Unified-Loop Structured H-Infinity Control for Aerodynamic Steering of Reusable Rockets

This paper investigates the use of structured robust techniques for the control design of the aerodynamic descent phase of a reusable rocket. A unified control strategy based on the use of linear-time-invariant structured H-infinity controllers for both attitude and position is proposed and verified in both frequency and time domains. The architecture of the controller and the observed performance are discussed. Moreover, the nonlinear behavior of the control strategy is analyzed by looking at both the gain-scheduling law in conditions of plant-controller misalignment through the use of misalignment matrices, and simulation results obtained with a high-fidelity, nonlinear six-degree-of-freedom closed-loop model in perturbed conditions. All the results are based on Cooperative Action Leading to Launcher Innovation in Stage Tossback Operations (CALLISTO), a reusable rocket demonstrator jointly developed by German Aerospace Center (DLR), Japan Aerospace Exploration Agency (JAXA), and National Centre for Space Studies (CNES).