Combined feedback linearization and sliding mode control for reusable launch vehicle reentry

A combined feedback linearization (FBL) and sliding mode control (SMC) method is proposed for reusable launch vehicle (RLV) reentry flight control system designing. The feedback linearization is based on the full rotational equations of motion rather than on a conventional model derived from time-scale separation. The control system design is split into two separate tasks, control law and control allocation. First, the control law is designed by a sliding mode control method. The chattering brought by the SMC is eliminated efficiently by choosing a suitable reaching law and a continuous sign function. Then, a bridging function based on dynamic pressure is used to blend continuous control effectors and pulsed thrusters to generate moments commanded by the sliding control law, that is the control allocation problem. An optimal control allocation method based on standard linear programming is used to distribute control command to each aerosurface accounting for position and rate constraints. And a 0-1 linear programming technique is used for reaction control thrusters control allocation. When coupled with fault detection and isolation logic, the control effectors can be reconfigured to minimize the impact of control effector failures or damage. Analysis and nonlinear simulation results show that the composite controller achieves the requirements of performance.