The Simons Observatory: Design and Measured Performance of a Carbon Fiber Strut for a Cryogenic Truss

TL;DR

This paper introduces a new carbon fiber strut design for cryogenic support in the Simons Observatory, demonstrating its strength, thermal performance, and potential for broader cryogenic applications.

Contribution

The paper presents a novel carbon fiber strut design with measured performance data, suitable for cryogenic telescope support structures.

Findings

Strut strength limited by fasteners and end caps, not the carbon fiber or epoxy.

Thermal conductivity measurements indicate less than 1 mW heat load from 4 K to 1 K.

Design shows promise for use in other cryogenic support applications.

Abstract

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.