Major subsystems that may be included in the flight vehicle are guidance and control fuze and warhead, motor, and airframe. The guidance and control system is often subdivided into individual subsystems as shown in Figure 1. If a missile has a seeker, the onboard guidance system usually is composed of the seeker and autopilot.  

Fig. 1 Guidance and Control Terminology

Figure 2 is a longitudinal cross-section of a typical surface-to-air missile having all of these subsystems onboard. If a missile does not have a seeker, the only onboard guidance components may be antennas for receiving information from the ground-based guidance components and an autopilot to translate guidance information into control commands.

Fig. 2 Major Component Segments of a Homing Missile