Authors:

Gabriel S. Guedes

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About Paper:

The rapid expansion of Low-Earth Orbit (LEO) satellite services has made it essential to understand how satellite positioning errors affect signal propagation. Some orbit determination methods exhibit initial errors on the order of kilometers, which grow over time due to unmodeled forces such as atmospheric drag. The goal of this research is to quantify how satellite ephemeris errors translate into ionospheric signal delay, and how this relationship varies across different phases of the solar cycle. The Sun follows an 11-year magnetic activity cycle that directly influences the Total Electron Content (TEC) of Earth's ionosphere, which in turn governs the delay experienced by satellite signals. Our hypothesis is that ephemeris-induced delay errors are not negligible in high-precision applications and that they are significantly larger during periods of maximum solar activity. Vertical TEC profiles were generated using the International Reference lonosphere (IRI) model at 1 km altitude resolution for two contrasting solar conditions: solar minimum (December 1, 2019) and solar maximum (August 1, 2024), at a location near Chicago (42° N, -88° W). Earth was modeled as an ellipsoid, and slant signal paths through the ionosphere were formulated as a function of elevation angle. The slant TEC was computed by integrating the vertical electron density profile along the discretized signal path using the trapezoidal rule. Orbital position offsets of 2.5 km and 10 km were applied to simulate ephemeris errors, and both the absolute (TECU) and percentage delay errors were calculated. Results show that for a 500 km altitude satellite, absolute and percentage errors peak at elevation angles near 20° and 30°, respectively. Counterintuitively, the solar minimum period exhibits higher percentage errors. For a Ku-band satellite (10.7 GHz) such as Starlink, a 2.5 km orbital error introduces delays of up to 1.8 picoseconds during solar maximum, while lower-frequency VHF-band meteorological satellites (137 MHz) can experience delays reaching 11 nanoseconds. These findings demonstrate that satellite ephemeris errors produce measurable ionospheric delays that should be accounted for in mission planning and high-precision system design.

Source:

Illinois Institute of Technology

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Co-authors:

Gabriel S. Guedes