Studies on operation characteristics of triaxial telescope for satellite-ground laser communications

An approach to control the pointing direction of a telescope in which one more rotation axis is added to the conventional set of the azimuth axis and the elevation axis is studied. The aim is to find a possibility to reduce loads on driving mechanisms by decreasing the rotational angular velocity required when the telescope tracks a moving object. In such a tri-axial telescope system, the multiple sets of solutions are mathematically found as the rotation angles around the three axes respectively, because the pointing direction of the telescope can be in principle determined by two independent angles such as a set of the azimuth angle and the elevation angle. Therefore, to obtain the unique set of angles, the process to calculate the solution is divided into two steps. The algorithms are described, and the rotation angles and the angular velocities of the three axes are calculated with a case of a LEO satellite tracking. The results show that the tri-axial telescope can track the LEO satellite without the requirement of too fast rotation angular velocity even when the satellite passes through almost the zenith, which implies that the load on driving mechanisms can be reduced much.