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.

Second order perturbation solutions of profiles of bubbles suspended in liquid and liquid gas interfaces when liquid all sinks in the bottom under different accelerations are derived. Six procedures are developed based on these solutions, and they are divided into two types. One takes coordinates of endpoints of profiles as inputs, and the other takes liquid volume or gas volume as inputs. Numerical simulation are performed with the Volume of Fluid method and numerical results are in good agreement with predictions of these procedures. Besides, the bigger the acceleration, the more flatter the bubble will be until all liquid sinks to the bottom. Effects of accelerations on bubbles shape must be considered. When liquid all sinks to the bottom, predictions of liquid volume with the same liquid meniscus height as inputs differs a lot under different accelerations. The most significant change of liquid volume is when Bond is much smaller than 1. Effects of accelerations and liquid contact angle on liquid gas interfaces must be considered during evaluating liquid residue, and these findings will be great helpful for liquid residue measurement and fine management in space.

The liquid in the satellite propellant tank is inevitably sloshing due to the vibration excitation of the rocket body. During the process of launch and satellite orbit change, the vibration excitation will be transmitted to the propellant tank. The resulting sloshing of liquid in the tank will generate additional sloshing force and moment applied on the satellite, which will have a serious impact on the satellite's attitude. In this paper, the sloshing performance of liquid in the large capacity propellant tank on the satellite is tested. The liquid sloshing tests were carried out on upper and lower tanks with a porous damping structure under different filling ratios, respectively. The mechanics data was collected by the sensor and analyzed using the classic pendulum model. Based on the test data and classic theory, the sloshing frequency, sloshing quality and sloshing damping parameters of upper and lower tanks were computed and compared. The results showed that the sloshing performance of the propellant tank was significantly affected by the internal damping structure. The research results of sloshing provide reference and support for the design and optimization of satellite attitude control.