Absolute orientation of Galileo orbits from simulated VLBI and GNSS observations

Abstract

The possibility of observing Galileo satellites with Very Long Baseline Interferometry (VLBI) telescopes may become possible in future as there are plans to put VLBI transmitters on these satellites. This would not only bring improvements for products, such as the International Terrestrial Reference Frame (ITRF), but would also allow to determine the absolute orientation of the satellite orbit with respect to the celestial frame. In this study, we investigate the determination of the right ascension of the ascending node Ω of a Galileo satellite orbit using simulated VLBI observations to quasars and a Galileo satellite. Therefore, a schedule including VLBI observations to a satellite covering an ultra short orbit arc of 40 minutes of the satellite surrounded by quasar observations is created, simulated and analysed. There are two different analysis options examined, first estimating Ω in a shorter interval of ten minutes and secondly estimating only one value for the whole 40 minute satellite period. The repeatability of Ω by estimating it in a ten minute interval is between 0.3 and 0.5 mas which corresponds to 4.5 cm and 7.5 cm at the altitude of the orbit. If there is only one value estimated the repeatability is below 0.2 mas which corresponds to approximately 3 cm at the altitude of the orbit.