Spacecraft – Plasma Interactions for a LEO – GEO Mission Tug with Direct Drive Hall Effect Thruster

Electric propulsion has long been believed to be a key technology for the future of space exploration. The advantages in consumption and continuous improvements in performance have made it a worthy alternative to chemical propulsion. In particular, the use of EP systems on new generation geostationary telecommunications satellites leads to substantial savings in the propellant mass. The electric propulsion is not based on the reactive nature of the propellants to obtain the energization of the flow, but it provides the acceleration by means of electrical systems of various nature. One of the most promising methods is based on the Hall current. Hall Effect thrusters represent a versatile solution, thanks to their scalability and performance in terms of thrust efficiency and specific impulse. Used since the 60s for station keeping applications onboard of Russian satellites, expanding towards the high power they are rekindling the interest of the scientific community. One of the most interesting applications is to create a transport system (a tug) that is powered by solar cells and allows a payload to be brought into higher energetic orbits by providing taxi service. The combination of Hall Effect thrusters and Direct Drive technology with innovations in the field of the solar array makes this mission not only possible but also desirable. This study aims to evaluate how the coupling of various state of art technologies can influence mission architectures and scenarios. In first chapters, we try to introduce the reader to the basic concepts of electric propulsion and to the base physics of the HT-20k engine designed by SITAEL. (This engine will be the basis of all our simulations). Having studied the various constraints and requirements of a space tug, we will define the transport mission and provide preliminary simulations for different sub-cases. We will detail the study of a particular configuration. The following chapters will present the analysis of the problem of charging the surfaces of the tug in contact with the plasma plume exhausted by the engine. A schematization of the problem, after presenting the sheath theory, will allow us to write a Matlab code to forecast currents and voltages on the individual parts of the spacecraft, so make changes to the configuration and prevent structural damages. Simulations of the trend of the plume over time, through programs in PIC, joined the study in order to know local temperature and density. The last chapters are dedicated to conclusions and suggestions for some future ideas and developments. The appendages show the programs realized based on the proposed models, some examples of system sized with their use and the simulations made during the mission analysis.