Predefined-Time Approximation-Free Attitude Constraint Control of Rigid Spacecraft

In this article, a predefined-time approximation-free attitude constraint control scheme is proposed for rigid spacecraft with external disturbances. By combining the backstepping technique, an approximation-free controller is systematically developed to maintain the spacecraft attitude within a prescribed small region in predefined time, and the minimum upper bound of the settling time can be exactly given by adjusting a single control parameter. Instead of employing some piecewise continuous functions, the quadratic-fraction functions are constructed in the controllers design to circumvent the possible singularity issue resulted from the differentiation of the virtual controller. With the presented approximation-free control scheme, the computational burden is reduced due to the avoidance of introducing any function approximators. The effectiveness of the proposed scheme is verified by the numerical simulations.