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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) No virus found in this message. Checked by AVG - www.avg.com Version: 10.0.1204 / Virus Database: 1435/3528 - Release Date: 03/25/11 Internal Virus Database is out of date. =