New and Improved GPS Satellite Constellation Availability Model

Rhonda Slattery, Karl Kovach

Abstract:	This paper describes a new and improved Global Positioning System (GPS) satellite constellation availability model. As used here, improved means a model that corresponds more closely to the actual GPS satellite constellation availability seen in the real world than currently existing models. Realistic models are very important in this area, since the satellite constellation availability is a key factor in determining whether GPS can ever become a sole/primary means of navigation. The improvements in this new model are primarily gained by accounting for the realities of GPS satellite constellation management. The model accomplishes this by emulating the processes for scheduling satellite downtimes, dealing with the presence of on-orbit surplus satellites, and planning replenishment satellite launches. Secondary improvements come from using better estimates of the Mean Time Between Failure (MTBF) and Mean Time to Repair (MTTR) for the various classes of satellite outage events. The results of the new and improved model are presented and compared with the observed on-orbit history to serve as a qualitative validation of the model. The results give an interesting prediction of what the “steady-state” GPS satellite constellation will eventually look like, barring any unforeseen changes in the constellation management processes.
Published in:	Proceedings of the 12th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1999) September 14 - 17, 1999 Nashville, TN
Pages:	2103 - 2112
Cite this article:	Slattery, Rhonda, Kovach, Karl, "New and Improved GPS Satellite Constellation Availability Model," Proceedings of the 12th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1999), Nashville, TN, September 1999, pp. 2103-2112.
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