Charateristics and stress analysis of sheath of parallel conducting tethers for the electric sail
Authors: Chen Mao-Lin  , Xia Guang-Qing  , Wei Yan-Ming  , Yu Yang  , Sun An-Bang  , Mao Gen-Wang  ,   Science and Technology on Combustion, Internal Flow and Thermo-Structure Laboratory, Northwestern Polytechnical University, Xi'an 710072, China;,   State Key Laboratory of Structural Analysis for Industrial Equipment, Dalian University of Technology, Dalian 116024, China;,   Beijing Institute of Control Engineering, Beijing 100080, China;,   Harbin Institute of Technology, Harbin 150001, China;,   State Key Laboratory of Electrical Insulation and Power Equipment, School of Electrical Engineering, Xi'an Jiaotong University, Xi'an 710049, China
Published: December 2020

The interaction between the solar wind plasma and the bias electric field of long conducting tethers is the basic operation mechanism of the electric sail thruster. A two-dimensional (2D) full particle model is established to investigate the momentum transfer process between the solar wind plasma and parallel conducting tethers, while normal incidence and oblique incidence of the solar wind are taken into account. To ensure the accuracy and stability of the present PIC method, we take a grid space step of 2.5 m that is smaller than the Debye length and a time step of 162.5 ns that is limited by the plasma frequency. The main features including the spatial electric potential and ion number density distribution are represented under the influences of tether distance and solar wind incidence angle, in addition, the effect of the bias voltage on momentum transfer process is analyzed. At a steady state, the number of electrons is slightly higher than that of ions, owing to the attraction of the positive potential of tethers. Different tether distances (i.e., from 15 m to 85 m) are taken and show that a high potential bias voltage of tethers can slow down, cease, reflect and deflect a large number of ions, resulting in a plasma cavity in the vicinity of the tethers. An ion trap forms and captures many ions, owing to the interaction between the sheaths of the two conducting tethers. In general, a bias voltage of 1 kV produces a thrust of 30 nN/m with two tethers, on the assumption that the solar wind incomes normally. If we increase the distance between two conducting tethers, both trap captured ions and thrust show a first increase and then decrease trend. Furthermore, the investigations of the solar wind oblique incidence show that the thrust of the electric sail is determined by its attitude and is separated into force components in two directions:a horizontal force that is along the solar wind and a lift force that is perpendicular to the solar wind. We conclude that the present work first shows that the lift force is less than zero when the tether plane leans to the right, and greater than zero if the tether plane turns left. The increasing of the pitch angle leads to a variation of the thrust from -40° to 40°. The presented dependence of the thrust on the attitude of the tether plane provides an important reference for the optimal design of the orbit dynamics of the electric sail spacecraft.