Atmospheric Reentry Physics :Fundamentals of Environment- Materials Interactions, Models and Design Approaches to meet Emerging Space Needs

Abstract

The "Atmospheric Reentry Physics" conference will provide a single focal point to allow for the better integration and advancement of a multidisciplinary research community of scientists and engineers, representing government agencies, the private sector, and University systems across the world. The primary objectives of the conference are to foster improved communication across national and discipline boundaries, and to expose the atmospheric reentry community to new ideas and techniques from adjacent disciplines in the hopes of bringing new experimental techniques to bear on the problem as well as brainstorm about challenges faced by expanding the range of application of existing techniques. The topic area encompasses the physics and chemistry relevant to a spacecraft entry into the Earth or a planetary atmosphere. At hypersonic speeds, strong shock waves form in front of the reentry spacecraft, and the boundary layer is typically highly turbulent, leading to complex compressible fluid dynamics. Such entries are further characterized by dissociation, ionization, and excitation of the gaseous species behind the hypersonic shock wave. At sufficiently high velocity, the hot atmospheric gas begins to radiate due to atomic and molecular excitation. This radiation can become strong enough that it is a significant source of heat transfer to the spacecraft. At the higher entry velocities, the heat generated at the vehicle surface is large enough that no material can withstand it without degrading. Therefore, a spacecraft design typically relies on ablating thermal protection materials, which are intended to pyrolize and char in response to the incident heat. These materials thus efficiently cool the spacecraft via energy absorption of the endothermic breakdown of the polymeric constituents, transpiration cooling as the pyrolysis gases percolate from the interior of the material toward the surface, and re-radiation from the hot char layer that forms on the surface. At the high altitude conditions typical of atmospheric entry, many or all of these processes can be in non-equilibrium, which greatly complicates the required physical models that must be employed in their simulation. Finally, all of these phenomena, including the fluid dynamics, molecular chemistry, radiation emission and transport, and ablative material response, can be coupled, requiring the development and validation of complex multi-physics models. Such models exist today at varying levels of fidelity and validation. A significant impediment to properly validating the models has been the inability to conduct truly flight-like experiments in ground-based laboratories. However, we believe that, under the auspices of the GRC, the current state of the art can be considerably advanced by bringing new ideas and methodologies to bear on the problem. The GRC series will focus on each of these elements (or the coupling between them) in turn, ensuring a dynamic, ever changing research discussion for many years to come.