A fluid experiment was conducted on China’s SJ10 satellite to assess the instability of thermocapillary convection under microgravity. Oscillations of thermocapillary convection in an annular pool were investigated when the difference in temperature exceeded a certain threshold. Dynamics and transitions of the wave pattern were observed using an infrared camera. This work is concerned with the effect of the surface configuration on the wave patterns. There are 3 types of surface configurations that depend on the volume ratio: Vr < 0.77 (zone 1), 0.77 < Vr < 1 (zone 2), and Vr > 1 (zone 3). An irregular local wave occurs at Vr < 0.65, and a regular azimuthal wave occurs at Vr > 0.65. We observed the regular wave with the wavenumber m = 3 in zone 1 and zone 3 and the competition between m = 3 and m = 4 in zone 2. The nonlinear dynamics of traveling waves, standing waves, and counterpropagating waves were studied. The standing wave appears near the onset and transitions to the traveling wave. With a similar mechanism, counterpropagating waves with m = 3 and m = 4 occur in some cases at the onset. Additionally, counterpropagating waves also act as a transitional mode when the traveling wave transitions from m = 4 to m = 3. The traveling wave is very stable, but it develops into standing waves or Benjamin-Feir instability under highly supercritical conditions.

A 4-probe laser interferometric displacement sensor (4pLIDS) has advantages over a single-probe LIDS in a micro-thruster calibration system. By synchronously measuring the displacements at four points and differentiating the measured data, the common-mode noise can be greatly suppressed, thereby improving the measurement accuracy. Based on the design requirements of the nanometer-resolution 4pLIDS, we discussed the connections among various performance aspects of LIDS, designed evaluation schemes, and conducted tests. We devised the schemes to evaluate the 4-probe performances related to synchronicity using a single nanopositioning stage as the displacement reference, and considering the agreement and output temporal uniformity from each probe. We further analyzed the influences of the non-ideal performances of the displacement reference on the evaluation results to ensure that the results truly reveal the LIDS's performances. The evaluation results show that the resolution of the 4pLIDS reaches 0.7 nm, the standard deviation (SD) of the 4pLIDS repeatability is no more than 0.15 nm and the inconsistency error among the 4 probes is within ±0.4 nm. The actual differential measurement results using the 4pLIDS conform to the predictions from the evaluated performances and demonstrate the effectiveness of the evaluation.

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.

Micro-thrusters play a pivotal role in achieving drag-free control in space-based gravitational wave detection missions. Dynamic micro-thrust reconstruction is crucial for comprehensive evaluation and understanding of the operational process of micro-thrusters, and for the advancement of higher-performance micro-thrusters. The conventional dynamic thrust reconstruction method, inversion of dynamic equation (IODE), heavily relies on the dynamic equation model. And this dependence leads to performance decline when discrepancies emerge between the model and the actual system, coupled with a time-consuming parameter estimation process. To overcome these limitations, this paper introduces an innovative algorithm breaking free from the constraints of parametric models, named the dynamic matrix control algorithm-based dynamic thrust reconstruction (DMC-DTR) algorithm. In this paper, the underlying principles and algorithm process of DMC-DTR are presented. Comparative analyses of DMC-DTR and IODE are conducted through both simulated and real dynamic thrust measurement experiments. The results indicate that DMC-DTR closely matches the performance of IODE when the dynamic equation model aligns with the actual system. Notably, when the model diverges from reality, DMC-DTR outperforms IODE significantly, showing the enhanced universality of the proposed algorithm. In addition, simulation reveals that DMC-DTR exhibits better performance than IODE at lower sampling frequencies. Moreover, the dynamic thrust from a cold gas micro-thruster is reconstructed by DMC-DTR to demonstrate its practical application.