Evaluation of DoD GPS Satellite Orbits Using NASA Laser Ranging Data

James O’Toole and Michael Merrigan

Abstract:	The Global Positioning System (GPS) satellites, designated as PRN5 (SVN35) and PRN6 (SVN36), are equipped with laser retroreflectors. Satellite laser ranging (SLR) observations have been collected by the National Aeronautics and Space Administration (NASA) at a number of their tracking sites since November of 1993. NASA quick look normal points have been processed over selected periods throughout 1993, 1994, and 1995 in order to provide an independent evaluation of two GPS ephemeris products calculated by the Department of Defense (DOD). One product is the real time Kalman filter estimates calculated by the GPS Operational Control System (OCS) and the other is the Defense Mapping Agency (DMA) post fit precise ephemeris. Since the NASA laser ranging data are accurate to a few centimeters, this data type can be used to independently evaluate DOD ephemeris accuracy. While the laser data distribution is sparse, the combined results from several selected analysis periods provide an adequate data sample size for this study. SLR residuals were calculated, using the DOD orbit products, by correcting for tropospheric effects, relativistic effects, the laser retroreflector offset from the satellite’s center of mass, station tides, and plate motion. Results are provided in the form of SLR residuals that vary in value from a few centimeters to a few meters. A statistical summary of these residuals is provided. The results are significant because they have been determined without the use of DMA or OCS processing software or L-Band tracking data.
Published in:	Proceedings of the 8th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1995) September 12 - 15, 1995 Palm Springs, CA
Pages:	45 - 54
Cite this article:	O’Toole, James, Merrigan, Michael, "Evaluation of DoD GPS Satellite Orbits Using NASA Laser Ranging Data," Proceedings of the 8th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1995), Palm Springs, CA, September 1995, pp. 45-54.
Full Paper:	ION Members/Non-Members: 1 Download Credit Sign In