ESO’s Extremely Large Telescope

[Toliman]

ESO's Extremely Large Telescope is half completed by summer 2023 Good news although there is still long way to first light. With 39 meters big primary mirror it will be masterfully the biggest telescope on the world


ESO's Extremely Large Telescope is now half completed
https://www.eso.org/public/news/eso2310/
The European Southern Observatory's Extremely Large Telescope (ESO's ELT) is a revolutionary ground-based telescope that will have a 39-metre main mirror and will be the largest telescope in the world for visible and infrared light: the world's biggest eye on the sky. Construction of this technically complex project is advancing at a good pace, with the ELT now surpassing the 50% complete milestone.

[Toliman]

First segments of the world's largest telescope mirror shipped to Chile
https://www.eso.org/public/news/eso2319/

The construction of the European Southern Observatory's Extremely Large Telescope (ESO's ELT) has reached an important milestone with the delivery to ESO and shipment to Chile of the first 18 segments of the telescope's main mirror (M1). Once they arrive in Chile, the segments will be transported to the ELT Technical Facility, at ESO's Paranal Observatory in the country's Atacama Desert, where they will be coated in preparation for their future installation on the telescope main structure. Unable to be physically made in one piece, M1 will consist of 798 individual segments arranged in a large hexagonal pattern, with an additional 133 being produced to facilitate the recoating of segments. With a diameter of more than 39 metres, it will be the largest telescope mirror in the world.

The final stage in the production process of M1 segments — polishing — was carried out by world-leading optical systems manufacturer Safran Reosc near Poitiers, central France, at a building completely refurbished to work on this delicate task. As part of the process, Safran Reosc developed new automation workflows and measurement techniques to ensure that the polishing met the high standards required for ESO's ELT. The surface irregularities of the mirror are less than 10 nanometres (less than one thousandth of the width of a human hair). To reach this level of performance, Safran Reosc used a technique called ion-beam figuring, in which a beam of ions sweeps the mirror surface and removes irregularities atom by atom.

While only 18 segments have been shipped thus far, many more will soon be delivered by Safran Reosc to ESO. On 1 November 2023, the 100th segment went out of the production line and entered into the extensive inspection phase that takes place before final delivery. Furthermore, Safran Reosc has achieved a production rate in excess of four segments per week, with a target of five a week expected soon, a remarkable achievement for the series production of incredibly high-accuracy optics.

The construction of ESO's ELT has required the close involvement of multiple companies in Europe and Chile with ESO's teams, highlighting how the telescope is a true international endeavour. The mirror segments were cast by the German company SCHOTT at their facility in Mainz, Germany, before being delivered to Safran Reosc in France for polishing. Other companies involved in the work done on the segment assemblies include: Dutch company VDL ETG Projects BV who produced the delicate segment supports, German-French FAMES consortium who developed and manufactured the 4500 nanometric-accuracy sensors monitoring the relative position of each segment, and German company Physik Instrumente who designed and manufactured the 2500 actuators able to position the segment to nanometric precision. The delicate task of transporting the segments was assigned to Danish company DSV.

Having left France last week, the 18 polished mirror segments are now on their journey of over 10 000 km to the ELT's construction site in the Atacama Desert. From there, ESO's ELT will tackle the biggest astronomical challenges of our time and make yet unimaginable discoveries once it starts operating later this decade.

[Toliman]

And yet it moves
https://elt.eso.org/public/videos/potw2405a/

Like a flower following the Sun, the dome of ESO's Extremely Large Telescope (ELT) will be able to rotate to allow the telescope to track objects in the sky. Seen under the bright blue skies of Cerro Armazones in the Chilean Atacama Desert, this video shows a test of the dome rotating for the first time.

The test moved the dome 10 m in either direction at 1 cm/s, but the final operating speed will be a walking pace of 5 km/h. The test was performed by engineers of Cimolai, the company contracted by ESO to design and build the ELT dome and telescope structure. The humans hard at work in this sped-up video show, for scale, the sheer size of the telescope dome. Rotating the dome is no small feat, as its skeleton currently weighs about 2500 tons, and will eventually weigh around 6100 tons when finished. This first test was carried out "manually" with special hydraulic devices, but eventually the enclosure will rotate via motorised bogies. While the motion of the dome is designed to be smooth, and was found to be during this test, the dome stands separate from the rest of the structure in order to limit vibrations to the telescope itself.

The dome, in its final form, will have an insulated aluminum cladding to protect the telescope from the elements and sliding doors to open it to the stars. Building this marvel of engineering in the middle of the desert presents unique challenges, and yet, recent achievements such as the dome rotating and the first mirror segments stored at Paranal show the ELT is moving closer to becoming reality.

[Toliman]

Which telescope will be 1st to find alien life? Scientists have some ideas
https://www.space.com/telescope-alien-biosignatures-extraterrestrial-life-elt

A new study shows the European Extremely Large Telescope will be able to directly image and study the atmospheres of some potentially habitable exoplanets.

A peek into the future of exoplanet science suggests the forthcoming European Extremely Large Telescope (ELT) is going to give us our best chance in the next two decades of detecting biosignatures on nearby rocky worlds orbiting other stars. Such is the conclusion of a new study that simulated what it will take to characterize worlds outside our solar system with the tantalizing prospect of hosting life, such as Proxima Centauri b.

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Dance of the cranes
https://elt.eso.org/public/videos/potw2410a/

A watched pot never boils, but luckily that doesn't apply to us watching ESO's Extremely Large Telescope (ELT) being constructed. This Picture of the Week shows a timelapse overlooking Cerro Armazones in the Chilean Atacama Desert over the course of 2023, as the dome of the ELT is pieced together in smooth choreography.

Partly built at a nearby base camp, large steel elements arrive at the peak ready to be neatly assembled together into the dome. The steel structure provides the skeleton around which a protective insulated cladding is now being applied. It rests on a concrete foundation separated from the central pier where the telescope will be, to reduce vibrations propagating through the ground. The dome can rotate on 36 trolleys, allowing the telescope to observe the whole sky.

A new webcam inside the dome shows progress in the azimuth structure that will support the telescope, as well as the two huge platforms that will hold the ELT's scientific instruments.

In this timelapse, each frame was captured at the same time every day; the Sun's apparent position in the sky changes with seasons as the Earth orbits around the Sun. This webcam view provides an incredible peek at the ELT construction progress, and we cannot wait to see the wonders its 39-metre eye will discover.

[Toliman]

First segments of world's largest telescope mirror have a shiny new surface
https://elt.eso.org/public/announcements/ann24005/

The construction of ESO's Extremely Large Telescope (ELT) in the Chilean Atacama Desert has reached a new milestone: a team at ESO's Paranal Observatory have added a reflective, shiny layer, as well as special sensors, to the first segments of the telescope's primary mirror. This "coating" means the segments are now essentially ready to start observing the skies, once installed at the heart of the world's largest optical telescope later this decade.

The 39-metre primary mirror of ESO's ELT, known as M1, will be by far the largest mirror ever made for a telescope. Too large to be made from a single piece of glass, it will consist of 798 glass-ceramic hexagonal segments, each about five centimetres thick and 1.5 metres across. The mirror segments are manufactured in Europe in a multi-step, multinational process. The first 18 made their way across the ocean to Paranal earlier this year, and coating is the next step on their journey — a milestone that three segments have now reached.

Coating an M1 mirror segment is a complex process that takes about two hours. In addition to a reflective layer, which uses 1.7 grams of silver, the coating includes additional layers of nickel chromium and silicon nitride to improve adhesion to the mirror blank and protect the silver from tarnishing. Overall, the coating is around 120 nanometres thick, or about one thousand times thinner than a human hair.

To make sure that all segments can work together as a single mirror, they are equipped with sensors to detect misalignments. Besides adding a coating to the first M1 segments, ESO engineers have also installed these so-called edge sensors, two per side of each segment, and integrated the electronics and mechanical supports needed for them to work. Finally, they have performed inspections and health checks to ensure that the segments are ready to be installed on ESO's ELT. The entire process takes place inside a 'clean room' — where the number of particles in the air is carefully controlled to avoid contamination — in the ELT Technical Facility in Paranal.

The coating and integration procedures will be repeated for all other M1 segments. Meticulously testing and documenting the process for the first three segments was therefore key to ensure the operation can be ramped-up once new segments arrive at Paranal.

Once the telescope is operational, the coating process will be repeated on each segment every 18 months, to ensure the best reflectivity and sensitivity. In practice, this means that two segments will need to be recoated every day for the entire lifetime of the telescope. To facilitate this with minimal disruption to the scientific observations, an extra 133 segments are being manufactured, in addition to the 798 needed for the mirror. The world's biggest eye on the sky is poised to tackle the most profound astronomical challenges of our time, promising groundbreaking discoveries once it sees first light later this decade.