[GeoffW1 (Geoff)]

Hi,

I have been reading a few back issues of Scientific American, and came across an interesting article on very large telescopes of the future, in Vol 294, No 5, for May 2006, by Roberto Gilmozzi.

Several design studies are discussed, the largest being a 100 m whopper which would weigh 15000 tonnes and cost the equivalent of A$1.54 billion. The author refers to it as the OWL, for “overwhelmingly large”.

This telescope would have several cost saving features. For instance the primary mirror would be spherical, and consist of 3048 hexagonal segments, each positioned by sensors and three pistons on the rear face.

To correct the aberrations so introduced, there would be 4 corrector mirrors after the flat secondary. It could not have a traditional dome because of the expense, so would be protected by a roll-back lightweight hangar.

Gilmozzi suggests a law of telescope cost, which varies directly as the diameter in metres raised to the power of 2.6. After applying the current exchange rate and a couple of actual examples he gives, it works out to about (in AUD)

Cost = 576500 x D^2.6

Now this shows what a great deal we can get from Bintel, Andrews and others. The Gilmozzi rule says that for a 200 mm truss dob (these large telescopes are nearly all truss construction) we should pay about $8800, and for a 300 mm, $25200.

So we are well ahead. In fairness he does mention that the exponent 2.6 is lower if you can manufacture multiple smaller telescopes and use a Very Large Array design.

GeoffW1