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 a rocket booster. As a lightweight underactuated aircraft, the parafoil and booster combination (PBC) motion characteristics are strongly nonlinear and extremely vulnerable to unknown disturbances, such as model uncertainty and wind disturbance. Therefore, a prescribed-performance-based backstepping (PPB) attitude tracking controller of the PBC with a fixed-time disturbance observer (FDO) is proposed. First, a nine-degree-of-freedom multibody flexible nonlinear model of the PBC is built based on kinematic, dynamic, and computational fluid dynamics analyses. Then, to ensure that 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 the traditional backstepping method, which deals with the system nonlinearity effectively. Furthermore, to restrain the complex unknown complex disturbances and enhance the robustness of the PPB controller, an FDO is introduced to accurately estimate the unknown external environmental and internal model uncertainty disturbances of the PBC. Finally, numerical simulation experiments and hardware-in-the-loop experiments of PBC attitude tracking control are conducted thoroughly, whose results demonstrate that the PPB controller with the FDO proposed in this article can satisfy the prescribed performance and robustness requirements and achieve precise recovery within the error requirements under unknown complex disturbances.