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.
Design-to-cost exercises and innovative design have resulted in remarkably
high performing half-meter class wide field astronomical telescopes. This
approach is being extended to meter+ class telescopes with further innovation
on mounts and optics. Custom motors, drives and bearings have been
developed to keep performance up and cost down. We will also report on a
concurrent engineering campaign with Brashear Optics to ensure optical
performance while maintaining the highest value for primary mirrors in our line
of meter (and larger) class astronomical telescopes.
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