CD6 completes the mirror calibration system for the Extremely Large Telescope
19/05/2026
The Centre for Development, Instrumentation and Sensors (CD6) of the Universitat Politècnica de Catalunya (UPC), based at the Terrassa Campus, has completed the design and construction of the optical system that will be used to calibrate the primary mirror of the Extremely Large Telescope (ELT), the world's largest ground-based optical and infrared telescope, currently under construction in the Atacama Desert (Chile).
The project was carried out in collaboration with IDOM Engineering, and the resulting system, known as the Local Coherencer, is a critical instrument for the correct operation of the ELT. The solution is based on an original optical concept — a variant of the interferometer that CD6 developed for the Gran Telescopio Canarias 20 years ago — and was selected by ESO through an international competitive tender. It is a non-contact metrology system, lightweight, compact and robust, capable of simultaneously measuring the position difference and tilt between each mirror segment and its six neighbours, with an accuracy below 300 nanometres. The project was led on behalf of CD6-UPC by researcher Santiago Royo.
The ELT's primary mirror, 39.3 metres in diameter, is the largest ever built. Composed of 798 hexagonal segments acting as a single reflective surface, it will collect tens of millions of times more light than the human eye. The Local Coherencer ensures that all these segments remain aligned to a precision of two nanometres, roughly one ten-millionth of a centimetre.
The system was delivered to ESO in Munich in May for validation, and will subsequently be installed at the ELT in Chile. Once fully operational, the telescope will produce images 15 times sharper than those of the Hubble Space Telescope and could become the first to detect evidence of life beyond our solar system. First scientific observations are expected in September 2027.
The project was carried out in collaboration with IDOM Engineering, and the resulting system, known as the Local Coherencer, is a critical instrument for the correct operation of the ELT. The solution is based on an original optical concept — a variant of the interferometer that CD6 developed for the Gran Telescopio Canarias 20 years ago — and was selected by ESO through an international competitive tender. It is a non-contact metrology system, lightweight, compact and robust, capable of simultaneously measuring the position difference and tilt between each mirror segment and its six neighbours, with an accuracy below 300 nanometres. The project was led on behalf of CD6-UPC by researcher Santiago Royo.
The ELT's primary mirror, 39.3 metres in diameter, is the largest ever built. Composed of 798 hexagonal segments acting as a single reflective surface, it will collect tens of millions of times more light than the human eye. The Local Coherencer ensures that all these segments remain aligned to a precision of two nanometres, roughly one ten-millionth of a centimetre.
The system was delivered to ESO in Munich in May for validation, and will subsequently be installed at the ELT in Chile. Once fully operational, the telescope will produce images 15 times sharper than those of the Hubble Space Telescope and could become the first to detect evidence of life beyond our solar system. First scientific observations are expected in September 2027.
