Tomography of thermospheric density from Starlink Ephemeris: initial report

This report presents the first demonstration of successful tomographic analysis of thermospheric density using orbital data from a massive Starlink satellite constellation. Thermospheric density, the neutral atmospheric density at altitudes between 100 and 1000 km, is essential for advancing upper-atmosphere science and supporting space engineering operations. While traditional observation methods rely on Two-Line Element (TLE) data, this study presents a novel tomographic analysis using Starlink Ephemerides, i.e., detailed orbital information publicly released by SpaceX. Unlike TLEs, these ephemerides provide high-resolution position and velocity vectors, allowing for precise estimation of satellite energy loss due to atmospheric drag. We developed a method to quantify energy loss and a coefficient that relates it to thermospheric density. We calculated the energy dissipation for approximately 1200 satellites at an altitude of 482 km and an inclination of 53°, which served as the basis for a tomographic analysis. We employed a spherical harmonic expansion to model the longitude-by-latitude density distribution, but only diurnal variation was considered in this report. The density-height distribution was assumed to decrease exponentially with a single scale height of 60 km. The analysis was conducted for the period September 1–7, 2025, and captures features of thermospheric density that the NRLMSIS 2.1 model predicts. The results were validated against independent density measurements from the SWARM satellites. The tomographic estimates demonstrated high consistency with SWARM observations, e.g., density variations along satellite trajectories. Quantitative comparisons across 19 cases showed that the estimated density values ranged from 0.6 to 1.2 times the SWARM measurements, with an overall average ratio of 0.95. These findings suggest that this method has the potential to provide rapid, high-resolution thermospheric density data.