ESA's Dual concept is using ASTERM on SiCARBON and is manufactured by Joining of ASTERM and SiCarbon with adhesive: (a) Graphite, (b) Al2 O3, and (c) ZrO2 -ZrSiO4. The advantage is a hybrid structure that provides mass savings and enhancement of the dimensional stability of the heat shield (Figure 6)[10-12] . Processing and fabrication of dual layer (DL) TPS concept was adapted by KAI[8] (a) (b) Figure 5. (a) Photo of HEEET TPS material and (b) Close-up photo of HEEET TPS material showing infused high density carbon weave and infused low density blended yarn. . Nano ceramic was dispersed into UHTR (polysiloxane) resin with use of magnetic stirring and ultrasonication for ablator layer and loading study samples. The nano ceramic particles were used to promote char formation in the UHTR. Neat UHTR was used for the glass composites. Resin was applied to fiber using hot melt prepreg technique. Several 10-inch (25.4-cm) fiber squares are weighed and contained with peel ply. A measured portion of resin is added, and sheet is pressed at 150°C and 50 psi for 5 minutes. Carbon was cut into 0.5-inch (1.27-mm) squares while the glass was shaped to the size of the mold [5-inch (12.7-cm) squares or 3-inch (7.62-cm) discs] (Figure 7). Figure 6. SEM of cross-section of ASTERM and SiCARBON with adhesive. The KAI DL concept is carbon nanocomposite with tandem loading of 3 wt.% nano zirconia and 2 wt.% nano boron carbide as high-density ablator top recession layer. The nano zirconia and nano boron carbide are to promote char formation and to form a tougher char. Low-density glass composite is used as bottom support insulating layer. We used two joining methods: (a) join in layers through the molding process and (b) join with high temperature graphite adhesive. Figure 8 (a) shows the filled 5- x 5-inch (12.7- x 12.7-cm) steel mold used for composite fabrication and (b) shows the 30 mm in diameter and 15 mm thick DL carbon nanocomposite (top ablative layer) and glass polysiloxane composite (bottom insulative layer) joined via molding processing. III. THERMAL CHARACTERIZATION Initially, two types of thermal properties characterization were evaluated using Thermogravimetric Analysis (TGA)[13] Calorimetry (MCC)[14] and Microscale Combustion of the (a) neat resin and (b) Figure 7. Glass mat and carbon prepreg sheets (top) and white glass/ UHTR prepreg and carbon molding compound (bottom). NASA's HEEET is a 3D carbon woven with varying density infiltrated with a phenolic resin to reduce labor and allows for more complexity[9,10] . It uses ~30% ablator (top layer) and 70% insulator (bottom layer) by layer thickness. The advantages are: (a) Improved mass efficiency of 30-40% and (b) Facilitates different material properties by changing the weave pattern as shown in Figure 5. www. sampe.org virgin composite systems. Compression and shear char strengths are characterized for determining the relative strength of the char after OTB treatment. Eventually, the down selected TPS materials will require detailed thermophysical properties of virgin and char materials at elevated temperature for material response modeling in Section VI Numerical Modeling. A. Thermogravimetric Analysis (TGA) A thermogravimetric analyzer (TGA/DSC 1 STAR® System by Mettler Toledo) was used to compare the thermal stability and char yields of the MX4926N and CF/UHTR composites[13] . TGA measures weight loss of testing materials as temperature increases. MARCH APRIL 2024 | SAMPE JOURNAL | 29http://www.sampe.org