30cm离子推力器在轨环境下的工作点及热控措施研究

Working Points and Thermal Control of 30cm Diameter Ion Thruster in Orbit

栅极间距变化是影响离子推力器在轨环境下从冷态条件正常点火启动的重要因素,同时也决定了离子推力器的在轨工作时机和热控实施策略。采用有限元仿真与地面热平衡试验验证相结合的方法,建立起30cm离子推力器有限元分析模型并进行了模型校验,对离子推力器在轨受太阳光照影响的栅极温度场分布和间距变化,以及推力器在5kW工况下的三个典型温度点所对应的栅极间距变化进行了仿真分析,考虑了主动热控干预对推力器最恶劣工作点的栅极间距变化影响。结果显示:纯太阳光照影响下的栅极组件存在周期性温度变化,栅极最大温差可达到100℃,栅间距缩小量在0.06~0.16mm内波动;在太阳光照基础上实施60W的主动热控后,栅极最大温差降低至60℃,栅间距缩小量波动则变为0~0.03mm;栅极最高温度点和最低温度点分别是推力器冷态启动最容易和最困难的两个工作时机点,两点所对应的启动后屏栅和加速栅最小间距分别为0.22和0.04mm;在10,70和120W的热控加热功率下,从最低温度点启动后的屏栅和加速栅最小间距分别为0.06,0.20和0.29mm;采取主动热控措施能够有效降低推力器工作过程中的栅极热形变位移峰值,且加热功率为120W,即温控点温度为50℃的主动热控可以满足30cm离子推力器在轨冷态启动时的0.25mm安全栅极间距要求。

The grid gap variation is an important factor influencing the normal start-up in orbit of ion thruster under cold condition,and determines the time to start-up and thermal control strategies.Based on finite-element method and ground thermal balance test,an analytical model of the 30 cm ion thruster is built and has been demonstrated by test results.The grid temperature distribution and gap variation effected by solar illumination are firstly simulated.After that,when the ion thruster is working in 5 kW power and starts up from different initial temperature,the gap variations are considered.Finally,when the thruster starts up from the worst situation,the influence of thermal control on gap variation is calculated.The results show that if solar illumination is only considered,the temperature of grid gap varies periodically and the highest temperature is 100℃higher than the lowest one and the grid gap deduction varies in the range of 0.06~0.16 mm.When 60 W active thermal control is applied,the maximum temperature difference decreases to 60℃and the range of grid gap deduction changes to 0~0.03 mm.From the highest temperature point,the ion thruster start-up is most likely to be successful whereas from the lowest temperature point,it is the hardest.In these two situations,the minimum grid gap between the screen grid and the accelerator grid is 0.22 and 0.04 mm,respectively.When ion thruster starts up from the lowest temperature point and the thermal control power is 10,70 and 120 W,the minimum grid gap between the screen grid and the accelerator grid is 0.06,0.20 and 0.29 mm,respectively.Active thermal control can effectively reduce the maximum thermal deformation displacement of the grids and 120 W heat power(then corresponding target temperature is 50℃)can guarantee a safe grid gap for the 30 cm ion thruster starting up from the worst situation.