CAESAR (Comet Astrobiology Exploration SAmple Return), selected by NASA as a 2019 New Frontiers finalist, was designed as a comet surface sample-return mission to 67P/Churyumov-Gerasimenko, the comet successfully explored by the European Space Agency’s Rosetta mission. Data from the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA) instrument indicate the primary gas species present in the coma were H2O, O2, CO, CO2, H2S, CH3OH, and HCN with minor species such as formaldehyde (CH2O), formic acid (HCO2H), and SO2. As part of the CAESAR sample return package the Gas Containment System (GCS) was be designed to store such species for the duration of the return flight and Earth re-entry. This means that all GCS materials that with the potential to be exposed to cometary volatiles were to remain inert for nearly a decade at temperatures ranging from −80 °C to almost 0 °C. Materials considered for use as coatings, valves, windows, and sealants on the GCS were exposed to environments that simulated the composition and cumulative pressure/temperature conditions expected for sample return. Interior coatings such as Au, Pt, and Si were applied to CRES 304L stainless steel by commercially available methods were investigated. Valve components included CRES 304L, In, and a Ni-Ti alloy. Infrared spectroscopic analysis of H2O and CO2 released from the sample during collection inside the GCS will be conducted inside a gas cell through windows made from CaF2, GeAs, or diamond and possibly sealed by using nickel-cobalt alloy. Candidate materials were exposed to gas or gas/aqueous mixtures at temperatures in the range predicted for CAESAR GCS system exposure. Samples having pinhole defects in the coating often showed high reactivity and substantial production of by-products from the CRES 304L substrate. Gas head-space in each sample was evaluated and quantitated by using gas chromatography and mass spectrometry (GCMS). Solid residues, surface phenomena, and corrosion products were analyzed by using scanning electron microscopy (SEM) in combination with energy-dispersive X-ray (EDX) spectroscopy to determine chemical composition. Results will be presented in context and decisions about materials chosen for coatings, seals, and valves on the CAESAR GCS will be explained.

Investigating surface reactions in a gas containment system for a comet sample return mission

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.