Dr Anil Kumar Maini is former director, Laser Science and Technology Centre, a premier laser and optoelectronics research and development laboratory of Defence Research and Development Organisation of Ministry of Defence

Nakul Maini is currently pursuing Masters at University of Bristol, UK. He was working as a technical editor with Wiley India Pvt Ltd

Infra-red-guided [(IR)-guided)] weapons are no less important than laser-guided munitions

Fig. 1: Hot spots on the target aircraft as seen by an IR seeker
Fig. 1: Hot spots on the target aircraft as seen by an IR seeker

considering their usage in tactical warfare. While laser-guided munitions are predominantly used in air-to-surface and surface-to-surface roles, IR-guided weapons are largely surface-to-air man-portable air defence systems (MANPADSs) and air-to-air missiles. The IR-guided air-to-air missile has been a feature of the fighter armament since 1950’s and is likely to remain a key weapon for decades to come.

While laser and radar-guided weapons use semi-active or active homing for guidance, and therefore need an external laser source or radar for the purpose, IR-guided weapons make use of passive homing guidance in which the weapon homes on to the IR signatures due to hot areas of the target. For this reason, these are popularly known as heat-seeking weapons. Of course, for the weapon to be reliable, the guidance system processor has to perform the complex task of detecting and identifying the genuine signal in the presence of noise produced by unwanted IR emissions from the background due to reflection of solar radiation from the Earth’s surface, clouds and mountains, and IR countermeasures such as chaff and flares deployed by the target.

Fig: 2: Sources of IR signatures
Fig: 2: Sources of IR signatures
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Initial development of IR-guided (or heat-seeking) missiles began in late 1950’s. AIM-4 Falcons and AIM-9 Sidewinders are important air-to-air heat-seeking missiles of that time. These weapons were not very successful, initially, due to certain issues that were mainly related to reliability. Modern IR-guided missiles are a vast improvement over the ones developed in yesteryears. These not only have increased operational ranges and hit accuracy, these are far less vulnerable to countermeasures and are capable of discriminating the intended target from passive and active countermeasures.

IR homing guidance

There are two broad categories of IR-guided weapons, namely, those employing non-

Fig. 3: Spectral profile of an IR emission from a typical target aircraft
Fig. 3: Spectral profile of an IR emission from a typical target aircraft

imaging-type IR-seeker heads and those employing imaging infra-red (IIR) seekers. Non-IIR-guided missiles home on to IR signatures produced by hot areas of the target. Fig. 1 shows hot spots on the target aircraft as seen by the seeker head of an IR-guided missile.

Fig. 2 shows different sources of IR signatures of the aircraft. The IR sensor used in this case is a single detector. In the case of IIR seekers, it is an imaging IR sensor, which is a focal plane array of IR/UV detectors. Imaging sensor array sees in IR in a manner similar to the

Fig. 4: Transmission characteristics of the atmosphere
Fig. 4: Transmission characteristics of the

functioning of a CCD sensor in a webcam or a digital camera.

IIR sensor output requires much more complex signal processing. In addition to being more resistant to IR countermeasures, such as flares and decoys, imaging seekers are also less likely to be fooled into locking onto the sun, another common trick for avoiding heat-seeking

Fig. 5: IR spectrum as seen by the seeker head of an IR-guided missile
Fig. 5: IR spectrum as seen by the seeker head of an IR-guided missile

missiles. By using advanced image processing techniques, the target shape can be used to find its most vulnerable part. This information can then be used to steer the weapon towards the target.

Non-IIR-guided missiles make use of IR emission corresponding to thermal signatures of the exhaust and the mainframe of the target aircraft to home on it. Emission in 3-5 and 8-12 micron bands is characteristic of electromagnetic emission from jet exhaust and mainframe of the aircraft. Fig. 3 shows the spectral profile of IR emission from different parts of a typical target aircraft. Spectral content of IR emission as received by a seeker head is the superposition of spectral emission of the aircraft on the transmission characteristics of the atmosphere (Fig. 4).

Fig. 5 shows a typical IR-emission spectrum that would be seen by the non-imaging seeker head. This wavelength signature is judiciously used in guidance of air-to-air and surface-to-air IR-guided missiles.
Modern IR seekers also operate in the 8-12 micrometre wavelength range, which is absorbed least by the atmosphere. Such seekers are called two-colour systems. Two-colour seekers are harder to defeat with countermeasures such as flares and jammers.

IR-guided missiles developed in 1970s and 1980s used single-colour IR seekers employing 3-5 micron band. IR seekers used in these missiles were most effective in detecting IR radiation of shorter wavelengths such as 4.2 micron emission of carbon dioxide efflux of a jet engine. Seekers responding to 3-5 micron band were called single-colour seekers and missiles as single-colour missiles.

MAGIC series air-to-air missiles from France and R-73 air-to-air missiles from Russia are some examples. State-of-the-art IR-guided missiles use seekers that respond to both 3-5 and 8-12 micron bands to offer improved false alarm rejection and immunity to deception by flares. These seekers are called two-colour seekers and missiles, two-colour missiles. Python from Israel and RVVAE from Russia are examples of missiles using two-colour seeker heads.

Also, both surface-to-air and air-to-air IR-guided missiles receive target’s IR signatures in the presence of background radiation from the sky and also IR signatures of flares, if any, deployed by the target aircraft platform. The seeker head should be able to discriminate between IR signatures of the background and flares from those of the target.

Advantages and limitations
IR-guided missiles and radar-guided missiles are deployed in similar roles, predominantly as surface-to-air and air-to-air guided weapons. It would therefore be nothing but logical to compare the two types of guided weapons.

IR-guided missiles offer several advantages over radar-guided missiles. One, IR-guided missiles are far more immune to electronic countermeasures than their radar counterparts.

Two, IR-guided missiles offer greater safety of pilots of the aircraft carrying these weapons. Due to the inherent fire-and-forget capabilities of IR-guided missiles, after releasing the missile, the pilot can leave the area while the missile guides itself to the target.

Three, IR-guided missiles are almost impossible to detect during launch preparation. On the other hand, radar-guided missiles employ either beam rider or semi-active or active guidance. In all forms, it employs a radar, which can be detected through radar emission during launch preparation or flight.

Four, IR-guided missiles are manoeuvring missiles and are particularly suitable for close engagement.
Five, IR sensors perform well during day and night conditions.

Six, IR sensors employed by heat-seeking missiles cost less per unit.

While radar-guided missiles are all-weather weapons and have relatively much longer operational ranges, heat-seeking missiles perform better in close-in ranges. Also, heat-seeking missiles are vulnerable to the use of passive and active IR countermeasures. Use of chaff, decoys and flares to deceive heat-seeking missiles is a common occurrence. Heat-seeking missiles employing IIR seekers though are far less vulnerable to these countermeasures.

In the early days of development of heat-seeking missiles, these missiles could only lock on to intense sources of heat such as jet exhaust pipes, and therefore could be fired only from behind the aircraft. Present-day missiles using advanced IR sensors can even lock on to friction-heated air streaming back from the aircraft’s nose. These missiles can be fired from any angle.

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IR-guided-missile seekers
Two broad categories of seekers are used in heat-seeking missiles. These are reticle seekers using single IR detectors and imaging seekers that use a focal plane array of IR/UV detectors. Both types have different variants.

Fig. 6: Basic reticle seeker
Fig. 6: Basic reticle seeker

In the most basic reticle seeker (Fig. 6), IR energy emitted by the target is collected by the

Fig. 7: Representative reticles
Fig. 7: Representative reticles

optical system and focused on the detector through a rotating reticle. A reticle is nothing but an optical modulator made up of a circular element having sequentially-arranged transparent and opaque spokes on it (Fig. 7). The reticle chops the scene represented by IR energy. The output of the detector is a sequence of pulses whose amplitude is proportional to the magnitude of IR energy and whose frequency is equal to the product of spin rate of the reticle and the number of transparent/opaque spoke pairs.

Also, modern reticle-seeker based heat-seeking missiles use spinning mirrors and a fixed reticle. The phase of detector signal with respect to a reference phase is used to determine the angular position of the seeker axis with respect to the target. The angular error is then used to keep the seeker axis pointed towards the target within its field-of-view and also control the flight path of the missile to intercept the target.

We have spin-scan seekers that suffer from the problem of centre-null and conical-scan seekers that eliminate this problem. We shall not go into details of these techniques. Lead-sulphide (PbS) with peak sensitivity in the wavelength region of two micron when uncooled, indium-antimonide (InSb) with peak sensitivity in 4-5 micron band when cooled to liquid nitrogen temperature and mercury-cadmium-telluride (HgCdTe) with peak sensitivity in 8-12 micron band when cooled to liquid nitrogen temperature are the commonly used detector materials.

Lead sulphide detectors were used in older missile seekers, which forced missiles to look at stern engagements as the missile had to look at the hot turbine in the tail-pipe region to get sufficient signal to track the target. Modern missiles almost invariably use InSb or HgCdTe detectors.

Missile seekers would find it very easy and convenient to detect and track a hot target against a uniform benign cool background than doing so in the presence of clouds and extended IR sources. Sunlight reflected from the edge of a cloud would be as attractive a target, if not more, for the missile seeker than a jet aircraft. Reticle seekers handle all these issues by having very small instantaneous field-of-view (IFOV) and/or advanced signal processing.

Fig. 8: Pure pursuit navigation
Fig. 8: Pure pursuit navigation
Fig. 9: Proportional navigation
Fig. 9: Proportional navigation

Navigation to the target is the next important step after target acquisition and tracking. In

Fig. 10: Imaging focal plane arrays
Fig. 10: Imaging focal plane arrays

one method called pure pursuit, also called direct pursuit, the navigation technique ensuresthat the seeker is looking at the target continuously throughout the engagement duration till it eventually hits the target. In the case of pure pursuit engagement, the flight path is not the most direct one, as shown in Fig. 8, and the trajectory has an ever-decreasing radius-turn towards the end of the engagement. This poses a problem as the missile may not be left with enough energy to complete the turn in close-in range, allowing the target to escape.

Proportional navigation or proportional pursuit, which is invariably followed in air-to-air missiles, allows the missile to have the shortest flight path towards the intercept, and therefore eliminates the need for a high-g manoeuvre towards the end. Proportional navigation flight path is established by a constant look angle as shown in Fig. 9 for a given constant missile velocity and assuming that target does not manoeuvre. In practice, target does manoeuvre and the missile velocity is also not constant through engagement duration. Therefore look angle is updated as and when required.

Fig. 11: Imaging IR seeker concept
Fig. 12: FGM-148 Javelin

A variant of the reticle seeker is the pseudo imaging seeker. This seeker uses one or more detectors enabling both spatial and temporal information from reticle seekers. A small IFOV (≅ two milliradian) is scanned in a preset pattern and spatial information is used to determine the time instant of appearance of the target within the field-of-view. Detectors are therefore activated only within the time gate around the predicted time. This allows the missile to avoid large clutter and false targets outside the time gate. It also makes seeker highly immune to IR countermeasures. Imaging seekers use an array of detectors called imaging focal plane arrays (Fig. 10) instead of reticles to build an image of the scene in front (Fig. 11). The image may be created by scanning the scene and using a linear array or a two-dimensional staring array.

Fig. 13: PARS 3 LR
Fig. 13: PARS 3 LR

Imaging seekers are very expensive, require huge processing power and complex tracking algorithms. These are therefore employed only under demanding operational requirements. Reticle seekers, on the other hand, are less expensive and easy to manufacture and operate, and have a proven reliability and accuracy.

IR-guided missile systems
Some of the better known IR-guided missile systems are briefly described in the following paragraphs. These missile systems have been grouped into three categories, namely, anti-tank-guided missiles (ATGMs), surface-to-air missiles (SAMs) and air-to-air missiles (AAMs).

Anti-tank-guided missiles. ATGMs, also known as anti-armour missiles or anti-tank missiles, are designed to precisely hit and destroy heavily-armoured military vehicles including all combat and transportation vehicles. Different variants of anti-tank missile systems include shoulder-fired weapons, large-tripod-mounted weapons, vehicle-mounted weapons and systems launched from airborne launchers. American Javelin, German PARS-3 LR, Israeli Spike and Indian Nag are some examples.

American FGM-148 Javelin (Fig. 12) is a man-portable third-generation fire-and-forget anti-tank-guide missile jointly developed by Raytheon and Lockheed Martin. It has an effective firing range of 75m to 2500m, with 4750m being the maximum range. It uses a tandem-shaped charge warhead that can penetrate reactive armour. The missile can be used in both top attack mode to hit usually thin-top armour of the target vehicle and direct mode to hit buildings and airborne targets. It uses an IIR seeker and on-board tracker to make it a fire-and-forget missile. It was introduced into service in 1996 and is in service till date. It was successfully used in Operation Enduring Freedom (war in Afghanistan) and Operation Iraqi Freedom.

Fig. 14: Flight trajectory in top-attack (top) and direct-attack (bottom) modes
Fig. 14: Flight trajectory in top-attack (top) and direct-attack (bottom) modes

PARS 3 LR (Fig. 13) is an autonomous fire-and-forget missile intended for long-range

Fig. 15: NAG ATGM
Fig. 15: NAG ATGM

applications and designed to destroy ground (tanks and armoured vehicles), air (helicopters) and other individual targets. Manufactured by Parsys GmbH, MBDA Deutschland GmbH and Diehl BGT Defence, PARS 3 LR is also known as TRIGAT-LR and AC-3G. The missile can be launched from a ground vehicle or a helicopter and can be fired in salvos of up to four missiles in eight seconds. The missile has a specified operational range of 500m to 5000m, which is extendible up to 7000m. It can be used in both top (terminal dive) mode as well as direct mode. Fig. 14 (top part) shows the flight trajectory for top-attack mode employed for anti-armour role with the missile launched from either a land vehicle or a helicopter.

It also shows the flight trajectory for direct-attack mode (bottom part) employed for an anti-helicopter role with the missile launched from either a land vehicle or a helicopter. The missile uses a passive IR seeker that locks on to the target before the missile is fired. It uses tandem-shaped charge for maximum lethality against modern reactive armour. German army has authorised series production of the missile system. The delivery began in mid-2013 and shall continue till 2016.

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Spike is a fourth-generation man-portable fire-and-forget anti-tank and anti-personnel missile designed and developed by Rafael Advanced Defence Systems. The missile can be launched in fire-and-forget mode, destroying targets within the line-of-sight of the launcher and also in fire, observe and update guidance mode while following a top-attack flight trajectory.

In fire-and-forget mode, the tracker is locked on to the target. The missile is launched and it automatically propels itself towards the target. The missile uses a tandem-charged high explosive anti-tank (HEAT) warhead that can penetrate explosive reactive armour.

Fig. 16: Stinger missile system being fired (a) from shoulder, and (b) from a land vehicle
Fig. 16: Stinger missile system being fired (a) from shoulder, and (b) from a land vehicle

The guidance system of Spike comprises a charge-coupled device (CCD) and an IIR seeker. The IIR sensor, in addition to providing higher sensitivity, offers improved thermal background rejection characteristics for all-weather day and night operation.

Different variants of Spike missile system include Spike short range (Spike SR) with a maximum operational range of 800m, Spike medium range (Spike MR) with maximum operational range of 2500m, Spike long range (Spike LR) with maximum operational range of 4000m, Spike extended range (Spike ER) with maximum operational range of 8000m, Spike non line-of-sight (Spike NLOS) with maximum operational range of 25km and Mini Spike with engagement range of 1300m. Mini Spike is an anti-personnel-guided weapon.

The Spike missile system is currently in service with Dutch, Chilean, Colombian, Finnish, German, Polish, Italian, Peruvian, Spanish and Singaporean armed forces. The missile system has been successfully used during Lebanon war in 1982, Second Intifada beginning year 2000, Afghanistan war from 2001 till date and Iraq war in 2006.

Nag (Fig. 15) is a third-generation fire-and-forget ATGM from India, designed and developed by Defence Research and Development Organisation (DRDO) and manufactured by Bharat Dynamics Ltd. It has two variants employing an active IIR seeker and a millimetric wave seeker. The operational range for the land version is 500m to 4000m, and 7km to 10km for air-launched version. It is likely to be inducted into service in 2015.

Surface-to-air (SAM) missiles. Short- to medium-range missiles used in the air defence role against attack helicopters and aircraft are the most common surface-to-air missiles that use IR homing guidance. A large proportion of these missiles belong to the category of MANPADS. Some of the more common and better known IR-guided surface-to-air missile systems are Stinger, Igla (Igla and Igla-1) and Strela (Strela-2 and Strela-3).

FIM-92 Stinger is a man-portable IR-guided surface-to-air missile designed by General Dynamics and manufactured by Raytheon Missile Systems in the USA, in Germany by European Aeronautic Defence and Space Co. (EADS) and in Turkey by ROCKETSAN. It entered into service in 1981 and continues to be in service till date. It is adaptable to be shoulder fired [Fig. 16(a)] or from land vehicles [Fig. 16(b)] as surface-to-air missile and helicopters as air-to-air missile. Stinger missile has evolved over the years and has undergone significant technological improvements.

Three main variants of stinger include FIM-92A, FIM-92B and FIM-92C. These are known by the names of Stinger basic (FIM-92A), Stinger passive optical seeker technique or Stinger POST (FIM-92B)], and Stinger reprogrammable microprocessor or Stinger RMP (FIM-92C).

Stinger is intended to fulfil short-range air defence (SHORAD) role till 2018. It consists of a

Fig. 17: 9K 338 Igla-S (SA-24 Grinch) missile system
Fig. 17: 9K 338 Igla-S (SA-24 Grinch) missile system

Stinger round encased in a launch tube and separates a grip-stock assembly. Stinger basic employs an IR seeker. Stinger POST uses a dual IR and UV seeker, thereby providing higher immunity to countermeasures as compared to Stinger. Stinger RMP is so-called because of its ability to load a new set of software via an ROM chip inserted in the grip at the depot. The missile has maximum effective firing range of 4.8km and maximum speed of 2.2Mach (750m/s).
Stinger made its debut in warfare in 1982 during Falklands war between the UK and Argentina. Subsequently, it was used in the Soviet War in Afghanistan, Angolan civil war, Libyan invasion of Chad, Chechen War, Sri Lankan civil war and Syrian civil war.

Russian Igla is a MANPADS manufactured by KBM. The missile has a maximum operational range of 5.2km and a peak speed of 800m/s. It has three variants, namely, 9K310 Igla-1E (NATO designation SA-16 Gimlet), 9K38 Igla (NATO designation SA-18 Grouse) and 9K 338 Igla-S (NATO SA-24). Igla missile system was inducted into service in 1981, and its different variants developed over the years continue to be in service till date.

9K310 Igla-1 with its 9M313 missile uses liquid nitrogen cooled indium-antimonide IR seeker head. 9K38 Igla with its 9M39 missile was inducted into service in 1983. It used liquid nitrogen cooled indium-antimonide and uncooled lead-sulphide IR seeker head that has higher sensitivity and improved resistance to countermeasures and jamming.

Igla-S (SA-24 Grinch) shown in Fig. 17 is the latest generation of portable air defence missile system designed to target visible aerial platforms, such as helicopters, tactical aircraft, unmanned aerial vehicles and cruise missiles. It is an improvement over earlier SA-16 and SA-18 versions. It employs a dual-band IR seeker and has a maximum engagement range of 6km as compared to 5.2km in the case of SA-16 and SA-18. It also uses a heavier warhead, which allows it to destroy the target even if it misses the target by 1.5m.

Strela family of missiles is man-portable surface-to-air missiles that use passive IR homing guidance and a high explosive warhead. Different members of the family are 9K31 Strela-1, 9K32 Strela-2, 9K34 Strela-3 and 9K37 Strela-10. Strela-1 is commonly known by its NATO designation SA-9 Gaskin and is a short-range, low-altitude, self-propelled SAM-carrying system based on the BRDM-2 chassis, an amphibious patrol car mounting two pairs of ready-to-fire 9M31 missiles. The missile has a maximum operational range of 4.2km and speed of 1.8Mach. It uses a lead-sulphide IR seeker.

9K32 Strela-2 (NATO designation SA-7 Grail) is a man-portable, shoulder-fired, low-altitude surface-to-air missile system with maximum firing range of 3700m (Strela-2) and 4200m (Strela-2M). It was inducted into service in 1968. SA-7 Grail is a tail-chase missile system whose efficacy depends on its ability to lock onto the heat source of low-flying fixed and rotary-wing aircraft. The simple IR seeker mechanism of the missile is easily prone to simple countermeasures and environmental effects.

9K34 Strela-3 (NATO designation SA-14 Gremlin) was developed to overcome the shortcomings of its predecessor Strela-2. 9M36-1 missile of SA-14 Gremlin used a new IR homing seeker that was less vulnerable to jamming and decoy flares as compared to SA-7 Grail. It has a maximum operational range of 4.5km and average supersonic speed of 410m/s.

9K35 Strela-10 (NATO designation SA-13 Gopher) was designed to replace Strela-1. It was an improvement on Strela-1 and had an effective firing range of 5km. The 9M37 missiles of Strela-10 used a higher quality IR seeker than was used in 9M31 missiles of Strela-1 system.

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Air-to-air missiles. Air-to-air missiles are broadly grouped as short-range air-to-air missiles (SRAAM), also sometimes known as within-visual-range air-to-air missiles (WVRAAM) or dogfight missiles, and medium-range air-to-air missiles (MRAAM) and long-range air-to-air missiles (LRAAM). The second group of missiles is also known as beyond-visual-range air-to-air missiles (BVRAAM).

While missiles of the first group that have engagement ranges up to 30km are usually heat-seeking missiles, missiles of the second group largely employ radar guidance. In the case of long-range missiles, IR signatures of the target aircraft would be too weak for the detector to be able to track the target. The short-range IR-guided air-to-air missiles have seen five generations of development. These developments have mainly been in IR seeker technologies and to some extent in digital signal processing.

The first generation of these missiles used IR seekers that had a field-of-view of 30° and the attack aircraft needed to position themselves behind the target aircraft during attack. The target in that case could easily move out of the seeker’s field-of-view with a simple manoeuvre. Second-generation missiles used IR seekers with field-of-view of 45°. Third-generation missiles were all-aspect missiles, which meant that, the attack aircraft did not have to position itself behind the target aircraft.

Fourth-generation missiles used advanced seekers that had higher resistance to IR countermeasures and increased field-of-view of 120°, giving these higher off-bore sight capability of 60°. Fifth-generation missiles used IIR seekers and more powerful digital signal processing, which gave these higher immunity to IR countermeasures like flares, greater sensitivity and ability to hit vulnerable points on the target.

Some of the well-known contemporary air-to-air missiles include IRIS-T of Germany, Vympel R-73 of Russia, MBDA MICA-IR of France, AIM-132 ASRAAM of Great Britain, AIM-9X Sidewinder and Python-5 of Israel.

IRIS-T is a short-range air-to-air missile manufactured by Diehl BGT Defence. It employs an IIR seeker. It has a maximum speed of 3Mach and operational range of approximately 25km. It was developed to replace AIM-9 Sidewinder missile. IRIS-T has a higher resistance to IR countermeasures such as flares. Extreme close-in agility of IRIS-T with capability to make 60g turns at 60°/s allows the missile to engage targets even behind the launching aircraft. It was inducted into service in 2005.

Vympel R-73 (NATO designation AA-11 Archer), manufactured by Tbilisi Aircraft Manufacturing, is also a short-range air-to-air missile with maximum speed of 2.5Mach and maximum operational range of 20km (R-73E), 30km (R-73M1) and 40km (R-73M2). It employs a cryogenically-cooled all-aspect IR homing seeker with high off-bore sight capability, allowing the missile to see 40° off the missile’s centre line. It was inducted into service in 1982. R-73 is also on the inventory of Indian Air Force.

Fig. 18: MICA-IR air-to-air missile
Fig. 18: MICA-IR air-to-air missile

MICA-IR (Fig. 18), manufactured by MBDA, is a short- and medium-range air-to-air missile having a maximum operational range of 50km and a maximum speed of 3Mach. It uses an IIR seeker that gives the missile high resistance to countermeasures such as chaff and decoy flares. It can lock on after launch, which means that it can engage targets outside the missile’s acquisition range at the time of launch. It is in service since 2000. Indian Air Force has ordered Mica-IR missiles for its MIRAGE upgrade 2000H multi-role fighters.

Fig. 19: AIM-9X air-to-air missile
Fig. 19: AIM-9X air-to-air missile

AIM-132 ASRAAM is a short-range air-to-air missile manufactured by MBDA. It uses an IIR seeker with lock-on after launch capability, has a maximum speed of 3+Mach and maximum operational range of 50km. It is in use in Royal Air Force and Royal Australian Air Force having replaced AIM-9 Sidewinder. Indian Air Force is also acquiring ASRAAM to replace the ageing Matra Magic missiles. These missiles will be integrated on Jaguar strike aircraft.

AIM-9X (Fig. 19) is the latest addition to the Sidewinder family of short-range air-to-air missiles developed by Raytheon Co. It features an IIR seeker focal plane array seeker with off-bore sight capability of 90°. The IIR seeker gives it higher resistance to IR countermeasures. The first Sidewinder missile was developed in the 1950s. AIM-9X is the fifth-generation Sidewinder and is now in production. AIM-9X uses passive IR energy emitted by target aircraft for acquisition and tracking, which provides a launch-and-leave air combat missile capability. AIM-9X Sidewinder is characterised by an operational range of about 35km and a speed of 2.5Mach.

AIM-9X Block-I was the first in the family of these missiles. Currently, AIM-9X Block-II has entered full-scale production. Block-II missiles are the upgraded version of Block-I missiles with lock-on-after-launch being the main added feature. The development work has commenced on AIM-9X Block-III missiles. Block-III missiles will have 60 per cent longer range and use insensitive munitions warhead for increased ground crew safety in addition to replacing old components with state-of-the-art ones. Block-III Sidewinder missiles are expected to achieve operational capability by 2022.

Python-5 is one of the most advanced air-to-air missiles in the world. Different variants of Python family include Shafrir-1, Shafrir-2, Python-3, Python-4 and Python-5.

Python-5 is the latest addition to the family and is the fifth-generation air-to-air missile. Manufactured by Rafael Advanced Defence Systems in Israel, it has many advanced features such as an IIR seeker to give it high immunity to IR countermeasure, target lock-on before and after launch capability to engage targets beyond visual range, higher kill probability and revolutionary full-sphere-launch envelope from very short to beyond visual ranges. It can lock on to the target after launch even when the target is 100° off the bore sight. The missile has an operational range of more than 20km and a speed of 4Mach.

Modern IR-guided missiles using IIR seekers with advanced digital signal processing techniques have much wider detection angles, giving them the capability to launch missiles from large off-bore sight angles. Helmet-mounted sights with pilots of the launch aircraft allow them to distinguish between the target aircraft and a point source of intense heat, such as a flare. These missiles almost invariably have lock-on-after-launch feature, enabling them to engage targets from a very small range to beyond the visual range.

Another recent advancement in missile guidance is the use of electro-optical imaging. The electro-optical seeker scans the designated area for targets via optical imaging. Once the target is acquired, the missile locks-on to it for the kill. Electro-optical seekers can be programmed to hit the designated spot on the target aircraft. The designated spot could be the most vulnerable point of the target. Since electro-optical imaging does not depend on the target aircraft’s heat signature, it can be used against low-heat targets such as unmanned aerial vehicles and cruise missiles.

There have been advances in control systems for better manoeuvrability of the flight path. Crew safety on ground has been another concern and it has led to the development of insensitive munitions warheads that do not detonate accidently.