# Hybrid Shielding for Hypervelocity Impact of Orbital Debris on Unmanned Spacecraft
## 4 Conclusions  
This research proposes a set of numerical models to improve the design practice of unmanned hypervelocity impact shields. These are validated with experimental observations, including the debris-spread half-angle. Critical design parameters such as the honeycomb core cell density (i.e., the number of cells per unit length of the standoff gap), the thickness of the honeycomb core shell, the material of the honeycomb and the location of the impact relative to the honeycomb, are thoroughly analysed. The observations and results from this research clearly show that the proposed hybrid Whipple shield exhibits a significantly increased kinetic energy dissipation of the debris from the impactor and shield front plate.  
The extent of the effect of altering both the material properties and the location of impact is not comparable to the cases in which the geometry of the honeycomb core was altered (the number of honeycomb cells and the thickness of the honeycomb shell). The dissipation of the kinetic energy of the debris particle is more sensitive to geometrical changes than to changes in the material properties and location of impact. The observed relative increase in energy dissipation can reach 86.8% by including the honeycomb core and increasing the thickness of its shell.  
From a shield design perspective, however, there are a number of other factors that cannot be accounted for in the present work. These include, for example, component and assembly level cost, component and assembly level weight and geometrical constraints beyond those considered in this research. The work presented here is not intended to be a multi-parameter optimisation study, but instead a detailed analysis of the main design parameters affecting the shielding performance under hypervelocity impact. With these constraints, the following conclusions can be drawn:  
* Adding a honeycomb core can significantly improve the shielding ability.
* Increasing the honeycomb core density also improves the performance of the shield, although these effects are significantly less pronounced for cell densities beyond 4, as can be seen in Table 3 and Figures 12 and 14.
* Increasing the thickness of the honeycomb core shell also increases efficiency, although this parameter has the opposite effect on the cost and weight of the shield.  
It should be added that no definite conclusion should be drawn regarding the location of the impact, as this parameter cannot be controlled by design. These observations clearly suggest that the proposed hybrid honeycomb structure concept provides a highly efficient alternative to a standard Whipple shield design without significantly compromising the weight of the structure.  
Conceptualization, K.F. and F.T.-D.; methodology, K.F. and F.T.-D.; validation, K.F. and F.T.-D.; formal analysis, K.F. and F.T.-D.; resources, F.T.-D.; writing--original draft preparation, K.F.; writing--review and editing, K.F. and F.T.-D.; supervision, F.T.-D. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.  
Data Availability StatementNot applicable.  
Figure 21: Comparison between varying points of impact: single edge (model L-SE, **left**), mid-point (model L-MP, **centre**) and double point (model L-DP, **right**).  
**Acknowledgments:** For the purpose of open access, the authors have applied a Creative Commons Attribution (CC BY) licence to any Author Accepted Manuscript version arising from this submission.  
**Conflicts of Interest:** The authors declare no conflict of interest.