Absolute Photoelectric Yield Measurements of the Rashid Lunar Rover Materials at the BABE Synchrotron Facility

We report on the spectral photoelectric yields of the surface materials of the lunar rover Rashid 1, built by the Mohammed Bin Rashid Space Centre in Dubai. The materials investigated are magnesium alloy, indium-tin-oxide, titanium, the commercial off-the-shelf solar panel cover-glass, and the graphite coatings on the Langmuir probes, namely Aerodag (R) G and Graphit 33. The yields of gold and silver plates were also measured for reference and calibration purposes. The photoelectric yield of some of these materials was measured in the past but only with photon energies up to 25 eV. The measurements were performed at the BABE facility (stemming from the BACH and BEAR synchrotron beamlines) within the framework of the European AHEAD2020 project operated by the Italian National Research Council CNR-IOM at the synchrotron light source Elettra, Italy. We scanned the 2.8-1240 eV energy region, covering most of the solar spectrum that can potentially lead to photoelectron emission on the Moon. The total electron emission rate per unit surface was estimated by combining the measured photoelectric yield curves with the solar spectral irradiance data from TIMED-SEE/SORCE experiments. The results of this study are needed as input in numerical simulations of the electron sheath forming around Rashid 1 or any similar lunar rover. Such numerical models help estimate the background signal for in-situ measurements of the density of the electron sheath forming above the Moon's surface.