Thermal test of the JWST Pathfinder structure
In this photograph taken on 1 September 2016, the James Webb Space Telescope Pathfinder structure has been configured for the Thermal Pathfinder Test at NASA Johnson Space Center's giant thermal vacuum chamber, called Chamber A. The Pathfinder is a test version of the structure that supports the telescope. This is where end-to-end testing of the actual telescope will occur in 2017.
The dummy Aft Optical System (AOS) is visible in the centre of the primary mirror segments. The AOS 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 one gold-coated flight-spare beryllium segment (just in front of the AOS), one uncoated beryllium engineering unit segment, and ten gold-coated aluminium thermal simulator segments.