History and State of the Art in Advanced Thermal Protection Systems

This report documents the current state of the art of thermal protection systems (TPS) relevant to missile application materials and MTCR control language.The information is intended to provide data on current TPS for determining the current state of development and identifying potential research directions.Various vehicle configurations and types of TPS are described, including the evolution of materials and systems.Vehicle configurations such as high drag rocket and capsule systems and low-drag air-breathers are discussed.TPS are complex, transitioning from often very low temperatures to temperatures exceeding 3000C and heat fluxes of up to 30,000 W/cm 2 .They can take the form of blankets, sheets, tiles and fabricated rigid structures, and can be made from high temperature capable alloys, refractory metals, ceramics, ceramic matrix composites, ultra-high temperature ceramics, carbon-carbon composites or ablative carbonaceous materials.Current state of the art in TPS is based on materials any systems developed for the initial space program.TPS was upgraded to the point of the Space Shuttle development and has stagnated since them.Raw materials used to create TPS for the U.S. space program are often not available, so fabricators have to do some redevelopment to create similar TPS with currently available feedstock.Most recently, C/SiC with a SiC coating provided protection for the hottest portion of the Shuttle during reentry, the nose and wing leading edges.That system should be good to about 1700C, the limit for SiO 2 -based protection.C/C is currently the highest temperature capable TPS being employed, because it ablates, shedding material and temperature.Unfortunately, C/C requires a coating in order to be shape stable, a requirement for hypersonic missiles.C has a near zero coefficient of thermal (CTE) expansion, making it incompatible with coatings, which all have 6-10 times the CTE.Ultra-high temperature ceramic and composite (UHTC) coatings with multimaterial refractory metal compounds such as ZrC, ZrB 2 , HfC, HfB 2 , TiB 2 , often mixed with SiC, are being developed and applied to C/SiC, which has a higher CTE than C/C, providing potential for shape-stable ultra-high temperature capable composites.This is an area of current research and the efforts should be expanded significantly.The continued evolution of advanced manufacturing capabilities shows promise to make it easier to produce ultra-high temperature near net shape structural materials using multi-component powders.These shapes may include the geometric shapes addressed within the MTCR (tubes and limited wall thicknesses).This may decrease material and manufacturing costs.In addition, advanced densification processes for UHTCs, such as chemical vapor infiltration and polymer infiltration pyrolysis have the potential to be developed to create graded matrix structures, and this should be another technical area of focus.