E-sail attitude control with tether voltage modulation

An Electric Solar Wind Sail is a propellantless propulsion system that gains thrust from the interaction of solar wind particles with a grid of long and charged tethers, which are deployed by spinning the spacecraft about its symmetry axis. In an ideal arrangement, the tethers are all stretched out and the sail takes the shape of a spoked wheel. Actually, the solar wind dynamic pressure warps the tethers and, therefore, the expressions of thrust and torque vectors are difficult to predict in analytical form. Recent works have shown that the bending of the tethers induces a disturbance torque, which can be counterbalanced through a modulation of the tether electrical voltage. Under the assumption that the Electric Solar Wind Sail behaves like an axially-symmetric rigid body, this paper proves that a modulation of the tether electrical voltage is also a feasible option for actively controlling and maintaining the spacecraft attitude. The proposed control law, which is analytically derived as a function of time and spacecraft attitude, is validated through numerical simulations.