Research On Thruster Configuration And Low-thrust Transfer Design Of GEO Satellite

With the increasing requirements of the high load and high lifetime Geostationary Earth Orbit(GEO) satellite, low thrust propulsion, which is represented by electric propulsion, is the subject of worldwide interest among today's engineering community. In contrast with conventional high-thrust orbit transfer, low-thrust transfers are characterized by greatly improved fuel efficiency at the expense of relatively long transfer times. What's more, satellites can be easily caught by detection systems during the low-thrust GEO transfer.In this paper the application of electric propulsion systems in GEO satellites is studied. Thruster configuration in the satellite platform is presented, and the ability to complete the space mission, such as station-keeping, orbit-raising, and orbit-transfer, is discussed. This paper addresses the design for a low thrust GEO satellite transfer control strategy which takes into consideration the low observable constraint, and discusses Earth shadow and perturbation. The main research contents are as follows:Firstly, the dynamical models of satellite motion and space environment are analyzed. The classical dynamic equations and the modified equinoctial equations are respectively used for the analysis and calculation of the low-thrust transfer. The space environment factors, including Earth's oblateness, atmospheric drag, light pressure, secondary body, are studied. And in this paper Earth's oblateness and Earth-shadow are taken into account.Secondly, the thruster configuration of the satellite platform is studied. According to the characteristics of low thrust propulsion, three kinds of thruster configuration are introduced, namely the 4-thrusters configuration, the 8-thrusters configuration and the 16-thrusters configuration. The ability of these three configurations to complete space task is discussed. Furthermore in the light of the 16-thrusters complex configuration, a thrust allocation method based on attitude and orbit integration control is proposed, which satisfies the constraints of thrust configuration error, control accuracy and fuel consumption. The effectiveness of the proposed method is verified by simulation.Thirdly, a considerable challenge associated with a low thrust GEO satellite is the minimum-time transfer. A new method for computing minimum-time transfers for electric propulsion spacecraft has been developed, and is presented in this paper. The thrust-time history is computed by designing a control law based on control-parameter analysis, and the parameter's traversing is utilized to solve the optimal control problem. The effects of Earth-shadow and perturbations are included in a simulation of the method. The implications of this new approach for thrust error and switching times are also discussed. Simulation results exhibit robust convergence properties with no initial guess. The control law can be used to correct unexpected errors with real-time elements analysis.Finally, in an effort to address the risk of increased radar threat, satellite low observability has been considered and implemented. Low observability design already has been added in the low thrust transfer. The low observable satellite is designed to minimize its frontal RCS, requiring lowobservable shape design and flight attitude adjustment. The satellite keeps its front toward Earth when it is flying over ground-based radar detection areas. In addition the platform of low thrust transfer is designed, involving the transfer modules and the graphical user interface.