Optimal Design of a Third Pair of Gravity Satellites to Augment Two Existing Polar Pairs to Enhance Earth's Temporal Gravity Field Recovery

Based on its unique sensitivity to Earth's temporal gravity, and since 2002, the gravity recovery and climate experiment (GRACE) twin satellites, and its successor, GRACE follow-on (GRACE-FO) missions have accumulated a two-decade-long and continuing Earth's mass change climate data record. Additionally, the Chinese gravimetry mission was launched as the last polar-pair satellite formation in 2021. With the opportunity of two existing polar-pair gravity satellite formations (EPGF) in operations, we explore the ideal configuration to launch a third-pair satellite formation to construct the triple-pair gravity satellite constellation (TGSC). Here, we examine the selection of initial orbit parameters of the third satellite formation based on subcycles and orbit parameters of EPGF to augment TGSC. The simulation study explores the effectiveness of the monthly temporal gravity field from the TGSC in potential contributions to geosciences. Our study reveals that TGSC improves continental hydrological signal recovery by approximately 24% and 38% in large and small basins (above/below 10 6 km 2 ), as compared with GRACE-FO, which would be the polar-pair gravity satellite in operations. TGSCs effectiveness varies across drainage systems of the Greenland ice sheet (GrIS) due to different ground track coverage. Compared with GRACE-FO, TGSC enhances GrIS mass balance recovery by 37%-56%. Simulations for six mega earthquakes (above Mw 7.7) reveal that TGSC outperforms GRACE-FO by approximately 46%-58% in extracting coseismic signals. Our study reveals the importance of incorporating existing on-orbit gravity missions into the design of future gravity satellite constellations. This strategy aims to not only accomplish the predefined objectives of gravity satellite missions but also potentially provide additional benefits to the field of geosciences.