MUST: Multi-Body Dynamics Simulation Tool to Support the GNC Design for Active Debris Removal with Flexible Elements

Space debris mitigation and remediation are well-known and urgent issues that are being tackled by the Clean Space initiative at the European Space Agency (ESA) in order to ensure the safety of current and future space systems. Active Debris Removal (ADR) is one of the options studied in the frame of this initiative, when remediation actions have to be provided. New challenges for GNC design arise especially due to the presence of flexible elements and connections. Moreover, the captured targets do not cooperate and have a complex, free, not completely known dynamics. Activities conducted by the Guidance Navigation and Control section at ESA for ADR applications, highlighted the need for a tool to accurately model the dynamics of different complex ADR systems. In order to cover the currently foreseen ADR system concepts, the tool needs to take into account any flexibility that affects the coupled dynamics due the presence of flexible devices that are exploited for capture and retention of the debris, such as nets and tethers. As a consequence, the need to resort to a multi-body dynamics approach is evident. This paper describes the Multiple-Body Dynamics Simulation Tool (MUST) for Active Satellite Removal System Modelling that has been developed at Politecnico di Milano in the Department of Aerospace Science and Technologies under an ESA contract. This tool answers the aforementioned needs by providing a fast but accurate simulation environment focused on the deorbiting phase, suited to design guidance and control laws. Entirely developed in MATLAB/Simulink, MUST is an extension of SimMechanics libraries and provides the capability for the user to define and rapidly model the orbital and attitude dynamics of different ADR systems configurations. The peculiarity is to be able to model the multi-body dynamics that the debris and the capturing system experience after the flexible connection is established. A multi-body dynamics approach is presented for the tether and net elements as the means to perform such capturing. The tool also includes the modelling of many different aspects affecting the dynamics such as fuel sloshing and uncertainties management functionalities. This paper provides a description of the mathematical models, which the software is based on, as well as the modelling environment and toolbox capabilities. Finally, the effectiveness of the tool is shown via the modelling and analysis of a complex ADR scenario and preliminary simulation results are discussed.