Studies of an orbital gradiometer mission

The goal of using an orbital gradiometer mission to provide an accurate (1 to 2 mgal), high resolution (1 by 1 deg), global map of the earth's geopotential is currently being investigated. This investigation involves the simulation of the satellite ephemeris and the corresponding gradiometer measurements which can be used in the study of various techniques and methodologies that were proposed to recover the parameters used in modeling the geopotential. Also, the effects on the mission of various time varying forces acting on the spacecraft were included in the studies

FLIGHT DYNAMICS ASPECTS OF THE GRACE FORMATION FLYING

Three key items have been studied at the mission control center (GSOC) for the build-up and control of the GRACE formation (along-track separation of about 220±50 km): 1. The safe ejection of both satellites from the upper stage and the intial acquistion of the nominal formation. 2. The control of the semi-major axes of both spacecrafts to maintain the inter-satellite separation within tolerable margins while minimizing any perturbations of the science operations. 3. The use of the SGP4 orbit model as on-board orbit propagator to allow a pery precise prediction of the relative position perpendicular of the line-of-sight vector

Large Scale Ocean Circulation from the GRACE GGM01 Geoid

The GRACE Gravity Model 01 (GGM01), computed from 111 days of GRACE K-band ranging (KBR) data, is differenced from a global mean sea surface (MSS) computed from a decade of satellite altimetry to determine a mean dynamic ocean topography (DOT). As a test of the GGM01 gravity model, large-scale zonal and meridional surface geostrophic currents are computed from the topography and are compared with those derived from a mean hydrographic surface. Reduction in residual RMS between the two by 30–60% (and increased correlation) indicates that the GGM01 geoid represents a dramatic improvement over older geoid models, which were developed from multiple satellite tracking data, altimetry, and surface gravity measurements. For the first time, all major current systems are clearly observed in the DOT from space-based measurements