Advancements to the Micro-Cathode Arc Thruster: Linear Actuator, Ablative Anode, and Modular Designs

Abstract

The Micropropulsion and Nanotechnology Laboratory (MpNL) of The George Washington University began designing the Micro-Cathode Arc Thruster ( µCAT) in 2008 to improve upon the vacuum arc thruster design and efficiency. This system has worked very well, successfully flying aboard two Cube Satellite (CubeSat) missions. The MpNL continues to iterate and strives to optimize the thruster to find the ideal subsystem to fulfill the small satellite’s needs. The biggest obstacle is removing the external magnetic field, because it can interfere with the on-board instruments. Removing this feature would make the thrusters more desirable to the wider CubeSat community. Three newly designed versions of the µCAT are presented. Each system contributes a change in order to see how these new models fair in comparison with the current scheme and if they can be just as effective sans external magnetic field.

Each of the new designs was characterized via arc current, ion current, ion velocity, erosion rate, and thrust stand experiments. The Linear Actuated µCAT entailed swapping the polarities of the central and outer electrodes to remove the external magnetic field, and utilizing a stepper motor in place of the spring-feed mechanism. The second system was the Ablative Anode µCAT employing a metal with low melting temperature and high vapor pressure to replace the standard anode, or positive, central electrode. The third system was the Modular µCAT consisting of multiple thruster heads allowing for a thruster to be replaced once it has ceased arcing. After characterizing the systems, they were compared to each other and the Standard µCAT to determine the optimal configuration.

All three systems performed on par or better than the Standard µCAT in most arenas. Once a magnetic field was added, the ion current increased and provided an average transport efficiency of 40%, in comparison to the standard system’s 35%. The ion velocity was found to be on par or better at 12-13 [km/s] without a magnetic field, and achieving almost 100 [km/s] with an external magnetic field seated slightly behind the face of the thruster. Furthermore, the hypothesis that the ablative anode materials would erode in addition to the cathode, proved to be correct as it presented a positive erosion rate. The thrust stand experiments conveyed that the Ablative Anode µCAT attained the highest thrust and thrust-to-power ratio. The data presented demonstrates that the systems are comparable to the standard system, and each other. Therefore, the MpNL can move forward to optimize each thruster design.

The purpose of this work was to assess three new iterations of the µCAT and compare them to the standard scheme , from which each system possessed a major difference to be evaluated on its merit and usefulness. The results of this dissertation shed light on which path is optimal to improve upon the µCAT.