Shun Imai

This paper reports on our study to develop a magnetic circuit with a discrete outer coil and test its performance in a Hall thruster. The results were compared to those of a Hall thruster on board the Engineering Test Satellite-9 (ETS-9), which used a cylindrical outer coil. At the normalized magnetic field strength of 0.58 for the 6 kW operation using a six poles discrete outer coil, the thrust, discharge current, Isp, thrust-to-power ratio, thrust efficiency, and discharge oscillation were 386.7 mN, 19.0 A, 1890 s, 66.9%, 62.0%, and 13.5% respectively. The Hall thruster with the new magnetic circuit achieved equivalent performance (including discharge stability) to the Hall thruster on board the ETS-9. Further, the study investigated the effect of the number of poles on the performance of the Hall thruster: the performance with the three pole coil was lower than that with the six poles coil. This paper also reports on the effect of pole numbers on utilization efficiency. Mass and current utilization efficiency were more affected by the magnetic field generated by the three poles outer coil.

The drifting trajectory analysis of the reentry recovery module RATS with inflatable deployable aeroshell is validated with the drifting trajectory based on the flight experiment data. The RTOFS sea surface current forecast data and the GFS ocean wind forecast data, released from NCEP, are employed in the drifting trajectory analysis. It is shown that the RATS can float for a long time, although the inflatable ring is filled with CO₂ gas, which has large gas permeability of the gas-tight layer. The leeway coefficient for drifting trajectory analysis is estimated to be 0.038 based on the floating design of the RATS. The drifting trajectory analysis was performed using the RATS landing point as the initial position. It was confirmed that the predicted drift direction agrees with the RATS drifting trajectory. However, the difference between the predicted result and the drifting trajectory increases with time in the ocean wind direction. The difference is approximately 0.8 km after 100 minutes from splashdown.

<p>The ion energy angle distribution and its relationship to plasma parameters for spot and plume modes are elucidated for a LaB₆ hollow cathode with a radiative heater. Measurements were conducted using a retarding potential analyzer (RPA) and a single Langmuir probe. The ion energy distribution function (IEDF) characteristics showed different tendencies in the current density and mass flow-rate dependence under different plasma modes. The IEDF peak potential for the spot mode varied from 16 to 23 V with increasing current density, and the IEDF peak potential for the plume mode varied from 16 to 32 V with decreasing mass flow rate. Considering angle dependency of ion energy, when the observation angle was changed from the radial direction to the axial direction, the IEDF peak potential increased from 29 to 40 V for the plume mode (10 A, 10 sccm) and increased slightly from 16 to 18 V for the spot mode (20 A, 30 sccm). The probe measurement analysis revealed that the IEDF peak energies are the same as, or exceed, the plasma potential and have a qualitative correlation with the electron temperature spatial distribution.</p>