Accurate attitude information is necessary for advanced space missions. Among existing instruments providing attitude information to spacecraft control systems, star trackers are most accurate for attitude estimation without requiring a priori information. For use of the star tracker data, it is required to identify stars in the field of view (FOV) of a star tracker. Many algorithms for star identification have been developed to determine the correspondence between the imaged stars and the reference stars stored in onboard star catalog. However, few algorithms could realize a robust star identification with the small amount of memory. This paper presents a new algorithm that, by using a defocused onboard star catalog, realizes a robust star identification with the small amount of memory. The robustness of this algorithm is evaluated by the sky simulation. The sky simulation results demonstrate that the proposed algorithm is a robust star identification method with the small amount of memory and suitable for the charge-coupled device (CCD) star tracker with a small FOV.
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