1. a Observatoire de la Côte d'Azur—CERGA, Grasse, France
2. b Centre National d'Etudes Spatiales, Toulouse, France
3. c Institut Géographique National—CNES, Toulouse, France
4. d NOVELTIS, Ramonville Saint Agne, France
5. e Jet Propulsion Laboratory, Pasadena, California, USA
6. f University of Colorado, Department of Aerospace Engineering, Colorado Center for Astrodynamics Research, Boulder, Colorado, USA