Arc-Jet Tests of Carbon–Phenolic-Based Ablative Materials for Spacecraft Heat Shield Applications

Abstract

We developed and tested two carbon–phenolic-based ablators for future Korean spacecraft heat shield applications. The ablators are developed with two layers: an outer recession layer, fabricated from carbon–phenolic material, and an inner insulating layer, fabricated either from cork or silica–phenolic material. The ablator specimens were tested in a 0.4 MW supersonic arc-jet plasma wind tunnel at heat flux conditions ranging from 6.25 MW/m2 to 9.4 MW/m2, with either specimen being stationary or transient. Stationary tests were conducted for 50 s each as a preliminary investigation, and the transient tests were conducted for ~110 s each to stimulate a spacecraft’s atmospheric re-entry heat flux trajectory. During the tests, each specimen’s internal temperatures were measured at three locations: 25 mm, 35 mm, and 45 mm from the specimen stagnation point. During the stationary tests, a two-color pyrometer was used to measure specimen stagnation-point temperatures. During the preliminary stationary tests, the silica–phenolic-insulated specimen’s reaction was normal compared to the cork-insulated specimen; hence, only the silica–phenolic-insulated specimens were further subjected to the transient tests. During the transient tests, the silica–phenolic-insulated specimens were stable, and the internal temperatures were lower than 450 K (~180 °C), achieving the main objective of this study.

Thermal Behavior of Carbon-Phenolic/Silica Phenolic Dual-Layer Ablator Specimens through Arc-Jet Tests

“…Since the ablator is developed using carbon-phenolic material, and the ablation process is confined to it (as confirmed in the previous study [22]), owing to its role as the primary flow-facing recession layer, the dual-layer ablator is classified as belonging to the CPBAM category of TPS materials.…”

“…In this experimental study, the tested ablative material (henceforth referred to as 'ablator') is developed based on the second method, where an outer primary carbonphenolic recession layer is augmented with an inner secondary silica-phenolic insulating layer, thus constituting the dual-layer ablator. This dual-layer ablator is developed based on our two previous studies [21,22]. In this ablator, the average ratio of temperature-wise thermal conductivity, measured up to 773.15 K (i.e., 500 • C) of the ablator's silica-phenolic material, is 1/3.5 of that of the carbon-phenolic material [22].…”

“…This dual-layer ablator is developed based on our two previous studies [21,22]. In this ablator, the average ratio of temperature-wise thermal conductivity, measured up to 773.15 K (i.e., 500 • C) of the ablator's silica-phenolic material, is 1/3.5 of that of the carbon-phenolic material [22].…”

“…In the follow-up study [22], two different dual-layer ablators were developed. Based on the observations made in the preceding study [21], one of the ablators was developed by adding the cork material as the inner insulating layer to the 30 • carbon-phenolic material.…”

“…In the same study [22], another ablator was developed by adding a silica-phenolic material as the inner insulating layer to the 30 • carbon-phenolic material. The ablation processes of silica-phenolic materials have also been extensively studied due to their TPS applications [28][29][30][31][32].…”