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 or missiles against ships or the supersonic Wasserfall against slow-moving B-17 Flying Fortress bombers this system worked, 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.
[edit]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 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.
[edit]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 do not 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.[5]
[edit]Homing guidance
[edit]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
[edit]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.[6]
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.
SALH is a similar system using a laser as a signal. However, most laser-guided weapons employ a turret-mounted laser designator which increases the launching aircraft's ability to maneuver after launch. How much maneuvering can be done by the guiding aircraft will depend on the turret field of view and the systems 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).
[edit]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".[7]
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 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".
[edit]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.