The Effect of Reduced Ambient Pressure on Plume-Surface Interaction Cratering Dynamics

Abstract

This study investigates the differences in plume-surface interaction (PSI) cratering behavior between Earth atmospheric (101,325 Pa) and subatmospheric (33 Pa) ambient pressures. A stereo-photogrammetry technique was used to nonintrusively obtain 3D, time-resolved measurements of the full-domain crater geometry. Tests were conducted inside an optically accessible vacuum chamber where the PSI process was simulated using a sonic jet impinging on a bed of regolith simulant. Crater geometry measurements were taken at nozzle heights of 4.6 to 55.6 nozzle diameters above the simulant surface. Results show that the highly underexpanded plume under subatmospheric conditions resulted in broad and shallow craters compared to craters formed under Earth atmosphere. Some craters under subatmospheric conditions exhibited lobed geometry characterized by azimuthal depth variations. In these same cases, the deepest portion of the crater was located radially away from the center, and particles were observed moving toward the center resulting in fountain-like particle movement. Craters formed under Earth atmospheric conditions had an axisymmetric parabolic geometry with the location of maximum depth at the center. In general, subatmospheric crater growth was slower than Earth atmospheric. However, subatmospheric crater formation at nozzle heights of 9.3D and below was characteristically like Earth atmospheric crater formation at large nozzle heights.