Eyes and ears for drones.
To some people--notably 'the-man-in-the-street'--such robot aircraft are 'new concepts', but the reality is that recce drones have been around since the 1960s. As technology has provided better performance and reliability plus a reduction in size and weight of the systems, their use has been expanded and accelerated. From pure reconnaissance, the recce drone has been brought into an enlarged portfolio embracing intelligence, surveillance, target acquisition and reconnaissance; now often referred to as istar.
Recce drones have come a long way since the BQM-34 Firebee and BQM-74 Chukar target drones were adapted to carry cameras and air-launched from a modified C-130 Hercules over Vietnam in the mid-1960s. Their initial raison d'etre was to take recce photographs. While this is still the case for today's aircraft, onboard electronics miniaturisation also enables them to be used for other types of intelligence-gathering missions and as a countermeasures platform. They have even been adapted to perform as weapons carriers--the Unmanned Combat Air Vehicle (Ucav) role--although that is outside the scope of this feature.
Eyes in the Sky
The original camera systems carried to snoop on the enemy were traditional 'wet film' cameras (as still was the case of the CL 289 in Kosovo, for example). This meant that the drones had to be used in good weather to take their pictures, then recovered to a base, the film processed and analysed and the results relayed to the command authority. The process was, to all intents and purposes, a parallel of the manned recce aircraft mission.
Today, wet film has all but vanished, and electro-optical sensors (digital photography) have taken its place, recording the images on videotape and digital videodisks. Also, by using low-light charge-coupled device cameras, thermal imagers, infrared sensors and full-up flir systems, their images can be taken by day and night and in inclement weather conditions. Additionally, their digital format allows images to be relayed to the ground by datalink, where all the tricks of computer-aided image enhancement can be applied. Thus the gap between 'discovery' and 'destruction' (sensor to shooter time) is much reduced and drones have emerged from being purely tactical systems to strategic ones.
While some of these sensors are mounted in fixed directions on the airframe, many drones have them installed in gimballed turrets, allowing 360[degrees] coverage in azimuth and at least 900[degrees] in elevation. Such turrets were initially developed for helicopter use and have been adapted for drone applications.
Many turrets were, initially, fitted with one prime sensor but as sensor technology improved in sensitivity and reduced in size and weight it became possible to pack more sensors into each size of turret.
A typical example of a single-sensor turret would be the original Wescam (now L-3 Wescam) Model 12, which could be fitted with a daylight colour TV camera, a low-light TV camera or a thermal imager. Such systems equipped early models of the Bombardier CL-227 and General Atomics Gnat 750. A dual sensor version--the Model 12DS--was introduced in 1996 especially for drone applications. A lightweight (20.9 kg) turret featured a four-axis, actively gyro-stabilised gimbal which carried a colour charge-coupled device daylight camera (with a x20 zoom lens) and a three to five-degree indium antimonide (InSb) high resolution (256 x 256-pixel) staring array thermal imager. This was ordered for the upgraded RQ-2B Pioneer.
As mission requirements became more complex, the additional sensors being packaged into these turrets included laser rangefinders, designators, laser (spot) trackers, laser illuminators and laser pointers. Such additions allowed more complex information to be gathered, as the drone could be used to designate targets for smart munitions deployed from a number of ground-based or airborne platforms.
Wescam's follow-on to the Model 12, the Model 14, is available in three versions: 14TS (tri-sensor), 14QS (quad-sensor) and 14PS (penta-sensor). The 14TS (selected for the RQ-1 Predator) features a Sony XC-999 daylight TV camera with a x10 zoom lens, a second XC-99 with a 955 mm long-range spotter scope and a five-position three to five-[mu] PtSi multi field-of-view (FoV) thermal imager. The 14QS adds either a 1.06-[micro] Nd:YAG LRF/D or an eye-safe, 1.54-[micro], erbium glass type laser rangefinder. The 14PS brings a fifth sensor to the ensemble--a diode laser illuminator, operating at a pulse repetition rate of four to five per second and a beam power of 800 mW.
It is interesting to note that since July 2004, one of these sensor turrets--Elop's Compass mounted on a Silver Arrow Hermes 450--has been used by the US Department of Homeland Security's Customs and Border Protection group to provide surveillance of the Arizona-Mexico border.
The Mosp family from the Tamam division of Israel Aircraft Industries has been produced for the IAI/Northrop Grumman RQ-5 Hunter, IAI Searcher/ Heron, Ruag Ranger and Silver Arrow Hermes 450. The same company's Plug-in Optronic Payload is the primary sensor equipment on the AAI RQ-7 Shadow 200 surveillance drone.
While some companies just package and integrate other company's sensors (especially where a multi-sensor package is produced) others actually manufacture their own thermal sensors, integrating only the TV camera and laser products. Israel's Moked family of turret payloads, originally developed by Tadiran but acquired by IAI Tamam in 1996, is an example of the former group. The Moked 200 (with an Ashei 525-line TV camera) was used on the IAI Mastiff Mk III, while the Moked 400 with a day/night infrared seeker saw service on IAI/AAI RQ-2A Pioneer during Operation 'Desert Storm in 1991. The latest model, the Moked 2000, is more compact, carrying either a flir (with a three to five-[mu] focal plane array or eight to twelve-[mu] parallel scan model) or a CCD TV camera (0.4 to 0.75-[micro] bandwidth with a x16 zoom).
Flir Systems, on the other hand, is an example of the latter type of company; its Ultra 8500 multi-sensor surveillance system in a fully sealed turret with a 229 mm gimbal diameter is its latest drone-based product. The Ultra 8500 comprises a three to five-[mu], 320 X 240-pixel InSb focal plane array thermal imager, charge-coupled device day camera, an autotracker, a continuous zoom facility, three preset fields of view and a Class IIIb diode laser pointer. Other Flir Systems sensor turrets with established helicopter applications, notably the Star Satire III and Brite Star, are being promoted for drone applications.
Among the second-generation thermal imaging cameras adapted for drone use is the Zeiss Optronic Ophelios--initially on the now-cancelled Franco-German Brevel but also reportedly on the Rheinmetall KZO. Using a 7.5 to 10.5-[micro] HgCdTe infrared charge-coupled device detector cooled by a linear or rotary split Stifling engine it scans 576 lines at 768 pixels per line.
Elop of Israel produces a family of lightweight thermal imaging modules featuring a parallel-scanning flir based on an integral CMT detector with focal plane signal processing and a Dear cooling system. One member of this family, the Cotim-B. is particularly suitable for drone use and operates in the eight to twelve-[mu] range.
South Africa's Denel (formerly Kentron) has produced the Kenis imaging infrared camera since 2001. The Kenis is a modular system that is adaptable to customer requirements. Based on a three to five-[mu], 288 X 384-pixel staring array with an integral Stirling cooler, it has a x2 zoom and multiple field-of-view lenses with high sensitivity.
Raytheon's AN/AAS-44(V) is a thermal imaging sensor turret for detecting, ranging and tracking lasers to support AGM-114 Hellfire and other laser-guided munitions. Sensor options include near-infrared and colour TV cameras (with a x2 and x4 zoom), laser illuminator and spot tracker. These turrets have been installed in some RQ-1 Predators, but the more recent AN/AAS-52 Multispectral Targeting System (MST), which adds a thermal infrared sensor and laser rangefinder, has begun to replace the AN/AAS-44(V) on the MQ-1 version of the Predator.
While turret mounts may be prevalent, conformal camera systems, such as the Controp Mini-Eye, are also available, usually for the smaller airframes. The Mini-Eye, which is understood to have been test-flown on a Silver Arrow Mini-V drone, comprises a high-resolution colour television camera with a x10 zoom lens, using NTSC or PAL standard video formats in a two-axis gimbal. It offers 1.8[degrees] x 1.3[degrees] or 6 x 13.3[degrees] fields of view.
The Alpha family of infrared cameras was jointly developed by the US Army's Night Vision and Electronic Sensors Division and Indigo Systems (now part of Flir Systems) in 1998. It operates in the 7.5 to 13.5-[micro] waveband, using a 160 x 128-pixel array with an uncooled microbolometer detector (of 51 x 51 microns). It is carried in Schiebel's Camcopter.
The use of radars, including synthetic aperture types, specifically developed for drones is increasing. Typical of a 'conventional' radar modified for drones is the EL/M-2022U from Elta Electronics (a subsidiary of Israel Aircraft Industries--Elta/IAI), which is a re-packaged variant of the multimode radar used for fixed-wing maritime surveillance applications. This is a payload option for the IAI Heron high-altitude drone.
On the synthetic aperture radar front, a joint Thales/Eads-Dornier project known as the Sword (System for all-Weather Observation by Radar on Drone) is intended to upgrade the effectiveness of the CL-289 recce drone which will also have a moving target indication capability. A derivative system--the Awards (All-Weather Airborne Reconnaissance Drone Sensor)--is marketed by Eads-Dornier. It is a high-resolution (1.4 metres for ground range and along track, 10 metres in moving target indicator mode) J-band synthetic aperture radar for use on slow-flying drones operating below 16,400 ft.
Another example of radar comes from Elta/IAI in the form of the EL/M-2055. Understood to use a stabilised, low sidelobe, planar array antenna with coherent transmission, it is said to produce near photographic quality imagery with true all-weather day and night coverage.
The Ericsson Microwave Systems Carabas III (Coherent All Radio Band Sensing) drone is still under development in this mode. It operates in the 20 to 90-MHz range and, due to weak radar backscatter from surrounding vegetation, is seen as ideal for foliage penetration to detect camouflaged targets. The two UHF synthetic aperture antennas would be conformally mounted in the Carabas III twin tail-booms, while a 60 to 90-MHz MTI antenna would be pod-mounted on each wingtip. The Carabas technology has attracted interest in Brazil.
General Atomics produces the AN/APX-8 Lynx Synthetic aperture radar developed by the US Department of Energy's Sandia National Laboratories for the company in 1996, using cots components. It uses an offset-fed dish antenna on a three-axis gimbal in a 483-mm radome, giving a slant range of 30 km. Known applications include the company's MQ/RQ-1 Predator and I-Gnat plus the rotary wing Northrop Grumman RQ-8 Fire Scout.
Northrop Grumman's AN/ZPQ-1 Tesar based on a radar developed for the US Navy's long-cancelled A-12 attack aircraft, is a lightweight high-performance J-band surveillance radar. It equips General Atomics MQ/RQ-1 Predators in US Air Force service and can operate in moving target indicator modes. In strip mode the synthetic aperture radar has a range of 10 to 25 km, while in spot mode range stretches to between 18 and 28 km depending on the altitude.
A scaled-down version of the AN/ZPQ-1 Tesar known as Tuavr (Tactical UAV Radar) is still in development. Two trial systems have been mounted in RQ-5 Hunters, although it is understood that the Tuavr is intended to equip the RQ-7A Shadow 200.
The Electronic Support Measures (ESM) and Electronic Intelligence (elint) gathering scene has seen variants of standard kits being repackaged for drones. This is exemplified by the Elisra AES-210/V derivative designed to detect, identify and locate ground-based and shipborne radar emitters. With frequency coverage in high and low bands operating at altitudes up to 30,000 ft, it can be remotely operated from a ground control station via the host platform's datalink using a Windows NT-based man-machine interface.
Elta/IAI produces an intelligence gathering payload in the form of the EL/L-8385 Iuelis that is able to search for, intercept, measure, locate, analyse, classify and monitor signals from ground-based, airborne and naval radar emitters. The signals are measured and pre-processed onboard the drone before being downlinked.
Also from Israel, Rafael produces the Top-Scan elint system, which is intended to detect, identify and locate ground-based emitters operating in the 0.5 to 18 GHz frequency range.
In South Africa, Avitronics produces an Electronic Surveillance Payload described as being in production and in service on the Kentron (now Denel) Seeker II. The company is also producing an Emitter Location System for drone use. Technical information on both systems is unavailable at this time.
In the United States, L-3 Communications Systems--East is developing a sigint and comint payload for the US Army's tactical RQ-TA Shadow 200. It consists of two high-performance receivers able to detect low-probability-of-intercept communication signals. Missions will be dedicated for either narrow or wideband operations. A multifunction sigint payload with an advanced digital receiver is also being developed.
All Together Now
As drones develop and certain types get larger, we can look forward to more fully integrated sensor suites. It is fitting, therefore, to conclude this review with a look at Raytheon's Integrated Sensor Suite (ISS) for the Northrop Grumman RQ-4A Global Hawk.
Brought into service earlier than planned, the RQ-4 Global Hawk (see title picture) is only just exploring the combinations of payload beyond its initial Integrated Suite System from Raytheon. The Global Hawk's ISS comprises three main elements--an electro-optical system, an infrared unit and a radar. The optical system brings together a 3.7 to 5-[micro] Gen 3 InSb sensor and a Kodak 0.55 to 0.8-[micro] digital CCD day camera. The infrared unit features a staring focal plane array with 480 x 640 detector elements, while the Kodak CCD camera has a silicon staring focal plane array (1024 x 1024 elements) with nine million pixels. It can cover a ten km swath in wide area search mode and in spot collection mode a two sq/km area. The X-band radar provides synthetic aperture imagery with moving target indication capability, is based on the commercial Hisar recce system and is known as the Hisar 2K.
Imagery can be transmitted by datalink in near-real-time over numerous communication paths. The Global Hawk's ISS can cover 138,000 [km.sup.2] in a 24-hour period.
Strangely enough, autopilots seldom get any limelight in drone payload articles. Yet, such packages simply are what makes a preprogrammed drone mission possible as indeed this item enables not only the aircraft to maintain a determined course, but also to stir, alter its altitude and find its way back home.
Certain drone manufacturers, like Mavionics who is developing the Carolo minidrones under the banner of Rheinmetall (see Armada 6/2004, page 31), have designed their own system, which they are offering to the market. In the United States, Cloud Cap Technologies have designed an autopilot known as the Piccolo Plus, which in addition to the obvious piloting tasks, also handles the control of lights, parachute deployment and brakes. Cloud Cap has already delivered over 450 Piccolos that have been, amongst other things, been integrated with the Falcon View and used in the Silver Fox deployment programme.
Other navigation, attitude and sensor system manufacturers include Novatel (Span), O-Navi (Gyrocube), MicroStrain, Athena (GuideStar), MicroPilot.
While this review of the various types of drone payloads must, perforce, be far from comprehensive, it is representative of the spectrum of systems being taken aloft for the various elements of the Isar requirement.
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|Title Annotation:||Drones: electronics|
|Author:||Biass, Eric H.|
|Date:||Feb 1, 2005|
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