Abstract
Abstract. 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.
Highlights
The level of used propulsion technology is the decisive factor which sets the scale and scope of human space activity
To calculate the force acting on the wire, it is sufficient to know the potential pattern because from that one can compute the solar wind proton trajectories numerically
We found the given numerical value for K from a testparticle proton Monte Carlo simulation with potential (2); in other words we launched a number of solar wind protons into the potential pattern and recorded their momentum change after they had finished their interaction with the potential
Summary
Consider a long positively charged wire placed in solar wind which blows perpendicular to it to the x-direction. To calculate the force acting on the wire, it is sufficient to know the potential pattern because from that one can compute the solar wind proton trajectories numerically. Sandroos: Solar wind electric sail propulsion potential pattern. The plasma electrons shield the potential and make the potential vanish faster than the vacuum solution at high distances. The force per unit length acting on the wire is the solar wind dynamic pressure Pdyn=mpn0v2 times the effective width of the potential structure. In practise the wire cannot be a single filament because micrometeors would soon break it, but it must instead consist of more than one subwires which are attached together at regular intervals. In Appendix A we consider how to calculate the effective electric radius of such a multiple wire
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