Mass Spectrometry for In Situ Planetary Research

Fausch, Rico Georgio (2020). Mass Spectrometry for In Situ Planetary Research (Unpublished). (Dissertation, University of Bern, Faculty of Science)

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This thesis describes the activities undertaken to improve the performance of three miniature mass spectrometers to perform highly sensitive chemical analyses of gaseous samples. Miniature time-of-flight mass spectrometers become important analytical tools for in situ chemical analysis offering sensitive measurements of chemical composition of either planetary surfaces or their atmospheres. Mass spectrometry data harbour key information about the origin and evolution of the Solar System and the variety of its planetary objects. This thesis focuses on three missions which will include a time-of-flight mass spectrometer in their scientific payload. Each instrument benefits from heritage from the Reflectron Time-Of-Flight mass spectrometer (RTOF/ROSINA/Rosetta). However, the individual requirements of each mission such as restrictions concerning power budget, size, and weight available on the spacecraft have driven further developments of these instruments. In the light of the enormous costs of the transport of the scientific instruments to space, each spacecraft needs highly customized instruments to maximize the return on science.

For this thesis, I have improved the following three prototypes by introducing new concepts that led to significant improvements of the existing systems. First, the Gas Chromatograph – Neutral Gas Mass Spectrometer (NGMS/Luna-Resurs) was selected to analyse the lunar regolith and exosphere on-board the Roscosmos’ Luna-Resurs mission. This energy-efficient and highly sensitive flight instrument is described focussing on key concepts such as the front-end, the high-voltage pulser, and the voltage set optimizer. A maximal power consumption of 23 W could be established for the NGMS instrument at a mass resolution of m/Δm of > 1000 (FWHM) for higher masses and a sensitivity comparable to its prototype, which was demonstrated to be superior to the current state-of-the-art instrument on Mars (SAM/MSL).

Second, the Neutral species and Ion Mass spectrometer (NIM/PEP/JUICE) was selected to analyse Jupiter’s Icy Moons’ exospheres on-board ESA’s JUICE mission. The electron emitters for the NIM/PEP/JUICE instrument were studied and suitable types for flight were selected. They show a nominal power consumption of around 1 W, which equals a power reduction of more than 50 % when compared to NGMS’s emitter despite the increased lifetime.

Third, a CubeSat-type mass spectrometer (CubeSatTOF) was designed for analysis of planetary atmospheres on-board a descent probe or an orbiter. I combined the results from my scientific case study with measurements from the prototype to propose two possible mission scenarios. My studies indicate that the measurements’ sensitivities equal those of the NGMS/Luna-Resurs instrument, but at a lower mass resolution m/Δm of > 240 (FWHM) for higher masses. The lower resolution is accounted for by impactful size reduction of the instrument. It can be completely enclosed into a volume of (10 x 10 x 11.3) cm3, which is 1U of a CubeSat.

These miniature time-of-flight mass analysers are expected to contribute to our understanding of the current status and evolution of the analysed planetary objects. Possible results are expected to provide knowledge about the presence of water and other volatiles at or in the lunar surface, the origin and habitability of Ganymede and Europa, and the detailed understanding of the terrestrial exosphere. The latter can serve as benchmark studies while investigating extra-terrestrial exospheres for comparative planetology.

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