## 1 Introduction
The second concept (USV3-based) is designed to operate a re-entry mission performing a wing deployment prior to the atmospheric re-entry and to operate all the aerodynamic regimes with a \"winged\" configuration. In terms of the deployment mechanism, the first concept is, of course, more demanding due to the fact that the deployment happens in the atmosphere and, therefore, the actuation system can withstand the aerodynamic forces and be quickly performed to guarantee a significant synchronization level in the wings deployment. Further, some mechanism components would be exposed to the space environment during the orbital phase. These issues are avoided for the second concept, because the wing releasing phase occurs at the beginning of the orbital phase. On the other hand, the mechanism components of the second concept shall be designed considering the presence, on the wing, of a significant thermal protection system (TPS) layer, reducing the available clearance for mechanism housing. By means of the trade-off analysis, a configuration based on the wing deployment at the beginning of the orbit phase was defined as the best one. Figure 1 shows the selected configuration (identified as USV3 \"WB-B3\") in operative condition (deployed wings) and in stored configuration inside the schematic VEGA-C fairing (folded wings). The entire CAD model was developed using CATIA V5-6R2016. The deployable wing system (DWS) guarantees the connection between the fuselage cold structure and the deployable wing structure and is basically composed of the actuation system and at least two hinges, the shape of which has been conceived to ensure a stable and strong connection both in the folded and deployed configuration. The position of the DWS rotation axis has been defined considering the need to minimize the portion of fixed wing, to minimize the gap between the fixed wing portion and deployable wing, and to avoid any interference during wing deployment as shown in Figure 2.  
The locking subsystem concept is basically made up of a set of pins moved by a linear actuator that has the purpose of retracting the pin (release function) before the deploying phase, and re-inserting the pins into their seats when the deployment phase is completed (Figure 3). A set of main preliminary requirements (summarized in Table 1) has been defined as the input for performing a trade-off study to define the best position of the DWS hinges. Figure 1: (**A**) USV3 “WB-B3” with deployed wings; (**B**) USV3 “WB-B3” in stored configuration inside the VEGA-C fairing. Figure 3: Hook pins with linear actuator CAD 3D schematic view. Figure 2: USV3 “WB-B3” DWS: reduced gap and avoided interferences requirements. The proposed work presents a positioning study of the hinges that enable the deployment of the wing of the USV3 DWS. The results of the optimization process adopted to evaluate the best configuration for the hinges are shown below. The critical parameters are the interface forces generated both in the unfolded and folded configuration; therefore, the analyses aimed to identify the optimal position in terms of the minimization of these forces. These results are the input data and represent the general requirements for the design of the deployment system (DWS). The position of the right hinge can reduce the applied loads as much as possible, leading to a component with a reduced mass (key aspect for space application).