terminal guidance
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In the field of
weaponry A weapon, arm or armament is any implement or device that can be used to deter, threaten, inflict physical damage, harm, or kill. Weapons are used to increase the efficacy and efficiency of activities such as hunting, crime, law enforcement, s ...
, terminal guidance refers to any
guidance system A guidance system is a virtual or physical device, or a group of devices implementing a controlling the movement of a ship, aircraft, missile, rocket, satellite, or any other moving object. Guidance is the process of calculating the changes in po ...
that is primarily or solely active during the "terminal phase", just before the weapon impacts its target. The term is generally used in reference to
missile guidance Missile guidance refers to a variety of methods of guiding a missile or a guided bomb to its intended target. The missile's target accuracy is a critical factor for its effectiveness. Guidance systems improve missile accuracy by improving its P ...
systems, and specifically to missiles that use more than one guidance system through the missile's flight. Common examples include long-range
air-to-air missile The newest and the oldest member of Rafael's Python family of AAM for comparisons, Python-5 (displayed lower-front) and Shafrir-1 (upper-back) An air-to-air missile (AAM) is a missile fired from an aircraft for the purpose of destroying a ...
s that use
semi-active radar homing Semi-active radar homing (SARH) is a common type of missile guidance system, perhaps the most common type for longer-range Air-to-air missile, air-to-air and surface-to-air missile systems. The name refers to the fact that the missile itself is ...
(SARH) during most of the missile's flight, and then use an
infrared seeker Infrared homing is a passive weapon guidance system which uses the infrared (IR) light emission from a target to track and follow it seamlessly. Missiles which use infrared seeking are often referred to as "heat-seekers" since infrared is radi ...
or
active radar homing Active radar homing (ARH) is a missile guidance method in which a missile contains a radar transceiver (in contrast to semi-active radar homing, which uses only a receiver) and the electronics necessary for it to find and track its target aut ...
once they approach their target. Similar examples include
surface-to-air missile A surface-to-air missile (SAM), also known as a ground-to-air missile (GTAM) or surface-to-air guided weapon (SAGW), is a missile designed to be launched from the ground to destroy aircraft or other missiles. It is one type of anti-aircraft syst ...
s,
anti-ballistic missile An anti-ballistic missile (ABM) is a surface-to-air missile designed to counter ballistic missiles (missile defense). Ballistic missiles are used to deliver nuclear weapon, nuclear, Chemical weapon, chemical, Bioagent, biological, or conventiona ...
s, and some
anti-tank missile An anti-tank guided missile (ATGM), anti-tank missile, anti-tank guided weapon (ATGW) or anti-armor guided weapon is a Missile guidance, guided missile primarily designed to hit and destroy Armoured fighting vehicle, heavily armored military v ...
s.


Concept

Radar Radar is a detection system that uses radio waves to determine the distance (''ranging''), angle, and radial velocity of objects relative to the site. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, w ...
beams are cone-shaped, spreading out from the diameter of the antenna at a characteristic angle that is a function of the size of the antenna and its wavelength. This means that as one moves away from the radar, its accuracy continues to degrade while the signal grows weaker. This makes it difficult to use the radar signal itself as the guidance signal, a system known as beam riding, except for very short-range engagements. However, the signal being reflected off the target also forms a cone shape centred on the target, but with a much greater spread angle. This leads to one of the most common types of radar-based missile guidance,
semi-active radar homing Semi-active radar homing (SARH) is a common type of missile guidance system, perhaps the most common type for longer-range Air-to-air missile, air-to-air and surface-to-air missile systems. The name refers to the fact that the missile itself is ...
, or SARH. This places a small receiver in the nose of the missile that listens for the signals reflected off the target, and therefore grows ''more'' accurate and powerful as the missile approaches the target. However, after launch the target return is at a minimum. While the launch platform may have no trouble picking up the signal from a distant target, the much smaller antenna in the missile may not be receiving enough of a signal to properly track. In these cases, some other form of guidance is used to get the missile into the range where the signal is stronger. Examples would be
radio control Radio control (often abbreviated to RC) is the use of control signals transmitted by radio to remotely control a device. Examples of simple radio control systems are garage door openers and keyless entry systems for vehicles, in which a small ...
(command guidance) or
inertial guidance An inertial navigation system (INS) is a navigation device that uses motion sensors ( accelerometers), rotation sensors ( gyroscopes) and a computer to continuously calculate by dead reckoning the position, the orientation, and the velocity ...
systems, which fly the missile closer to the target. In this role, these are known as "midcourse guidance" systems. In practice, terminal guidance systems are often optical or active radar systems, in an effort to greatly increase accuracy. These systems often have many times the accuracy of solutions like SARH, but operate only at short ranges, on the order of a few kilometers. Missiles that are designed to operate entirely within the range of these sorts of systems, like
heat seeking missile Infrared homing is a passive weapon guidance system which uses the infrared (IR) light emission from a target to track and follow it seamlessly. Missiles which use infrared seeking are often referred to as "heat-seekers" since infrared is rad ...
s, do not use the term "terminal guidance" because they use the same guidance system throughout their flight.


See also

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Countermeasure A countermeasure is a measure or action taken to counter or offset another one. As a general concept, it implies precision and is any technological or tactical solution or system designed to prevent an undesirable outcome in the process. The fi ...
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Precision bombing Precision bombing refers to the attempted aerial bombing of a target with some degree of accuracy, with the aim of maximising target damage or limiting collateral damage. An example would be destroying a single building in a built up area causing ...
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Precision-guided munition A precision-guided munition (PGM, smart weapon, smart munition, smart bomb) is a guided munition intended to precisely hit a specific target, to minimize collateral damage and increase lethality against intended targets. During the First Gul ...
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Guided bomb A guided bomb (also known as a smart bomb, guided bomb unit, or GBU) is a precision-guided munition designed to achieve a smaller circular error probable (CEP). The creation of precision-guided munitions resulted in the retroactive renaming of ...
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Guidance system A guidance system is a virtual or physical device, or a group of devices implementing a controlling the movement of a ship, aircraft, missile, rocket, satellite, or any other moving object. Guidance is the process of calculating the changes in po ...
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Proximity fuze A proximity fuze (or fuse) is a Fuze (munitions), fuze that detonates an Explosive material, explosive device automatically when the distance to the target becomes smaller than a predetermined value. Proximity fuzes are designed for targets such ...
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Proximity sensor A proximity sensor is a sensor able to detect the presence of nearby objects without any physical contact. A proximity sensor often emits an electromagnetic field or a beam of electromagnetic radiation (infrared, for instance), and looks for ...
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Artillery fuze An artillery fuze or fuse is the type of munition fuze used with artillery munitions, typically projectiles fired by guns (field, anti-aircraft, coast and naval), howitzers and mortars. A fuze is a device that initiates an explosive function in a ...
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Magnetic proximity fuze A magnetic proximity fuse was patented by P.J. Eliomarkakis, (United States Patent US2434551 of January 13, 1948) although similar devices had been in service for nearly a decade. It is a type of proximity fuze that initiates a detonator in a pie ...
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Missile In military terminology, a missile is a guided airborne ranged weapon capable of self-propelled flight usually by a jet engine or rocket motor. Missiles are thus also called guided missiles or guided rockets (when a previously unguided rocket i ...


References

{{refbegin
"The Guidance of Space Vehicles"
NASA Missile guidance