A Recovery Algorithm of Star Energy Distribution for Star Sensor under High Dynamic Condition

Under the condition of high dynamic, there is a pixel shift phenomenon which is called smear in the star image sampled by star sensor. The recovery algorithm of star energy distributing for star sensor is presented in the paper. The quaternion of next frame is calculated with the previous continuous quaternion. All the ideal star coordinates of star image in the FOV is calculated with the quaternion of next frame. Then the angle between the two previous continuous axis directions is calculated with the previous continuous axis directions calculated with the previous continuous quaternion. The radius of threshold scan window of star image is calculated according to the angle. Finally, within the star image radius of the threshold scan window, shift the original star image to make the shifted star energy distribution continuous. So the star image distribution subjects to 2-D Gaussian distribution, and the star coordinates is obtain with centroiding algorithm. A star sensor featuring a recovery algorithm of star energy distributing for star sensors proposed in this paper was for demonstration at night sky experiment.

An Autonomous Predictive Centroiding Algorithm for Star Sensor

Of all current methods for measuring spacecraft attitude, the use of star sensors produces the most accurate measurements. Conventional star sensors repeat these processes with Lost-In-Space case. To advance the methods available to solve these problems, this paper presents an autonomous predictive centroiding algorithm for the star sensor. The star sensor works in the star predictive centroiding case while few recognized stars within the FOV (Field of View). The ideal locations of unrecognized stars and recognized stars in star image are predicted at first. Then the corresponding real locations of recognized stars and unrecognized stars are obtained in the threshold scan window of predictive centroiding. It enables only several hundred pixels to be scanned. The speed and the accuracy of this algorithm are successfully demonstrated in comparison with the ordinary centroiding algorithms which don't use the previous image data. Finally the autonomous predictive centroiding algorithm was successfully demonstrated with real sky experiment in 2008 and on-orbit in 2010.