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 possibly through a wire connecting the missile to the launcher: Wire-guided missile) and tell the missile where to steer in order to intercept its target. Additionally, it is possible to send a command to the missile to detonate, even if the missile itself has a fuze or fuzes. (It may be possible to detonate the missile and destroy or damage the target, even though the missile was not actually going to strike the target, due to the blast radius of the warhead).

Typically, the system giving the guidance commands is tracking both the target and the missile or missiles via radar. It determines the position and velocity of the target and the position and velocity of the missile and calculates whether their paths will intersect. If not, the guidance system will relay commands to the missile(s), telling them to move their fins in such a way to steer themselves in the direction necessary for them to end up on an interception course with the target. If the target maneuvers, the guidance system can notice this and update the missiles' course continuously to counteract the maneuvering. If the missile passes close to the target, either its own proximity or contact fuze will detonate the warhead, or the guidance system can estimate when the missile will pass near the target and send a detonation signal.

On some systems there is a dedicated radio antenna or antennas for communicating with the missile(s). On others, the radar itself is actually able to send coded pulses which the missile can pick up and interpret as guidance commands. Sometimes to aid the tracking station, the missile will contain a radio transmitter, making it easier to track. Also, sometimes there is a dedicated radar antenna on the tracking station for tracking the missile as well as one or more for tracking targets. It is especially these types of systems which may be able to communicate with the missile via the same radar energy it uses for tracking it.

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 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 to commanded 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 (MCLOS)

Main article: 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 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)

Target tracking is automatic, while missile tracking and control is manual.

Semi-Automatic Command to Line-Of-Sight (SACLOS)

Main article: Semi-automatic command to line of sight

Target tracking is manual, but 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)

Target tracking, missile tracking and control are automatic.

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 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)

Main article: Beam riding

LOSBR uses a "beam" of some sort, typically radio, radar or laser, 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, 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.

Track-via-missile

Track-via-missile is a variation of command guidance, the main difference being that the missile itself sends target tracking information back to the guidance system to aid it in calculating the intercept. This negates much of the accuracy disadvantage of pure command guidance.

Examples

Examples of missiles which use command guidance include:

• Russian: SA-1 'Guild', SA-2 'Guideline', SA-3 'Goa', SA-15 'Gauntlet'
• American: Nike Ajax, Nike Hercules, Nike Zeus
• Indian: Akash

Note that older western missiles tended to prefer using pure semi-active radar homing.

Pure command guidance is not normally used in modern SAM systems since it is too inaccurate during the terminal phase (when the missile is about to intercept the target). This is because the ground-based radars are distant from the target and the returned signal lacks resolution. However, it is still quite practical to use it to guide the missile to a location near the target, and then use another more accurate guidance method to actually intercept the target. Almost any type of terminal guidance can be used, but the most common are semi-active radar homing (SARH) or active radar homing.

Examples of missiles which use command guidance with terminal SARH include:

• Russian: SA-4 'Ganef', SA-6 'Gainful', SA-11 'Gadfly', SA-17 'Grizzly'

Examples of missiles which use command guidance with terminal active radar homing include:

• Russian: SA-5 'Gammon'