1. National Institute for Space Research, Av. dos Astronautas, 1758, São José dos Campos, SP 12227-010, Brazil
2. Department of Space Studies, Southwest Research Institute, 1050 Walnut Street, Boulder CO 80302, USA
3. School of Aeronautics and Astronautics, Purdue University, 701 West Stadium Avenue, West Lafayette, IN 47907-2045, USA