ACQUISITION AND TRACKING

guidance (missiles), and evaluation (intercept and target destruction). Figure 1-23 illustrates the fire control problem sequence. DETECTION.—In this phase, the radar looks for a target. After the radar (usually a search radar) detects a target, the system obtains precise target position information. This information can be provided by the same source that detected the target, or it can be provided from some other source, such as another radar. In the majority of the cases, a second radar, a fire control radar, is used. The search radar establishes the target’s initial position and transmits this information to the designated fire control system. ACQUISITION AND TRACKING.—During this phase, the fire control radar director/antenna is aligned with the search radar’s target position information until it locks on the reflected target signal (acquisition). Either an operator or an automatic control circuit maintains that alignment (track) while the ship and target are moving. In this way, continuous, accurate target position information is available to the weapon system for processing. Not only is the continuous present position of the target obtained, but its movement (course and speed) is also determined. Data other than target data is equally important for weapon flight path (trajectory) determination. Wind, for example, could blow the weapon off its flight path. Appropriate corrections would require that wind direction and velocity be determined. The course and speed of the launching ship and its motion, because of t h e s e a ( p i t c h a n d r o l l ) , a r e a l s o i m p o r t a n t considerations. If this type of data is not included in the flight path determinations, it could cause large errors in the flight path (trajectory). Data of this nature, along with target data, is transmitted to the fire control system’s computer. The computer performs the necessary calculations for computing the launcher or gun mount position angles and the weapon’s flight path. After target detection and target acquisition have occurred, the fire control system provides three operations for the tracking, computation (prediction), and positioning functions. The first operation tracks the target and provides all necessary data on the target. The fire control radar performs this function by establishing a tracking Line Of Sight (LOS) along which it receives the returned or reflected energy from the target. It also provides accurate range data. Since the speed of the propagated RF energy is about 186,000 miles per second (the same as the speed of light), and since the target ranges involved are relatively small, the time for the energy to travel to and from the target can be considered as instantaneous. Therefore, the radar indications of the target can be considered as instantaneous, present-target positions. PREDICTION.—The second operation of the fire control problem that must be performed is the computation of the gun/launcher positioning angle (line of fire) and the weapon flight path trajectory. This operation consists of two parts. First, the system processes received data into a usable form. Then the fire control computer performs arithmetic operations to predict the future position of the target. 1-19 Figure 1-22.—Typical fire-control radar.