Air-to-ground weapons systems: from sight to seeker; a reader's guide to current and future systems.
Many combat aircraft are still equipped with simple reflector sights, which restrict the pilot to making standardised attacks, and in addition give inaccurate results. Even if the increased aircraft attrition associated with the need for repeat attacks is ignored, it is far more cost-effective to incur the relatively modest expenditure of a more efficient weapon-aiming system.
The simple reflector sight with a manually-set depressed aiming-mark is 1930s technology. From 1943 onwards this began to be replaced by the gyro-gunsight (GGS). The change was made primarily to improve accuracy in air-to-air firing, but the GGS also provided automatic compensation for crosswind in ground attacks. Britain pioneered the GGS, and during World War II supplied sights to both the United States and Soviet Union.
After the end of World War II, responsibility for British gyro gunsight development passed from RAE Farnborough to Ferranti. In the 1960s the company began the development of the lightweight ISIS series, with the accent on the ground attack role. Air-to-ground attacks with the ISIS are normally carried out according to a set pattern and with a manually inserted depression angle, but some ISIS models make a provision for laser-range inputs.
Although smaller than the old GGS, and because it retains the gyro within its main body, the size of the ISIS sight still makes it a difficult retrofit in certain aircraft. To overcome these installation problems, Saab developed the RGS series, in which the sight head is controlled by remotely located gyros. In the case of a trainer, both sight heads are controlled by the same gyro unit; this saves cost and weight, and ensures that both pilots see identical displays.
In high-speed, low-level missions the pilot requires a head-up display (HUD) to eliminate the need to look down at flight instruments and navaids. The HUD is normally associated with a digital weapon-aiming computer (WAC), which provides accurate release computation, and allows flexibility in the choice of approach path. A modern head-up display can also provide sophisticated presentations, such as the CCIL (Continuously Computed Impact Line) and a warning display that instructs the pilot to pull up. It can also introduce an automatic time delay in the release of retarded weapons, which may otherwise require an unacceptably large depression angle.
Second-generation HUDs can also display a FLIR picture of the outside world for night operations. Early experience demonstrated the need for a wider field of view (FOV) to permit safe manoeuvring at low level, and this led to the development of wide-angle HUDs, frequently using diffractive or holographic techniques.
Helmet-mounted sights (HMS) allow the pilot to designate targets for guided weapons, even when the targets are at wide, off-boresight angles. In the case of a helicopter, an HMS may be used to direct turret-mounted guns. The main pioneer in this field was probably Honeywell, which developed its first helmet-mounted sight in 1963. Honeywell has also produced 500 HMS for F-4s, and is responsible for the HMS used in many American helicopters, including the AH-64.
The current aims in helmet-mounted sights development are to reduce the weight and to integrate a HUD-type display system within the normal helmet shape. The display of either NVG or steerable FLIR pictures would thus be possible.
In 1988 it was announced that Polhemus (part of McDonnell Douglas) had been selected to modify its Magnetrak system to provide the basis for the standard HMS for all US Navy aircraft. McDonnell Aircraft is meanwhile working with Kaiser on the development of a helmet providing HUD-type displays known as Agile Eye. In essence, a CRT embedded in the helmet projects a monocular display on to the visor, and a magnetic head-tracker continuously measures the pilot's head movements and orientation.
Having outlined recent developments in weapon-aiming displays and target-designation systems, the next question is how the impact point for an unguided weapon may be computed more accurately. The problem is how to determine very precisely the position of the target relative to the aircraft, which is basically a matter of measuring slant range.
Laser ranging was introduced in the early 1970s; it is much more accurate than radar ranging due to its very narrow beam (less than 2 milliradians) and short pulse (e.g. 20 nanoseconds).
Current examples of laser rangers include the Thomson-CSF TMV 630, used in the Mirage and Alpha Jet, and the Ferranti LRMTS fitted to RAF Harriers and Jaguars.
Western manufacturers are now marketing a variety of attack aids in podded form. For example, the TIALD (Thermal Imaging Airborne Laser Designator) is a joint development by GEC Sensors, Ferranti and British Aerospace, combining a Ferranti laser designator/tracker/ranger with a GEC thermal imager and a BAe video auto-tracker. The dual-mode sensor is held on the target either by contrast-lock or the laser tracker. The pod provides the crew with a TV-type picture of the target. It also gives ranging and target bearing data for ballistic weapons delivery, and provides target designation for laser-homing bombs.
The first day/night all-weather laser-based attack pod was the Ford Aerospace Pave Tack, which became operational on the F-111F, F-4E and F-111C in the early 1980s. It employs inertially-aided manual tracking of the target, as shown on an electro-optical/FLIR display. The Pave Tack provides both laser ranging and designation. Ford is also responsible for the AAS-38 day/night attack pod of the F/A-18, which has automatic tracking for one-man operation, as does its Nite Owl derivative, which incorporates its own cooling system for the infra-red sensor.
Hughes Aircraft is one of the leaders in the FLIR field. Its products include the AAS-33 TRAM (Target Recognition and Attack Multisensor) system for the A-6E, in which FLIR and laser facilities are integrated in a stabilised chin turret. Hughes is also responsible for the ARBS (Angle-Rate Bombing Set) fitted in the nose of the A-4M and AV-8B. In this system the target is tracked automatically by TV contrast-lock or laser spot-tracking (giving a day/night capability), and slant range is computed continuously from the depression angle of the target and the rate of increase of this angle. The ARBS has resulted in extremely accurate weapon deliveries in British trials with the Harrier GR5.
Martin Marietta is responsible for the LANTIRN (Low Altitude Navigation and Targeting IR for Night) system for the F-16C/D and F-15E. The AAQ-14 targeting pod of LANTIRN combines FLIR, auto-tracking facilities and a Litton laser designator/ranger. Martin Marietta is also prime contractor for the TADS (Target Acquisition and Designation Sight) for the AH-64. Housed in the nose turret, the TADS has FLIR, TV and direct-view optics, together with a Litton laser designator/ranger. Martin Marietta is also responsible for the LST (Laser Spot Tracker) of the F/A-18.
Thomson-CSF is now producing the ATLIS II (Automatic Tracking and Laser Designation System) for the Jaguar, Mirage 2000 and F-16. It combines automatic tracking, a high-power telescope for long-range target acquisition and a CILAS laser. The system was developed by Martin Marietta under contract to Thomson-CSF for the French Air Force. The latter company is now developing the CLDP (Convertible Laser Designator Pod), in which either a TV camera head or a FLIR may be fitted, to suit day or night attacks.
Let us now look at current armament developments, first automatic weapons and then rocket projectiles, bombs and guided missiles.
Guns and Cannon
At the lower end of the armament spectrum, recent years have witnessed considerable activity in the field of heavy machine-guns, basically to replace the 12.7 mm Browning. One example is Singapore Technologies' 50MG, which is gas-operated and can quickly be switched from one type of ammunition to another. It may be noted that the effectiveness of 12.7 mm weapons is being enhanced by ammunition improvements, such as the pyrotechnically-ignited Raufoss MP (Multipurpose) and high-penetration APS rounds.
The BRG-15 developed by FN Herstal is an even heavier gun, designed to fire a new 15.5 mm round, and is intended to fill the gap between the 12.7 mm machine-gun and the 20 mm cannon. Last year FN announced that it was developing a three-barrel Gatling derivative of the BRG-15 for aircraft applications.
As a replacement for the 7.62 mm M134 Minigun, General Electric Defense Systems has developed the 12.7 mm GECAL-50. The production gun will reportedly fire 2000 rd/min in three-barrel form and 4000 rd/min with six barrels, although these are only half the design rates. The initial application for the GECAL-50 is the USAF's MH-60G rescue helicopter. The company is also manufacturing the GPU-5/A gun-pod for some Air National Guard F-16A/Bs. The GPU-5/A uses the four-barrel GAU-13/A version of the 30 mm seven-barrel GAU-8/A installed in the A-10. The GPU-5/A is already used on F-4Es and A-7Ds.
For attack helicopters needing a heavier automatic weapon than the GECAL-50, GE has developed the twin-barrel (Gast-type) 25 mm Lightweight Gun or GE-225, which in gas-operated form fires up to 2000 rd/min. For fixed-wing attack aircraft the latest Gatling is the 25 mm GAU-12/U, which equips the AV-8B. This gun has five barrels and fires at 3600 rd/min. The British version of the AV-8B, the Harrier GR5, replaces the GAU-12/U with a pair of 25 mm Royal Ordnance Aden-25 cannon, each giving a cyclic rate of 1650-1850 rd/min.
Returning to helicopter weapons, linear-action cannon are exemplified by the 20 mm Oerlikon KAD and by the 30 mm Giat Type 781 which is being developed for the Franco-German Tiger. The McDonnell Douglas Chain Gun series ranges from the 7.62 mm EX-34 to the 30 mm M230 used on the AH-64. New Chain Gun models include the 20 mm Pit Viper proposed for the LHX.
The principal cannon development on the Soviet side appears to be a 23 mm GSh-23 pod which can be depressed during strafing attacks.
Rockets and Retarded Bombs
Turning to unguided rockets, the best-known of the well-established types are probably France's SNEB 68 mm and Thomson Brandt 100 mm, Switzerland's Oerlikon 80 mm SURA and 81 mm SNORA and America's 2.75-inch (70 mm) FFAR and 5-inch (127 mm) HVAR. Oerlikon sold its SNORA rights to SNIA-BPD which has since developed a number of rocket systems, including the 81 mm Medusa for the A.129 helicopter.
Meanwhile Thomson Brandt and PRB-Gechem have combined their aircraft rocket activities in SA Forges de Zeebrugge (FZ). The product range of FZ now includes the Cargo 70 series with the 9-submunition FZ-100 warhead and the FZ-122, which delivers 240 flechettes weighing 13.7 grammes each. The company has also taken over TBA's Multidart family. The Multidart 68 rockets carry either eight 190-gramme 13.5 mm diameter darts or 36 lighter (35 grammes) 9 mm darts. The larger Multidart 100 carries either 36 darts of the 190-gramme type, or 192 of the 35-gramme type, six 24 mm diameter darts each weighing 1650 grammes. Another recent FZ development is the GRCS (Gun and Rocket Control System) for helicopters.
The Belgian company's rocket activities began with the FFAR, which has served as the basis for many derivatives. Canada's Bristol Aerospace manufactures the CRV7, with improvements in velocity and accuracy, and a range of new warheads. America's own derivative of the FFAR is the Hydra-70 by BEI Defense Systems, which offers both a 9-submunition warhead and two flechette versions. Two types of launcher are produced by Hughes aircraft for the Hydra-70: the 7-tube M260 and the 19-tube M261.
The Soviet Union appears to be switching to heavier rockets: an 80 mm to replace the old 57 mm, and a 370 mm to take over the top of the range from the 240 mm.
In low-level bombing attacks retarded weapons are often used to ensure aircraft safety and to produce a more effective fragmentation pattern (due to the steeper angle of descent). The Matra 2000 bomb retardation system was introduced in 1965 for 250 and 400 kg bombs, and was followed by the SFA (Systeme de Freinage et d'Amorcage) for the SAMP 125 and 250 kg bombs.
In a lighter category, Thomson Brandt produces the 34 kg BAT 120 retarded bomb, of which up to 18 can be carried on a single pylon.
If a bomb is released at low level in order to explode beneath a runway, then retardation (for a high-angle impact) may be followed by rocket-powered acceleration to ensure penetration of the paving. The two principal examples of this type of bomb are the 32.5 kg Thomson Brandt BAP (Bombe Anti-Piste) 100 and the 220 kg Matra Durandal.
The modern trend towards low-level attack produces large along-track weapon delivery errors. These errors can be offset by employing a stick of bombs, or a bomb that breaks up into a number of smaller warheads. The latter concept is used in the Thomson Brandt BM400 (now Cascad Mk. 1), which contains three 90 kg anti-armour submunitions. These are extracted from the bomb casing at preset intervals by individual parachutes.
Cluster bomb units contain much larger numbers of bomblets, which are scattered (e.g., by inflating bags or by spinning the bomb) to give an impact pattern roughly corresponding to along-track and across-track aiming errors. Specialists in this field are ISC Technologies (Rockeye), Matra (Belouga - submunition manufactured by Thomson-Brandt Armements) and Hunting Engineering (BL755). Hunting has developed the Hades, an area-denial derivative of the BL755 containing 49 Ferranti HB876 minelets.
Recent years have seen major advances in the effectiveness of submunitions; these may be dispensed from large containers attached to the aircraft (and subsequently jettisoned) or from dispensers that are lofted toward the target from a distance, thus allowing the launch aircraft to remain outside short-range defences.
As an example of the former system, Lacroix and Alkan have collaborated on the development of a dispenser pod family for 74 mm grenades. In terms of heavier submunitions, Hunting's JP233 carried by the RAF Tornado GR1 dispenses the company's own SG 357 anti-runway submunition and the Ferranti HB876 minelet. The German Air Force Tornado uses the Raketen-Technik MW-1, which can be loaded either for airfield attacks or to deal with armoured fighting vehicles. The MW-1 also provides the basis for the MDS (Modular Dispenser System), which is suitable for carriage on smaller aircraft.
It is probably true to say that the United States has led the way in the field of wingless submunition-dispensers of the type used in stand-off attacks. A family of such dispensers has been developed on the basis of the Marquardt TMD (Tactical Munitions Dispenser). The Aerojet Ordnance CEM (Combined Effects Munition) is a TMD with BLU-97B bomblets. The DAACM (Direct Airfield Attack Combined Munition) comprises Ferranti HB876 minelets and Avco Systems BKEPs (Boosted Kinetic Energy Penetrators). Avco's SFW (Sensor-Fuzed Weapon) is a TMD with 10 BLU-108/B submunitions, each with four Skeet anti-armour warheads. Avco is also responsible for several other important weapons, including the anti-armour WAM (Wide-Area Mine), which can be laid from aircraft and fires a sensorfuzed warhead over its target. European dispensers include the Hunting CMD-18, which contains 18 SG357 anti-runway submunitions.
As air defences improve, the trend is towards increased launch range for the dispenser, by adding wings and some form of propulsion. Currently under development for the JAS 39 Gripen, the DWS 39 dispenser is a derivative of the MDS mentioned above.
The future of the multi-national MSOW (Modular Stand-Off Weapon) is now very much in doubt, and this situation must improve the prospects for the Matra/Aerospatiale Apache, which is going ahead at present on a national basis. The Apache is inertially guided, and carries a new family of Matra submunitions: the general-purpose Mimosa, the anti-tank Arcadie, and the runway-piercing Samanta. Another European project is Italy's Skyshark, with an airframe developed by Aeritalia and submunitions by SNIA-BPD as part of a consortium known as Casmu. Both the Apache and the Skyshark will begin as glide vehicles, but will later have propulsion units.
The simplest form of air-to-ground homing weapon (as distinct from submunition) is the guided bomb, since this is produced merely by adding a homing head and control surfaces to an existing low-cost weapon. The most important series to date has been Texas Instruments' Paveway LGB (Laser-Guided Bomb), which has led to the GBU-24 with larger tailfins and two-stage guidance for longer range and low-level release.
Another American line of development is Rockwell's TV/IIR-guided GBU-15 Cruciform wing Weapon, which uses either a standard Mk.84 or a CBU-75 warhead. With a rocket motor attached, the GBU-15 becomes the AGM-130, increasing low-level delivery range from nine to 24 km. However, whether the AGM-130 will reach the production stage remains to be seen.
Matra produces laser-guided bomb systems of 250, 400 and 1000 kg, with ranges in excess of seven kilometres and an accuracy better than seven metres. The top of the range is the 1000 kg Arcole, designed to meet a French Air Force requirement for a weapon to destroy bridge piers.
Israel has developed several types of guided bomb, although it appears that only IAI's Griffin LGB and Elbit Computers' Opher IR guidance kit are currently in service with the Israeli Air Force. Other projects include IAI's longer range (30 km) Guillotine LBG and Rafael's Pyramid TV-guided glide bomb.
Both Northrop and Boeing have been funded to produce bomb guidance kits under a joint USAF/USN inertially-guided technology demonstration (IGTD) programme, and it is hoped to start full-scale development of such a bomb in FY92. At Le Bourget last year France's SAMP showed its new Excalibur, an inertially-guided 250 kg bomb fitted with a small vectored-thrust rocket to ensure good control in a high altitude release. Small canard surfaces are extended from the nose of the bomb, apparently to reduce stability and thus increase control response. The target coordinates are passed to Excalibur from the aircraft navigation computer immediately prior to release.
Compared to the simple glide bomb, conventional guided missiles offer longer ranges from a given release height, higher speeds and greater accuracy. The Aerospatiale AS.30L is a supersonic weapon that is now operational on French Air Force Jaguars and Mirage Fls and 2000s. It delivers a 240 kg warhead over a distance of up to 10 km from a low delivery, and employs a combination of gyro-controlled mid-course guidance and semi-active laser homing.
The Hughes AGM-65 Maverick series has a typical range of 13 km from low release and 24 km from altitude. The various Mavericks available provide a choice of TV, laser or IIR guidance, and of a 57 kg shaped charge or a 136 kg penetrator warhead for use against hardened structures. Indicative of new technology, LTV's Hypervelocity Missile (HVM) will employ automatic command guidance by laser datalink to enable several targets to be engaged in a single pass. The HVM relies on the kinetic energy of high-density rods to penetrate the target armour.
Anti-radiation missiles (ARMs) were first used in the Vietnam War, the Texas Instruments AGM-45 Shrike later being supplemented by the heavier, longer range General Dynamics AGM-78 Standard. The Shrike was subsequently used by the Israelis in the 1973 Yom Kippur War and the 1982 invasion of the Lebanon, and by Britain's RAF during the Falklands conflict of 1982.
In principle both the Shrike and the Standard will be replaced in US inventories by the Texas Instruments AGM-88 HARM, which entered service in 1984. It is planned that the AGM-88C will have a new-generation seeker by Texas Instruments or Ford Aerospace, though both types may be procured.
Current European anti-radiation missile developments include the British Aerospace ALARM, which is to be carried by RAF Tornados and features a parachute-borne search mode. Matra (which collaborated with BAe on the earlier Martel, and since 1984 has produced the ARMAT), is developing a supersonic anti-radiation missile for the Super Etendard and Rafale. Reports indicate a firing range of up to 150 km. This project was initially designated STAR, but it now appears to be referred to as ARF (Anti-Rada Futur). This may well be the first ramiet-powered missile of this type.
The use of a turbofan engine makes possible a long search, which largely overcomes the problem of the target radar transmitter shutting down briefly when the ARM is fired. The leader in this category is the Northrop AGM-136 Tacit Rainbow, due to be carried externally on the A-6E and internally on the B-52G, which will house up to 30 on new rotary launchers. The Tacit Rainbow has a Williams F107 tubofan engine (similar to that of the Boeing ALCM), Doppler navigation and an 18 kg fragmentation warhead.
In addition to the comparatively heavy defence-suppression anti-radiation missiles mentioned above, there is a need for lightweight self-protection missiles that can be carried in addition to a strike aircraft's normal armament. The first example of this category is the Motorola AGM-122 Sidearm. The USMC has had 500 AIM-9C Sidewinders modified to Sidearm I standard by the substitution of a passive RF homing head. The Sidearm IA is an export version, while Sidearm II, which is still in development, has a longer-range, wide FOV seeker.
As air defence systems improve, there is increasing interest in missiles that provide a higher penetration speed or longer range, or ideally both.
The Aerospatiale ASMP carries a 300 kT nuclear warhead over a range of 80-250 km (depending on launch altitude) at a speed of up to Mach 3. The ASMP is powered by a solid rocket booster and a liquid fuel ramjet. It entered service in May 1986 on the Mirage IVP, and will also equip some Mirage 2000Ns and the Super Etendards on the carrier "Foch" and "Clemenceau" (and later "Charles de Gaulle").
It initially appeared that the Royal Air Force would adopt a derivative of the ASMP (designated ASLP) as a replacement for the WE177 free-fall nuclear bomb, but press reports currently favour the Boeing SRAM-T, a derivative of the AGM-131A SRAM-2, which has a range of 400 km.
The USAF is meanwhile funding the TV-guided 80 km Rafael Popeye under the Have Nap programme. The US Navy for its part is developing the 110 km (plus) SLAM (Standoff Land Attack Missile) derivative of the McDonnell Douglas AGM-84 Harpoon anti-ship missile. Guidance for SLAM combines a Global Positioning System receiver (GPS), Maverick IIR seeker for terminal homing, and the Walleye datalink. However, it could be that SLAM is only an interim weapon system, pending the availability of the low-cost, unpowered AIWS (Advanced Interdiction Weapon System), which will equip the A-12. Three US contractor teams are currently competing in the demonstration and validation phase of the AIWS.
The long-range cruise missile category is at present dominated by the Boeing AGM-86 ALCM, which is turbofan-powered and carries a 150 kT warhead over a distance of up to 2500 km. The ALMC is scheduled to be replaced by the General Dynamics AGM-129 ACM (Advanced Cruise Missile), which is to combine a 3000 km range with stealth characteristics.
Perhaps surprisingly, both the US Air Force and US Navy have an interest in a very long-range cruise missile with a non-nuclear warhead. The LRCSW (Long Range Conventional Stand-off Weapon) is a joint programme managed by the US Navy, which is aimed at producing a missile that can be launched by aircraft, ships and submarines. Initial operational capability is scheduled for the late 1990s. Compared to the existing Boeing AGM-86 air-launched cruise missile, the LRCSW will have a longer range, a heavier warload and more accurate guidance. Five companies have been funded to carry out concept definition studies.
Turning finally to airborne anti-ship missiles, this category came into prominence with the successes of the Aerospatiale AM.39 Exocet in the Falklands conflict in 1982, when it was employed with conspicuous success by the Argentinians against Royal Navy vessels. The Exocet was also employed operationally in the Gulf War, mainly by Iraqi Fls. It has a launch weight of 655 kg, a two-stage rocket motor, active radar terminal homing, a 165 kg warhead and a range of 50-70 km.
Aerospatiale has also developed the smaller helicopter-launched 96 kg AS.15TT, which equips Royal Saudi Navy SA.365Fs and operates in conjunction with a Thomson-CSF Agrion radar which, in the case of Saudi Arabia, is mounted under the chin of the helicopter. The equivalent British anti-fast patrol boat missile is the BAe Sea Skua, which weights 145 kg and employs semi-active radar homing. Italian Navy SH-3Ds carry the 340 kg OTO-Melara Marte Mk.2, which has active radar homing and is also proposed for the fixed-wing MB.339K. Norway's 372 kg Norsk Forsvarsteknologi AGM119 Penguin reached operational status on Royal Norwegian Air Force F-16s last year, and is being evaluated for possible use on US Navy SH-60Bs.
The future trend in towards longer ranges and higher speeds. The use of turbine engines was pioneered by the 520 kg McDonnell Douglas AGM-84 Harpoon, which has a Teledyne CAE J402 turbojet and a range of more than 130 km. The Harpoon is used on the US Navy A-6E, P-3CM F/A-18, and S-3B, and on the Royal Air Force Nimrod. It was fired operationally against Libyan vessels in 1986. Other air-breathers include the BAe Sea Eagle and Saab-Bofors RBS15F, which both weigh about 600 kg at launch and use the Microturbo TRI-60 turbojet.
Future anti-ship missile projects include the lightweight ANL (Anti-Navires Leger), as a replacement for the AS.15TT, and the supersonic ANS (Anti-Navires Supersonique), which will replace both the AM.39 Exocet and MBB's Kormoran. Both the ANL and ANS are being studied jointly by MBB and Aerospatiale.
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|Date:||Apr 1, 1990|
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