Carbon-carbon composites are candidate materials for the conception of the thermal shield of the "Solar Probe" space mission. To understand their behavior under solar aggressions and know the possible interactions with the shipped-in instruments, these materials were tested in a facility that allows to partially simulate the solar environment and to carry out in situ measurements. In this paper, we present the experimental results obtained for the alpha/epsilon ratio, i.e. the ratio of the solar absorptivity a to the total hemisherical emissivity E that controls the thermal equilibrium of the thermal shield. The objective is to find the lower ratio alpha/epsilon in order to have the lowest temperature on the shield at 4 solar radii. (c) 2006 Elsevier B.V. All rights reserved.