|Thermal Protection System (TPS) and Materials|
Space vehicles that enter a planetary atmosphere (i.e. earth) like the Space Shuttle Orbiter require the use of a thermal protection system (TPS) to protect them from aerodynamic heating. The aerodynamic heating is generated at the surface of an entering object due to the combination of compression and surface friction of the atmospheric gas. The vehicle's configuration and entry trajectory in combination with the type of thermal protection system used define the temperature distribution
on the vehicle. The Space Shuttle features a TPS system based on the use of surface materials with a high temperature capability in combination with an underlying thermal insulation to inhibit the conduction of heat to the interior of the vehicle. The heat developed from the aerodynamic heating process is thereby radiated back into space by virtue of the high surface temperature. The leading edges of wings and the nose cap are the highest temperature regions. Due to the wide variation of
these temperatures the TPS selected for Space Shuttle was composed of many different materials. Each material's temperature capability, durability and weight determine the extent of its application on the vehicle. Improvements to these materials have been the subject of much research as enhanced capability material (i.e., more durability, higher temperature capability, greater thermal shock resistance and lower thermal conductivity) improves thermal protection material and vehicle
performance. Future reentry vehicles capabilities will depend upon the capabilities of TPS being developed and available to them.
A TPS development at NASA Ames Research Center is Ultra High Temperature Ceramics (UHTC). Ultra High Temperature Ceramics are a family of ceramic materials with extremely high melting temperatures, good oxidation resistance in reentry type environments, and reasonably good thermal shock resistance for a monolithic ceramic. These materials show potential for use as passively cooled sharp leading edges on future reentry vehicles. Sharp leading edges offer advantages in aerodynamic
performance and crew safety over current blunt leading edges. Ames is developing the UHTC materials for use in sharp leading edge applications. The materials being investigated include HfB2/SiC and ZrB2/SiC composites among other compositions. Recent work has included ground based arc jet experiments along with the SHARP B1 and SHARP B2 flight experiments. Future work includes improving the thermal and mechanical properties of the materials and development of attachment designs.