ESA GNC Conference Papers Repository

Robust stability analysis is a key issue for control design and validation of a flexible launcher during atmospheric flight. Such a control law shall ensure robust stability and performance of the time varying launcher dynamics in the presence of multiple slightly damped bending modes. In this paper, we propose an enhanced validation methodology for robust stability analysis (guarantee of stability for the whole domain of uncertainties and worst case identification) of a flexible launcher with multiple uncertain high frequency bending modes. We have implemented global and hybrid optimization methods for stability and crosschecked the results with ?-analysis tools. ?-analysis was satisfactory for rigid mode analysis but presents some limitations for launcher flexible modes that are characterized by narrow picks combined with real uncertainties. Hybrid Differential evolution (HDE) has proven to be the best optimization tool for stability analysis of bending modes. For all configurations, it has allowed identification of worstcase directions that were intuitive but not easily defined by hand (especially with multiple sensors); therefore HDE optimization tool represent a great innovation for bending modes stability analysis. Furthermore, the strength of optimizationbased methods is their flexibility and their use could be extended to check all clearance criteria as far as they can be expressed as mathematical objective functions. This perspective should be analyzed in the next future to extend these results to discrete time and time variant real industrial system such as Ariane 5 (TRL4).