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.
Compensation Method of Dynamic Angle Measurement for Missile-Borne Star Sensor
A compensation method of dynamic angle measurement is proposed to solve the image motion question for star sensor caused by the attitude change during measuring.Firstly,the mathematical model of star point pixel gray distribution is established when the star point being on constant velocity straight line motion relative to the photosensitive surface of image sensor.Secondly,the principle and method of angle measurement compensation is presented.Thirdly,the results of simulation experiment show that the compensation method is not sensitive to star point velocity on the photosensitive surface of area array image sensor.The compensated dynamic angle measurement error is almost the same as the static angle measurement error.The maximum compensated dynamic angle measurement error is 2″.
Fast all-sky autonomous star identification
An improved star identification algorithm based on the traditional triangle method is proposed in this paper to overcome the low character dimensions and high percentage of redundant matches in star identification.When a triangle is recognized by a labeling method,the fourth star is introduced as a vertex to make up a tetrahedron with the triangle,and the accessorial angular distances among them can be used not only as the supplementary character to reduce redundancies,but also to verify whether the result is correct.The proposed algorithm takes the angular distance as the main identification character and relative magnitude information as the assistant character,so that the capacity of guide star database decreases to 0.4 Mb.During star-pair matching,the hashing search is used to construct the function for identification characters to reduce travelling times and time consumption for the guide star database and to speed up the identification process,and the average identification time is 0.43 ms.The result of simulation demonstrates that the improved identification algorithm has advantages of high identification efficiency and short identification time in the all-sky autonomous star identification.