# On the Integration of VLBI Observations to GENESIS into Global VGOS Operations
## 5 Discussion
The modeling of orbit errors applied in this work is simplified. The errors are derived from disturbances at the level of orbital elements, rather than from the forces acting on the satellite. Consequently, they may not fully reflect the anticipated errors for real observations. Therefore, our simulations should be regarded as lower limits. We perform frame tie realization from a VLBI perspective. The simulations presented here reflect standard practices for VLBI simulation studies. It should be noted, however, that the displayed frame tie realization based on a two-step approach represents merely one possible method of combining the space geodetic techniques via the GENESIS satellite. At this stage, several working groups are engaged in conceptualizing an optimal strategy for rigorously combining and commonly analyzing observations of the four space geodetic techniques at the observation level. Prior research has demonstrated that VLBI has the potential to contribute to the orbit determination of satellites equipped with VLBI transmitters (e.g., [18; 31]). Consequently, VLBI observations of GENESIS could play a significant role in the satellite's orbit determination. For observations of geodetic sources, we assume scan lengths of 30 s, as this is the common practice currently employed in VGOS experiments. However, VGOS operations are still developing and the implementation of adaptive scan lengths could reduce the duration antennas observe each source. Theoretically, scan lengths of 10 s or less are feasible with VGOS. Shorter scan lengths would increase the number of scans of geodetic sources in between GENESIS scans while maintaining unchanged MRTs. This could further decrease the impact of GENESIS on VGOS operations. Another aspect of VGOS that could develop more significance in the future is the concept of twin telescopes. At present, the three space geodetic observatories in Ny-Alesund, Onsala, and Wettzell are equipped with twin telescopes. The advantages are obtained by assuming that the tropospheric activity above the two antennas is identical and that they are connected to the same clock. An additional observing mode inherent to twin telescopes is multidirectional observing, whereby the two antennas point in different directions to observe different sources. In this way, each antenna is part of a different subnetwork. The advantage of this observing mode for observations of VLBI transmitters on board satellites, such as GENESIS, is that geodetic sources can be observed with no interruptions. With regard to GENESIS, the signal characteristics are currently the subject of discussion. Consequently, the signal-to-noise ratio, scan length, and precision of actual observations of GENESIS may deviate from the assumptions presented in this study. Prior to the launch of GENESIS in 2028, the VLBI technique still requires further development in the processing of observations of near-field targets to actually support the mission with dedicated VLBI observations [35]. In particular, the generation of the schedule files and station-specific control files need to be modified to seamlessly implement satellites in experiments with geodetic sources. Furthermore, due to the lack of tracking support of the antenna control units, some antennas are unable to continuously track GENESIS across the sky. Instead, stepwise or static tracking could be viable alternatives that require further investigation. These adjustments primarily necessitate software changes rather than hardware updates. In this study, we limited our analysis to VLBI observations of GENESIS with VGOS networks. It is intended that the legacy S/X network will continue its operations with the weekly R1 and R4 experiments, thus maintaining the time series of observations. By additionally integrating GENESIS in these experiments, the legacy antenna network can contribute with observations of be tied to the GENESIS frame and contribute to a common analysis of VLBI and the other space geodetic techniques.