A bootstrap filter algorithm, which uses a sequence of the number of stars to estimate the attitude of a spinning object, is presented. This choice of measurement makes the algorithm practicable to apply to the spinning object without any initial acquisition lock. The statistical model of measurement is derived and incorporated to make a star-density map. The conic fitting method is used to obtain measurements in the star sensor images. The simulation result is presented which demonstrates the ability of attitude estimation and the fast convergence property of the proposed algorithm.