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The Global Positioning System (GPS) satellite orbits were estimated using the National Aeronautics and Space Administration's GEODYNII software, a batch least-squares estimator. Three deterministic models were tested: the solar radiation pressure scale factor and y-bias acceleration; the solar radiation pressure scale factor and radial, GPS X and GPS Y axes accelerations; and Colombo's resonant harmonic model which supplements the radial, GPS X and GPS Y axes accelerations with sine and cosine terms with frequencies equal to the nominal GPS orbital frequency. For one-day GPS orbits all models had an RMS of fit to the Final International GPS Geodynamics Service (IGS) orbit of 26 cm. [Full text of abstract available in document.]