Research On Integrated Orbit And Attitude Determination For Small Satellite And Formation

Autonomous state determination is the basis of satellite control. Due to the strictlimits of weight and cost, there are always few sensors on small satellite. So how to makefull use of the limited sensor resource to accomplish orbit and attitude determination,improve determination accuracy, and then improve the functional density of smallsatellite has become a hot and difficult problem in the field of aerospace. Under thebackground of orbit and attitude determination for small satellite and formation, thisdissertation focuses on autonomous state determination for single satellite andrelative/absolute state determination for formation satellite. The major contents of thisdissertation consist of the following parts.To make full use of earth magnetic field measurement data, an orbit and attitudecoupled determination method is proposed based on traditional separate processing mode,which combines sequential and parallel modes for orbit and attitude determination. Wheninitial estimation error is large, orbit and attitude are sequentially determined in thesequential mode to ensure the convergence. Then they are synchronously determined inthe parallel mode both using earth magnetic field vector measurement when theestimation error becomes small enough, which improves the estimation accuracy.Meanwhile, an innovation-based robust Kalman filter is designed to reduce the influencebetween the orbit and attitude determination systems through adjusting the Kalman gain,which improves the determination accuracy and enhances the robustness of the system.Considering the coupling between orbit and attitude from satellite motion andsensor measurement, coupled dynamic model and measurement model are established,and a multi-rate-based integrated orbit and attitude determination algorithm is proposed.System observability is analysed based on local observability theory, and degree ofobservability is analysed through condition number and singular value decomposition ofobservability matrix, which can verify the feasibility in theory for integrated orbit andattitude determination. In order to avoid the large computation induced by the increase ofsystem dimension, a multi-rate filter is introduced. At the short-period sampling time, aSchmidt-EKF is adopted to estimate attitude and propagate orbit. While at the long-period sampling time, a unified Kalman filter is used to estimate orbit and attitudesimultaneously. Simulation results indicate that this method can reduce computation loadeffectively with guarantee of estimation accuracy.Regarding to deputy sensor measuring direction vectors of different beacons onchief, a Gauss second-order Kalman filter is proposed to determine the relative positionand attitude for formation satellite. For relative state estimation of the point apart from the center of mass on deputy, a coupled relative translational and rotational dynamics isestablished, and an UKF algorithm is proposed to estimate relative position and attitude.Besides, the influence of relative distance, number of beacons and their distribution onestimation accuracy is analysed through the traces of the Fisher information matrix anderror covariance matrix. These can lay the foundation for vision-based relative statemeasurement system design and application for formation satellite.For the absolute state determination of formation satellite with magnetometer, gyroand relative measurement, federated filter and two-step filter are designed respectively toestimate the absolute orbit and attitude of formation satellite based on integrated orbitand attitude determination method for single satellite and relative state estimation methodfor formation satellite, both of which improve the reliability and fault tolerance undercondition of guarantee of estimation accuracy. State estimation with sensor failure is alsoinvestigated. When deputy magnetometer fails, a chief and deputy state sequentialdetermination scheme is proposed based on a spherical sampled UKF, thus thecomputation load is reduced. In view of the magnetometer failure of both satellites, thefeasibility of absolute orbit determination only based on relative measurement is analysed.These researches can provide a viable approach for absolute orbit and attitudedetermination of formation satellite with limited measurement.