Arc-Jet Testing of a Variable-Transpiration-Cooled and Uncoated Carbon–Carbon Nose Cone

The last decade has witnessed a considerable effort in the development of materials and structures for reusable thermal protection systems with the final goal of enabling long-duration hypersonic flights and more affordable access to space by multiple reuse of recoverable rocket stages. While the development of materials such as carbon-based and silicon-based ablators has extended the typical lifespan of heat shields for extremely high heating-rate environments, the limited reusability yet prevents their use for the aforementioned applications and, therefore, active cooling techniques have to be considered to preserve the thermostructural integrity of thermal protection systems. For all of these reasons, active cooling of thermal protection systems is required and transpiration cooling has been demonstrated to be one of the most promising cooling strategies in terms of coolant mass saving and minimum disturbances of the external flow. The prototype heat shield used for the experiment on variable transpiration cooling is an axisymmetric uncoated carbon–carbon cone having tailored porosity and variable thickness prescribed at the manufacturing level in order to reproduce a variable blowing profile. The high-enthalpy test demonstrated the capability of transpiration cooling to preserve the cone, characterized by a 0.25-in. radius of curvature, for approximately 92 s while being exposed to a peak heating rate of 637 (stagnation region). Heat shield failure was detected after 92 s due to a high-temperature flow leak inside the sheeting sleeve of the coolant line upstream the sample.