Design and Characterization of a Variable High Temperature/Low Pressure Facility for Evaluating Thermal Protection Systems in Reentry Environments

Abstract

A variable high temperature / low pressure facility has been developed to characterize the thermal response of candidate thermal protection materials in reentry environments. Transient, non-linear finite element models were developed to optimize the design of the test facility. All models used temperature dependent material properties and time dependent boundary conditions based on thermocouple data obtained during checkout runs. These experimental runs were based on simulated reentry profiles. A one-dimensional model was developed considering only the axial heat flow through the thickness of the test stack. It was used as a benchmark when considering multi-dimensional heating effects. Axisymmetric and three-dimensional models were developed to minimize transverse heating and edge effects through a unique combination of material selection and geometry. The final, optimized configuration is capable of temperatures as high as 4500 °F with pressures as low as 100 mTorr in inert atmosphere. Heating rates that produce surface temperature changes of 300 °F / min are attainable. Pyrometers are used to measure the element temperature and the specimen hot face temperature. Up to thirty-five thermocouples are used to measure internal specimen, cold-face, and insulation temperatures within the stack. A PID algorithm is used to control the furnace, while a data acquisition system is used to log all data.