Position Actuator for the ELT Primary Mirror
This research focuses on the analysis, design and realisation of position actuators (PACTs) for the Extremely Large Telescope. Dynamic analyses have been performed on previous PACT prototypes and a cost-effective design has been proposed. Experimental validation shows a positioning performance of 1.7 nm RMS and a stroke of more than 15 mm.
The Extremely Large Telescope (ELT) will be the largest optical and near-infrared telescope in the world, available by the middle of the next decade. The ELT primary mirror (M1) has a diameter of approximately 39 m. The M1 mirror consists of 798 hexagonal segments. Each segment is made of a glass-ceramic, about 1.4 m wide and 50 mm thick, and, with its support integrated, it weighs almost 270 kg. The segments have to be accurately aligned with respect to each other to function as one 39-metre mirror. Three position actuators (PACTs) are responsible for the active alignment of each segment in presence of frame vibrations, deformations of the telescope structure at various orientations, and the effect of wind on the mirror surface. Compared to position actuators of previous telescopes, the required stroke and positioning performance are increased, while the allowed thermal dissipation requirements have remained approximately the same.