore indispensable to prevent this and transport the UAV away from the location before either disarming the explosives or detonating them in a safe environment

If other solutions have been used to disable the UAV, then birds or a net would be able to stop it hitting the ground in the same way as they’d take down the UAV in solution 5. In addition, the multiple-UAV arrangement suggested in solution 5 could form a circular arrangement with the net in the middle underneath the disarmed UAV to catch it.

5 https://www.digitaltrends.com/cool-tech/watch-japans-bizarre-net-wielding-police-drone-in-action/6 https://dronecatcher.nl/#Applications

Figure 5.1: Eagle taking down a UAV

Figure 5.2: UAV with net attached capturing a threatening UAV

Limitations:- There is a chance the bird or net miss the UAV as they do not have machine accuracy.- The UAV may explode on impact with a fast travelling bird or net.- The UAV would take no more than 10 seconds to hit the ground from freefall, so birds or UAVs with nets would need to

be stationed all around the location to get to the UAV as quickly as possible.

ConclusionsCost ought not to be a consideration to our national security, keeping the infrastructure of the UK safe is absolutely paramount, therefore although economic viability is important, we shouldn’t disregard a more expensive solution. Because if tragically we have a type 3 intrusion, the cost of recovering after whatever events occur will be enormous.

The first layer of defence should be legislation to prevent types 1 and 2, and then using lasers is the most effective way to prevent a successful type 3 intrusion, followed by a pickup by either a bird or a net attached to a UAV(s). While hijacking and jamming are both potentially viable methods which wouldn’t result in a freefalling UAV, malign sophisticated operators may become aware of the jammer’s or hijacker’s existence, and it is likely that they can design the communications around them. Physical confrontation is effective but relying on a bird or another UAV to chase after a UAV is risky and time-consuming, as the UAV may be particularly small, fast and agile and may be able to manoeuvre. Time is precious when facing a type 3 intrusion, and so the safest and most clinical takedown is necessary.

Image sources:Figure 1.1 - http://www.bbc.com/future/story/20161208-how-is-is-using-consumer-dronesFigure 1.2 - https://www.youtube.com/watch?v=KyfPaUuYZhYFigure 1.3 - https://www.researchgate.net/figure/UAV-mounted-passive-radar-for-intruder-drone-detection-top-during-public-events-hovering_fig3_326319840Figure 2.1,2,3,4,5 - https://www.youtube.com/watch?v=6qQXVUze8oEFigure 3.1 - https://www.globalspec.com/reference/66146/203279/2-4-electronic-attackFigure 4.1 - https://en.wikipedia.org/wiki/AN/SEQ-3_Laser_Weapon_SystemFigure 5.1 - https://www.peplnews.net/eagles-take-drones/Figure 5.2 - https://www.telegraph.co.uk/technology/2016/01/21/tokyo-police-are-using-drones-with-nets-to-catch-other-drones/