On the opportunities of co-location in space for envisaged space-tie satellite missions

Co-location in space is an alternative combination strategy of the four main space geodetic techniques. All four of them, namely DORIS, GNSS, SLR, and VLBI, currently contributing to the determination of the terrestrial reference frame (TRF) can be combined using a so-called space-tie satellite, ideally equipped with receivers and/or transmitters for all of the techniques. The early GRASP and E-GRASP satellite mission proposals to NASA and ESA had not been recommended for the next phase, but recently, the GENESIS mission got green light from ESA which opens a unique opportunity for geodesy. We perform simulations and subsequent precise orbit determination (POD) of all four space geodetic techniques and solving also for the TRF, and combine them at one satellite using the space tie. Real data analysis including POD to prominent satellite missions like LAGEOS, TOPEX, and Sentinel-6A MF was done for most realistic simulations. In particular, the impact of biased space ties is investigated in terms of 14-parameter Helmert transformations compared to a perfect modeling solution. We will also present first simulation results of the GENESIS mission.