[ATM] Mirror Lateral Supports

["mbyorick" <mbyorick@starband.net>]

There is an interesting paper (PDF format) on a lateral support for
mirrors, "Mirror Segment Support System of the GSMT" at

http://www.aura-nio.noao.edu/book/ch4/4_5_C.pdf

Most interestingly, the mirror is laterally supported from the BACK
surface.

[The GSMT (Giant Segmented Mirror Telescope) is a proposed 30 meter
scope comprising 618 hexagonal segments, where the length of each side
of the hexagon is .665 meter.  Each segment has an 18 point whiffletree
axial support system.]  

Three bi-pod supports, spaced 120 degrees apart radially, are proposed
for the lateral support.  The line of action of the push-pull forces of
the support mechanism is in the mid-plane of the segment to avoid a
lateral gravity-imparted moment.  Put another way, the intersection of
the support force vectors is at the mirror (segment) mid-plane, even
though the lateral support is attached to the rear of the mirror
(segment).  See Figure 5 in the above paper for a diagram of the lateral
support devices (the 'bipods'), and Figure 6, which shows,
crystal-clearly, the simple but ingenious principle of operation. 

The main hardware for each lateral support consists of the following
parts:
-A bi-pod made from steel tubing. One end is connected to the support
structure frame, the other is connected to the segment.
-A lateral force pad (invar) that is glued to the segment with a
silicone RTV. It works for the lateral shear force from the support for
the horizontal gravity component of the segment lateral weight.
-Flexures at the both ends of the lateral support tube.  They transfer
the lateral shear force from the lateral support tube to the segment.

RTV is used (or proposed) both for attachment of the mirror to the axial
support system (the 'cell') and to the lateral supports.  Maybe now
those pesky slings can be tossed (slung?).

Cheers,
Mike Byorick
SW New Mexico

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