Recent developments in the production of spin-cast epoxy mirrors

摘要

NASA is currently developing optical communications to use with its spacecraft-both in earth-orbit and in deep space. This may allow spacecraft to use small, pencil-beam telescopes instead of large, wide-beam microwave antennas, potentially saving weight, reducing transmission power, and increasing communications bandwidth. The Earth side of such communications links will require a network of low cost, ground-based telescopes. The ground support mission mentioned above would benefit from the development of lightweight, low cost, 1 to 2 meter aperture telescopes. The key is the development of low cost, diffraction limited mirrors that cost orders of magnitude less than NASA's current telescope mirrors, have a drastically reduced manufacturing time, with significant weight reduction (low areal density). Spin-cast epoxy mirrors do not require any grinding, polishing, or figuring and therefore have the potential for low cost, short production time, and light weight. The specially-formulated thin epoxy described here naturally forms a parabolic surface when spun at constant velocity and once it hardens, the mirror surface is ready for use except for a reflective coating. A recently produced 50cm diameter f/2 spin-cast epoxy mirror has been measured to have a 6-8 micron RMS surface figure deviation and approximately 1 nm microroughness. Other advances include the synthesis and co-polymerization of spiro orthocarbonate compounds (SOCs) to reduce chemical shrinkage and the engineering of a stiff mold to hold the curing epoxy as it spins.