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Ultra-cleaning test campaign on exomars sample pathway parts

: Saverino, Antonio; Lobascio, Cesare; Margheritis, Diana; Gommel, Udo; Kreck, Guido; Giuliani, Marco

Volltext urn:nbn:de:0011-n-2196444 (565 KByte PDF)
MD5 Fingerprint: a75ca4a9952586ae6a9c949b8d1f6631
Erstellt am: 23.11.2012

Semprimoschnig, Christopher (Chair) ; European Space Agency -ESA-, Paris; European Space Research and Technology Centre -ESTEC-, Noordwijk:
12th International Symposium on Materials in the Space Environment, ISMSE 2012. Proceedings. CD-ROM : Noordwijk, The Netherlands, 24-28 September 2012. Final Programme and Abstracts
Noordwijk, 2012 (ESA SP 705)
8 S.
International Symposium on Materials in the Space Environment (ISMSE) <12, 2012, Noordwijk>
Konferenzbeitrag, Elektronische Publikation
Fraunhofer IPA ()
Raumfahrttechnik; Reinigungsvalidierung; Reinigungsverfahren; CO2-Reinigung; CO2-Schnee; cleaning; CO2-Cleaning; technical cleanliness; Reinheit

The ExoMars spacecraft will carry instruments aimed at detecting microscopic evidence of life on Mars, looking for minute traces of selected chemicals from samples of Martian soil.
Since the onboard scientific instruments are characterized by an extremely high sensitivity, even a tiny amount of organics could interfere with their in-situ measurements. Therefore, the samples collected on Mars must not be contaminated by terrestrial matter and in particular, it is essential to avoid chemical-physical interferences that could result in a "false positive" (a compound carried from Earth is misinterpreted as from Martian origin) or even a "false negative" (a terrestrial contaminant acts to suppress the detection of a Martian species).
A requirement of Total Organic Carbon (TOC) at the end of the mission in the order of 1ng TOC per gram of sample is applicable. This general requirement was flowed down by TAS-I to all ExoMars S/Ss and translated in extremely stringent MOC and PAC cleanliness levels for the H/W coming in direct contact with the Martian samples; in addition, suitable cleanliness levels for the AIT clean environment were assigned, as part of the C&CC approach for the Mission.
The maximum allowable molecular and particulate contamination levels dictated by the instruments' scientific requirements were first assessed by means of semiempirical models. Usual precision cleaning methods are not sufficient to achieve the extremely stringent cleanliness levels (in the order of ng/cm2) required for the most sensitive parts of the ExoMars rover (i.e. the sample pathway surfaces in the compartment where Martian samples are processed) therefore a dedicated Test Campaign in collaboration with Ultra Cleaning centre of excellence (i.e. Fraunhofer IPA) has been put in place, to identify and validate an Ultra Cleaning process capable to reach, verify and maintain a surface cleanliness level of about 1 ng Total Organic Carbon per cm2, and to tailor the process on the peculiar implementation needs for the ExoMars project.
The validation of cleaning processes is required to ascertain that the needed cleanliness for ExoMars rover parts can be achieved. This study and related testing was conducted to determine the most promising cleaning technologies, to setup a quantitative verification concept to assess these cleaning technologies and finally to suggest a suitable cleaning process (pre-, main and post-cleaning).
After an extensive research and a trade-off of available cleaning technologies, Carbon Dioxide Snow cleaning was conducted on four different parts of ExoMars spacecraft parts with defined levels of particulate, organic and biological contamination. The levels of cleanliness after cleaning were measured by means appropriate to the contamination (directly and indirectly). From this a procedure was developed that could be used during spacecraft AIV and a plan proposed for the qualification of any cleaning process that required indirect measurement of results.