Results of the GPS JPO’s GPS Performance Baseline Analysis: The GOSPAR Project

Rob Conley

Abstract:	In 1981 the ability of GPS to meet, let alone sustain per-formance at a 6 meter User Range Error (URE) specifica-tion was still in question. Several years of intense effort within the GPS community resulted in a 4.5 meter URE system by the time the first Block II satellites were launched in 1989. At that time, the fact that we were performing so well relative to specification, coupled with the improved geometries of the 24 satellite constellation as compared with the 18 satellite constellation, meant that we were providing a positioning service much better than expected to the mili-tary user community. By the time GPS became operational in 1993, GPS was performing so much better than specifi-cations or user expectations, that emphasis was not placed in efforts to understand the nature of errors still resident in the system. This situation has changed. The user community has be-come more sophisticated in their understanding and appli-cation of satellite navigation, and are pushing the GPS pro-gram to provide increasing levels of availability, reliability, integrity and accuracy. Users are in fact beginning to re-quire performance beyond which we believe the system is currently providing. In an effort to understand GPS per-formance, and more importantly the behaviors driving our perceptions, the GPS Joint Program Office (JPO) initiated the GPS OCS Performance Analysis and Reporting (GO-SPAR) project. The GOSPAR project provided the JPO a mechanism for examining GPS Precise Positioning Service (PPS) performance attributes over an extended period of time, on a global scale. * It also established a baseline for performance for the next-generation GPS Operational Con-trol System (OCS), currently in development. This paper provides a description of the key findings of the GOSPAR project to date. Specifically, the following topics are addressed: · Project Overview · Performance Metric Review · How is GPS Doing? · Why is GPS Doing So Well? · Bottom Line to Users The results of the GOSPAR project establish a GPS per-formance baseline, and set the stage for the Accuracy Im-provement Initiative (AII) program. AII has an objective to reduce GPS PPS UREs to 1.5 meters Root Mean Square (RMS) or better.
Published in:	Proceedings of the 10th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1997) September 16 - 19, 1997 Kansas City, MO
Pages:	365 - 374
Cite this article:	Updated citation: Published in NAVIGATION: Journal of the Institute of Navigation
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