VGOS – current status, challenges, and prospects

During the last decade, the next generation VLBI system, called the VLBI Global Observing System (VGOS), has been developed. It involves new, fast moving radio telescopes, that are equipped with dual-polarization broad-band receivers covering a broad frequency range from upper S-band to lower Ku-band. VGOS is planned to become the major VLBI contribution to the Global Geodetic Observing System (GGOS), surpassing the legacy S/X VLBI contribution by about one order of magnitude in terms of precision and accuracy of the geodetic products. While still being in its roll-out phase, VGOS started to become operational in 2020. The International VLBI Service for Geodesy and Astrometry (IVS) is now operating two VLBI networks in parallel, the legacy S/X VLBI network, and the new VGOS network. In early 2024, up to 13 VGOS stations are observing together in 24 h network sessions three times per month. These sessions are meant for the determination of the terrestrial reference frame (TRF), the earth orientation parameters (EOP), and the celestial reference frame (CRF). Additionally, several short (1 h) VGOS sessions are performed on several days each week, involving two or three VGOS stations only and focussing on the determination on earth rotation, i.e. the UT1-UTC parameter. There are several ongoing projects worldwide to establish further VGOS stations. It is expected that several of these will become operational in the near future, some even already in 2024, thus improving the geographical distribution of the VGOS network. In conjunction to an improved and densified VGOS network it is also planned to intensify the observation plan. In this presentation, the current status, challenges, and prospects of VGOS are reviewed and discussed. This includes a review of the expectations and obtained results of the geodetic parameters derived from the analysis of VGOS sessions.