Tracking and Thrust Vectoring of E-Sail-Based Spacecraft for Solar Activity Monitoring

The Electric Solar Wind Sail (or E-sail) is a propellantless propulsion system conceived by Dr. Janhunen in 2004. An E-sail extracts momentum from the charged particles constituting the solar wind by means of long and electrically charged tethers, which are deployed and kept stretched by spinning the spacecraft about a symmetry axis. Trajectory analysis of an E-sail-based spacecraft is usually performed assuming that the tether arrangement resembles that of a rigid disc. However, this assumption may be inaccurate since the actual shape of each tether is affected by the chaotic interaction between the solar wind dynamic pressure and the centrifugal force due to the spacecraft spin. The first goal of this chapter is therefore to describe the thrust and torque vectors of a non-flat E-sail. Then, the orbital and the attitude dynamics of a spinning E-sail are analyzed separately due to the marked separation between their characteristic timescales, showing that the torque acting on the E-sail induces a perturbation on the orientation of the thrust vector. Accordingly, the modulation of the tether electrical voltage is proposed and investigated as a possible attitude control strategy. An effective control law is first obtained as a function of spacecraft attitude and time, and then validated through numerical simulations. Finally, two heliocentric mission scenarios (useful, for example, for the monitoring of near-Earth objects or the surveillance of solar activity) are analyzed, where the thrust vectoring of the E-sail is exploited for the generation of Earth-following orbits or the maintenance of a heliostationary equilibrium point.