Terminal sliding mode control based impact time and angle constrained guidance

In this paper, an impact time and angle constrained guidance (ITACG) is proposed based on the nonsingular terminal sliding mode control (NTSMC) theory. First, the guidance law is derived for stationary targets. The proposed ITACG consists of two parts. One part is designed for a missile to intercept a target from the desired impact angle and the other part aims to achieve the desired impact time. Two different terminal sliding mode surfaces are designed so that the missile can satisfy the impact time and angle constraints simultaneously. Corresponding to the designed sliding mode surfaces, two different Lyapunov candidate functions are proposed and analyzed, and stability conditions are obtained. Then, we extend the proposed guidance for constant acceleration targets. The time-to-go estimation method is modified based on the conception of predicted-intercept-point (PIP) with the constant acceleration targets and stability conditions are also revised. Compared with traditional sliding mode control (SMC) based ITACG, the proposed guidance law is a direct online method. It does not need to design the line-of-sight angle curve off-line, nor does it need to switch between impact time constrained guidance and impact angle constrained guidance. In the end, numerical simulation results show that the proposed impact time and angle constrained guidance law has a good performance even though the missile has a constant acceleration. Salvo attack of multi-missiles against one target is shown in the simulation part by applying the proposed guidance law.