Guidance is a generic term that describes the hardware, the functions, and the processes used to steer a missile to intercept a target. Steering a missile to a target is analogous to steering any other vehicle, e.g., an automobile.

Continuing the analogy and for the moment restricting the discussion to a missile with a seeker, the eyes of the missile are the seeker head its brain is the combination of the seeker electronics processor and the autopilot, and its nerve system (muscle control) and muscles are contained in its control system. Any such process in which the error is continuously observed, i.e., measured, and corrections are made to reduce the observed error is a closed loop process. In this application the process is described by the guidance loop illustrated in Figure 1.

Fig. 1 Guidance Loop

Referring to Figure 1, the sequence of events in guiding a Missile begins when the seeker (intercept error sensor) senses the scene and determines the instantaneous intercept error. The guidance Process, then determines the appropriate maneuver command, based on the guidance law, to reduce the error. The autopilot in turn determines the control that is needed to achieve this command and transmits the control signals to the control system actuators to deflect the control surfaces. The control surfaces aerodynamically change the heading of the missile in a direction to reduce the heading error. The loop is closed as the intercept error sensor determines the new instantaneous intercept error.