Full lifetime demonstration of a Micro-Cathode-Arc thruster evolution characteristics

Ground lifetime test is the most crucial experiment to assess the performance, reliability, and flight qualification of electric propulsion, and it can bring new insights for understanding the operation characteristics. This work demonstrates a full lifetime test of 140000 cycles on a Micro-Cathode-Arc Thruster (μCAT) with 160 μs charging time and 86 mJ charging energy. A four-probe resistivity measurement method is utilized to investigate variations in the conductive film thickness and resistivity throughout the thruster lifespan. Direct film parameters show that the lifetime of the μCAT can be divided into three stages. In the initial stage, the film thickness decreases by 1.2 μm and the resistivity increases significantly due to the high discharge intensity and intense film ablation; In the steady stage, the change of the film thickness is within 5%, and the resistivity of the film increases slowly from 0.050 Ω·mm to 0.223 Ω·mm. In the end stage, the resistivity exponentially increases from 0.223 Ω·mm to 1.176 Ω·mm, with the increase accounting for 81%, ultimately resulting in the failure of the thruster open circuit. Additionally, the evolution of discharge parameters, and the variation of plume parameters are measured throughout the lifetime. The discharge characteristics also show significant differences in the duration of voltage and current in these three stages. The results of plume shape and plasma parameters are also well consistent with the discharge parameters and film state. These results suggest that, for evaluating the steady stage lifetime of thrusters, the film thickness is the best indicator compared to the variations in resistivity and voltage-current characteristics. For the end stage, the plasma plume morphology, discharge duration, and plume parameters can conveniently and clearly characterize the thruster failures and irregularity.