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Air-to-air missile

Encyclopedia : A : AI : AIR : Air-to-air missile

 

A US Navy VF-103 Jolly Rogers F-14 Tomcat fighter launchers an AIM-54 Phoenix long-range air-to-air missile. Photo courtesy U.S. Navy Atlantic Fleet.
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A US Navy VF-103 Jolly Rogers F-14 Tomcat fighter launchers an AIM-54 Phoenix long-range air-to-air missile. Photo courtesy U.S. Navy Atlantic Fleet.

An air-to-air missile (AAM) is a guided missile fired from an aircraft for the purpose of destroying another aircraft. It is typically powered by one or more rocket motors, usually solid fuelled but sometimes liquid fuelled.

Contents

Guidance

Guided missiles operate by detecting their target (usually by either radar or infra-red methods, although rarely others such as laser guidance or optical tracking), and then "homing" in on the target on a collision course.

The target is usually destroyed or damaged by means of an explosive warhead, often throwing out fragments to increase the lethal radius, typically detonated by a proximity fuze (or impact fuze if it scores a direct hit). Some missiles rely partially or wholly on their kinetic energy to damage the target, but almost all contain some kind of warhead, even if it is small.

Note that although the missile may use radar or infra-red guidance to home on the target, this does not necessarily mean that the same means is used by the launching aircraft to detect and track the target before launch. Infra-red guided missiles can be "slaved" to an attack radar in order to find the target and radar-guided missiles can be launched at targets detected visually or via an infra-red search and track (IRST) system, although they may require the attack radar to illuminate the target during part or all of the missile interception itself.

Radar guidance

Radar guidance is normally used for medium or long range missiles, where the infra-red signature of the target would be too faint for an infra-red detector to track. There are two major types of radar-guided missile - active and semi-active.

Active radar(AR)-guided missiles carry their own radar system to detect and track their target. However, the size of the radar antenna is limited by the small diameter of missiles, limiting its range which typically means such missiles have to use another method to get close to the target before turning their radar set on, often inertial guidance).

Semi-active radar (SAR) homing missiles are simpler and more common. They function by detecting the radar energy reflected from the target of the launch aircraft's own radar signal. However, this means the launch aircraft has to maintain a "lock" on the target (keep illuminating the target aircraft with its' own radar) until the missile makes the interception, limiting the attacking aircraft's ability to maneuver, which may be necessary should threats to the attacking aircraft appear. It also makes jamming the missile lock easier because the launching aircraft is further from the target than the missile, so the radar signal has to travel further and is greatly attenuated over the distance.

An earlier form of radar guidance was "beam-riding" (BR). In this method the attacking aircraft directed a narrow beam of radar energy at the target. The air-to-air missile was launched into the beam where sensors on the aft of the missile controlled the missile, keeping it within the beam. So long as the beam was kept on the target aircraft, the missile would ride the beam until making the interception. While simple in concept, the problem of keeping the beam solidly on the target, a target which couldn't always be counted on to cooperate by flying straight and level, and continue flying the attacking aircraft and keeping an eye out for enemy countermeasures, can be appreciated.

Although radar beam-riding air-to-air missiles are obsolete, the technology has since evolved toward laster-beam guided air-to-ground munitions, such as laser-guided bombs (LGB). These precision-strike munitions are sometimes called "smart weapons" by the press.

Radar guided missiles can be countered by rapid maneuvering (which may result in them "breaking lock", or may cause them to overshoot), deploying chaff or using electronic counter-measures.

Infrared guidance

Infrared guided (IR) missiles home on the heat produced by an aircraft. Early infra-red detectors had poor sensitivity, so could only track the hot exhaust pipes of an aircraft. This meant an attacking aircraft had to maneuver to a position behind its' target before it could fire an infra-red guided missile. This also limited the range of the missile as the infra-red signature soon become too small to detect with increasing distance and after launch the missile was playing "catch-up" with its' target.

More modern infra-red guided missiles can detect the heat of an aircraft's skin, warmed by the friction of airflow, in addition to the fainter heat signature of the engine when the aircraft is seen from the side or head-on. This, combined with greater maneuverability, gives them an "all-aspect" capability, and an attacking aircraft no longer had to be behind its target to fire. Although launching from behind the target increases the probability of a hit, the launching aircraft usually has to be closer to the target in a tail-chase engagement.

An aircraft can defend against infra-red missiles by dropping flares that are hotter than the aircraft, so the missile homes in on the brighter, hotter target. Towed decoys and infra-red jammers can also be used. Some large aircraft and many combat helicopters make use of so called "hot brick" infra-red jammers, typically mounted near the engines. Current research is developing laser devices which can spoof or destroy the guidance systems of infra-redguided missiles.

However, the latest missiles such as the ASRAAM use an "imaging" infra-red seeker which "sees" the target (much like a digital video camera), and can distinguish between an aircraft and a point heat source such as a flare. They also feature a very wide detection angle, so the attacking aircraft does not have to be pointing straight at the target for the missile to lock on. The pilot can use a helmet mounted sight (HMS) and target another aircraft by looking at it, and then firing. This is called "off-boresight" launch. The Russian Su-27 is equipped with an infrared search and track (IRST) system with laser rangefinder for its HMS-guided missiles.

In order to maneuver sufficiently from a poor launch angle at short ranges to hit its target, missiles are now employing gas-dynamic flight control methods such as vectored thrust, which allow the missile to start turning "off the rail", before its motor has accelerated it up to high enough speeds for its small aerodynamic surfaces to be useful.

Electro-optical

A recent advancement in missile guidance is electro-optical imaging. The Israeli [Python-5] has an electro-optical seeker that scans designated area for targets via optical imaging. Once a target is acquired, the missile will lock-on to it for the kill. Electro-optical seekers can be programed to target vital area of an aircraft, such as the cockpit. Since it doesn't depend on the target aircraft's heat signature, it can be used against low-heat targets such as UAV's and cruise missiles.

Design

Air-to-air missiles are typically long, thin cylinders in order to reduce their cross section and thus minimize drag at the high speeds at which they travel.

At the front is the seeker, either a radar system, radar homer, or infra-red detector. Behind that lies the avionics which control the missile. Typically after that, in the centre of the missile, is the warhead, usually several kilogrammes of high explosive surrounded by metal that fragments on detonation (or in some cases, pre-fragmented metal).

The rear part of the missile contains the propulsion system, usually a rocket of some type. Dual-thrust solid-fuel rockets are common, but some longer-range missiles use liquid-fuel motors that can "throttle" to extend their range and preserve fuel for energy-intensive final maneuvering. Some solid-fuelled missiles mimic this technique with a second rocket motor which burns during the terminal homing phase. There are missiles in development, such as the MBDA Meteor, that "breathe" air (using a ramjet, similar to a jet engine) in order to extend their range.

Modern missiles use "low-smoke" motors - early missiles produced thick smoke trails, which were easily seen by the crew of the target aircraft alerting them to the attack and helping them determine how to evade it.

Missile range

Missiles are often cited with their maximum engagement range, which is very misleading. A missile's effective range is dependent on factors such as altitute, speed, position, and direction of target aircraft. For example the Vympel R-77 has stated range of 100 km. That's only true for a head-on, non-evading target at high altitude. At low altitude, the effective range is reduced by as much as 75%-80% to 20-25 km. If the target is taking evasive action, or in sterm-chase position, the effective range is further reduced. See [Air-to-Air missile non-comparison table] for more information.

Poorly-trained pilots from third world countries, and mercenary pilots more interested in collecting their pay and going home alive than dead, are known to fire their missiles at maximum-range engagement with poor results. In the 1998-2000 Ethiopia-Eritrea war, fighters from both sides shot over a dozen medium-range R-27 (AA-10) missiles at distance with little effect. But when better-trained Ethiopian Su-27 pilots decide to give chase and attack with short-range R-74 (AA-10) missiles, the results were often deadly to the Eritrean aircraft. [link]

List of missiles by country

For each missile, short notes are given, including an indication of its range and guidance mechanism.

Brazil

France

Germany

European

India

Israel

Italy

People's Republic of China

Russia/Soviet

United Kingdom

United States

List of missiles
Air-to-air missile (AAM) | Air-to-surface missile (ASM) | Surface-to-air missile (SAM) | Surface-to-surface missile (SSM)
Ballistic missile | Intercontinental ballistic missile (ICBM) | Submarine launched ballistic missile (SLBM) | Anti-ballistic missile (ABM)
Cruise missile | Anti-ship missile (AShM) | Anti-submarine Rocket (ASROC) | Anti-tank guided missile (ATGM) | Anti-satellite weapon (ASAT) | Anti-radiation missile
Wire-guided missile | Infrared guidance | Beam riding | Laser guidance | Active radar guidance | Semi-active radar guidance


Lists of Aircraft | Aircraft manufacturers | Aircraft engines | Aircraft engine manufacturers

| Airlines | Air forces | Aircraft weapons | Missiles | Timeline of aviation

See also

External Links

 

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