Research On Orbit Coordination And Beam Synchronization Control Of Distribited SAR Under Communication Constraints

Spaceborne synthetic aperture radar(SAR)is one of the most important means of earth observation.With the rapid development of small satellite and its formation technology,distributed SAR satellite formation system has attracted more and more attention because of its unique advantages and broad application prospects.In distributed SAR system,formation configuration design,orbit configuration maintenance and beam synchronization control are the main contents of the current research.Under the background of certain tasks,the above key issues will be studied in this paper.Firstly,the formation mechanism of spacecraft formation is introduced,and two formations are designed for ground moving target detection(GMTI)mission.The basic concept,the related coordinate system and the formation configuration parameters of the satellite formation are briefly explained.For the GMTI mission,the along track formation and space symmetry formation are proposed.The formation configuration parameters are optimized by genetic algorithm,with the velocity ratio and the aging ratio as the performance indexes.Then,the optimized formations configuration are analyzed,and the performance advantage of the multi baseline distributed SAR system is proved.Then,considering the satellite communication delay and external disturbance,a six degree of freedom(6-DOF)controller with coupled attitude and orbit is designed.The 6-DOF relative motion equation and the equation of motion about the state error are derived from the dynamics and kinematics equations of the spacecrafts relative motion.In the presence of communication delay and external disturbance,a 6-DOF cooperative control method for coupled attitude and orbit is proposed.And the numerical simulation of the coupled attitude and orbit control method is carried out with the optimized formation configuration above.It is proved that the control method has good effect on the maintenance of the orbit configuration and the attitude consistency control.Finally,considering the communication delay,external disturbance and model uncertainty,a beam synchronization control method is designed.The two beam synchronization modes of Doppler guidance and beam pointing synchronization are introduced,and the main satellite taking Doppler guidance and the following satellites taking beam pointing synchronization with the main satellite are adopted as the control strategy in this paper.The desired attitude of the spacecrafts under the control strategy is derived,and a sliding mode robust control method based on the inverse optimal control is proposed.The numerical simulation of the control method is carried out in the case of communication delay,external disturbance and model uncertainty.It is proved that the control method has high precision of beam synchronization control and also has a certain advantage in fuel consumption.