Analysis of Spacecraft Charging Effects of SPT-100 Hall Thruster Plumes

The backflow plume from an electric thruster can lead to the accumulation of electrostatic charge on the spacecraft, typically leading to a negative charge. Interactions between the plume and solar wind can further influence the charge distribution, resulting in variations in spacecraft potential and interference with sensitive instruments. A 3-D particle-in-cell (PIC) simulation tool within the Spacecraft Plasma Interaction Software (SPIS) is used to compute spacecraft charging effects from 0.044 to 1 astronomical unit (AU) in the solar wind. The study examines the effects of ambient electrons and ions, thruster electrons, and charge exchange ions (CEX-ions), as well as photoemission and secondary electron emission, on the spacecraft potential. The main finding is that the high dominance of CEX-ions and thruster electrons leads to a low and stable negative potential ranging from −2 to −6 V from 0.044 to 1 AU, respectively, when the thruster is <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on</small>, as opposed to the varying range of −28 to +9 V with the thruster <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">off</small>. Another finding is that without photoelectrons, the spacecraft acquires a significantly more negative charge compared with when the thruster is active. This is due to these processes being quantitatively important when the thruster is <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">off</small> but being dominated by a collection of thruster electrons when the thruster is <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on</small>, which leads to relatively small and negative spacecraft potentials across the heliocentric distances studied.