While the Counter-Unmanned Aerial Systems developers steadily increase in numbers and expertise, it can be the detection of low, slow and small UAVs that poses the biggest challenge.
One of the main contributors to today’s ever more congested and contested battlespace is the proliferation of unmanned aerial systems (UAS). Once the preserve of large and sophisticated military forces, and deployed and controlled by higher command echelons, the development of smaller, cheaper, tactical systems means that they can now be deployed at platoon or even squad level. These systems are already being deployed, making life more difficult on the frontline in Ukraine by dropping everything from grenades to small bomblets, for example, having previously seen use against Armenian forces in the Nagorno-Karabakh War.
In this issue’s Unmanned Systems listings, more than 90 unmanned aerial vehicles (UAVs) have been included, ranging from man-portable systems with an endurance measured in minutes to aircraft-like, long endurance systems with continental range. And with the rapid development of new systems, and the increasing use of hastily-modified commercial drone systems, the listed aircraft represent the tip of an ever-growing iceberg.
At the top end of the UAV ‘food chain’ many systems can directly deliver effect, attacking targets and launching their own weapons, or on a smaller scale being fitted with a warhead themselves and being used as ‘suicide drones’ (such as the Iranian-made HESA Shahed 136 being used by Russia against Ukraine).
But even where an unmanned system does not represent a direct lethal threat, it cannot be ignored, as it can provide an enemy with vital intelligence and may be used to cue enemy artillery or an air attack.
In some environments, the mere presence of a drone may represent a threat – unauthorised civilian drone use may present a safety risk in airport/air base environments, because of the risk of collision between manned aircraft and the UAS. A drone incursion at London’s Gatwick airport in December 2018 effectively closed the airport for three days disrupting 1,000 flights and more than 140,000 passengers and cost the airport $1.7 million (£1.4 million), with airlines losing even more (an estimated $65m). More recently Gatwick was closed again for nearly one hour on 14 May due to suspected drone activity. Because this latter kind of threat affects commercial airports in peacetime, it has led to the development of dedicated counter-UAS systems that may also have military applications.
Tactical UAS systems offer particular challenges. Group 1 and 2 systems weighing less than 121 pounds (55 kilograms) and operating at 3,500 feet (1,066 metres) or less above ground level, are large enough to represent a lethal threat, while being able to operate from dispersed locations, close to the front line, often well hidden by the clutter of the battlefield and difficult for traditional air defence systems and forward ground-based air defences (GBAD) to detect and counter. These defences could also be otherwise engaged, committed to protecting particular critical or high value assets. And they often will be unavailable, as there will seldom be sufficient air defence assets available to protect every potential target.
In Ukraine, it is now recognised that there is always a possibility that a UAS could be watching every move, and this is a constant concern and a psychological burden.
Group 1 and 2 UASs are difficult to detect in the first place, with vertical take-off and landing (VTOL) systems able to operate from restricted and inconspicuous sites, without needing a separate launcher in a large open area and then following an unpredictable flight path. There are now a number of hybrid designs which can take off vertically, but which have fixed wings allowing higher air speeds and longer range.
Serious effort and investment is now being made in the field of Counter-UAS (C-UAS) research and development. In FY2023, for example, the US Department of Defense (DoD) plans to spend at least $668 million on research, and a further US $78 million on C-UAS procurement.
Knowing What’s There
The first step in countering a UAS lies in detecting, identifying and tracking it! This may be far from straightforward, as smaller tactical UAS systems may have only a relatively short mission duration, during which they may represent a very low signature target. Consequently, many smaller UASs cannot be detected by traditional air defence systems due to their size, construction, and flight profile and altitude. Consequently, great attention is being paid to the development of effective detection, tracking and identification sensors, techniques and processes.
There are a range of sensors available that can detect tactical UAS targets, including radar, electro-optical (EO), infrared (IR), acoustic and radiofrequency (RF) sensors, though their small size and limited signature can make them hard to detect, and a combination of sensors can be useful, particularly if fused.
Doppler radars can be well suited to detecting a UAS since they detect speed differences and are thereby able to detect and track moving objects while ignoring or discarding static objects. The Dutch Robin EVIRA, a Frequency Modulated Continuous Wave (FMCW) radar, is a mini-doppler radar that offers accurate and fast tracking with a quick update rate, making it a good choice for finding and tracking small agile targets.
Danish company Weibel Scientific, a specialist radar company with decades of research has developed its Multi-Frequency Surveillance Radar XENTA-series, based on Continuous Wave (CW), Frequency Modulated CW (FMCW) and Multi-Frequency CW (MFCW) 3D Air Surveillance and Tracking Radar technology. This dual capability technology has been particularly developed for Short Range Air Defence (SHORAD) requirements, in addition to a lighter version primarily applied for detecting, tracking and classifying Low, Slow and Small (LSS) targets within the C-UAS threat band.
The XENTA-C radars have the ability to distinguish hovering drones from ground clutter through the detection of micro-Doppler generated by the rotors of the drone, allowing drone detection even when just hovering in the air.
Small AESA (active electronically scanned array) radar systems can also be most effective, with the Ascent Vision RADA Multi-mission Hemispherical Radar (MHR) providing a good example of the kind of compact and energy-efficient technology available for detecting small UASs out to a range of 3-4 miles (5-6.5 kilometres). The latest version, the ieMHR from DRS RADA Technologies offers users offers enhanced SWaP-C and On-The-Move operation capabilities.
Optical and electro-optical systems are frequently used in C-UAS systems, including high resolution colour and heat sensing infra-red cameras. Their use is most frequently for providing positive identification, rather than initial target detection. Optical sighting systems are also frequently used for tracking and for aiming whatever weapon is used to engage the UAS target.
Infra-red Search and Track (IRST) can provide continuous scanning to detect targets from their thermal emissions. They can be useful for search and surveillance, and even for target recognition and identification if a target’s heat-signature is sufficiently distinctive. The HBH Infrared Systems Spynel-X series of IRSTs has already demonstrated its usefulness for perimeter surveillance. IRSTs are fully passive and are often quite compact, and may be useful against a wide range of threats.
Acoustic sensors, already in use in vehicle-mounted ‘shot’ and gunfire detection systems have shown some ability to detect the presence and even the bearing of a UAS by its sound signature. When networked, these systems can provide accurate geolocation through triangulation of the detected sound signature. When used in conjunction with a digital threat library acoustic signature may even be used to identify the specific type of UAS target, giving the operator an idea of threat capabilities and helping with target prioritisation and the selection of the most appropriate countermeasures.
RF (radio frequency) sensors can be used to identify the wireless signals used to control the UAS, using triangulation to accurately geolocate the threat system, and perhaps even its control station. This can allow the control site to be engaged by direct or indirect fires, or even to facilitate the physical capture of the enemy operator and his equipment.
By combining several sensor types, a more effective, layered detection capability can be leveraged, maximising the chances of defeating the threat in the shortest possible time.
Having detected and located a UAS target, the next step is to stop it achieving its mission goals. This can entail physically destroying the drone, or simply preventing it from completing its mission. Both of these approaches are referred to as ‘interdiction’.
One of the ways in which a UAS can be ‘interdicted’ is by jamming – using transmitted electronic energy to disrupt, interrupt or entirely block the communications and control links with its operator, or by interfering with the GNSS/GPS signals on which it relies to navigate. This may cause the drone to crash, or to enter a ‘loss of contact’ procedure – perhaps simply landing, or perhaps returning to its launch point. Jamming devices can be light enough to be man-portable but are more usually heavier, and limited to use in fixed locations or mounted on vehicles. Some drones may even be disrupted by ‘dazzling’, especially by using laser energy, effectively blinding them or their sensors.
Alternatively, and arguably more subtly, a UAS may be ‘spoofed’, with the spoofer taking over the UAS’s communications link and sending a false GPS signal that mimics a legitimate signal, duping the onboard GPS receiver.
Jamming or spoofing has the advantage of being effective against difficult targets, including multi-direction swarm attacks, and against manually controlled drones.
Sometimes, though, it may be necessary or desirable to achieve a ‘Hard Kill’, physically destroying the drone, or capturing it. UASs can be neutralised or destroyed using guns, including by traditional air defence (anti-aircraft artillery) systems. There have even been C-UAS systems based on the use of nets to capture drones in flight, or interceptor drones designed to collide with the target system.
Alternatively, directed energy weapons, including laser or high-powered microwave systems might be employed. High Power Microwave (HPM) Devices are a high cost/high impact technology and use an intense microwave beam sufficiently powerful to destroy a small drone within seconds. They can target either individual drones or even swarms of autonomous drones because they employ a wide beam effective over a wide area. One high-power microwave experiments, the Tactical High Power Microwave Operational Responder (THOR), is being developed by the US Army and US Air Force, to disable swarms of small drones. It is already undergoing testing, with several prototype Leonidas systems built by Epirus.
Often, a coordinated combination of systems will be used to achieve a full spectrum C-UAS solution, operating as a system of systems, and including fixed sites, mobile and man-portable systems.
Perhaps unsurprisingly, the US armed forces are at the forefront of Counter-UAS efforts. In December 2019, the US Department of Defense (DoD) named the Army as the executive agent tasked with overseeing the Department’s various counter-small UAS (C-sUAS) programmes and developmental. The implementation of a new office, known as the Joint C-sUAS Office, was approved by the Secretary of Defense on 6 January 2020. The DoD also plans to establish a Joint C-sUAS academy at Fort Sill, Oklahoma by FY2024. This academy will be tasked with synchronising training in counter-drone tactics across all of America’s military services.
Up to now, US C-UAS efforts had been piecemeal and largely undertaken by the individual services. The Navy fielded the world’s first operational directed-energy weapon, the 30-kilowatt Laser Weapon System (LaWS), aboard the USS Ponce (LPD-15) in 2014. The US Navy also deployed an optical dazzler, Odin, designed to interfere with UAS sensors, and later Helios, a 60-kilowatt laser, aboard the USS Preble (DDG-88) in 2021.
In 2019, the US Marine Corps completed testing of the Marine Air Defense Integrated System (MADIS), mounted on the 4×4 Joint Light Tactical Vehicle (JLTV). There are two MADIS variants, the Mk 1 employing a combination of turret-launched Stinger missiles, a direct-fire weapon (a 30-mm cannon) on a remote weapons station, multi-function electronic warfare capability with an SNC Modi II system, and a Lockheed Martin Electro Optical/Infra-Red (EO/IR) turret. The MADIS Mk 2 is optimised for the C-UAS role, and adds a 360° RADA RPS-42 radar and C2 suite, but lacks Stinger and uses a six-barreled 7.62-mm M134 Minigun, as its direct fire weapon. The Marine corps also fields the Light MADIS (LMADIS) on Polaris MRZR all-terrain vehicles. These have the same radar and EW suite and served as a testbed and interim C-UAS solution before the fielding of the full standard MADIS Mk1 and Mk2.
As part of its suite of GBAD systems, the US Marine Corps is now procuring the first DoD-approved ground-based laser, the so-called Compact Laser Weapons System (CLaWS), available in 2-, 5-, and 10-kilowatt variants and built by Boeing. CLaWS is a vehicle-mounted laser designed to disable or shoot down small unmanned aerial systems, mounted on the new Joint Light Tactical Vehicle. The CLaWS laser is designed to burn off parts of the drone’s body or ignite its onboard fuel supply or explosive warhead, “like applying a blowtorch to a drone,” according to one Boeing engineer and taking just 15 seconds for the laser to down a flying target.
The Air Force is heavily involved in a “directed energy experimentation campaign,” with a Directed Energy Combined Test Force (DE-CTF) inaugurated at Kirtland AFB in New Mexico in 2018. In October 2019, the Air Force received delivery of a vehicle mounted High-Energy Laser Weapon System (HELWS) C-UAS prototype which then underwent a year-long overseas field test. When connected to a generator HELWS can produce “a nearly infinite number of shots” and the system is now certified for use in combat. Multiple additional systems have now been deployed.
Raytheon Intelligence & Space (RI&S) has conducted a capability demonstration HELWS at White Sands, destroying nine Group 1 and Group 2 drones in the live-fire exercise, during which the system was paired with the National Advanced Surface-to-Air Missile System (NASAMS) for firing cues. The USAF is now testing HELWS2 (High Energy Laser Weapon System 2).
While vehicle-mounted systems are now being deployed, man-portable C-UAS technologies have proved problematic. Commandant of the Marine Corps David Berger testified to Congress that they “have not panned out” due to weight and power requirements.
For future threats, the Defense Advanced Research Projects Agency (DARPA) is funding a host of C-UAS technology development programmes intended to develop systems for defeating autonomous systems of the future, including CounterSwarmAI.
by Jon Lake
