This thesis investigates the use of H-infinity Open Loop Shaping (OLS) for designing Thrust Vector Control (TVC) systems during the atmospheric ascent of flexible launch vehicles (LVs). The research has two main goals. The first goal is to assess whether H-infinity OLS can produce rigid body controllers for launch vehicles with comparable or superior robustness, stability, and performance to controllers designed with H-infinity Closed Loop Shaping (CLS), while also reducing design complexity and time. The second goal is to explore an integrated H-infinity OLS approach that tunes both the rigid body controller and the bending filter simultaneously, simplifying the traditional separate design process.
Results demonstrate that H-infinity OLS and H-infinity CLS yield controllers with identical performance, robustness, and stability when applied to design controllers with the same order and structure. However, H-infinity OLS significantly simplifies the design process by avoiding the manipulation of multiple transfer functions, offering higher reproducibility between flight points, and automatically ensuring robustness at both the plant input and output. Although these benefits come at the cost of converting requirements into open loop specifications and setting loop shaping weighting filters to meet the specifications, both challenges have been addressed and simplified in this thesis.
The thesis also extends the rigid body H-infinity OLS design process into an integrated methodology that simultaneously tunes both the rigid body controller and the bending filter, achieving identical results to the traditional separate design approach while reducing overall design time and complexity.
This research demonstrates that H-infinity OLS provides a robust framework for simplifying the design of TVC systems for launch vehicles, without compromising performance and robustness. Additionally, the integrated H-infinity OLS methodology for tuning both the rigid body controller and bending filter effectively streamlines the design process while achieving identical results to the traditional separate approach. These findings validate H-infinity OLS as a viable alternative to H-infinity CLS and introduce a more efficient methodology for designing both the rigid body controller and the bending filter for TVC control systems in launch vehicles.