Fixed Shutter Dome (FSD), an enabling technology for all telescope
enclosure applications, was invented by Ethan Cliffton following
design work for the Keck Observatory where 110km/h winds were
a limit on viewing in otherwise clear weather owing to telescope
shaking. That limit may be exceeded with a sturdier windscreen.
Multiple shutter segments, folding metal shields, and high-tech
fabrics were reviewed and discarded in favor of structural protection.
The Pic-du-Midi Observatory achieved this protection for its 2-meter
telescope. However, the use of swinging doors at larger diameters,
as occur in the new spuncast and meniscus mirrors, was unworkable.
The hard spacesuits developed by Vic Vykukal at NASA Ames Research
Center used split spheres for body and limb joints. These joints
typically open over more than half their diameter. The FSD synthesis
arrived by applying the hinged sunshield from the spacesuit helmet
to the chords of the split spheres. Reducing the working parts
locked the shield, now the shutter, to the lower spherical segment,
the antrum, kinetics defined the aperture, and the FSD was created.
Resolution of skin stresses into a series of rings resists deflection
from wind, snow, or ice and puts robust structure between the
telescope and the weather, even at the zenith. Dames & Moore
have prepared an engineering analysis of the structural characteristics
of a 20-meter diameter FSD.