Abstract
Theoretical nominal GPS orbits are parallel and share six ascending nodes of orbital planes. However, due to the perturbations and continuous modernization of the system, this state does not occur. The configuration of satellite orbits is continuously monitored by the control segment and presented regularly in the form of a GPS almanac. Almanacs, however, do not contain a parameter defining the convergence of orbits. This work presents a novel method of assessment of the configuration of orbit ascending nodes compared with the nominal constellation state. The method is a tool for space segment monitoring and detection of anomalies. The source data were 7035 System Effectiveness Model almanacs published from the 847th to 2123rd GPS weeks (March 1996–September 2020). The algorithm uses the procedure of assigning satellites to orbital planes and both the robust estimation and the least-squares methods to determine the estimates of the angular separation of orbit ascending nodes. A long-term analysis of the symmetry and trend of changes in the position of the ascending nodes was conducted. The study showed the occurrence of significant anomalies. The research provides information on the trend of satellite orbit separations and deviations of orbital planes from the initial hexagonal GPS symmetry.
Highlights
Studies on the space segments of global navigation satellite systems (GNSS) in most cases are focused on the accuracy of satellite orbit determination
The algorithm uses the procedure of assigning satellites to orbital planes and both the robust estimation and the least-squares methods to determine the estimates of the angular separation of orbit ascending nodes
The obtained results were saved to separate files grouped with respect to orbital planes (OPs) and identified by the SVN and PRN identifiers of the satellites
Summary
Studies on the space segments of global navigation satellite systems (GNSS) in most cases are focused on the accuracy of satellite orbit determination. Researchers have considered satellites in low Earth orbit (LEO), medium Earth orbit (MEO), and geostationary orbit (GEO) systems. Montenbruck et al [1] showed the accuracy of determining orbits in the. A study regarding the Galileo system was conducted by Steigenberger and Montenbruck [2]. Gunning et al [3] published the results of analogous research on the GLONASS system. Ouyang et al [4] analyzed the Beidou system broadcast navigation messages. Kim and Kim [5] conducted a long-term analysis of satellite orbits based on Standard Product 3 (SP3). A similar study was carried out by Wang et al [6]
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