The Unmanned Aerial System (UAS) is as much an attackers’ delight as it is a defenders’ nightmare. In that, while the attackers are celebrating many a virtues of the unmanned phenomenon (long range, tremendous endurance, precision kill, all weather all-terrain employability and above all teaming with manned aircrafts in joint operations and more), the defenders are at their wits in finding new and innovative ways of bringing down the unmanned machines. The most prominent talk in the defenders’ domain is that of the growing imbalance between the total cost of a UAS vis-à-vis the cost of the SAM, manned or ground based kill system that may be deployed to kill it. Since the latter is far-far higher than the former, the major concern today is to reduce the cost of killing the UAS by using innovative technologies, preferably in the soft-kill mode.

Challenges Galore in the Path of Bringing Down a UAS

Bringing down a UAS throws up multiple challenges. The first of all is the detection challenge defined by low radar cross section (RCS), small size, low acoustic signature and low IR signature of the UAS. Though Predator or Reaper type of UAS flying at about 100 miles per hour at low altitudes may be a child’s play to shoot down for a manned jet fighter, however, if a drone flies higher, it will pose problem for electronic detection due to its lower RCS. For example, the Predator is undetectable beyond 3000 feet and inaudible beyond 1000 feet. The smaller drones have their survivability (implied high degree of difficulty in detection) built into their miniature sizes or stealthy features. Both these manifest as low RCS signature.

What is being Done in the Defenders' Camp?

Defenders are busy researching new and innovative methods to detect small UAS. Cutting edge research has shown that phased array radar technology coupled with the tremendous growth in radar computing and processing power has the capability to pick up small maneuverable UAS using the technique of electronic beam switching. UAS possess lower speeds in comparison to aircraft which aids in radar detection. In this scenario pulse doppler radars with MTI facility prove to be quite effective. The optimal frequency bands include S band, X band or a combined S/X band. For detection of small, un-cooperative, low RCS targets in high clutter environment, like the unmanned systems, the trend is to go for higher speeds of scanning incorporating multiple solutions on the same platform, viz, pure RF/Radar solution, electro-optical solution or even visual warning, as the last resort¹.

Another vulnerability of UAS based on its electro-magnetic uplink and downlink is being used by passive sensors to perform the function of alerting and cueing. Equipment in this category include IR alerters and ESM acoustic alerters. A typical passive IR detection system based on IR is a two tier system to include a wide-area, panoramic search sensor platform with passive IR sensors and a tracking and verifying sensor platform with a high resolution IR sensor and a Laser Range Finder (LRF). Once a tentative track is established by wide-area search sensors, the verification sensor’s line of sight is directed instantaneously to the track co-ordinates indicated by the search sensors with the help of rapidly steerable mirror gimbals. A closed-loop control using the viewer’s IR image, links the LRF’s line of sight on to the target for precise laser ranging. The target in range velocity is determined by means of computed range measurement. Such silent mode air surveillance systems are normally employed in conjunction with other active systems which aim to have the incoming threat on a closing-in-track with the silent passive system focused on the end game. IR sensor based detection systems are also ideal for areas in the ‘radar shadow’ or as a gap-filler in certain geographical areas².

A number of ESM based solutions are also useful in detecting the UASs through recognition of their RF/EM signatures. Though the ESM based sensors have been around since World War II, a host of new technologies have entered this field to improve the probability and accuracy of detection. The traditional frequency range is between 1-2GHz to18GHz. Some technologies being put to use include ‘Instantaneous Frequency Measurement’ and higher speeds in sampling and digital processing of signals³. Acoustic sensors have the advantage of not being restricted to the line-of-sight operations. Besides, these can have all weather operational capability. They can also deploy search-while-track capability and can provide useful track information about UAS. Unlike their electro-magnetic or electro-optic counterparts, acoustic sensors are capable of searching all frequencies and all angles allowing for a wide open range capability. Heat and electromagnetic radiation seeking sensors are easily fooled through countermeasure like dispensing flares or jamming, while to avoid an acoustic sensor, the aerial vehicle must hide its acoustic signature. This is not easy, as many a UAS cannot operate without generating a certain (albeit low) acoustic signature. Acoustic sensors have the further advantage of operation in cloudy or overcast battle environments undeterred by smoke blanketing. On the flip side, such sensors however do not have enormous long range capability. Besides, these are also affected by atmospheric conditions. The presence of mean temperature profiles can cause sound waves to refract, thus reducing the effectiveness of such sensors⁴ .

The Kill Game.

Once detected, the UAS are a soft target for conventional hard kill systems. Conventional fair weather/all weather VSHORAD (Very Short Range Air Defence) systems consisting of guns and man-portable/short range SAMs, (such as Star Streak, Igla 1M, Strela 10M, OSA-AK, etc.) which have the capability to kill a UAS, provided it has been detected, either visually or electronically, by their surveillance/tracking/missiles guidance radars.

During the Kosovo War, machine gun fire from helicopters was effectively used to shoot down UAS in the visual domain. Yugoslav forces also brought down a few Pioneer UAS using ground based fire. In the context of UAS kills, the experts, however, count gains vs losses in terms of the number of ‘pilots’ lives saved’ and the ‘cost of doing business’⁵. In yet another kill option, defender's UAS can be pitched against adversary’s UAS in a kinetic-kill mode wherein, a mini/micro UAS can be used to hit the target UAS. The challenges of initial acquisition, tracking and providing continued guidance to own UAS need to be surmounted. Active seeker, fire and forget, laser designation, riding on the guidance beam of a mother system and more, are options under active implementation.

Besides the VSHORAD system, designers of several Short Range SAMs (SRSAMs) have claimed that their weapon systems are capable to take on the UAS. The Israeli IAI industries claim that their Barak SRSAM, is capable to take on UAS besides aircraft and anti-ship missiles. While Barak-1 has an operational range of 10-12 kilometers, its higher versions (Barak 8) goes up to longer ranges of 70/100/120 kilometers. Similarly, the Spyder (Surface to Air Python and Derby) anti-aircraft missile system developed by M/s Rafael of Israel is also claimed to be effective against unmanned systems.

Open media also reports about engagement of UASs using manned aircraft. In one such event, a manned US aircraft was launched to pro-actively kill a Reaper UAS over Afghanistan when its ground control station lost control over the drone⁶. There is a report of Israeli manned aircraft shooting down a UAS by using an Air to Air Missile (AAM). The UAS was alleged to be an Iranian UAS, launched from Lebanon and tasked to carry out reconnaissance deep inside Israeli airspace⁷. Iran probably used its SU-25 fighter jets to fire on a US Predator UAS in November 2012⁸.

While the hard kill options for the UAS using SAM system or worse, the manned aircraft, may appear to be straight, it is obviously badly out of balance in terms of cost consideration between the arsenal being used and the target being addressed. Besides, such hard kill measures can address individual targets or at best, a few; what about Swarms? For these threats, such options may neither be viable, nor effective. The most potent option to take on a UAS is the soft-kill option. This kill method is anchored on debilitating the real-time data link between the UAS and its Ground Control Station. The UAS’s ground-to-air or air-to-ground data link signal to its GCS can either be jammed (which in all probability may result in UAS abandoning its mission and returning to base) or be hacked and exploited, in which case, the UAS’s control can be taken over from the adversary and made compliant to the defenders’ commands.

In the above context, Iran claimed that its Electronic Warfare unit downed a US RQ 170 Sentinel UAS that had violated Iranian airspace. The photographs of the downed UAS show the aircraft relatively un-damaged except for minor damage on its left wing. This ruled out the possibility of a crash/engine/navigational malfunction. Experts feel that either it was a cyber/ electronic warfare attack system (indicating a soft kill) that brought the system down or it was a glitch in the command and control system⁹. Essentially, the soft killing of UAS involves attacking its communication links. Normally, UAS use a line of sight radio link in the Military C band 500-1000 MHz or satellite communication in the KU band between10.95-14.5 GHz (uplink band to satellite is normally13.75-14.5GHz and the down-link from the satellite is normally10.95-12.75 GHz). If the UAS’s communications to its GCS are jammed then the GCS operator becomes blind and the UAS flies around till it crashes or is out of fuel. In order to block the safe return route of UAS to GCS, both the above communication links must be jammed¹⁰.

There was a report in the open media from the Russian aircraft industry site, Aura Port, that efforts are on to incorporate ELINT based UAS killing capability in Ground Based Short Range AD Weapon System. For this, the existing radars of the Ground Based AD Weapon Systems (GBADWS) are being revamped with ELINT stations along with opto-electronic sensors, thus making such weapons capable of detecting the EM signature of the UAS. The soft kill is achieved by jamming the communication data links of the UAS. There are also reports of Britain developing Directed Energy (DE) weapon package applicable for use against UAS. The kill energy was to be derived on the higher power microwave route. Specific details about the weapon system are not known. Laser based killing of UAS is already an established option. Boeing mounted a 1KW laser system on its established Avenger platform and showed its capability to shoot down a handful of small UAS. In the next phase of this weapon system, it installed a10 Kilo Watt solid-state laser on a Higher Energy Laser Mobile Demonstrator to take on various threat representative targets which includes UAS¹¹. M/s Raytheon has already demonstrated its capability wherein, a 50 Kilo Watt solid-state laser had a UAS in flames. The manufacturers are developing a low-cost directed energy laser system to complement the close-in-kinetic energy systems¹². Laser Area Defence Weapon is already a reality. It promises to provide an effective kill solution to short range threats like the rockets, missiles, UAS and such other targets. The kill speed is the speed of light and the magazine is nearly ‘unlimited’.

Kinetic kill vehicles to take on UAS type of threats are old wine. Cougar is a kinetic kill solution manufactured by M/s QinetiQ of UK as a cost effective counter to low cost tactical UAS. In this system, a low cost un-cooled long wave IR seeker is used to acquire the target and guide an interceptor on a collision course. The Cougar interceptor is designed to approach a UAS threat with closing speed that will be sufficient to cause catastrophic structural, damage to the target, giving an observable hard kill. Target UAS’s low signatures in all wavebands necessitates mid-course guidance to place the Cougar interceptor in the collision course from where its on board seeker could acquire and home on to the target. Peregrine Eagle is another air launched decoy/drone system employed as an anti-UAS system in the Kinetic Energy kill domain having a range of 800 miles with a service ceiling of 40,000 feet. It employs high power microwave and is an electronic counter to UAS control.

A Suggested Way Ahead

With such high proliferation of UAS in our immediate neighbourhood, building and refining capabilities to killing them in the combat domain is an operational need whose time has long come. Some thoughts on proceeding forward in our scenario are offered as followed:-

• Our basic premise must remain anchored on achieving cost-effective kill on UAS. Bringing them down using close-in-weapons like the air defence guns, man-portable missiles or more 'inappropriately' using VSHORADS or SRSAMs, or worst by scrambling air defence aircrafts in search-n-shoot missions should remain the last option.
• Going with the flow of realised technology at the cutting edge today, we need to go in for two types of cheap kill solutions, namely, 'hit-to-kill' and laser kill.
• Developing a cheap 'hit-to-kill' system of the type of Peregrine Eagle or Cougar is well within the capability of our defence research organisations with technological and software support from the private industry, where many a start-ups are emerging in the unmanned sector.
• We already possess the capability of having a Basic Pilotless Target Aircraft (BPTA), the missing component is to design a kill vehicle; either strap-on or as a detachable integral, that can be put on a guidance course to the UAS. This guidance package must make use of the existing sensors keeping the kill vehicle as cheap and simple as possible.
• Interaction with the representatives from the Defence Public Sector Undertakings (DPSUs), Private Industry, and the Defence Research and Development Organisation (DRDO) during the recently concluded International Seminar on UAVs on 26-28 Sep 16 reveals that we already have all the tools required. The need is to realise this capability by bringing the sub-set capabilities residing in various domains on one integrating platform.
• The second and parallel direction in which to move simultaneously is to develop the anti UAS Laser kill system. In this field also, the excellent work already at hand (details not covered) must be taken further and must get amalgamated with the nascent players offering technological capability in the field of Lasers.
• In the above context, it is relevant to bring out, that the cutting edge technology today is already addressing the following erstwhile challenges in the domain of laser kill weapons:-
1. Capability to aggregate the power of a number of laser sources at the point of impact so as to generate the kill beam of sufficient intensity.
2. Capability to auto-focus multiple beams from co-located sources at a single chosen point of impact (target) in near real time through an 'auto cue-on' arrangement.
3. Use of optics (gimbaled mirrors/reflectors and more) on board aerial kill vehicles to reflect multiple laser beams aggregated from different sources at earth as a strong 'cumulated kill beam' (unlimited magazine) on the target UAS.
• The research in the field of charged particle beam and high power microwave must be kept alive as these fields may offer alternate kill means for the UAS.
• Certain old and vintage radars which cover such bands (low E/F of VHF) which are optimal for UAS detection must be kept in use as long as feasible
• And lastly, why kill the UAS when the following can be easily done:-
1. Make the UAS stream the audio/video data not only to its Ground control Station (GCS) but also to the hacker station.
2. Make the UAS send deliberately wrong data to its operator.
3. Confuse the UAS with false GPS information, waylay it or direct it in wrong direction. Just hijack it.
4. Take command of the UAS and make it fly to your wish/ make it crash/ use it like a guided missile. (remote hijacking)
5. Covertly extract valuable seed data from the built-in threat library of the UAS and use it to your advantage.
• There is a whole bad world of hacking and phishing which need to be followed up with exclusive discussions to elaborate as to how the dull, dirty and dangerous can be tamed to submission.

Endnotes

1. http://www.detect-inc.com/security/html/applied-radar-technologies.
2. http://www.zmnl.her/tanzekek/etic/konferencia/april 2001/prokob.html/surveillance of - UASs.
3. Ftb.rta.nato.int/public/publicfulltext/RTO/MP/RTO/esm-sensor-for-technical-information-in-air-defence systems.
4. http://www.ieeexplore.ieee.or/ie!5/4803720/4806498/04806528.pdf/low-cost-acoustic-array-function-small-UAS-detection and tracking.
5. http://www.internet data.info/…/UAS-decoy-strategies-theories-and-the-modern-art-of-war.
6. http:/www.popsei.com/when-drones-go-wild-airfoce-shoots-them-down.
7. http:/www.state.com/Israel-shoot-down-drone-that.may-have-been-made-by-Iran.
8. http://www.guadian.co.UK>Glen Green World on security and liberty.
9. Dave Mazumdar, “Iran Captured RQ 170: How Bad is the Damage?” http://www.en.wikipedia.org/wiki.
10. http:/www.howtokillUAS.
11. http:/www.news.c net.com>news>cutting edge>boeing-trucks-ahead-with-8-wheeling-laser-weapon.
12. http:/www.raytheon.com/newsroom/feature/stellant groups /laser-area-defence-system.

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Published Date: 18^th October 2016, Image Source: http://www.airforce-technology.com
(Disclaimer: The views and opinions expressed in this article are those of the author and do not necessarily reflect the official policy or position of the Vivekananda International Foundation)