Exploring Electrostatic Regolith Interactions and Charging Behaviors with Reduced Gravity Experiments

EXPLORING ELECTROSTATIC REGOLITH INTERACTIONS AND CHARGING BEHAVIORS WITH REDUCED GRAVITY EXPERIMENTS. A. Dove1, J. Phillips III2, M. Daughtry1, K. Acosta2, 1University of Central Florida (4111 Libra Dr, Orlando, FL 32816), 2NASA Kennedy Space Center, Introduction: In the natural lunar environment, regolith grains may exist in a neutral or charged state, depending on the charging currents. Undisturbed regolith may charge due to incident light, solar wind, and other plasma sources. Disturbed regolith may charge due to additional plasma sources, or dynamic effects such as tribocharging, which occurs due to grain-grain and grain-surface contacts (e.g. [1, 2]). The magnitudes of these forces will then determine both the static and dynamic behaviors of these grains. Instrumentation is being developed to measure the magnitude of the grain charging, and may include detectors for lofted dust, or contact probes. The Experiment: The Electrostatic Regolith Interaction Experiment (ERIE) is a payload designed to operate on a suborbital flight in order to study electrostatically charged dust particle dynamics under microgravity, with the goal of informing both scientific and technological applications for lunar and planetary exploration. Jointly developed by University of Central Florida (UCF) and NASA Kennedy Space Center (KSC), ERIE combines components from two systems, the COLLisions Into Dust Experiment (COLLIDE, UCF) and the Wheel Electrostatic Spectrometer (WES, NASA KSC), to advance understanding of charged grain behavior on low gravity bodies such as the Moon and asteroids. The overall experiment design was built off of the existing COLLIDE design, components of which have heritage from a flight on a Space Shuttle payload, and which had previously flown on suborbital flight experiments. To measure charged particle and surface interactions, we integrated an updated design of the WES electrometer into a door that slides over a bed of regolith. We also observe the behavior of the tribo-charged particles in microgravity, as they remain in the bed or are lofted due to repulsive forces. We have previously reported on the design and initial results from the electrometer instrument, and basics of the flight hardware. We have now collected data from the flight instruments on three suborbital flights, with varying levels of mission and experiment success. We have also undertaken a series of ground-based experiments on the benchtop and in vacuum in order to further characterize the behavior of the electrometer and of the charged particles in the electric field created in the chamber. Ground-based testing has been done to characterize the response of the electrometer to a wide range of induced charges. It also allows us to test over a variety of regolith compositions, particle sizes, and size distributions, which are limited in-flight. While no one flight produced all of the desired data, we find that the electrometer performs as expected under both microgravity condition and the high-g, high-vibration conditions of launch and landing. The experiment is designed to enable contact between the regolith grains and the electrometer sensors, but sensors are able to measure induced charge even when not in direct contact. Analysis of images from flight indicate that significant compaction of simulants occurred in the simulant bed on one of the flights. In all cases, some grains were lofted, and we also observed clumping of the smaller grains into structures, which were then modified in the presence of the electric field. We will discuss observations of dust grain dynamics, comparisons with ground-based studies, and the system adaptation for and performance on the suborbital flights. Photo of the ERIE hardware, showing the chamber, with a bed of regolith under the arrow, a representation image of lofted, charged dust particles, and a schematic of the electrometer. References: [1] Farrell B. et al (2008) GRL, 35, [2] Yeo L. et al. (2024) Adv. Sp. Res. 72 [3] Johansen M. R, et al. (2014) Annual Meeting of the Electrostatics Society of America. No. KSC-EDAA-TN14993. [4] Colwell J. (2003) Icarus, 164, 188-196. Graphic Goes Here t d char