In this study, we first considered the influence of micro-nozzle wall roughness structure on molecular collision and reflection behavior and established a modified CLL model. The DSMC method was used to simulate and analyze the flow of the micro-nozzle in the cold gas micro-propulsion system, and the deviation of simulation results before and after the improvement of CLL model were compared. Then, the rarefied flow characteristics under a small needle valve opening (less than 1%) were focused on the research, and the particle position, molecular number density, and spatial distribution of internal energy in the micro-nozzle were calculated. The spatial distributions of the flow mechanism in the micro-nozzle under different needle valve openings were compared and analyzed. It was found that when the needle valve opening is lower than 1%, the slip flow and transition flow regions move significantly upstream of the nozzle, the free molecular flow distribution region expands significantly, and the relationship between thrust force and needle valve opening is obviously different from that of medium and large needle valve openings. The effect of nitrogen temperature on the rarefied flow and thrust force is also discussed in this research. The numerical results showed that as gas temperature increases, the molecular internal energy, momentum, and molecular number density near the nozzle exit are enhanced. The thrust at small needle valve openings was significantly affected by the temperature of the working mass. The results of this study will provide key data for the design and development of cold gas micro-thrusters.

The cold gas micro-propulsion system can provide low noise and ultra-high accuracy thrust for satellite platforms for space gravitational wave detection, high-precision earth gravity field measurement. In this study, the effect of different needle valve opening ratios on the rarefied flow characteristics of a micro-nozzle in a cold gas micro-propulsion system was investigated based on DSMC method. The special feature of the currently studied micro-nozzle is that it has a section of micro-channel with a large length–diameter ratio up to 4.5. Due to the extremely small needle valve displacement of the nozzle (minimum needle valve displacement up to 1.7 μm), a finely structured mesh was used. The molecular particle and macro flow characteristics inside the micro-nozzle were calculated for the conditions of a needle valve opening ratio from 5% to 98%. The throttling effect of the throat has a significant effect on the rarefied flow in the micro-nozzle; especially under the tiny opening, this effect is more significant. The spatial distribution of continuous flow, transition flow, and free molecular flow in the micro-nozzle varies at different needle valve opening ratios. As the needle valve opening ratio increases, the continuous flow will gradually fill the microfluidic region.

In recent years, cold gas thrusters have been successfully deployed in numerous missions, showcasing their exceptional reliability and enabling ultra-precise space operations across a broad thrust range. This article introduces an integrated cold gas thruster that integrates flow, pressure, and displacement sensors. The thrust range of this thruster can exceed 1000 μN at most, and the resolution can reach up to 0.1 μN at low thrust. The results of the high-precision displacement sensor are good, showing that the thruster performs well in terms of flow control accuracy and thrust output sensitivity. The measurement accuracy of the force frame itself is also excellent, and it can detect small thrust changes of 0.1 μN. The thrust noise level of the thruster is good, comparable to the standard noise levels of the experimental environment.