Structured H-infinity Control Design for the VEGA Vehicle: Recovery of the Legacy Control Behaviour

This article addresses the design of the atmospheric ascent-flight control system of a launch vehicle using the structured H-infinity synthesis technique. The main goal is to provide a methodological robust control design framework and transfer it to industry. This article presents the first step towards this transfer, which consists of: first, providing guidelines to tune the weighting functions based directly on physical effects of the launch vehicle and system requirements; and second, to demonstrate that a baseline, classically-design controller can be recovered with this design framework. The latter is very important for an industrial transfer as it establishes a common point of reference. The system is used based on the actual VEGA VV05 mission data, and classical VEGA TVC structure. These data and structure are then used together with H-infinity metrics to guide the structured H-infinity design to recover the same controllers as the baseline along different design points. Finally, the fixed-order H-infinity controllers are gain-scheduled and validated using a non-linear high-fidelity simulator, which shows the perfect performance and robust recovery.