Non-intrusive, 3D Optical Measurements of Crater Formation due to Plume-Surface Interactions

View Video Presentation: https://doi.org/10.2514/6.2021-0831.vid Plume surface interactions (PSIs) are one of the biggest challenges in safely returning humans to the moon and ultimately enabling human exploration of other planetary bodies. The PSI process leads to crater evolution and dust formation during descent and touch down that poses a threat to the space craft and to equipment and persons on the surface. This investigation focused on obtaining 3D, time-resolved, non-intrusive, full-domain measurements of crater geometry during the plume surface interaction (PSI) process in an atmospheric experimental facility using stereo photogrammetry. The PSI exhaust process was simulated using a supersonic jet at heights of 25, 40, 55, and 70 nozzle diameters above the lunar regolith simulant bed. Sand particles ranging from 600 to 850 microns in diameter were used for all tests. From the stereo photogrammetry data, time-resolved 3D reconstructions of the crater geometry were generated, and both crater depth and radius time histories were extracted from the geometry. Multiple nozzle heights above the surface were tested to investigate the effects of nozzle height on the crater formation process. Results show that stereo photogrammetry can be used to successfully measure the crater geometry in cases where optical access to the crater is not completely degraded by ejected particles. The crater depth and radius were observed to grow logarithmically with time for all nozzle heights. The angle of repose of the resulting crater after the nozzle flow was stopped was calculated and found to match expected values for an angle of repose dominated by the dynamic friction coefficient.