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Engineering the 30-Meter Telescope
yyzmcleod writes "When completed in 2018, the Thirty Meter Telescope (TMT) will be the world's largest and most powerful, with a resolving power 100 times that of Hubble. As TMT's preliminary design review nears, this article details how its enclosure, segmented mirror and adaptive optics will work to let astronomers peer back to the beginning of the Cosmos."
"World's largest and most powerful".
Yeah, except for the 42-m E-ELT, also slated for 2018-ish. And that's still excluding radio telescopes...
As the actual article notes on its first page, TMT will have roughly 100 times the collecting area of Hubble: this goes as the square of the diameter of the telescope, so with TMT = 30m and Hubble = 2.5m, that's about right.
Resolving power (if the TMT can be made diffraction-limited, which it is aiming to do, but which is hard nevertheless) gets better linearly with the diameter, so TMT will have roughly 10 times the resolving power of Hubble.
The more appropriate space-based comparison in 2018 will be JWST which has a diameter of 6.5m, although JWST and ground-based ELTs are more properly thought of as being complementary, not competitive: they do different things.
But as already noted, the more appropriate comparison is with the European E-ELT which is under Phase B study now and is baselined for 42m diameter.
More interesting is where the TMT and E-ELT will be located: same hemisphere or not? Current bets are on E-ELT being in Chile, with TMT possibly going to Mauna Kea. This would be a better outcome for us astronomers than having both in the south, IMHO.
1 'tube sag' only applies to telescopes which HAVE a long tube, that is, long focal-length refracting telescopes which have a lens at the front end, not reflectors, which have a mirror at the back end.
2 almost all large telescopes do not use any sort of 'tube' at all for supporting the optics, any solid tube would be too heavy to be useable, they use open-frame supports
3 'detail'....if by this you mean 'angular resolution' then no, a 6" telescope can NEVER beat a 24" one, the angular resolution [THETA] is determined by the equation sin THETA = 1.22 X [wavelength of light] / [telescope diameter], so a 24" scope will *always* have 4 times better (ie smaller) angular resolution than a 6" does.
4 even with this taken into consideration, large observatory-class telescopes are made large for their light-gathering capabilities, which allow them to see extremely faint objects, -not- for their angular resolution, which is limited not by the telescope design but by atmospheric seeing conditions, these fall far below the theoretical limit of a large telescope.
5. The 30m scope is not a Cassegrain, it's a Ritchey-Chretiene, same design as used in many other large and very successful observatories, and trust me, the people who build observatory-grade optics are very able to construct ANY shape of mirror they are asked to without mucking it up. Perhaps you're thinking of -amateur- telescope makers having a go at grinding a Schmidt-Cassegrain corrector plate in their garage/shed/back room using a grinding-rig they made out of broom-handles and a washing machine motor?
Your father may well be an optical designer and astronomer, you're not though.
Not trying to be nasty, it's just that nearly everything you wrote is either wrong, misleading, or half-right but mis-applied, and to the wrong thing.