电磁监测试验卫星离子漂移计探测技术

依据电磁监测试验卫星的任务要求,自主研发了等离子体分析仪,用于探测电离层等离子体的离子密度、温度、成分、漂移速度和密度的涨落.等离子体分析仪由阻滞势分析器、离子漂移计和离子捕获计组成,其中离子漂移计用于探测离子垂直轨道方向的漂移速度.通过分析电离层等离子体的离子漂移速度特性,确定仪器的性能指标.离子漂移计传感器采用多层栅网压紧结构,栅网材料选用铍铜,各层栅网之间采用聚酰亚胺绝缘.依据技术指标,详细设计了离子漂移计传感器的窗口尺寸、传感器几何高度和收集极半径.在电子学电路设计时通过前放电路三个可调量程的设计,保证了电路测量范围和精度,并通过实验进行验证.在此基础上,借助意大利国家天体物理研究院行星际物理研究所的地面等离子体环境,完成了离子漂移计的等离子体环境测试.测试结果表明,离子漂移计垂直轨道方向漂移速度测量结果的变化趋势与转台设定值变化趋势一致,且测试精度指标满足设计要求,能够满足电磁监测试验卫星的任务需求.

Ion drift meter aboard China seismo-electromagnetic satellite

A lot of electromagnetic anomalies observed by satellites before earthquakes indicate that there is interrelation between earthquake and ionosphere.China seismo-electromagnetic satellite (CSES) is the first Chinese space-based platform of three-dimensional earthquake monitoring system.The scientific payload of plasma analyzing package (PAP) aboard CSES is designed to study the possible influence of the seismic activity on the ionospheric plasma and thereby to monitor the earthquakes from space.The PAP is made up of three sensors,retarding potential analyzer (RPA),ion drift meter (IDM),and ion capture meter (ICM).The main objective of IDM is to detect the ion bulk velocity from-3 to 3 km/s with a precision better than ±20 m/s,perpendicular to the sensor-look direction.The IDM sensor consists of six-layer grids and a collector.The grid is made of beryllium copper,plated with gold.Polyimide is used to achieve electrical insulation between grids.The grid transmission rate of signal layer is designed to be 82.64%,and total transmission rate of six layers is 31.85%.To ensure the performance of IDM,the side length of the square aperture and the depth of the sensor are designed to be 40 and 20 mm,respectively.The radius of segmented planar collector is 50 mm.The arrival angle of the ions is determined by measuring the ratio between the currents from the different electrically isolated collector segments.Accordingly,velocity perpendicular to the sensor-look direction is calculated,based on arrival angle and ion velocity parallel to the sensor-look direction which is measured by the RPA.In addition,a wide-range and high-precision current measurement circuit is designed to measure the current of IDM.The preamplifier circuit has three measurement ranges,providing different amplification factors.The right measurement range is chosen automatically by the field programmable gate array (FPGA).The test results show that the circuit provides a total measuring dynamic range from 20 pA to 6μA with an accuracy better than 0.4%.Finally,the method of testing in the plasma environment and the measurement results are discussed.The plasma environment test of the IDM flight model is carried out in the Institute for Space Astrophysics and Planetology,National Institute of Astrophysics (INAF-IAPS).Since the plasma source is fixed to a large volume vacuum tank,the arrival angle of the plasma with respect to the sensor-look direction is changed by horizontally or vertically mounted IDM on the rotating platform in the vacuum tank.As the platform rotates,the performance of IDM is proved by testing different ion arrival angles in vacuum tank.The ion velocities along the Y and Z axes of the spacecraft are validated by testing the horizontal arrival angle and the vertical arrival angle respectively.The IDM test data are consistent with those obtained under the setting angle of the rotating platform.The experimental results show that the detector has good performance and will fulfill the mission goal of monitoring the bulk velocity of ion,perpendicular to the sensor-look direction.