Due to the elliptical shape of Mercury’s orbit and the slow planetary spin rate, Mercury has a large surface temperature difference that creates highly variable spacecraft thermal environments that are a function of both planet solar distance and spacecraft orbit plane position. Being able to analytically simulate the severe thermal environments experienced by a spacecraft over the lifetime of a Mercury orbiting mission make it possible to realize a feasiable spacecraft thermal design.The analysis described throughout this paper was used to characterize the temperature response as a function of initial phase angle conditions (αρ) when referenced at Mercury perihelion for a 3-axis stabilized spacecraft. Variables in the analysis include solar distance, argument of periapsis, and αρ. The selected orbit is highly elliptical, with a 720-minute period and a near polar inclination. Analysis results presented in this paper are specific for the spacecraft configuration, orbit geometry and inclination used, but the analytical techniques described can be applied to any spacecraft configuration, orbit geometry or inclination.