Arc Jet Test and Thermal Characteristics Analysis of High-Temperature Composite Materials for Reusable Space Vehicles

Reusable space vehicles, such as those used in space exploration and satellite deployment, face significant thermal challenges during re-entry into the Earth's atmosphere. The intense aerodynamic heating generated by hypersonic speeds necessitates the use of advanced materials and thermal protection systems (TPS) to safeguard the vehicle's structural integrity. The TPS must be designed to withstand the extreme thermal environment while maintaining reusability for multiple missions. The design of TPS for reusable space vehicles requires careful consideration of material properties, including thermal resistance, oxidation resistance, and mechanical strength. Different parts of the vehicle, such as the fuselage, wing leading edges (WLE), and nose cone, are exposed to varying heat fluxes and temperatures, necessitating the use of different materials tailored to each region's specific requirements. Among the materials used in TPS, ceramic composites have gained prominence due to their excellent thermal stability and resistance to oxidation and ablation. NPC/SiC (Needle Punching-Carbon/Silicon Carbide) is one such composite that has shown promise for use in high-temperature environments. The needle-punching process used to manufacture NPC/SiC enhances interlayer bonding, while additional densification processes, such as Chemical Vapor Infiltration (CVI) and Polymer Impregnation and Pyrolysis (PIP), further improve the material's mechanical properties and reduce porosity. In this study, we conducted a series of thermal characterization tests on NP-C/SiC using a 0.4 MW arc-heated wind tunnel (AWT) at Jeonbuk National University. The goal was to evaluate the material's performance under simulated reentry conditions, focusing on its thermal stability, mass loss, surface recession, and internal structural changes. The thermal characterization tests were conducted using the 0.4 MW AWT, a facility capable of simulating the high-enthalpy, supersonic flow conditions experienced during space vehicle re-entry. Although the power output of this AWT is lower than that of facilities in other countries, it provides a controlled environment for testing small-scale specimens. NP-C/SiC specimens, approximately 1 cm in diameter, were exposed to heat fluxes of 5.06 MW/m² and 7.51 MW/m² for varying durations, as shown in Table 1. These conditions were chosen to simulate the thermal loads experienced by space vehicles at different stages of re-entry. Real-time temperature measurements were taken using a pyrometer and thermocouples inserted into the specimens. High-speed cameras captured the physical changes in the specimens' shapes throughout the testing process. To assess the internal structural changes in the material, micro-CT imaging was performed before and after the tests. This technique allowed for a detailed analysis of porosity trends within the specimens, providing insights into how exposure to high heat fluxes affects the material's integrity at the microstructural level. (Table presented) All NP-C/SiC specimens exhibited minimal mass loss and surface recession, even under the highest heat flux conditions tested. The surface recession rates ranged from approximately 0.001 to 0.0018 mm/s, and mass loss remained between 1% and 1.5%. These findings indicate that NP-C/SiC possesses excellent resistance to oxidation and ablation, making it a reliable material for TPS applications. The surface temperature of the specimens was measured using a pyrometer. The maximum observed temperature was 1902°C. For NPCS-02 and NPCS-03, which underwent repeated testing, a decrease in both average and maximum temperatures was noted during the second test. Internal temperatures were measured using thermocouples placed 10 mm and 15 mm from the stagnation point. NPCS-03 exhibited a higher internal temperature (1120°C) and a significant difference between the two thermocouples. In this study, Micro-CT (SKYSCAN 1272, BRUKER) was used to capture and analyze internal images of the specimens before and after testing. The specimens were rotated at 0.3° intervals, capturing 1, 200 projection images at a resolution of 5.5 um per pixel. These images were reconstructed into approximately 5, 500 8-bit tomographic images, which were integrated into a 3D volume dataset using VG STUDIO MAX software. Porosity was calculated by applying a threshold to the greyscale values, with regions between 0 and 30 classified as pores. To analyze porosity changes after testing, a region of interest (ROI) was defined as shown in Fig.1. This ROI, measuring 1×1×5 mm, was divided into five cubic sub-ROIs (1×1×1 mm each). (Figure presented) Analysis showed that large pores were mainly located near the surface, with the highest porosity observed in ROI 1 (0-1 mm from the surface). NPCS-04, exposed to the highest heat flux, had the highest total ROI porosity of 24.02%, while NPCS-02 had the lowest at 22.39%, likely due to cooling between its two 60-second test sessions. Beyond 3 mm depth, porosity in ROI 4 and ROI 5 settled around 20%, indicating minimal pore formation due to matrix oxidation. In this study, the thermal characteristics of the ceramic composite material NP-C/SiC for use in the TPS of reusable space vehicles were evaluated using a 0.4 MW AWT. The test results were analyzed to evaluate the thermal characteristics of the material. All specimens exhibited low post-test mass loss and recession, with NPCS-01 showing an increase in length due to the formation of a SiO2 layer. Internal temperatures measured were mostly below 1, 000°C. And a decrease in the average temperature was observed in the repeat test, attributed to the influence of the SiO2 layer formed on the specimen surface due to oxidation. Internal image analysis using micro-CT revealed that specimens exposed to higher heat flux environments showed an increase in porosity, with larger pores located primarily near the surface. In addition, a decrease in porosity was observed in specimens subjected to repeated testing. The results of this study are expected to provide critical data for the design and application of TPS in reusable space vehicles.