# Closing Force Evaluation of a Sample Return Capsule for a Phobos Sample Return Mission
## 6 Conclusions  
During the testing campaign, two types of sealing elements and two shapes of the sealing surfaces for the Sample Container were investigated to obtain smaller forces during the closing operation. The seals with a U-shaped spring and jacket made of Fluorology A28 (Type II seal) require a smaller force than the other one (Type I seal). It was concluded that the toroidal shape piston needs a smaller force to enlarge the jacket and spring of the sealing elements. The sealing elements are composed of a plastic jacket and a metallic spring. The flexibility of the jacket material is temperature-dependent, stiffer at lower temperatures and softer at higher temperatures. Due to this behaviour, the testing campaign was performed considering different temperatures (environmental temperature (20 \({}^{\circ}\)C), \(-\)20 \({}^{\circ}\)C, \(-\)60 \({}^{\circ}\)C and +70 \({}^{\circ}\)C) which confirmed that the closing force is temperature-dependent too. Using the results from the testing campaign, especially the ones at \(-\)60 \({}^{\circ}\)C, which represent the worst-case scenario, the maximum closing force which shall be ensured by the mechanical press was identified. The testing campaign is available at the Supplementary Materials. The obtained results from the testing campaign were used as input for the mechanical press motorization, which consists in dimensioning the helical compression springs foreseen to deliver the closing force. More exactly, based on these tests and calculations, the necessary spring rate to develop a sufficiently large force to ensure the vault closing was established. During the testing campaign of the closing and sealing system, the mechanical press design was validated through functional closing tests. As each Space Agency (i.e., ESA, NASA, JAXA) is focused on exploring planet Mars or Martian Moons and collecting regolith samples from Mars natural satellites in future missions, the work carried out in the design, manufacturing and testing a sealing and closing mechanism for a Phobos Sample Return Mission was highly appreciated by ESA. This represents a high possibility that the system architecture designed by COMOTI to be used in future scheduled missions. It should also be highlighted that the possibility of the mechanism to be scaled up and used in Sample Return Missions will need a higher closing force or be able to cope with higher robotic arm misalignments. Figure 28: Mechanical press design and spring characteristics. **Supplementary Materials:** Testing campaign [[https://youtu.be/dVGQD0](https://youtu.be/dVGQD0) cqMDk?list=LL]([https://youtu.be/dVGQD0](https://youtu.be/dVGQD0) cqMDk?list=LL), Video S1: Sealing and Closing System--Breadboard Testing Campaign (accessed on 4 May 2020). **Author Contributions:** Conceptualization, G.M. ; methodology, R.M., G.M., D.M. and A.P. ; software, R.M., D.M. and I.F.P. ; validation, R.M., G.M., D.M. and I.F.P. ; formal analysis, R.M., G.M. and D.M. ; investigation, R.M., G.M. and D.M. ; resources, R.M., D.M., I.S.V. and A.P., data curation, R.M., G.M., D.M. and I.F.P. ; writing--original draft preparation, R.M., D.M., I.F.P. and I.S.V. ; writing--review and editing, I.F.P. and I.S.V. ; visualization, I.F.P. and I.S.V. ; supervision, R.M. ; project administration, R.M. ; funding acquisition, R.M. All authors have read and agreed to the published version of the manuscript. **Funding:** This work was performed in the frame of Breadboard of Sealing and Closing System for a Phobos Sample Return Mission, contract number 4000115017/15/NL/PA, funded by the European Space Agency (ESA). The APC was funded by the \"NUCLEU\" Program TURBO 2020+, Grant no. 2N/2019, supported by the Romanian Minister of Research, Innovation and Digitalization. **Institutional Review Board Statement:** Not applicable. **Informed Consent Statement:** Not applicable. **Data Availability Statement:** Not applicable.