Towards a GEodesy and Time Reference In Space (GETRIS): A simulation study

Progress in precise satellite orbit determination (POD) and navigation depends on the future ranging and time transfer capabilities. This leads to the need for high-precision links as well as high-precision clocks. However, not only a higher accuracy is required, but also the use of combination of complementary observation techniques to reduce systematic errors within an observation network. In a simulation study, we show our first concept of a GEodesy and Time Reference In Space (GETRIS). The initial GETRIS concept is based on the idea to have the reference in space build on geosynchronous orbit (GSO) satellites, but using Medium Earth Orbit (MEO) satellites is also possible. The goal is to achieve orbit accuracies of the GETRIS satellites at the same level as for ground stations – a few millimeters. Using high-precision optical links, the GETRIS shall establish connections to satellites in the near Earth environment and in deep space. When creating our GETRIS concept, we focus on three key pillars of a simulation study: Instrumentation, geometry and modelling. In terms of instrumentation, we performed scenarios using the synergy between L-band observations as well as high-precision dual one-way Optical Inter-Satellite Links (OISL) and ground-space based dual one-way links, called Optical Two-Way Links (OTWL), in different combinations. The geometry changes depending on the used observations network and the satellite constellation. Thereby, we analyze scenarios using a MEO-only and MEO+GSO constellations. To finally achieve mm-level orbit accuracies, an advanced modelling of non-gravitational forces is essential. A GETRIS can not only help with the connection of near Earth and deep space satellites, but also support the Global Geodetic Observing System (GGOS) and satellite missions such as GENESIS, which aim to realize a precise terrestrial reference frame with 1 mm accuracy and a stability of 0.1 mm/year.