Very low Earth orbit (VLEO) satellites are confronted with the challenge of orbital decay caused by thin atmospheres, and the volume and power limitations of micro satellites further restrict the application of traditional electric propulsion systems. In response to the above requirements, this study proposes an innovative scheme of radio frequency plasma micro-thrusters based on magnetic nozzle acceleration technology. By optimizing the magnetic nozzle configuration through the system, the plasma confinement efficiency was significantly enhanced. Combined with the mixed working medium (5 sccm Xe + 10 sccm air), the thrust reached 1.7 mN at a power of 130 W. Experiments show that the configuration of the magnetic nozzle directly affects the plasma beam morphology and ionization efficiency, and a multi-magnet layout can form a stable trumpet-shaped plume. The air in the mixed working medium has a linear relationship with the thrust gain (60 μN/sccm), but xenon gas is required as a “seed” to maintain the discharge stability. The optimized magnetic nozzle enables the thruster to achieve both high thrust density (13.1 μN/W) and working medium adaptability at a power level of hundreds of watts. This research provides a low-cost and miniaturized propulsion solution for very low Earth orbit satellites. Its magnetic nozzle-hybrid propellant collaborative mechanism holds significant engineering significance for the development of air-aspirating electric propulsion technology.

Air-breathing electric propulsion enables sustained operation in very low Earth orbit by using in situ atmospheric gases as propellants. Radio-frequency ion thrusters operated with nitrogen–oxygen mixtures generate multiple ionization products, making single-species thrust calculations inadequate. In this study, an RIT-13 thruster was experimentally investigated under different nitrogen-to-oxygen flow ratios and RF powers to characterize ion beam behavior and ionization-product composition. Residual gas analysis was used to identify the discharge products. To resolve the overlap of N₂ and CO related signals at m/z = 28, a composition reconstruction method based on Dalton’s law of partial pressures and nitrogen/oxygen atom conservation was developed. The reconstructed composition was incorporated into a multi-component thrust model by summing the contributions of individual ion species. Results show that the nitrogen-to-oxygen ratio strongly affects the ion beam composition, while RF power mainly adjusts the relative species fractions. Increasing oxygen fraction shifts the beam from N₂⁺ dominance toward multi-component coexistence involving O₂⁺, O⁺, and NO⁺. Calculated thrust agrees with direct measurements, with relative errors below 5% under all tested conditions. The method provides a practical basis for thrust prediction of air-breathing radio-frequency ion thrusters.

Systematic experimental characterization of the electron extraction characteristics of a radio-frequency plasma bridge neutralizer (RPN) in the actual ion-plume environment of a radio-frequency ion thruster (RIT) remains limited, particularly regarding the effects of ion-beam conditions and the relative configuration between the RIT and RPN. In this study, an experiment consisting of an RIT-13 and an RPN-2.5 was established, in which the RIT-13 operated with an Xe + N₂ + O₂ mixed propellant and the RPN-2.5 operated with Xe. Experimental investigations were conducted to systematically examine the effects of collector bias voltage, ion beam current, screen-grid voltage, RPN installation angle, and spatial position on electron extraction. The results show that the collector bias voltage is the primary parameter governing the electron extraction state, and two distinct jumps occur as the magnitude of the negative collector bias voltage increases, while the ion beam current mainly modulates the electron extraction state near the threshold of the first jump. The 60° and 90° configurations generally exhibit stronger electron extraction capability than the 0° and 30° configurations and require smaller magnitudes of negative collector bias voltage to reach the high-current electron extraction state. A pronounced spatial dependence is also observed. At an ion beam current of approximately 440 mA and a screen-grid voltage of 1200 V, the region of X = −10 mm and Y = 20–40 mm exhibits favorable electron extraction characteristics. Among the investigated configurations, the 90° configuration at (−10, 40) mm requires the smallest magnitude of collector bias voltage, approximately 13.5–14 V, for the RPN electron extraction current to match the RIT ion beam current. This current-matching bias is defined in the present study as the equivalent floating potential U_eq. These results provide an experimental basis for the matching design and spatial configuration of RITs and RPNs in an air-breathing electric propulsion system.