Critical Aspects of Material Selection in the Packaging and Transporting of Returned Extraterrestrial Samples

In the framework of the EU-funded EURO-CARES project, aimed at determining the actions to develop a European facility for curation of extraterrestrial samples returned by space missions, we identified the requirements (mainly in terms of materials selection) of the transportation containment facility which should contain the Sample Return Capsule (SRC), which in turn contains the extraterrestrial material returned to Earth. Transportation box design for restricted (i.e., possibly related to biological life) and unrestricted samples is different. Packaging and transport of restricted samples must guarantee the samples' preservation from the terrestrial environment and the safety of people performing these operations and, hence, must be done according to World Health Organization (WHO) rules. In the case of unrestricted samples, the only requirement is sample preservation. We propose a triple packaging as follows: (1) primary receptacle; (2) secondary package (plastic material), optional for unrestricted samples; (3) rigid, cushioned outer layer. Only for restricted samples, an additional layer is proposed, that is, the overpack. The primary receptacle coincides with the SRC. The plastic material of the secondary package must have a low outgassing rate (i.e., <10-7 torr/s) and preferably low permeability and cost. Teflon and Neoflon would be the best choices. The outer package must be rigid and resistant to breakage, and our trade-off analysis identified stainless steel and aluminum alloys as best options. The outer should be filled with an inert atmosphere to inhibit oxidation within the sample in case of leak: argon is more inert than nitrogen, but the latter is easily available. The overpack allows the box environment control (e.g., real-time contamination monitoring); ISO containers could be used to this end. Contamination of the environment inside the box can be monitored by different instruments, which should be selected on the basis of mission requirements. There are no mass limitations for box transport by ground or ship, but these solutions imply a long journey duration. Any aircraft might be used for transporting unrestricted samples. Only cargo aircraft may be used for transporting restricted samples, unless the total sample mass is lower than 50 g (WHO guidelines).