On-Orbit Enhancements and the Evolution of GPS Modernization

John A. Rajan, Sugandhi Sue Rajan and Michael Policano

Abstract:	GPS Block IIR satellites have been on orbit over six years providing outstanding performance [1-7]. A key feature of Block IIR is its on-orbit reprogrammable GPS payload software. This feature has been tremendously useful in adding new features and resolving discrepancies after the satellite is launched. Modularity of the software has also contributed to the generation of robust software builds. The GPS Satellites have been reprogrammed several times and each time the software has and continues to function with no failure (100% availability). The software is currently executing 24/7 on nine satellites. This paper describes the GPS modular payload software design that resides in the Mission Data Unit (MDU). This paper also walks through the on-orbit enhancements that have been made since the first launch. The GPS IIR MDU software is the backbone of GPS IIR- M software. The modularity of the software enabled the IIR-M specific software to be incorporated with minimal perturbation. The modernized GPS IIR-M software is a modular enhancement to the GPS IIR software. The GPS IIR-M payload includes the M-code and the L2 Civil (L2C) waveform generation hardware that was not present in IIR. The MDU software modernization, in addition to supporting the new Waveform Generator interface, provides the management and control of the M- code, L2C code and their message generation. The architectural approach taken for modernization is also discussed in the paper. The software architecture and payload initialization are covered. Key software performance metrics such as Memory Utilization and Throughput before and after modernization are discussed. The system performance trend as IIRs enter the fleet is highlighted.
Published in:	Proceedings of the 60th Annual Meeting of The Institute of Navigation (2004) June 7 - 9, 2004 Dayton Marriott Hotel Dayton, OH
Pages:	76 - 87
Cite this article:	Rajan, John A., Rajan, Sugandhi Sue, Policano, Michael, "On-Orbit Enhancements and the Evolution of GPS Modernization," Proceedings of the 60th Annual Meeting of The Institute of Navigation (2004), Dayton, OH, June 2004, pp. 76-87.
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