Analysis and design of ultra high temperature ceramics hot structures for ground and flight tests

Recently an alternative way to re-enter Earth atmosphere based on slender vehicles with sharp edges, flying at moderate angles of attack [1], improving safety and lowering maintenance costs, has been proposed. Sharp leading edges would also imply lower aerodynamic drag, improved flight performances and crew safety, due to the larger cross range and maneuverability along with more gentle re-entry trajectories . However, the temperature at the tip of the leading edge is inversely proportional to the square root of the leading edge nose radius, resulting in much higher surface temperatures than in the case of conventional blunt vehicles with conventional Thermal Protection System (TPS) materials. Accordingly, a new class of ceramic materials, the Ultra High Temperature Ceramics (UHTC), has been proposed as TPS for these new vehicle concepts, based on the hot structure concept. Metallic diborides, such as Zirconium and Hafnium, with different additives, are candidates for thermal protection materials in both re-entry and hypersonic cruise vehicles because of their high melting points (>3000o C) and excellent chemical stability [2]. The authors are presently involved in research and development of UHTC materials in the frame of national and international programs focused on the integration of this class of materials on future hypersonic cruise and re-entry vehicles. In the following design and analysis of on ground experiments of UHTC materials are illustrated, substantiated by appropriate Computational Fluid Dynamics (CFD) computations and design of in flight research activity are presented.