A Low Cost, High Accuracy Automated GPS-Based Orbit Determination System for Low Earth Satellites

George W. Davis, Kenneth L. Gold, Penina Axelrad, George H. Born, Thomas V. Martin

Abstract:	An automated software system has been developed to provide low cost, high-accuracy GPS-based orbit determination for low Earth orbiting spacecraft. The software system consists of a PERL shell script that controls the execution of the MicroCosmÒ precision orbit and geodetic parameter determination software system. The script is executed from command line inputs and is capable of providing end-to-end orbit determination for a low Earth satellite on a standard UNIX workstation or PC. The script is designed to automatically retrieve ground-based GPS tracking data from the IGS, solar flux and geomagnetic indices from NOAA, and earth orientation parameters from the USNO. The script then executes the processing modules required to generate the spacecraft ephemeris. The various levels of orbit accuracy that can be obtained for GPS-tracked spacecraft are assessed by computing orbits for the TOPEX/POSEIDON (T/P) and RADCAL satellites. The T/P spacecraft occupies a 1330 km altitude orbit and carries a dual-frequency P-code GPS receiver. T/P orbits computed with the automated software system are compared with a precise orbit ephemeris computed from laser and doppler tracking. Given the 3 cm radial orbit accuracy of the T/P POE, such comparisons help to define the current limits on GPS-based orbit determination using a variety of data types. The RADCAL satellite occupies an 800 km altitude orbit and carries a single-frequency C/A code GPS receiver. Such a combination of orbit altitude and GPS receiver is representative of many missions scheduled for launch within the next ten years. Processing the RADCAL data therefore provides some insight on the accuracy that can be obtained for satellites with altitudes lower than that of T/P and that are tracked with lower cost, reduced-capability GPS receivers.
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:	723 - 733
Cite this article:	Davis, George W., Gold, Kenneth L., Axelrad, Penina, Born, George H., Martin, Thomas V., "A Low Cost, High Accuracy Automated GPS-Based Orbit Determination System for Low Earth Satellites," Proceedings of the 10th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1997), Kansas City, MO, September 1997, pp. 723-733.
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