Very soon, two satellites will be launched for measuring the changes in Earth's gravitational force due to mass changes equivalent to 1 cm of water over a quarter of a million square kilometres. The CHAMP mission (a joint German, US and French venture) in 1999 and a US National Aeronautics and Space Administration mission in 2001 called GRACE will carry out precise measurements of the Earth's gravity. These will provide scientists a record of the mass distribution of the Earth which could then be used to understand the structure and dynamics of our planet.