## 5 Conclusions  
The present work aims to develop the current CubeSats architecture from the typical \"cube structure with a stack of circuit boards inside\" [4] (p. 7). The concepts of the CubeSat volumetric efficiency (Section 2.1) and the amplitude of the payload design space (Section 2.2) are introduced and the methods for their quantification in the CubeSats preliminary design phase are developed. In Table 1, it is shown that the CubeSat volumetric increment can reach 36.97% with the use of six smart tiles that have the same volumetric efficiency of the embedded battery tile prototype. It is shown that the multifunctional smart tiles approach is advantageous from these points of view. The advantage is major for the smaller form factors 1U and 2U with respect to the bigger form factors 3U and 6U. The structural mass ratio of the 1U CubeSat (Section 3.2) varies with the smart tiles configuration and is shown to be between 16.7% and 28.8%.  
The design of an innovative 1U CubeSat smart tile, employing lightweight, composite materials in multifunctional structures was performed (Section 3.1). The construction of the prototype (Section 3.2) proved that the design is technologically feasible with a traditional autoclave curing of CFRP commercial prepregs, although CFRP components are miniaturized and ultrathin.  
A new experimental procedure for the modal testing of miniaturized, ultralight, and ultrathin CubeSat components has been defined (Section 4.1). The test procedure and experimental setup proved suitable for the modal testing of miniaturized CFRP components, printed circuit boards, and smart tiles, up to a minimum mass of 3.0 g and a minimum thickness of 0.23 mm. The results for the entire embedded battery tile (Section 4.4) showed a good correlation between the experimental results and the numerical results for the first and the second eigenmodes. The modal characteristics of the prototype are compatible with the Vega [26], the Ariane 6 [27], the Falcon 9, and the Falcon Heavy [28] launch vehicles. Therefore, the proposed design for the embedded battery tile is adequate from the point of view of the modal behavior.  
In conclusion, the results of the present work for the embedded battery tile are encouraging, and the employment of multifunctional structures and lightweight, composite materials is shown to be advantageous for nanosatellites. CubeSat designers may benefit this type of space structures either by adopting smaller form factors, thus saving launch costs with the same mission objectives, or by designing more sophisticated missions, able to reach more ambitious and complex mission objectives saving a significant amount of volume and mass for the payload.  
Finally, the applications of the presented results on structural batteries are promising for future electric or fuel cell aircrafts. The proposed embedded battery tile design could be adapted to fit into the wing structures of electric aircrafts. The requirements may be significantly different, but the design philosophy would be the same. Structural batteries can be beneficial to uninhabited aircrafts but also to inhabited aircrafts [35; 36].  
Figure 18: Results for the complete tile prototype: (**a**) crossMAC; and (**b**) mean frequency response spectra.  
**Author Contributions:** Conceptualization, G.C., E.C. and L.R.; methodology, G.C., E.C. and L.R.; software, G.C. and E.C.; validation, G.C., E.C. and L.R.; formal analysis, G.C. and E.C.; investigation, G.C., E.C. and L.R.; resources, E.C. and L.R.; data curation, G.C.; writing--original draft preparation, G.C., E.C. and L.R.; writing--review and editing, G.C., E.C. and L.R.; visualization, G.C., E.C. and L.R.; supervision, E.C.; project administration, G.C., E.C. and L.R. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This research received no external funding.  
**Acknowledgments:** The authors would like to thank professor [PERSON] for his support and advice.  
**Conflicts of Interest:** The authors declare no conflict of interest.