Thrust Vector Control for Flexible Launch Vehicles: An H-Infinity Open Loop Shaping Approach

Abstract

This paper continues previous work on the application of H-Infinity Open Loop Shaping (OLS) to the design of thrust vector control (TVC) systems for launch vehicles (LVs). The contributions are threefold: first, further insight is provided into the selection and role of weighting filters within the loop shaping step; second, through two examples, it is shown that H-Infinity OLS and H-Infinity Closed Loop Shaping (CLS) result in equivalent controllers for rigid LVs, with neither approach outperforming the other; third, the H-Infinity OLS methodology is extended to flexible LVs, introducing a simultaneous attitude controller and bending filter design strategy. Compared to H-Infinity CLS, H-Infinity OLS simplifies the design process by avoiding the simultaneous tuning of multiple closed loop transfer functions and ensuring robustness at the plant input and output. These advantages, combined with the demonstrated performance parity, support the use of H-Infinity OLS for LV control applications. The flexible OLS framework was also benchmarked against the traditional separate design method, yielding similar results with reduced workload. Additionally, using the integrated approach in combination with a multi-model framework, a controller was developed and validated through linear simulations under both nominal and dispersed conditions, satisfying all TVC system performance and robustness requirements. Future work will address sloshing dynamics and develop a full-envelope controller for nonlinear simulation to further consolidate the methodology’s applicability.