Introduction

The purpose of this project was to determine the feasibility of constructing a parabolic telescope mirror from composite materials using a spin-casting method. A typical 18 in. diameter mirror is made from glass, usually Pyrex or plate, and is ground from a cylindrical blank into a parabolic mirror. This report will constrast a possible composite mirror with this glass standard. Some of the advantages a spin-cast composite mirror could have over a ground glass one are the following:

• Spin-casting allows for large, low f/ratio mirrors to be constructed without rough grinding, a very time consuming process for an 18 in. glass mirror. More importantly, spin-casting produces an exact paraboloid, eliminating the 'parabolizing' phase in grinding a glass mirror.
• Certain composite materials offer greater tensile strength than glass, allowing for thinner and lighter weight mirrors. A lighter mirror has the advantages of taking less time to reach thermal equilibrium and reducing the weight of a telescope.
• Spin-casting could offer a more economical route to mass producing mirrors by reducing grinding time and material costs (although the low-cost materials used in the project were not ultimately successful and it may be that more expansive alternatives are necessary).
• A composite mirror offers the amateur telescope maker an opportunity to actually produce the entire mirror in the sense that he/she does not have to buy a manufactured glass blank.

My primary hypothesis in conducting this project was:

Hypothesis.

There exists available composite materials that can be used to produce diffraction limited telescope mirrors which are lighter and easier to produce than glass mirrors.