The magnetosphere protects the Earth from electron, proton and ion particles fired from the Sun. But some reach the atmosphere causing electric storms that can affect communications networks and knock out satellites. They can also influence the climate over the long term. The project is one of the cornerstones of the ESA's Horizons 2000 science programme. Each satellite includes 11 instruments which will provide unique three dimensional images of the magnetosphere and its interactions with solar wind.
Space is an unforgiving business.