Optimal observing strategy of GENESIS in geodetic VLBI experiments 

One of the major deficiencies in the realization of the International Terrestrial Reference Frame (ITRF) stems from the combination of the four space-geodetic techniques, that are contributing: Very Long Baseline Interferometry (VLBI), Global Navigation Satellite Systems (GNSS), Satellite Laser Ranging (SLR), and Doppler Orbitography and Radiopositioning Integrated by Satellites (DORIS). The GENESIS satellite mission, a component of the European Space Agency’s (ESA) FutureNAV program, will address this problem. Scheduled for launch in 2027, the GENESIS satellite embodies a dynamic space-geodetic observatory, equipped with instruments encompassing all four space-geodetic techniques. The mission’s objective is to facilitate the in-orbit combination and co-location of these techniques in space, known as space ties. It is not yet known how GENESIS will be implemented in geodetic VLBI operations. In this talk, we will present a dedicated simulation study of VLBI observations to the GENESIS satellite. We look at the realistic observability given current and foreseeable antenna networks and session cadence. We schedule and simulate VLBI observations to the GENESIS satellite to investigate the accuracy with which VLBI antenna positions of a global network can be derived. In addition to the most common VLBI error sources, troposperic delays, clock inaccuracies, and white noise, we simulate satellite orbital errors. The observations to the GENESIS satellite are scheduled within regular, geodetic experiments. We compare different schedules varying the amount of time that is dedicated to observe the satellite. We analyse how incorporating these observations reduces the amount of time quasar sources are observed and, consequently, how fundamental geodetic VLBI observables, i.e. Earth Orientation Parameters (EOPs), are affected. We try to answer the question whether it would be necessary to include observations to the GENESIS satellite outside of regular geodetic experiments in the form of dedicated GENESIS sessions. The fact that VLBI is organized in sessions instead of continuous observing further raises the question to assess a minimal mission lifetime to achieve desired accuracies.