Star extraction method for star sensor at a high angular rate
When a star sensor slews at a high angular rate, the stars in the sensed image are smeared out over many pixels, which results in a decreasing signal-to-noise ratio (SNR). Therefore, the faint stars are not capable of being detected, and the centroidal precision of the bright stars decrease when using traditional image threshold segmentation algorithm and centroid method. In this paper, we propose a method to obtain accurate star location for star sensor at a high angular rate. We first utilize Laplacian to segment the star image, and then each pixel is marked after it is compared with the neighbouring one. Finally, the centroids of stars are calculated by using target pixels, and the centroiding errors are compensated. The experiment results illustrate that the proposed technique can extract more stars than other traditional methods under the condition of high angular rate, and also can improve the locating precision of star effectively.
New Ball Aerospace star tracker achieves high tracking accuracy for a moving star field
Star tracking at Ball Aerospace has reached a new level of performance with the development of the High Accuracy Star Tracker (HAST). This new tracker builds on the experience gained from the Chandra Aspect Camera which attained better than 0.2 arc-seconds on-orbit overall performance with a stationary star field. The HAST is optimized to achieve similar performance on stars moving between 0.07 and 1.0 degrees/second and can maintain track on stars moving 0 to 4 degrees/second. HAST is capable of tracking multiple stars, further enhancing the accuracy performance. This paper examines the principal error components that affect star tracking accuracy. We further examine the physical basis for three error sources: 1) boresight alignment bias, 2) transit dependent bias, and 3) random measurement. We develop the design trade space used to optimize tracker performance within these error constraints. Finally, we present the working specifications for HAST, describe the HAST implementation, and review the flight qualification test results.
Star Map Identification Based on a Modified Triangle Algorithm
With 486 partitions,an equal partition method of celestial sphere without overlap is firstly presented to speed up guide star indexing.And then star angular distances are directly stored according to their length in- creasing.The star angular distances are matched quickly by labeling status for the star angular distances.Final- ly,a verification identification is used to solve the redundancies of the observed star triangle and the mapped navigation star triangle.Simulation is carried out,and shows that the algorithm proposed in this paper has the advantage in terms of robustness against the star position noise and star magnitude noise.Also the identification rate and the storage requirement are improved by the algorithm,as compared with the conventional triangle al- gorithms.