THIS PROPOSAL ADDRESSES TOPIC 6 OF THE SPACETECH-REDDI-2015 EARLY STAGE INNOVATIONS (ESI) ENTITLED ATMOSPHERIC ENTRY MODELING DEVELOPMENT USING ORION EFT-1 FLIGHT DATA. THE OBJECTIVE IS TO DEVELOP IMPROVED THERMAL RESPONSE MODELS OF THE AVCOAT THERMAL PROTECTION SYSTEM (TPS) FROM FIRST PRINCIPLES AND TO VALIDATE THE RESULTS OF THESE MODELS WITH MEASURED IN-DEPTH TEMPERATURE AND CALORIMETER DATA FROM EFT-1 AND ANY AVAILABLE RADIOMETER DATA. TRUE HIGH-FIDELITY POROUS TPS MODELING IS NOTORIOUSLY DIFFICULT. CURRENT FIAT STAB AND CHAR MODELS FROM THE 1960S ERA RELY ON CONTINUUM CONSIDERATIONS OF BOTH THE FLOW RATE AND MATERIAL RESPONSE. HOWEVER THE DECOMPOSITION OF THE POROUS TPS MEDIA INVOLVES COMPLEX MULTI-COMPONENT AND CHEMICALLY REACTING GAS FLOW WITH KNUDSEN NUMBER IN THE TRANSITIONAL REGIME; THE HETEROGENEOUS THERMOCHEMICAL REACTIONS CAUSES GRADUAL RECESSION OF BOTH THE FIBERS AND RESIN WHICH MAKE UP THE TPS MATERIAL. TO ACHIEVE NEW BREAKTHROUGHS IN OUR PREDICTIVE CAPABILITIES NEW NON-CONTINUUM APPROACHES THAT ACCOUNT FOR THE EVOLVING MICROSTRUCTURE OF THE TPS MEDIUM AS WELL AS THE ABLATION PHYSICS AND CHEMISTRY AT THE ATOMIC LEVEL ARE REQUIRED. HERE WE PROPOSE TO CREATE A TPS RESPONSE MODEL BASED ON KINETIC-PARTICLE SIMULATIONS OF BOTH GAS TRANSPORT AND CHEMISTRY. LARGE-SCALE MASSIVELY-PARALLEL MOLECULAR DYNAMICS (MD) SIMULATIONS WILL BE USED TO CHARACTERIZE THE ABLATION CHEMISTRY AND THE RATE OF VOID FORMATION IN AVCOAT. USING INFORMATION PROVIDED BY THE MD MODELING DIRECT SIMULATION MONTE CARLO (DSMC) SIMULATIONS WILL BE USED TO MODEL GAS TRANSPORT HEAT TRANSFER AND TPS MATERIAL REGRESSION AT THE MESOSCALE LEVEL. THE MACROSCOPIC MATERIAL PROPERTIES DERIVED FROM DSMC WILL BE USED IN A ONE-DIMENSIONAL MACROSCOPIC HEAT TRANSFER MODEL TO ENABLE DIRECT COMPARISON WITH THE EFT-1 DATA. THIS HIGH-FIDELITY MULTI-SCALE APPROACH WILL SIMULATE THE PENETRATION OF REENTRY-FLOW ACTIVE CHEMICAL SPECIES INTO THE VOIDS OF THE COMBINED RESIN/FIBROUS CHARRING ABLATOR AVCOAT MODELING AT THE KINETIC LEVEL THE PYROLYSIS GAS FLOW AS IT PERCOLATES THROUGH THE POROUS MEDIUM TOWARDS THE TPS SURFACE. UNLIKE TRADITIONAL APPROACHES FOR MODELING POROUS MEDIA OUR PROPOSED NOVEL GRID-FREE DSMC METHOD CAN ACCURATELY ACCOUNT FOR BOTH HOMOGENEOUS AND HETEROGENEOUS CHEMISTRY INSIDE THE COMPLEX-SHAPED TPS MATERIAL AND AT THE SAME TIME ACCOUNT FOR THE TRUE MATERIAL MORPHOLOGY. IN ADDITION THE APPROACH WILL ALLOW US TO CAPTURE THE DETAILED PHYSICS OF THE CHARRING ABLATOR-BOUNDARY LAYER FLOW OCCURRING OVER THE RANGE OF LENGTH SCALES FROM CHEMICAL REACTIONS AT THE ATOMIC-SCALE TO STRUCTURAL-THERMAL RESPONSE AT THE MACROSCOPIC LEVEL. THE INFLUENCE OF RADIATION AS A MECHANISM FOR ENERGY REMOVAL DURING THE VOLUMETRIC ABLATION PROCESS WILL BE ACCURATELY MODELED WITH THE NEW GRID FREE DSMC TOOL CHAOS. THE POSSIBILITY OF USING THE RADIOMETER MEASUREMENTS OBTAINED FROM THE EFT-1 FLIGHT TO CONFIRM BLOWING SPECIES TEMPERATURES AND MOLECULAR COMPOSITION WILL ALSO BE EXPLORED. WHILE FOCUSING ON AVCOAT THE FUNDAMENTAL KINETIC-PARTICLE MODELING FRAMEWORK CAN BE APPLIED TO A VARIETY OF OTHER POTENTIAL TPS MEDIA ALLOWING NASA THE ULTIMATE FLEXIBILITY AND CONFIDENCE TO CHOOSE THE REQUIRED TYPE AND MINIMUM QUANTITY OF TPS MATERIAL FOR ATMOSPHERIC ENTRY.