GammaPC - Gammascopes
Some of our most recent experiments have been with Mylar mirrors. Aluminized Mylar is 93% reflective, which is only 2% less reflective than aluminized (or silvered) glass mirrors.
MemBrain TelescopesSo, the new title for this page, and, perhaps, the new name for what we would lke to present.
Part 1 Mathcad Calculations
In this first video, some fundamental calculations must be performed prior to beginning the design phase of this project. First we must decide on the properties of the telescope we plan to build, whether to be agressive or simple, how large, what aperture, what focal length, what type of telescope and more. Of course, we have elected to make a Newtonian reflector, with an 18" aperture, a focal length of 175 cm and an f-stop (speed) of 3.828.
In the past, it was believed that using air pressure (or vacuum) to make a spherical mirror with Polyester would produce a catenary shape. But recent calculations and other research show, instead, that it actually does produce a spherical shape. Beyond this, electric fields are used to modify the shape of the mirror to correct for aberrations in the image.
Part 2 Designing the TemplateThe cost of the material to make a one-meter mirror: about $2.00. In Part 2, we design the template for the next step in the production of the prototype telescope, which is based upon the properties we first defined, above.
Part 3 Making the TemplateIf you want to make a device and you have no tool to make it, then you first have to build the tool. In Part 3, we make the tool that will help us make the telescope. This tool will shape the mold that will be used to give shape to the electrostatic node base plate, which will be made out of a material similar to concrete.
The cost to make a one-meter mirror out of glass: about $100,000.
Part 4 Making the Base Plate Mold
In Part 4, we shape the mold for the electrostatic node base plate.
The cost of putting telescopes in space is astronomical (pun intended), but a lightweight telescope made of Mylar would cost a fraction of what it would cost to put a similarly-sized glass telescope in space.
Part 5In Part 5, we make a non-stick paper layer that will allow the concrete material to be poured into the mold without sticking to or seeping into and combining with the sand that makes up the mold. In the actual step, because a great deal of time had elapsed between the making of the mold and the pouring of it, the non-stick paper layer had become damaged and unuseable, so it was not used, and the concrete was poured directly onto the molded sand.
Our experiments have shown that we can actually bend a stretched sheet of aluminized Mylar into whatever shape we like with electric fields. Controlling electric fields and their shape is in the thrust of this project. Very large electric fields (roughly 100kV) are required to do this.
Part 6In Part 6, the mold has been poured and the finished electrostatic node base plate has been removed from the its mold. The surface is very rough and uneven, and must be sanded down, and then all of the little errors and problems corrected, by "painting" an additional layer of grout onto the surface, to make it smooth. This is then sanded down to fix additional surface defects.
In the next video, we will go over some of the equations used to do the design, and introduce a change in the design program. Initially, there was a bit of uncertaintly as to how to arrange the electrostatic nodes on the base plate. The several options that were consided will be discussed, and then how a final selection was made.
Part 7Part 12 is the simple construction of mount brackets for the telescope baseplate, using a 3-D printer.
Part 12While this is an excellent example of this use of Mylar in space exploration (in fact, Mylar was originally developed for use by NASA in early spaceflight), it can also be used on the ground by amateur and professional astronomers to replace the large and expensive telescopes we use now. To buy the die for a 20" telescope mirror (just the glass, then you have to grind it) costs around $15,000. The same amount of aluminized Mylar costs about 50 cents. The only things that remain to be worked on are the electronic circuits and adaptive controls for the electric bending fields.
This type of technology puts the price of professional astronomer-class telescopes within economical reach of the ordinary amateur astronomer. If aluminized Mylar can be made in large enough sheets, these types of telescopes could eventually rival the very large telescopes throughout the world in quality and speed. Normally, a sheet of aluminized Mylar can be purchased that is 50" wide, which limits the maximum size of a telescope mirror to that aperture. Now we can use aluminized Mylar for making something besides toy balloons.
By this time, I am certain, NASA has probably used up its interest in membrane telescopes, so I propose a private enterprise to put an ultra-large telescope in space, made of Aluminized Mylar. Be certain to contact me if you have an interest in this. Once we determine, on the ground, a viable alternative to expensive and heavyweight telescopes, then we will pursue a space-based solution.
In the meantime, it would be a marvelous adventure to put large, ground-based telescopes into the hands of every amateur astronomer who wants one.
References: 1. Mylar Polyester Film, DuPont Teijin Films, Data Sheet. 2. Theory of Plates and Shells, S. Timoshenko, S. Woinowsky-Krieger, 2nd. Ed., McGraw-Hill Book Company, 1959. 3. Mechanics of Materials, Sixth Ed., James M. Gere, Thomson Learning, Inc., 2004 4. Large Deflection of a Circular Clamped Plate under Uniform Pressure, Wei-Zang Chien, Chinese Jour. Phys., vol. VII, no. 2, pp 102-113, 1947 5. A NonLinear Theory of Bending and Buckling of Thin Elestic Shallow Spherical Shells, A. Kaplan & Y. C. Fung, National Advisory Commitee for Aeronautics (NACA), Technical Note 3212, 1954 6. Experiments with Pneumatically-Formed Metalized Polyester Mirrors, Chapter 24, Bruce D. Holenstein, Richard J. Mitchell, Dylan R Holenstein, Kevin A Iott and Robert H. Koch, The Alt-Az Initiative: Telescope, Mirror, & Instrument Developments, 2010, Genet. 7. Stretched Membrane with electrostatic curvature (SMEC): A new technology for ultra-lightweight space telescopes, Roger Angel, James Burge, Keith Hege, Matthew Kenworthy and Neville Wolf, Steward Observatory, UA Tucson. 8. Basic Wavefront Aberration Theory for Optical Metrology, James C. Wyant and Katherine Creath, Applied Optics and Optical Engineering, Vol. XI, Academic Press, 1992. 9. Flat Membrane Mirrors for Space Telescopes, Brian Stamper, Roger Angel, James Burge and Neville Woolf 10. Large Deflections of Clamped Circular Plates Under Initial Tension and Transitions to Membrane Behavior, Mark Sheplak and John Dugunji, TBI Journal of Applied Mechanics.