The objective of this study was to determine temperatures that would be experienced by a solar-sail designed at Virginia Tech for a journey to Mars. Knowledge of these temperatures is necessary in the design process of the spacecraft. The temperatures are determined for thermal equilibrium cases during spirals around Earth and Mars. To verify the validity of the equilibrium temperatures the cool-down times are calculated, i. e., the time periods needed for the sail and hub to cool down from a certain temperature to an equilibrium temperature after a sudden change in the thermal environmental conditions (e.g. at the Earth shadow entry point). This calculation shows that the cool-down for the sail requires a very small amount of time, so that the procedure of estimating the temperatures in thermal equilibrium cases is a reasonably good assumption. The hub cool-down, however, needs much more time so that the hub shadow temperatures are probably higher than the equilibrium temperatures. Because of their high dependence upon material properties, the temperatures are calculated for three different sets of parameters and presented in graphs and tables. Furthermore, the temperatures which would occur during a heliocentric transfer are calculated. These temperatures are dependent upon the distance from the sun and the angle of incidence of the sun rays. The results show how close to the sun a solar sail may travel without experiencing any damage. Suitable sets of material properties for the sail are presented in this report. Finally, the temperature distribution over the hub is determined. This distribution is needed to determine the heat exchange between the hub and the equipment contained in the hub. The chosen passive thermal control of the hub (coating) ensures temperature ranges which make it possible to accomplish this mission without a cooling system. However, due to the non-uniform temperature distribution over the hub, the heating system, which is needed for the hub, needs to be capable of | distributing the heat non-uniformly. That means the system must supply the bottom and top part of the spacecraft with different amounts of heat. The maximum energy which is needed at Mars is approximately 35 W. No heating will be needed at Earth.