## 6 Conclusions  
As composite materials are increasingly being addressed attention in the aerospace sector, leading to lightweight, flexible, and high performing components, this paper assesses the performance of a piezoelectric-based active vibration control on an innovative carbon-reinforced thermoplastic (CF-PEEK) composite panel. In the first phase, the properties of the composite specimen are numerically and experimentally validated by simulating the material in Digimat environment, and performing three-point bending tests. As a result, the mechanical properties and damping characteristics of the CF-PEEK are derived and used to build a finite element model of the composite panel. The vibration suppression system is applied to an aerospace system subjected to rigid/flexible dynamics interaction: two solar panels equipped a satellite. A finite element model of the composite structure with integrated piezoelectric actuators and sensors is presented. This is used to perform re-orientation attitude maneuvers to assess the performance of the control system. This approach was shown to be able to relevantly dampen the elastic vibrations of the composite material, while reducing both the amplitude and the duration of the flexible oscillations.  
This work highlights the need to address the problem of vibration control for innovative carbon-based materials for aerospace applications, as demonstrated by analyzing and experimentally evaluating the damping properties of a CF-PEEK specimen. Moreover, the current research proposes an effective active vibration control framework, based on an innovative piezoelectric configuration. Such architecture can easily be transferred to other applications by properly scaling the system and reconsidering the best placement and number of smart devices.  
Future developments will include the improvement of the mathematical model of the actuators/sensors by including their nonlinear behavior (such as hysteresis and creep effects) directly in the FE formulation. Moreover, different types of hosting structures realized in composite material will be analyzed for vibration control purposes by using OPSA actuators. Lastly, it is worth mentioning that experimental tests will be performed to evaluate the effectiveness of system on a floating platform on a granite table, able to reproduce the attitude and flexible dynamics of the spacecraft, once the proposed vibration control devices are implemented on scaled solar panel structure realized in composite material.  
Conceptualization, F.A.; methodology, F.A., D.T., S.L. and P.G.; validation, F.A., S.L. and P.G.; formal analysis, F.A. and D.T.; investigation, F.A., D.T. and S.L.; writing--original draft preparation, F.A. and D.T.; writing--review and editing, F.A., D.T., S.L. and P.G.; supervision, S.L. and P.G.; funding acquisition, F.A., S.L. and P.G. All authors have read and agreed to the published version of the manuscript.  
The work was partially financed by the European Union--NextGenerationEU (National Sustainable Mobility Center CN00000023, Italian Ministry of University and Research Decree n. 1033-17/06/2022, Spoke 11--Innovative Materials and Lightweighting). The opinions expressed are those of the authors only and should not be considered as representative of the European Union or the European Commission's official position. Neither the European Union nor the European Commission can be held responsible for them. This research was partially funded by Sapienza University of Rome (Grant MA21916B865F6B61) to S.L.  
Not applicable.  
The authors declare no conflict of interest.