Numerical and Hardware-In-The-Loop Validation of an Attitude Estimation Algorithm for CubeSat Free-Space Optical Communication Terminals

Abstract

Optical Inter-Satellite Link (ISL) promises better performances than RF counterparts regarding data rates and SWaP (Size, Weight, and Power). The latter is of fundamental importance within the rapidly expanding picosatellite market. For such small satellites, the poor body-pointing accuracy and an attitude estimation update of a few Hz represent the main limitations for a successful ISL. These factors significantly impact the acquisition time of the ISL, which exponentially increases with the miss-pointing error. The difficulties of optical ISL between CubeSats are being addressed at DLR-IKN within the CubeISL mission. This work validates with Hardware-In-The-Loop simulations a secondary attitude estimation algorithm implemented on the terminal microcontroller. It aims to augment estimation frequency, utilize precise satellite attitude data, and minimize ISL acquisition time. Initial Software-In-The-Loop simulations and hardware tests discarded an unscented Kalman Filter-based approach due to poor observability and high computational load. Instead, a gyro attitude propagation-based algorithm was selected for its computational efficiency, facilitating higher estimation rates. Furthermore, an online calibration method was tested to guarantee precise propagation between satellite estimates.