1. Space Science Department, European Space Agency, European Space Research and Technology Centre, 2200 AG Noordwijk, Netherlands
2. Instituto di Fisica Cosmica e Tecnologie, Relative del CNR, Milan, Italy
3. Mullard Space Science Laboratory, University College, London, England
4. Instituto di Fisica Cosmica del CNR, Palermo, Italy
5. Mullard Space Science Laboratory
6. Instituto di Fisica Cosmica del CNR
7. Space Science Department, European Space Agency, European Space Research and Technology Centre