Semi-automatic command to line of sight (SACLOS) is a method of missile command guidance.[1] In SACLOS, the operator must continually point a sighting device at the target while the missile is in flight. Electronics in the sighting device and/or the missile then guide it to the target.
Many SACLOS weapons are based on an infrared seeker aligned with the operator's gunsight or sighting telescope. The seeker tracks the missile, either the hot exhaust from its rocket motor or flares attached to the missile airframe, and measures the angle between the missile and the centerline of the operator's sights. This signal is sent to the missile, often using thin metal wires or a radio link, which causes it to steer back toward the center of the line-of-sight. Common examples of these weapons include the BGM-71 TOW wire-guided anti-tank guided missile (ATGM) and the Rapier radio-command surface-to-air missile (SAM).
Another class of SACLOS weapons is based on the beam riding principle. In this case, a signal is sent from the operator's sights toward the target. The signal is generally radio or a laser. The missile has receivers for the signal on the rear of the fuselage. Some form of encoding is used in the signal so that the missile can steer itself into the center of the beam. Changing frequencies or dot patterns are also commonly used. These systems have the advantage that the link between the launcher and missile cannot easily be broken or jammed. But, they have a disadvantage because the guidance signal may be detected by the target. Examples include the laser-guided RBS 70 SAM and 9M120 Svir ATGM.