ESA Activities and Perspectives on Quantum Space Gravimetry

In the past twenty years, gravimetry missions have demonstrated a unique capability to monitor not only major climate-related changes of the Earth directly from space - quantifying the melt of large glaciers and ice sheets, global sea level rise, continental draught, major flooding events, and also effects of large earthquakes and tsunamis. Adding to fundamental knowledge of the Earth, a quantum gravimetry mission will provide essential climate variables (ECV) of unprecedented quality for ground water, mass balance of ice sheets and glaciers, heat and mass transport,.. as demonstrated – within limits of past technology – by successful missions like GOCE and GRACE (FO). In order to respond to the increasing demand of the user community for sustained mass change observations at higher spatial and temporal resolution, ESA and NASA are at the moment coordinating their activities and are harmonizing their cooperation scenarios in an implementation framework, called MAGIC (MAss change and Geosciences International Constellation). In future post -MAGIC mission, a combination of classical sensors with CAI, or at a later stage a full quantum sensor will bring up the Quantum Missions for Climate to sensitivity that will open to many applications and user needs with respect to water management and hazard prevention among others [1] [2]. Special note must be taken also on the adoption of Quantum Technology (QT) for Earth Observation by the European Commission (COM), notably in the Horizon Europe programme, under the thrust of Commissioner T. Breton, and of the inclusion of QT in ESA Agenda 2025.COM and ESA are setting up a process that would realize a Pathfinder Mission to demonstrate the scientific and technical maturity of quantum gravimetry in space with a view to implement a ground-breaking Quantum Mission for Climate and other applications in the next decade.Several studies related to these new sensor concepts were initiated at ESA, mainly focusing on technology development for different instrument configurations (gravity gradiometers and satellite-to-satellite ranging systems) and including validation activities, e.g. two successful airborne surveys with a CAI gravimeter. A new study has been initiated in 2022, the Quantum Space Gravimetry for Earth Mass Transport (QSG4EMT) with the focus on QSG mission architectures that monitor Earth's mass transport processes and development of QSG user requirements.A technology roadmap will also be outlined for potential implementation of a Quantum Space Gravimetry Pathfinder mission before the end of this decade, aimed at improving state of the art accelerometers in the low frequency band and pave the way to developing a Quantum Mission for Climate in continuity and enhancement of MAGIC. [1] ESA-EC User Requirements workshop for Space Gravimetry Mission, Nov 2021.[2] Towards a sustained observing system for mass transport to understand global change and to benefit society, NASA/ESA Interagency Gravity Science Working Group (IGSWG), TUD-IGSWG-2016-01.