Advanced Attitude Control System for Electrospray Thrusters

Electric thrusters are propulsion devices that provide a thrust that operates on the spacecraft using the idea of momentum conservation. Electric thrusters have become a popular option for micro-satellite propulsion because of their propellant efficiency, reliability and versatility. Propellant is accelerated using various electrical and/or magnetic physical principles. Because the propellant is ejected at velocities significantly higher than a conventional chemical thruster, electric propulsion is much more fuel efficient, ultimately requiring smaller amounts of propellant. Several electric thruster technologies exist, covering a large range of missions and requirements. Over the years, these technologies have faced operational challenges and enabled several types of maneuvers, such as electric transfer from GTO to GEO, station keeping, inter-orbital transfer, interplanetary cruise, deorbiting and collision avoidance maneuvers. Electrospray thrusters are a type of electric propulsion that works by applying a voltage to an ionic liquid and extracting ions to generate thrust. Due to their great performance and adaptability to a variety of operating environments, these thrusters are seen as a promising option for advanced spacecraft control. In this thesis, a mathematical model of an electrospray thruster is taken into consideration to find a robust and effective attitude control for the spacecraft by studying several control laws. One of the most common control laws used and analyzed in this thesis is the Super Twisting Sliding mode. This controller makes use of a dynamic function that can adapt to system changes and disturbances continuously, ensuring the stability and accuracy of the control. Results from the simulations show the efficacy of the control laws tested, especially the Dynamic Super Twisting Control law, confirming that electrospray thrusters are capable of providing spacecraft attitude control for micro-satellites. The work in this thesis can serve as a starting point for more investigation and experimentation into the use of these thrusters.