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 ...

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 ...

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 ...

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 and surface-to-air missile systems. The name refers to the fact that the missile itself is only a passive det ...

(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 ...

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 au ...

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 missiles, 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 guided missile primarily designed to hit and destroy heavily armored military vehicles. ATGMs range in size from shoulder ...

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 Beam-riding, also known as Line-Of-Sight Beam Riding (LOSBR) or beam guidance, is a technique of directing a missile to its target by means of radar or a laser beam. The name refers to the way the missile flies down the guidance beam, which is a ...

, 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,

, 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 (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 (d ...

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 missiles, do not use the term "terminal guidance" because they use the same guidance system throughout their flight.

References

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

Concept

See also

References