Description: The physics of plume surface interactions (PSI) when a rocket-powered spacecraft performs an extraterrestrial surface landing involves producing soil erosion/cratering and high-speed ejecta which are fundamentally coupled. The crater shape and growth effects the speed and direction of the ejecta particles that may in turn be entrained by the flow field to alter the plume aerodynamic structure, the cratering process and even a space lander's orientation. A recent touch-down event by the Odysseus lunar lander where the lander tripped and fell onto its side on the cratered lunar surface may have resulted from a PSI phenomenon, highlighting the extent of the problem. Relevant mitigation techniques require understanding the physics of PSI events. More specifically, accurate 3D characterization of the high-speed ejecta particles in terms of particle size distributions, trajectories and velocities is needed by NASA to assess mitigation measures and for benchmark validation of modeling and simulation (M&S) tools. The current state of experimental findings on PSI is scarce and the in-situ diagnostics used to obtain data only provide two-dimensional information that are highly dependent on ambient light and visibility conditions making measurements difficult close to touchdown. Given these shortcomings, this work proposes to demonstrate the feasibility of high-speed digital holography (DH) in providing high resolution time-resolved 3D trajectories, velocities and particle size distributions of ejecta particles generated by PSI events of rocket powered spacecraft landings. Since digital holography makes it possible to numerically focus on discrete depth planes, a single digital holographic video is equivalent to 1000 conventional videos, each recorded at a different plane of focus. The effort will provide a prototype instrument for physics focused ground testing and a preliminary design for a compact DH flight instrument (HoloCam) for NASA's future mission needs.

Benefits: The onboard DH instrument can be installed on rover and lander missions to perform volumetric particle-field characterization during descent and extraterrestrial touch down. This will enable understanding turbulence, boundary-layer development, crater formation and high-speed regolith impact during PSI events. Measurements post touchdown will provide valuable climate data, especially particle density fluctuation in Martian storms. Applications in improving Whipple shield mechanisms are possible by understanding 3D ejecta formation in hypervelocity space impacts. The high-speed digital holography (DH) prototype instrument developed for terrestrial research facilities will be deployed in NASA's Physics Focused Ground Test (PFGT) campaigns at the Marshal Space Flight Center (MSFC) to understand the physics of the PSI problem in three dimensions. These tests will closely replicate the space environment the digital holography (DH) instrument will be subjected to on the space lander that will showcase the performance of the system in real-life application scenarios and hence, indicate any design flaws and limitations that can be improved with modifications. The ground testing instrument is expected to serve as an extremely important tool and capability to aid in the development of in-flight instruments. 3D particle field investigations are critical for understating various physical processes including combustion, mixing, diffusion and turbulence among many other phenomena. A vast number of industrial applications and research activities experiencing these processes require non-intrusive diagnostics that can provide three-dimensional characteristics of the particle field. The technology is thus relevant to a multitude of aerospace, defense and manufacturing companies who are pursuing 3D particle field measurements in fuel injectors, nozzles, bubble chambers, sprays and aerosols for developing efficient combustion engines, spray devices and mixing chambers. In addition, the U.S. Navy, Missile Defense Agency (MDA), Space Force and other branches of DOD are actively interested in hypersonic defense systems and Whipple shield mechanism that can withstand impact by foreign materials and rain/hail in adverse weather conditions. Studies of these systems include investigating the ejecta/debris size and velocity distributions from the impact of a hypersonic missile on a solid target and water drops in ground testing facilities that the digital holography (DH) instrument developed under this program will be capable of measuring. Lastly, atmospheric, life science and biological applications are also possible to characterize airborne particles, detect hazardous respiratory environments and characterize the three-dimensional motility of bacteria. MetroLaser has already developed DH microscopes demonstrating 3D microbial visualization in plant rhizosphere that can be modified based on learnings from this work to enable investigating bacterial motility in extraterrestrial soil samples.