Feasibility of Managing a Dynamic Constellation to a Fixed Constellation Definition

Bruce P. Ayati and Paul D. Massatt

Abstract:	The GPS satellite constellation is dynamic. Earth gravitational forces cause orbits to vary, and solar and lunar gravitational forces produce out-of-plane perturbations. Launch dispersions often result in orbits that are not nominal. Even the number of satellites in the constellation can vary over time given anticipated and actual satellite failures and routine maintenance. The GPS satellite constellation is operationally managed to sustain the global-averaged availability of 3Dnavigation coverage by routinely moving satellites within the constellation. Long-term planners and builders of GPS augmentation systems often use fixed “orbital planes and slots” as defined in various GPS specifications. These reference orbits were meant to inform contractors that build GPS satellites, not users of the GPS, of what is needed in the way of satellite capability. These documents were not intended to convey that actual GPS satellites are in fixed orbits. In this paper, we discuss the technical balance between operational flexibility and the demands of long-term planners. We show the sensitivity of positioning dilution of precision to perturbations in right ascension of ascending node, mean anomaly and inclination. Lastly, we give examples of how a flexible constellation structure can be adjusted to preserve and manage GPS coverage in a dynamic environment.
Published in:	Proceedings of the 57th Annual Meeting of The Institute of Navigation (2001) June 11 - 13, 2001 Albuquerque, NM
Pages:	140 - 148
Cite this article:	Ayati, Bruce P., Massatt, Paul D., "Feasibility of Managing a Dynamic Constellation to a Fixed Constellation Definition," Proceedings of the 57th Annual Meeting of The Institute of Navigation (2001), Albuquerque, NM, June 2001, pp. 140-148.
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