Unveiling the true plasma behaviour around comets by spacecraft charging simulations

2019年，彗星拦截器被ESA选为首个f级任务。这次任务将飞越一颗长周期彗星，并首次在彗星环境中进行多点测量，使用三个航天器：航天器a (ESA)，探测器B1 （JAXA）和探测器B2 （ESA）。所有航天器都将携带等离子体仪器，首次对彗星等离子体环境进行三维研究。然而，等离子体测量预计会受到航天器潜力的影响，正如其他彗星任务（例如罗塞塔任务，Bergman等人，2020年）已经观察到的那样。在整个飞越过程中，航天器将经过几个具有不同特征的等离子体区域，因此航天器的潜力预计会有所不同。在这项研究中，我们利用粒子池（PIC）模拟估算了彗星拦截器探测器B1在彗星飞越过程中的航天器潜力，并研究了对等离子体测量的影响。主要结果如下：(1)在较低的相对飞掠速度下，更有效地冷却内部彗发中的电子导致哈雷彗星的负航天器电位较小。(2)中性撞击产生的二次电子发射在大多数环境下以较高的相对飞掠速度使航天器带正电荷。

In 2019, Comet Interceptor was selected by ESA as the first F-class mission. This mission will make a flyby of a long-period comet and for the first time make multi point measurements in the cometary environment using three spacecraft: Spacecraft A (ESA), Probe B1 (JAXA) and Probe B2 (ESA). All spacecraft will carry plasma instruments, allowing, for the first time, a threedimensional study of the cometary plasma environment. The plasma measurements are, however, expected to be affected by the spacecraft potential, as already observed by other cometary missions (e.g. the Rosetta mission, Bergman et al., 2020). Throughout the flyby, the spacecraft will pass by several plasma regions with different characteristics, and hence the spacecraft potential is expected to vary. In this study, we estimated the spacecraft potential of Probe B1 of Comet Interceptor throughout the cometary flyby using Particle-In-Cell (PIC) simulations and study the influence on the plasma measurements. The main results are as follows:(1) At a low relative flyby velocity, a more effective cooling of the electrons in the inner coma results in less negative spacecraft potentials for a Halley-type comet.(2) Secondary electron emissions from neutral impacts charge the spacecraft positive in most environments at a high relative flyby velocity.