Since 2011 GFZ has been involved in the GETRIS (Geodesy and Time Reference in Space) ESA study aiming at the realization of a geostationary reference for space- and ground-based geodesy and timing applications. The space segment shall consist of several geostationary satellites (GEO) equipped with precise clocks providing time transfer as well as ranging to low Earth orbiting (LEO) satellites and to ground stations. One of the main goals of the proposed study is to investigate possible improvements in precise orbit determination (POD) of the LEO satellites and reduction of systematic offsets between current tracking systems (e.g. GNSS, VLBI, SLR, or DORIS). Another goal, where GFZ is mainly active, is to investigate the potential improvement in Earth gravity field determination for the GRACE configuration case augmented by the precise GEO-LEO ranging links
Additionally, two new observation techniques are introduced and analyzed in this study: a) the inclusion of VLBI observations of beacon signals emitted from GEO satellites and b) the use of space laser communication terminals for ranging and time transfer.
The other institutions participating in the project are TimeTech GmbH (lead), Stuttgart, Technical University Munich (TUM), Institute for Geodesy and Geoinformation (IGGB), Bonn, and the Physikalisch Technische Bundesanstalt (PTB), Braunschweig.