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Abstract:
The next-generation Global Navigation Satellite Systems (NextGNSS) satellites are planned to be equipped with inter-satellite links and ultra-stable clocks as well as a dedicated Very Long Baseline Interferometry (VLBI) transmitter. This will enable the VLBI network to observe the satellites along with extra-galactic radio sources. The study aims to evaluate the potential benefits by placing VLBI transmitters on NextGNSS satellites. This will empower the NextGNSS to determine UT1-UTC, which is otherwise impossible directly. Furthermore, VLBI observations of satellites would allow for independent validation of satellite orbit determination. In this study, we investigate geodetic parameters such as station positions and Earth Rotation Parameters (ERPs) and the impact of different network geometry on these parameters. Based on the initial findings, it appears that using satellites and quasars in VLBI can define a datum with No-Net Rotation (NNR) without the need for No-Net Translation (NNT) conditions. When both NNR and NNT are imposed, the Helmert transformation parameters are smaller compared to when only NNR is imposed. This can be improved by optimizing the network geometry. Furthermore, the study’s findings indicate that VLBI observations can determine the satellite’s orbit with cm-level accuracy. The performance of the ERPs is better in a uniformly distributed network especially when only NNR condition is imposed.
