Performance Superiority of Dual-Pair Cartwheel/Pendulum Over Bender-Type in Four-Satellite Gravity Constellations: An Equitable Evaluation

This study quantitatively evaluates four candidate 4-satellite constellations-Dual-pair (DP) GRACE-type, Bender-type, DP Cartwheel-type, and DP Pendulum-type-for recovering Sub-Weekly to Weekly Earth time-variable gravity fields (TVGF). Using controlled numerical closed-loop simulations (identical altitude, satellite count, and sub-cycles), we conduct an equitable comparison of these constellations' performances in spectral and spatial domains under identical conditions. Comparative analyses under the optimal spatial resolution for each constellation configuration reveal that the DP Cartwheel-type and DP Pendulum-type configurations outperform the Bender-type configuration in recovering time-variable gravity field models at higher temporal resolutions. Spectral and spatial analyses confirm that the DP Cartwheel and DP Pendulum configurations surpass the Bender-type configuration, reducing the error by approximately 12%. In geoscience applications, the DP Cartwheel-type and DP Pendulum-type configurations slightly outperform the highly advocated Bender constellation design. Specifically, compared to the Bender-type, the DP Cartwheel-type and DP Pendulum-type configurations improve large-basin signal recovery accuracy by 7.4%, Greenland Ice Sheet's southern sector mass balance signals by 3.2%, and co-seismic signals by 13.2%. The simulation results indicate that the DP Cartwheel-type and DP Pendulum-type configurations show superior performance in gravity signal detection. However, due to current limitations in fuel consumption, laser pointing accuracy, and mission budget, maintaining these configurations remains technically and economically challenging. With future reductions in launch costs and advances in relevant technologies, these two configurations may become promising candidates for next-generation gravity missions.