Research on micro thrust testing of microwave plasma thruster
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摘要: 本研究聚焦于微波等离子体推力器在微小卫星应用中的关键测试技术难题。针对实验室真空环境下的空间约束条件，创新性地开发了多种推力测量方案。实验采用1.5 kW功率的2.45 GHz磁控管微波源，通过氦气工质产生等离子体推力。研究重点突破了传统推力测量装置在有限空间内的应用限制，建立了包括直接力学测量和间接参数推算在内的完整测试体系。测试结果表明，在0～600 mN推力范围内，这四种方法在不同工况下均表现出良好的测量效果，且推拉力计和单摆推力计的测量结果高度一致，验证了方法的有效性。此外，基于谐振腔特性的间接计算方法在放电实验中提供了与直接测量相符的推力估计值，进一步证明了其可行性。本研究为微小推力器的地面测试提供了可靠的技术方案，其模块化设计思路特别适合立方星等微小卫星平台的推进系统验证需求。Abstract:
Background With the rapid development of microsatellite platforms such as CubeSats, microwave plasma thrusters have become ideal for orbit maintenance and attitude control due to their high specific impulse, no electrode ablation, compact structure, and flexible working fluid. However, the thrust of such thrusters (at the 1000W power level) is usually in the millinewton range, and its accurate measurement is crucial for performance verification. Existing thrust measurement schemes require at least 50 cm of space, conflicting with the extreme spatial constraint of 18 cm×16 cm in the current laboratory vacuum chamber; traditional indirect measurement also needs 2-3 parameters, increasing experimental complexity.Purpose This study aims to address the spatial limitation of the vacuum chamber, develop miniaturized thrust measurement schemes, establish a complete testing system including direct mechanical measurement and indirect parameter estimation, and verify the effectiveness and feasibility of these methods for ground testing of thrusters.Methods Four thrust measurement methods were developed: 1) Modified NH-2 electronic push-pull force gauge (2 N range, 0.001 N resolution) with a 5.5 cm metal target and 3D-printed bracket; 2) Pendulum thrust meter using an eddy current displacement sensor (2 mV/μm sensitivity) to measure small displacements, with force analysis under small angles (<10°); 3) Thrust calculation based on resonant cavity gas temperature (measured by WRe26 thermocouple, 0-1800 ℃ range) using adiabatic process and ideal gas equations; 4) Thrust calculation based on resonant cavity pressure (measured by a precision pressure gauge) via derived formulas. Experiments used a1500 W 2.45 GHz magnetron microwave source with helium as the working fluid, conducted under cold gas (microwave off) and discharge (microwave on) conditions.Results In cold gas experiments, thrust increased almost linearly with helium flow; push-pull force gauge and pendulum data were highly consistent, while temperature- and pressure-based calculated values were higher. In discharge experiments, thrust still increased with flow (slower at high flow), specific impulse remained stable (slight drop at high flow), and temperature- and pressure-based values showed better consistency. All four methods performed well within the 0-600 mN thrust range, with indirect methods consistent with direct measurements.Conclusions The four methods effectively solve the spatial constraint issue. Direct measurements (push-pull force gauge, pendulum) are effective, and indirect calculations (temperature, pressure) are feasible. The modular design is particularly suitable for CubeSats, providing reliable, low-cost, and easy-to-implement solutions for micro thruster performance verification and optimization, with promising application prospects.-
Key words:
- microwave electric thruster /
- thrust measurement /
- pendulum method /
- thrust gauge /
- plasma
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图 6 基于谐振腔气体温度的推力测试系统
Figure 6. Thrust testing system based on resonant cavity gas temperature
图 7 基于谐振腔气体压强的推力测试系统
Figure 7. Thrust testing system based on resonant cavity gas pressure
图 9 冷气实验中推力器推力随He流量变化图
Figure 9. Diagram of thrust variation of thruster with He flow rate in cold air experiment
图 10 冷气实验中推力器比冲随He流量变化图
Figure 10. Diagram of the variation of thruster specific impulse with He flow rate in the cold air experiment
图 11 放电实验中推力器推力随He流量变化图
Figure 11. Diagram of thrust variation of thruster with He flow rate in discharge experiment
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