Missile guidance refers to a variety of methods of guiding a
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 ...
or a
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 ...
to its intended target. The missile's target accuracy is a critical factor for its effectiveness. Guidance systems improve missile accuracy by improving its Probability of Guidance (Pg).
These guidance technologies can generally be divided up into a number of categories, with the broadest categories being "active", "passive", and "preset" guidance. 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.
History
The concept of unmanned guidance originated at least as early as World War I, with the idea of remotely guiding an airplane bomb onto a target, such as the systems developed for the
first powered drones by Archibald Low (The Father of Radio Guidance).
In World War II, guided missiles were first developed, as part of the German
V-weapons
V-weapons, known in original German as (, German: "retaliatory weapons", "reprisal weapons"), were a particular set of long-range artillery weapons designed for strategic bombing during World War II, particularly strategic bombing and/or aer ...
program.
[Siouris, George. ''Missile Guidance and Control Systems.'' 2004] Project Pigeon
During World War II, Project Pigeon (later Project Orcon, for "organic control") was American behaviorist B. F. Skinner's attempt to develop a pigeon-controlled guided bomb.
Overview
The testbed was the same National Bureau of Standards-de ...
was American behaviorist
B.F. Skinner
Burrhus Frederic Skinner (March 20, 1904 – August 18, 1990) was an American psychologist, behaviorist, author, inventor, and social philosopher. He was a professor of psychology at Harvard University from 1958 until his retirement in 1974.
...
's attempt to develop a pigeon-guided bomb.
The first U.S. ballistic missile with a highly accurate inertial guidance system was the short-range
PGM-11 Redstone
The PGM-11 Redstone was the first large American ballistic missile. A short-range ballistic missile (SRBM), it was in active service with the United States Army in West Germany from June 1958 to June 1964 as part of NATO's Cold War defense of W ...
.
Categories of guidance systems
Guidance systems are divided into different categories according to whether they are designed to attack fixed 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.
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. A moving target can be an immediate threat to the missile launcher. The target must be promptly eliminated in order to preserve the launcher. In GOLIS systems, the problem is simpler because the target is not moving.
GOT systems
In every go-onto-target 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 (see
Wire-guided missile
A wire-guided missile is a missile that is guided by signals sent to it via thin wires connected between the missile and its guidance mechanism, which is located somewhere near the launch site. As the missile flies, the wires are reeled out behi ...
). These systems include:
:* ''
Command guidance
Command guidance is a type of missile guidance in which a ground station or aircraft relay signals to a guided missile via radio control or through a wire connecting the missile to the launcher and tell the missile where to steer to intercept its ...
'' – The missile tracker is on the launching platform. These missiles are fully controlled by the launching platform that sends all control orders to the missile. The two variants are
::* ''Command to line-of-sight'' (CLOS)
::* ''Command off line-of-sight'' (COLOS)
:* ''Line-of-sight beam riding guidance'' (LOSBR) – The target tracker is on board the missile. The missile already has some orientation capability meant for flying inside the beam that the launching platform is using to illuminate the target. It can be manual or automatic.
Command to line-of-sight
The CLOS system uses only the angular coordinates between the missile and the target to ensure the collision. The missile is made to be in the line of sight between the launcher and the target (LOS), and any deviation of the missile from this line is corrected. Since so many types of missile use this guidance system, they are usually subdivided into four groups: A particular type of command guidance and navigation where the missile is always commanded to lie on the line of sight (LOS) between the tracking unit and the aircraft is known as command to line of sight (CLOS) or three-point guidance. That is, the missile is controlled to stay as close as possible on the LOS to the target after missile capture is used to transmit guidance signals from a ground controller to the missile. More specifically, if the beam acceleration is taken into account and added to the nominal acceleration generated by the beam-rider equations, then CLOS guidance results. Thus, the beam rider acceleration command is modified to include an extra term. The beam-riding performance described above can thus be significantly improved by taking the beam motion into account. CLOS guidance is used mostly in shortrange air defense and antitank systems.
=Manual command to line-of-sight
=
Both target tracking and missile tracking and control are performed manually. The operator watches the missile flight, and uses a signaling system to command the missile back into the straight line between operator and target (the "line of sight"). This is 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 or missiles against ships or the supersonic
Wasserfall
The ''Wasserfall Ferngelenkte FlaRakete'' (Waterfall Remote-Controlled A-A Rocket) was a German guided supersonic surface-to-air missile project of World War II. Development was not completed before the end of the war and it was not used operati ...
against slow-moving
B-17 Flying Fortress
The Boeing B-17 Flying Fortress is a four-engined heavy bomber developed in the 1930s for the United States Army Air Corps (USAAC). Relatively fast and high-flying for a bomber of its era, the B-17 was used primarily in the European Theater ...
bombers this system worked, but as speeds increased MCLOS was quickly rendered useless for most roles.
=Semi-manual command to line-of-sight
=
Target tracking is automatic, while missile tracking and control is manual.
=Semi-automatic command to line-of-sight
=
Target tracking is manual, but missile tracking and control is automatic. It is similar to MCLOS but some automatic systems position 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. It is the most common form of guidance against ground targets such as tanks and bunkers.
=Automatic command to line-of-sight
=
Target tracking, missile tracking and control are automatic.
Command off line-of-sight
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 target tracker and the missile tracker can be oriented in different directions. The guidance system ensures the interception of the target by the missile by locating 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 mid-course 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 uses a "beam" of some sort, typically
radio
Radio is the technology of signaling and communicating using radio waves. Radio waves are electromagnetic waves of frequency between 30 hertz (Hz) and 300 gigahertz (GHz). They are generated by an electronic device called a transmit ...
,
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 ...
or
laser
A laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation. The word "laser" is an acronym for "light amplification by stimulated emission of radiation". The fir ...
, which 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
Semi-automatic command to line of sight (SACLOS) is a method of missile command guidance. In SACLOS, the operator has to continually point a sighting device at the target while the missile is in flight. Electronics in the sighting device and/or th ...
, but do not have to be; in other systems the beam is part of an automated radar tracking system. A case in point is the later versions of the
RIM-8 Talos
Bendix RIM-8 Talos was a long-range naval surface-to-air missile, and was among the earliest surface-to-air missiles to equip United States Navy ships. The Talos used radar beam riding for guidance to the vicinity of its target, and semiactive r ...
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
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 ...
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
Proportional navigation
Proportional navigation (also known as "PN" or "Pro-Nav") is a
guidance principle (analogous to
proportional control
Proportional control, in engineering and process control, is a type of linear feedback control system in which a correction is applied to the controlled variable, and the size of the correction is proportional to the difference between the desi ...
) used in some form or another by most homing air target
missiles
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 ...
. It is based on the fact that two objects are on a
collision course
{{wiktionary
A collision course, also known as a ''kamikaze run'', is the deliberate maneuver by the operator of a moving object (or often in Sci-Fi a spaceship) to collide with another object. It is a desperate maneuver since it often damages ...
when the direction of their direct
line-of-sight does not change. PN dictates that the missile velocity vector should rotate at a rate proportional to the rotation rate of the line of sight (line-Of-sight rate or LOS-rate) and in the same direction.
Radar homing
=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
Resolution(s) may refer to:
Common meanings
* Resolution (debate), the statement which is debated in policy debate
* Resolution (law), a written motion adopted by a deliberative body
* New Year's resolution, a commitment that an individual mak ...
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
Fire-and-forget is a type of missile guidance which does not require further external intervention after launch such as illumination of the target or wire guidance, and can hit its target without the launcher being in line-of-sight of the targe ...
" air-to-air missile systems such as the
AIM-120 AMRAAM
The AIM-120 Advanced Medium-Range Air-to-Air Missile, or AMRAAM (pronounced ), is an American beyond-visual-range air-to-air missile (BVRAAM) capable of all-weather day-and-night operations. It is 7 inches (18 cm) in diameter, and employs ...
and
R-77
The Vympel NPO R-77 missile (NATO reporting name: AA-12 Adder) is a Russian active radar homing beyond-visual-range air-to-air missile. It is also known by its export designation RVV-AE. It is the Russian counterpart to the American AIM-120 AMRA ...
.
=Semi-active homing
=
Semi-active homing systems combine a passive radar receiver on the missile with a separate
targeting radar This is a list of different types of radar.
Detection and search radars
Search radars scan great volumes of space with pulses of short radio waves. They typically scan the volume two to four times a minute. The waves are usually less than a meter ...
that "illuminates" the target. 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, and reducing the weight of the missile.
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) is by far the most common "all weather" guidance solution for anti-aircraft systems, both ground- and air-launched.
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 the aircraft within range of shorter-ranged IR-guided (infrared-guided) missile systems. It is 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.
SALH is similar to SARH but uses a laser as a signal. Another difference is that most laser-guided weapons employ turret-mounted laser designators which increase the launching aircraft's ability to maneuver after launch. How much maneuvering can be done by the guiding aircraft depends on the turret field of view and the system's ability to maintain a lock-on while maneuvering. As most air-launched, laser-guided munitions are employed against surface targets the designator providing the guidance to the missile need not be the launching aircraft; designation can be provided by another aircraft or by a completely separate source (frequently troops on the ground equipped with the appropriate laser designator).
Passive homing
Infrared homing
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 ...
is a passive system that homes in on the heat generated by the target. Typically used in the
anti-aircraft
Anti-aircraft warfare, counter-air or air defence forces is the battlespace response to aerial warfare, defined by NATO as "all measures designed to nullify or reduce the effectiveness of hostile air action".AAP-6 It includes surface based, ...
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 seeker
Optical contrast seekers, or simply contrast seekers, are a type of missile guidance system using a television camera as its primary input. The camera is initially pointed at a target and then locked on, allowing the missile to fly to its target b ...
s use a
television camera
A professional video camera (often called a television camera even though its use has spread beyond television) is a high-end device for creating electronic moving images (as opposed to a movie camera, that earlier recorded the images on film). O ...
, 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
AGM-65 Maverick
The AGM-65 Maverick is an air-to-ground missile (AGM) designed for close air support. It is the most widely produced precision-guided missile in the Western world, and is effective against a wide range of tactical targets, including armor, ...
, 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
Camouflage is the use of any combination of materials, coloration, or illumination for concealment, either by making animals or objects hard to see, or by disguising them as something else. Examples include the leopard's spotted coat, the ...
can render them unable to "lock on".
Retransmission homing
Retransmission homing, also called "
track-via-missile
Track-via-missile or TVM refers to a missile guidance technique which combines features of semi-active radar homing (SARH) and radio command guidance. This avoids the problems with terminal accuracy normally seen by command guided missiles, esp ...
" or "TVM", is a hybrid between
command guidance
Command guidance is a type of missile guidance in which a ground station or aircraft relay signals to a guided missile via radio control or through a wire connecting the missile to the launcher and tell the missile where to steer to intercept its ...
,
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 ...
and
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 ...
. 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.
AI guidance
In 2017, Russian weapons manufacturer
Tactical Missiles Corporation
, type = Joint-stock company
, location =
, industry = Defense industry Aerospace industrySpace industry
, founded =
, founder =
, hq_location_city = Korolyov, Moscow Oblast
, hq_location_country = Russia
, area_served = worldwide
, key_peop ...
announced that it was developing missiles that would use
artificial intelligence
Artificial intelligence (AI) is intelligence—perceiving, synthesizing, and inferring information—demonstrated by machines, as opposed to intelligence displayed by animals and humans. Example tasks in which this is done include speech re ...
to choose their own targets. In 2019, the
United States Army
The United States Army (USA) is the land service branch of the United States Armed Forces. It is one of the eight U.S. uniformed services, and is designated as the Army of the United States in the U.S. Constitution.Article II, section 2, cla ...
announced it was developing a similar technology.
GOLIS systems
![Arrow-3 Jan-03-2013 (c)](https://upload.wikimedia.org/wikipedia/commons/9/91/Arrow-3_Jan-03-2013_%28c%29.jpg)
Whatever the mechanism used in a go-onto-location-in-space guidance system is, it must contain preset information about the target. These systems' main characteristic is the lack of a target tracker. The guidance computer and the missile tracker are located in the missile. The lack of target tracking in GOLIS necessarily implies navigational guidance.
Navigational guidance is any type of guidance executed by a system without a target tracker. The other two units are on board the missile. These systems are also known as self-contained guidance systems; however, they are not always entirely autonomous due to the missile trackers used. They are subdivided by their missile tracker's function as follows:
:* Entirely autonomous – Systems where the missile tracker does not depend on any external navigation source, and can be divided into:
::* Inertial guidance
:::* With a
gimballed gyrostabilized platform
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 (dir ...
or
fluid-suspended gyrostabilized platform
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 (direc ...
:::* With
strapdown inertial guidance
::* Preset guidance
:* Dependent on natural sources – Navigational guidance systems where the missile tracker depends on a natural external source:
::* Celestial guidance
::* Astro-inertial guidance
::* Terrestrial guidance
:::* Topographic reconnaissance (Ex:
TERCOM
Terrain contour matching, or TERCOM, is a navigation system used primarily by cruise missiles. It uses a pre-recorded contour map of the terrain that is compared with measurements made during flight by an on-board radar altimeter. A TERCOM system ...
)
:::* Photographic reconnaissance (Ex:
DSMAC
Terrain contour matching, or TERCOM, is a navigation system used primarily by cruise missiles. It uses a pre-recorded contour map of the terrain that is compared with measurements made during flight by an on-board radar altimeter. A TERCOM system ...
)
::*
Magnetic guidance
A compass is a device that shows the cardinal directions used for navigation and geographic orientation. It commonly consists of a magnetized needle or other element, such as a compass card or compass rose, which can pivot to align itself with ...
:* Dependent on artificial sources – Navigational guidance systems where the missile tracker depends on an artificial external source:
::* Satellite navigation
:::* Global positioning system (
GPS
The Global Positioning System (GPS), originally Navstar GPS, is a Radionavigation-satellite service, satellite-based radionavigation system owned by the United States government and operated by the United States Space Force. It is one of t ...
)
:::* Global navigation satellite system (
GLONASS
GLONASS (russian: ГЛОНАСС, label=none, ; rus, links=no, Глобальная навигационная спутниковая система, r=Global'naya Navigatsionnaya Sputnikovaya Sistema, t=Global Navigation Satellite System) is ...
)
::* Hyperbolic navigation
:::* DECCA
:::*
LORAN
LORAN, short for long range navigation, was a hyperbolic radio navigation system developed in the United States during World War II. It was similar to the UK's Gee system but operated at lower frequencies in order to provide an improved range u ...
C
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 of the guidance components (including sensors such as
accelerometers
An accelerometer is a tool that measures proper acceleration. Proper acceleration is the acceleration (the rate of change of velocity) of a body in its own instantaneous rest frame; this is different from coordinate acceleration, which is accele ...
or
gyroscopes
A gyroscope (from Ancient Greek γῦρος ''gŷros'', "round" and σκοπέω ''skopéō'', "to look") is a device used for measuring or maintaining orientation and angular velocity. It is a spinning wheel or disc in which the axis of rotat ...
) 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
The V-2 (german: Vergeltungswaffe 2, lit=Retaliation Weapon 2), with the technical name ''Aggregat 4'' (A-4), was the world’s first long-range guided ballistic missile. The missile, powered by a liquid-propellant rocket engine, was developed ...
.
Inertial guidance
![Missile Maintainer inspects missile guidance system of the LGM-30G Minuteman ICBM](https://upload.wikimedia.org/wikipedia/commons/1/16/Missile_Maintainer_inspects_missile_guidance_system_of_the_LGM-30G_Minuteman_ICBM.jpg)
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 gyro
A ring laser gyroscope (RLG) consists of a ring laser having two independent counter-propagating resonant modes over the same path; the difference in phase is used to detect rotation. It operates on the principle of the Sagnac effect which shif ...
s that are accurate to within metres over ranges of 10,000 km, 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 100 m at intercontinental ranges. Many civilian aircraft use inertial guidance using a 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.
Inertial guidance is most favored for the initial guidance and reentry vehicles of
strategic missiles, because it has no external signal and cannot be
jammed.
Additionally, the relatively low precision of this guidance method is less of an issue for large nuclear warheads.
Astro-inertial guidance
Astro-inertial guidance is a
sensor fusion
Sensor fusion is the process of combining sensor data or data derived from disparate sources such that the resulting information has less uncertainty than would be possible when these sources were used individually. For instance, one could potentia ...
-
information fusion
Information integration (II) is the merging of information from heterogeneous sources with differing conceptual, contextual and typographical representations. It is used in data mining and consolidation of data from unstructured or semi-structured ...
of
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 (dire ...
and
celestial navigation
Celestial navigation, also known as astronavigation, is the practice of position fixing using stars and other celestial bodies that enables a navigator to accurately determine their actual current physical position in space (or on the surface of ...
. It is usually employed on
submarine-launched ballistic missile
A submarine-launched ballistic missile (SLBM) is a ballistic missile capable of being launched from submarines. Modern variants usually deliver multiple independently targetable reentry vehicles (MIRVs), each of which carries a nuclear warhead ...
s. Unlike silo-based
intercontinental ballistic missile
An intercontinental ballistic missile (ICBM) is a ballistic missile with a range greater than , primarily designed for nuclear weapons delivery (delivering one or more thermonuclear warheads). Conventional, chemical, and biological weapons c ...
s, whose launch point does not move and thus can serve as a
reference
Reference is a relationship between objects in which one object designates, or acts as a means by which to connect to or link to, another object. The first object in this relation is said to ''refer to'' the second object. It is called a ''name'' ...
, SLBMs are launched from moving submarines, which complicates the necessary navigational calculations and increases
circular error probable
In the military science of ballistics, circular error probable (CEP) (also circular error probability or circle of equal probability) is a measure of a weapon system's precision. It is defined as the radius of a circle, centered on the mean, wh ...
. This stellar-inertial guidance is used to correct small position and velocity errors that result from launch condition uncertainties due to errors in the submarine navigation system and errors that may have accumulated in the guidance system during the flight due to imperfect
instrument calibration
In measurement technology and metrology, calibration is the comparison of measurement values delivered by a device under test with those of a Standard (metrology), calibration standard of known accuracy. Such a standard could be another measurem ...
.
The USAF sought a precision navigation system for maintaining route accuracy and target tracking at very high speeds.
Nortronics,
Northrop's electronics development division, had developed an
astro-inertial navigation system (ANS), which could correct
inertial navigation
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 ...
errors with
celestial observations, for the
SM-62 Snark
The Northrop SM-62 Snark is an early-model intercontinental range ground-launched cruise missile that could carry a W39 thermonuclear warhead. The Snark was deployed by the United States Air Force's Strategic Air Command from 1958 through 1961 ...
missile, and a separate system for the ill-fated
AGM-48 Skybolt
The Douglas GAM-87 Skybolt (AGM-48 under the 1962 Tri-service system) was an air-launched ballistic missile (ALBM) developed by the United States during the late 1950s. The basic concept was to allow US strategic bombers to launch their weapons ...
missile, the latter of which was adapted for the
SR-71.
It uses star positioning to fine-tune the accuracy of the inertial guidance system after launch. As the accuracy of a missile is dependent upon the guidance system knowing the exact position of the missile at any given moment during its flight, 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
Trident missile 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
Terrain contour matching, or TERCOM, is a navigation system used primarily by cruise missiles. It uses a pre-recorded contour map of the terrain that is compared with measurements made during flight by an on-board radar altimeter. A TERCOM system ...
, 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
A radar altimeter (RA), also called a radio altimeter (RALT), electronic altimeter, reflection altimeter, or low-range radio altimeter (LRRA), measures altitude above the terrain presently beneath an aircraft or spacecraft by timing how long it t ...
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
A cruise missile is a guided missile used against terrestrial or naval targets that remains in the atmosphere and flies the major portion of its flight path at approximately constant speed. Cruise missiles are designed to deliver a large warhe ...
guidance, but is being supplanted by
GPS
The Global Positioning System (GPS), originally Navstar GPS, is a Radionavigation-satellite service, satellite-based radionavigation system owned by the United States government and operated by the United States Space Force. It is one of t ...
systems and by
DSMAC
Terrain contour matching, or TERCOM, is a navigation system used primarily by cruise missiles. It uses a pre-recorded contour map of the terrain that is compared with measurements made during flight by an on-board radar altimeter. A TERCOM system ...
, 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 lacking in robustness that destruction of prominent buildings marked in the system's internal map (such as by a preceding cruise missile) upsets its navigation.
See also
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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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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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Electronic warfare
Electronic warfare (EW) is any action involving the use of the electromagnetic spectrum (EM spectrum) or directed energy to control the spectrum, attack an enemy, or impede enemy assaults. The purpose of electronic warfare is to deny the opponen ...
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List of missiles
Below is a list of missiles, sorted alphabetically into large categories and subcategories by name and purpose.
Other missile lists
Types of missiles:
* Conventional guided missiles
** Air-to-air missile
** Air-to-surface missile
** Anti-radiat ...
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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 pi ...
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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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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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Terminal guidance In the field of weaponry, terminal guidance refers to any guidance system 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 systems, ...
References
External links
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{{DEFAULTSORT:Missile Guidance
Missile operation
Missile technology
Tracking
Targeting (warfare)