Andrew Nowicki wrote:
AN As a near-term technology, making large mirrors from
AN small segments is unbeatable. In the long term, however,
AN technology based on glass blowing looks attractive:
AN http://www.islandone.org/LEOBiblio/S....HTM#telescope

Henry Spencer wrote:
HS That page, unfortunately, trips my bogometer repeatedly.
HS (E.g., he does not seem to understand that at the scale
HS he is talking about, there is no such thing as a rigid
HS object, and active control of mirror shape by a supporting
HS structure is utterly mandatory.) I would give this approach
HS more credence if it were endorsed by someone with expertise
HS in either astronomical telescope construction or large
HS optics. As far as I know, *those* folks all say that when
HS the size gets really big, it's just got to be segmented.

Why so much venom?

This used to be a moderated newsgroup for open-minded
discussion of new ideas. Unfortunately, there is hardly
any moderation, creativity, or open-mindedness left here.

A terrestrial mirror is subject to gravity which distorts
the mirror when it tilts. Temperature variation may also
distort the mirror. A space mirror is free of these
distortions, so dividing a space mirror into segments
is less urgent than dividing the terrestrial mirror.
Segmentation drives the cost up, so it is only natural
to avoid it. Plastic flow of hot glass seems to be
cheap way to change the shape of large space mirror.
This method is useless on the Earth, because the force
of gravity would ruin the soft glass mirror.