Precise orbit determination of Spire nano satellites

Spire Global, Inc. operates a growing fleet of currently more than 100 CubeSats in different low Earth orbits for commercial Earth observation. These satellites are equipped with dual-frequency GPS receivers and an attitude determination and control system, allowing for precise orbit determination. For three different satellites and a time span of six months we analyze the performance and quality of the on-board collected GPS and attitude data and employ it for precise orbit determination using the Bernese GNSS Software and Napeos, two independent state-of-the-art GNSS processing software packages. We describe technical details crucial for POD and present and compare the in-flight calibrated phase center variation maps. Reduced-dynamic and kinematic orbits are then inter-compared between the two software packages as well as to the orbit solutions produced by Spire Global. We report pseudo-range and carrier phase residuals at the level of 3-4 m and 8-9 mm RMS and a good agreement between the reduced-dynamic and kinematic orbits of around 5 cm 3D RMS. The reduced-dynamic orbit positions and velocities produced with the two employed software packages agree in average on the level of 6-7 cm and 0.05-0.07 mm/s 3D RMS, while the comparison to the orbits produced by Spire Global is markedly worse with 27- 30 cm and 0.32-0.36 mm/s 3D RMS. The presented results are an encouraging first step towards using GPS data from the Spire con-stellation for geodetic, geophysical and ionospheric applications. (c) 2023 COSPAR. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).