Eighteen of the 798 optical mirrors that will make up the largest optical telescope ever built are now on a journey across the North Atlantic, from France to Chile’s Atacama Desert. Once this giant 39-meter telescope is finished, in about 4 years, ground-based astronomy will never be the same again.
But as fabulous as it is, the European Southern Observatory’s Extremely Large Telescope is an astronomical dinosaur. In fact, a single-aperture optical telescope, much larger than ESO’s ELT, will be technically unfeasible, Luis Chavarría Garrido, ESO’s representative in Chile, told me. in an interview here in Santiago.
For a single aperture telescope more than double the size of the current ELT, a conventional observatory dome would probably not be workable, says Chavarria Garrido. With its 80-meter-tall dome, the current ELT is already pushing current infrastructure technology. So, it will probably be impossible to build the kind of dome needed for a 100-meter telescope, he says.
And if such a monstrous telescope were left undomed and simply exposed outdoors, Garrido says cleaning and maintaining its mirrors would be problematic.
The task at hand is finishing ESO’s current ELT, however.
A telescope with a mirror larger than the length of this ELT will be physically manufactured in one piece, ESO explains. Therefore, the main mirror segments of the ELT will be arranged in a giant hexagonal pattern. The 1. 5-metre mirror segments themselves are manufactured through German company Schott before being handed over to French optomechanical systems manufacturer Safran Reosc for polishing, ESO said.
And after losing a year of structure time due to Covid, Chavarría Garrido says that the ELT structure has moved forward.
The first technical light is expected to take place in early 2028, at which point the ELT will receive its first photons from a celestial target. The clinical commissioning is expected to take at least a year and a half.
We don’t know exactly, because it’s the first time someone has tried something like this,” says Chavarría Garrido. That doesn’t mean that we can’t use commissioned photographs for clinical purposes; Yes, we can,” he said. But it depends on the quality or poor quality of the first photographs, he says.
As for the ELT’s next step?
The next element to be installed is the side doors of the dome that will cover the telescope’s segmented mirror. Installation of those doors is not expected to begin until the end of next year and they are so heavy that installation may take at least a year.
It’s one of the moving parts and there’s a lot of weight that has to be moved every day to open and finish them,” says Garrido. The dome is about 6,000 tons of steel that have to move with a precision of about two millimeters, he says.
It wouldn’t have been possible to build the ELT without the VLT, says Chavarria Garrido. The VLT was the first time we tried to do something to that level of precision in every sense, from the domes to the polishing of the mirrors, he says, noting that many things could have gone wrong.
But the VLT’s wonderful good fortune prompted ESO to take a big step forward with the ELT.
Currently, at the ELT we will have 150 workers working on site,” says Chavarría Garrido. It’s not sustainable, you have to reduce it to 30 people,” he says.
The key, says Garrido, is to use synthetic intelligence in the daily mechanical maintenance of the ELT to make the entire operation more efficient. “We want to know in advance when screw number 11,341 is going to fail, because we have been reacting to these types of problems lately,” he says.
Of course, there is no such thing as screw number 11,341, but Garrido used this metaphor only to emphasize that the ELT will want to use AI to be much more proactive than simply reactive when it comes to the long-term maintenance of the observatory.
Do ELTs have long-term voters?
People are waiting to see the reaction of this ELT first, says Chavarría Garrido. The first thing is to think about the questions that the existing ELT will seek to answer, he says. “As we strive to answer those questions, we are going to find others that we don’t have answers to,” he notes.