Abstract DGP2026-37

Rock-forming minerals exhibit diagnostic spectral features in the mid- and long-wavelength infrared range, enabling in-situ compositional analysis. For example, silicates show a characteristic Christiansen feature between 7.5 and 9 µm, with Reststrahlen bands and transparency features located between 9 and 13 µm. Consequently, spectral coverage from approximately 7.5 to 13 µm allows extensive mineralogical and compositional characterization of planetary materials. Mineralogical features in this wavelength range are typically broad (>0.5 µm), resulting in moderate spectral resolution requirements that can be addressed using MEMS-based Fabry-Pérot interferometers. When operated in the first interference order, these filters provide free spectral ranges of a few micrometers with spectral resolutions λ/Δλ around 50, sufficient to resolve diagnostic mineral features. MEMS Fabry-Pérot technology offers compact size, high optical throughput, and electrical tunability, making it well suited for miniaturized space instrumentation.

Scientific questions in lunar exploration that can be addressed using this technology include the investigation of regolith olivine content and layering as well as the identification of materials relevant to in-situ resource utilization (ISRU). To assess the capability of the instrument concept to detect mineralogical variations, we have performed laboratory measurements of bi-directional reflectance of end-member minerals (pyroxene, plagioclase, and olivine) as well as minerals relevant for ISRU (albite, ilmenite). Measurements were performed under vacuum conditions on granular samples representative of lunar regolith grain sizes. As would be expected, increasing olivine content results in a systematic shift of the Christiansen feature towards longer wavelengths and a deepening of Reststrahlen bands between 9 and 12 µm. Further, while adding ilmenite to the mixture has little effect on the spectra, albite would be detectable by its distinct effect on Reststrahlen features.

We present the design and first results of a compact thermal infrared point spectrometer based on a MEMS Fabry–Pérot interferometer combined with a single-pixel thermopile detector. The instrument builds on flight-heritage radiometer technology previously deployed on several planetary missions. The interferometer is electrically tunable between 7.5 and 10.5 µm using control voltages between 0 and 70 V, and spectra are generated in the time domain by stepping through the cavity spacing while recording the radiative flux. First results indicate a spectral resolution λ/Δλ close to 30, with a noise-equivalent emissivity difference of about 0.5%. The current sensor prototype has reached TRL 4, with functional verification performed under ambient conditions. The sensor head mass is approximately 100 g, and total instrument mass including electronics is estimated to be 300 g. The compact design is well suited for deployment on small platforms such as micro-landers, rover, or legged robots.