Study On Space Tethered Satellite System Dynamic Modeling And Simulating

As a new development of today's space technologies, space tethered satellite system has extensive prospects in application. Since the 1960s and 1970s, the research on the space tethered system has been made all the while. To resolve the space tethered maneuver and net-casting, the "bead model" and Newton-Euler method are used to describe and simulate the tethered dynamics and control.Firstly, the research on the space tethered dynamics is summarized, and the dynamic model is introduced briefly. Then the "bead model" is defined and built in the local-vertical coordinate system, and the relative dynamic equations of the tether are deduced adopting Newton-Euler method, compared with those from Lagrange method. Based on the local part of the tether, the Newton-Euler method analyses the force which put on a single bead; and the Lagrange method analyses the energy of the system based on the whole of the tethered system.Moreover, the models of some motion processes are established, including the deployment, retrieval and station-keeping of tethered system. Its common control laws are also analyzed, such as the tension control law, rate control law and subsatellite gas thruster control law. Finally, the dynamic characteristics of the "bead model" and "simple model" are simulated and the results are analyzed, using the tension and rate control law respectively. The "simple model" does not take account of the tether's mass and shape property.For the "bead model", the results indicate that the tether's deployment is stable but its retrieval is unstable; and the dynamic processes under different control schemes are different, which is consistent with the theoretical analysis. For the rigidity model, the tether's motion trend is similar to that from the "bead model".Because of the elasticity and distributed mass of the tether, the characteristic of the model, the "bead model" could detailedly depict the motion of longitudinal and transverse vibration, it can depict different mode shape, and there are two modes of vibration, one is low frequency vibration which is induced by the in-plane and out-of-plane swing motions, the other is high frequency vibration which is induced by the elasticity and distributed mass of the tether. But "simple model" couldn't detailedly depict the motion of longitudinal and transverse vibration, so we can apply the "bead model" to study the motion of longitudinal and transverse vibration.The model and method which is studied in this paper could be applied to study the space tethered maneuver and net-casting.