Towards 30-years of mass change observations: GRACE Follow-On extended mission phase, and GRACE-Continuity developments 

The GRACE Follow-On (GRACE-FO) satellite mission, a partnership between NASA (US) and GFZ (Germany), successfully completed its nominal five-year prime mission phase in May 2023, and is currently in its extended mission phase. GRACE-FO continues the unique essential climate data record of mass change in the Earth system initiated in 2002 by the GRACE mission (2002-2017). The combined GRACE & GRACE-FO data records now span 23 years and provide foundational observations of monthly to decadal global mass changes and transports in the Earth system derived from temporal variations in the Earth’s gravity field.  In parallel, as part of NASA’s Earth System Observatory (ESO), a continuity mission called GRACE-Continuity (GRACE-C) scheduled for launch end of 2028 is being developed in partnership between NASA (US) and DLR (Germany), leveraging heritage elements considerably in the design.  One departure from heritage, is that the primary ranging instrument on GRACE-C will be a higher precision laser interferometer, capitalizing on the successful demonstration of this technology on GRACE-FO.  In this presentation, we will present updates on GRACE-FO in the context of satellite operations, data processing, and science/applications highlights, along with updates on the development of GRACE-C, which is meanwhile in Phase C and approaching the Critical Design Review in May 2025.  Prospects for achieving gap-free continuity between GRACE-FO and GRACE-C will be presented.