Simulations Of The Spacecraft Charging And Wake Effects

The space environment has a complex and dynamic structure,which can impact the safety of the spacecraft.Understanding the interaction between a spacecraft and the harsh space environment is a major consideration for all space missions.Spacecraft-plasma interaction can cause modifications to the natural environment,giving rise to local environment,such as spacecraft surface charging and wake effects,which in turn affect the spacecraft's behaviors.A study for this problem with analytic formulas is difficult,thus this has encouraged the use of the particle simulation method in terms of the dynamic equations.In this paper we use SPIS(Spacecraft Plasma Interaction Software)to perform PIC simulations for the spacecraft-plasma interaction in the solar wind,the magnetosphere sheath and the magnetosphere tail lobe,revealing the ion,electron,photoelectron and electric potential distributions around the spacecraft.The results show that,since the plasma in the solar wind is tenuous,the electrons collected by the spacecraft give a much smaller current than the photoemission current,the spacecraft may be charged to positive potential.Compared with the spacecraft in the solar wind,in the magnetosphere sheath,the fairly dense plasma and pretty high electron temperature lead to the low spacecraft potential.Yet in the magnetosphere tail lobe,owing to the quite tenuous plasma,the spacecraft potential can reach up to high values.The plasma moves at a relative speed exceeding the ion thermal speed but not the electron thermal speed.A negatively wake forms downstream the spacecraft.It is demonstrated that the wake features can be altered by the photoemission,the dimension of spacecraft and the plasma environment.Without the photoemission,the spacecraft in shadow tends to be highly negative and the scale of the wake becomes small,while the wake can be large downstream a sunlit spacecraft due to the surface photoemission.It is concluded that,since the bulk flow kinetic energy is much larger than the spacecraft potential energy,the size of the wake is dependent on the dimension of spacecraft.The wake can be substantially larger behind a larger spacecraft with the same parameters in the solar wind.It is also clear that the dimension of the wake may be determined by the plasma environment.In the solar wind,due to the high plasma flow speed and low ion thermal speed,with a large March number,the supersonic flow of plasma with respect to the ions causes a large wake.In the magnetosphere sheath,the wake size could be small with a small March number,on account of the relatively low streaming velocity and extremely high ion thermal velocity,which brings about more ions in the wake.Considering the rather low bulk flow speed and relatively high ion thermal speed,obviously there is no wake downstream the spacecraft in the magnetosphere tail lobe where the plasma flow is subsonically drifting with respect to the ions.