Robust Trajectory Tracking Guidance for Low L/D Lunar Return Vehicles Using Command Filtered Backstepping Approach

A reentry guidance method for low lift-to-drag (L/D) ratio vehicles in a lunar return mission is presented. Different from the reference drag tracking scheme, method in this paper tracks a weighted profile of altitude and downrange using a command filtered backstepping approach. First, the dynamics of the tracking error are established with dispersions and uncertainties explicitly taken into consideration. Then, in accordance with the backstepping technique, the weighted reference profile is tracked with the help of a virtual control signal. Next, by tracking the virtual control signal, a real control input is derived. Dispersions and uncertainties are accurately estimated by a well-designed disturbance observer and compensated for by the estimates. The derivatives of the virtual control needed by the backstepping algorithm are obtained by filtering the virtual control signal with a second-order command filter. Finally, the stability of the whole system is analyzed, and extensive numerical simulations are conducted to demonstrate the effectiveness and robustness of the proposed method.