As space development and exploration progress, the need for high-performance propulsion systems becomes increasingly crucial. Electric propulsion utilizing a strong magnetic field to enhance thrust performance emerges as a promising candidate. In this study, we propose a kilowatt-class plasma thruster incorporating a high-temperature superconducting magnet capable of generating a high magnetic field in the 1 T range. The thruster operates based on electrostatic ion acceleration, utilizing the potential difference across the magnetic field lines. To achieve high magnetic field strengths, the superconducting magnet is cooled by a cryocooler, enabling efficient power-saving operation up to a magnetic field strength of 0.8 T. During the experiment, it was observed that the ignitability of the thruster was compromised at high magnetic field strengths. However, through modification of the anode electrode shape, ignitability was improved. The experimental results demonstrate notable performance improvements with higher magnetic fields, culminating in a thrust efficiency of 26.5% with a specific impulse of 1930 s at 0.8 T. These findings underscore the potential of utilizing high-temperature superconducting magnets in plasma thrusters for achieving enhanced thrust performance. The successful development of this kilowatt-class plasma thruster represents a significant step towards realizing efficient propulsion systems for future space missions.

In Microwave Rocket, which uses beamed energy propulsion, a phenomenon has been observed by which plasma remains inside the thruster for some long period of time. A difficulty with this plasma retention is that it delays the next millimeter-wave pulse irradiation, thereby decreasing the pulse repetition frequency and reducing the time-averaged thrust of the rocket. Enhancing the millimeter-wave pulse repetition frequency of Microwave Rocket demands a better understanding of the phenomenon of plasma remaining inside a thruster. For this study, the plasma decay time of 28 GHz atmospheric millimeter-wave discharges was investigated experimentally using analysis of images taken using a high-speed camera. Findings indicated that the plasma decay time increased rapidly to over 1 ms with the decrease of millimeter-wave power density at 100 kPa atmospheric pressure. Moreover, the plasma decay time at 20 kPa showed no such drastic increase at low power density. The vibrational and translational–rotational temperatures measured in the earlier study and the zero-dimensional non-equilibrium analysis performed for this study suggest that once thermal equilibrium is achieved at the plasma front, the plasma might remain for a long period of time up to 10 ms.

A scramjet engine is expected as an engine which can be applied to a future space transportation system. Many technical challenges still exist, one of which is to establish a measurement method to observe flow and combustion states within the scramjet engine. The TDLAS measurement method, capable to measure distribution of concentration, was applied to a supersonic reacted flow simulating the inner flow of a scramjet engine in our previous research. However, the errors were 19.3% and 18.4% in temperature and concentration measurements, respectively. Therefore, improvement on the measurement accuracy of TDLAS using two-line technique was attempted in the present study. The TDLAS was applied to a double diaphragms shock tube experiment for calibration, resulting in reduced error of temperature measurements to 80 K from 250 K in the previous study with a flat flame burner. After that, the distribution measurement in a supersonic reacted flow was implemented using TDLAS. In conclusion, the errors of temperature and concentration measurements were improved to 12% and –3%, respectively.