Impact of large satellite constellations on VLBI radio astronomical observations for materialization of celestial and terrestrial reference frames and EOP estimation

Abstract Geodetic VLBI is an application of the radio astronomy observation technique to study planet Earth. It is one of the geodetic space techniques which provides information about Earth in space and its rotational behaviour, hence it is fundamental for the global geodetic reference frame (GGRF). In particular with this technique ICRF can be determined at radio wavelengths, further it contributes with other space techniques to ITRF materialisation. Daily geodetic VLBI measurements are vital for determining and predicting the time-varying alignment of the Terrestrial Reference Frame with respect to the celestial reference frame (Earth Orientation Parameters). The routine work is coordinated by the IVS as a service for IAG and IAU and carried out by different institutions such as mapping authorities, space agencies, universities and research centres. In 2015 a UN Resolution emphasised the importance of the GGRF for sustainable development and asked member countries to extend these activities. At the same time the telecommunication networks are expanded on ground and in space increasing the number of transmitters. Large satellite constellations can have an impact on Geodetic VLBI products since they almost all broadcast downlink high power signals in the K band, and uplink signals (e.g. 14.0-14.5 GHz for Starlink). Owing to the increasing number of large constellations, an aggregate effect should also be considered, since they use different frequencies, usually in the K band. Furthermore their unwanted electromagnetic noise degrades the VLBI observations of faint cosmic noise. The signal strength of radar systems can even be destructive to the high-sensitive receivers at VLBI radio telescopes. The strategy is to answer the question of how to protect the global geodetic network infrastructure (locations of VLBI telescopes) in the corresponding study group at ITU-R and to seek for protection of the observed bands (32 channelised frequencies) in geodetic VLBI (which exceed the bandwidths of those bands already allocated to RAS).