Bhattarai, Santosh; Peto-Madew, Felicia; Constant, Charles; (2025) Toward an On-Orbit Reference Network for Enhanced Ephemeris Quality Testing in Low Earth Orbit. In: Proceedings of the 2025 AMOS Conference. Maui Economic Development Board: Wailea, HI, USA. (In press).

Text LEO_Ephemeris_Quality_Eval_AMOS25_Bhattarai_220825-13.pdf - Accepted Version Access restricted to UCL open access staff Download (2MB)

Abstract

The evaluation of orbit determination accuracy and precision for non-cooperative space objects is crucial for Space Situational Awareness (SSA). A common practice involves comparing orbit solutions derived from space surveillance and tracking sensor networks against high-accuracy, high-precision reference orbits published by the International Laser Ranging Service (ILRS). This method may yield overly optimistic assessments. The geodetic spheres used for validation—such as LAGEOS satellites—are spherical with low area-to-mass ratios. This makes their trajectories susceptible to non-conservative forces in a relatively predictable manner. However, this is not representative of most of the resident space object (RSO) population. To address this limitation, we propose establishing a reference network of satellites in Low Earth Orbit (LEO) for ephemeris data quality validation. This on-orbit network will comprise satellites from scientific missions that routinely publish precise orbits, featuring centimeter-level absolute position accuracy, which are freely available. To date, we have identified 45 satellites in LEO that could contribute to our precise orbit network. We investigate the merits of setting up this precise orbit network by analyzing a representative subset from the list of candidate satellites we have identified. Altitude, area-to-mass ratio (AMR) and geometry define our search space. We will select satellites that give representative coverage across that space, spanning roughly 500 km to 1,500 km. In this contribution, our assessment focuses on the calendar-year 2024. The analysis will employ ephemerides from both non-cooperative methods (using SGP4 propagations) and precise orbit products from public archives maintained by NASA, the German Research Centre for Geosciences (GFZ) and other international centers. Differences between non-cooperative and precise orbits will be computed in radial, along track and cross track directions over a full year, using regularly spaced ephemeris samples. The resulting error statistics will reveal how orbit quality varies with satellite shape and AMR, providing an evidence base for improved validation practices. We expect larger errors for high-AMR or geometrically complex spacecraft, relative to low-AMR spheres in similar orbital neighborhoods. These findings will inform ongoing initiatives such as NOAA’s Traffic Coordination System for Space (TraCSS), which is developing orbit-quality assurance processes that blend government and commercial data. By highlighting where current validation methods succeed—and where they require refinement—this study aims to guide the community toward a robust, practically achievable benchmark for LEO orbit data quality assessment.

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