Numerical Analysis of Potential Structure around Solar Sail in Solar Wind Plasma

Abstract

We had numerically analyzed the charged particle profiles and the potential structure around a solar sail at 1.0 AU. The quantitative estimation of these issues can be of importance for the payload design of a solar sail such as the location of onboard scientific instruments and solar arrays. In addition, estimation of the electrostatic force on the IKAROS spacecraft was made to determine whether the force was significant for the deformation of the membrane. A 3-D electrostatic, full-Particle-In-Cell code was used to study precise charged particle behaviours around a solar sail, and MUSCAT, a spacecraft charging analysis tool, was additionally used to obtain differential voltage of the sail. The numerical results showed that a wake potential was formed due to a large ion wake in the downstream of a sail obstructed the diffusion of the photoelectrons to the downstream surface. The size of the photoelectron cloud around a sail was estimated to be 17.5 m in the upstream hemisphere at 1.0 AU. The floating potential of the sail was +8.3 V, where double Maxwellian photoelectron spectrum model was adopted in the computation. The reduction of the electron sheath due to the photoelectron cloud was recognized. The differential voltage on the insulator surface of the sail of -15.8 V was obtained by the MUSCAT computation, that showed the charging of a solar sail itself was not serious in this environment but would affect the photoelectron diffusion and the wake potential. The electrostatic force at the numerical grid on the membrane assuming the IKAROS spacecraft was estimated under the observed real plasma environment. The magnitude of the force was of 10-8 N at the edge of the insulator that could not be negligible to a small-scale deformation on the membrane during the flight.