Re-coating a VERY LARGE telescope mirror

this is not the most amazing-looking building at the European Southern Observatory it's the main maintenance building or the MMB as it's cleverly cold but some really cool stuff happens here and the reason for that is if you can imagine those big eight point two meter mirrors up at the VLT that we've already seen basically about every year and a half they need to recoat them they need to get the aluminium covering replenished replaced because obviously it's been exposed for a year and a half so they bring it down the mountain they bring the mirror together with the cell that the mirror is embedded in which weighs 45 tons they bring that down the mountain and then they bring it to here actually they bring it to about here and then the interesting part begins because I've got to get it into the building and then they've got to take it all apart and get some work done and that's what we're going to have a look at now inside the MMB okay we're inside now and we're actually in luck because what you see there on top of this yellow bed is a dummy of the cell that the mirror sits in so you can kind of get an idea of the sizes we're talking about here so that roll the door there that's the one I was the other side of before so that opens up obviously and then the cell and the mirror together get put on this this yellow bed which is actually sort of like a hovercraft and it lifts up in the air on a cushion of air they don't want any shaking or vibrating of the mirror because the glass ceramic is so fragile so they gently bring it along to about here and then you look up there that's a big lifting device and this is really cool to look at actually because what happens is I think this comes down and picks the mirror up well actually first the mirror is kind of pushed up by its own actuators from its active optics but that only lifts at a short distance and then this thing's got to come down and pick it up and if you have a look I'll zoom in on these in a minute they're in these little hooks basically all around the edge that do the lifting but because the mirrors got a hole in the middle obviously we know about telescope mirrors and why they have a hole in the middle there's actually a few little hooks there that can lift the mirror up in its middle as well so it all gets a big lift and then the next stage is behind that door and we can look through this window in a minute but we can't go the other side because it has to be super super clean in there I'm looking through the window the first thing you see there is that kind of big tub with the yellow and black striped ring around it that's basically what the mirror will get held in so the mirror over here gets put into that through this door and into there and then above you see what well it's been described I've heard it described as a bit like a washing machine that's kind of what it is they put a whole bunch of chemicals onto the mirror to strip the old aluminium coating off the glass ceramic sort of bulk of the mirror leaving it kind of naked I guess and once that's done the mirror which is no longer shiny of course goes through to a vacuum chamber down the back we can't see that from where we are but it goes inside the vacuum chamber and there they put a tiny amount of aluminium coating over it to give it its reflectiveness again they're only use about 20 grams of aluminium it's put on using an electric field in a you know very scientific way of course we'll talk about that more later that actually takes about 45 minutes the recoating of the mirror so it's all shiny as good as new and then the whole process goes backwards well the stripping part doesn't happen again but everything else happens backwards to bring everything back out back out through here out the door back up the mountain back into the telescope now I said it takes 45 minutes to do the recoating but everything else all this delicate work here actually takes about a week so it's a good thing they only have to do it every year and a half it's also really high stakes stuff I mean they don't have a replacement mirror and those mirrors I don't even want to think about how much money they're worth they're worth a fortune and making another one is something you don't really want to think about so the whole process is is really high stakes and everything has to be done super super carefully and well this is where most of it's done

Channel: DeepSkyVideos

Views: 49,886

Rating: 4.9923296 out of 5

Keywords: astronomy, mirror, aluminium, aluminum, very large telescope, VLT

Id: goNtYKB0ecg

Length: 4min 35sec (275 seconds)

Published: Thu Jan 14 2016