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

为了减小卫星的体积和重量，研究了一种低轨卫星定轨的新方法。该卫星用于对水汽的空间分布及其时间变化进行高灵敏度观测。利用小直径天线的射电干涉仪接收卫星信标给出的互相关相位变化率进行定轨。轨道确定精度的目标是由卫星上的GPS接收机给出的，这是几厘米。通过数值模拟和真实的观测验证了该方法的有效性，并将安装在鹿儿岛大学的西南-东北基线为75 m的射电干涉仪作为目标仪器。根据对Globalstar-31号卫星的模拟，确认轨道要素中10公里的初始位置误差和10米/秒的初始速度误差分别减少到18.6米均方根和34.9毫米/秒均方根。从真实的观测数据中可以看出，干涉仪测量的相关相位与用轨道根数估计的相位相差不大，并分析了轨道根数估计精度随干涉仪基线长度变化的趋势。定位误差基本上随着基线长度的增加而变小，并达到由状态估计滤波器中的灵敏度矩阵给出的下限，约为0.4 m 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.