A Robust Predefined Performance Controller for Reusable Launch Vehicles Under Mismatched Disturbance and Input Saturation

This paper addresses the attitude tracking control issue for reusable launch vehicles (RLVs) in the presence of non-matching disturbances and saturation effects. An enhanced predefined performance function (PPF) is derived based on a novel anti-saturation predefined-time compensator (ASPC) to ensure stability during saturation. Additionally, a fixed-time disturb observer (DO) is introduced for estimating both mismatch and matching perturbations within a fixed-time interval. Based on the error transformation, a fixed-time dynamic surface control (DSC) is proposed, ensuring that the transformed system state converges to the residual set at the origin promptly. The simulations demonstrate that the attitude tracking error reliably converges to a predefined region within a predetermined time.