The thruster ADD SIMP-LEX (ADvanceD Stuttgart Impulsing Magneto-Plasmadynamic Thruster for Lunar EXploration) has been developed at the Institute of Space Systems (IRS) in Stuttgart, to provide secondary and primary propulsion capabilities to small satellites. Extensive optimization led to a mature design of world leading thrust efficiency around 30 % with russian APPT devices. The thruster was chosen for development into a stand-alone system in 2010. The system is capable of operating under satellite-like vacuum conditions in a test chamber, foregoing the usual outside laboratory equipment. The only connections required for system operation are a serial command interface, thermal housekeeping and a 28 V power line. Telemetry of the system for thruster health monitoring includes measurement of the pulsed current signal at up to four thruster capacitors. Requirements of the thruster and operation conditions ruled out any available COTS solutions for this task. A custom designed current measurement system was developed at the ETH Zürich and successfully integrated into the ADD SIMP-LEX design at IRS. The measurements revealed the current signal for every capacitor terminal and allowed for reconstruction of the combined flow. This data showed a current ringing effect between capacitors, which is undesirable for efficient thruster operation. The capacitor setup was changed and impact on the ringing was analyzed. The results showed reduction of the effect. Although complete elimination was not achieved, the data suggest careful consideration of the power train configuration can achieve satisfying mitigation levels. The sensor data quality was significantly improved by overcoming electromagnetic compatibility issues through introduction of a fiber-optical (LWL) transfer interface.
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