Optimal Guidance Command Generation and Tracking for Reusable Launch Vehicle Reentry

Abstract

The objective of this work is to develop a robust guidance and control architecture for autonomous reusable launch vehicles that incorporates elements of recent advances in the areas of optimal trajectory generation and reconfigurable control. This work integrates three separately developed methods to form a coherent architecture with the potential to manage control effectors failures, vehicle structural/aerodynamic degradation, uncertainty, and external disturbances. Outer-loop guidance commands in the form of body-frame angular rates (roll, pitch, and yaw) are generated from an optimal reference trajectory that is computed off-line with a direct pseudospectral method and then tracked by a reconfigurable inner-loop control law. The appropriate open-loop state histories from the psuedo-four-degree-of-freedom reference trajectory are converted using a modified back stepping approach that complements the inner-loop control law in a six-degree-of freedom simulation. The inner-loop control law is capable of reacting and compensating for off-nominal conditions by employing nonlinear reconfigurable control allocation, dynamic inversion, and model-following/anti-windup prefilters. The results show that the inner-loop control can adequately track the desired optimal guidance commands; thus, confirming the applicability of this control architecture for future development involving on-line, optimal trajectory generation and high-fidelity guidance and control for reentry vehicles.