Non-intrusive, 3-D Crater Formation Measurements Due to Plume-Surface Interactions Under Sub-Atmospheric Pressure Conditions

Plume surface interactions (PSIs) have been identified as a significant challenge in returning humans safely to the Moon. The PSI process encompasses the interaction of the exhaust plume of a landing spacecraft with the surface of a planetary body. This process results in crater formation and ejecta blowing, especially in the case of loose rocky surfaces such as that of the Moon. The crater and ejecta pose a threat to both the landing craft and to equipment and persons already on the surface. This investigation focuses on obtaining 3-D, time-resolved measurements of crater formation during the PSI process under sub-atmospheric conditions using a non-intrusive stereo-photogrammetry measurement technique. An experimental apparatus was constructed inside of a 1.2 m cube vacuum chamber to simulate the PSI process using a supersonic jet impinging on a bed of regolith simulant. Crater geometry measurements were taken at an ambient pressure of 33 Pa (0.25 Torr) and nozzle heights of 37.1, 23.2, 13.9, 9.3, and 4.6 nozzle diameters above the simulant surface. Qualitative analysis of sub-atmospheric versus atmospheric crater formation is provided. Quantitative analysis of the crater formation is provided by extracting the time evolution of maximum depth, center depth, radius, and volume from the 3-D crater measurements.