Re: [ATM] Plop Flop

[Mark Holm <mdholm@telerama.com>]

Hi Jay,

I stayed up too late last night watching the fun at JPL as Cassini - 
Huygens did it's orbit insertion (gota love the way that Doppler curve 
tracked the prediction even when the s/n dropped to where the data was 
all fluffed up), so I am not up for running out all the numbers tonight, 
But in the next couple of days, I will do it for you.

The first thing though is to convince you to give up the 27 point 
design.  You don't need it.  According to Plop, a vanilla 18 point 
design will more than suffice.  (see the 18 point designs at  
http://pong.telerama.com/~mdholm/atm/cells/index.html  I plan on giving 
you a slightly less optimized one than those, because the dimensions 
will be easier for fabrication.  The decrement in performance will be 
much too small to worry about.)

I am hoping you will take my advice on this point.  In the last year,  
two stubborn (perhaps just a bit ignorant too?) atm's have stuck to more 
complex designs after I used Plop to show that simpler ones would do 
just fine for them.  I don't know what the lure of complex cell designs 
is.  Seems to be hard to break.

Let me say one more thing on that point.  Kriege and Berry is a great 
book.  The authors wrote the best they knew, but, they were working with 
just plain bad methods when they sized and laid out their cells.  So was 
every other atm at the time.  Plop, with a (very) little help from me, 
is going to give you a much more scientific result.

Plop says the 18-point cell residual deformation will be approximately 
1/500 wave RMS.   If you think that isn't good enough, well (it is hard 
to say it politely) you are mistaken.

I hope that a couple of the other Plop experienced atm's on the list 
will run your case at 18 points and back me up.  (Jeff Anderson-Lee and 
Tom Krajci are you listening?)  The backup isn't for my peace of mind.  
I am dead certain of the result.  Just want to make sure I convince you.

Jay's mirror dimensions are:

>508mm
>diameter, 54mm thickness, 2895.6mm fl (yes, f5.7), and a 79mm obstruction.
>

It would be slightly helpful, Jay, if you told us the glass type.  The 
numbers will be a little different for different glasses.  Actually, 
this design is so far from being critical that the glass type won't 
matter a lot, but might as well do it right while we are at it.

I can and will translate the results into the same format used in Kriege 
and Berry..

May be Saturday before I can get back to it.  Remind me if you don't 
hear from me in a couple of days.  Sometimes I forget things.

Mark Holm
mdholm@telerama.com

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