A Hybrid Approach Using Real and Simulated Data to Assess the Performance of VGOS Sessions with Added Genesis Observations

The Genesis mission of the European Space Agency (ESA) aims to provide near-continuous space ties among the four major space geodetic techniques. These ties are expected to help improve the accuracy and stability of the International Terrestrial Reference Frame (ITRF) by allowing the determination of inherent inter-technique biases. One of these techniques is Very Long Baseline Interferometry (VLBI). For Genesis, VLBI observations are planned to be made possible by emitting signals with an onboard VLBI transmitter, which can be observed using the VLBI Global Observing System (VGOS). Many technical and operational challenges are currently being addressed to make sure that VGOS can observe Genesis successfully. This is done through studies that rely on simulations or on experiments using non-Genesis-like satellites. So far, combining real and simulated data has been underutilised, even though it provides both realistic observation conditions and flexible scenario designs, which could be used to answer remaining open questions. Two examples of remaining challenges are the determination of how often Genesis should be observed without degrading the estimation of geodetic parameters and station positions, and the assessment of how and if Genesis observations can contribute to those estimates.In this study we apply a hybrid approach of combining real and simulated data. The aim is twofold: first, we want to investigate the impact of reducing the number of quasar observations on real 24-hour VGOS sessions as if Genesis was being observed; and second, we want to assess real 24-hour VGOS sessions which include simulated Genesis observations that are partially based on real data. The latter is done by combining real quasar observations and simulated satellite observations that are based on estimates from the real quasar observations. We also investigate the estimation of the geocentre, which is possible due to the added simulated satellite observations.