The Validation and Refill Architecture of GRACE and GOCE

Abstract

The Gravity Recovery and Climate Experiment (GRACE) and Gravity field and steady-state Ocean Circulation Explorer (GOCE) missions are widely presented as satellite-only determinations of Earth’s gravity field. Examination of primary source documents reveals two structural features that complicate this narrative. First, pre-launch planning documents and post-mission high-resolution models explicitly incorporate airborne and terrestrial gravity data—particularly NIMA/NGA Arctic Gravity Project measurements—as calibration, validation, and densification layers. Second, the GRACE attitude and orbit control system relied on cold-gas nitrogen thrusters whose propellant accounting, consumption rates, and long-duration maintenance are absent from the official launch documentation, despite a mission lifetime more than three times the design specification. These patterns parallel the documented use of airborne reference data in the ICESat/IceBridge system. The combined evidence indicates that the final high-resolution gravity products of the GRACE/GOCE era were hybrid constructs whose short-wavelength content and operational longevity rest on lower-altitude systems and unelaborated propellant margins.