A low earth orbit satellite with a fixed solar array always has a sun-pointing attitude during daylight, and changes into a nadir-pointing attitude for a imaging mission. Since external heating sources to the satellite panels are Earth　irradiation and Albedo during most of daylight in a sun-pointing attitude, the thermal environment condition is relatively stable. However, direct sunlight which is the greatest environmental heating has an affect on the satellite panels during a mission period (10% of one orbit) in a nadir-pointing attitude. In satellite thermal design, thermal effects of a nadir-pointing mission attitude due to this thermal environment change need to be evaluated although the duration of a nadir-pointing attitude is short. Therefore, a nadir-pointing attitude during a mission is incorporated into thermal model and by the thermal analysis result, thermal effects on the satellite are investigated.