深空探测器的VLBI逆相位参考定位

Positioning of spacecraft with VLBI inverse phase reference

深空探测器的VLBI相位参考定位一般是以河外源为参考源,深空探测器为目标源,通过对河外源的观测数据进行条纹拟合,获得延迟和延迟率,用以改正这些效应对深空探测器的VLBI观测相位数据的影响,由于两者角距较近,主要误差源如传播介质延迟的影响通过对两者相位的差分得以基本消除,通过成图后可以获得两者的高精度相对位置.然而,这种传统的VLBI正相位参考定位方法对河外源的强度有较高的要求,即观测数据必须有足够高的信噪比来确保可靠的条纹拟合结果.通常深空探测器射电信号的流量密度远高于河外源,为此本文提出逆相位参考定位方法,即以行星探测器作为参考源,对相位校准后的河外源进行成图,来实现高精度的相对定位.本文基于实测的VLBI观测资料,验证了该方法的可行性;并通过模拟资料表明,在河外源较弱的情况下,逆相位参考可以获得更高精度的相对定位结果.

For positioning of spacecraft with VLBI phase-reference, an extragalactic radio source was usually served as phase reference. After fringe fitting on the radio source, the solutions including delays and rates mainly from the propagation media were adapted to calibrate the observed phase of the spacecraft. The common phase errors of the nearby source pair were significantly reduced in their differential phases, allowing accurate relative position measurement. However, this traditional phase-reference method requires strong and nearby extragalactic radio source, which is hard to fulfill due to the lack of strong calibrators on the sky. Since the radio flux density from the spacecraft is much stronger than that of the extragalactic radio source, it is possible to use the spacecraft as phase reference. In this paper, we investigated the feasibility and advantages of this so called inverse phase reference method, based on real VLBI observations. We compared the data analysis results using the two phase reference methods, it proved that the inverse phase reference is capable to measure accurate relative positions, and could achieve better results that the traditional methods, especially when the extragalactic radio source was weak.