Next Generation Gravity Mission (NGGM) status overview and scientific outlook
Authors: Daras Ilias , Massotti Luca , Willemsen Philip , March Guenther , Francois Michael , Carnicero Dominguez Bernardo 
Published: March 2024

The Next Generation Gravity Mission (NGGM) is European Space Agency&#8217;s (ESA) next Mission of Opportunity. &#160;It aims to extend and improve time series of satellite gravity missions by providing enhanced spatial and temporal resolution time-varying gravity field measurements with reduced uncertainty and latency to address the international user needs as expressed by the International Union of Geodesy and Geophysics (IUGG[1]) and the Global Climate Observing System (GCOS[2]) and demonstrate the critical capabilities for a potential future operational gravity mission.The NGGM principal observable is the variation of the range (distance) and range rates between two satellites measured by a laser interferometer; ultra-precise accelerometers measure the non-gravitational accelerations to correct the gravity signal retrieval in the on-ground data processing. The current baseline NGGM mission concept comprises a pair of satellites on a 397km-altitude circular orbit, at 220 km separation with an inclination of 70&#176;. The satellite-to-satellite tracking technique for detecting the temporal variations of gravity was established by GRACE (300-400 km spatial resolution at monthly intervals) using tracking in the microwave band. Today, GRACE is being continued by GRACE-Follow-On, with similar objectives, where the laser interferometry has improved the measurement resolution by a factor of 100 (upper Measurement Bandwidth.MAss Change and Geosciences International Constellation (MAGIC) is the European Space Agency (ESA) and National Aeronautics and Space Administration (NASA) jointly developed concept for collaboration on future satellite gravity constellation that addresses the needs of the international user community. MAGIC will consist of the GRACE-C (NASA and German Aerospace Center (DLR)) and NGGM (ESA) staggered deployment of 2 satellite pairs, with progressively improving measurement performance, to form a Bender-type constellation. It builds on the success of previous missions such as GOCE, GRACE and GRACE-FO therefore is considered a mature system architecture, that maximises the scientific benefit and enables new applications.This presentation provides a status overview of the NGGM system and technology development activities resulting from NGGM Phase A, entering NGGM Phase B1 as currently implemented by the European Space Agency and the scientific outlook of NGGM and MAGIC. In preparation for the MAGIC constellation, ESA and NASA have established a joint science and application plan on MAGIC, with the priority to identify and resolve the challenges in the development of the new MAGIC constellation products. We will present ESA&#8217;s plans on the development of the MAGIC higher-level products which involves the optimal combination of GRACE-C and NGGM data. We will also highlight the expected impact of NGGM and MAGIC on dedicated scientific research fields and applications.
[1] Pail, R., Bingham, R., Braitenberg, C. et al. Science and User Needs for Observing Global Mass Transport to Understand Global Change and to Benefit Society. Surv Geophys 36, 743&#8211;772 (2015). https://doi.org/10.1007/s10712-015-9348-9

[2] Terrestrial Water Storage ECV Requirements: The 2022 GCOS ECVs Requirements (GCOS 245)