LINEAR MODEL EVALUATION OF COMMAND GUIDANCE SYSTEM

ABSTRACT:
The primary design of a missile control system is commonly derived from a linearized model of that system. Gain selection is accomplished by examining both the performance and the relative stability of the linear representation of the system at various operating conditions given by incidence angles, mach number and flight altitude. Most often, classical phase and gain margins are used as measures of relative stability. The linearized model assumes the linearity of
hardware comprising the guidance loop and the missile dynamics. The reliability of the linearization assumptions determines the robustness and performance of the primary design. This paper is devoted for the study of the linearization assumptions evaluation. A typical command guidance system is considered as a
case study. In spite of the nonlinear behavior of the various subsystems comprising the guidance system, the guidance-commands limiters are assumed the only nonlinear elements in the guidance loop due to their obvious direct effect on the guidance process. Computation analysis shows that the effect of these limiters appears only during the early guidance period which does not exceed 5 percent of the entire flight time. The missile dynamics nonlinearities are also studied. A comparison between the results of the six-degree-of-freedom nonlinear model and the linearized model is carried out. Comparison shows that the linear dynamical model can be relied-on in cases where sudden target maneuver or sudden variation of flight environmental conditions are not considered. However, during steady guidance periods, the linear model results can be fairly adopted.