The Simons Observatory: A large-diameter truss for a refracting telescope cooled to 1 K

Area of Science:

• Astronomy and Astrophysics
• Materials Science
• Mechanical Engineering

Background:

• The Simons Observatory requires robust cryogenic support structures.
• Traditional support struts can be a source of heat load in cryogenic systems.

Purpose of the Study:

• To design and evaluate a novel carbon fiber strut for cryogenic applications.
• To assess the mechanical strength and thermal performance of the new strut design.

Main Methods:

• Cryogenic cycling and destructive pull-testing of strut samples.
• Non-destructive pull-testing of the complete truss structure.
• Measurement of carbon fiber tube thermal conductivity.

Main Results:

• Strut strength was limited by mounting fasteners and end caps, not the carbon fiber or adhesive.
• Numerical predictions of strut strength were consistent with experimental results.
• Conductive heat load through the struts is predicted to be less than 1 mW from 4 to 1 K.

Conclusions:

• The developed carbon fiber strut design meets performance requirements for the Simons Observatory.
• The strut design demonstrates suitability for other cryogenic support applications.
• Minimizing heat load is critical for sensitive cryogenic instruments.