GEO卫星表面充电的阈值条件及触发行为特征研究

Geosynchronous plasma is likely to induce severe spacecraft surface charging during sub-storm due to injection of high energy plasma components from magneto tail, which is one of the key factors leading to space system anomalies. It’s desirable to predict occurrence of high negative spacecraft charging, which will prevent discharging and significantly improve space system securities on orbit. For such purpose, it’s necessary to investigate the threshold condition for onset of spacecraft surface charging, which is the main objective of our research. The program is based on the critical temperature theory by Lai, S.T. and extrapolates it to the case of multiple Maxwellian plasma which better models sub-storm geosynchronous plasma, so as to investigate the threshold condition for onset of surface charging, pursuit reasonable description of the threshold. Meanwhile, the program aims to disclose the charging performance and associated pattern at the threshold, and finally clarify the underling mechanism for geosynchronous spacecraft charging in depth. The research is also to be verified by experiment simultaneously. Space measurements suggests that geosynchronous surface charging sometimes occurs by abruptly jumping from initial uncharged to a high negative potential, such a strange charging onset is undesirable and very threatening. Such an interesting phenomenon will be investigated in detail so as to understand the specific condition in terms of plasma and material properties, and the associated mechanism driving potential jump.

地球静止轨道（GEO）等离子体在磁暴期间由于来自磁尾的高能等离子体注入而极易诱发卫星表面高充电，是导致卫星系统异常的重要因素。若能预测或预报卫星充电的发生，将有可能使在轨卫星采取主动应对及防护措施，大大提高在轨卫星的安全。而预测的前提是了解触发卫星表面充电（负电位）的阈值条件和特征性前兆。研究和观测表明，在有些强扰动环境下GEO卫星表面充电常以突变方式发生，因此，研究GEO卫星表面充电的阈值条件、充电被触发的模式及行为特征具有特别的意义。本项目在Lai S.T.等的阈值温度理论基础上，进一步针对磁暴环境下的多麦克斯韦等离子体进行拓展深化，探索扰动等离子体中触发表面充电的阈值条件及表征方法，揭示在阈值条件下充电被触发的模式及特征，建立判断电位突变的物理判据，同时开展原理实验验证，阐明驱动电位跳变的物理机制，为未来形成GEO表面充电在轨预示能力奠定理论和技术基础。

本项目揭示了GEO航天器在磁暴等离子体注入时表面充电的阈值条件以及表面电位跳变规律，对于理解高轨航天器表面充电具有重要的指导意义。在磁层亚暴期间，高能带电粒子从磁尾注入，此时航天器周围的空间等离子体近似服从双麦克斯韦分布，因此表征空间等离子体的环境参数包括两种组分电子/离子的密度、温度，这些参数对航天器表面充电均具有重要的作用。本项目针对单麦克斯韦和双麦克斯韦分布下航天器表面充电阈值条件进行了分析，可以看到由于航天器表面电位与电子温度及密度密切相关，在固定的等离子体条件下存在着三重根区域，同时航天器表面电位会随着等离子体参数的变化而发生跳变。同时，针对航天材料二次电子发射系数的测试表明，金属和介质材料表面充电水平受二次电子发射性能的影响，且二次电子发射系数与航天器表面充电阈值密切相关，当二次电子发射系数大于1时，航天器表面电位会由负变正，表面充电极性会发生变化，在电子温度发生变化时，航天器表面充电电位会在阈值附近发生跳变。因此，为了能够动态分析航天器表面充电电位变化，需要掌握不同等离子体环境参数对航天器表面充电的影响，同时需要对阈值条件表面充电电位跳变规律进行归纳和总结。本项目在分析已有航天器在轨探测数据的基础上，建立了航天器表面充电电位与电子温度之间的关系，揭示了航天器表面充电阈值条件的存在，随后建立了单麦克斯韦和双麦克斯韦分布下航天器表面充电阈值条件与等离子体环境参数的关系，以及航天器表面电位在有磁层亚暴电子注入后的跳变规律，对评估航天器在等离子体环境发生剧烈变化时表面充电危害程度提供支撑，可为未来航天器严重不等量充电防护及减缓提供方法和依据。