5:15 PM - 6:45 PM
[PCG20-P14] Development of a vacuum sealing system for gas analysis insturments on airless bodies
Keywords:Volatile analyses, Vacuum sealing, Robotic missions
Background: Recent lunar missions, notably the LUPEX REIWA water resource instrument, have highlighted the significance of studies aimed at extracting and analyzing gases from solids, such as rocks and regolith. Considering sample containers with a volume of approximately 1 L, maintaining the extracted gas of pressures between 1-100 Pa within the leak-tight containers is essential for the gas analyses. The Sample Manipulation System (SMS) within the Mars Curiosity rover, which houses multiple sample cups, effectively seals these cups to avoid contamination and subsequently extracts and analyzes the gases (Mahaffy et al. 2012 Space Sci. Rev.).
Limitations of previous studies: Conventional vacuum seal systems, reliant on manual adjustments such as tightening valves or screws, present challenges for robotic missions. These systems achieve vacuum by compressing a copper gasket against a sharp-edged flange, a process that requires considerable force, complicating its application in the lightweight mechanisms necessary for space exploration. The Sample Analysis at Mars (SAM) unit within NASA's Curiosity rover, due to its small opening of the sample cup (less than 10 mm), restricts the size of analyzable samples, rendering it unsuitable for pebble analysis. In contrast, achieving a seal in the missions of airless bodies, such as asteroids or the Moon, could potentially require less force in vacuum sealing because of the lack of surrounding atmosphere. However, methods for maintaining a leak-free sample container in such conditions have not been investigated yet.
Research Objectives: This study aims to enhance the sample handling system for lander missions, enabling precise gas analysis with minimal leakage from the sample container. We specifically focused on determining the necessary force to maintain gas pressures of 1-100Pa inside a vacuum container. Considering potential errors up to 10% in other subsystems, this study sets a benchmark that gas loss must not exceed 5% during a 10-minute analysis period.
Method: We constructed a vacuum system with one section directly connected to a turbo-molecular pump to simulate lunar vacuum conditions, while the other section, separated by vacuum sealing material, simulates a sample container on the lunar surface. We developed a titanium lid soldered with a copper ring, pressed against an ICF34 standard knife edge to reduce the force required for the seal material's deformation. Connected to the vacuum system through a bellows, the pressure applied to the lid was adjusted while monitoring a force gauge to measure the applied force accurately. Once we applied the predetermined force to the lid, a variable leak valve was opened to introduce air at the desired pressure (1-100Pa) into the sample container for assessment. We then measured the pressure development in the container using a vacuum gauge.
Results & Discussion: The investigation focused on the correlation between the applied force to the lid and the resultant pressure changes in the gas extraction container. At 100N of applied force, for example, a rapid decline in pressure was observed, indicating significant gas leakage into the simulated lunar vacuum. Increasing the force on the lid gradually reduced the rate of pressure drop, suggesting improved airtightness. The analysis of the leak rate, represented in [Pa·L/s], demonstrated that a seal could be maintained across a pressure range of 300-800 N for 10 minutes. In comparison to the Curiosity's SMS, which necessitates a force of roughly 1350 N, these findings imply that in the high vacuum conditions expected on asteroids or the Moon, achieving an effective vacuum seal is feasible with less force and for larger diameters gaskets than on Mars. Our results thus strongly suggest the practical feasibility of a vacuum seal system for gas extraction analysis in lunar and asteroid lander missions.
Limitations of previous studies: Conventional vacuum seal systems, reliant on manual adjustments such as tightening valves or screws, present challenges for robotic missions. These systems achieve vacuum by compressing a copper gasket against a sharp-edged flange, a process that requires considerable force, complicating its application in the lightweight mechanisms necessary for space exploration. The Sample Analysis at Mars (SAM) unit within NASA's Curiosity rover, due to its small opening of the sample cup (less than 10 mm), restricts the size of analyzable samples, rendering it unsuitable for pebble analysis. In contrast, achieving a seal in the missions of airless bodies, such as asteroids or the Moon, could potentially require less force in vacuum sealing because of the lack of surrounding atmosphere. However, methods for maintaining a leak-free sample container in such conditions have not been investigated yet.
Research Objectives: This study aims to enhance the sample handling system for lander missions, enabling precise gas analysis with minimal leakage from the sample container. We specifically focused on determining the necessary force to maintain gas pressures of 1-100Pa inside a vacuum container. Considering potential errors up to 10% in other subsystems, this study sets a benchmark that gas loss must not exceed 5% during a 10-minute analysis period.
Method: We constructed a vacuum system with one section directly connected to a turbo-molecular pump to simulate lunar vacuum conditions, while the other section, separated by vacuum sealing material, simulates a sample container on the lunar surface. We developed a titanium lid soldered with a copper ring, pressed against an ICF34 standard knife edge to reduce the force required for the seal material's deformation. Connected to the vacuum system through a bellows, the pressure applied to the lid was adjusted while monitoring a force gauge to measure the applied force accurately. Once we applied the predetermined force to the lid, a variable leak valve was opened to introduce air at the desired pressure (1-100Pa) into the sample container for assessment. We then measured the pressure development in the container using a vacuum gauge.
Results & Discussion: The investigation focused on the correlation between the applied force to the lid and the resultant pressure changes in the gas extraction container. At 100N of applied force, for example, a rapid decline in pressure was observed, indicating significant gas leakage into the simulated lunar vacuum. Increasing the force on the lid gradually reduced the rate of pressure drop, suggesting improved airtightness. The analysis of the leak rate, represented in [Pa·L/s], demonstrated that a seal could be maintained across a pressure range of 300-800 N for 10 minutes. In comparison to the Curiosity's SMS, which necessitates a force of roughly 1350 N, these findings imply that in the high vacuum conditions expected on asteroids or the Moon, achieving an effective vacuum seal is feasible with less force and for larger diameters gaskets than on Mars. Our results thus strongly suggest the practical feasibility of a vacuum seal system for gas extraction analysis in lunar and asteroid lander missions.