Numerical and experimental investigation of an automatic brazing vacuum seal system for Mars soil sample return

Abstract

The successful retrieval of samples from Mars stands as a pivotal objective for future scientific exploration. The Martian environment presents numerous challenges for preserving the hermeticity of collected samples. An automatic brazing vacuum seal system (ABVSS) is investigated to enhance the sealing performance of the Mars soil sample container. After certain adaptive enhancements, the ABVSS can be applied in the Mars, minor planet, comet or other extraterrestrial soil sample return projects. The ABVSS comprises a cylindrical container, an annular knife edge on a cylindrical lid, a pre-welded indium alloy annulus, and a heating plate. This study examines the influence of brazing temperature through numerical and experimental investigations. Besides, coating materials, brazing temperature and heat preservation time experiments are conducted to assess the impact of wettability and element diffusion on the leakage and sealing reliability of the ABVSS. The results obtained demonstrate that the theoretical simulation results are consistent with the experimental ones. Once indium is melted completely, the ABVSS reaches a minimum temperature of 155.91 °C. The minimum temperature, exceeding 125 °C, effectively autoclaves the container, thereby ensuring compliance with planetary protection regulations. Furthermore, silver, with its higher melting temperature and lower wetting angle, emerges as the optimal electroplating material for enhancing sealing reliability. The optimal leakage rate of 4.3 × 10−5 Pa m3/s is achieved at room temperature with a brazing temperature of 250 °C and a heat preservation time of 20 min.