Matthias Lau

Investigation of the Magnetic Field in a Pulsed Plasma Thruster

The magnetic field between the electrodes of an 80 J ablative pulsed plasma thruster was both measured and determined analytically. This was done to better understand the acceleration process and assess the accuracy of the analytical method. The measurements at different positions in both breech-fed and side-fed propellant configurations were performed using a shielded induction probe of 1 mm in diameter. To calibrate the probe, a Helmholtz coil was built. The magnetic field was calculated using the law of Biot-Savart and assuming a current sheet thickness of 3 mm. The measured magnetic field showed an overall peak at 0.7 T. It was possible to confirm the induced current loop formed between the electrodes at the time when the overall current passes through zero. The comparison between the magnetic field model and the measurements at the propellant surface of a breech-fed thruster showed reasonably good accordance.

Experimental Investigation of the Current Density in the Discharge Plasma of ADD SIMP-LEX

the ablative iMPD ADD SIMP-LEX of the Institute of Space Systems in Stuttgart, represents a promising and cheap solution to todays propulsion challenges in space. The work presented in this paper covers new information on the electromagnetic conditions during thrust generation by revealing the temporal and spatial distribution of the vectorial current density between the thruster electrodes. At IRS this is achieved by utilizing self-made and calibrated miniaturized induction probes. The local magnetic eld components of all three spatial directions are combined to derive the current density vector. Quantitative determination of the temporal behavior of vectors at 27 points evenly distributed in three planes delivers for the rst time a comprehensive picture of the position and development of the current sheet in a PPT. Maximum current densities of 80 kA=m 2 and magnetic ux densities of up to 0:82 T have been observed close to the surface of the solid Teon T M -propellant. It should be noted, that in contrast to the slug model by Jahn no distinct movement of the current sheet was observed. The current density data is discussed and compared to high-speed camera pictures taken at IRS.

Power Train Configuration Study on a Pulsed Plasma Thruster with State-of-the-Art High Current Monitors

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 Zurich 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.