A computational method capable of calculating radiative heat transfer in a porous carbon-based material is developed in this study. In the method, a radiative conductivity value is statistically evaluated using a three-dimensional model of the material constructed using X-ray computed tomography images. The method is applied for thermal response analysis of a non-ablative heat shield called the Non-Ablative Lightweight Thermal protection system (NALT), which is heated in an arcjet flow. The arcjet heating environment is calculated in a coupled manner between nonequilibrium arcjet flow computation and NALT thermal response analysis. The results shows that the computational method developed satisfactorily reproduces the surface and in-depth temperature data measured.