|Last Updated: Mon Jan 27 11:18:09 UTC 2014
|MAN PORTABLE SURFACE-AIR MISSILES
First published in Australian Aviation
by Carlo Kopp
The proliferation of the second generation man portable Surface-Air-Missile must rank as one of the most important military developments of the decade. These insidious little weapons have rendered battlefield airspace unusable by any aircraft other than high performance tactical jets, while effectively countering the principal weapon of counterinsurgency forces, the helicopter gunship.
The massed deployment of the FIM-92A Stinger in Afghanistan tipped the scales in favour of the Mujahedeen insurgents who shot down large and medium transports, helicopters and significantly, tactical aircraft. This forced the Soviets to change their weapon delivery profiles much to the detriment of bombing accuracy.This in turn rendered Soviet air superiority meaningless, as the low density point targets typical of such warfare cannot be accurately hit from altitude with dumb weapons. The Soviets lost their greatest tactical advantage in the campaign and the result is evident in this year's reluctant withdrawal. It is hardly therefore necessary to elaborate upon the potential of the modern man portable SAM in the hands of a competent terrorist cleverly positioned within a couple of miles of a major airport. The sheer military incompetence of many Third World governments makes the use of supposedly independent terrorist organisations a very attractive option.
The man portable SAM has forced major changes in thinking by those confronted with it, those yet to be confronted still allow themselves the luxury of flying helos and tactical transports without exhaust infrared(IR) suppressors, IR jammers and chaff/flare dispensers the latter tied into IR warning systems and Radar Warning Receivers(RWR).
Second and first generation man portable SAMs use much like point defence SAMs heatseeking, command link or beamriding guidance therefore each class of weapon will have unique strengths and weaknesses. This will become very apparent upon closer examination.
Beam Riders - Bofors RBS-70
Beam riding guidance is one of the conceptually simplest techniques available. A beam riding missile will be equipped with a set of aft facing antennas (or optical detectors) usually mounted on the tips of its cruciform wings. These antennas(detectors) will sense the missile's orientation within a microwave (laser) beam which will track the target. The missile will continuously adjust its flightpath to maintain its position within the beam (ie 'ride' the beam) until it collides with the tracked target. So much for the basic idea. In practice beam riding is a somewhat more complex affair. The flight of a beamrider will be divided into two phases, gathering and guided flight. The gathering phase takes place immediately after launch when the missile's position relative to the beam centreline is is uncertain, this results from various tolerances in the hardware, variations in propellant performance, wind velocity and jitter/pointing errors in the launcher. Gathering involves the use of a radio or optical command link to steer the missile into the centre of the tracking beam, the position of the missile is usually sensed by an infrared device which tracks the missile exhaust plume. Once the missile has been gathered into the beam the beam riding guidance may be engaged and the missile can then corkscrew its way up the beam until collision with the target. The strength of the beamrider lies in simplicity, complete or nearly so immunity to jamming and seduction and the ability to kill targets from all aspects, particularly head-on. A generic weakness of beamriders is a poor kill rate against crossing targets (ie beam aspect)which results from the very high sustained turn rates required of the missile in order to stay within the rapidly slewing beam. Under such circumstances the missile's control surfaces may stall resulting in loss of control and destruction of the weapon. Operator skill level is very important (this requirement itself may be considered a weakness), a clever operator can apply some lead bias in tracking the target during the missile's flight thus preempting the above. The most widely deployed beamrider today is the Swedish laser beam riding AB Bofors RBS-70. This weapon first flew in 1971 entering production by the mid seventies. The weapon fire unit is comprised of an integral missile container/launch tube, a sighting/guidance unit, both attached to a tripod stand/operator seat. The sighting/guidance unit provides a gyro stabilised optical sight with target fine tracking by thumb lever, the optics are boresighted with the laser. Target tracking is achieved by keeping crosshairs on target thus directing the laser beam at it. The missiles are fielded in the sealed container/launch tubes which are discarded after use. The high explosive warhead is proximity and impact fused.
Command to Line Of Sight Guidance - Shorts Blowpipe and Javelin
An alternative form of guidance with many similar characteristics is command link guidance a specific type of which is Command to Line Of Sight (CLOS) guidance. Commonly used in land based and naval point defence SAMs, command link guidance involves fitting the missile with radio (usually VHF to microwave) band receivers via which it receives steering commands from its launcher/ operator. The Blowpipe and Javelin are both optically tracked CLOS (..to target) weapons, where the operator directly (or indirectly) steers the missile into the line-of-sight (LOS) to the target and eventually collision. Like beam riders, CLOS missiles must first be gathered into the field of view of the operator and then steered to impact.
As with beamriders the strength of CLOS guided weapons lies in implicit immunity to seduction, high resistance to jamming and all aspect capability. Their weaknesses are also alike in that operator skill is a prerequisite and performance against crossing targets can be poor, although in this respect a CLOS guided weapon is unlikely to fall out of control but rather fail to sustain the required turn rate and miss the target. The most commonly used CLOS man portable SAM is the Shorts Missile Systems Division Blowpipe. This weapon was introduced over a decade ago and now equips twelve users with a number of weapons used by the Mujahedeen in Afghanistan. The Blowpipe missile is fielded as two assemblies, a reusable Aiming Unit and a factory sealed expendable launching canister. The missile itself is a metal tube containing a two stage solid propellant rocket, a warhead and at its tapered nose, a nose cone fitted with cruciform delta control surfaces. The nose cone is attached via a low friction bearing , the missile is steered by moving the whole nose. The missile has tail mounted cruciform wings wings which are attached to a sliding collar. Stowed in the launcher the collar and folded wings occupy together with the nose cone/controls the large forward part of the launcher. At launch a thermal battery is fired up, the launcher cap blown off by gas pressure, the missile gyro fired and the first stage engine ejects the missile from the canister, extracting and unfolding the wings during exit. The pistol grip aiming unit contains the command link radio transmitter, an optical sight, an autogathering device and optionally an IFF interrogator. Controls comprise a trigger, thumb control joystick, fuse, autogather and command frequency selection switches. An engagement involves clipping the Aiming Unit to the launcher, acquiring the target in the graticuled optical sight and squeezing the trigger. After the first stage burns out at a safe distance the second stage brings the missile up to supersonic speed. Autogathering steers the missile into the centre of the optics field of view (FOV) after which the operator steers the weapon with the joystick to impact judging missile flightpath by the exhaust flare. The Blowpipe has not been as successful as the heatseeking Stinger in Afghanistan primarily due to the need for a skilled operator who can judge the missile and target trajectories and apply appropriate lead. As the operator must account for gravity drop and crosswind drift accuracy can suffer. This can be difficult and the newer Javelin, evolved from Blowpipe, solves much of this with the use of Semi-Automatic CLOS (SACLOS) guidance. This technique involves the infra-red tracking of the missile's flightpath and the automatic transmission of steering commands which keep the missile on the LOS between the aiming reticle and the target. The Javelin Aiming Unit is more complex with additional electronics and optics. An engagement will proceed much like with Blowpipe but with the Aiming Unit projecting a stabilised illuminated aiming mark into the operator's field of view. The target is initially tracked to gain lead, the missile launched and steered to target by the operator who keeps the aiming mark on target with the joystick. In addition to Blowpipe switches and controls the Javelin is fitted with an automatic crosswind cancellation switch. Both Blowpipe and Javelin are proximity and impact fused.
Infra-Red Homing Guidance - General Dynamics FIM-92A/B/C Stinger
The Stinger family of missiles evolved from the FIM-43A Redeye, itself conceptualised by General Dynamics and US Army MICOM in the 1950s, developed in the early sixties and deployed in 1966. The Redeye was designed to shoot down hostile Close Air Support (CAS) aircraft operating against US Army land forces and was the first such weapon ever fielded. The design of such a missile was no mean feat as the state of the art in heatseeking missiles, the AIM-9 Bravo Sidewinder was a cumbersome 70 kg/2.8m weapon with an uncooled lead sulphide (PbS) detector and two channel rotating reticle seeker (see TE March 1982, Heat Seeking Missile Guidance) capable only of tail chase engagements. A new approach was required and GD pioneered several new design features to create the Redeye. Redeye was the first Rolling Airframe Missile (RAM). Unlike conventional roll stabilised missiles which are steered in two axes, pitch and yaw, by two (pitch, yaw) control channels a RAM uses a single control channel which is 'phased' to introduce pitch and yaw commands subject to the missile's instantaneous orientation (roll angle) in roll. In this fashion a single pair of control surfaces can do the work of two pairs saving weight and volume with some penalty in manoeuvre performance. GD applied further new technology to Redeye designing all of the guidance and control electronics with solid state transistor and integrated circuit technology, a first in tactical missiles. Another major weight saving measure was the use of electrical control actuators displacing bulkier conventional hydraulics. Internal wiring harnesses in the missile were replaced with lighter flexible flat printed wiring harnesses . Finally the seeker itself employed conical scanning never previously used in a heatseeking missile. The Redeye warhead was also an unconventional titanium design, built to burn through the skin of the target. The Redeye's short wavelength seeker however limited it to tail aspect shots and it was found to be susceptible to flares, which seduce a heatseeker by presenting a greater infra-red signature than a real target. This was recognised by the US Army who together with the US Marine Corps sought an all aspect Redeye II, subsequently redesignated Stinger. Development of the Stinger proceeded from 1972 to 1977 concurrently with a post-1974 Aeronutronic Ford Alternate Stinger semi active laser homing weapon which was later abandoned. The Stinger design was a much improved Redeye, 1.52m rather than 1.2m long weighing 15 kg a 16% increase in weight. The missile fuselage is divided into functional blocks. The tail of the Propulsion Section mounts a launch rocket engine with canted nozzles to impart spin (roll) during launch, it burns out and separates within the disposable wound Kevlar launch tube. The missile fuselage boat tail mounts the tail assembly with its folding canted cruciform tail surfaces, these lock after launch and sustain the fuselage roll during flight. The dual burn Atlantic Research engine high energy propellant is claimed by GD to be the state of the art in production propellants, it will accelerate the missile to cca twice the supersonic speed of Redeye. Forward of the Propulsion Section is the Warhead Section also containing the Motorola proximity fuse. The missile is designed to hit the target and inflict as much damage as possible kinetically, the 3kg Picatinny Arsenal fragmentation warhead will enhance this damage. The nose of the missile contains the Guidance Section the aft part of which contains the missile battery, controls and umbilical interfaces. One pair of unfolding cruciform canard surfaces is fixed and the other controlled by the seeker. The battery powers both electronics and controls. The Alpha model seeker uses gyro stabilised optics to focus infrared energy received through the nose window on to a gas cooled detector. The missile will fly a proportional navigation trajectory homing in on the target's exhaust plume until its terminal phase, where a Target Adaptive Guidance (TAG) algorithm steers the missile into the target's aft fuselage to damage structure and powerplant hot end. GD claim the ability to acquire, track and hit targets from all aspects. The cooled single colour seeker was a vast improvement over Redeye but didn't provide the flare rejection sought by users. In 1986 it was supplanted by the FIM-92 Bravo Stinger-POST (passive Optical Seeker technique) seeker which introduced a new rosette-scanning dual band infrared(IR) and ultraviolet(UV) detector/optics assembly. The POST seeker exploits the low UV reflectance of aircraft compared to a sky background and initially acquires and guides the missile on to the UV 'hole' in the sky represented by the target. The concurrent use of UV and IR allows unambiguous rejection of flares which are bright in both the UV and IR bands. The expectation that the threat will use IR jammers led to the 1989 phase-in of the FIM-92 Charlie Stinger-RMP (Reprogrammable MicroProcessor) version which is field reprogrammable with new guidance software if required. A memory module in the gripstock can be swapped, it would contain executable software which is downloaded to the memory of the microprocessor chip in the missile via the umbilical interface. The missile is supplied as a complete round with the launch tube sealed and pressurised with Nitrogen to keep out moisture, the seeker sees out through a fragile IR and UV transparent membrane. The gripstock contains the launcher control electronics and mounts a pistol grip with trigger and a Battery/Coolant Unit (BCU). The BCU supplies electrical power to the gripstock electronics and missile prior to launch and Argon gas coolant to cool down the detector. If a launch doesn't occur a fresh BCU is fitted. A lightweight IFF interrogator is also fitted with electronics and a battery in a belt pack. A typical engagement will involve the visual acquisition of a target by the observer in the two man fire team, using field glasses. The gunner will then clip a fresh missile to the gripstock while the observer tracks the target. A safety switch on the gripstock is then used to apply coolant and power to the missile spinning up the seeker gyro and cooling down the detector. The seeker is initially caged to the missile centreline, the gunner must track the target in his graticuled optical sight for seeker acquisition. Once the seeker has acquired the target an acquisition tone is produced and the seeker may be uncaged to track the target, this is done with a gripstock switch. To provide proper lead against a crossing target and elevation to compensate gravity drop during missile launch the gunner must track the target with one of three markers in the optical graticule, one for each aspect. Depressing the trigger then fires the missile battery which retracts the umbilical connector, this in turn fires the launch engine after which the missile exits the tube. The use of optical homing with proportional nav means that the missile will collide with an approaching target or pursue a crossing or receding target. As Stinger is a true fire and forget missile the fire team may quickly run for cover since the missile exhaust plume has betrayed their location.
The SA-7 Grail, SA-14 Gremlin and SA-16
The Russians were understandably alarmed by the discussion surrounding Redeye and sought to build an equivalent - this missile is the ubiquitous 9M32 Strela 2. Work on the 9M32 commenced in 1959 with development completed in 1965 and deployment a year later. The missile was conceptually similar to Redeye as a RAM using an uncooled PbS seeker sensitive to 2 micron band IR emissions. The missile uses a launch engine and sustainer and carries a 1.8 kg high explosive/fragmentation warhead with an impact/grazing fuse. The 9M32 suffered major performance limitations resulting from poor propellant performance and a crude IR seeker with a habit of locking on to clouds, the sun and hot pieces of countryside. It was supplanted in production from 1972 by the upgraded 9M32M Strela 2M with a 50% improvement in range to 3 n.mi. resulting from better propellant, an improved warhead and an IR filter to prevent extraneous IR radiation from upsetting the seeker. Both versions of the Grail employ an expendable fibreglass launcher and a reusable gripstock, a battery/coolant unit is mounted below the front of the tube. The limitations of the SA-7 led to its replacement in front line service by its derivative designated the SA-14 Gremlin which entered service in the early eighties. Concurrently the Russians fielded an entirely new missile the SA-16. The SA-16 is a larger 1.55m weapon with a conical (or perhaps ogival) low drag nose cone and presumably better aerodynamic performance. Both missiles are credited with true all aspect performance.
The Man Portable SAM in Combat
The man portable SAM was first fired in anger in 1971 over the Suez Canal, when an SA-7 embedded itself in the tail of an Israeli jet and failed to explode. By mid 1972 the SA-7 was being fired in South Vietnam in large numbers accounting for 45 aircraft in 500 launches by the US withdrawal. The initial kill rate of 33% soon dropped to several percent with evasive manoeuvring and the use of flares. Most kills were against helicopters and slow moving prop transports and fire support gunships. The SA-7 performed poorly in the 1973 Yom Kippur war as most of its targets were fast and agile tactical jets. The conflict where the SA-7 was seen to perform best was the final phase of the SE Asian conflict in 1975 where the SA-7s took a devastating toll of the South Vietnamese AC-47, AC-119 gunships and A-37 strike aircraft. The SA-7 attracted little further attention until the the escalation of the Rhodesian civil war where missiles fired by black nationalists downed several unfortunate civilian transports.
The Afghan conflict saw the SA-7 in use again when CIA and Arab nation supplied missiles used by Mujahedeen successfully destroyed several helicopters and transports. The Russians responded by dropping flares and fitting IR suppressors to helo exhausts countering the SA-7s simple seeker. The Afghans were subsequently supplied with Stingers and Blowpipes, the former achieving a good kill rate throughout the conflict. While many sources question the overall impact of the Stinger in this war, pointing to the furious Russian retaliatory strikes on areas known to harbour SAM fire teams, the reduction in CAS sortie rates, bombing accuracy and additional cost in operations cannot be ignored. The successful destruction of CAS aircraft and Hind gunships was shown to have a major psychological impact upon Soviet and Afghan communist aircrew, while the destruction of transports clearly disrupted internal logistical operations. The success of the man portable SAM in Hind killing in Angola was a major factor in the success of insurgent operations. It will be interesting to see the real statistics when they become available.
Defeating the man portable SAM will in most instances require a combination of manoeuvre and countermeasures. The diversity of guidance techniques and missile aerodynamic performance to be countered will rule out any simple strategy. Third world governments and associated terrorist groups where applicable may well be using US, UK, French, Chinese and Russian weapons of various vintages and revision types purchased legally or illegally. The first aspect of defence is knowing that a missile has been launched at you. Lookout is therefore essential although a beam or tail aspect shot may not be sighted. It is therefore desirable that fixed wing aircraft and helicopters carry IR detection equipment (eg Cincinnati AAR-44) which can detect and track the missiles exhaust plume, very hot with high energy propellants, providing audible and azimuth warning to the pilot. This may be the only warning available of an optical/IR missile launch. Beam riders and CLOS/SACLOS weapon guidance equipment will transmit radio or optical(ie laser) guidance signals which may be detected by a suitable Radar Warning Receiver (RWR) or Laser Warning Receiver (LWR). It is not clear from published literature whether established types such as the Dalmo Victor APR-39 RWR integrated with the Perkin Elmer AVR-2 LWR have such a capability. The dominance of optical homing missiles will eventually dictate the use of an IR warning receiver. Once the missile is detected and its plume sighted the best combination of measures is the dropping of flares to seduce a heatseeker or at least degrade its seeker performance while entering a hard break turn to attain beam aspect relative to the inbound missile (see TE July 1987 for a detailed discussion of evasive tactics). This manoeuvre will force the missile to sustain a high turn rate which may in itself defeat the weapon, it may stall its controls or fall out of control. At least this manoeuvre will slow the weapon down due to the drag induced by the body lift used to turn the missile. This is desirable as the propellant will burn out very quickly and the less energy (speed/altitude) the missile has the less likely it is to get you. As is apparent this tactic applies primarily to tactical jets with the thrust/weight and speed to make a difference to a supersonic projectile. It is thus mandatory that a CAS aircraft even when employed in counterinsurgency operations has the aerodynamic performance to sustain high G high speed manoeuvring at low altitude (the reported RAAF interest in using the PC-9 or Macchi for CAS could be questioned in this context). Helicopters and transports do not have this option and are certain kills if not equipped with IR exhaust radiation suppressors and suitable IR jammers. Exhaust suppressors mix cold air into the exhaust plume to cool it down while also preventing direct IR radiation from the turbine hot end. While flares are often carried by transports and helos second generation heat seeking SAMs are certain to reject them and jammers are a must. An IR jammer such as the Northrop AAQ-4, AAQ-8, MIRTS or Loral Matador will typically pulse an IR source at such a rate that it will interfere with the seeker/reticle scan of a heatseeking missile. The effectiveness will depend upon the knowledge of the missile to be countered, like all jammers it must be threat specific to be really effective. An aircraft or helo venturing over unsanitised territory would therefore preferably carry a suite including an IR launch warning receiver, suitable IR jammers and a flare dispenser. Penetration should be at very low level to provide terrain masking or where the situation permits well above 10,000 ft so as to stretch the threat performance envelope to the limit. Jammers and expendables should be tied into the warning receivers to provide automatic dispensing and emission upon detection of a launch. Given the possibility of manportable SAMs being deployed in the immediate vicinity of friendly landing zones or air strips it is almost mandatory that a 3 n.mi. area beyond either threshold be cleared or at least protected from intruders. On climbout at full power and low airspeed a transport is a textbook target for a heatseeker.
The second generation of man portable SAMs has yet to see large scale combat use but its immunity to trivial countermeasures and improving engagement envelope render it a major threat to helicopters, tactical transports, slower close air support/counter-insurgency aircraft and poorly flown tactical jets. The counter to such weapons lies in a combination of tactical flying, warning equipment and countermeasures none of which alone are likely to be adequate. Given the off-the-shelf availability of these weapons and thus almost non-existent warning time to deployment, those air forces and air arms which fail to suitably equip and train do so at their peril.
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