Establishing Stratosail's 6-DOF dynamics models

The stratosail has the tensile force of the tether but no engine thrust and the size and direction of the tensile force is constantly changing. Also the changes in the size and direction of wind speed have direct influence on the aerodynamic force and spatial position of the stratosail. The establishment of the stratosail's 6-DOF models includes the modeling of a flexible tether, that of the position restriction body and that of the aerodynamic force of the stratosail, thus being a complicated flexible and rigid coupled modeling process. This paper analyzes the forces received by the stratosail and establishes its dynamics model and kinematics model under the stratosail's coordinate system. The forces include the gravity and aerodynamic force exerted on the stratosail and the tensile force and moment of the tether. According to theoretical mechanics principles, it also establishes the stratosail's mass center dynamics equation and the dynamics equation rotating around its mass center, laying the foundation for further analysis of the changes in the attitude of the stratosail and in the spatial position of its mass center.