Geosynchronous satellites expanding a future GNSS satellite constellation: A precise orbit determination study

The integration of geosynchronous orbit (GSO) satellites in Global Navigation Satellite Systems (GNSS) is mostly discussed to enable a regional enhancement for tracking. But how do GSO satellites affect the orbit determination of the rest of the constellation? How accu-rately can these orbits be determined in a future GNSS tracking scenario with optical links? In this simulation study we analyze the ben-efit of GSO satellites as an expansion of a MEO (Medium Earth Orbit) satellite constellation - we selected the Galileo satellite constellation - for MEO Precise Orbit Determination (POD). We address not only the impact on POD of MEO satellites but also the possibility to precisely determine the GSO satellites - geostationary orbits (GEO) and inclined geosynchronous orbits (IGSO) - in such an expanded MEO constellation. In addition to GNSS microwave observations, we analyze the influence of different optical links between the participating entities: Optical two-way Inter-Satellite Links (OISL) and ground-space oriented Optical Two-Way Links (OTWL). These optical measurements together with the GNSS microwave observations give a remarkable benefit for the POD capabil-ity. In the case of GNSS and OTWL, we simulate the measurements with regard to a network of 16 ground stations. We pay great atten-tion to the simulation of systematic effects of all measurement techniques. We discuss the influence on the systematic errors as well as the formal orbit uncertainties. A MEO constellation expanded with GSO satellites as well as the use of optical links together with GNSS observations not only improves the MEO satellite orbits but also the GSOs to a great extent. (c) 2022 COSPAR. Published by Elsevier B.V. All rights reserved.