Context. The electrostatic potential of a spacecraft, VS, is important for the capabilities of in situ plasma measurements. Rosetta has been found to be negatively charged during most of the comet mission and even more so in denser plasmas. Aims. Our goal is to investigate how the negative VS correlates with electron density and temperature and to understand the physics of the observed correlation. Methods. We applied full mission comparative statistics of VS, electron temperature, and electron density to establish VS dependence on cold and warm plasma density and electron temperature. We also used Spacecraft-Plasma Interaction System (SPIS) simulations and an analytical vacuum model to investigate if positively biased elements covering a fraction of the solar array surface can explain the observed correlations. Results. Here, the VS was found to depend more on electron density, particularly with regard to the cold part of the electrons, and less on electron temperature than was expected for the high flux of thermal (cometary) ionospheric electrons. This behaviour was reproduced by an analytical model which is consistent with numerical simulations. Conclusions. Rosetta is negatively driven mainly by positively biased elements on the borders of the front side of the solar panels as these can efficiently collect cold plasma electrons. Biased elements distributed elsewhere on the front side of the panels are less efficient at collecting electrons apart from locally produced electrons (photoelectrons). To avoid significant charging, future spacecraft may minimise the area of exposed bias conductors or use a positive ground power system.
Spacecraft Charging of the Morazán MRZ-SAT Satellite in Low Earth Orbit: Initial Results on the Influence of Energetic Electron Anisotropy on Differential Charging
Modelling spacecraft-emitted electrons measured by SWA-EAS experiment on board Solar Orbiter mission
Institute of Atmospheric Physics of the Czech Academy of Sciences（捷克科学院大气物理研究所）；Astronomical Institute of the Czech Academy of Sciences（捷克科学院天文研究所）；Czech Technical University in Prague（布拉格捷克理工大学）；Mullard Space Science Laboratory, University College London（伦敦大学学院穆拉德空间科学实验室）；Swedish Institute of Space Physics (IRF)（瑞典空间物理研究所）；LIRA, Observatoire de Paris, Université PSL, CNRS, Sorbonne Univers（巴黎天文台 LIRA 实验室，PSL 大学，法国国家科学研究中心，索邦大学）
Plasma densities, flow and Solar EUV flux at comet 67P - A cross-calibration approach
在对67 P彗星的两年任务中，罗塞塔几乎连续监测了彗发内部等离子体环境中气体产生率的变化超过三个数量级，距离彗核从几公里到几百公里。为了实现最佳的测量，需要对等离子体仪器进行交叉校准。我们构建了两个不同的物理模型，以交叉校准的电子密度测量的互阻抗探针（MIP）的离子电流和航天器的电位测量的罗塞塔朗缪尔探针（ESTA），后者验证的离子成分分析仪（ICA）。我们检索了一个连续的等离子体密度数据集，为整个彗星的任务与任何单独的等离子体仪器相比，有很大的改善动态范围，有时，提高时间分辨率从0.24-0.74赫兹到57.8赫兹。新的密度数据集与现有的MIP密度数据集一致，并涵盖了密度太低而无法通过MIP测量的长时间段。物理模型还产生了3小时时间分辨率的离子流速度以及来自朗缪尔探针的光电发射的太阳EUV通量的代理。我们报告两个独立的任务范围内的离子流速的估计是一致的散装H $_2$ O $^+$离子速度ICA测量。我们发现在整个任务中，离子流始终比中性气体快得多，这进一步证明了在昏迷中离子与中性气体的碰撞解耦。因此，RPC对离子速度的测量结果与先前发表的彗星电离层等离子体密度模型在任务开始和结束时所作的假设不一致。此外，测量的EUV通量与Johansson等人（2017）先前发表的独立推导值完全一致，并支持其中得出的结论。
Secondary drift-driven instabilities in the presence of a parallel-propagating electromagnetic ion cyclotron wave and cold multi-component ions
University of California San Diego（加州大学圣地亚哥分校）；Los Alamos National Laboratory（洛斯阿拉莫斯国家实验室）；Space Science Institute（太空科学研究所）；University of Helsinki（赫尔辛基大学）
