Thermal design, build, and test of the JWST Aft Optics Subsystem

•Establishment of thermal requirements and design of 40 K passive system.•Cryogenic performance test methodology and results presented.•Most of the margin for the cryogenic radiators is retained in as-built hardware.

Ball Aerospace and Technologies Corporation (BATC) has completed the design, construction, and qualification of the James Webb Space Telescope (JWST) Aft Optics Subsystem (AOS). This paper summarizes the evolution of the thermal design, technical challenges, and the results of thermal performance testing at temperature (30–40 K) of this passively cooled subsystem.