1. Office of Space Research and Technology; Academy of Athens; Athens Greece
2. Department of Astrophysics; Astronomy and Mechanics, Faculty of Physics, National and Kapodistrian University of Athens; Athens Greece
3. Applied Physics Laboratory; Johns Hopkins University; Laurel Maryland USA
4. Department of Physics; University of Maryland at College Park; College Park Maryland USA
5. Max-Planck-Institut für Sonnensystemforschung; Katlenburg-Lindau Germany