Abstract
Star trackers are currently the most accurate spacecraft attitude sensors. As a result, they are widely used in remote sensing satellites. Since traditional charge-coupled device (CCD)-based star trackers have a limited sensitivity range and dynamic range, the matching process for a star tracker is typically not very sensitive to star brightness. For active pixel sensor (APS) star trackers, the intensity of an imaged star is valuable information that can be used in star identification process. In this paper an improved brightness referenced star identification algorithm is presented. This algorithm utilizes the k-vector search theory and adds imaged stars' intensities to narrow the search scope and therefore increase the efficiency of the matching process. Based on different imaging conditions (slew, bright bodies, etc.) the developed matching algorithm operates in one of two identification modes: a three-star mode, and a four-star mode. If the reference bright stars (the stars brighter than three magnitude) show up, the algorithm runs the three-star mode and efficiency is further improved. The proposed method was compared with other two distinctive methods the pyramid and geometric voting methods. All three methods were tested with simulation data and actual in orbit data from the APS star tracker of ZY-3. Using a catalog composed of 1500 stars, the results show that without false stars the efficiency of this new method is 4∼5 times that of the pyramid method and 35∼37 times that of the geometric method.
Highlights
Star trackers are the most accurate attitude sensors for spacecraft attitude determination [1] and are typically used on space missions that have requirements for precise attitude knowledge
This paper presents an improved star ID method based on an existing search technique
An efficient and robust star identification algorithm is presented in this paper that utilizes star brightness to narrow search scopes
Summary
Star trackers are the most accurate attitude sensors for spacecraft attitude determination [1] and are typically used on space missions that have requirements for precise attitude knowledge. After taking photos of the stars, star trackers locate and identify the stars in the image. Using this information, the spacecraft’s inertial attitude can be determined [2]. This paper presents an improved star ID method based on an existing search technique. This method employs the intensity of imaged stars to increase the matching efficiency. Sections 1~3 introduce background information on the star trackers used for data collection as well as existing centroiding and star ID algorithms.
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