ESA Science & Technology - JWST mirror taking shape

This photograph shows the James Webb Space Telescope mirror taking shape, with 12 of the 18 mirror segments that make up the primary mirror installed.

The first of the hexagonal-shaped mirror segments was installed on 22 November 2015, and since then a team of scientists and engineers have worked tirelessly to install the remaining mirror segments onto the telescope structure in the large cleanroom at NASA's Goddard Space Flight Center in Greenbelt, Maryland. The twelfth mirror was installed on 2 January 2016. The individual segments are placed on the telescope's backplane using a robotic arm, guided by engineers.

Each mirror segment measures just over 1.3 metres across and weighs approximately 40 kilograms. After being pieced together, the 18 primary mirror segments will work together as one large 6.5-metre mirror. The primary mirror will unfold and adjust to shape after launch using actuators on the back of each segment.

The mirror segments are made of ultra-lightweight beryllium chosen for its thermal and mechanical properties at cryogenic temperatures. Since JWST will search for infrared light from the first stars and galaxies in the early Universe, the mirrors need to be cold, below -220 degrees C, to minimise any glow from the mirror itself.

A thin gold film, chosen for its ability to reflect infrared light, coats each mirror. During the installation process, the mirrors are protected with black covers, as can be seen in this picture.

The mirrors were built by Ball Aerospace & Technologies Corp., Boulder, Colorado. Ball is the principal subcontractor to Northrop Grumman for the optical technology and lightweight mirror system. The installation of the mirrors onto the telescope structure is performed by Harris Corporation of Rochester, New York. Harris Corporation leads integration and testing for the telescope.

The James Webb Space is an international project led by NASA with its partners, ESA and the Canadian Space Agency.