Radiative heating predictions for Huygens entry

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, C₂ Swan, and at early trajectory points by the first and second positive systems of N₂. 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.