Radiative heating predictions for Huygens entry

Abstract

[1] Radiative heat flux predictions for the Huygens probe entry into Titan's atmosphere are presented in this paper. Radiative heating was computed with the radiation code SPECAIR, assuming a Boltzmann distribution of the excited electronic levels at a characteristic temperature taken as the vibrational temperature of the gas. CN violet is found to be the most intense emitter, followed by CN red, C 2 Swan, and at early trajectory points by the first and second positive systems of N 2 . Solutions of the 1-D radiative transport equation along stagnation streamlines show that self-absorption by the plasma layer reduces the total emission by up to about 20%. The fine structure of the CN violet spectra (spin-splitting) was taken into account to accurately determine self-absorption by CN violet. The potential importance of argon radiation was estimated and shown to be negligible. The resulting fluxes were found to be sustainable by the Huygens's Thermal Protection System. The feasibility of the mission was deemed possible under the updated entry parameters and atmospheric composition.

Uncertainty Quantification in Computational Science

“…Caillault et al [31] showed using Boltzmann distributions in thermo-chemical nonequilibrium, that the radiative heating during entry of Huygens probe is primarily attributable to the CN violet system [transition CN(B → X)] and to a lesser extent to the CN red system [transition CN(A → X)]. Hence, an important aspect of this work is the direct assessment of radiative heat flux from the CN populations for which we propose a simplified model for the intensity based on the CN number density.…”

Radiative Heat Transfer Measurements in Low-Density Titan Atmospheres

“…To investigate this assumption, the line-by-line radiation model Specair [30] was used to calculate the absorption coefficient of the test gas at each of the three test conditions. The Specair model was extensively tested and found to provide accurate predictions of the radiation of Titan mixtures [9].…”

“…However, there is a significant level of disagreement between the models and the published experimental data, which creates a need for further data across a wider range of conditions. At gthe peak heating point of the Titan entry trajectory, the CN radical formed by the dissociation of atmospheric methane and nitrogen is the dominant radiator [8][9][10][11]. Recently, a number of shock tube facilities have been used to investigate the radiative emission in Titan mixtures.…”

Systematic validation of non-equilibrium thermochemical models using Bayesian inference

“…In order to model the EAST experimental setting, we will use the one-dimensional, shock-fitting Euler code Shocking [13][14][15] that simulates the shock-tube flow field by solving the Rankine-Hugoniot (RH) jump equations to determine the post-shock conditions -i.e. by solving the conservation equations of mass, momentum, and global energy across the shock.…”