| Tethered Satellite System(TSS)is a satellite system that contains two or more satellites connected by electrodynamic tethers or insulated tethers.TSS could be used widely in many aerospace fields including space travel and on-orbit servicing.Recently,Rendezvous and docking with tethered satellite is one of the hottest fields in aerospace research.Funded by 2014 National Natural Science Foundation and Canada Natural and Engineering Research Foundation,this paper focuses on the catching target phase when the tether has already been released totally:the trajectory optimization problem of the TSS when the sub-satellite approaches the target satellite and the attitude control problem of the sub-satellite when it has approached the target and was influenced by other torque.The main research and contributions of this dissertation include:1.A dynamic model in presented based on the combination of Modified Rodrigues Parameters(MRPs)and their shadow.The model successfully resolves singularity when the cosine of external angle is zero in the traditional model and the discontinuous switching between MRPs and their shadows will not influence the continuous change of Euler angle.2.In terms of sub-satellite's approaching object using thruster,continuous nonlinear optimal control problem is solved Using Gauss pseudospectral method.Trajectories and control torques are compared under time optimization,with and without path constraints based on MRPs.This trajectory is compared with that using Euler angles and is proven to be global(enhances 2.8% orbit plane utilization).For the attitude control problem under interferences,the nonlinear " state feedback control method is learnt.The nonlinear dynamic system using a linear feedback is conducted and proven.MRPs and their shadows are chosen in state feedback torque with Euler angle.to avoid singularity.This method is compared with traditional state feedback control method using Euler angles to illustrate effectiveness. |
PDF Full Text Request