CHAMP, GRACE and GOCE: mission concepts and simulations

For the first time in satellite geodesy, three gravity missions have the
potentia1 of being realized: (1) CHAMP is a low-cost mission, an intermediate step
between our present knowledge and the ambitious goa1s 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
spatia1 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 rea1istic 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.