Dish and Mirror System Fabrication and Assembly

     This is the part that I think that I am going to have the most trouble with. I have solicited Professor Ravi in the materials department, and he has promised to help me out with the material processing procedures. Current mirror designs incorporate a 1/4 " or 1/8" or 1/16" thick glass which then has a layer of silver applied to the back side of the glass. Then a copper coating is added followed by a sealer or paint. The mirror is then adhered with an adhesive to a carbon graphite honeycomb mounting plate that has the same basic shape as the mirror. Typically the mirrors are flat plate or spherical and are then attached to a more or less parabaloid focusing shape.

    Problems that have recently developed have occurred with the adhesives, the sealer paint and thermal stress and or wind induced bending stresses. Cracks appear within one year of installation, and the cracks allow oxygen to make contact with the copper backing plate. This soon oxidizes the copper and when it is depleted the silver goes next. The paints turn out to be rather porous and given the outdoor operating conditions, moisture and oxygen can creep in through the bonding material which leads to the the same conditions as the cracks except that a much larger area of reflective material is affected. Dark spots, pits and gray areas appear as the silver oxidizes, or separates away from the glass, and while the spectral reflectivity and efficiency is not seriously threatened, operating lifetimes past 5 or 10 years seems rather dubious.

    I have yet to contact a manufacturer of dish mirror systems in the United States. It would seem that we have here a giant financial and business opportunity as the single / sole supplier of "Quality" dish mirror systems in the United States. Right now one guy makes the mirrors... typically flat plate the same way you make the mirror glass you hang in your house, and another guy makes the carbon fiber honeycomb mounting plates and still another guy might build a unique and one of a kind superstructure holds it all together. Then you have someone else building the engines and generator sets. Seems to me like a wonderful opportunity with little or no "Serious" competition.

    My fist idea was to try a thermal plasma spray gun to spray the glass onto the mirror. Not being familiar with thermal spray equipment, I called a manufacturer and told them my idea. They had never heard of anything like it, and referred me to a specialist in Van Nuys. I told the specialist that I wanted to make a 40 ft diameter mirror to go along with the 25 H.P. stirling engine that had just been donated to the project. They told me that what I wanted to do was impossible. That the average rms value of the surface roughness was somewhere around 25. I asked if that meant microns, and all I got was silence on the other end of the telephone. Yes they were talking to dummy. Fortunately I found out later in my ME-233 class what the roughness scales mean and also what rms 25 looks and feels like. Anyway he asked me if I knew how much it would cost to do something like a 40 ft mirror. I imagined a can of silver spray paint at about $2.50 a can, and told him no... that I had no idea.... He said try about $250,000.00, and if I wanted optical quality like what you would expected to find at the Mt. Palomar observatory, I could expect to pay something like $1.2 million.  HA.

    I wonder if anyone will pay me $250,000.00 for a mirror? Mine's going to be 60 ft. Anyway the manufacturer of the spray equipment said that they could probably arrange a demonstration somewhere if I really wanted to pursue it. But that is when summer vacation came along, and Prof. Ravi wasn't teaching so I decided to leave the whole thing up in the air until he returned in the fall.

    Besides I found the "Perfect Mirror" developed by Prof. Edwin L. Thomas and graduate student Yoel Fink at M.I.T. under the funding umbrella of the Air Force Office of Scientific Research (AFOSR). They say it can be used to make a space telescope, so I don't see any reason why we can't try it here on earth first.  Reference document OSR-99-04 at Air Force Office of Scientific Research. (*** note *** These links keep changing under the direction of Wright Patterson Air Force Base. OSR-99-04 is a copy of a document originally found at AFOSR, which appears now to be NOT publicly available. At the least I don't have time to search for it any longer if it has moved to some other web location.)

    For the plasma spray gun... they want about $100,000.00 for one of those rigs, so unless someone wants to donate some equipment to the project, this process is probably out of the question at this particular moment in time. A little more research and guess what I came up with.... A microwave plasma torch made out of rectangular aluminum wave guide, and old used microwave oven parts. Reference document Atmospheric Microwave Plasma Jet for Material Processing by Ahmed I. Al-Shamma'a, Stephen R. Wylie, Jim Lucas, and Jiu Dun Yan from the IEEE. You will need to login to your Cal Poly Library account, access the IEEE Explorer and search for document 0093-3813 on the IEEE Transactions on Plasma Science, Vol 30, No.5, October 2002. They give information on a setup to melt glass. HA. HA.

    So this part of the story will not continue until after the fall quarter begins, and I can sit down with Prof. Ravi and discuss what needs to be done.

    What I expect to do is to machine a parabolic, or spherical surface out of some kind of metal that is probably only about two feet in diameter, polish it to a mirror finish and then see if it is possible to spray on some glass and then extract the thin shell in one piece without breaking it. If so then we may have a process. If not then I will be looking for help and some other direction.