A report describes a series of computational models conceived as an improvement over prior models for determining effects of solar-radiation pressure on orbits of Global Positioning System (GPS) satellites. These models are based on fitting coefficients of Fourier functions of Sun-spacecraft- Earth angles to observed spacecraft orbital motions. Construction of a model in this series involves the following steps:
- Form 10-day "truth" orbit arcs from precise daily GPS orbit data gathered during more than four years.
- Construct a model of the solar-radiation pressure and estimate model parameter values that make a least squares best fit of the model-predicted trajectory to each of the "truth" 10-day orbit arcs.
- Using a least-squares procedure and utilizing the full covariance information from each 10-day fit, combine the estimates from all satellite arcs into a single set of model parameters for the two GPS constellations of the satellites now or soon to be placed in service.
- Evaluate the model thus derived by means of orbit-data-fit and orbit-prediction tests.
In evaluations performed thus far, these models have been found to offer accuracies significantly greater than those of the prior models.
This work was done by Yoaz Bar-Sever and Da Kuang of Caltech for NASA's Jet Propulsion Laboratory. For further information, access the Technical Support Package (TSP) free on-line at www.techbriefs.com/tsp under the Information Sciences category. NPO-41395