小功率直流氨电弧等离子体推力器性能和等离子体特性研究

In recent years, with the development of the satellite miniaturization, there has been an urgent need for small propulsion thruster technology with the purpose of obtaining precise location in orbit. Arc-heated plasma thruster is one type of electric propulsion device, which has had long periods of successful applications, is simple in structure, and can be made compatible with the small satellite system. Ammonia is a propellant of high density, easily storable and safe to carry on board. In this project, very-low-power DC ammonia arc plasma thruster will be investigated, mainly experimentally, supplemented by theoretical analysis and numerical simulation. For the plasma thruster with arc power lower than 100W, electric discharge behavior within the 0.3mm-diameter channel, the arc root attachment on the inner wall of the anode, plasma plume status leaving the nozzle exit, and mN class thrust produced by the thruster will be experimentally studied. Numerical methods will be used to simulate the plasma flow from continuum to free molecular, and to analyze the energy conversion process within the nozzle. The effect of thruster structure and working parameters on the arc discharge mode, volt-ampere characteristics, plume parameters and thruster performance will be systematically investigated. The parameter combinations enabling stable operation of the thruster under the extreme conditions of pressure gradient up to 104 Pa/mm in the small discharge channel of 300 ?m will be explored. Through these studies, the main factors controlling stable discharge and performance of the thruster, the discharge processes and mechanisms of this kind of DC arc plasma will be better understood, and they will also provide reference data for the design of stable and high performing very-low-power ammonia plasma thruster.

卫星小型化的应用发展对其在轨精确定位的小推力器技术提出了迫切需求。本项目依此背景，选择空间电推进中有成熟应用积累、结构简单、易于小型化、与卫星系统协调性好的电弧加热推进方法，以高密度方便携带且安全性好的氨为推进剂，采用实验诊断为主，辅以理论分析和数值模拟的方法，对低于100W的推力器放电参数、0.3mm直径通道内放电行为、在阳极表面贴附形态、离开喷管的羽流状态、推力器产生的毫牛级推力进行实时观测；数值模拟由连续介质流动向自由分子流过渡的等离子体流动；分析阳极/喷管内的能量转换过程。系统研究推力器结构和工作参数对等离子体放电模式、伏安特性、羽流参数以及推力器性能的影响，探寻约0.1mm直径的氨电弧在高达10000Pa/mm的流向压力梯度下稳定运行的参数组合，掌握影响稳定放电和推力器性能的主控因素；深化对该类等离子体放电过程、特性和机理的认识，为高性能小功率氨等离子体推力器设计提供参考数据。

卫星的小型化对相应推进系统提出了更高的要求。本项目采用实验为主、辅以理论分析及数值模拟的研究方法，对用于小卫星姿态/轨道控制的100W级小功率氨电弧等离子体推力器的放电过程、特性和机理，以及推力器性能进行了系统研究。研制了多种不同喷管结构的小功率电弧等离子体推力器，建立和完善了10mN量级的小推力精确测量系统、直径0.3mm通道内的等离子体放电及弧根运动贴附观测系统，采用静电探针、发射光谱等多种诊断方法对电弧推力器性能参数进行了测量，获得了较为系统的小功率电弧等离子体推力器性能和特征参数实验数据。研究结果显示，研制的小功率氨电弧推力器可在数千秒的时间内长时间稳定运行，并具有良好的可重复性；采用研究中最优结构的小功率电弧等离子体推力器，获得的最高比冲达到340s，较研究初期提高了近100s；推力效率超过40%，接近1kW级电弧推力器的推力效率；小功率电弧等离子体推力器更趋向于小电流、高电压的工作模式，阳极壁面电流密度只有数十mA/mm2，几乎不存在阳极壁面烧蚀的现象，有利于推力器的长时间稳定工作。与实验工作相配合，数值模拟了低功率电弧发动机内的流动放电过程及传热特性，结果显示推力器喷管扩张段内流动明显偏离局域热力学平衡状态。本研究加深了对该类小功率电弧等离子体推力器的放电特性和运行机理的认识，可为稳定、高性能的小功率电弧推力器设计提供参考数据。