Effect of station selection on VLBI-to-GNSS orientation transfer using space-ties onboard a next generation Galileo satellite

Abstract Each geodetic technique realizes its specific reference frame and traditionally these independent frames are linked through the local-ties at collocation sites. Space ties onboard of a spacecraft can be also used to connect different frames as another complementary approach. Observations of a broadband VLBI transmitter (VT) onboard Galileo satellite by a VLBI ground station network can create such a link between GNSS and VLBI reference frames. In this study, we simulate observations of a VT onboard Galileo satellites and investigate the effect of VT observing network/station selection on the rotation transformation parameters between the VLBI and GNSS frames. We find that the rotation transformation uncertainties can be inflated by more than 25% when a geometrically critical station is removed from the network of 21 ground stations. We additionally analyze various VLBI networks consisting of 8-9 ground stations dedicated to IVS R1/R4 sessions. We report that by adding individual stations into some networks uncertainties are reduced by up to a factor of three in daily solutions and up to 50% for all orientation components when combining solutions covering a Galileo repeat cycle of ten days.