Advantages of eccentric orbits for geodetic satellites

Abstract Most of the geodetic satellites observed with Satellite Laser Ranging (SLR) are placed in near-circular orbits. This paper uses simulations to discuss the advantages of launching a satellite into an eccentric orbit from the perspective of the quality of geodetic parameters. For the first time, we evaluate how eccentricity, inclination, and semi-major axis affect the accuracy of determining SLR-based parameters, including station coordinates, Earth rotation parameters, geocenter coordinates, and low-degree Earth's gravity field coefficients. We found that eccentric orbits substantially improve gravity field recovery, especially for low-degree zonal, tesseral, and sectorial coefficients. The greatest impact is observed for the odd-zonal terms: the formal errors for C 30 and C 50 decrease by over 90% compared to the current 10-satellite constellation. The even-degree zonal coefficients (C 20 , C 40 , C 60 ) also improve, achieving gains of 70–80% at optimal inclinations. Even-degree coefficients prefer eccentric orbits, and their importance increases substantially with a large semi-major axis, leading to a more noticeable improvement in the quality of the estimated coefficients. To minimize formal errors of the gravity-field coefficients, inclinations of 20–40° or 140–160° are favored for even-degree zonal and tesseral coefficients. In contrast, sectorial and odd-degree zonal coefficients prefer inclinations of 75–105°, particularly for satellites with a semi-major axis of 7800 km. Additionally, eccentric orbits improve visibility from the southern hemisphere for specific perigee placements and increase the separability of the coefficients of the gravity potential in terms of the correlations.