在空间引力波探测中，无拖曳任务对微推力器提出了推力连续可调，亚微牛级推力分辨力与噪声，一百毫秒响应时间等要求。因为冷气微推力器可靠性高、无污染、电磁噪声和热噪声低等优点，所以选择冷气微推力器作为本文的研究对象。首先开展了微型拉瓦尔喷管气体流动机理研究。然后通过实验验证了两种冷气微推力器变推力实现方法的可行性。为满足研究过程中推力测试需要，发展并优化了一套基于扭摆的亚微牛级推力测量系统。最后实现了冷气微推力器的工程化，并对其推力性能完成了测试评估。

首先，根据气体一维可压缩流动理论，推导出了变喉部尺寸下，与推力有关的各项参数与扩张比的理论关系。通过实验研究发现微喷管喉部雷诺数越大，通过的流量与理论流量之比越大。研究了扩张比一定的条件下4种不同扩张角度喷管对比冲的影响，阐述了出口速度发散与内部摩擦耗散相互竞争共同制约喷管比冲的流动状况。还研究了背景气压变化对推力的影响，发现了完全不同于现有理论以及前人研究的反常现象，本文提出了两种可能的解释，背后的流动机理还需要进一步研究。

其次，提出了两种实现变推力调节的冷气微推力器设计方案，其一是通过脉宽推力调制（PWM）的方法调节推力。研制的PWM推力器推力分辨力可达0.2μN，推力开环响应时间可达28ms以下。研究发现，压力控制器到推力器之间的气容大小变化对推力噪声影响较小，压力控制的不稳定性是推力噪声的主要来源。其二是针对空间引力波探测卫星无拖曳任务的压电式冷气比例推力器，经过推力测试与优化最终确定了阀芯球面与喷管锥面密封方式，环形陶瓷双向位移驱动模式，热式流量传感器等方案。实验结果表明，推力器原理样机可实现0-30sccm范围的流量控制，流量控制分辨力可以达到0.01sccm，流量控制噪声在2mHz到10Hz频段内小于0.006sccm/√Hz，流量开环响应时间约30ms。

然后，发展并优化了一套基于扭摆的亚微牛级推力测量系统，以静电力作为标准力标定该推力测量系统。结果表明该系统的推力测量分辨力达到0.025μN，推力测量范围为0.025~400μN，背景噪声功率谱密度在0.4mHz~1Hz频段内优于0.1μN/√Hz。单一冲量元测量范围为0.05μN‧s-220μN‧s，分辨力可达到0.02μN‧s。实验研究了基于扭摆动力学方程的响应时间测量方法，推力测量系统可以比较准确的测量到一两百毫秒的响应时间，最快可测响应时间达十毫秒量级，并指出了提高响应速度的关键。提出了一种新的推力响应时间的测量方法，通过仿真计算证明了该方法的可行性，并阐述了使用该方法时需要满足的条件。

最后，研制了面向空间引力波探测无拖曳任务的冷气微推力器工程样机，并即将进行在轨验证。完成了全方位推力性能测试，实现了0到220μN的推力控制输出。推力分辨力达0.1μN，推力噪声在10mHz到1Hz频段优于0.1μN/√Hz，低于10mHz频段则在-40dB/dec斜率以下。1μN升到100μN上升时间为110ms（10%-90%），下降时间120ms（90%-10%），比冲可以达到66.9s（氮气）。

Drag free mission in space gravitational wave detection requires the micro-thruster to have the characteristics of continuously adjustable thrust, sub-micron thrust resolution and noise, and response time of 100 milliseconds. Because of the advantages of high reliability, non -polluting, non -pollution, electromagnetic noise and low thermal noise, the cold gas micro-thruster was chosen as the research object of this paper. The research on gas flow mechanism of micro Laval nozzle was carried out. Then, the feasibility of the two methods to realize variable thrust of the cold gas micro-thrust is verified by experiments. In order to meet the thrust test needs in the research process, a set of sub-micron-level thrust measurement system based on torsion pendulum was developed and optimized. Finally, the engineering of the cold gas micro-thruster was realized, and the test and evaluation of its thrust performance was completed.

Firstly, according to the one-dimensional compressible flow theory of gas, the theoretical relationship between the parameters related to thrust and the expansion ratio is deduced when the throat size changes. Through experimental research, it is found that when the Reynolds number of the micro-nozzle throat increases, the ratio of the passing flow to the theoretical flow also increases. The effects of four different expansion angle nozzles on the impulse were studied under the condition of a certain expansion ratio. The situation that the exit velocity divergence and the internal friction dissipation compete with each other to restrict the nozzle specific impulse is expounded. The effect of changes in background air pressure on thrust was also investigated. A phenomenon completely different from existing theories and previous studies was discovered. This paper proposes two possible explanations, and the underlying flow mechanism needs further study.

Secondly, two design schemes of cold gas micro-thruster to realize variable thrust adjustment are proposed. One of the two methods is to adjust the thrust by means of Pulse Width Thrust Modulation (PWM). The thrust resolution of the developed PWM thruster can reach 0.2μN, and the thrust open-loop response time can reach below 28ms. In the experimental study, it is found that the change of the gas volume between the pressure control and the thruster has little effect on the thrust noise, and the source of the thrust noise is the fluctuation of the pressure control. The second is a piezoelectric cold gas proportional thruster for space gravitational wave detection satellites without towing missions. After thrust testing and optimization, the sealing method between the spherical surface of the valve core and the cone surface of the nozzle, the two-way displacement driving mode of annular ceramics, and the thermal flow sensor were finally determined. The test results show that the thruster principle prototype can achieve flow control in the range of 0-30sccm, the flow control resolution can reach 0.01sccm, the flow control noise is less than 0.006sccm/√Hz in the 2mHz to 10Hz frequency band, and the flow open-loop response time is about 30ms.

Thirdly, A torsion pendulum-based sub-micron thrust measurement system was developed and optimized. The thrust measurement system was calibrated with the electrostatic force as the standard force. The results show that the thrust measurement resolution of the system reaches 0.025μN, the thrust measurement range is 0.025~400μN, and the background noise power spectral density is better than 0.1μN/√Hz in the frequency range of 0.4mHz~1Hz. The measurement range of a single impulse element is 0.05μN·s-220μN·s, and the resolution can reach 0.02μN·s. The response time measurement method based on the torsional pendulum dynamic equation is experimentally studied. The thrust measurement system can accurately measure the response time of one or two hundred milliseconds, and the fastest measurable response time is on the order of ten milliseconds. The key to improving the response speed is pointed out. A new measurement method of thrust response time is proposed. The feasibility of the method is proved by simulation calculation, and the conditions that need to be satisfied when using the method are expounded.

Finally, engineering prototype of cold gas micro-thrusters for space-oriented gravitational wave detection drag free missions were developed and will be verified on-orbit soon. Comprehensive thrust performance testing was completed. The CGMT-50 achieves a thrust control output of 0 to 220μN. The thrust resolution is 0.1μN. The thrust noise is better than 0.1μN/√Hz in the 10mHz to 1Hz frequency band, and below the -40dB/dec slope in the lower than 10mHz frequency band. The rise time from 1μN to 100μN is 110ms (10%-90%), and the fall time is 120ms (90%-10%). The specific impulse can reach 66.9s (nitrogen).