Apollo missions revealed how much dust is problematic, making the safety of future long-term lunar activities a difficult challenge. To tackle this issue, it is of paramount importance to understand the underlying charging mechanisms of dust under a representative environment.

ONERA has developed characterization means in order to address the problem. The DROP platform, located in Toulouse, hosts a vacuum chamber that reproduces the lunar radiative environment (VUV/electron irradiation). This platform is useful to investigate several questions, including the charging behavior of lunar dust simulants under VUV/electron beam.

The upcoming lunar missions offer unique opportunities for in-situ characterization of the charging mechanisms. ONERA is currently involved in the development and testing of instruments for in situ analysis of lunar dust properties in the frame of a project led by BIRA-IASB and funded by the European Union. The objective of this project is to develop a sensor package by the end of 2024, which will include a dust charge detector, a Langmuir and an E-field probe, for charge measurements of single dust particles under irradiation. The present study focuses on the charge detector which is a polarized Faraday cup connected to a transimpedance amplifier (10^11 V/A gain, 200 Hz bandwidth) and a digitization stage. The background noise is low enough to measure charges of dust particles on a layered surface after VUV irradiation with a precision of 1 fC. We also show that both positively and negatively charged dust particles are equally mobilized and collected by the Faraday cup. More than half of the detected dust grains have a charge lower than 10 fC in absolute value. This study thus paves the way for future lunar exploration missions that will require accurate measurements of the electrostatic properties of the lunar ground and allow us to define better safety margins.