Document Type : Original Article
Ass. Lecturer, Radar and Guidance Dpt. , Military Technical College, Cairo, Egypt.
Ass. Prof., Radar and Guidance Dpt., Military Technical College, Cairo, Egypt.
By progressing of time, the effectiveness and importance of smart weapons become more obvious. Among the wide varieties of known smart weapons, guided bombs are of special interest since they enable precise destruction of enemy targets in quite safe manner. The smart bombs are formed by attaching seeker and control units to the conventional unguided bombs. The seeker type determines the type of the bomb. Television (TV), millimeter waves, laser, or infrared seekers may be employed. The seeker involves the target acquisition and tracking systems. It provides the bomb-target line-of-sight signal to the guidance section which in turn produce the guidance commands to the control unit. The control unit contains the control fins and the necessary subsystems for the instantaneous execution of the guidance commands.
In this paper, attention will be paid to the design of the bomb guidance loop. The design process passes through two steps. In the first step, an identification to the bomb airframe is carried out. The nonlinear flight dynamical behavior of the airframe is linearized around a chosen trim operating point. The identification is made via a six-degrees-of-freedom (6-DOF) flight model of the bomb, wherefrom the transient response of the airframe is computed. Out of this step, the transfer function of the bomb airframe (that relates the airframe maneuver to the control fins deflection) is obtained. In the second step, the guidance loop is analyzed. First, Ideal (inertialess) and real (with finite inertia) seekers are considered. In view of the problem kinematics, the guidance loop stability can not be maintained throughout the flight. The design criterion is that the stability of the guidance loop is maintained over most the entire bomb flight trajectory. It is shown that this can be achieved via a proportional-plus-differential (PD) controller that is placed in the bomb board.
In this paper, noise free system is considered as a primary step in the design. However, the effect of inherent noises and external disturbances can be studied by inserting them as additional inputs to the seeker, and this is beyond the scope of the present paper.