Working without a Net -- Operating the Modernized GPS Block IIR Space Vehicles Prior to OCX

Willard Marquis

Abstract:	The first three modernized Block IIR (IIR-M) satellites have been placed in orbit in the past two years. This new version of the GPS IIR space vehicle (SV) produces the first new signals since GPS started operating in 1978. It provides three new codes (L1M, L2M, and L2C) on the existing L1 and L2 carriers in addition to all of the classic GPS signals. SVNs 53, 52, and 58 (PRNs 17, 31, and 12, respectively) are now operating with the same excellent user accuracy and availability we have grown accustomed to with the other Block IIR SVs over the past 10 years. Additionally, the first new L5 signal will be broadcast from space in the next year by a Block IIR-M SV modified to include an L5 demonstration payload. Limitations in the current and near-future Control Segment (CS) prevent full access to the modernized capabilities on the IIR-M. Neither the existing Legacy CS nor the soon-to-come Architecture Evolution Plan (AEP) CS provide modernized capabilities in terms of commanding, data upload and signal monitoring. The reprogrammable capability of the GPS IIR-M provides for on-orbit changes to the SV’s program and data. This allows for limited operation of the IIR-M SVs beyond legacy mode prior to the modernized CS (the Next Generation GPS Control Segment, designated ‘OCX’). While only three of 30 SVs currently on-orbit are capable of broadcasting these new signals, and Initial Operational Capability (IOC) and Final Operational Capability (FOC) are still years away, exercising these new capabilities is part of the progression leading towards GPS III. Methods of operating these new capabilities and glimpses at their performance can be seen now and pave the way toward the future. This paper will discuss the on-orbit operation of the new IIR-M SVs, as well as their testing and performance. The future of modernized operations will also be discussed. The results show that all users will benefit significantly from the service provided by these first modernized GPS SVs, both in terms of signal broadcasts and signal strength. This information is important to all users who want to be aware of the latest status of the GPS constellation and how this universal utility will be changing in the near future.
Published in:	Proceedings of the 20th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2007) September 25 - 28, 2007 Fort Worth Convention Center Fort Worth, TX
Pages:	2466 - 2477
Cite this article:	Marquis, Willard, "Working without a Net -- Operating the Modernized GPS Block IIR Space Vehicles Prior to OCX," Proceedings of the 20th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2007), Fort Worth, TX, September 2007, pp. 2466-2477.
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