## 4 Conclusions and Perspectives  
In this study, the effects of the contact dynamics of a capturing net on an Envisat mock-up have been analysed in terms of their potential for generating secondary space debris. To simulate such an event, a sequential modelling strategy is implemented which decouples the net dynamics model from the Envisat translational and rotational dynamics. Furthermore, the Envisat geometry is significantly simplified in order to simplify the modelling implementation and focus on its long flexible appendages.  
To verify if structural failure occurs, a specific case study is chosen. This implies a frontal 30 \(\times\) 30 m net impact with a relative velocity of 20 m/s onto an Envisat mock-up. The net is discretised with point masses using the lumped mass or Multi-Spring-Damper model, in which the net threads were only allowed to experience tensile stresses. The simulation results implied that two of the three main long appendages of Envisat, namely the solar array and the Ka-band antenna, have a significant likelihood of breaking during the impact and wrapping process. Thus, a major conclusion from this study is that net capturing is riskier than originally expected.  
Given the severity of these results, we highly recommend analysis of the effect of ejection parameters (i.e., impact velocity) and to improve the dynamic modelling by (1) removing the sequential nature of the modelling strategy, (2) improving the internal net  
Figure 16: Total rotational energy of Envisat during the impact and capturing process as a function of time. Alongside the latter is the rotational energy and contact moment dissipation work.  
dynamics to include bending stiffness, (3) providing an experimental approach to estimate the contact dynamics constant for net impacts and (4) validating the computed structural forces and stresses by applying more accurate Finite Elements Methods.  
Conceptualization, M.C.-G. and E.G.; methodology and software, M.C.-G.; validation, M.C.-G. and E.G.; formal analysis, M.C.-G.; investigation, M.C.-G.; writing--original draft preparation, M.C.-G.; writing--review and editing, M.C.-G. and E.G.; visualization, M.C.-G.; project supervision, E.G. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.  
Not applicable.  
No new data were created or analyzed in this study. Data sharing is not applicable to this article.  
We thank [PERSON], from the Structures and Materials Department of the Faculty of Aerospace Engineering at Delft University of Technology, for his support in providing guidance in translating dynamic to structural loadings.  
The authors declare no conflicts of interest.  
The following abbreviations are used in this manuscript:  
\begin{tabular}{l l} ASAR & Advanced Synthetic Aperture Radar \\ ASDR & Active Space Debris Removal \\ ANCF & Absolute Nodal Coordinate Formulation \\ CFRP & Carbon Fibre-Reinforced Polymer \\ CG or cg & Centre of Gravity \\ CM & Centre of Mass \\ ECM & Elastic Continuum Model \\ EOL & End-of-Life \\ EoM & Equation of Motion \\ Envisat & ENVIronmental SATellite \\ GEO & Geostationary Earth Orbit \\ LEO & Low Earth Orbit \\ LVLH & Local-Vertical-Local-Horizontal \\ MDOF & Multiple Degree of Freedom \\ MEO & Medium Earth Orbit \\ MMOI & Mass Moment of Inertia \\ MSD & Mass-spring-damper model \\ MRB & Multi-rigid-body model \\ PDM & Primary Deployment Mechanism \\ PIP & PDM Interface Plate \\ RK4 & Runge-Kutta 4 (integrator) \\ ROGER & Robotic Geostationary Orbit Restorer \\ SDOF & Single Degree of Freedom \\ TSR & Tethered Space Robot \\ \end{tabular}