Observing GNSS Satellites with the AuScope VLBI Array: A Testbed for the VLBI Component of the GENESIS Mission

Set for launch in 2028, geodesy’s flagship mission GENESIS is equipped with the instruments of the four space geodetic techniques. The co-location satellite aims to improve the accuracy and stability of future realizations of the ITRF. However, VLBI observations to satellites are not standard and are not performed routinely yet. In the past, observations were limited to specific telescopes and setups. At the moment, most VLBI antennas are not capable of observing currently available satellite signals. This makes testing difficult, although further research on the VLBI component of GENESIS is urgently needed to achieve the accuracy for the mission goals. We present the newly accessible capability of the Australian VGOS telescopes to observe GNSS satellites in L-band.  With this new discovery, we are able to generate geodetic delay observables with a full continental-wide telescope array on a routine basis in the style of IVS observations. In particular, we report on a series of successful observations to satellites of the GPS, Galileo and BeiDou constellations with the AuScope 12-m antennas in Hobart, Katherine and Yarragadee using the standard VGOS equipment. We describe the experimental setup, signal chain and key developments enabling these observations. Furthermore, we report on the ongoing efforts in the fringe fitting phase with critical effects on the delay. This crucial development is a valuable opportunity to further develop VLBI observations to satellites in preparation for the GENESIS mission. In addition, such observations could realize the first-ever inter-technique ties between VLBI and GNSS in the Australian region.