Astronomy’s most accurate ever edge sensors and actuators delivered for ESO’s ELT

After years of work, and thousands of edge sensors and actuators later, the last batches of these high-tech pieces for the main mirror of ESO’s Extremely Large Telescope (ELT) have been completed.  

With a diameter of 39 metres, this mirror (M1) is the largest ever made for an optical telescope; too large to be made of a single piece, it consists instead of 798 individual segments. Each hexagonal segment will have multiple sensors attached to its edges, and will be mounted on three position actuators. The edge sensors, around 4500 pairs, and actuators, about 2400, are critical to precisely adjust the position of all segments and make them work as a single unit. To achieve a mirror shape with a perfect, smooth curvature, the edge sensors will measure potential misalignments, which are then corrected by the ultra-precise actuators. 

The sensors for the ELT are the most accurate to ever be used in a telescope. They are able to measure the relative position of the segments with an accuracy of a few nanometres. If a cricket were to land on a segment corner, moving it by a millionth of a millimetre, the sensors would be able to pick up the tiny disturbance. The sensors were produced by the FAMES consortium, a cooperation between the sensor specialists Micro-Epsilon Messtechnik (Germany) and Fogale Nanotech (France) that was created specifically for this one goal. 

The position actuators will provide support for the segments, actively controlling them in three directions, known as piston, tip and tilt. This involves moving considerable weights, since each mirror segment weighs 250 kg. Designed and developed by Physik Instrumente  (PI, Germany), these unique actuators, that push technology to its limits, will be able to smoothly adjust the position of the segments with a precision of just a couple of nanometres. 

Once delivered to ESO, the edge sensors and position actuators are shipped to Chile, where they are later integrated with the mirror segments and within the telescope, respectively. The ELT is currently under construction atop Cerro Armazones in Chile’s Atacama Desert. Once finished, it will make unique, revolutionary and exciting new discoveries that will change our understanding of the cosmos. 

Courtesy of European Southern Observatory