Three-dimensional Nonlinear Impact Time Guidance Accounting for Autopilot Lag

In this paper, a nonlinear impact time constrained three-dimensional guidance strategy to intercept a stationary target is proposed. The guidance strategy is based on non-singular terminal sliding mode control that uses an improved time-to-go estimate in the design process, thereby provisioning for the interceptor's large heading angle errors. Unlike existing approaches in the literature of three-dimensional terminal guidance, the proposed technique does not decouple the nonlinear three-dimensional engagement kinematics to design the guidance commands. Additionally, the proposed technique also considers the effect of autopilot whose dynamics are usually ignored. The stability of the proposed guidance strategy is certified using Lyapunov stability theory. Simulation results show the effective performance of the proposed guidance commands for various engagement conditions. The results in this paper are further backed with a comparison with an existing strategy that vindicates the superior performance of the proposed strategy.