Calibration and Verification of Pointing and Tracking System for Optical Communication Terminal

This paper presents the experimental verification of the pointing and tracking system of the flight model of an optical communication terminal for small satellites. The terminal, called LaserCube, fits in two CubeSat units and is conceived to operate onboard spacecraft starting from the 6 U (CubeSat units) form factor. The terminal is provided with a dual stage pointing system, composed of a coarse pointing mechanism used to orient the optical head and a fast-steering mirror for the fine pointing of the received and transmitted lasers. The coarse pointing mechanism is based on the parallel platform configuration and alone can provide 50  μrad rms pointing accuracy when operating in conjunction with a beacon laser sent by a remote terminal and used for feedback. The control algorithm operates the two pointing stages synergically, targeting an overall pointing accuracy of 10  μrad rms while rejecting the disturbances coming from the satellite bus. The pointing system of the LaserCube flight model has been calibrated and experimentally verified in laboratory conditions that replicate real operational scenarios for what concerns the beacon signal attenuation and the disturbances generated by the host satellite. A dedicated setup was used to directly measure the pointing error and asses the system performance.