Abstract: A satellite attitude estimation system 20 includes a determination unit 21 which determines the maximum pixel, which is a pixel with the largest luminance, and the minimum pixel, which is a pixel with the smallest luminance, respectively, in an infrared image, which is an image taken by an infrared sensor of a target satellite that is a satellite whose attitude is to be estimated, an association unit 22 which associates the determined maximum and minimum pixels with coordinates on the 3D structure of the target satellite, respectively, a computation unit 23 which computes normal vectors for a surface including the coordinates associated with the pixel, respectively, over the coordinates associated with each pixel, and a sun direction estimation unit 24 which estimates the direction of the sun relative to the target satellite before the infrared image is taken using the computed normal vectors.