Research On Key Technologies Of CCD Star Sensor

The star sensor is the highest accuracy and the most advanced technology ofattitude sensitive equipment. It has such as high precision, high sensitivity, noattitude accumulative error advantages to make it become the most popular attitudesensors. This article based on the actual star sensor production projects researchesthe key technology of CCD Star Sensor about CCD (Charge Couple Device) drivedesign, star coordinate extraction and attitude algorithm. Main work are as follows:The design scheme of hardware circuit of star sensor electrical parts is given.Itincludes four parts,which are photoelectric conversion, timing driving, Image signalprocessing and power supply.Design the CCD drive.Accurate and cooperate timing signal is the key forspreading the image signal successfully.Timing driving can be divided intohorizontal shift register timing driving and vertical shift register timing driving twoparts.Take complex programmable logic device combined with hardware descriptionlanguage method to achieve it. Use the mean of Binning improves signal-to-noiseratio. Put forward the method of finite state machine to generate the proper CCDtiming driving signal. Through the simulation test and experimental verification, theresult proves that the timing driving signal fully complies the requirement of CCD.The image signal could be transmitted successfully.The key algorithm of target star extraction is analyzed. High precision starextraction is the basis of the fast star map recognition and high precision attitudecomputation. Combining with the traditional algorithm and star map featuresproposes an improved centroiding method. This method takes the adaptive thresholdfor calculating the threshold value method and eliminates the influence of the star inthe process of calculating the background threshold. The threshold is more accurateand closer to the real background threshold. After comparing it with other twomethods, the result proves that the proposed method has higher precision and is easyto realize in the star sensor.Do some researches on the attitude determination algorithm. Attitudecomputation directly influences the star sensor output attitude accuracy and updaterate. In the aspect of static attitude determination, several kinds of typical methodswhich are Triad，Q-，Quest are analyzed. And utilize an example to compare with theprecision of each method. In the aspect of dynamic attitude estimation, introduce thePredictive Kalman filtering algorithm to the attitude estimation of the star sensor.The method estimates the attitude through the Kalman filtering and the error ofdynamics model through the Predictive filtering. Through the simulation to validate the attitude estimation algorithm is better than the tradit ional EKF in the aspect ofaccuracy, convergence speed and model error allowance. Do theoretical analysis andsimulation analysis for the selection of the weighting matrix and give thequalification of the matrix.The precision of star sensor is analyzed. The limitation vectors of the precisionare given. Find out the error source. Also the math expression of the whole error isderived. Establish the overall error model. Introducing how to calibrate the starsensor in the situation based on the laboratory observation and zenith observation.At last, do the simulation precision test for the whole star sensor system.