Ricerc@Sapienza

Space activities, such as On-Orbit Servicing (OOS) missions, are currently experiencing a deep transformation thanks to the advances in space robotics. Refueling, maintenance and many other services could be provided in future by suitable spacecraft equipped with robotic arms able to safely grasp a client satellite. However, these types of missions pose several technical challenges never faced until now. Of utmost relevance is the modelling and control of such a complex dynamical system (i.e. relative motion, robotic arms control, appendages' flexibility and sloshing phenomena), needed to effectively achieve the mission objectives.
Furthermore, multidisciplinary field such as automation, guidance and navigation, multibody and structural dynamics are involved in the design of the various phases of an OOS mission. As a result, this work will only focus on the last steps of a refueling mission and the major contribution will be given in the modelling of flexible elements (i.e. solar array, robotic arms and joints) and sloshing dynamics. Nevertheless, while the modelling of flexible appendages is nowadays common practice via the well-known modal decomposition technique, no unique model exists to accurately represent fuel sloshing in every scenario except for Computational Fluid Dynamics (CFD), which is however impractical for control design purposes. To address such issue, several Equivalent Mechanical Models (EMM) will be implemented to characterize the fluid dynamics and variation in the fuel mass during refueling will be opportunely accounted with time-varying parameters in the EMM.
The resulting dynamical model will be then used both for control synthesis and for verification and validation purposes. Structured Hinf and µ-synthesis methods will be used for the generation of the robust controllers required for the capture phase and the post-grasping operation. Finally, µ-analysis and non-linear Monte Carlo tests will be presented to check the required performances.