Transition to a 30 Satellite GPS Constellation

Clifford W. Kelley

Abstract:	The Air Force GPS Modernization Acquisition Master Plan (AMP) made a preliminary recommendation to expand the GPS constellation to 30 satellites. Enhanced GPS constellations consisting of 30 satellites in 3 planes and 30 satellites 6 orbital planes respectively have been developed by Boeing and Aerospace Corporation, Performance analysis demonstrated that with S/A turned off, a second civil frequency, improved URE expected from the Accuracy Improvement Initiative (AII), and GPS Block IIF cross-link navigation that the vertical accuracy availability to meet the wide area augmentation system requirements for the FAA Cat 1 Precision Approach is within reach for the expanded constellation. The study of reference 2 demonstrated that a 30 satellite constellation provides many benefits and that the 3 plane constellation offered better performance than the 6 plane constellation (7.25 m and 8.25 m 95% vertical accuracy respectively at a worst case latitude with availability of 99.9%). Although the 3 plane constellation provides better performance than the 6 plane constellation, the constellation requires a more complex, but feasible, transition strategy to maintain GPS performance throughout the transition period. A computer model was developed to determine optimal transition strategies to go from 21+3 satellites in 6 planes to 30 satellites in both 3 plane and 6 plane constellations. The effect on accuracy availability for both civil and military users, and various availability figures of merit were examined. Transition plans to move to 30 satellites in 3 or 6 planes show nearly identical trends. Therefore performance during the transition should not be a consideration in deciding on which constellation to use. The analysis demonstrated that it is feasible and practical to transition to both constellations with no degradation in performance and no significant risk.
Published in:	Proceedings of the 1998 National Technical Meeting of The Institute of Navigation January 21 - 23, 1998 Westin Long Beach Hotel Long Beach, CA
Pages:	371 - 380
Cite this article:	Kelley, Clifford W., "Transition to a 30 Satellite GPS Constellation," Proceedings of the 1998 National Technical Meeting of The Institute of Navigation, Long Beach, CA, January 1998, pp. 371-380.
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