Flight electronics of GC-mass spectrometer for investigation of volatiles in the lunar regolith

Abstract

We introduce electronics designed to control measurement cycles performed with the compact neutral gas mass spectrometer (NGMS), which is a time-of-flight (TOF) system. NGMS is combined with a gas chromatograph (GC) and a pyrolysis oven to form a gas analytic complex on board the Russian Luna-Resurs spacecraft to land on the Moon. The instrument will investigate chemical composition of the soils at lunar polar regions and the tenuous lunar exosphere. NGMS measures the elemental, isotopic and molecular composition of gaseous samples including CHON compounds, water and noble gases, by recording TOF spectra that are converted to mass spectra during data analysis. Our miniature mass spectrometer has a robust and modular design. It combines an ion storage source with redundant thermionic electron emitters, a pulsed ion extraction for ion acceleration, ion drift path, ion mirror, a second ion drift path, and a high-speed microchannel plate detector. Starting from the ion source where species are ionized and the consecutive mass separation in the field free regions of a TOF section, ion packages arrive some microseconds later at the multichannel ion detector. The detector produces current pulses with peak widths of nanoseconds allowing for measurements with a high mass resolution in spite of a short drift tube length. During test measurements, we achieved mass resolution > 1000 together with a dynamic range of up to 106 within 1 second integration time. Hence, the instrument depends on high electric field strengths in the ion-optical system and a high-speed and low-noise data acquisition system resulting in highly customized control electronics. We developed the complete electronic system complying with the mission requirements (power consumption of 25 watt maximum, size, mass and radiation tolerance) for controlling the instrument operation and acquiring data from this complex analytical package. Given the heritage from LASMA/Phobos-Grunt, CaSSIS/Exo-Mars, RTOF/Rosetta and P-BACE/MEAP missions, the presented design demonstrates that NGMS is capable to investigate chemical composition with allocated resources of power and size. Our flight-proven control unit operating NGMS represents a reliable system for further similar applications as the Neutral Gas and Ion Mass spectrometer NIM/PEP on board ESA's JUICE mission.