One possibility for propellantless propulsion in space is to use the momentum flux of the solar wind. A way to set up a solar wind sail is to have a set of thin long wires which are kept at high positive potential by an onboard electron gun so that the wires repel and deflect incident solar wind protons. The efficiency of this so-called electric sail depends on how large force a given solar wind exerts on a wire segment and how large electron current the wire segment draws from the solar wind plasma when kept at a given potential. We use 1-D and 2-D electrostatic plasma simulations to calculate the force and present a semitheoretical formula which captures the simulation results. We find that under average solar wind conditions at 1 AU the force per unit length is (5±1×10⁻⁸ N/m for 15 kV potential and that the electron current is accurately given by the well-known orbital motion limited (OML) theory cylindrical Langmuir probe formula. Although the force may appear small, an analysis shows that because of the very low weight of a thin wire per unit length, quite high final speeds (over 50 km/s) could be achieved by an electric sailing spacecraft using today's flight-proved components. It is possible that artificial electron heating of the plasma in the interaction region could increase the propulsive effect even further.

The electric solar wind sail (E-sail) is a space propulsion concept that uses the natural solar wind dynamic pressure for producing spacecraft thrust. In its baseline form, the E-sail consists of a number of long, thin, conducting, and centrifugally stretched tethers, which are kept in a high positive potential by an onboard electron gun. The concept gains its efficiency from the fact that the effective sail area, i.e., the potential structure of the tethers, can be millions of times larger than the physical area of the thin tethers wires, which offsets the fact that the dynamic pressure of the solar wind is very weak. Indeed, according to the most recent published estimates, an E-sail of 1 N thrust and 100 kg mass could be built in the rather near future, providing a revolutionary level of propulsive performance (specific acceleration) for travel in the solar system. Here we give a review of the ongoing technical development work of the E-sail, covering tether construction, overall mechanical design alternatives, guidance and navigation strategies, and dynamical and orbital simulations.

An electric sail uses the solar wind dynamic pressure to produce a small but continuous thrust by interacting with an electric field generated around a number of charged tethers. Because of the weakness of the solar wind dynamic\ud\ud pressure, quantifiable in about 2 nPa at Earth’s distance from the sun, the required tether length is of the order of some kilometers. Equipping a 100-kg spacecraft with 100 of such tethers, each one being of 10-km length, is sufficient\ud\ud to obtain a spacecraft acceleration of about 1 mm/s^2. These values render the electric sail a potentially competitive\ud\ud propulsion means for future mission applications. The aim of this paper is to provide a preliminary analysis of the\ud\ud electric sail performance and to investigate the capabilities of this propulsion system in performing interplanetary\ud\ud missions. To this end, the minimum-time rendezvous/transfer problem between circular and coplanar orbits is considered, and an optimal steering law is found using an indirect approach. The main differences between electric sail and solar sail performances are also emphasized