Flow Behaviour of Lunar Regolith in a Low-Gravity Environment

Rheological models applicable on Earth tend to fail in reduced gravity. Below a critical gravitational acceleration, cohesive forces become predominant. For granular processing in space, notably to sustain human presence on the Moon, this can have disastrous consequences: it can lead to clumping of the material, unexpected clogging of hoppers, and in the end, compromises the complete processing pipeline. Yet, the influence of (low) gravity on granular flows is not accounted for in most existing models.

The Granular Rheology in Space (GRIS) project aims to contribute to the development of  rheological models applicable to lunar regolith, in space environment (including reduced gravity and low pressure). This contribution will present results from hourglass experiments, conducted in low gravity using an active drop tower and parabolic flights. To access partial gravity, a centrifuge is placed inside the plane, allowing us to generate gravities from 0.1g to 1g (where g is the Earth gravity). The flow rate and clogging probability were measured for different regolith simulants and analysed dependent on the granular Bond number. We generalise the granular behaviour in reduced gravity for all simulants studied, by scaling the clogging probability using the granular Bond number. We also propose an explanation for the deviations observed from the gravity-scaling of the Beverloo equation.