Imaging position error compensation of scan mirror for spacecraft

An imaging position error compensation algorithm was proposed for a two-degree-of-freedom scan mirror of a geostationary spacecraft. The investigation aimed to eliminate the detecting area error on the earth surface by compensation of the mirror scanning angles. The formulas for calculating the geocentric longitude and latitude of the imaging point were deduced in which three types of errors, the mirror normal deviation, satellite attitude error and orbit error, were considered. Then the descriptions of the error sources were presented, and the effects of the errors on the imaging point position were analyzed. Based on the small quantity assumption of the angular errors, the compensation algorithms for east-west scanning angle and south-north stepping angle were proposed in explicit formulations. As the normal deviation was difficult to be measured accurately, an estimation algorithm for normal deviation was proposed based on the ability of accurate orientation determination of the optical axis in special operation mode and the long-period characteristic of the normal deviation. The simulation results indicate that the proposed compensation scheme and algorithm improve the imaging position accuracy evidently.