Download 11 04 11 Mylar Mirror in Ireland

11 04 11 Mylar Mirror in Ireland
From: Eamonn Ansbro [mailto:[email protected]]
Sent: Friday, April 08, 2011 2:37 PM
To: Bruce D. Holenstein
Subject: Re: Experiments with Pneumatically-formed Metalized, Polyester Mirrors
Dear Bruce,
Thanks for the links.
I can understand the challenges of developing pneumatic mirror cells. The key to solving
it is not just the cell
design/structure, but the specific polymer which has to be applied. 300 types were
explored, only one had the parameters that was acceptable. This final one had to be
aluminized.
BTW, I only met Russ Genet in 1992 in Ireland.
It was an IAU meeting on Robotic Telescopes held in Carlow.
Wishing you all the best in your endevours.
Kind regards
Eamonn
On 07/04/2011 19:30, Bruce D. Holenstein wrote:
Dear Eamonn,
Both Dr. Russ Genet and I are very interested in your research (Russ – I attached his
article).
My associates and I built a number of pneumatic mirrors over the past twenty years –
negative pressure cells from a few inches up to 42-inches in diameter. We also, built a
44-inch diameter positive pressure mirror with a clear faceplate. Two chapters of the
recent Alt-Az Initiative book describe our progress with pneumatic mirrors in more depth.
http://www.altazinitiative.org/AA%20Publications.htm. Also note that there are some
books edited by Christopher Jenkins on Gossamer Spacecraft (Vols. 191 and 212 of
Progress in Astronautics and Aeronautics series), among others, that you may want to
peruse.
Mylar-type films make an attractive reflecting surface. Overall, however, we found that
the complexity, tolerances, and total cost of suitable pneumatic mirror cells are far larger
than that for a traditional mirror cells. Further, new technologies outlined on the Alt-Az
Initiative site and books for lightweight mirrors such as for foamed glass and slumped
meniscus mirrors produce 10x to 100x better optical performance than our best
pneumatic mirrors – all at a cost and weight that is comparable. As a result, my group is
no longer actively pursuing pneumatic mirrors for general astronomical observing
purposes.
I hope this information helps. Good luck with your program – please keep us informed
on your progress. Perhaps you will solve the mirror cell issues that slowed our progress
and will be willing to present at our conference in Hawaii on Portable Meter-Class
Telescopes next January, 2012.
Sincerely,
Bruce Holenstein
From: Eamonn Ansbro [mailto:[email protected]]
Sent: Thursday, April 07, 2011 11:50 AM
To: Bruce D. Holenstein
Subject: Experiments with Pneumatically-formed Metalized, Polyester Mirrors
Dear Bruce,
First of all I am an amateur astronomer and have an interest of building another large telescope.
see my website: www.kingslandobservatory.com
I recently saw your talk within an image of a Gravic 42 inch Pneumatic mirror ( PPT presentation
at the Lightweight Alt-Az Telescope Conference 2010-2011).
.
I understand that you and your colleagues have been experimenting with pneumatically-formed
metalized polyester mirrors.
I was involved about 10 years ago in membrane mirror technology as a possible application for
large telescopes.
See attached SPIE science paper.(2004). I also gave a similar presentation to the 'Extremely
Large Telescope' meeting in London (2005),
highlighting the advantages of membrane mirrors as a secondary gregorian mirror having N focal
lengths.
You will garner from the paper the experiments and knowledge gained in creating possible large
mirrors for telescopes.
Do you have a detailed technical write up/article/paper on your experiments on
pneumatically-formed metalized polyester mirrors?
This would be most useful in comparing my experience with your approach.
Since that paper a 1.25m mirror was developed. Their are some refinements needed, to develope
an apparatus for controlling the barametric pressure. That part was never started. A large fork
mounting is under construction. No decisions have been made as to the final f/ratio.
You can appreciate you have f/n variables to decide upon. The main mirror 1.25m has a weight
of 100 lbs. Therefore the fork is remarkably light.
This may all lead to consolidating a final mirror for LBT astronomy.
Best wishes
Eamonn Ansbro
Ireland
(Europe)
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