GRGS numerical simulations for a GRASP-like mission A way to reach the GGOS goal for terrestrial reference frame

In 2009, the geoscience community has fixed an objective of 1 mm accuracy and 0.1 mm/yr stability for the terrestrial reference frame (TRF) realization (Global Geodetic Observing System, GGOS, Meeting the Requirements of a Global Society on a Changing Planet in 2020, Plag and Pearlman in Global geodetic observing system: meeting the requirements of a global society on a changing planet in 2020. Springer, Berlin, 2009. ). This accuracy and stability are needed for diversified studies like climate change, tectonic sciences and more generally any geoscience requiring the use of an accurate and precise TRF. Unfortunately, they are still not reached by the last International Terrestrial Reference Frame. To reach this goal, the use of "multi-technique" satellites as "space-ties" has been studied since 2011 and a few proposals have been made in response to different space agency calls: the Geodetic Reference Antenna in Space (GRASP) mission-NASA Earth Venture 2 call, Eratosthenes-GRASP (E-GRASP)-ESA Earth Explorer 9 (EE9) call, MOBILE-ESA EE10 call, MARVEL-CNES Seminaire de Prospective Scientifique 2019). In this article, we present the numerical simulations carried out by the French Groupe de Recherche de Geodesie Spatiale (GRGS) for the E-GRASP proposal in response to the ESA EE-9 call and their improvements carried out afterwards. These simulations aim to answer three different questions:Is it possible to reach the GGOS requirements for the TRF with the measurements of a GRASP-like satellite like E-GRASP alone?If it is possible, which level of accuracy for the positioning of the on-board antennas is needed?What is the minimal lifetime of a E-GRASP mission to reach the GGOS requirements?The results of these simulations show that a E-GRASP satellite can allow us to reach, after five years, an accuracy close to 1 mm and a stability better than 0.1 mm/yr for the TRF. However, it is necessary to ensure a positioning better than 1 mm for the on-board antennas. We therefore encourage the new ESA GENESIS mission proposal, accepted during the ESA last Ministerial meeting on 23rd November 2022, which takes up the concept of a GRASP-type satellite.