Sun sensing on the Mars exploration rovers

NASA will send two identical scientific rovers to different locations on Mars in 2003. Two Panorama Cameras (Pancams) are included in the nine cameras on each rover. One function of these Pancams is to image the Sun in order to determine its vector relative to the rover. The vector is determined by centroiding the solar image. This vector is used, in combination with information from an inclinometer, a clock, and ephemeris data, to determine north, and to point the high gain antenna at Earth and provide a reference for the inertial measurement unit that is used for rover navigation. The Pancams, their detectors, optics, electronics, and the Sun detection/centroiding algorithm are described. The required accuracies are shown and an error budget is constructed to demonstrate that the Pancam meets these requirements. The functions and performance of the Pancams are verified at a dedicated solar observing facility. The facility, its calibration, and the transformation of the intensity and angular subtense of the Sun at Mars, are described.