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International Journal of Aerospace Engineering
Volume 2013, Article ID 627509, 11 pages
http://dx.doi.org/10.1155/2013/627509
Research Article

Relative Navigation in LEO by Carrier-Phase Differential GPS with Intersatellite Ranging Augmentation

1Department of Aerospace Engineering, University of Naples “Federico II,” Piazzale Tecchio 80, 80125 Naples, Italy
2Department for Technologies, University of Naples “Parthenope,” Centro Direzionale, Isola C4, 80143 Naples, Italy

Received 31 August 2012; Revised 21 December 2012; Accepted 4 January 2013

Academic Editor: Paul Williams

Copyright © 2013 Alfredo Renga et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Carrier-phase differential GPS (CDGPS) is a promising technology for accurate relative navigation in LEO formations of cooperating satellites, but navigation filter robustness against poor GPS geometry and noisy measurements has to be improved. This can be performed by augmenting the navigation filter with intersatellite local ranging measurements, as the ones provided by ranging transponders or GNSS-like systems. In this paper, an augmented CDGPS navigation filter is proposed for the formation of two satellites characterized by a short, varying baseline, relevant to next generation Synthetic Aperture Radar missions. Specifically, a cascade-combination of dynamic and kinematic filters which processes double-differenced code and carrier measurements on two frequencies, as well as local inter-satellite ranging measurements, is used to get centimeter-level baseline estimates. The augmented filter is validated by numerical simulations of the formation orbital path. Results demonstrate that the proposed approach is effective in preserving the centimeter-level accuracy achievable by a CDGPS-only filter also in the presence of a poor GDOP or a limited number of GPS satellites in view.