Stratospheric Teraherz Observatory (STO) Telescope Overview
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The telescope is a heritage component from the STO mission. The telescope 
consisted of a light-weighted f/1.5 hyperboloid 80 cm diameter primary 
mirror made of honeycombed Ultra Low Expansion titanium silicate glass 
weighing 50 kg, and a secondary mirror to provide an f/17.5 beam mounted 
on graphite epoxy spider arms for high thermal stability. The primary 
mirror surface roughness is of optical quality and the mirror was recoated 
by Nu-Tek to maximize performance in the 300 – 5000 nm wavelength range.

The primary mirror was mounted to a support structure consisting of inner 
and outer rings. This support structure was modified to accommodate the 
optical benches and instruments necessary for this flight. Carbon fiber 
support struts were designed, built, and mounted on the inner aluminum 
ring to support the COTS optics bench. This master optics bench is 
composed of layered carbon fiber epoxy approximately 5 inch thick and 
rested just beyond the second outer aluminum ring. A hole bored in the 
center of optics bench passed the f/17.5 illumination of the telescope 
that also passed through a field stop and then to a two-position mirror on 
the optics bench, to direct the illumination either to the UVVis 
UV/Visual) instrument or to the BIRC (BOPPS Infrared Camera) instrument.