all about missiles

Guided missile





A guided missile is a self-propelled projectile used as a weapon. Missiles are typically propelled by rockets or jet engines. Missiles generally have an explosive warhead, although other weapon types may also be used.




Etymology

The word missile comes from the Latin verb mittere, literally meaning "to send".

In common military parlance, the word missile describes a powered, guided munition, whilst the word "rocket" describes a powered, unguided munition. Unpowered, guided munitions are known as guided bombs. A common further sub-division is to consider ballistic missile to mean a munition that follows a ballistic trajectory and cruise missile to describe a munition that generates lift.

Technology

Guided missiles have a number of different system components:

* targeting and/or guidance
* flight system
* engine
* warhead



Guidance Systems

Missiles may be targeted in a number of ways. The most common method is to use some form of radiation, such as infra-red, lasers or radio waves, to guide the missile onto its target. This radiation may emanate from the target (such as the heat of an engine or the radio waves from an enemy radar), it may be provided by the missile itself (such as a radar) or it may be provided by a friendly third party (such as the radar of the launch vehicle/platform, or a laser designator operated by friendly infantry). The first two are often known as fire and forget as they need no further support or control from the launch vehicle/platform in order to function. Another method is to use a TV camera - using either visible light or infra-red - in order to see the target. The picture may be used either by a human operator who steers the missile onto its target, or by a computer doing much the same job. Many missiles use a combination of two or more of the above methods, to improve accuracy and the chances of a successful engagement.

Targeting Systems

Another method is to target the missile by knowing the location of the target, and using a guidance system such as INS, TERCOM or GPS. This guidance system guides the missile by knowing the missile's current position and the position of the target, and then calculating a course between them. This job can also be performed somewhat crudely by a human operator who can see the target and the missile, and guides it using either cable or radio based remote-control.

Flight System

Whether a guided missile uses a targeting system, a guidance system or both, it needs a flight system. The flight system uses the data from the targeting or guidance system to maneuver the missile in flight, allowing it to counter inaccuracies in the missile or to follow a moving target. There are two main systems: vectored thrust (for missiles that are powered throughout the guidance phase of their flight) and aerodynamic maneuvering (wings, fins, canards, etc).

Engine

Missiles are powered by an engine, generally either a type of rocket or jet engine. Rockets are generally of the solid fuel type for ease of maintenance and fast deployment, although some larger ballistic missiles use liquid fuel rockets. Jet engines are generally used in cruise missiles, most commonly of the turbojet type, due to it's relative simplicity and low frontal area. Ramjets are the only other common form of jet engine propulsion, although any type of jet engine could theoretically be used. Missiles often have multiple engine stages, particularly in those launched from the ground - these stages may all be of similar types or may include a mix of engine types.

Warhead

The warhead or warheads of a missile provides its primary destructive power (many missiles have extensive secondary destructive power due to the high kinetic energy of the weapon and unburnt fuel that may be onboard). Warheads are most commonly of the high explosive type, often employing shaped charges to exploit the accuracy of a guided weapon to destroy hardened targets. Other warhead types include submunitions, incendiaries, nuclear weapons, chemical, biological or radiological weapons or kinetic energy penetrators.

Early development

The first missiles to be used operationally were a series of German missiles of WW2. Most famous of these are the V1 and V2, both of which used a simple mechanical autopilot to keep the missile flying along a pre-chosen route. Less well known were a series of anti-shipping and anti-aircraft missiles, typically based on a simple radio control system directed by the operator. However, these early systems had a high failure rate so they were very unreliable.

Basic roles

Missiles are generally categorized by their launch platform and intended target - in broadest terms these will either be surface (ground or water) and air, and then sub-categorized by range and the exact target type (such as anti-tank or anti-ship). Many weapons are designed to be launched from both surface or the air, and a few are designed to attack either surface or air targets (such as the ADATS missile). Most weapons require some modification in order to be launched from the air or ground, such as adding boosters to the ground launched version.

Surface to Surface/Air to Surface

Ballistic missiles

After the boost-stage, ballistic missiles follow a trajectory mainly determined by ballistics. The guidance is for relatively small deviations from that.

Ballistic missiles are largely used for land attack missions. Although normally associated with nuclear weapons, some conventionally armed ballistic missiles are in service, such as ATACMS. The V2 had demonstrated that a ballistic missile could deliver a warhead to a target city with no possibility of interception, and the introduction of nuclear weapons meant it could do useful damage when it arrived. The accuracy of these systems was fairly poor, but post-war development by most military forces improved the basic inertial platform concept to the point where it could be used as the guidance system on ICBMs flying thousands of miles. Today the ballistic missile represents the only strategic deterrent in most military forces; the USAFs continued support of manned bombers is considered by some to be entirely political in nature.[citation needed] Ballistic missiles are primarily surface launched, with air launch being theoretically possible using a weapon such as the canceled Skybolt missile.

Cruise missiles

The V1 had been successfully intercepted during the Second World War, but this did not make the cruise missile concept entirely useless. After the war, the US deployed a small number of nuclear-armed cruise missiles in Germany, but these were considered to be of limited usefulness. Continued research into much longer ranged and faster versions led to the US's Navaho missile, and its Soviet counterparts, the Burya and Buran cruise missile. However, these were rendered largely obsolete by the ICBM, and none was used operationally. Shorter-range developments have become widely used as highly accurate attack systems, such as the US Tomahawk missile or the German Taurus missile.

Cruise missiles are generally associated with land attack operations, but also have an important role as anti shipping weapons. They are primarily launched from air, sea or submarine platforms in both roles, although land based launchers also exist.

Anti-shipping

Another major German missile development project was the anti-shipping class (such as the Fritz X and Henschel Hs 293), intended to stop any attempt at a cross-channel invasion. However the British were able to render their systems useless by jamming their radios, and missiles with wire guidance were not ready by D-Day. After the war the anti-shipping class slowly developed, and became a major class in the 1960s with the introduction of the low-flying turbojet powered cruise missiles known as "sea-skimmers". These became famous during the Falklands War when an Argentine Exocet missile sank a Royal Navy destroyer.

A number of anti-submarine missiles also exist; these generally use the missile in order to deliver another weapon system such as a torpedo or depth charge to the location of the submarine, at which point the other weapon will conduct the underwater phase of the mission.

Anti-tank
PARS 3 LR, a modern anti-tank fire-and-forget missile of the German Army

By the end of WWII all forces had widely introduced unguided rockets using HEAT warheads as their major anti-tank weapon (see Panzerfaust, Bazooka). However these had a limited useful range of a 100 m or so, and the Germans were looking to extend this with the use of a missile using wire guidance, the X-7. After the war this became a major design class in the later 1950s, and by the 1960s had developed into practically the only non-tank anti-tank system in general use. During the 1973 Yom Kippur War between Israel and Egypt, the 9M14 Malyutka (aka "Sagger") man-portable anti-tank missile proved potent against Israeli tanks. While other guidance systems have been tried, the basic reliability of wire-guidance means this will remain the primary means of controlling anti-tank missile in the near future. Anti tank missiles may be launched from aircraft, vehicles or by ground troops in the case of smaller weapons.

Surface to Air

Anti-Aircraft
The Stinger shoulder-launched surface-to-air missile system.

By 1944 US and British air forces were sending huge air fleets over occupied Europe, increasing the pressure on the Luftwaffe day and night fighter forces. The Germans were keen to get some sort of useful ground-based anti-aircraft system into operation. Several systems were under development, but none had reached operational status before the war's end. The US Navy also started missile research to deal with the Kamikaze threat. By 1950 systems based on this early research started to reach operational service, including the US Army's Nike Ajax, the Navy's "3T's" (Talos, Terrier, Tartar), and soon followed by the Soviet S-25 Berkut and S-75 Dvina and French and British systems. Anti-aircraft weapons exist for virtually every possible launch platform, with surface launched systems ranging from huge, self propelled or ship mounted launchers to man portable systems.

Anti-ballistic

Like most missiles, the Arrow missile and MIM-104 Patriot for defense against short-range missiles, carry explosives.

However, in the case of a large closing speed, a projectile without explosives is used, just a collision is sufficient to destroy the target.

Air-to-air
A modern IRIS-T air-to-air missile of the German Luftwaffe.

Soviet RS-82 rockets were successfully tested in combat at the Battle of Khalkhin Gol in 1939.

German experience in WWII demonstrated that destroying a large aircraft was quite difficult, and they had invested considerable effort into air-to-air missile systems to do this. Their Me262's jets often carried R4M rockets, and other types of "bomber destroyer" aircraft had unguided rockets as well. In the post-war period the R4M served as the pattern for a number of similar systems, used by almost all interceptor aircraft during the 1940s and '50s. Lacking guidance systems, such rockets had to be carefully aimed at relatively close range to successfully hit the target. The US Navy and USAF began deploying guided missiles in the early 1950s, most famous being the US Navy's AIM-9 Sidewinder and USAF's AIM-4 Falcon. These systems have continued to advance, and modern air warfare consists almost entirely of missile firing. In the Falklands War technically inferior British Harriers were able to defeat faster Argentinian opponents using AIM-9G missiles provided by the United States as the conflict began. The latest heat-seeking designs can lock onto a target from various angles, not just from behind, where the heat signature from the engines is strongest. Other types rely on radar guidance (either on-board or "painted" by the launching aircraft). Air to Air missiles also have a wide range of sizes, ranging from helicopter launched self defense weapons with a range of a few miles, to long range weapons designed for interceptor aircraft such as the Phoenix missile.

Anti-satellite weapon (ASAT)

The proposed Brilliant Pebbles defense system during the 1980s would use kinetic energy collisions without explosives. Anti satellite weapons may be launched either by an aircraft or a surface platform, depending on the design. To date, only a few known tests have occured.

Guidance systems


Missile guidance systems generally fall into a number of basic classes, each one associated with a particular role. Modern electronics has allowed systems to be mixed on a single airframe, dramatically increasing the capabilities of the missiles.

The missile's target accuracy is a critical factor for its effectiveness. Guidance systems improve missile accuracy by improving its "Single Shot Kill Probability" (SSKP).

These guidance technologies can generally be divided up into a number of categories, with the broadest categories being "active," "passive" and "preset" guidance’s. Missiles and guided bombs generally use similar types of guidance system, the difference between the two being that missiles are powered by an onboard engine, whereas guided bombs rely on the speed and height of the launch aircraft for propulsion.

Categories of guidance systems

Guidance systems are divided into different categories according to what type of target they are designed for - either fixed targets or moving targets. The weapons can be divided into two broad categories, Go-Onto-Target (GOT) and Go-Onto-Location-in-Space (GOLIS) guidance systems.[citation needed] A GOT missile can target either a moving or fixed target, whereas a GOLIS weapon is limited to a stationary or near-stationary target. The trajectory that a missile takes while attacking a moving target is dependent upon the movement of the target. Also, a moving target can be an immediate threat to the sender of the missile. The target needs to be eliminated in a timely fashion in order to preserve the integrity of the sender. In GOLIS systems the problem is simpler because the target is not moving.

GOT systems

In every GOT system there are three subsystems:

* Target tracker
* Missile tracker
* Guidance computer

The way these three subsystems are distributed between the missile and the launcher result in two different categories:

* Remote Control Guidance: The guidance computer is on the launcher. The target tracker is also placed on the launching platform.
* Homing Guidance: The guidance computers are in the missile and in the target tracker.

Remote control guidance

These guidance systems usually need the use of radars and a radio or wired link between the control point and the missile; in other words, the trajectory is controlled with the information transmitted via radio or wire.

System include

* Command Guidance - The missile tracker is on the launching platform. These missiles are totally controlled by the launching platform that sends all control orders to the missile. The 2 variants are

* Command to Line-Of-Sight (CLOS)
* Command Off Line-Of-Sight (COLOS)

* Line-Of-Sight Beam Riding Guidance (LOSBR) - The missile tracker is on board the missile. It has already some orientation capability, in order to fly inside the beam that the launching platform is using to illuminate the target. It can be manual or automatic.[1]

Command to Line-Of-Sight (CLOS)

The CLOS system uses only the angular coordinates between the missile and the target to ensure the collision. The missile will have to be in the line of sight between the launcher and the target (LOS), correcting any deviation of the missile in relation to this line. Due to the amount of missiles that use this guidance system, they are usually are subdivided into four groups:

* Manual Command to Line-Of-Sight (MCLOS), The target tracking and the missile tracking and control is performed manually. The operator watches the missile flight and uses some sort of signaling system to command the missile back into the straight line between the operator and the target (the "line of sight"). Typically useful only for slower targets where significant "lead" is not required. MCLOS is a subtype of command guided systems. In the case of glide bombs missiles against ships or the supersonic Wasserfall against slow-moving B-17 Flying Fortress bombers this system worked fine, but as speeds increased MCLOS was quickly rendered useless for most roles.
* Semi-Manual Command to Line-Of-Sight (SMCLOS), The target tracking is automatic and the missile tracking and control is manual
* Semi-Automatic Command to Line-Of-Sight (SACLOS), The target tracking is manual and the missile tracking and control is automatic. Is similar to MCLOS but some automatic system positions the missile in the line of sight while the operator simply tracks the target. *SACLOS has the advantage of allowing the missile to start in a position invisible to the user, as well as generally being considerably easier to operate. SACLOS is the most common form of guidance against ground targets such as tanks and bunkers.
* Automatic Command to Line-Of-Sight (ACLOS), The target tracking, missile tracking and control are automatic.

Command Off Line-Of-Sight (COLOS)

This guidance system was one of the first to be used and still is in service, mainly in anti-aircraft missiles. In this system, the missile tracker and the target tracker can be oriented in different directions. The guidance system ensures the interception missile-target by locate both in space. This means that they will not rely on the angular coordinates like in CLOS systems. They will need another coordinate which is distance. To make it possible, both target and missile trackers have to be active. They are always automatic and the radar has been used as the only sensor in these systems. The SM-2MR Standard is inertially guided during its midcourse phase, but it is assisted by a COLOS system via radar link provided by the AN/SPY-1 radar installed in the launching platform.

Line-Of-Sight Beam Riding Guidance (LOSBR)

LOSBR uses a "beam" of some sort, typically radio, radar or laser, is pointed at the target and detectors on the rear of the missile keep it centered in the beam. Beam riding systems are often SACLOS, but don't have to be; in other systems the beam is part of an automated radar tracking system. A case in point is later versions of the RIM-8 Talos missile as used in Vietnam - the radar beam was used to take the missile on a high arcing flight and then gradually brought down in the vertical plane of the target aircraft, the more accurate SARH homing being used at the last moment for the actual strike. This gave the enemy pilot the least possible warning that his aircraft was being illuminated by missile guidance radar, as opposed to search radar. This is an important distinction, as the nature of the signal differs, and is used as a cue for evasive action.

LOSBR suffers from the inherent weakness of inaccuracy with increasing range as the beam spreads out. Laser beam riders are more accurate in this regards, but are all short-range, and even the laser can be degraded by bad weather. On the other hand, SARH becomes more accurate with decreasing distance to the target, so the two systems are complementary
Homing guidance

Active homing

Active homing uses a radar system on the missile to provide a guidance signal. Typically electronics in the missile keep the radar pointed directly at the target, and the missile then looks at this "angle" of its own centerline to guide itself. Radar resolution is based on the size of the antenna, so in a smaller missile these systems are useful for attacking only large targets, ships or large bombers for instance. Active radar systems remain in widespread use in anti-shipping missiles, and in "fire-and-forget" air-to-air missile systems such as AMRAAM and R-77

Semi-active homing

Semi-active homing systems combine a radar receiver on the missile with a radar broadcaster located "elsewhere". Since the missile is typically being launched after the target was detected using a powerful radar system, it makes sense to use that same radar system to track the target, thereby avoiding problems with resolution or power. SARH is by far the most common "all weather" guidance solution for anti-aircraft systems, both ground and air launched. SALH is a similar system using a laser as a signal. It has the disadvantage for air-launched systems that the launch aircraft must keep moving towards the target in order to maintain radar and guidance lock. This has the potential to bring it within range of shorter-ranged IR-guided missile systems, an important consideration now that "all aspect" IR missiles are capable of "kills" from head on, something which did not prevail in the early days of guided missiles. For ships and mobile or fixed ground-based systems, this is irrelevant as the speed (and often size) of the launch platform precludes "running away" from the target or opening the range so as to make the enemy attack fail.

Passive homing

Infrared homing is a passive system in which heat generated by the target is detected and homed on. Typically used in the anti-aircraft role to track the heat of jet engines, it has also been used in the anti-vehicle role with some success. This means of guidance is sometimes also referred to as "heat seeking".

Contrast seekers use a television camera, typically black and white, to image a field of view in front of the missile, which is presented to the operator. When launched, the electronics in the missile look for the spot on the image where the contrast changes the fastest, both vertically and horizontally, and then attempts to keep that spot at a constant location in its view. Contrast seekers have been used for air-to-ground missiles, including the famous AGM-65 Maverick, because most ground targets can be distinguished only by visual means. However they rely on there being strong contrast changes to track, and even traditional camouflage can render them unable to "lock on".

Retransmission homing

Main article: Track-via-missile

Retransmission homing, also called Track Via Missile(TVM), is a hybrid between command guidance, semi-active radar homing and active radar homing. The missile picks up radiation broadcast by the tracking radar which bounces off the target and relays it to the tracking station, which relays commands back to the missile.

GOLIS systems

Whatever the GOLIS guidance system, it must contain preset information about the target. These systems' main characteristic is the lack of target tracker. The guidance computer and the missile tracker are located in the missile. There is only one type of guidance system of this kind: Navigational Guidance.

Navigational guidance is any type of guidance executed by a system without target tracker. The other two units are on board the missile. These systems are also known as Self Contained Guidance Systems, however they're not always entirely autonomous due to the missile trackers used. They are subdivided function of their missile tracker's type:

* Entirely autonomous - Systems where the missile tracker is not dependent of any navigation external source, and can be divided in:

* Inertial Guidance

* With gyro-stabilized platform
* With strapdown platform

* Preset Guidance

* Dependent on natural sources - Navigational guidance systems where the missile tracker depends of some external source that is provided by nature:

* Celestial Guidance
* Terrestrial Guidance

* Topographic Reconnaissance (Ex: TERCOM)
* Photographic Reconnaissance (Ex: DSMAC)

* Magnetic Guidance

* Dependent on artificial sources - Navigational guidance systems where the missile tracker depends of some external source that is provided by any artificial means:

* Satellite Navigation

* Global Positioning System (GPS)
* GLObal NAvigation Satellite System (GLONASS)

* Hyperbolic Navigation

* DECCA
* LORAN C

Inertial guidance

Main article: inertial guidance

Inertial Guidance uses sensitive measurement devices to calculate the location of the missile due to the acceleration put on it after leaving a known position. Early mechanical systems were not very accurate, and required some sort of external adjustment to allow them to hit targets even the size of a city. Modern systems use solid state ring laser gyros that are accurate to within metres over ranges of 10,000km, and no longer require additional inputs. Gyroscope development has culminated in the AIRS found on the MX missile, allowing for an accuracy of less than 100m at intercontinental ranges. Many civilian aircraft use inertial guidance using the ring laser gyroscope, which is less accurate than the mechanical systems found in ICBMs, but which provide an inexpensive means of attaining a fairly accurate fix on location (when most airliners such as Boeing's 707 and 747 were designed, GPS was not the widely commercially available means of tracking that it is today). Today guided weapons can use a combination of INS, GPS and radar terrain mapping to achieve extremely high levels of accuracy such as that found in modern cruise missiles.[citation needed]

Preset guidance

Preset guidance is the simplest type of missile guidance. From the distance and direction of the target, the trajectory of the flight path is determined. Before firing, this information is programmed into the missile's guidance system, which, during flight, maneuvers the missile to follow that path. All the guidance components (including sensors such as accelerometers or gyroscopes) are contained within the missile, and no outside information (such as radio instructions) is used. An example of a missile using Preset Guidance is the V-2 rocket.[2]

Celestial guidance

Celestial guidance was first used in the American Poseidon missile and uses star positioning to fine-tune the accuracy of the inertial guidance system after launch. As the accuracy of a ballistic missile is dependent upon the guidance system knowing the exact position of the rocket at any given moment during its boost phase, the fact that stars are a fixed reference point from which to calculate that position makes this a potentially very effective means of improving accuracy. In the Polaris system this was achieved by a single camera that was trained to spot just one star in its expected position (it is believed that the missiles from Soviet submarines would track two separate stars to achieve this), if it was not quite aligned to where it should be then this would indicate that the inertial system was not precisely on target and a correction would be made.

Terrestrial guidance

TERCOM, for "terrain contour matching", uses altitude maps of the strip of land from the launch site to the target, and compares them with information from a radar altimeter on board. More sophisticated TERCOM systems allow the missile to fly a complex route over a full 3D map, instead of flying directly to the target. TERCOM is the typical system for cruise missile guidance, but is being supplanted by GPS systems and by DSMAC, Digital Scene-Matching Area Correlator, which employs a camera to view an area of land, digitizes the view, and compares it to stored scenes in an onboard computer to guide the missile to its target.

DSMAC is reputed to be so precise that destruction of prominent buildings in the internal map of the system (by preceding cruise missiles, among other things!) will spoil navigation.