Future exploration of the Moon, or Mars, will require the development of landing vehicles, whose primary task is to decelerate its cargo and safely touch down on the surface. However, this is not a trivial task for these types of environments. As the jet/plume from the rocket engine, used to decelerate the vehicle, encounters the surface, the low atmospheric pressure, low gravity, and cohesive soil properties result in large dust clouds and even crater formation. These phenomena are called plume surface interactions (PSI). Incremental progress is being made to study PSI through a series of proposed test campaigns being conducted at multiple NASA Research Centers and utilizing large vacuum chamber facilities, such as the MSFC TS300 or LARC 60' Sphere, and tested under relevant conditions. One critical instrumentation need that NASA has identified for these tests is direct surface (wall) shear stress measurements. In the Lunar environment, surface shear stress is the primary driving force by which surface erosion occurs. To overcome this technology gap, Ahmic Aerospace and our assembled team propose to adapt our state-of-the-art wall shear measurement technology to target surface erosion environments occurring in plume surface interactions. In Phase I, Ahmic will conduct a series of incremental steps along two parallel paths to meet this end goal. The first path will simplify the PSI problem and consider a series of static-surface erosion tests utilizing existing wall shear sensors and known erosion geometries, thus circumventing the immediate need for an active erosion sensor. These tests will serve to compare direct and indirect wall shear measurement approaches in a jet impingement environment and examine the influence of surface erosion geometry on wall shear. The second path will consist of a feasibility study to develop a wall shear measurement methodology for active surface erosion environments and examine the steps necessary to achieve this goal.
The proposed wall shear diagnostic techniques present a direct solution for NASA’s PSI ground testing needs. As part of the recent project focused on advancing modeling and simulation capabilities, PSI validation data is being acquired in a campaign known as the Physics Focused Ground Test (PFGT). Much of this initial work is being carried out in NASA’s Marshall Space Flight Center (MSFC) in the Test Stand 300. This test campaign would directly benefit from Ahmic’s proposed instrumentation and methodology.
The Air Force and SpaceX represent non-NASA markets for the proposed diagnostic techniques. These entities are currently investigating the technical feasibility of using rockets for point-to-point transport of high-value cargoes to remote landing sites. To do this safely will require knowledge of PSI, viscous erosion physics, and how the granular particles will be ejected from the surface.