Impact of GPS Block IIR Space Vehicle Lifetime on Constellation Sustainment

W. Marquis, J.D. Riggs

Abstract:	The GPS Block IIR and IIR-M Space Vehicles (SVs) have begun to reach extended lifetime regions, even as the final two were launched last year. Now that IIR constitutes more than half of the GPS constellation, the question arises as to how long these SVs will last. Will it be 5 years, 10 years, 20 or more? How will this impact GPS constellation sustainment? Will sufficient satellites be available to meet the user requirements until the GPS III SVs are operational? This paper will explore the current predictions for IIR and IIR-M lifetime. It will also examine the implications of this extended life for the IIR/IIR-M sub-constellation and what it means to the full constellation sustainment, performance, availability, and maintenance. The history of GPS Block I, Block II, and Block IIA SVs will be briefly examined. The future Block IIF and GPS IIIA SVs will also be discussed since they will be required to supplement and then replace the IIR SVs, respectively. With the background of current SV performance and lifetime predictions, maintenance requirements for extended life will be discussed. Long term performance will also be analyzed: does accuracy improve or degrade with age? Does availability improve or degrade with age? Projections for GPS constellation sustainment will be made with an eye toward the first launch of IIIA in 2014. The results show that the GPS constellation will be robust for many years to come, so long as the currently planned SV acquisition and launch schedule are not unreasonably delayed.
Published in:	Proceedings of the 23rd International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2010) September 21 - 24, 2010 Oregon Convention Center, Portland, Oregon Portland, OR
Pages:	1554 - 1565
Cite this article:	Marquis, W., Riggs, J.D., "Impact of GPS Block IIR Space Vehicle Lifetime on Constellation Sustainment," Proceedings of the 23rd International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2010), Portland, OR, September 2010, pp. 1554-1565.
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