CubeSat orbit determination using on-board GNSS velocity solutions

In December 2018 and April 2019, two 3-unit cube satellites of the company Astrocast were launched into space. Both satellites are equipped with our low-cost single-frequency multi-GNSS payload board, which can provide continuous on-board navigation solutions containing position, velocity and time. By fitting a dynamic orbit to these on-board solutions using the Bernese GNSS Software, we can evaluate the quality of the on-board solutions. Usually, only the receiver positions of the satellite are used to fit a dynamic orbit without considering the receiver velocity information that is also available. In this study, we develop and analyse an extension and refinement of the dynamic orbit determination by using not only the satellite positions but also the satellite velocities of the onboard solution in the orbit fit. To study the use of velocity observations in the determination of a precise dynamic orbit, we consider three different approaches: fitting the equation of motion of the satellite orbit (1) to the positions only, (2) to the velocities only and (3) to both positions and velocities. For the combined orbit estimation with positions and velocities, we apply an appropriate relative weighting of the two observation types based on the RMS of the residuals from the orbit fits. After removing a few outliers, the standard deviation of the position residuals from the position-only approach is about 5 m, the standard deviation of the velocity residuals from the velocity-only approach is about 15 cm/s. However, when looking at the positions computed from the velocity-only approach they deviate by much more than a few meters from the orbit obtained by the position-only fitting. These deviations show a periodicity of one revolution with an amplitude of up to 60 m. In the differences between the velocity-only and position-only orbit fit we see an offset of about -0.01 m/s in the radial component of the velocities and an offset of about 15 m in the along-track component of the positions. Additionally, a periodicity of ...