Quote:
Originally Posted by Stonius
Just curious - I wonder how this works. It's hard enough when your gear weighs 10's of kilos. I can't even imagine how they go about doing it when the equipment weighs in the 10's or 100's of tons!
Anyone know how they manage this in the massive installations?
-Markus
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Quote:
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Originally Posted by Stonius
I read that the Anglo Australian Telescope was EQ, but I don't know if that's uncommon.
So are the big ones mostly just go-to's with *really good tracking (essentially making it a software / drive system solution)?
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Hi Markus,
The AAT was among the last of the large equatorial telescopes ever built.
It was modelled after the Kit Peak Observatory horseshoe yoke design.
Given that it needs to point at sub-arc-second accuracy and weighs
some 265 tonnes, it required impressive levels of mechanical engineering
design. Structures of this size and weight will appreciably distort under
their own weight and they need to be extremely stiff and stable with
frictionless bearings.
Highly accurate surveying was required to align it and star pointing
measurements over the years have recorded how its concrete piers have
slowly sunk by small amounts over time.
Many of the problems of constructing such large telescopes had already been
confronted with the building of scopes like the 200-inch Palomar.
Serruier trusses and oil-pad bearings were part of the engineering arsenal.
The AAT was the first large telescope to be designed to be computer
controlled and it seems strange to think about now but at the time that
decision was seen as an ambitious risk.
The computer would be responsible for pointing and tracking and making
pointing and tracking corrections in real-time. So it was responsible
for ironing out the flexures of the mount under the influence of gravity.
An Interdata Model 70 minicomputer controlled it. It had 64K of memory
and a 16-bit word length and even had single-precision floating point
support. An excellent computer with a nice architecture at the time.
In fact the Interdata was only retired in 2008 after operating for 34 years.
That says a lot about what a good computer design it was for real-time control.
One important aspect that came out of the operation of the AAT was that
all professional telescopes from then on would be computer controlled.
This then also paved the way for the large Alt/Az designs with field
de-rotators that dominate today. As you will be aware, the computers
now even control adaptive optics on the world's largest scopes.
The big telescopes are Alt/Az design, like the 
