High-accuracy VLBI technique using ΔDOR signals

During the Chinese Lunar Project Chang'E-2 mission, a series of experiments on ΔDOR (delta differential one-way ranging) technology was carried out over a two week period starting on April 2, 2011. ΔDOR technology was first adopted in China deep space navigation, and the ΔDOR delay observables were obtained and used for orbit determination. In this paper, we introduce the ΔDOR observing technology, including the ΔDOR measurement principles. We also discuss the experiment design, the rules for selecting the calibration quasars, the switching time choice, the signal recording setup for the channels, the ΔDOR data processing method implemented in the software, and our analysis of the error sources of the ΔDOR delay and its contribution to orbit determination based on the characteristics of the Chinese VLBI network. Through these analyses and verification studies on the orbit determination from the satellite orbits in the CE-1 and CE-2 missions, we conclude that the accuracy of the ΔDOR delay is about 0.5 ns, an improvement of about one order of magnitude compared with that from S-band telemetry signals of less than 1 MHz. This study presents an important technique for high precision orbit determination of lunar and deep space explorations.