Terminal impact angle constrained guidance laws using state-dependent Riccati equation approach

Abstract

The guidance problem of intercepting ground targets by air-launched missiles is considered in this paper. In addition to achieving a minimal miss distance, the proposed guidance law can also lead to desired terminal impact angles in both azimuth as well as elevation simultaneously. The guidance law is developed on the basic principle of state-dependent Riccati equation (SDRE) approach by considering nonlinear engagement dynamics of the missile. The proposed SDRE-based guidance law is first conducted in a vertical plane, followed by its extension to three-dimensional engagement scenario. High terminal accuracy is ensured by employing a state weighting matrix defined by functions of altitude-to-go. To enlarge the available impact angle region, the guidance law is further modified to achieve interceptions in the case where impact angle in the pitch plane is too large or too small. Third-order autopilot lag is also synthesized in the implementation of the guidance law. Numerical simulations are performed to demonstrate the effectiveness and accuracy of the proposed guidance method in both planar and three-dimensional engagement scenarios.