Advancing Lunar Exploration: The Neutral Gas Mass Spectrometer for Regolith and Exosphere Analysis

The Neutral Gas Mass Spectrometer (NGMS) for the Luna 25 and Luna 27 missions represents a pivotal advancement in lunar exploration technology. This compact time-of-flight (TOF) spaceborne instrument is integrated with a gas chromatograph (GC) and a pyrolysis oven, designed to investigate the chemical composition of volatiles in the lunar polar regolith and the tenuous lunar exosphere. NGMS measures element, isotope, and molecular compositions, including CHON compounds, water, and noble gases. It features a robust design with an ion storage source, redundant thermionic electron emitters, pulsed ion extraction, ion drift paths, an ion mirror, and a high-speed microchannel plate detector, achieving a mass resolution better than 1000 and a dynamic range of up to 6 decades within a 1-second integration time. Preparations for the mission included the successful coupling of the TOF-MS with GC, enabling chemical pre-separation of species. Test measurements with hydrocarbons and noble gases confirmed the system's high sensitivity and extensive dynamic range, with detection limits for volatile species in lunar regolith estimated at <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$2\cdot 10^{-10}$</tex> by mass for hydrocarbons and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$2\cdot 10^{-9}$</tex> by mass for noble gases. The NGMS design ensures high sensitivity with moderate resource requirements, recording all masses simultaneously. The instrument's control electronics were developed to meet stringent mission requirements, including a maximum power consumption of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$23\mathrm{W}$</tex>, compact size, and radiation tolerance, all assessed at technical readiness level 8. The complete instrument weighs 3.2 kg. This outstanding compact design was achieved by creating a miniaturized, integrated ion optical system, relying on a metal-ceramic brazed structure rather than discrete ion optical elements. By omitting bulky connecting components, a narrow opening angle of the ion beam inside the ion optical system was possible, minimizing ion optical aberrations. Although NGMS ultimately did not fly to the Moon due to programmatic considerations, its architectural baseline continues to shape ongoing advances in lunar and planetary exploration. Thanks to its exceptional achievements, it served as a baseline for the design of three instruments on board space missions: NIM on board ESA's JUICE mission and MANIaC on the Comet Interceptor mission, both specifically designed to analyze tenuous exospheres, and CODEX on board NASA's DIMPLE payload which is designed to analyze and date lunar rocks in situ.