ESO’s Extremely Large Telescope

Started by Toliman, October 01, 2023, 01:23:13 PM

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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
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.


First segments of the world's largest telescope mirror shipped to Chile

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.


And yet it moves

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.


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Dance of the cranes

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.


First segments of world's largest telescope mirror have a shiny new surface

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.




Final design of the ELT's METIS instrument completed

The Mid-infrared ELT Imager and Spectrograph, or METIS, has passed its Final Design Review, with ESO now giving the go-ahead on the manufacturing of all instrument components. METIS is a sophisticated multi-tool instrument that will operate on ESO's upcoming Extremely Large Telescope (ELT). It is the first of the ELT instruments to formally pass its Final Design Review, marking an important step for the METIS consortium, the ELT project, and the instrument-building community.

METIS is a first-generation instrument on the world's biggest eye on the sky, the ELT, meaning it will start operating when or shortly after the telescope itself starts observing the skies. It has a broad range of science goals, from probing the formation history of our Solar System to peering into the centre of galaxies, to studying their enigmatic supermassive black holes. The main scientific focus of METIS is on the study of planet-forming discs, and recently formed — as well as nearby — exoplanets.

The design process is one step in the journey from a concept to a realised instrument, which takes years to complete for such large, complex, and technologically advanced instruments. METIS passed its first design milestone at its Preliminary Design Review in 2020, while in late 2022, the design of the main instrument components was finalised. Now, with the official completion of the METIS Final Design Review, the consortium can begin the manufacturing phase for all of the instrument's components. The closure of this review marks the exciting transition from METIS being described in documents to being constructed, assembled and tested.

METIS is designed to observe in the mid-infrared, making it ideal to study cold objects or those enshrouded in dust. While very hot objects at thousands of degrees like our Sun emit mostly visible light, colder ones like planets or dust clouds radiate mostly in the mid-infrared. By analysing light in this frequency range, METIS will study how stars and planets form within dust and gas clouds, and can peer through the dust at the centre of galaxies to study their supermassive black holes. In addition, METIS is expected to make exciting contributions to the field of exoplanets by observing small, rocky exoplanets and investigating the temperature, weather, and chemical composition of their atmospheres in the search for habitable worlds.

METIS is a powerful three-in-one instrument. It has a camera to capture images of the sky, a spectrograph to split the light into its component colours or wavelengths, and its own adaptive optics module to correct for the disrupting turbulence in the atmosphere, working in tandem with the ELT's adaptive telescope mirrors.The entire instrument will be encased in a cryostat, keeping the instrument at minus 230 degrees Celsius or less so its own heat doesn't interfere with the infrared measurements.


The ELT's M5 mirror blank is finalised

M5, the fifth mirror on the light path of ESO's Extremely Large Telescope (ELT), has reached an important milestone: its blank, the shaped piece of material that is later polished to become the mirror, has just been finalised. The ELT will be equipped with five mirrors in total, and M5 is the smallest of them — but building its blank was no small feat. The French company Mersen Boostec manufactured this remarkable piece in their facilities near Tarbes, in France's southwest.

M5 is a flat, elliptical mirror measuring 2.7 by 2.2 metres, constructed from six segments brazed together. It might not seem much in comparison to the ELT's enormous 39-metre primary mirror, but in reality, it is the largest tip-tilt mirror in the world.

Together with M4, M5 is a crucial component of the ELT's adaptive optics system: their unique synergy will allow the ELT to take extremely sharp images, compensating for perturbations caused by the telescope mechanisms, wind vibrations, and atmospheric turbulence. To stabilise the images, M5 will adjust its position 10 times per second, without bending.

This challenge required Mersen Boostec to make the M5 blank out of a very special material: silicon carbide, which is simultaneously very stiff and very lightweight. On top, a thin layer of silicon carbide was deposited atom by atom, to ensure the surface of the blank can be polished to an accuracy of less than a hundredth of the thickness of a human hair.  

The French company Safran Reosc, which has now received the blank, will inspect it and later integrate it with its support, polish the assembled blank, and supply the equipment required for its handling, transport, operation, and maintenance. The Spanish company SENER Aeroespacial is carrying out the design, construction, and verification of the mirror cell (its support system), as well as its control system and auxiliary equipment. 

ESO's Extremely Large Telescope, 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. The construction of its individual components, like the M5, is pushing technology to the limit.


The smallest ELT mirror is a big challenge

The ELT's M5 mirror blank has been completed. M5 is the smallest mirror on the telescope, but it has a big task: through a tip-tilt system, it can adjust its position to compensate for atmospheric turbulence and other factors, and yield extremely sharp images. To do this without breaking, the mirror blank needs to be very stiff and very lightweight at the same time — and made of a special material, which you can discover in this video.