Drag and propulsive forces in electric sails with negative polarity

Abstract

An electric solar sail (E-sail) is a recent propellantless propulsion concept for a direct exploration of the Solar System. An E-sail consists of a set of bare, conductive tethers at high positive/negative bias, prone to extract solar wind momentum by Coulomb deflection of protons. Additionally, a negatively biased E-sail has been proposed as a concept for de-orbiting space debris with drag forces produced in Low Earth Orbit (LEO). The present work focuses on the negative-bias case with a sheath that must be correctly modeled for a flowing plasma ambient. Ion scattering within the sheath and the resulting force are determined for several plasma conditions. Since the plasma flow does reduce the effective range for the ion scattering within the sheath, the resulting force is then reduced. Tethers at very high negative bias should be required for extremely high plasma flow.