Junichiro Aoyagi

Development of a Novel Power Processing Unit for Hall Thrusters

A newly developed power processing unit (PPU) offers the advantages of smaller size and lighter weight than conventional PPUs. The thrust performance of a magnetic layer type Hall thruster developed at Kyushu University with this new PPU was investigated; it showed a good performance as compared with conventional power supplies. The thrust to power ratio was improved to 58 mN/kW at discharge voltage of 150 V and anode xenon mass flow rate of 1.0 mg/s.

Feasible Study on Low Frequency Plasma Jet as Ignition System for HAN based Propellant

A low frequency (LF) plasma jet is proposed as an ignition system candidate for hydroxyl ammonium nitrate (HAN) based propellant, especially focused on SHP163, as substitution of conventional hydrazine. Plasma generation capability and power consumption characteristics were investigated as functions of frequency, applied voltage, and distance between high-voltage and ground electrodes. LF plasma jet in itself was generated at 5 Hz of frequency, 5 KV of applied voltage, and 5 mm of electrodes distance; and its power consumption was 16 W. At lower frequency and higher voltage, plasma generation capability was increased. Power consumption was decreased at lower frequency, lower applied voltage, and shorter electrode distance. At same applied voltage, lower power consumption was obtained at lower frequency and shorter electrodes distance. Additionally, LF plasma jet was applied to initiate SHP163. 1.1 × 10 -2 g/s of mass reduction rate was obtained at 5 Hz of frequency and 5 KV of applied voltage, and its power consumption was 30 W. This result indicates that LF plasma jet has excellent possibility to be a good reaction initiation/enhancement system.

Experimental Investigation of Inductively Coupled Plasma Cathode for the Application to Ion Thrusters

The inductively coupled plasma cathode (ICP/C) has been developed as electron source for ion thrusters to liberate the thrusters from the limitations of hollow cathodes. The power consumption efficiency of this cathode was not sufficient for practical use in space. Therefore, in order to improve the cathode performance, its ignition and electron emission characteristics were investigated experimentally as functions of orifice dimensions, ion collector shape and total number of coils in this study. It becomes clear that inner pressure and electric field in the discharge vessel are dominant factors of plasma ignition in ICP/C. Thus, the pressure rise by changing orifice dimensions and the RF voltage rise by increasing total number of coils cause the enhancement of ICP/C ignition capability. Electron emission current in ICP/C is limited by collected ion current in the ion collector, which depends on the ion saturation current at the ion sheath formed on the collector surface. Additionally, the ion saturation current strongly depends on electron number density, vessel inner pressure and ion collection area. Increase of total number of coils causes the enhancement of ignition capability and the improvement of electron emission performance. Moreover it is desirable for ICP/C lifetime to increase the number of coils. As the improved cathode performance, 0.52 A of anode current was obtained at 24 W of RF power, 0.15 mg/s of xenon mass flow rate and 40 V of anode voltage.

Basic Characteristics of Reaction Initiation System Using Dishcharge Plasma for 1N-class Thruster with Green Propellants

A new reaction initiation (ignition) system using discharge plasma is proposed for 1Nclass reaction control system (RCS) thruster with green monopropellant, especially, one of hydroxyl ammonium nitrate (HAN) based liquid monopropellant, SHP163. This reaction initiation system is designed in substitution for conventional catalytic decomposition system. In this study, fundamental reaction initiation characteristic of SHP163 by discharge plasma, based on total amount of energy applied, were investigated. Better propellant reaction initiation was achieved at larger number of discharge attributed from frequency even though levels of applied energy were same. It became clear that reaction initiation characteristics depend on not only total amount of energy but also number of single discharge. Additionally, a laboratory model of new reaction initiation system was designed and built. Fundamental characteristics based on power consumption were investigated. The new reaction initiation system was demonstrated with 100 to 5000 Hz of frequency and 3.2 to 27.8 mg/s of helium mass flow rate. At any cases in this experiment, stable discharge plasma generation was observed, and highest power consumption was 35 W.