Expected improvements in modeling Earth's time-variable gravity field using multiple GRACE-like satellite constellations

The Gravity Recovery and Climate Experiment (GRACE) mission has been a principal contributor in the study and quantification of Earth's time-varying gravity field. With continuing missions like GRACE Follow-On and the Gravity Field and Steady-State Ocean Circulation Explorer (GOCE) capitalizing on improved technologies such as laser interferometry and drag-free flying systems, respectively, the temporal aliasing of high frequency geophysical processes is anticipated to be the primary source of errors for future missions. Micro-satellite technology has presented the feasibility of improving the architecture of future missions with the implementation of a constellation of satellites having similar characteristics as GRACE. Such a configuration is suggested and analyzed to help address these under-sampling errors. The initial series of simulations is designed to build off the current GRACE mission with a near polar orbit, 450 km altitude, but with each satellite spaced approximately 120 km apart. Because of atmospheric and residual ground interference the reliability of ranging data diminishes at greater distances and therefore scenarios involving distances between satellites greater than 1,100 km are not evaluated. A multi-satellite orbit determination package (MSODP) is used to simulate these configurations and the observations corresponding to their orbits. This data is then processed using the Center for Space Research's Advanced Equation Solver for Parallel Systems (AESoP) linear least squares estimator providing high degree and order gravity field map solutions for each case. A sensitivity analysis is performed by varying certain parameters including: satellite spacing, altitude, and technological improvements. The multiple case results are consolidated to help ascertain the most optimal configuration for error reduction. Another series of data is provided from simulations which represent a constellation of satellites in a similar orbit except for the orbital plane being inclined at 72° with the same methodology implemented. This data is then combined in various configurations with the original data set of measurements and compared with the data from the original polar orbit scenario to determine the impact of a second train of satellites and their mitigation of detrimental effects like longitudinal striping. An analysis is performed to quantify the improvements of these configurations and is then evaluated to find optimal parameters for single and multiplane constellations. These results are extrapolated to show their impact on assessing metrics that would most benefit the water market's interests.