Numerical rebuilding of two trajectory points ( ？s and ？s) of the Fire II mission has been carried out to predict the radiative heat flux for nonequilibrium and close-to-equilibrium conditions. The simulations have been performed with eilmer3 in an uncoupled way and using a tangent slab method for the radiation transport. Different population models (QSS and Boltzmann) have been compared, and the influence of catalytic wall condition was taken into account. An analysis on the spectral range and on the spectral resolution has also been carried out. 1. Introduction During atmospheric (re)entries, planetary probes encounter high heat fluxes due to their significant speed (up to 11？km/s for an Earth reentry). Such excessive thermal loads can damage the on-board equipment and compromise the safety of the passengers in case of a manned-flight mission. As a consequence, the sizing of the thermal protection system (TPS) is a crucial step in the preliminary design study of a probe. The Fire II mission took place in May 22nd, 1965 [1]. Its main goal was the assessment of the radiative heating environment during an Earth reentry. The vehicle geometry was an Apollo type with a reentry velocity of 11.4？km/s. The fore body consisted in a three layer configuration formed by phenolic-asbestos heat-shield sandwiched between beryllium calorimeters. The contribution from the radiation of the hot plasma to the total heat flux received by the probe was up to 40%. This paper concentrates on this radiative contribution. The reconstruction of radiation spectra for the Fire II experiment has been already discussed in numerous papers [2–4]. Two points of the trajectory of the Fire II mission have been numerically rebuilt. The first one at ？s corresponds to nonequilibrium conditions whereas the second one at ？s is close to equilibrium conditions, even if a small region behind the shock is nonequilibrium. Figure 1 gives the temperature profiles of the translational-rotational temperature and the vibrational-electronic temperature for the two simulations. Figure 1: Temperature profiles on the stagnation line for the two trajectory points. In this work, the code retained for the simulations is eilmer3, a multiblock compressible Navier-Stokes solver described in Section 2. Section 3 is dedicated to the results of the simulations. An analysis of the spectral range has been performed to assess the wavelength range of interest and the number of points needed for a good accuracy. Then two different population models (QSS and Boltzmann) have been compared and the influence of the
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