Putting a pathfinder through its paces

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The James Webb Space Telescope Pathfinder structure is shown here configured for the Thermal Pathfinder Test at NASA Johnson Space Centre’s giant thermal vacuum chamber, Chamber A.

The Pathfinder is a test version of the structure that will support the telescope. 

The dummy Aft Optical System is the upright piece at the centre of the primary mirror – it contains the telescope’s tertiary and fine steering mirrors.

Among the mirror segments that can be seen are a gold-coated flight-spare beryllium segment (just in front of the Aft Optical System), an uncoated beryllium engineering unit segment, and 10 gold-coated aluminium thermal simulator segments.