Lunar Mineralogical Spectrometer on Chang’E-5 Mission

Abstract

The Lunar Mineralogical Spectrometer (LMS) is one of the main payloads on the Chang’E-5 (CE-5) lunar probe, belonging to the China Lunar Exploration Program. The scientific objective of the LMS is to explore the mineralogical composition and search for evidence of -OH/H2O in the sampling area. The LMS consists of an optomechanism unit, a dustproof calibration unit (DPCU) and an electronic unit. The LMS is installed on the lander about 1.4-m above the lunar surface, the field of view (FOV) is $4.17\times 4.17^{\circ }$ 4.17 × 4.17 ∘ , the instant FOV of the visible imaging channel is 0.28 mrad, and the typical spatial resolution is 0.56 mm/pixel @ 2 m distance. The rotation range of the 2D scanner is $\pm 22.5^{\circ}$ ± 22.5 ∘ along the azimuth axis and $0\sim 30^{\circ }$ 0 ∼ 30 ∘ along the elevation axis, making it possible to observe the sampling area or to select important observing targets. The dispersing beam uses acousto-optic tunable filters, and target detection is performed with a 2D scanner. The LMS acquires spectral imaging information covering 480–950 nm, and reflectance spectra of 900–3,200-nm, both at a 5-nm/band sampling interval. The spectral resolution is $2.4\sim 9.4\text{ nm}$ 2.4 ∼ 9.4 nm in the visible and near-infrared channels and $7.6\sim 24.9\text{ nm}$ 7.6 ∼ 24.9 nm in the short–medium-wave infrared channel. The LMS has a 588-band detection capability designed for fine spectral observation of sampling points and wields a 20-band full-view multi-spectral mode to observe candidate areas prior to sampling. The DPCU of the LMS is integrated with a calibration diffuser that is used for in-flight calibration on the lunar surface using solar irradiation, thus improving the quantitative level of scientific data.

Chang'E‐5 In Situ Spectra Reveal Photometric Properties of the Lunar Surface

“…They have a good consistency (Figure 6), and the total RMSE and MAPE between them are 0.0087% and 10.7%, respectively. The uncertainties of radiometric calibration of LMS are below 6% (Xu et al, 2022), the difference between our Hapke modeled RADF and the LMS measured RADF is acceptable. We also plotted Modeled/Measured RADF ratio versus the angles in Figure 6b-6c, the Modeled/Measured RADF ratios are randomly distributed around 1 and showing no significant variation with angles.…”

“…The SWIR detector and MWIR detector shared a FOV of 4.17° × 4.17°, as well as the VIS detector and NIR detector, and the two FOVs have a deviation of 16 pixels. The VIS detector is an imager of 256 × 256 pixels in size, and its spatial resolution is ∼1–4 mm/pixel when its inflight detection distance is approximately 1.5 ∼3.5 m, while the other three are non‐imaged single‐point detectors (Xu et al., 2022).…”

Chang’E-5 In Situ Spectra Revealing Meter-scale Surface Temperature Distribution Characteristic of the Moon

“…The main tasks of LMS are to collect in situ spectra of the lunar surface before and after sample collection, to analyze the mineral distribution of the sampling area, and to provide in situ spectra for the future comparison with the laboratory-measured spectra of returned samples (Liu et al 2022). The LMS consists of a visible and near-infrared imaging detector (VIS, 480-950 nm) and three infrared single-point detectors (NIR: 900-1450 nm; SWIR: 1400-2450 nm; MWIR: 2400-3200 nm) with a field of view (FOV) of 4°.24 × 4°.24 (Xu et al 2022).…”