mproving and homogenizing Earth’s reference frames with an accuracy of 1 millimeter (mm) and a long-term stability of 0.1 mm/year are relevant for many scientific and societal endeavors. For instance, quantifying sea level change from satellite altimetry strongly depends on an accurate determination of the geocenter motion and the orbits of satellites. Sea level change is also determined from tide gauges that need to be precisely located with respect to continental and island reference stations. Reaching mm level accuracy in sea level change needs positioning the satellites and the reference frame with even better accuracy and with a long-term stability of 0.1mm/year. Numerous other applications in geophysics require also such absolute accuracy. This is the case, for instance, when monitoring tectonic motions or crustal deformations. It is thus important to reach high accuracy and precision in such observations in order to advance our understanding of the physical processes involved in the Earth dynamics (see Figure), as well as to contribute to a better understanding of natural hazards. Reaching such low errors in the measurements is also essential for positioning and navigation in the civilian applications and for proper geo-referencing of geospatial information.

We will in the future benefit from the future ESA GENESIS mission (to be launched in 2027), a spacecraft co-locating four geodesic techniques in order to enable a more precise realization of the reference frames, satisfying the above-mentioned requirements.