The purpose of the Launch Thermal Analysis is to check the thermal compatibility Spacecraft/Launcher during stand-by on ground and flight up to injection into transfer orbit.This paper first presents briefly a typical spacecraft thermal model. It then reveals the method used to integrate the payload numerical model into the launcher upper section model.The attention is turned on the determination of the air flow inside the fairing taking into account the complexity of the velocity field induced by the fairing ventilation. This part puts forward examples of typical velocity fields used to determine the convective coefficients and to check the maximal velocity criteria on payload.Regarding trajectory parameters, the treatment of the various attitudes depending on the mission characteristics is possible using a Monte Carlo ray-tracing technique. This hence allows an accurate determination of the radiative external loads encountered during flight.Software aspects are discussed pointing out the possibility of developing automatic calculation chains.Typical thermal behavior during ground and flight phases are shown. In addition, results are given based on the measurements campaigns carried out during launch. These are compared to the predicted temperature levels.An accuracy close to 3°C is obtained for critical equipment.Although the ARIANE thermal analyses are described, informations are given based on the heritage of SOYUZ thermal studies.The aim of this paper is finally to give a presentation of the main physical phenomena encountered during a launch mission and to assess how their thermal impact on the payload is treated in the scope of the ARIANE launch programme.