Novel method of fast satellite movement information acquisition from VLBI observations

Abstract

Very Long Baseline Interferometry (VLBI) is a radio astronomy technique. The diameter of a VLBI synthetic telescope equals the longest baseline (>1000 Km). Therefore, VLBI can achieve very high angular resolution, and has unique advantage in the deep space tracking compared with the traditional radio ranging and Doppler tracking technologies. In the satellite VLBI observations, the spacecraft movement information such as delay or delay rate observable is very useful in the spacecraft position and orbit determination. This paper introduces an algorithm of obtaining satellite VLBI delay and delay rate based on short time correlation. Using the Differential One-way Doppler of the telemetry carrier, this method is able to complete fast fringe search, correlation, producing delay and delay rate with high accuracy from the satellite telemetry signals automatically, without any apriori orbit information. A special software correlator--Fast Fringe Searcher (FFS) was developed and successfully used in the data processing of the satellite VLBI experiments, such as the Chinese TC-1 Geospace satellite and the European SMART-1 lunar probe VLBI observations. The delay and delay rate produced by FFS were used in TC-1 orbit determination, which was the first Chinese VLBI satellite orbit determination experiment. Besides, an accurate VLBI correlator delay model can be constructed from FFS output. According to this model, a general VLBI correlator can produce more precise delay and delay rate through long time integration. This method will be applied to the real-time VLBI correlator system of the Chinese lunar exploration project in the near future.