# Closing Force Evaluation of a Sample Return Capsule for a Phobos Sample Return Mission
## 2 Sample Containment and Closing System-Design Overview  
The vault is a metallic component that is placed inside an Earth Return Capsule (ERC, Figure 5). Its outside geometrical shape is a consequence of the ERC interior space geometry defined by Airbus Defence and Space UK and also, specified by one of the requirements. On the outside surface, the Vault has a flange with several holes used to fix the Vault on the ERC internal structure. There are several circular grooves on the Vault's inside. Two of these grooves are featured to mount the sealing elements and are closed type grooves. It is worth mentioning that these types of grooves were chosen due to the reasons of shape simplicity and reduced mass of the vault while accepting a more difficult mounting of the sealing elements, as well as their irreversible damage when removing them from the \begin{table}
\begin{tabular}{c c} \hline \hline
**Req. No.** & **Description** \\ \hline
1 & The sample container vault shall be sealed using a maximum force of 40 N. \\
2 & A redundant and fail-safe containment sealing system shall be envisaged for the vault. \\  & The vault shall withstand a shock load of 2000 g for 10 ms without failure (leak tightness of the \\
3 & vault correlated with the SR1 requirement-no particle or droplet of a fluid \textgreater{} 1 um shall escape \\  & or enter the sample canister, to be evaluated before and after the test). \\  & The vault shall withstand the thermal environment encountered during the lifetime of the \\
4 & \(\bullet\) & Operational: \(-40\)\({}^{\circ}\)C/\(+80\)\({}^{\circ}\)C; \\  & \(\bullet\) & Non-Operational: \(-100\)\({}^{\circ}\)C/\(+90\)\({}^{\circ}\)C; \\  & The sealing technologies to be considered shall be at the minimum: O-ring (including \\  & composite gaskets with metallic spring energizer), metallic gasket and knife edge. \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Driving requirements considered for the development of the closing and sealing system. Figure 4: Sample return configuration after the closing operation (image courtesy: Airbus Defence and Space UK). grooves. The other ones are foreseen to collect the regolith particles attached to the exterior surface of the SC to minimize the risk of deteriorating these surfaces when introducing the SC in the Vault. As a safety measure, all the grooves edges are also rounded to ease the passive alignment of the SC during the closing operation. The Vault is sealed using the SC consisting of two mechanical subassemblies with different functional roles that were designed by, COMOTI and AIRBUS. COMOTI designed the upper part, highlighted with light green in Figure 6 which assures the vault sealing. Airbus designed the lower part highlighted with grey in Figure 6, which accommodates the sampled regolith. The sealing surfaces of the Sample Container are featured with conical, rounded and cylindrical surfaces, without any sharp edges. Their purpose is to allow the initial interference between the surfaces and energization of the sealing elements [21] while inserting the SC inside the Vault and sealing the inner space of the Vault. These design particularities were the results of the closing force evaluation and they will be pursued in the following paragraphs of the paper. The Vault and the SC are closed using a dedicated mechanism called a Closing Mechanism, shown in Figure 7. This device has two main subassemblies, a special coupling, designed to overcome the robotic arm misalignments (not included in the current paper) and a Mechanical Press (MP) which ensures the closing operation. The MP uses the force provided by the helical springs which are maintained in compression state and, by whose relaxation during the closing operation, the SC is pushed inside the Vault, thus achieving the tightness. Figure 5: Vault design: (**a**) isometric view, (**b**) section through the leakage ports. Figure 6: Sample Container: (**a**) isometric view, (**b**) section view.