Dynamics And Control Of Attitude By Space Tether System

Space tether system is a system using tether to connect two or more satellites.It has attracted the attention of many researchers around the world because of its many unique advantages compared with conventional spacecrafts.For the successful implementation of the next space mission,the accurate and steady deployment of an end body to the designated orbit is essential to achieve initial goals of space tether system.The space mission fails if the attitude of sub-satellite is unstable at the end of the deployment.This paper mainly studies the factors and stable control of sub-satellite's attitude motion during deployment in order to ensure the success of space tether system missions.The main work in this dissertation is as follow:1.The dynamic models of space tether system whether to consider the attitude of sub-satellite is derived from Lagrange method by analyzing kinetic energy,potential energy and generalized force in moving coordinate system.In addition,the dynamic model of sub-satellite's attitude motion is derived from the Newton-Euler equation in body coordinate system.2.The sub-satellite's attitude motion is studied by simulating and analyzing the dynamic model of space tether system considering the attitude of sub-satellite and the dynamic model of sub-satellite's attitude motion without considering the outer surface movement of tether.The various factors that affect sub-satellite's attitude motion are compared and simulated.3.During deployment,it is inevitable for tension control mechanism to produce errors on the deploying tethered sub-satellite.Therefore,tension feedback control law is used to studying sub-satellite's attitude motion in this paper.The dynamic programming theory is applied to obtain optimal feedback coefficients and design optimal tension feedback control law.Simulation results and their analysis are demonstrated preliminarily,indicating that sub-satellite's attitude motion can be enormously suppressed by employing optimal tension feedback control law.4.Based on the nonlinear characteristic of dynamic equations and Lyapunov stability theory,a Lyapunov type nonlinear attitude controller is derived for the attitude motion of the sub-satellite and it is shown to be fundamentally stable.Simulation results and their analysis demonstrated preliminarily that the newly proposed controller is effective and efficient.