What material is JWST's spacecraft bus primarily made of?

JWST’s spacecraft bus is primarily made of graphite composite. The bus is the observatory’s warm-side support structure, carrying the systems that keep the telescope powered, pointed, communicating, and operational.

Graphite composite combines carbon fibers with a binding material. It offers high strength with relatively low mass and can be engineered for the dimensional stability required by a precision spacecraft. That matters because Webb had to survive launch loads while supporting the telescope, sunshield, computers, propulsion hardware, batteries, communications equipment, and other subsystems.

The bus is not the same thing as Webb’s optical telescope or its sunshield. The optical telescope element contains the segmented primary mirror and instruments, while the bus provides the spacecraft-like infrastructure around them. Together with the sunshield, it forms the spacecraft element on the warm side of the observatory.

“Graphite composite” is the quiz’s intended answer, although descriptions may also call the material carbon-fiber composite. That wording refers to the same general class of lightweight reinforced composite rather than to a bus made from ordinary graphite blocks. The structure was assembled by Northrop Grumman in California before integration with the rest of Webb.