MISSILE GUIDANCE RADAR

secondary air-search radars; in emergencies, fire-control radars have served as surface-search radars. A multi-dimensional air-search radar is shown in figure 1-15. MISSILE GUIDANCE RADAR The purpose of a guidance subsystem is to direct the missile to target intercept regardless of whether or not the target takes deliberate evasive action. The guidance function may be based on information provided by a signal from the target, information sent from the launching ship, or both. Every missile guidance system consists of two separate systems—an attitude control system and a flight path control system. The attitude control system maintains the missile in the desired attitude on the ordered flight path by controlling it in pitch, roll, and yaw (fig. 1-16). This action, along with the thrust of the rocket motor, keeps the missile in stabilized flight. The flight path control system guides the missile to its designated target. This is done by determining the flight path errors, generating the necessary orders needed to correct these errors, and sending these orders to the missile’s control subsystem. The control subsystem exercises control in such a way that a suitable flight path is achieved and maintained. The operation of the guidance and control subsystems is based on the closed-loop or servo principle (fig. 1-17). The control units make corrective adjustments to the missile control surfaces when a guidance error is present. The control units also adjust the wings or fins to stabilize the missile in roll, pitch, and yaw. Guidance and stabilization are two separate processes, although they occur simultaneously. Phases of Guidance Missile guidance is generally divided into three phases (fig. 1-18). As indicated in the figure, the three p h a s e s a r e b o o s t , m i d c o u r s e , a n d t e r m i n a l . STANDARD SM-2 missiles (MR & ER) use all three of these phases. Not all missiles, however, go through the three phases. As shown in figure 1-18, some missiles (STANDARD SM-1, SEASPARROW) do not use midcourse guidance. With that thought in mind, let’s examine each phase, beginning with boost. I N I T I A L ( B O O S T ) P H A S E . — N a v y surface-launched missiles are boosted to flight speed by the booster component (which is not always a separate component) of the propulsion system. The boost period lasts from the time the missile leaves the launcher until the booster burns up its fuel. In missiles with separate boosters, the booster drops away from the missile at burnout (fig. 1-18, view A). Discarding the burnt-out booster shell reduces the drag on the missile and enables the missile to travel farther. SMS missiles with separate boosters are the STANDARD (ER) and HARPOON. The problems of the initial (boost) phase and the methods of solving them vary for different missiles. The method of launch is also a factor. The basic purposes, however, are the same. The missile can be either pre-programmed or physically aimed in a specific direction on orders from the fire control 1-14 Figure 1-16.—Missile axes: pitch, roll, yaw. Figure 1-17.—Basic missile guidance and control systems. Figure 1-15.—Multi-dimensional (3-D) radar.