To alleviate the sensitivity of homing guidance with respect to initial state errors and enhance the anti-disturbance capability of missile at the final time

this paper presents an optimal guidance law with impact angle constraint based on a class of hyperbolic tangent weighting function using the indirect Gauss pseudospectral method. First

an impact angle coordinate system was established based on the desired impact angle and the position of the target

in which the motion kinetics for the engagement was constructed and the homing guidance model with impact angle constraint was obtained. Second

the two-point boundary problem was derived by utilizing the minimum principle

which was then discretized into a set of algebraic equations by employing the Gauss pseudospectral method. Finally

the optimal guidance law was easily obtained via explicitly solving the algebraic equations. This approach does not need to solve the Riccati differential equations and avoids cumbersome integral operations

which leads to a low computational load. The derivation of the proposed guidance law does not rely on the concrete form of weighting functions

and it can handle complex weighting functions. Simulation results demonstrate the performance of the proposed guidance law and show that the trajectory and acceleration command of missile could be shaped as desired by employing different types of weighting functions. The proposed algorithm could effectively reduce the sensitivity of homing guidance with respect to initial state errors and ensure the operational margin to cope with external disturbances at the end of the homing phase

provides more degrees of freedom in the guidance law design to accomplish specified guidance objectives.