SAM-GC INSTRUMENT ON MSL ROVER
SAM is an instrumental suite which objective is the in-situ analysis of the soil and near underground of Mars. Its principle is based on the coupling between a solid or gaseous sampling preparation module and a gaseous phase analysis module. A direct sampling of the atmosphere will also be performed.
SAM suite is composed of different sub-systems (solid sample manipulation, samples preparation (pyrolysis, deriving, combustion, enrichment) and pumping means) and of 3 instruments: a Quadrupole Mass Spectrometer (QMS), a Gas Chromatograph (GC) from the Service d'Aéronomie, and a Tunable Laser Spectrometer (TLS).
The Gas Chromatograph (GC) realizes the separation and the detection of the compounds presents in the gaseous samples. The separation is done in chromatographic columns (CC, metallic capillary tubes). The choice to use 6 columns is due to the requirement to analyze simultaneously a wide variety of organic and inorganic compounds. Each column is connected upstream to the helium circuit and downstream to the detectors. Their temperature is individually controlled between about 30°C and 250°C.
The detection is performed in series by thermal conductivity detectors (TCD) with a dynamic and linear response area, suited to melting ratio ranging from a few hundreds to a few ppm (part per million). The resulting signal is a peack corresponding to each molecule present in the gas. The detectors used by SAM are nano-TCD (similar to those used by COSAC instrument on board ROSETTA/Philae). An advantage of these detectors is that, by being non destructives, a mass spectrometer, with a lower detection threshold, can be placed after the detectors, which will ensure a partial redondancy.
The use of injection traps (IT) will enable the gas enrichment that pass through the columns, and thus, improve the species detection sensitivity.
From the mechanical point of view, the GC is composed of a support plate on which are fixed 6 analysis modules.
Paul Mahaffy, PI from Goddard Space Flight Center (GSFC) NASA, is responsible for the instrumental suite SAM.
Michel Cabane, Co-PI from LATMOS (ex-Service d'Aéronomie), is responsible for the french contribution to SAM (SAM-GC).