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Bio-Containment of Samples in the Frame of the Mars Sample Return Mission: A mixed Experimental/analytical Approach for the Verification of Basic Planetary Protection Requirement
"The Mars Sample Return (MSR) Mission foreseen in the 2020s envisages the collection of some tens of samples of Martian soil for return to Earth. Once collected from the surface and sub-surface, the samples will be stored into a dedicated Container (Orbiting Sample - OS) which is launched into Mars orbit. After being captured by the orbiting Spacecraft, the OS is placed and sealed inside a dedicated Bio-Container and finally transferred into the Earth Re-entry Capsule (ERC) for the return trip to Earth. In the frame of a recently performed activity for ESA/ESTEC, the Bio-Container has been designed as a double walled metallic containers with hermetically closing lids each equipped with triple gasket system. Another lid with a gasket barrier and self-sterilisation capability is also present with the purpose of breaking the biological chain of contact with Mars. The so conceived Bio-Container has undergone a thorough Bread-boarding and Testing activity including: one full vessel, one full lid capable to host the three types of gaskets (of different materials and different operative principles), the lid closing mechanism, the monitoring system (pressurizing stage, wireless power/data transfer, pressure and temperature sensors) and, a chain breaking lid (with gasket and self-sterilizing mean). The Bio-Container, with all its components, is therefore one of the key elements to guarantee the very stringent Planetary Protection requirements. The main requirement is summarized as the following: “The bio-container shall ensure that the probability that a single unsterilized particle larger than 10 nm class particles in diameter is released from containment in the terrestrial biosphere is below 10-6”. The verification of this requirement can be quite difficult due to both the very small size of the referred particles and the very low probability figure involved. The approach proposed in the frame of the MSR Bio-Containment activity recently completed for ESA/ESTEC is based on the following steps: Helium leak rate characterization by test of calibrated hole and of the different type of gaskets; particle escape rate characterization from calibrated hole and from the different type of gaskets (using nano-particles); preparation of a mathematical model for the gas (Helium, Argon) leak rate and particle escape rate across capillary holes based on a molecular plus viscous approach; calibration of the mathematical model for gas leak against measured leaks of calibrated hole and gaskets and gaskets characteristics reconstruction; calibration of the mathematical model for particle leak against measured particle leaks of a calibrated hole; projection of gas leak and particle escape from the whole Bio-container by utilizing the calibrated leak model across the gaskets. The proposed paper presents the main issues related to the verification approach used for the main Planetary Protection requirement (related to particle escape) according to the above steps. Furthermore, for completeness, the main achievements in terms of Bio-Container configuration, developed hardware and main tests results are summarized."
Magnani Piergiovanni, Senese Samuel, Fumagalli Alessandro, Terribile Antonio, Pedrini Alberto, Indrigo Dennis, Guest Michael, Romstedt Jens
Paper for Seminar/Symposium/Conference
IAC 2013 - International Astronautical Congress (23-27 September 2013, Beijing, China)
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