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Originally Posted by multiweb
Very cool report and photos to boot Gary. Those lava fields are impressive. The road looks like a carpet laid out on top of black bubble wrap. Amazing to see some shrubs still growing on top of it.
I had no idea there were so many types of actuators at the back of those segments. Must be a lot easier to realuminize them too given their size (just picturing the AAT primary move). I assume they have more segments than the scope primary needs so they can rotate them for maintenance? Are they interchangeable or do they have a very specific base profile for the spot they fit in? Or do they have a "generic" profile then the actuators push it in place depending where they are located in the mirror array? Also if that's the case can they use them on the other primary mirror next door seamlessly?
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Thanks Marc,
Each mirror has 36 hexagonal segments and the surface shape of
a segment depends on its distance from the center. It turns out that there
are six different surface shapes.
So they carry spares which they can swap-out during re-aluminizing.
Each segment is 1.8m across and as you mentioned it is a lot easier to
handle something of that size compared to the logistics of each time they
re-aluminize the 3.8m AAT.
We were given the opportunity to stare down through a glass porthole
into the aluminizing chamber itself and the technician kindly showed us
a high speed video of the aluminizing process where the pellet of
aluminum is vaporized.
The glass itself was manufactured by Schott in Germany and is a material
they trademarked called Zerodur. It has a particularly low coefficient of
thermal expansion, a couple of orders of magnitude better than
borosilicate.
There was a sample of it at the Visitors Center and it is a golden/yellow
transparent color. When you pick it up, because it looks, weighs and
feels different to everyday materials you normally handle, you instantly
know you are holding something "spacey" and different. Even if you
didn't know what it is, because it doesn't feel like glass but is so
optically pure, you would guess it is probably expensive.
One of us (not me) was presented with a small cube of it as a memento.
A beautiful gift and a real talking point.