Fixed-time disturbance observer-based nearly optimal control for reusable launch vehicle with input constraints

Area of Science:

• Aerospace Engineering
• Control Systems Theory
• Robotics

Background:

• Reusable launch vehicles (RLVs) face complex challenges including model uncertainties, input constraints, and unknown disturbances.
• Accurate attitude control is critical for RLV mission success and safety.
• Existing control methods may struggle with the combined effects of these factors.

Purpose of the Study:

• To propose a novel fixed-time disturbance observer-based nearly optimal control (FTDO-NOC) scheme for RLV attitude motion.
• To address unknown mismatched and matched disturbances, model uncertainties, and input constraints.
• To enhance the robustness and performance of RLV attitude control systems.

Main Methods:

• Developed an adaptive-gain multivariable generalized super-twisting (AMGST) controller for the outer-loop subsystem to handle mismatched disturbances and uncertainties.
• Designed modified gain-adaptation laws for the AMGST controller to efficiently attenuate chattering.
• Utilized a fixed-time disturbance observer (FTDO) for the inner-loop subsystem to estimate matched disturbances and virtual control input derivatives.
• Integrated the FTDO with a critic-actor neural network (NN)-based nearly optimal controller (NOC) to generate control moments within input constraints.

Main Results:

• The proposed FTDO-NOC scheme demonstrates effective management of RLV attitude dynamics under various uncertainties and disturbances.
• The AMGST controller successfully mitigates chattering through novel gain-adaptation laws.
• The integration of FTDO and NOC ensures that tracking errors and NN weight estimation errors remain uniformly ultimately bounded (UUB).

Conclusions:

• The developed FTDO-NOC scheme provides a robust and effective solution for controlling reusable launch vehicles.
• The proposed control strategy significantly improves RLV attitude control performance in the presence of complex disturbances and uncertainties.
• Simulation results validate the superiority and effectiveness of the proposed control scheme over existing methods.