The internal parameters of star sensor such as focal length

principal point and focal plane distortion change after putting into use due to the impact of lunch

space circumstance

aging

etc. Therefore

the precision of attitude measurement decreases. As a kind of key technique to maintain high performance of star sensor during flight

autonomous on-orbit calibration is needed to correct the changed internal parameters. Independent of external attitude

an on-orbit calibration method of star sensor based on RAC (Radial Alignment Constraint) is proposed in this paper. Imaging model of star sensor is established according to radial alignment constraint firstly. Then

external and internal parameters are calculated from a single sky image using a two-stage method

and optimal solution of internal parameters is achieved from global optimization of multiple sky images. Simulation indicates that the proposed method can eliminate the coupling between external parameters and internal parameters effectively

and calculate these parameters precisely.