From: "Good, Donald" 
To: "'McHatten, Shawn'" , atm{at}shore.net
Reply-To: "Good, Donald" 


Here is another way to visualize it.  Think of a four legged chair.  If one
of the legs is out of adjustment, then the chair will wobble, corresponding
to uneven support pressure.  For a mirror cell, a temperature change can
cause a solid four (or more) point support to wobble, even after the entire
scope reaches a new temperature equilibrium.  A three legged stool will
never wobble, even if one leg is slightly shorter.  It will just tip a
little bit (this would correspond to a little adjustment in the
collimation).

A support based on bars instead of triangles is like an automobile
suspension.  The front and rear axle can tip side to side to compensate for
an uneven surface, and the chassis (another bar) keeps it stable front to
back.

So two and three point components lead to dynamic stability.  They can also
be used together, as in a 6-point (1 triangle and 3 bars) or 18-point (1
triangle, 3 bars, and 3 triangles) support.

A mirror cell is dynamically stable if the force supplied by each contact
point provides an even pressure distribution, and is composed of
dynamically stable components, also supported by an even pressure
distribution.

-----Original Message-----
From: McHatten, Shawn [mailto:Shawn.McHatten{at}aliant.ca]
Sent: Friday, December 13, 2002 3:01 PM To: 'tkrajci{at}san.osd.mil'; atm{at}shore.net
Subject: RE: ATM 12 point mirror cell - examples



Hey Tom
        Umm? I don't understand. Why must the platforms be three points (or
triangular). This 12 point designs looks perfect for three squashed
diamonds. Each made up of three outer ring points and one of the inner ring
points. Collimation bolts go in the middle of each of the diamonds.
        Hmmm?? Now I got something ELSE!! to read up on :). I obviously
don't understand mirror cell design :). Shawn

-----Original Message-----
From: tkrajci{at}san.osd.mil [mailto:tkrajci{at}san.osd.mil]
Sent: Friday, December 13, 2002 11:42 AM To: atm{at}shore.net
Subject: ATM 12 point mirror cell - examples


I've updated my web page at:
http://overton.tamu.edu/aset/krajci/
specifically
http://overton.tamu.edu/aset/krajci/cell-12-pt/cell-12-pt.htm

Please let me know if I'm correctly laying out some useful, general design
principles.

Here's the $64 question - which of my two versions is better...or are they
equivalent?

Thanks in advance,
Tom Krajci
Tashkent, Uzbekistan

PS.  I'm still digesting stuff on compliant hinges, main mirror focusing,
etc.  Once I get firmer ideas about it I'll post them.

--- BBBS/NT v4.00 MP