GFZ Potsdam, Department 1

Introduction

GRACE is a joint project between the National Aeronautics and Space Administration (NASA) and the Deutsches Zentrum f�r Luft- und Raumfahrt (DLR).

The primary objective of the GRACE mission is to provide with unprecedented accuracy estimates of the global high-resolution models of the Earth's gravity field for a period of up to five years. The temporal sequence of gravity field estimates will yield the mean Earth gravity field, as well as a time history of its variability. An secondary science objective of the GRACE mission is to provide several hundred globally distributed profiles each day of excess delay or bending angle of the GPS measurements due to the ionosphere and atmosphere using limb sounding. These can be converted to total electron content and/or refractivity in the ionosphere and troposphere, respectively.

GRACE will succeed the CHAMP mission in the area of Earth gravity field measurements. The anticipated increase in accuracy will be achieved by utilizing two satellites following each other on the same orbital track. These satellites are interconnected by a K-band microwave link to measure the exact separation distance and its rate of change to an accuracy of better than 1 �m/s. To consider precise attitude and non-gravitational forces both satellites will be equiped with star cameras and accelerometers. The position and velocity of the satellites will be measured using onboard GPS antennae.

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