Aiming at the issue of missiles attacking on-ground maneuvering targets in three-dimensional space, a three-dimensional finite-time guidance law with impact-angle constraints is proposed. In order to improve convergence speed and restrain chattering phenomenon, the nonsingular fast terminal three-dimensional second-order sliding mode guidance law with coupling terms is designed based on the theory of nonhomogeneous fast terminal sliding surface and second-order sliding mode control. The system model need not be linearized during the design process, and the singular problem is avoided. A nonhomogeneous disturbance observer is designed to estimate and compensate the total disturbance, which is caused by target maneuvering information and coupling terms of line of sight. And the stability and finite-time convergence of the guidance law are proved strictly and mathematically. Finally, simulation results have verified the effectiveness and superiority of the proposed guidance law.
