Low-Gravity Size-Sorting, Conveying, Storage, and Delivery of Regolith for ISRU

This paper describes a feasibility study to determine whether simply adding screen-covered windows along the pipe-wall of a conventional open-coil screw conveyor can convert it into an effective size-separation system capable of functioning at any gravity level from terrestrial to micro-gravity. The granular material in a rapidly-rotated screw conveyor follows a swirling spiral path along the pipe wall involving high shear deformation rates. Size-segregation occurs in all granular solids when they are sheared in a body-force field (like in the centrifugal-acceleration `field' of a rotating reference frame). Covering successive windows (at different axial positions), cut into the pipe wall with sieve-screens of increasing gap-size, allows multiple streams of separately-sized particles to be extracted from the conveyed material. The sieving process involved does not utilize any pneumatic or fluid transport of solids. The sieved material delivery point for each sieved-size can be placed at any point along the open-coil screw conveyor. Thus, with only one moving part (the open-coil screw auger) multiple size separated streams can be delivered to different locations. This study demonstrated that the concept only works well when a very small gap (i.e., a few large-particle diameters) exists between the screw auger periphery and the screen windows in the pipe wall.