Integration and Testing of Vacuum Arc Thrusters for the University Würzburg Experimental Satellite (UWE-4)

University essay from Luleå/Department of Computer Science, Electrical and Space Engineering

Abstract: The University of Würzburg, Germany has for several years already a successful pico-satellite student project called University-Würzburg-Experimental satellite (UWE). The so far launched three satellites have proven the ability of determining and controlling the attitude using several sensors and magnetorquers and a reaction wheel as actuators.The next pico-satellite in the UWE series shall use coaxial "triggerless" Vacuum Arc Thrusters (VATs) as actuators for attitude and orbit control. The electric propulsion device including thruster heads and power processing unit is developed at the University of the German Federal Armed Forces (in german: Universität der Bundeswehr) (UniBW).In order to integrate this system in the already existing UWE platform, extensive testing is required. The power processing unit has been tested under nominal conditions for its performance and effects on other subsystems. It has been found that the current design of the power processing unit creates electromagnetic interference which leads to a reset of microcontrollers - even on other subsystems of the satellite, although several flaws in the design have been found and corrected. This fact disqualifies this design of a power processing unit for use on UWE. A new design of the Power Processing Unit (PPU) using a more thorough separation between analog and digital part of the electronics is currently under development at the UniBW.Two different thruster heads have been characterized with an experimental setup during a field campaign at the cooperating UniBW. The thrust to power ratio of a thruster head containing indium as propellant was found to be approx. 9.72 uN/W while using titan as propellant resulted in a thrust to power ratio of approx. 13.48 uN/W. In order to create a high thrust per second the thruster has to be fired with a frequency > 1 Hz. However, this lead to liquefaction of the indium propellant and disabled the operation of the thruster. Erosion of conducting surface material that enables the "triggerless" operation has shown to be an undesired effect that reduces the lifetime of the respective thruster head.