Closed-Form Nonlinear Impact Angle Guidance using State-Dependent Riccati Equation Approach

In this paper, a suboptimal impact angle control guidance law is proposed against non-maneuvering targets, by converting a problem of target interception at an impact angle into one of controlling the line-of-sight angle and its rate. The guidance commands are derived based on the state-dependent Riccati equation (SDRE) technique, which is further augmented with integral sliding mode control to account for uncertainties. The optimal performance of the guidance law is guaranteed by the use of SDRE technique. A closed-form expression of the guidance command, that satisfies the (state-dependent) Riccati equation, is also obtained. This obviates the need for numerical solution, thereby reducing the computational requirement during actual implementation. The performance of the proposed guidance scheme is evaluated via numerical simulations for different engagement scenarios, while also considering a variable speed interceptor model and is shown to be satisfactory.