In-orbit demonstration of acquisition and tracking on OSIRIS4CubeSat.

OSIRIS4CubeSat is the smallest commercially available laser communication terminal within the confines of 0.3-units. It was launched as PIXL-1 inside of a 3-unit CubeSat into space to demonstrate optical direct to earth links. This work primarily focuses on the commissioning phase, particularly emphasizing the performance of the active fine pointing and tracking mechanism. This steering mechanism, with a 1 degree radius field of regard, plays a decisive role in compensating for pointing inaccuracies from the satellite's attitude determination and control system. The design and validation of open-loop acquisition and closed-loop tracking are presented. The feedback sensor adapts to changing beacon power levels, that occur during a direct to earth link, by an adaptive gain control. Subsequent evaluation of satellite passes, with telemetry recordings obtained from the deployed CubeSat, showcases superior performance that meets the pointing requirements of the link budget. By using the developed control-loop logic, OSIRIS4CubeSat achieves a mean tracking error of 71 µrad, with a 3σ deviation of 140 µrad down to low power levels of 238 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.