Cooperative nonlinear guidance strategies for aircraft defense

This paper presents nonlinear guidance strategies for scenarios where an aircraft launches a defender missile as a countermeasure against an incoming attacking missile. The guidance system offers an additional degree of freedom due totwo available controls, the lateral accelerations of defender and aircraft. This extra degree of freedom is used in various ways to design guidance strategies. These guidance strategies, in addition to each ensuring interception of missile, also individually allow: 1) to reduce sensitivity of guidance law to erroneous time-to-go estimates, 2) the aircraft to perform optimal evasive maneuvers, and 3) either of the aircraft or the defender to maneuver independently with their maximum limit small as compared to that of missile. The design of guidance strategies is performed in a nonlinear framework, using sliding-mode control technique, with relevant zero-effort miss variables as switching surfaces. For reduction of sensitivity against time-to-go, an additional zero-effort velocity switching surface is proposed. Simulations are presented to validate the efficacy of the proposed guidance strategies and their superior performance compared to existing classical guidance laws. The protection envelopes, which depict the variations of minimum aircraft-missile distance with respect to heading angle of missile, to ensure successful interception, are also obtained.