Trajectory control of a gimbaled prism for hemispherical pointing in CubeSat optical communications

Free-space optical communications on CubeSats require precise pointing mechanisms to maintain stable links. State-of-the-art CubeSat-sized laser communication terminals rely on satellite body pointing, which imposes constraints on system flexibility. This paper presents the proposed control strategy of a gimbaled-prism-based coarse pointing assembly for hemispherical pointing in CubeSat optical communications. The gimbal design employs a compact mechanical structure with direct-drive actuation for azimuth and elevation control. A hierarchical control strategy is implemented, combining a cascaded servo control loop with an s-curve profiler for ephemeris-based pointing and a second-order trajectory controller for fine pointing assembly offloading. Therefore, the dynamics of the low-level controller can be decoupled from the trajectory control design. The performed experimental validation includes hardware characterization, system response identification, and closed-loop performance analysis, demonstrating the capability to achieve accurate and stable pointing of the developed coarse pointing assembly. Results confirm that the proposed approach meets stringent dynamics and stability requirements while maintaining a pointing accuracy suitable for CubeSat optical communication applications.