Adaptive nonsingular fast terminal sliding mode guidance law with fixed-time convergence

To deal with the terminal guidance problem of missiles for intercepting maneuvering targets, a nonsingular fixed-time convergent fast terminal sliding mode guidance law is developed with impact angle constraints. Compared with finite-time convergent terminal sliding mode guidance laws, the proposed guidance law ensures that the line of sight (LOS) angle and the LOS angular rate are fixed-time convergent. The convergence time is independent of the initial states of the guidance system and can be set in advance by the guidance law's parameters. Compared with conventional fixed-time convergent control, a novel nonsingular terminal sliding mode is designed to solve the singularity problem and the faster convergence rate is guaranteed by regulating the index of the approaching laws of the sliding surface and the LOS angle error. Besides, an adaptive law for unknown upper bound estimation of the target acceleration is presented and a priori information on the target acceleration is not required to be known. Finally, simulation results show that the missile can intercept the maneuvering targets effectively with the proposed guidance law. Besides, comparison with the existing guidance laws indicates that the faster convergence rate of the guidance system, the shorter intercept time and the higher intercept accuracy are achieved by the proposed guidance law.