Understanding and Mitigating the Charging Behavior of Next Generation Complex and Active Spacecraft

Spacecraft that are fundamentally more complex and higher powered are necessary to expand our scientific missions and take commercial space endeavors to the next level. However, as spacecraft become more sophisticated and interact with the environment in novel ways, their capabilities will become limited by their effectiveness in mitigating spacecraft charging. NASA identifies the impact of spacecraft charging as an area that requires further development. This cross cutting technology area directly affects the advancement of high power solar electric propulsion for future space missions. Under the Power Generation Technology Area Breakdown Structure (TABS) 3.1.3 the challenge is for solar power generation to effectively operate while interacting with various ambient environments as well as the plasma generated by high power electric propulsion thrusters. These conditions create a complex system that makes it difficult to predict the spacecraft's charging behavior and mitigate its effects. An active method of spacecraft charge mitigation uses a hollow cathode plasma source to balance the charge on the spacecraft by emitting charged particles through its plasma plume. They are currently used on the International Space Station (ISS) and the Defense Satellite Communication System satellite B-7 (DSCS-III B-7); however it is unclear if they are effective for all conditions. These spacecraft lend themselves to be valuable resources as platforms for experimentation. This project aims to reduce the risk of spacecraft charging for complex, high power spacecraft in both steady-state and transient conditions. Using data from the ISS and DSCS-III B-7 in conjunction with ground experiments, the plan is to create a hybrid model of spacecraft charging behavior and predict effective mitigation techniques. Experimental data from spacecraft will show the charging variations in the ambient space environment. Ground plasma chamber experiments will then allow the dependence between plasma source parameters and the ambient environment to be studied. The model will be validated using in-orbit measurements from the ISS. The ground experiments will be conducted at the Plasmadynamics and Electric Propulsion Laboratory (PEPL). The simulated spacecraft and plasma source will be electrically isolated from ground to provide charge to the system. The parameters of the plasma source will be varied as well as ambient environment conditions. The environment will also be simulated as closely as possible to the space environment. In this way, the spacecraft charging behavior can be observed in relation to changes in the plasma source and the nearby (ambient space) environment. The spacecraft charging model will contain two main components: a spacecraft structure and plasma plume. To capture the effect of spacecraft geometry, the structures are treated as a circuit. Capacitances, inductances, and resistances will be calculated for each section of the spacecraft while the photovoltaic cells and collected current will be regarded as non-linear voltage dependent sources. The plasma plume will be modeled using a collisional Boltzmann equation to obtain distribution functions for the plume's charged particles. This proposal's goals and focus are synergistic with the research conducted at NASA's MSFC (MSFC). Many researchers with extensive experience in spacecraft charging work at NASA's MSFC. These researchers have performed experiments using the ISS and DSCS-III instrumentation and can provide invaluable input when interpreting data. This research proposes a novel approach to modeling spacecraft charging in order to better understand and mitigate the process. Complex spacecraft such as the ISS and DSCS-III B-7 provide a wealth of data that can be used to help develop and validate a new model. This research will help determine effective means to mitigate spacecraft charging for the next generation of complex, high-powered spacecraft. More »