Arc heater code validation tests of heat shield materials

Results are reported for tests of candidate heat-shield materials for outer-planet entry probes, which were conducted in two different arc-heater facilities at heating rates below those predicted for entry. One facility supplied a combined radiative-convective heating environment in air while the other provided a hydrogen/helium environment for convective heating only. Both 'infinite-slab' and 'finite-slab' models consisting of various carbon phenolic (CP) and fused silica (FS) materials were tested. The test results obtained are expressed in terms of ablation rates and surface as well as in-depth temperature variations with time for the air environment and in terms of normalized ablation rate as a function of temperature for the H/He environment. The measured values are compared with calculations based on a charring material thermal response and ablation code. For the CP models, good agreement between predicted and measured mass-loss rates is noted, surface temperatures in air are predicted within 18%, and in-depth temperature predictions are shown to be conservative in comparison with measured values. For the FS models, discrepancies are found between the predicted and measured mass-loss rates and surface temperatures.