In-orbit optical calibration for acquisition and tracking on OSIRIS4CubeSat

OSIRIS4CubeSat, the smallest commercially available laser communication terminal, within the confines of 0.3- units inside of a three-unit CubeSat, was launched into space as PIXL-1 mission to demonstrate optical direct to earth links. This work primarily focuses on the commissioning, particularly emphasizing the performance of the active fine pointing and tracking mechanism. This steering mechanism plays a decisive role in rectifying pointing inaccuracies from the satellite’s attitude determination and control system, within a 1-degree radius of its field of regard. A method is presented that mitigates acquisition and tracking irregularities, which occurred during commissioning in-orbit. Its root cause are reflections and introduced stray light of the internal transmission laser, which does influence the tracking receiver readings. The presented method allows to distinguish between the tracking beacon and the described crosstalk by calibrating the signal offsets on the detector with respect to the deflection angle of the fast-steering mirror. Subsequent evaluation of satellite passes, with telemetry recordings obtained from the deployed in-orbit calibration routine, showcase superior performance that meets the pointing requirements of the link budget. By using the developed optical calibration, OSIRIS4CubeSat achieves a mean tracking error of 71 μrad, with a 3σ deviation of 140 μrad down to low power levels of 119 pW. These results serve as validation of OSIRIS4CubeSat, demonstrating its capability to enable high-speed data transmission from low Earth orbit to the Earth’s surface at data rates of up to 100 Mbit/s.