From Nano to Notable: Advancing Earth Observation with CubeSats-Based Precise Orbit Determination

CubeSats, a widely used class of nanosatellites typically weighing between 1 and 10 kg, have revolutionized access to space by enabling rapid, cost-effective, lightweight, and energy-efficient innovations. These advances have broadened the scope of scientific research, supporting both geodetic and non-geodetic applications. In recent years, the Spire CubeSats constellation, comprising over 120 3U satellites (each 10 cm × 10 cm × 30 cm), has contributed to a range of scientific endeavors, including ice sheet height retrieval, precision altimetry, soil moisture estimation, and atmospheric studies. Equipped with zenith-looking, dual-frequency Global Positioning System (GPS) receivers and Attitude Determination and Control Systems (ADCS), these CubeSats have emerged as promising platforms for Precise Orbit Determination (POD) and related geodetic applications, such as Earth’s gravity field recovery. In this study, we investigated the capabilities of the Spire GNSS-RO CubeSats constellation by selecting 10 Flight Modules (FMs) operating at varying altitudes and inclinations throughout 2020. Using the raw observation approach, we derived precise reduced dynamic and kinematic orbits for each FM. Our findings demonstrate that the raw observation approach is a viable method for POD with commercial CubeSats. However, the accuracy of the POD solutions depends on multiple factors, including reliable a priori orbit determination and precise inertial attitude estimation. A 3D RMS difference of less than 5 cm between the reduced dynamic and kinematic solutions confirms a high level of internal consistency. Furthermore, the reduced dynamic orbits derived in this study were compared with those from the Astronomical Institute of the University of Bern (AIUB) for FM099 and FM103, as well as with Spire’s official L1B solutions for all processed FMs. The University of Luxembourg (UL) and AIUB solutions show strong agreement, with position differences of 7.76 cm and 8.92 cm, and velocity differences of 0.08 mm/s and 0.08 mm/s for FM099 and FM103, respectively. In contrast, comparison with the Spire L1B solutions revealed larger discrepancies, with position differences ranging from 22 to 29 cm, and velocity differences between 0.25 and 1.04 mm/s. Receiver clock stability was assessed using the modified Allan deviation (MDEV), computed daily with a time constant of τ = 60 seconds over the course of 2020. Significant clock instability was observed across the CubeSats constellation, FM103 exhibiting the highest level of instability, negatively affecting the consistency between reduced dynamic and kinematic solutions. In contrast, FM108 demonstrated the most stable clock performance, resulting in a much closer alignment between the two orbit types.