A Hierarchical Control Architecture for Space Robots in On-Orbit Servicing Operations

The Kessler syndrome describes the self-sustaining cascade of collisions that could render orbital regions unusable (see Kessler and Cour-Palais (1978)). To mitigate this threat, two key strategies have emerged: Active Debris Removal (ADR) and In-Orbit Servicing (IOS). ADR focuses on the active removal of defunct satellites and fragments, while IOS extends the operational lifetime of active satellites through tasks such as refueling, repair, and upgrading, as explained in Flores-Abad et al. (2014); Shan et al. (2016). Space robots represent a promising solution for both ADR and IOS. The design of a coordinated controller for this kind of systems, requiring autonomous capabilities in space environment, is complex due to the dynamic couplings between the spacecraft and the robotic arm. For this reason, they have been studied for many years, starting from the pioneering work of Papadopoulos and Dubowsky (1991) up to the most recent works of Giordano et al. (2020) and Giordano et al. (2019). The inherent complexity of robotic system is also due to the presence of uncertainties and external disturbances, which can be mitigated using robust control techniques. The works of Dubanchet et al. (2015) and Faure et al. (2022) represent the state of the art in the context of H