Study On Ship Attitude Measurement Based On Star Sensor

China’s spacecraft TT&C ship adopts the single station positioning systemwhich provides the platform for measuring equipment. Its measurements areconducted under the circumstances of dynamic conditions and the measuringequipment’s position and attitude are changing constantly, so, Synchronousmeasurement for both position and attitude of TT&C ship must be proceeded whenthe measuring equipment is tracking the target. Currently, our spacecraft TT&C isequipped with multiple navigation devices, such as Inertial Navigation Systems(INS), Global Position System (GPS), Celestial Navigation System (CNS) andDoppler Velocity Log (DVL) and so on. Each of these devices has their ownadvantages and disadvantages, but there is no any navigation device that couldcompletely meet with the mission requirements of the spacecraft TT&C ship.Star sensor is a high-precision attitude measurement device, and it is able togive high-precision attitude information with respect to inertial space and not driftwith time. Taking the fixed star as frame of reference, Star sensor is a high-precisionspatial attitude measurement device working with starry sky as objects, whichpossesses the ability of autonomous navigation, and makes calculations throughdetecting the stars at different locations on the celestial sphere.In this paper, the research object is ship attitude measurement system based onstar sensor, and the main purposes of this research are: Firstly, establish a mathematics model for ship attitude measurement based on star sensor, in order toprovide theoretical guidance for systematical realization; Secondly, design a shipattitude measurement system based on dual-star-sensor and testify relativealgorithms and designs.The paper also puts forward the static ship attitude computing method, thecorresponding coordinate transformation model and astronomical refractioncorrection model and compares various algorithms such as TRIAD algorithm,FOMA algorithm, QUEST algorithm base on Gaussian Elimination and the QUESTalgorithm based on the Newton-Raphson Iteration and so on.To improve ship attitude measurement precision based on star sensor and solveproblems of low measurement precision of roll angle by a single star sensor andinability to calculate attitude with no more than three stars in view field of a singlestar sensor, this paper comes up with a attitude measurement algorithm on acombination of double star sensor on the basis of “view-field spliced” and proceedsto deduce its model of such algorithm concerned.In order to improve the precision of measured data of measuring equipments inthe Spacecraft TT&C ship, filtering processing for ship attitude data based on starsensor is essential. According to the nonlinear and non-Gaussian characteristics ofship attitude data, the paper proposes a ship attitude data processing algorithm baseon a wavelet-domain hidden Markov model, and achieves a higher accuracy.To testify the correctness and accuracy of star point extraction algorithm in real-time image processing system, in term of the low signal to noise ratio, groundparasitic light or light cloud of the real star map, this paper raises a star map adaptiveclutter suppression method adopting the Kernel Rayleigh Quotient QuadraticCorrelation Filter to conduct the post-handling for the real star map and achievesexcellent results.To improve the measurement precision of star sensor is namely to improve thesingle star measurement precision. The calibration accuracy of parameters like mainpoint, focal length and the imaging distortion of optical system directly affect the angle measuring accuracy of star sensor. As to the requirements of single starmeasurement precision of star sensor in this project, new precision calibrationmethod is adopted to precisely work out focal length and main point of star sensor;as to the optical image distortion, a partition processing method is employed topromote the optical distortion correction match to the quadratic fitting in order toobtain a higher level of precision.This paper makes a systematical design based on the previous work, builds ahardware platform and completes designs and programming of related software.After system associated debugging, this paper completes the parameter calibrationsof star sensor and installation matrix calibration of star sensor in dockyard, andconducts stellar experiments, and makes analysis on the experimental data, thusverifying the validity of the measurement method and feasibility of the plan in thispaper. A large quantity of measurment experiments of TT&C ship proves that thissystem meets the ship attitude measurement requirements and basically achieves theexpected goal.