"RichA" wrote in message
...
On Tue, 11 Jan 2005 21:30:17 GMT, "Roger Hamlett"
wrote:


"Mike Maxwell" wrote in message
...
An article at http://www.ljworld.com/section/kunews/story/192798 talks
about a prototype telescope whose mirror is made of composites. The
16"
telescope (unclear exactly what they're talking about, but it appears
to
include the mirror, some kind of mirror mount, and the truss tube, all
in what I take to be a Cassegrain configuration) weighs 20 pounds. It
was built by Kansas University, San Diego State University, Dartmouth
College, and Composite Mirror Applications in Tucson.

Apparently it's a prototype for larger telescopes--the next one will
be
a one meter mirror. But if someone started making this sort of
telescope for amateurs... Of course, I suppose the cost of materials
would outweight (sorry for the pun) any savings from the construction
method.

An earlier story (before they built the prototype) is at
http://www.ljworld.com/section/archive/story/148016. And
http://www.physics.ku.edu/facilities.../specsfin.html is a rfp for
the one meter scope.
I think you have 'hit the nail on the head', with the cost of materials
'outweighing' any savings.
The obvious design idea, is to keep weights down, and distortions from
the
weight down, on larger scopes. I'd doubt if the design is
economic/practical for scopes any smaller than the prototype, and even
on
this, if produced in quantity, is still likely to be more expensive than
a
simple 'glass' and carbon fibre tube design...

Best Wishes


I could see this same argument occuring when they switched from
speculum metal to glass for mirrors.
-Rich
Except glass was every bit as heavy...
I'd suspect the key is to look at the cost of supporting a mirror. If you
look at small mirrors (up to about 12"), the extra costs involved in
supporting it are practially nil, and potential savings just don't really
exist. As you go up in size to perhaps 24", the costs rise, and by the
time you reach perhaps 36", they have become really significant, with the
weight of the glass, being greater than any other part in the scope, and
maintaining a rigid structure, to the accuracies needed when dealing with
light, have become a real bind. The materials involved in this technology,
may well fall in price in the future, but not because of the extra demand
from astronomers (most of the composites involved, are used in the
aerospace industries, in quantities far larger than astronomers are ever
likely to want). Hence my expectation, is that though 'production' units
will be a lot cheaper than the prototype, it is not likely to affect the
prices of scopes much below perhaps 24" in aperture. Though this may make
some of the current largest amateur observers, able to move up from 24"
scopes to 36" scopes, it is not likely to affect the purchasing of most
'normal' amateurs....

Best Wishes