Putting a pathfinder through its paces

Before the James Webb Space Telescope is launched in 2018, its various components and support structures must be tested here on Earth.

NASA / Chris Gunn

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.

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