Research On Positioning/Attitude Algorithm Of Star Sensor For Ship Basing On Ineritial Measurement Unit

Star sensor is always called Star tracker.It uses a Charge-coupled Device to process picture.Star sensor can output attitudes of star sensor coordinate system relative to the celestial coordinate system directly by shooting and processing star image,without any external information as supplementary information.Star sensor becomes hot because of its obvious advantages.There are many features such as high precise attitudes,no error accumulation,independent from human factors,etc.These advantages make star sensor has a very high value in the modern high-tech warfare application and widely used in ships,aircraft,missiles and space vehicles,etc.Star sensor can export attitudes relative to inertial space directly without any external information.However,aiming at the object of ship,the information which is relative to inertial space is not enough,we are more concerned about the navigation information of carrier coordinate system relative to the navigation coordinates.So when star sensor is navigating,there is external information provided and INS is always the external auxiliary systems.Star sensor can determine the position of the carrier if there is external level attitude reference and it also can determine the attitudes of the carrier if there is external position information.When star sensor is positioning and determining attitudes,external level attitude reference and external position information are necessary,making it heavily dependent on the accuracy of information of inertial navigation system.However,because of the long sailing time of ship,the defect that error accumulation of INS makes its horizontal datum and location information provided can not meet the needs of the star sensor and the error of inertial navigation system will affect the star sensor navigation accuracy.So it is necessary to reduce the star sensor's dependence on INS or process the output of the star sensor,which will reduce the impact of the INS and improve the accuracy of star sensor positioning/attitude determination.Inertial measurement unit offers external auxiliary information for star sensor attitude determination and positioning.This paper takes this as entry point.The paper puts forward solutions and research methods around the problems of the navigation of the star sensor.Firstly,summarizes the domestic and international research results and development of SINS,CNS,SINS/CNS.Then we give the basal coordinates around the SINS and CNS of ship.Aiming at the coordinates we also give the converse relationship of coordinates and attitudes measurement principle of star sensor.Then the navigation methods of star sensor which isused on the ship is given,and combining with the propagation process and characteristics of the main error source of SINS,we put forward the shortcomings and deficiencies.Because star sensor's attitudes will be affected by errors of INS,this paper derives the relations between attitudes error of star sensor and errors of INS,and uses the Kalman filter to estimate and modify the attitudes error of star sensor,which will reduce the affection of INS and increase the accuracy of attitudes.At last,focusing on the effect that horizontal datum of INS makes on the star sensor positioning,combining with actual situation when ship is sailing on the sea and according to the "slow drift" of the gravity vector in the inertial space,the paper designs an adaptive digital filter to process the information of accelerometer and uses the information of gravity vector in the inertial system to determine a high precise level attitude reference.This method will increase the star sensor's positioning accuracy,avoiding the dependence on the INS when star sensor is positioning and it will greatly meet the long stable positioning requirements of navigation when ship has a long voyage at sea.