Terminal Guidance Method Of The Escort Aircraft

Taking an escort aircraft as the research object,the terminal guidance method of the escort aircraft is researched in this paper.A detailed mathematical model of the terminal guidance and control system of the escort aircraft is established,and thus three kinds of terminal guidance laws are put forward: BANG-BANG variable structure guidance law,active defense adaptive sliding mode guidance law(AD_ASMG)and active defense nonsingular terminal sliding mode guidance law(AD_NTSMG).As the escort aircraft's initial velocity is large and flight time is small,and the upper bound of the interceptor aircraft's maneuver capability is unknown,the guidance methods existed cannot meet the requirements of the escort aircraft's terminal guidance phase.Nowadays,it is seldom seen about the guidance law design method when the upper bound of the interceptor aircraft's maneuver capability is unknown.The BANG-BANG variable structure guidance law is designed adopting guidance strategy of zeroing line of sight(LOS)rate,in order to testify the overload requirement of escort aircraft.The AD_ASMG and AD_NTSMG are designed adopting guidance strategy of both LOS and LOS rate.The AD_ASMG realizes adaptive guidance when the upper bound of the interceptor aircraft's maneuver capability is unknown,by designing a sliding mode switching term gain adaptive law.The AD_NTSMG is a terminal guidance law designed by finite time convergence and nonsingular terminal sliding mode control theory.The propulsive force achieved by the orbit control engine of the escort aircraft is not adjustable,so the BANG-BANG variable structure terminal guidance law is most easily implemented.However,the command of AD_ASMG or AD_NTSMG is continuously changing,so it cannot be achieved directly.By using the momentum equivalence principle,the two kinds of guidance laws are satisfied by controlling the working time of engine and thus changing the equivalent output of engine.After simulation tests,from the simulation results we can see that under the BANG-BANG variable structure guidance law,the miss distance is less than 0.5 m when the maximum acceleration is 5 g.However,under the AD_ASMG,the miss distance can be less than 0.3 m when the maximum acceleration is 3 g,and under the AD_NTSMG,the miss distance can also be less than 0.3 m when the maximum acceleration is 4 g,The results show that the AD_ASMG and AD_NTSMG designed can meet the task requirements of the terminal guidance phase when the overload capacity of the escort aircraft is weak.