Relative Navigation of High-Altitude Spacecraft Using Dual-Frequency Civilian CDGPS

Mark L. Psiaki and Shan Mohiuddin

Abstract:	Carrier-phase differential GPS techniques are used to perform high accuracy relative position estimation for pairs of spacecraft that orbit at altitudes above the GPS constellation. These techniques are being developed in support of planned high-altitude missions that make high resolution science measurements by using data from sensors aboard formations of spacecraft. Precise knowledge of relative spacecraft positions within a formation constitutes a key ingredient needed for feedback control of the formation or for processing of its science data. Kinematic techniques are developed to determine relative position. They use dual-frequency signals to remove ionospheric effects, and they use LAMBDA/integer-least-squares methods to estimate double-differenced carrier phase ambiguities. A truthmodel simulation is used to evaluate the performance of this system at high altitudes. In geosynchronous Earth orbit, the system can resolve ambiguities almost instantaneously, and it can achieve relative position accuracies of about 0.25 m over short baselines. At an altitude of 17 Earth radii, the resolution of ambiguities requires on the order of 500 sec, relative position accuracies degrade to about 10 m, and intermittent ambiguity errors occur on a small subset of the tracked signals. The largest relative position errors are in the altitude direction and result from the large GDOP values that are caused by having all available GPS satellites below the user spacecraft.
Published in:	Proceedings of the 18th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2005) September 13 - 16, 2005 Long Beach Convention Center Long Beach, CA
Pages:	1191 - 1207
Cite this article:	Psiaki, Mark L., Mohiuddin, Shan, "Relative Navigation of High-Altitude Spacecraft Using Dual-Frequency Civilian CDGPS," Proceedings of the 18th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2005), Long Beach, CA, September 2005, pp. 1191-1207.
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