电推进等离子体对航天器表面带电影响的理论研究

Theory Study of Ion Thruster Plume to Spacecraft Surface Charging

电推进在轨工作时将产生低温稠密等离子体,与地球同步轨道的空间离子体特性存在较大差异,且等离子体中的低速交换电荷离子易受到卫星表面电位的作用,形成返流并作用于卫星表面材料,对航天器表面充放电效应产生重要的影响。为此,综合考虑材料二次电子和背散射电子发射电流,分析电推进产生等离子体充电电流特性,基于充放电平衡方程进行电推进等离子体及空间等离子体共同作用下的表面带电机理研究。研究结果表明:地磁亚暴时期,航天器表面受到地球同步轨道等离子体的影响,其表面电位可高达–10~4 k V;电推进工作时,其羽流等离子体充电电流为10-3 A/m^2,远大于空间等离子体充电电流,从而成为卫星表面带电的主要影响因素;同时电推进等离子体将航天器表面电位中和至–10 V,即电推进交换电荷返流可以有效缓解由空间等离子体造成的危害性表面充放电效应。

Microthermal dense plasma is induced when electric propulsion thruster is working on the orbit, which is quite different from space plasma on geosynchronous orbit. The difference between thruster and space plasma may ensure spacecraft surface charging to become more complicated. Moreover, the charge-exchange（CEX） ion which exists in ion plasma is influenced by spacecraft surface potential, and it may form backflow and induce surface charge and discharge. Therefore, focusing on material secondary electron and backscattered electron emission current, we analyzed physic characteristics of the thruster plasma, and put forward a computation method of the surface charge potential by using charge and discharge balance equation. The research results reveal that the spacecraft surface is influenced by plasma on geosynchronous orbit, and the potential reaches –10^4 V during periods of geomagnetic activity. And the thruster plasma current is 10^-3 A/m^2（which is much higher than space plasma changing current） when the thruster plasma is working. It is the main reason why the spacecraft surface get charged. Moreover, the thruster plasma can neutralize the spacecraft surface potential to –10 V, which means the backflow and neutralization electron current can release damage effect caused by spacecraft charging.