Champ, GRACE and GOCE: mission concepts and simulations

For the first time in satellite geodesy, three gravity missions have the potential of being realized: (1) CHAMP is a low-cost mission, an intermediate step between our present knowledge and the ambitious goals that are formulated by geodesists, solid Earth geophysicists and oceanographers; (2) GRACE is planned as being a more advanced mission, especially aimed at monitoring long wavelength time variations of the gravity field; (3) GOCE will open a completely new range of spatial scales (in order of 100 km) of the geopotential spectrum to research. The three missions are based on different space segments which have in common the high-low satellite-to-satellite tracking (SST) from GPS; other common parts being the low-low SST in the case of the two co-orbiters of GRACE, and gradiometry on board the GOCE spacecraft. Many new numerical simulations have been conducted in a unified effort in order to: 1. compare the concepts in terms of idealized (e.g. polar) missions using only one technique at a time; 2. estimate the capabilities of more realistic missions, closer to the planned scenarios of GOCE, GRACE and CHAMP with instrument, orbit and mission parameters that will allow an easy scaling to the actual cases. The most significant results are reported in this paper.