NAVSTAR/GLOBAL POSITIONING SYSTEM 18-SATELLITE CONSTELLATIONS

P. S. Jorgensen

Peer Reviewed

Abstract:	The original baseline constellation for the Navstar/Global Positioning System consisted of 24 satellites. This would provide continuous world-wide three-dimensional navigation, and it would insure an accurate navigation solution 100 percent of the time at any location on earth. As a cost-saving measure, the Air Force has now been directed to develop Navstar/GPS with an M-satellite constellation scheduled to be operational in 1987. This results in a constellation which will cause Navstar users to experience occasional outages of the system. Studies have been performed of various alternative 18-satellite constellations with the goal being to minimize the impact of outages on the Navstar user. Until recently, it has been generally accepted that with 6 satellites in each of the 3 orbit planes, the best arrange- ment would be to have the satellites spaced uniformly 60 deg apart. Studies by The Aerospace Corporation have shown that this is not true. A three-plane non-uniform arrangement has been found to provide far superior performance from the point of view of minimizing outages. Still another approach is to have 18 separate orbit planes, one for each satellite, which also provides superior performance. This paper discusses the difficulties inherent with the uniform 3-orbit-plane constellation and how these difficulties are in large measure overcome by the adoption of an alternate arrangement of the 18 satellites.
Published in:	NAVIGATION: Journal of the Institute of Navigation, Volume 27, Number 2
Pages:	89 - 100
Cite this article:	Jorgensen, P. S., "NAVSTAR/GLOBAL POSITIONING SYSTEM 18-SATELLITE CONSTELLATIONS", NAVIGATION: Journal of The Institute of Navigation, Vol. 27, No. 2, Summer 1980, pp. 89-100.
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