Alternative mission architectures for a gravity recovery satellite mission

The Gravity Recovery and Climate Experiment (GRACE) mission has been providing unprecedented levels of accuracy in measuring the Earth's gravity field since its launch in 2002. GRACE employs a mission architecture consisting of a collinear satellite pair, with measurements of changes in distance between spacecraft used to infer variations in the Earth's gravity field. The measurements are constrained to the along-track direction due to the GRACE mission architecture, which contributes to longitudinal striping in the estimated gravity fields.;This study examines four different mission architectures for a future gravity recovery satellite mission in hopes of improved mission performance: a two-satellite collinear pair, two two-satellite collinear pairs flying together, a two-satellite cartwheel formation, and a four-satellite cartwheel formation. Cartwheel orbits consist of a satellite formation performing relative elliptical motion about their center of mass as the formation orbits the Earth. Measurements of changes in distance between such spacecraft are, at times, directed towards the center of the Earth rather than along the orbital track. This geometric difference can be advantageous for estimation of the gravity field.;The ability of each formation to recover the gravity field at both 250 km and 400 km nominal altitudes was compared using numerical simulations performed with JPL's GIPSY-OASIS software package. 60x60 gravity fields were estimated using 30 days of data. Data noise characteristics of an improved satellite-satellite ranging system were included, along with aliasing errors from Atmospheric and Ocean Dealiasing (AOD) models. Results showed the gravity field errors associated with the four-satellite cartwheel formation were approximately one order of magnitude lower than the collinear satellite pair when only data noise was considered. When aliasing was introduced, the gravity field errors for each formation were approximately the same. The cartwheel formations eliminated most of the longitudinal striping seen in the gravity field error. A covariance analysis showed the error spectrum of the cartwheel formations to be lower and more isotropic than that of the collinear formations.