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Laser Guidance

Australian Aviation & Defence Review, September, 1981
by Carlo Kopp
© 1981,  2005 Carlo Kopp

Since the earliest days of military aviation its prime objective has been the destruction of targets. Whether we look at the hand grenades of 1914 or 1945's Fat Man and Little Boy, we'll find one important factor they have in common. They were unguided, free-fall weapons, effective primarily due to the nature of their targets. However, modern warfare has brought significant changes to this world. Saturation bombing has lost a lot of its popularity, as it seems nobody feels like maintaining enormous fleets of fuel-guzzling, vulnerable bombers, just as nobody likes the public opinion backlash resulting from dropping a few tonnes of TNT in someone's backyard. As nuking people isn't really the "in" thing in this day and age, it would seem that the only course left to the modern military is to fly their aircraft through swarms of look-down, shoot-down fighters, dodge a great number of SAMs, keep out of the range of radar-guided AAA (flak for the traditional) and drop their bombs on the target.

However, here is where the real problem becomes apparent - hitting the actual target. Consider dropping a free-fall bomb on a small building from an aircraft travelling at 350 knots in level flight. An error in release time of 0.3 seconds will result in your bomb falling something like 60 metres from your target, if we neglect aerodynamic drag, wind velocity and other factors. In reality, you would be hedgehopping in at 500 kts, trying to conceal yourself to the last moment and trying to find a small, camouflaged target, possibly also mobile and hard-skinned. An improvement in bombing accuracy occurred with the appearance of computer-controlled bomb-release systems. The computer, knowing the altitude and velocity of the aircraft, weapon parameters and the position of the target, calculates the release time. The accuracy will depend, though, on a number of factors such as the errors generated by the radio/radar altimeter, airspeed sensors and inertial navigation system or radar, depending on which is used. If the target is stationary and the attacking aircraft doesn't have to zig-zag its way in, this is fine. But given a very hostile battlefield environment, this would hardly be the case.

Manual bomb-aiming cannot live up to the challenge posed by modern aerial warfare, computer-controlled bombing has limited accuracy and applicability.

For a weapon-aiming system to perform effectively in a modern environment, it must satisfy these requirements:

  1. Pinpoint accuracy (CEP-circular error probability of the order of metres) from low-flying, fast aircraft.
  2. Ability to operate at night under conditions of low or zero visibility.
  3. Simplicity, reliability and maintainability, all very obvious considerations.
  4. Ability to transfer targets from aircraft to aircraft or observer to aircraft.
  5. Resistance to jamming or other electronic countermeasures.

Laser weapon guidance fits these conditions very nicely. The development of laser-guided weapons began in the mid-1960s, when the USAF, in conjunction with Texas Instruments, began testing laser-guided bombs. In principle, laser guidance involves the illumination of a target with a laser - the weapon then homes in on the illuminated area, exploding on impact.

A laser weapon system is comprised of two principle elements: a designator and a weapon with a laser homing guidance head. A designator is a laser fitted with optics to aim it and very often fitted with a stabilisation system. Designators can be fitted to practically any vehicle or aircraft, they can be mounted on stands or hand-held. The versatility of laser weapon guidance is obvious - targets can be designated from the air, either by the attacking aircraft itself or by a Forward Air Controller (FAC), or they can be designated by troops on the ground, enabling their air support to knock out difficult targets in a first pass attack.

The Laser

A full understanding of the operating principles of a laser is far beyond the scope of this article, as it requires an understanding of quantum physical theory, however the following should give the reader some insight.

(Above) An RAAF Mirage 1110 fitted with three Texas Instruments GBU-12B / Mk82 laser guided bombs. The RAAF is upgrading it's tactical strike capabilities with the Mirage carrying LGBs and the F-111 C force acquiring the Pave Tack FLIR designator due to become operational in 1984. LGBs are a must for smaller air forces, which would find it simply impossible to reattack targets several times, considering the density of air defences which would be encountered. The Defence Science & Technology Organisation (DSTO) is currently perfecting the design of an airborne laser designator system for the RAAF. Fitted on the centreline station beneath a dual-seat Mirage IIID, the pod utilises a video display unit which acquires the target manually and vectors the LGB onto target via a steering cue operated by a controller in the second cockpit of the Mirage. With a maximum slant range of five kilometres the pod would be particularly useful when attacking large high-value targets such as fortifications, bridges and surface vessels.

In quantum theory, electromagnetic radiation (eg, light, radio waves) assumes not only its wave-like properties, but also behaves in a particle-like manner. Accordingly, light can be described as groups of particles (photons), which travel at the speed of light. The energy of the photons is given by E=hf=hc/lambda , where h is Planck's constant, f is the frequency of the light and lambda is the wavelength of the light (c=velocity of light in free space).

Another important conclusion of quantum theory is the fact that electrons surrounding a nucleus in an atom can only assume certain values of energy, given by the type of atom and its states.

As a result, an electron can only possess one of a number of allowed energies. The electron can change its energy to a higher or lower level by absorbing or emitting a photon of energy E2-E1=hf, respectively, where E2, E1 are the energies of the levels.

Spontaneous emission occurs when an electron decays from the higher energy level E2 down to the lower E1, stimulated absorption will occur when the electron absorbs a photon of energy E = E2-E1 and transitions from E2 to E1 . A third process, known as stimulated emission, occurs when an electron at energy E2 absorbs a photon of E = E2-E and decays to lower E1 , emitting two photons of energy E.

LASER is an acronym for Light Amplification by Stimulated Emission of Radiation. In a laser, energy from an external source is injected into a system, raising the energies of electrons in some of the atoms in the system. If a photon of the appropriate energy now enters the system, there is a chance it will either be absorbed by an electron at a lower level, which will transition up by stimulated absorption or it may be absorbed by an electron at a higher level, which will decay to a lower level by stimulated emission, releasing two photons with the same energy as the incident photon. If the number of atoms raised to higher energies greatly exceeds that of the atoms at the lower energy, stimulated emission will prevail over stimulated absorption, with that result, that incident light of frequency f=(E2-E1)/h will be amplified. This state is known as a population inversion.

However, this process will cause the number of atoms excited to higher energy states to drop, which would stop the process, therefore energy must be supplied into the system to maintain the ratio of higher energy states to lower energy states.

A laser, as a device, will consist of an enclosed volume of material (eg, a rod of ruby crystal, Neodymium doped Yttrium Aluminium Garnet [Nd:YAG] or a tube containing gases, eg, HeNe in a Helium-Neon Laser) placed into an optical resonator comprised of two parallel mirrors, one of which is partly transparent. When stimulated emission occurs, some of the photons escape, but those photons which travel along the axis of the system are reflected back when they reach the mirrors, thus stimulating further emission as they pass through the material. As the photons emitted are in phase with the incident photons, they generate a coherent light beam, part of which escapes through the partly transparent mirror. This laser effect only occurs for those frequencies of light which correspond to a difference in particular energy levels and the wavelength of which fits an integral number of times into the distance between the mirrors.

As a result, a laser generates a beam of coherent monochromatic light travelling in one direction. Because the energy levels are very sharply defined, this results in the frequency of the light being constant. Laser beams, by virtue of their high intensity and constant frequency and phase, are very easy to focus (note - the focal length of a lens varies with the frequency of the light passing through it, therefore it is impossible to perfectly focus light of various frequencies - eg, white) and because the beam is nearly perfectly unidirectional it diverges very little. These properties enable a laser beam to cover a large distance without significant dispersion and therefore retain a reasonably high intensity. A laser beam impinging on an object from a distance will create a spot of very bright light, the laser spot, which is then detected by spot trackers or guidance heads.

There are a large number of different lasers, with various applications, by mode of operation they can be divided into pulsed or continuous wave (CW), by construction into solid state or gas and by the means of energy injection into optically or electrically pumped, gas dynamic or chemical lasers.

The use of laser-guided weapons will significantly affect the tactics of future warfare, both medium/long range strike and close support benefitting. The first major application of laser-guided weaponry were long-range USAF strikes at difficult targets in North Vietnam, eg, the Lang Giai bridge, which lost six of its 11 spans in a single strike, or the Lang Chi hydro-electric powerplant, which was knocked out without damage to the adjacent dam and spillway. These missions were flown by F-4s of the 8th TFW, where one aircraft designated the target and the accompanying aircraft bombed it. The improved accuracy on this type of mission is one of the reasons why the USAF is replacing the F-4 with the smaller F-16.

Close support will gain the most from laser weaponry, because it will enable far closer co-operation between ground forces and their air support. Close support has always been plagued by a lack of accuracy and communication problems. Current tactics involve the use of ground-based designators to mark targets, which will then be attacked with laser-guided bombs, missiles or artillery projectiles. Close support aircraft also carry spot trackers which position a marker on the pilot's HUD-indicating the position of the laser spot in the pilot's FOV and enabling a first pass cannon kill (USAF A-10A).

Ground forces will be able to send laser-equipped scouts forward who would then designate enemy strongpoints from concealed positions, enabling surprise attacks. Laser designators and seeker heads have a pulse coding system which enables seekers to discriminate between individual designators and also avoid jamming or deception.

Anti-armour operations are one of the primary tasks for laser-guided weaponry, as armour is mobile, hard-skinned and relatively small. The US Army is currently in the process of equipping with a new generation of weaponry the AAH/Hellfire and the Copperhead.

Precision Guided Munitions - Texas Instruments GBU-10, 12, 16 Paveway

The Paveway "smart bomb" was the first laser-guided weapon to gain wider application and distinguished itself during the Vietnam conflict.

The Paveway is a modular guidance kit comprised of a Computer Control Group and Airfoil Group Assembly fitted to a standard Mk82, 83, 84 demolition bomb or SUU 54 cluster bomb. It functions as a semi-active laser-seeking ballistic projectile and requires no electrical connections with carrying aircraft prior to release.

The CCG consists of a laser energy sensor, a guidance command computer and a control actuator/control surface assembly (see diagram). The laser sensor is mounted in a gimballed, aerodynamically aligned (ring airfoil - it aligns the sensor assembly with the weapon's velocity vector) assembly. Laser light reflected off a target passes through a protective nose window and an infrared filter and is focussed by an aspheric lens on to a four-quadrant silicon photoelectric sensor. The sensor is slightly shifted along the longitudinal axis of the assembly so it lies in front of the focal plane of the lens and the image of the laser spot is slightly defocussed. If the spot is perfectly aligned with the weapon's velocity vector, all quadrants are equally illuminated. If the spot lies off-axis it will illuminate each quadrant differently. Each quadrant generates electric current proportional to its illumination. Voltages proportional to these currents are then amplified and fed into a mixer network which compares the signals and generates up/down, left/right commands - these are then fed into the guidance command computer.

Paveway uses a non-proportional 'bang-bang' guidance where control surfaces are not deflected proportionally to the guidance error, but are driven to the limit of their deflection; the guidance commands being up, down, left, right and no command. The computer receives the outputs from the sensor assembly and, after selecting the correct pulse code, it compares the outputs to select the appropriate control commands. Control actuation occurs if the difference between two channels exceeds a level given by the minimum guidance error; if not, the control fins are set to trail.

The control section is aft of the computer, it converts the computer's commands into control surface deflections and also powers the computer. The energy source is a hot gas generator which supplies electricity via a thermal battery and also supplies the high-pressure gas required to actuate the control surfaces.

The high-pressure gas is fed through a manifold into four piston/cylinder assemblies which are connected to the control surfaces. The gases are then vented through four solenoid valves which are controlled by the computer. A guidance command will shut a valve, allowing the full pressure of 7.5 MPa to build up, which will generate a torque acting on the control surface, deflecting it.

First ever GBU-16 trial drop from an F-16A, using the ATLIS II targeting pod (Texas Instruments).

If no command is present the surfaces trail, any motion being damped by oil dampers which are necessary to avoid flutter during carriage. For safety reasons, the gas generator cartridge is ignited two seconds after release, which results in a necessary unguided flight-time of at least two seconds. The wing assembly mounts on the rear of the bomb body and the wings deploy after release, when a retaining latch enables four coil springs to extend the wings.

The guidance system of Paveway attempts to align the weapon's velocity vector with the instantaneous line of sight to the target. Paveway kits are supplied separately from warheads. Under operational conditions, warheads are fitted with the airfoil assembly and then are mounted on the carrier aircraft's hard points. The guidance kit and control surfaces are then fitted and the weapon is ready for use. Due to its simplicity, the system is very reliable (TI claims over 95 per cent) and has a storage life of over 10 years. Providing a target designation capability is present, there are no modifications necessary to the carrying aircraft.

Laser-guided projectiles have one great advantage over TV and Infra Red Imaging weapons, aside from simplicity, as they do not require a TV signal transmission link from the weapon to the launch aircraft and an aircraft-to-weapon command link such as the Martel, GBU-15 or TV/IIR AGM-65 Maverick (the USMC is interested in a laser-guided version).

The second major player in the laser guided weapons export market was French missile manufacturer Matra, who widely exported the BGL family of 1,000 lb and 2,000 lb class LGBs. The French weapon uses a unique airfoil arrangement, quite different from the TI design, later borrowed by the Soviets for the KAB-500L/1500L series. The depicted Mirage 2000 is equipped with an ATLIS designator pod (Matra).

Arguably the most potent of the second generation laser guided weapons for battlefield interdiction and close air support is the Aerospatial AS30 Laser, a large supersonic laser guided missile designed to defeat fortifications, Hardened Aircraft Shelters and other high value targets. The AS30 later served with distinction in the Desert Storm campaign (Aerospatiale).

The US Army Laser Guided Antiarmour Weapons Program

The tank has probably been the greatest single influence on twentieth century ground warfare and, as it seems, will remain the principal offensive weapon of many an army. The Soviet Union, in particular, has been and is the foremost supporter of tank warfare, often using tanks under conditions hardly optimal to their operation, eg, Afghanistan. However, both Europe and the Middle East are environments where the tank can function effectively, as both the Wehrmacht and the Israeli Army proved on a number of occasions. Both the industrial wealth of Western Europe and the oilfields of the Middle East are easily accessible targets for the Red Army's armoured divisions and this is the primary cause behind the recent emphasis on tank busting. The USAF A-10 program and the Army TOW/Cobra system were configured to meet this threat. However, Soviet developments such as the Hind-D gunship and the SA-7B shoulder-launched SAM, aside from increased deployment of fighter aircraft with some look-down shoot-down capability, will definitely impair the effectiveness of the combination.

A significant improvement in the Army's tank busting capability should occur with the operational deployment of two new weapon systems: the Copperhead laser-guided artillery projectile and the Hellfire laser-seeking anti-armour missile carried by the Advanced Attack Helicopter.

Bullseye! This picture is enough to put any Soviet tank commander off his borshch - the terminal phase of a Martin Marietta M-712 Copperhead flightpath. Copperhead is fired from the 155 mm howitzer and has hit targets up to 16 km away with deadly accuracy.

Martin Marietta M-712 Cannon-Launched Guided Projectile - Copperhead

The Copperhead is a cannon-launched, laser-guided, 155 mm, indirect fire weapon configured for the destruction of small, hard-skinned targets at ranges of up to 16 km. Fired from M-109 self-propelled and M-197, M-114 towed howitzers, the Copperhead must withstand a 9000 g acceleration on launch. The projectile (see diagram) is comprised of a guidance section, seeker and electronics, a warhead section and a control section.

The seeker employs a four-quadrant detector, which is mounted fore of a gyro-stabilised focussing mirror, which receives laser energy through the nose window and optical filters. The gyro bearings are off-loaded during launch to avoid damage, the gyro is spun up mechanically and maintained electrically. The detector output signals are fed into the electronics section, where pulse codes are discriminated and the guidance commands are generated. Copperhead uses proportional navigation, where the projectile's rate of rotation relative to its line of sight to the target is proportional to the target's rate of rotation relative to the projectile's axis prior to the correction. The electronics assembly consists of a stack of printed circuit boards, each of which has a hole in the centre to enhance the effect of the shaped charge warhead. Extensive use was made of LSI chips.

The warhead section employs a shaped charge and dual channel fusing, with six external grazing sensors to detonate if a nose-on impact doesn't occur. The shaped charge was designed for single shot kills of hardened targets.

The control section contains the mechanisms for the deployable wings, the control actuation system and the thermal battery. A helium bottle provides 70 seconds of actuator power. A slip obturator on the aft of the projectile forms a gas seal and also limits the spin up during launch to 30 revolutions per second.

The laser code is set prior to launch, together with the activation time delay. The control fins are deployed by centrifugal force at muzzle exit, the projectile then follows a ballistic flight-path. After the set delay is over, the electronics activate, the gyro is released, the gas bottle and roll rate sensor activate, the fins unlock and the roll is cancelled out. Three seconds later, after gyro activation, the wings deploy and a ballistic or glide path is followed until the correct laser code is acquired by the guidance, which then guides to the target using proportional navigation with gravity compensation.

The demonstrated CEP was one-half of the specified. One to two rounds are required to kill a tank as compared to an average of about 1500 conventional HE rounds.

Artillery firing Copperhead need not expose itself to direct enemy fire as all that is required in the combat area is a designator. A forward observer would call for indirect fire support and then designate the target during the projectile's flight.

Rockwell Hellfire and the Hughes AH-64 Advanced Attack Helicopter (AAH)

The Hellfire and the AAH together form a fearsome combination. The Hellfire is a semi-active, laser-seeking, supersonic anti-armour missile with an effective range of up to 6000 metres. It can be used both for direct and indirect firing. In the former case, the carrier vehicle designates the target and launches the missile. In the latter, the missile can be launched from stand-off ranges or concealed locations, the missile acquiring the target when it enters the area of visual contact - the target being designated by ground forces or other helicopters.

Hellfire employs a laser seeker combined with an inertial guidance system. The missile uses inertial control during the initial phase of its flight, thus enabling launch from concealed positions. Once the seeker acquires a laser signature that matches the given pulse code, the missile transitions to laser guidance, homing in on the target. The warhead is a hollow charge weighing about 9 kg.

The ability to discriminate between laser codes enables Hellfire to be launched in salvoes, individual missiles then selecting and destroying separate targets. Hellfire is powered by a solid propellant rocket.

The AAH will be the principal carrier of the Hellfire, its high performance and capable target acquisition systems greatly enhancing the overall effectiveness of the Hellfire.

A remarkable helicopter, the AH-64 deserves far more attention than it will get in this treatment, which will concentrate on overall performance and sensor systems.

The Hughes AH-64 is a two-seat, twin-engined anti-armour attack helicopter optimised for nap of the earth (NOE), all-weather, day/night operation.

Production aircraft will be powered by two GE T700-GE-701 engines, each delivering 1690 shp, enabling the AAH to reach 196 kts (363 km/h) in forward level flight and achieve sustained climb rates better than 3000 fpm.

The AAH was designed with particular emphasis on survivability, the airframe being capable of withstanding damage, the control system being redundant, self-sealing fuel cells and a considerable amount of armour being used. The IR, acoustic and visual signatures of the aircraft are a vast improvement on current helicopters - the "black-hole" IR exhaust plume suppressors, the small-diameter, four-bladed rotors (50 per cent quieter than the AH-1 S), the small cross-section and flat plate canopies all having a noticeable effect. Hughes claim the AH-64 is invulnerable to 12.7 mm (.50 cal, for the traditionalist) rounds and has a low vulnerability to 23 mm HEI rounds (Hind-D gatling/ZSU-23-4P), blast shields protecting the crew and separating the cockpits.

The primary weapon for point target destruction is the Hellfire, a maximum of 16 can be carried. The secondary armament, for area suppression and self-defence, is the M-230E1 30 mm Chain Gun, supplemented by 2.75 in FFAR rockets. The Chain Gun fires 800 rounds per minute, using HE armour-piercing shaped charge rounds.

The AAH program payload/range/performance requirements are 450 fpm (137 m/min) vertical rate of climb with eight Hellfire and 320 rounds of 30 mm ammo, with a 1.83-hour mission endurance at the Army hot day (4000 ft/95 deg F - 1220 m/35 deg C). The main sensory system of the AH-64 is the Martin Marietta Target Acquisition Designation Sight and Pilot's Night Vision Sensor - TADS/PNVS.

The TADS is the most complex sub-system fitted to the AAH. It contains direct-view optics, FLIR, TV, a laser spot tracker and a laser designator/range finder, all bore-sighted. The gunner, in the forward cockpit, uses the TADS to detect and designate targets under all light conditions, enabling then the use of the aircraft's Hellfire or other laser-seeking weapons. The multi-purpose sight viewed by the gunner protrudes from the control panel, the turret controlled by two handpieces on either side of the sight.

The PNVS is a FLIR camera mounted in a small turret on top of the aircraft's nose. The turret is slaved to the pilot's helmet and automatically tracks the pilot's LOS. The pilot views the generated image on his helmet visor, where it is projected by a special CRT/optics assembly mounted on the side of the helmet. Both forward and aft cockpits have provision for the helmet-mounted sight, presumably to aim the Chain Gun in a similar manner to the AH-1J/T's gatling turret. Survivability, performance, armament and effective sensors make the AH-64 an effective tank killer and the Soviet Hind may very well find itself with a prey capable of turning tables on it.

Hughes OH-6D, competing with the Bell OH-58 (see June issue) for the US Army AHIP contract. The OH-6D has an OH-6A airframe fitted with 500D dynamics and a new communication / sensor system. Note the mast-mounted sight, GD Stinger SAMs (Hind defence) and the array of VHF / UHF multiband antennae [OH-58 MMS - the winning bidder - depicted].

Scout Helicopters - Hughes Army Helicopter Improvement Program

One of the main advantages offered by weapon systems such as the Copperhead and Hellfire/AAH is the possibility of stand-off kills. Firing from concealed positions eliminates the need to expose oneself to enemy fire (the Russians do possess laser-guided missiles, eg, the AT-6 Spiral carried by the Hind), however it raises the problem of having an effective capability to detect and designate targets.

Infantry-operated designators, such as the tripod-mounted Ground Laser Locater Designator (US Army AN/TVQ-2) or Modular Universal Laser Equipment (USMC Mule) are effective, however the mobility of a two-man infantry crew burdened with over 25 kg of equipment, aside from standard gear, is seriously limited, particularly when armoured units succeed in breaking lines farther along a battlefront, as is often the case in tank warfare. The solution to the problem is the deployment of designator-equipped scout helicopters, which are extremely mobile and, due to their available auxiliary power, may be fitted with FLIR cameras and a wide array of communication systems.

A contender for the US Army's future scout helicopter, the Hughes OH-6D is a modified OH-6A (Vietnam proven) fitted with Hughes 500D dynamic components and equipped with a development of the Mast Mounted Sight (MMS) program. The MMS, in the OH-6D fitted with FLIR from TADS/PNVS and a laser from the AN/TVQ-2 GLLD, enables the helicopter to conceal itself behind terrain features, such as trees, bushes or hills, and locate, track and designate targets without exposing itself. The OH-6D was configured for NOE operations, the pilot using a large, multi-function HDD displaying navigational data derived from a Singer-Kearfott Doppler Radar Velocity System and a Litton Heading and Attitude Reference System. The observer/co-pilot operates the MMS using a similar sight to the AAH TADS.

Aside from its terrain masking ability, the OH-6D has a low IR signature and is very small, making detection that more difficult. The US Army's laser anti-armour weapons should be operationally deployed by the mid-1980s. It will very probably force the Russians to seriously rethink the offensive strategy of their ground forces.

Designators for tactical aircraft

The demands placed upon airborne designators greatly exceed the requirements for ground-based designators. Where ground-based designators have damping systems, to attenuate vibration or operator-induced jitter, airborne systems, due to the nature of the platform they are fitted to, require full stabilisation in at least two axes of rotation and demand some automatic tracking ability.

Automatic trackers become that much more important in designator systems for single-seat aircraft, where the pilot simply cannot devote time or attention to tracking a target as he is preoccupied with flying the aircraft and avoiding local air defence.

An automatic tracker basically analyses successive images in order to find common features - these being either edges, areas or points. Using these common features, the tracker can identify the place it is to illuminate and point the laser in that direction.

The lasers often also double up as rangefinders, this being simplistically implemented by virtue of the fact that the velocity of light in a homogeneous medium is constant at 3.108 metres/sec in free space. Rangefinding then merely involves measuring the time it takes the laser beam to reach the target, reflect and travel back to the source, which can be easily accomplished electronically.

Current designators are either designed as part of a particular weapon system, eg, TADS/PNVS, MMS or TRAM, or they are designed as pods, to be retrofitted to several types of aircraft after the appropriate electronics refit, eg, ATLIS, LANTIRN, Pave Spike.

Grumman A-6E Intruder TRAM installation, combining FLIR and laser designator capabilities (Hughes photo).

Hughes AN/AAS-33 Target Recognition and Attack Multi-sensor (TRAM)

TRAM is a precision stabilised sensor turret containing a FLIR camera, laser spot tracker and a laser rangefinder/designator. In the mid-1970s, the USN recognised the need to update their fleet of A-6 bombers with a system enabling the all-weather delivery of precision guided weapons. The A-6 is fitted with the Digital Integrated Attack Navigation Equipment (DIANE) system, which enables all-weather operations - the A-6 was responsible for most of the USN's adverse weather strike operations during the Vietnam conflict. The TRAM turret is being gradually retrofitted to the A-6E fleet, the turret mounts under the aircraft's nose, aft of the bulbous radome. The FLIR image is displayed on the bombardier/navigator's head-down display, the turret is controlled by a short control stick which also carries the switches necessary to operate the system.

TRAM has three eyes; the largest, central one being the viewing window for the FLIR camera. The camera has a zoom capability, full travel being accomplished in three seconds without an intermediate loss of image. Under operational conditions, the B/N guides the A-6 to the target by radar, then switches to wide field of view FLIR to precisely locate and identify the target. The B/N can then zoom in on the target to take a close look, activate the laser and lock the tracking system on to the target. The aircraft can then release its bombs and head for home, the electronics maintaining the laser beam locked on to the target.

US Navy A-6 crews are very pleased with the system, though, as the author was told by a B/N of VA-115, the FLIR picture quality could degrade, particularly with a lot of moisture in the air. This would be due to scattering and diffraction effects, where the water droplets' diameter approaches the wavelength of the IR light viewed by the camera. In general, though, the picture quality apparently approaches that of black and white TV. Ships are easily visible at night, the heat sensitivity of the system allowing the identification of the engine room or oil tanks.

One of the main advantages offered by FLIR systems is their total lack of electromagnetic emissions, as compared to radar. This means a target may be approached without prior warning, with everything that has to offer.

ATLIS II TV/laser pod fitted to a French AF Jaguar. The ATLIS series pods were used for a range of US trials (Martin Marietta).

Martin Marietta Automatic Tracking Laser Illumination System (ATLIS)

The ATLIS tracker/designator was developed by Martin Marietta, under a contract with Thompson-CSF, for the French Armee de I'Air Jaguar strike aircraft.

The ATLIS pod contains an automatic TV tracker and a laser designator/rangefinder; a laser spot tracker is an optional fit. ATLIS is comprised of a roll turret housing the optics, camera, laser and stabilisation system, coupled to the fixed portion of the pod, which contains the electronics, computer, power supplies and environmental control system.

Real world images are reflected by a stabilised mirror, in the front of the turret, into fixed optics which focus the images into the camera. Laser energy (designation) is fed into the optics by the use of a dichroic (reflective to particular wavelengths) combiner glass so that the laser beam exits the optics via the same path that external images enter the system. The output from the camera (operating both in the visual and IR bands) is used to drive a cockpit CRT and the automatic tracker. The tracker has two modes, point tracking and area correlation. Point tracking is used for small, stationary or moving targets. Area correlation (a process in which two successive images are compared to find common features; these are then used to determine the relative positions of the images) is used for area or low contrast targets. ATLIS was designed for single-seat aircraft. The tracker can be cued from the aircraft's HUD, radar, inertial system or a helmet-mounted sight.

In early 1979 the ATLIS pod was tested on the USAF/GD F-16 prototype, successfully delivering GBU-10 and 16 PGMs in the course of a 46-flight test program.

Martin Marietta LANTIRN

The LANTIRN adverse weather navigation and attack system (see TE 2, March AADR) is being developed for the F-16 and A-10, and will be housed in two pods.

The navigation pod will be fitted with a wide field of view FLIR camera and a terrain-following radar (TFR) system, which will enable accurate low-level penetration under all weather conditions.

The targeting pod will carry a narrow FOV FLIR camera and laser ranger/designator, both integrated in an automatic target recognition and designation system.

The F-18, fitted for a strike mission, shows it's teeth. The aircraft pictured is carrying four Texas Instruments Laser Guided Bombs, the three weapons on the wing pylons being Paveway lls. The weapon on the centreline station, partly obscured by the forward undercarriage leg, is a TI Low Level Laser Guided Bomb (LLLGB), fitted with a proportional guidance seeker head. The aircraft is fitted with both attack pods, the AAQ-38 FLIR / Laser designator and the ASQ-173 Laser Spot TrackerlStrike Camera, on the left and right intake weapon mounts, respectively. The missile on the left outboard pylon is a TI HARM antiradiation missile, a weapon which should enhance the air defence suppression ability of F-18s. performing strike missions (MDC).

Ford Aerospace AAQ-38

Tailored to the USN's F/A-18A multi-role fighter, the AAQ-38 is often described as a "mini-Pave Tack". The AAQ-38 is a self-contained FLIR camera designator/tracker and is optimised for single-seat fighter operation. The system is housed in a pod (1.8 m, 0.3 m diam) which mounts on the port intake weapon mount (used to carry the AIM-7 Sparrow semi-active radar-guided missile, if the F-18 is to fly a fighter mission), the pod interfaces with the aircraft's electronics and draws air for cooling. A complementary laser spot tracker pod is in development- it will mount on the starboard weapon station.

The AAQ-38 was developed for the rough environment of carrier operations, ruggedness, small size and maintainability having priority over factors such as FLIR picture resolution or field of regard. Even so, though, FLIR imagery is reported as very good. The electronics are digital, as compared to the FA AVQ-26 Pave Tack (a larger system developed for the F-111 and F-4) which employs analogue electronics.

Field-of-view available is 12X12 deg and 3X3 deg. The field-of-regard (solid angle which can be accessed by the optics) is limited by the shape and position of the pod. Look-back is 150 degrees.

FLIR imagery is displayed on one of the F-18's cockpit CRTs, usually the starboard multi-function display (MFD). Autotrack cueing is either manual or by radar/inertial nav. The future LST pod will also incorporate cueing. With respect to Australia's NTF Mirage replacement, the F-18/AAQ-38 combination have more than a head start over the F-16/LANTIRN. The LANTIRN is yet to be developed and it seems the F-16 will require a bit more than just an interface fit to accommodate the system. It is also doubtful whether the NTF would require TFR to perform its mission - the laser spot tracker (F-18) being more suited for intended close support missions.

Ford Aeronutronics AVQ-10 Pave Knife laser targeting pod on an F-4E Phantom. Bomb Damage Assessment imagery of strikes on North Vietnamese targets using the Pave Knife and early Paveway variants (US Air Force).


Most designation systems can be divided into three groups, though the definition is a bit blurred in some instances. Systems forming an integral part of an aircraft's equipment fit are one group (TRAM, Pave Tack - though can be removed from the carrier aircraft), systems removable (pods), but designed for a specific aircraft (AAQ-38/F-18, LANTIRN/F-16 or A-10) and multi-purpose, self-contained systems for use with any aircraft possessing the appropriate interface fit (ATLIS II).

The first group offer the advantage of simplicity, as they can directly interface with a number of the aircraft's systems, eg, environmental control, inertial (stabilisation reference) systems, aside from electrical power. On the other hand, they become a weight/drag penalty if they are not to be used on a particular mission. This reflects in the fact that this class is fitted to dedicated bombers, eg, A-6E, F-111 C/D/E.

Specifically designed rapid conversion systems are tailored to the multi-role fighter. They usually require an interface with a limited number of inertial systems, eg, power, compressed air. However, they do put greater demands on the parent aircraft's display and information processing systems, as they cannot be hardwired to the aircraft. As they require more self-containment than the previous class, and must be small and light, performance is often compromised. The F-16 and F/A-18 are to carry this particular class, the rapid fighter to bomber conversion enhancing the flexibility of available air power.

Totally self-contained systems are the group suited to retrofits, as all they really require is power and some means of connecting to a cockpit display and control panel - obviously *hey suffer the penalty of having to handle all necessary functions themselves.

In principle, the more flexible the aircraft's display system, the easier to interface - the F-18 requires only software changes (all stored in the computer) to become a bomber - the =-16 requires a HUD refit, computer/display management and ire control refit for the same task.

Future designator/targeting systems will probably be self-contained units applicable to a number of aircraft and totally integrated into a central fire control or mission computer, which would also control the aircrafts flight-path. This would enable automatic pre-programmed ground attack manoeuvres and also lends itself to the possibility of laser-guided air-air weaponry (the USAF IFFC/Firefly III program seems to indicate some effort in this direction).

Precision guided weapons are developing at a fairly high pace and a number of new systems may find applications. Millimetre Wave, Inertial and advanced TV guidance may steal some of the laser-guided weapon's limelight but they can hardly displace a system which is as versatile and simple as laser guidance.

New laser-guided bombs, such as the Low Level Laser Guided Bomb (LLLGB) developed by Texas Instruments, fitted with more sensitive proportional control or laser-guided derivatives of air-to-ground missiles, are likely to increase accuracy and further broaden launch envelopes available to attacking aircraft.

Laser guidance has proved its viability in its first 15 years of life and, as it seems, will eventually displace conventional weapon delivery - by the same token itself becoming the "conventional" way of doing it.

Big enough to do a LOT of damage, this 2000 lb warhead LGB version of the trusty Mk.
84 iron bomb will move even the most stubborn bridge support.

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