Prescribed Performance Backstepping Attitude Control of Parafoil System for Rocket Booster Recovery Under Complex Unknown Disturbances

The parafoil system is an effective low-cost reliable methodology to fulfill the precise recovery and reuse of rocket booster. As a lightweight underactuated aircraft, the parafoil with booster combination (PBC) motion characteristics are strongly nonlinear and extremely vulnerable to unknown disturbances, such as model uncertainty and wind disturbance. So, a prescribed performance-based backstepping(PPB) attitude tracking controller of PBC with fixed-time disturbance observer(FDO) is proposed. Firstly, a 9-degree-of-freedom (DOF) multi-body flexible nonlinear model of the PBC is built based on kinematic, dynamic and computational fluid dynamics (CFD) analyses. Then, to ensure the attitude error converges to an arbitrarily small residual set, with steady-state error and settling time less than the prespecified values, the prescribed performance control is employed to improve traditional backstepping method which deals with the system nonlinearity effectively. Furthermore, to restrain the complex unknown complex disturbances and enhance the robustness of PPB controller, a FDO is introduced to accurately estimate the unknown external environmental and internal model uncertainties disturbances of the PBC. Finally, numerical simulation experiments and hardware-in-loop experiments of PBC attitude tracking control are conducted thoroughly, whose results demonstrate that the PPB controller with FDO proposed in this paper can satisfy the prescribed performance and robustness requirements and achieve precise recovery within the error requirements under unknow complex disturbances.