  We present the design and measured performance of a new carbon fiber strut
design that is used in a cryogenically cooled truss for the Simons Observatory
Small Aperture Telescope (SAT). The truss consists of two aluminum 6061 rings
separated by 24 struts. Each strut consists of a central carbon fiber tube
fitted with two aluminum end caps. We tested the performance of the strut and
truss by (i) cryogenically cycling and destructively pull-testing strut
samples, (ii) non-destructively pull-testing the final truss, and (iii)
measuring the thermal conductivity of the carbon fiber tubes. We found that the
strut strength is limited by the mounting fasteners and the strut end caps, not
the epoxy adhesive or the carbon fiber tube. This result is consistent with our
numerical predictions. Our thermal measurements suggest that the conductive
heat load through the struts (from 4 K to 1 K) will be less than 1 mW. This
strut design may be a promising candidate for use in other cryogenic support
structures.
