Ground Calibration Test Method for Chang’E-7 Lunar Soil Water Molecule Analyzer

The lunar pole’s water ice is essential for understanding the Moon’s evolution and building future lunar research station. Nevertheless, existing orbital remote-sensing missions and returned samples remain insufficient to resolve the key unknowns of polar water, including its occurrence modes (e.g., adsorbed water/hydroxyl, pore-filling ice, or ice-cemented regolith), its abundance and vertical variability, and its potential origin and evolutionary pathways. To address this gap, the Chang’E-7 mini-flying probe will carry the lunar soil Water molecule Analyser (LUWA) to conduct in-situ detection of water ice at the permanently shadowed region for the first time. This paper describes the compositional structure of LUWA and the detection approach, comprising drilling, sampling, sealing, heating and analysis. We detail the calibration parameters, apparatus, and procedures for its three core analytical modules: the Tunable Diode Laser Absorption Spectrometer (TDLAS), the Time-of-Flight Mass Spectrometer (TOF-MS), and the Differential optical Absorption Spectrometer (DAS). The operational chain is designed to release water through thermal extraction, quantify water content with high sensitivity across a wide dynamic range, and enable the determination of D/H isotopic signatures. A systematic ground calibration methodology and a unified calibration framework are established for three functional modules dedicated to water measurement. The framework defines calibration objectives, procedures, and traceability pathways to characterize module response functions, assess background and temperature-dependent effects, verify detection limits and linearity, and evaluate accuracy and repeatability, thereby supporting robust conversion from raw observables to calibrated water-content and isotope products in flight. In parallel, a dedicated lunar in-situ exploration test platform is developed to replicate LUWA’s full operational workflow using lunar regolith simulants, including drilling, sampling, sealing, heating, and analysis. Integrated tests validate key performance metrics and the measurement workflow, providing crucial technical support for interpreting Chang’E-7 LUWA data and for assessing the abundance and occurrence of water ice in lunar soil within PSRs.