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.

Mike Maxwell