A guided missile is a self-powered weapon, in the family of precision-guided munitions (PGM) that can alter its flight or ballistic characteristics in order to correct aiming errors and hit a target. Guided missiles are assumed to be independently powered during at least part of its flight, differentiated from guided bombs and artillery-launched guided shells. The part of the missile that contains the materials or mechanism that will affect the target is the missile's warhead; ballistic missile warheads are contained in reentry vehicles of various capabilities.
Missiles, in general, follow one of two guidance paradigms:
- Go-onto-location-in-space (GOLIS), where guidance directs the weapon to a specific set of geographical coordinates and whatever is located at those coordinates;
- Go-onto-target (GOT), in which the weapon recognizes a specific target, which may be moving, and adjusts its course based on sensor input or human commands, in order to hit that target.
A given missile may be command-guided, with it completely under the control of a human operator. It may be partially autonomous, where, for example, the person launches it points it at the target until onboard sensors can take control. It may be "fire and forget" or fully autonomous, such that it needs no human control once it has been give target information.
The radar transmitter is separate from the missile, which only contains a homing receiver.
Both a transmitter and receiver are in the missile, which is usually "fire and forget" but might have a command override.
Anti-radiation and home-on-jam
A set of accelerometers and gyroscopes allows the guidance system to sense every movement and compute the change from the last known position. Such systems require the firing platform to know its position as accurately as possible.
Typically used for ballistic missiles that rise above the atmosphere, the navigation system locates stars and computes position based on them.
While there are great detailed variations depending on the missile and launcher type, as well as its range and target, there are still usually three basic parts of the flight.
Launch and boost
The first phase includes preventing the missile from being launched at all, by hard or soft kill of the launch platform. In the Outer Air Battle that the United States Navy planned against a serious Soviet Naval Aviation attack against carrier battle groups, the motto is that it "is better to shoot the archer than the arrow". Clearly, it was more efficient to interfere with the Tu-95 radar aitcraft giving the general target location to the Tu-22 or other bomber that could launch two or three air-to-surface missiles.
Even immediately after launch, there may be techniques to neutralize the missile in what is called the boost phase with ballistic missiles, but still applies to other types. For example, cruise missiles may have a booster rocket motor to give initial thrust, with a turbojet or ramjet providing continuing propulsion. Before that booster drops away, it is a brilliant target to an infrared sensor. A boost-phase interceptor like NCADE will do its terminal homing on the bright launch signature; an airborne directed energy weapon will still aim at that heat source.
The key electronic warfare attack on the missile, in this phase, is to attack the search radar of an antiaircraft system, or other sensors that put it into the basic course.
Be they ballistic, cruise, or antiaircraft missiles, there is a next phase, in other than very short range missiles, where the missile flies a relatively straight course over distance, bringing into the area of final attack. A ballistic missile may coast in space before releasing reentry vehicle(s) and decoys. A cruise missile may fly at low altitude until it pitches up for final attack, although some cruise missiles, especially long-range antiship missiles, may fly at high altitude for aerodynamic efficiency in the midcourse.
A variety of guidance methods apply to midcourse. Ballistic missiles in space will probably use some combination of inertial and celestial means. Cruise missiles will use inertial, GPS, and possibly third-party radar updates to get into the target area. Antiaircraft missiles may use radar or command guidance, and either active or semi-active radar homing.
Electronic attack on missile in this stage try to break track: to force a maneuvering missile into an overly stressful turn, either masking its antenna or having the radar lose the general signal.
The missile usually is at its fastest speed in the terminal attack. While current ballistic warheads do not maneuever, their extremely high speed, and possibly decoys, make them difficult targets even though their trajectories are predictable. Cruise missiles often will curve or otherwise maneuver in the target area, then do a final pitch-up to dive into the target. Antiaircraft missiles may have final maneuvering thrusters, but often switch to infrared terminal homing or to a different, shorter-wave radar.
Final electronic attack can try to destroy the terminal seeker (e.g., with directed infrared contermeasures), use deceptive jamming appropriate to the terminal seeker, hide the target with flares or chaff, or, finally, use "seduction" to convince the missile that a sacrificial decoy is the real target (e.g., the AN/ALE-55 towed fiber optic detail will first try to break track, but its final defense is seduction.
Classification by launcher and target location
There are several ways to classify guided missiles. One of the most basic covers the launching platform and the target location, "location" here being agnostic to GOLIS or GOT. Each one of these types has further subdivisions, such as range, mobility, guidance, payload, etc.
- Note 1: anti-ballistic missiles may actually intercept in space, in the upper atmosphere, or lower atmosphere. For this chart, the types are all considered surface-to-space.