Orbit Determination Using Radio Interferometer of Small-Diameter Antennas for LEO Satellites

为了降低低轨卫星的体积和重量，研究了一种新的低轨卫星定轨方法。这颗卫星用于高灵敏度地观测水汽的空间分布及其时间变化。利用小直径天线无线电干涉仪接收卫星信标得到的互相关位相变化率进行定轨。定轨精度的指标是星载GPS接收机给出的精度指标，为几厘米级。以鹿儿岛大学安装的西南-东北基线为75m的射电干涉仪为目标仪器，通过数值模拟和实际观测对该方法进行了验证。通过对Globalstar-31卫星的仿真，证实轨道单元的初始位置误差为10公里，初始速度误差为10m/S，减小为18.6mRMS和34.9 mm/S RMS。从实际观测中可以发现，由干涉仪得到的相关相位与用估计的轨道元素计算的相位之间的差异与数值模拟的相差接近，并分析了估计轨道元素的精度与干涉仪基线长度的趋势。随着基线长度的增加，位置误差基本变小，并达到状态估计滤波器灵敏度矩阵所给出的下限，约为0.4m RMS。

A new orbit determination method for a low-earth-orbit (LEO)satellite is studied to reduce the size and weight of the satellite. The satellite is used for high sensitivity observations of spatial distributions and their temporal variations of water vapor. The orbital determination is made by using variation rates of cross-correlation phase, which are given by receiving the satellite beacons with a radio interferometer of small-diameter antennas. Target of the orbit determination accuracy is that given by a GPS receiver on board satellite, which is a few centimeters. Verification of the method is made by a numerical simulation and a real observation, where a radio interferometer installed at Kagoshima University with a southwest-northeast baseline of 75 m is set as a target instrument. From the simulation for the satellite Globalstar-31, it is confirmed that an initial position error of 10 km and a initial velocity error of 10 m/s in the orbital elements were decreased to 18.6 m rms and 34.9 mm/s rms. From the real observation, it can find that difference between the correlation phase obtained with the interferometer and the phase calculated by using the estimated orbital elements is similar level with that of numerical simulations.Tendency of the accuracy of the estimated orbital elements is analyzed to the baseline length of the interferometer. The position error basically becomes smaller as the baseline length get longer, and reaches to a lower limit given by the sensitivity matrix in the state estimation filter, which is about 0.4 m rms.